WebWhen to use primitive cell, conventional cell, or supercell¶. Always use the primitive cell for electronic or phonon band structure calculations. (For the calculation of phonon band structures, you should use the primitive cell but also specify the size of the supercell used internally by AMS).; Always use the conventional cell when creating a surface (slab) WebNCERT Exemplar Solutions Class 10 Science Chapter 1 – Free PDF Download. NCERT Exemplar Class 10 Science Chapter 1 Chemical Reactions and Equations will help you in getting an understanding of all the fundamentals of chemical reactions as well as their symbolic representation in terms of equations. Here students will recognize chemical WebHeterogeneous catalytic hydrogenation of carbon dioxide (CO2) to methanol is a practical approach to mitigating its greenhouse effect in the environment while generating good economic profits. Though applicable on the industrial scale through the syngas route, the catalyst of Cu/ZnO/Al2O3 suffers from a series of technical problems when converting Web08/02/ · I do not agree with referring to absorption and emission of photons as endo and exothermic. Thermal energy is not kinetic energy, it is heat. Heat is thermal energy, not energy flow/transfer (as defined in the text), otherwise, how can an objects release or absorb heat as described later? (p) A few additional, specific errors noted Web03/05/ · Due to the different constraints, there is room for more than one technological option for large-scale hydrogen storage. The lion's share of research related to the storage of hydrogen in recent years has focused on the storage of hydrogen onboard fuel cell vehicles (FCVs). This research has been reviewed extensively,,,. The primary ... read more
The atomic configurations, transition states, energetics, energy barriers, and reaction mechanisms derived from first-principles calculations can be used to predict the catalytic activities at an atomic level. The kMC showed how the catalytic surface coverages change with time and conditions on a microscopic scale, and resolve the surface coverage with atomistic detail Pavlišič et al. Microkinetic modeling is an important continuum model with even higher accuracy and reliability than DFT and kMC.
It is an ideal framework for integrating the data generated by latter. Like the kMC, it avails information on product distribution and estimates the catalyst activity in steady-state kinetics Li et al. In many cases, the catalytic performance data form Cu-based catalysts compared qualitatively with those obtained from the experiments in the literature.
For example, the results from these theoretical modellings were found to conform well to the experiments over Cu—ZnO—Al 2 O 3 or Cu—MgO—Al 2 O 3. The active sites of the catalysts Cu—ZnO or Cu—MgO were modeled by the DFT. Cu sites were modeled as a Cu surface on top of which ZnO or MgO cluster was placed in the most energetically favorable position. The methanol synthesis was investigated under different temperatures and pressures. Different surfaces and the presence or absence of surface defects have shown the ability to catalyze the methanol synthesis.
The stepped Cu surface was shown to enhance the selectivity for methanol about four orders of magnitude better than a flat Cu surface Kopač et al. The defective surface relative to the Cu surface promoted the H 2 COH hydrogenation pathway, resulting in higher CH 3 OH yields. A similar observation was recorded for the selectivity for methanol Liu et al. A comparison between the pure Cu and the Zn-doped Cu ZnCu surfaces showed differences in the reaction steps Zheng et al. For the ZnCu surface, the methanol formation pathway included the formation of CH 3 O instead of CH 2 OH species.
The kinetics further deviated on Zn-promoted Cu due to the reduced activation energies of several critical reactions, leading to the improved catalytic performance of ZnCu The simple pure-copper kinetic model can sufficiently describe the catalysts with different supports after modifying the model active site concentrations Jurković et al. Applying these could guide the rational design of multifaceted Cu catalysts for methanol synthesis by surface defects engineering.
However, other studies found that the catalytic activity was not certainly correlated linearly with the Cu surface area Nakamura et al. The active sites and the activity relations of a reversed co-precipitated prepared Cu-based catalysts were investigated by various characterization techniques Natesakhawat et al. The results revealed the presence of metallic Cu on the surface of fresh but reduced and spent catalysts.
CuO in the catalyst reduced to Cu 0 upon exposure to H 2 at °C. They also correlated the concentration of Zn 0 in the CuZn alloy nanoparticle with the catalytic performance CO 2 conversion and methanol selectivity and found that the latter could be significantly improved by increasing the Zn 0 content in the heterojunction catalysts Li et al.
With advanced characterization techniques, it is evident that Zn atoms can be reduced on Cu nanoparticles, resulting in a detectable change in the geometry and electronic structure of Cu due to Zn—Cu bimetallic properties Sanches et al.
As a result, it is concluded that the Zn—Cu alloy is an active catalytic site. On the contrary, other studies found that reactions occur at the atomic interface between ZnO and Cu.
Thus, the presence of the ZnO—Cu interface and the synergy of Cu and ZnO are essential for the production of methanol Li et al. The active site of Cu catalysts can also exist in the form of other species.
Recent studies have shown that stepped and ZnO x -decorated Cu surfaces are active sites of the industrial catalysts Studt et al. Both experimental and theoretical investigations have found that decorated Cu stabilized by bulk defects and surface species participate in the hydrogenation of CO 2 to methanol reaction Behrens et al. Evidence is also available for the existence of the Zn—Cu bimetallic sites or ZnO—Cu interfacial sites Kattel et al.
Generally, as summarized in this section, the active sites for the Cu—ZnO catalysts can be grouped into the following categories: a Cu species metallic or oxidized Cu species ; b Cu—ZnO interface; c defective Cu surface; d Cu—Zn alloy; and e ZnO decorated Cu.
FIGURE 7. D is a zoom-in of the marked area in C Behrens et al. Reproduced with permission from American Association for the Advancement of Science. The deactivation of heterogeneous catalysts is a severe problem in many reactions. Many studies have reported various deactivation mechanisms of the Cu-based catalyst in the literature; however, the mechanism of deactivation is not entirely clear. One of the major causes of catalysts deactivation is sintering.
The sintering of catalytic materials particles results in a decrease in catalyst activity. Catalyst particles sinter in the early stages by a coalescence mechanism, which involves the migration and coalescence of particles, while the Ostwald ripening mechanism is operative in the end phase of the process Bartholomew, The Ostwald ripening is caused by the surface diffusion of catalytic material and the higher thermodynamic stability of larger particles Fichtl et al.
The initial and rapid deactivation is due to loss of surface area when some of the finely dispersed Cu crystallites agglomerate Roberts et al. The later pathway, which is slow and approaches the steady-state, is caused by the surface coverage of some reaction products and intermediates, especially water, and carbonated species Roberts et al. It was found that the cause of catalyst deactivation was sintering of both Al 2 O 3 and Cu with water due to the decreasing Al 2 O 3 surface, and Cu particle size with increasing content of H 2 O Prašnikar et al.
Figure 8A shows that all phases exhibit a reduction in surface area or increase of particle size with an increasing amount of steam. The Cu particle growth was fitted to a coalescence model for sintering Figure 8B , which confirms coalescence as the operating mechanism. The increased particle migration is due to weak contact between the metal and support or increased surface diffusion of catalytic material Prašnikar et al. The structures of ZnO and Al 2 O 3 species and metallic Cu can be stabilized to improve the catalyst lifetime, which can be accomplished by forming stable Cu interface with support material, and by stabilizing the dynamic nature of ZnO under working conditions using hydrophobic or hydrothermally stable materials.
A promising approach is to confine the growth of Cu species in a porous oxide to stabilize and maximize Cu—support interface Chen et al. FIGURE 8. A H 2 O impact on the Cu and ZnO particle size and on the Al 2 O 3 surface. Reproduced with permission from American Chemical Society. The water generated in the RWGS during CO 2 reduction to methanol deactivates the catalyst, causing speciation of Cu active phase and phase separation Kung, ; Liang et al. Sahibzada et al.
Another possible effect of water in the deactivation of the methanol synthesis catalyst is the crystallization of ZnO and Cu particles Lunkenbein et al. The inhibiting effect of water during CO 2 reduction to methanol was caused by the adsorption on and blocking of the active sites for CO 2 hydrogenation Liu et al.
Water reacts with CO 2 , forming carbonate species that have been proven to block the active sites for CO 2 hydrogenation. The deactivation of Cu-based catalysts by water could also result from blocking of hydrogen adsorption sites, morphology changes of Cu, and the oxidation of the active Cu-phase Clausen et al.
These can be explained by recrystallization and an enhanced tendency for sintering of the Cu particles in the presence of water Wu et al. To further increase the activity and stability of the Cu—ZnO or Cu—ZnO—Al 2 O 3 catalysts, modifiers such as K, Ba Zr, Ce, Mn, La, Si, Pd, Ga, Mg, and Y were incorporated to promote the catalytic performance Iizuka et al.
An effective promoter should be able to achieve large Cu surface area, high Cu dispersion, and to ease the reducibility of CuO to metallic Cu Sanches et al. Modification to the basicity, methanol selectivity, CO 2 conversion, and temperature and pressure have been reportedly observed Gao et al.
Lee et al. The incorporation of Zr enhanced the performance for methanol synthesis by improving conversion and methanol yield, but the occurrence of intensified WGS reaction reduced CO 2 conversion.
On the other hand, the addition of Ga and Mg further lowered catalytic performance Table 2 , attributed to reducibility difficulties and the increased crystalline size of Cu particles Xiao et al. These catalysts were evaluated using a feed composed of both CO and CO 2.
TABLE 1. TABLE 2. Comparison of methanol synthesis performance between CZA and promoted CZA. TABLE 3. Catalytic activities of recently studied Cu-catalysts for methanol synthesis from CO 2 hydrogenation in fixed bed reactors. The CuO—ZnO—Al 2 catalysts modified with SiO 2 , TiO 2 , or SiO 2 —TiO 2 exhibited better catalytic performances than the CuO—ZnO—Al 2 O 3 without any promoter. Both SiO 2 and TiO 2 eased the reduction and dispersion of CuO, while SiO 2 —TiO 2 made the reduction of CuO slightly difficult.
SiO 2 —TiO 2 had the best performance than SiO 2 or TiO 2 as a result of synergistic interaction between SiO 2 and TiO 2 , leading to a weaker acid strength and a higher acid concentration on the surface of the catalyst.
This resulted in weaker adsorption of CO 2 but stronger adsorption of H 2 and the dissociated H species Zhang et al. The catalytic results revealed higher performance for the promoted CuO—ZnO—Al 2 O 3 catalysts. Maximum activity and methanol selectivity were obtained for the catalyst promoted with SiO 2 —TiO 2 , giving CO 2 conversion of The introduction of non-metallic ions e.
Although the CuO—ZnO—ZrO 2 ternary catalysts have exhibited comparative activity with the commercial catalyst, the introduction of promoters such as SiO 2 , CeO 2 , Ga 2 O 3 , TiO 2 can further improve the catalytic performance Zhang et al.
Analysis with various characterization techniques revealed modification of the catalyst structures. A low content of SiO 2 was more effective for modifying the geometric structure. Phongamwong et al. Słoczyński et al. Saito et al. The catalyst was very stable during long-term methanol synthesis Saito et al. A unique microstructure with a proper balance of Cu dispersion and exposure of active Cu—ZnO interface sites at a high total Cu content is essential for achieving methanol selectivity Behrens and Schlögl, Thus, the synthesis method that guarantees the structure sensitivity of methanol synthesis over Cu surfaces is appropriate.
The ternary Cu-based catalysts are prepared by co-precipitation from a mixture of copper, zinc, and aluminum nitrate using a carbonate as a precipitant Behrens and Schlögl, ; Behrens, The co-precipitation involves the simultaneous solubilization and solidification of copper and zinc precursors usually nitrate salts in the presence of alkaline metal carbonates, forming binary precipitates under suitable conditions Casey and Chapman, ; Kasatkin et al.
Finally, the catalyst is reduced under H 2 atmosphere during which CuO is reduced to metallic Cu. Over the years, many researchers have investigated the synthesis parameters of the co-precipitation route, and have achieved a high degree of optimization, usually by empirically adjusting the synthesis conditions Li and Inui, ; Baltes et al. Even so, further improvement of this catalyst is still needed.
The best catalyst is usually obtained by co-precipitation with Na 2 CO 3 solution at a constant pH 6 or 7 and at temperatures ranging from 60—70°C Li and Inui, ; Baltes et al.
The initial precipitate, which is made of hydroxycarbonates Mota et al. To further improve the microstructural and porous properties of the methanol synthesis catalysts, other synthesis methods have also been studied Guo et al.
The precipitation—reduction method involves first the co-precipitation step, followed by a reduction in the second step by a reducing agent such as NaBH 4. Then a reducing agent is added, and the resulting slurry is further aged at a specific temperature for sufficient time, followed by filtration and washing, drying, and calcination.
Compared with the conventional co-precipitation method, catalysts with smaller Cu particles are much more easily obtained by using the precipitation—reduction method. The sol—gel SG method is another way to prepare mixed oxides, especially for M—CeTiO x systems Chen et al. In a study utilizing CuCeTiO x as the catalyst, Ce and Ti ions were hydrolyzed to form the framework at low pH during the sol—gel transformation. Then the Cu species were solidified through evaporation of the solvents.
These steps can lead to elemental distribution that differs between the bulk and surface, resulting in catalysts with varying composition in CuCeTiO x on their catalytic properties. The preparation methods show an important influence on catalytic performance Figure 9. The CuCeTiOx—CP catalyst showed a higher CO 2 conversion than CuCeTiOx—SG. However, the CuCeTiOx—SG catalyst showed a higher selectivity to methanol than CuCeTiOx—CP at the same CO 2 conversion Chang et al.
The studied preparation methods influenced the surface area of the Cu-based catalysts, which directly impact their catalytic activities. The different preparation methods resulted in various structural changes in the aurichalcite precursors that were transformed into the final catalyst. From the catalytic evaluation results, it was concluded that the preparation methods had noticeable effects on the dispersion of Cu particles and the catalyst structure.
These effects were more pronounced for the catalysts prepared by homogeneous precipitation and co-precipitation Sanches et al. The characterization and catalytic performance showed that the preparation strategy had a strong influence on them Dasireddy and Likozar, The ultrasonic synthesis route provided catalysts with increased basic active sites and significant methanol selectivity in comparison with that prepared from the conventional co-precipitation route.
This method also improved the dispersion of metallic Cu particles, which altered the intrinsic reactivity of CuO—ZnO. FIGURE 9.
Selectivity-conversion relationships of CuCeTiO x —SG and CuCeTiO x —CP Chang et al. Until the present, Cu-based catalysts present the most desirable properties for the direct CO 2 hydrogenation to methanol at the industrial scale, thus proper to refer it as the methanol synthesis catalyst.
However, the low conversion of CO 2 below equilibrium and poor selectivity to methanol have necessitated further improvement of these catalysts.
Although the methanol synthesis catalyst is not a classical supported catalyst, suitable support not only provides a proper catalyst configuration but modify the interactions between the active component and the support Liu et al. Over the years, various support materials Figure 10 for the Cu-based catalysts have been studied Weigel et al.
Metal oxides are the most common supports for the methanol synthesis catalysts, and their properties greatly affect the catalyst activity in several ways. The non-metallic supports, including metal organic frameworks MOFs , porous silica materials, layered double hydroxides LDHs , carbon materials, metal carbides, graphene, and porous polymers, have also been investigated Rodriguez et al. Of the metal oxide supports investigated in the literature for Cu catalysts, ZnO, ZrO 2 , Al 2 O 3 , Ga 2 O 3 , SiO 2 , and CeO 2 have drawn the most attention in methanol synthesis.
These metal oxides have also been explored as promoters to the Cu-based methanol synthesis catalysts Toyir et al. FIGURE Classification of supports for Cu-based methanol synthesis catalysts.
The presence of ZnO improves the dispersion and stability of Cu Bonura et al. These functions lead to a more active Cu phase and larger surface area, thus preventing agglomeration of Cu particles Arena et al. The metallic copper surface areas in the reduced catalysts could be determined by the N 2 O titration technique Guo et al. Synergism between Cu and ZnO reportedly exists upon the incorporation of ZnO into the Cu based catalysts Kanai et al.
The catalytic activity of a Zn-doped Cu surface was much higher than that of the pure Cu as a result that ZnO modified the electronic properties of Cu sites by an electron exchange and interaction with Cu particles Twigg and Spencer, ; Koitaya et al. The role of ZnO in the reduction of Cu by H 2 was studied by Fierro et al. The temperature programmed reduction investigation of the CuO—ZnO catalyst synthesized by the co-precipitation method revealed ZnO promoted the reducibility of CuO.
It is believed that ZnO acts as a reservoir of atomic hydrogen and provides it for the CO 2 hydrogenation on the Cu surface, or as a binding site facilitating the adsorption of H 2 species and CO 2 via a spillover Chen et al. The atomic hydrogen then transfers from the Cu onto the ZnO surface and gradually hydrogenates the adsorbed CO 2 to methanol Sun et al.
ZnO, as a support, is also suggested to be an active component in the methanol synthesis catalyst Fujitani and Nakamura, ; Choi et al.
The formate species were firstly formed on both Cu and ZnO phases, and secondly, they were further hydrogenated to form methoxides located on the ZnO Lei et al. Thus, ZnO is actively involved in the synthesis of methanol by creating more stable reaction intermediates, which readily convert to methanol on further hydrogenation Chen et al.
The absorption strength of reaction intermediates like HCO, H 2 CO, and H 3 CO can be enhanced by the incorporation of ZnO, thus decreasing the energy barriers. Consequently, the formation rate of methanol is increased Behrens et al.
Sulfur and chlorine species are considered poisons for Cu-based methanol synthesis catalysts, and the addition of ZnO to the catalyst irreversibly scavenges sulfur or chlorine as ZnS or ZnCl 2 , respectively, militating against deactivation of the catalyst. On the negative, ZnO is a basic oxide that can neutralize the acidity of Al 2 O 3 in the commercial catalyst, preventing the transformation of CO 2 to methanol and promoting the agglomeration of active Cu particles Twigg and Spencer, ZrO 2 is a good support due to its hydrophobicity, and surface basicity.
Besides, its high thermal stability is superior to Al 2 O 3 under reducing and oxidizing atmospheres Li and Chen, The catalytic activity of ZrO 2 as a support is superior to that of Al 2 O 3 , SiO 2 , or ZnO Li and Chen, CuO can be uniformly dispersed on the ZrO 2 surface, forming an interface favorable for the methanol synthesis reaction Li and Chen, ZrO 2 exists in different crystal structural phases polymorphs —amorphous a -ZrO 2 and tetragonal t -ZrO 2 and monoclinic m -ZrO 2 Figures 11A—C.
The a-ZrO 2 and t-ZrO 2 transform to m-ZrO 2 at high temperatures. The calcination of Zr OH 4 at temperatures greater than °C transforms it mainly to m-ZrO 2 , so Cu species are easily incorporated into a-ZrO 2 Tada et al.
In general, the high TOF Methanol is due to a strong Cu—ZrO 2 interaction and a high surface concentration of atomic hydrogen to CO 2 Witoon et al. A highly loaded CuO For all catalysts, the CO 2 conversion increased, with increasing contact time, while the selectivity to methanol decreased, but the selectivity to CO increased Figure 11E.
The activity and selectivity of the prepared catalysts depended on the spray pyrolysis rate. The former feed rate led to the formation of smaller ZrO 2 particles, which provided more surface to stabilize small Cu particles and formed interfacial Cu-ZrO 2 active sites. The crystallite size and crystallinity of t-ZrO 2 could be controlled by varying the precursor feed rate Fujiwara et al. Compared with Al 2 O 3 , the impressive performance is linked with the possibility of interactions between Cu-species and ZnO—ZrO 2 oxides Li and Chen, Moreover, ZrO 2 exhibits a weaker hydrophilic character than either Al 2 O 3 or CeO 2 , which promotes the desorption of formed water, and benefits the formation of methanol Arena et al.
This indicates the presence of defective Cu structures resulting from the strong Cu—support interaction Yang et al. Both experiments and DFT calculations using Cu—ZnO—ZrO 2 have provided evidence on the separate functions of the Cu species and ZnO—ZrO 2 interface in the catalytic conversion of CO 2 to methanol by hydrogenation Wang Y. The catalytic evaluation at °C under 3. The binary oxides of ZnO—ZrO 2 showed a higher ability for CO 2 adsorption and the hydrogenation of carbonate species to formate and methoxy intermediates than the Cu—ZnO or Cu—ZrO 2 systems.
So far, efforts have been made to enhance the catalytic performance of CuO—ZnO—ZrO 2 catalysts further. Modification of CuO—ZnO—ZrO 2 catalysts with various additives is a feasible option to alter the physicochemical properties of the catalysts, improving the methanol synthesis activity and preventing the Cu sintering. The CuO—ZnO—ZrO 2 catalysts supported on graphene oxide GO gave a higher STY in comparison with the GO-free catalyst due to the increased active sites for the adsorption of CO 2 and H 2.
The methanol selectivity of GO supported catalysts was above that of the unsupported catalyst. Specifically, the highest methanol selectivity of This performance was attributed to a promoting effect of GO nanosheet serving as a bridge between metal oxides, which enhanced a hydrogen spillover from the Cu surface to the carbon-containing species adsorbed on the metal oxide particles Witoon et al.
The mixed oxides of Cr, Mo, or W and CuO—ZnO—ZrO 2 prepared by the co-precipitation method showed better activity for methanol synthesis. The results indicated an improved methanol selectivity and yield of the CuO—ZnO—ZrO 2 catalyst upon addition of MoO 3 or WO 3 but slightly dropped when doped with Cr 2 O 3.
The improved methanol yield over these catalysts can be attributed to the differences in their Brunauer-Emmett-Teller surface areas and adsorption capacities for CO 2. It was also found that the ratio of surface Zn to Cu, as well as the fraction of strong basic sites, improved the methanol selectivity Wang G. A layered double hydroxide Mg-Al LDH was used as a carrier for Cu—ZnO—ZrO 2 catalyst synthesized by the co-precipitation method.
Characterization results revealed CuO—ZnO—ZrO 2 nanoparticles were uniformly dispersed and attached to the surface of the LDH, which improved the specific surface area and Cu dispersion compared with a reference catalyst without the support.
The catalyst showed a high methanol selectivity of Raising the temperature of the CuO-ZnO—ZrO 2 —LDH catalyst slightly decreased the conversion. Very promising is that the activity of the can be recovered by reduction with H 2 Fang et al. CeO 2 has also been studied as a support or co-support for the methanol synthesis catalysts via the CO 2 hydrogenation route Hu et al.
It has a strong adsorption affinity for CO 2 due to its strong basicity and oxygen vacancies. The latter can improve the dispersion of Cu particles and promote the spillover of atomic hydrogen, which benefits the production of methanol Chang et al. In , Rodriguez and co-workers published a study that demonstrated the combination of Cu metal and oxide sites in the Cu—CeO 2 interface affords favorable reaction pathways for the conversion of CO 2 to methanol Graciani et al.
Reaction conditions: catalyst was exposed to 0. Reaction conditions: catalysts were exposed to 0. In ceria-containing Cu—ZnO oxide catalysts, the presence of CeO 2 promoted the surface activity of the Cu—ZnO system, although negatively influenced the catalyst texture and metal surface area in comparison to ZrO 2 Bonura et al. As discussed earlier, CeO x can improve the dispersion of Cu particles and promote the spillover of atomic hydrogen.
On the other hand, ZnO can improve the dispersion of the CeO x nanoparticles. Thus, the ternary CuZnCeO x exhibited higher performance than the binary CuZnO x catalyst Shi et al. A CuZnCeO x catalyst prepared by a parallel flow co-precipitation technique was evaluated in the hydrogenation of CO 2 to methanol and CO.
The amount of CeO x in the catalyst controlled the selectivity of the products. Cu played a critical role in the activation of H 2 , and CeO x strongly adsorbed CO 2 , improved the dispersion of Cu nanoparticles, and promoted the spillover of atomic hydrogen Shi et al.
The results of these studies suggest that CeO 2 in Cu—ZnO catalysts can offer a viable way to produce methanol or CO from CO 2 hydrogenation selectively. The selectivity toward the products methanol and CO can be regulated by changing the reaction conditions, catalyst formulation, or preparation method Hu et al. For example, the CuZnCeTiO x showed significantly enhanced activity in comparison with the CuCeTiO x catalyst and was twice more active than the commercial catalyst as measured by TOF values.
However, the stability is still not good enough, with high selectivity toward CO Chang et al. MgO showed a negative impact on the catalytic activity, but a positive effect on the stability of the catalyst Meshkini et al. Zander et al. The co-precipitation method resulted in catalysts with higher Brunauer-Emmett-Teller surface area and Cu dispersion, but with decreased catalytic activity. On the other hand, the fractional precipitation facilitated the Cu substitution by Zn in the sub-carbonate precursor, which cushioned the effect resulting from the former method, catalytically performed better than those prepared by the co-precipitation method Zhang et al.
In these catalysts, there was the formation of Mg—Al hydrotalcite unfavorable for methanol production. Ga 2 O 3 is reported to increase the activity per unit Cu surface area of methanol synthesis catalyst Toyir et al. The catalysts derived from the Ga-modified hydrotalcite showed improvement in the dispersion of Cu particles and the formation of active Cu—ZnO x sites, which enhanced the efficiency of Cu—ZnGa catalyst system for CO 2 hydrogenation to methanol An et al.
One reason for this improvement is that the hydrotalcite derived catalysts could maintain their morphology in ultrafine layers even after heat treatment at high temperatures, which transformed the phase to amorphous Guil-López et al.
The amorphous phase is more accessible with better dispersed metallic Cu crystal, and with a large surface area decorated with a small amount of Zn atoms. CuZnGa catalysts derived from the LDH precursor gave good catalytic activity in CO 2 hydrogenation to methanol.
LDH30Ga Cu: However, there is an obvious requirement of high temperature and pressure for realizing the high activity. The incorporation of titanium nanotubes TNTs support into CuO—ZnO—CeO 2 catalysts can promote CuO reducibility, improve metallic Cu dispersion and increase the specific surface area.
The selectivity was positively correlated with the number of basic sites, whereas the CO 2 conversion was a function of the specific surface area of Cu. In general, SiO 2 possesses large surface area and porosity, high thermal stability, and good dispersion capacity but weak interaction with metals Nitta et al. However, the presence of steam at high temperatures weakens its thermal stability due to its transformation to Si OH 2. Cu supported on high-purity silica was nearly inactive in methanol synthesis Fujita et al.
Some experimental results have reported higher activity and relatively better selectivity for methanol over silica-based than ZnO-based catalysts, due to the higher surface area of the former Nitta et al.
SiO 2 can function better as a support for Cu-catalyst for methanol synthesis in the presence of other metal oxides as a promoter or co-support, or for the copper bimetallic catalysts Sugawa et al. The results revealed the deposition of Cu and Zn ions in the pores of the SiO 2 and high distribution, which depended on the metal loadings.
The specific surface area of the catalysts increased with increasing loadings to a critical amount due to the formation of the porous structure of SiO 2. Beyond this loading, CO 2 conversion slightly reduced due to the blocking of the pores of the support. Other examples of the SiO 2 supported catalysts for methanol synthesis can be found in the literature Studt et al. Carbon materials possess a very large surface area, high thermal stability, high hydrogen uptake, mechanical strength, and facilitate H 2 dissociation.
All these properties contribute to the increasing rate of CO 2 hydrogenation to methanol at a lower temperature with high methanol selectivity than the equilibrium when used as supports, but unsuitable for a commercial application due to low conversion. GO as support for the Cu—ZnO catalysts was studied for the CO 2 hydrogenation to methanol.
Still, its application suffers from serious challenges that are undesirable for industrial applications—low conversion and instability at high temperatures. At a reaction temperature of °C under 4. Bimetallic Cu-based catalysts also have good catalytic performances in the direct CO 2 hydrogenation to methanol. Noble metals such as Pd have proper properties for activating hydrogen, which could spread through a hydrogen spillover mechanism to the neighboring catalytic sites Melián-Cabrera et al.
The hydrogen spillover can result in a catalyst surface with a highly reduced state that could facilitate the hydrogenation process. In the methanol synthesis application, Pd is reported with good catalyst improvement roles. It is suggested that Pd enhances the activity of Cu sites. Upon the addition of Pd, the Cu dispersion and surface concentration on the catalyst surface were improved.
The Cu dispersion and the surface Cu concentration increased with an increase in the amount of loaded Pd to a certain level. It was explained that the interaction between Pd and Cu decreased the Cu—Cu bond distance due to the strong electronic perturbation, resulting in well-dispersed Cu species Kugai et al. In this way, the aggregation or agglomeration of Cu particles was suppressed due to the interaction with Pd, which was highly dispersed on CeO 2 support Choi et al. Thus, Pd promotion generated more electron-rich Cu sites by electron transfer Choi et al.
Pd can also improve the reducibility of CuO and enrich the catalyst surface with electrons, enabling the activation of CO 2 by interaction with the carbon atom of CO 2 Choi et al. A strong Pd—Cu bimetallic promoting effect on the formation of methanol from CO 2 hydrogenation was observed, which is due to the synergetic effect between Pd and Cu as a result of the Pd—Cu alloy formation Jiang et al.
Some authors attribute the synergistic effect between Pd and Cu, which contributes to the improvement of catalytic activity to the alloy formation, as evidenced by the correlation between catalyst composition, structure and catalytic performance Jiang et al. The Pd—Cu bimetallic catalysts with total metal loadings 2. The improvement in catalytic performance was realized at lower metal loadings, and Pd—Cu 2.
At high loadings, Pd—Cu alloy exhibited high selectivity to CO Nie et al. The amount of alloy, as determined by quantitative X-ray diffraction, correlated with the observed promotive synergy; and the estimated TOFs, suggesting its involvement in methanol synthesis Jiang et al. It was found that the support structure played a significant role in the performance of this catalyst. The chemical recycling of CO 2 to renewable fuels and commodity chemicals represents an economic aspect of the CO 2 mitigation.
Methanol, a primary liquid product derived from the hydrogenation of CO 2 , aside being used directly as a fuel, can be efficiently processed into other products of high societal needs—DME, ethylene, propylene, gasoline, and other products currently obtained from petroleum and natural gas. The combustion of methanol and its derivatives will release CO 2 , which can be recycled back effectively, forming a carbon loop Goeppert et al.
Biomass is a form of recycled CO 2 that can be converted into DME, for example. Since CO 2 hydrogenation is carried out using hydrogen produced from renewable energy sources—electrical, wind, hydro or solar energy Goeppert et al. For example, solar and wind are seasonal, intermittent and fluctuating. The storage of electricity on a large scale and transportation at a very long distance are still challenging.
The electrical energy can be conveniently stored in chemical compounds such as hydrogen, methanol, methane and higher hydrocarbons that can then be stored, transported and used when needed to produce electricity or for various other applications such as heating, cooking and transportation Olah, ; Goeppert et al. It has been proposed that the carbon-based liquid fuels will continue to be important energy storage media in the future because of their higher volumetric stored energy density.
Methanol has great merits as a storage medium for renewable energy. As an energy storage medium, methanol displays high performance as an additive or substitute for gasoline in internal combustion engines. The direct conversion of the chemical energy in methanol to electrical power at ambient temperature has been demonstrated in methanol fuel cells McGrath et al. Methanol is also a feedstock for a number of chemicals such as formaldehyde and acetic acid.
It can produce light olefins, including ethylene and propylene, used in the synthesis of various polymers, and any hydrocarbons and products currently obtained from petroleum oil through the methanol-to-olefin process. DME produced from methanol can be easily liquefied at moderate pressure and applied as diesel fuel substitute with high cetane rating, producing little or no soot emissions Semelsberger et al.
It is a good substitute for liquefied petroleum gas in most applications, such as heating and cooking. The CO 2 hydrogenation to methanol can be processed by the thermochemical, electrochemical and photochemical methods.
These processes are challenging in several aspects. The thermochemical process applied in the commercial methanol synthesis from natural gas is a two-step process that transforms the energy and molecules in a fossil fuel Olah, The first step is the steam-methane reforming into synthesis gas, which subsequently converts to methanol in the second step. A few percent of CO 2 is also produced in the first step. Methanol cannot be directly generated electrochemically from CO 2 with high selectivities or current densities Malik et al.
Researches are continuously seeking new technologies to recycle CO 2 to liquid fuel most efficiently and economically. Patterson et al. They proposed combining solar methanol islands and human-made marine structures that use renewable energy to harvest CO 2 from seawater and catalysis to produce methanol. This approach uses clusters of marine-based floating islands on which photovoltaic cells convert sunlight into electrical energy to produce H 2 and extract CO 2 from seawater, where it is in equilibrium with the atmosphere.
H 2 and CO 2 then react to form methanol. H 2 is electrochemically generated and the extraction of CO 2 is possible using a series of membrane cells. Methanol is then synthesized using a looped gas-phase heterogeneous catalytic process. The process is particularly of advantage compared with the direct atmospheric CO 2 capture because CO 2 in seawater 0.
This innovative technology for renewable fuel synthesis from the marine environment has attractive features, such as abundant raw materials and large exposure to solar energy, and avoidance of local CO 2 depletion.
However, this technology relies on previously demonstrated chemical and physical processes to produce the solar methanol island on a significantly large scale. It is suggested that wind could also serve as a power source; thus, analyzing how other energy sources or energy mixture could contribute is expected to further the development of the process.
For a practical design of solar-powered artificial marine-islands to recycle CO 2 into methanol and other synthetic liquid fuel, some issues must be addressed. These include i how photovoltaic modules can be deployed on a large-scale in the marine environment, and properly maintained.
ii Is combined technology such as desalination and electrolysis a possibility to efficiently produce H 2 from seawater? Surface supercells of the primitive surface unit cells are given in matrix notation. The primitive same as conventional supercells are shown in blue. This notation can only be used if the angle γ between the lattice vector does not change when creating the supercell.
See Fig. The above three examples would translate to. Hexagonal bulk crystals e. The factor 2 appears because the slab exposes two surfaces. This means that the k-points in the surface calculation do not need to be extremely accurately converged. It is easiest to calculate the surface energy for slabs constructed from the optimized bulk lattice parameters, so that there is no strain the surface-lateral direction. If your intention is to model a surface of a bulk crystal, then do not optimize the lattice of the slab.
Optimize the lattice of the bulk , and use that to construct the slab. If your intention is to model a thin film , you can consider optimizing the lattice of the slab.
xyz file from the lattice optimization example. You can also run these calculations with BAND, ForceField UFF , ReaxFF, Quantum ESPRESSO, or VASP via AMS. To get the energy, either. Using method 1 , fit a straight line through the datapoints, as in Fig. Only the three thickest slabs were used for the linear fit blue line. The surface energy becomes. Download PLAMS python scripts to set up and run and postprocess jobs that generate the surface energy graph and numbers.
See also: the Python Scripting With PLAMS tutorial. The cleavage energy is the energy required to create a slab from the bulk. If the slab exposes two identical surfaces, the cleavage energy is double the surface energy. You can place an adsorbate on a surface substrate in arbitrary conformations by rotating and translating the molecule. Some surfaces have high-symmetry adsorption sites, like ontop , bridge , or hollow sites.
The second Cu layer is colored green, the third is colored yellow. xyz , or create a 4-layer Cu 5x5 surface supercell from the conventional Cu unit cell and add a water molecule somewhere on top of it.
For easier visualization, we will color the 2nd Cu layer green , and the 3rd Cu layer yellow. If you place the mouse cursor over an input field, you will get more information in a help balloon. All energies on the right hand side are calculated for geometry-optimized systems. With the above equation, a positive adsorption energy implies exothermic adsorption.
A different sign convention can also be used :. d The slab and molecule widely separated, used for the in-cell approach. In BAND, if your basis set is not large enough, the adsorption may become artificially stable from the basis set superposition error BSSE.
The best way to address BSSE is to increase the size of the basis set. Alternatively, you can also apply the counterpoise correction. The figure below shows calculated adsorption energies with and without counterpoise correction.
A more negative value implies more exothermic adsorption. Download PLAMS scripts that set up and postprocess jobs calculating the counterpoise correction and which generate this figure. In ReaxFF, the electronegativity equalization method EEM is used to determine the charges on the atoms, which in turn determine the Coulomb energy contribution to the total energy. In an isolated molecule, charge can only be redistributed among the atoms in the molecule.
Similarly, for an isolated slab, charge can only be redistributed among the atoms in the slab. This issue is similar to the basis set superposition error. For ReaxFF calculations , it is therefore an option to use the in-cell approach :. In this way, for both systems on the right hand side, the charges have the same freedom to redistribute.
Download a PLAMS python script calculating these numbers. This energy difference gets larger for larger supercells and thicker slabs, see Fig. ff Download a PLAMS python script and xyz file to generate this figure.
Keep the in-cell approach in mind when creating training sets for ReaxFF parametrization. For Quantum ESPRESSO and VASP, double-sided adsorption can prevent the formation of a dipole moment across the vacuum gap.
The other engines support 2D periodicity for which there is no vacuum gap. It is common to fix the positions of either the central or the bottom layers of the slab. When relaxing a clean without adsorbates slab, it is a good idea to relax either all atoms, or to keep the central layers fixed.
In this way, both the top and bottom sides of the slab relax. This relaxed slab can then be used for. Even in the case of one-sided adsorption on the top surface it is good to have a relaxed bottom surface when using DFTB, BAND, Quantum ESPRESSO, or VASP.
For metals the effect is smaller. In AMSinput, select the atoms that you would like to keep fixed. The lattice vectors of the slab models of the two materials must match exactly coincidence site lattice. Two materials usually have very different crystal structures, so to create such a model, supercells that are possibly strained or rotated need to be created, before adsorbing one slab on top of the other.
For more details, see the Solid-liquid interface tutorial. Index by engine ADF BAND DFTB ReaxFF ForceField MLPotential Hybrid MKMCXX Zacros Quantum ESPRESSO VASP COSMO-RS Getting Started Keyboard shortcuts GUI modules Getting started: Geometry optimization of ethanol Step 1: Preparations Start AMSjobs Make a directory for the tutorial Start AMSinput Undo Step 2: Create your molecule Create a molecule Viewing the molecule Molecular conformation Getting and setting geometry parameters Extending and changing your molecule Step 3: Select calculation options Task XC functional Basis set Numerical quality Geometry Convergence Other input options Step 4: Run your calculation Save your input and create a job script Run your calculation Step 5: Results of your calculation Logfile: AMStail Files Geometry changes: AMSmovie Orbital energy levels: AMSlevels Electron density, potential and orbitals: AMSview Browsing the Output: AMSoutput Convert results to spreadsheet.
Standard output 2. Logfile 3. KF browser 4. Spreadsheet Excel summary 5. AMSjobs Command-line bash, terminal 6. Command-line: amsreport 7. Command-line: dmpkf 8. Command-line: grep not recommended Python 9. Python: Load an AMSJob Python: Direct access to. rkf file Run Jobs from the Command Line An example shell script Run the job Visualize the results in the GUI Meaning of the run command Customize the run command Meaning of the shell script contents!
What are the next steps? Starting from reactant and product — Nudged Elastic Band NEB What can possibly go wrong? cleavage energy Adsorption Adsorption on surfaces in AMSinput Example: ontop, bridge, fcc hollow and hcp hollow sites on Cu Adsorption energy Basis set superposition error with BAND In-cell approach for adsorption energies with ReaxFF One-sided vs.
Temperature profiles Calculation of the glass transition temperature Thermal expansion coefficient Importing the polymer structure Annealing the polymer Extracting strain vs.
What functional, What basis set? Geometry Optimization 2. TDDFT Calculations 3. Analyzing TDDFT Calculations 4. Faster TDDFT variant: sTDDFT 5. Analyzing the Orbitals 6. Analyzing the NTOs 7. Localized Analysis of Canonical Molecular Orbitals CMO with NBO6 GW: Ionization Potential and Electron Affinity Set up and run the calculation Results Thermally Activated Delayed Fluorescence TADF General Remarks on Modelling OLED Emitters Electronic Structure of OLED Materials Computational Description of TADF 1: Electronic Structure Excited States Geometry Optimizations Vertical Absorption Computational Description of TADF 2: Spin-Orbit Coupling Calculating Spin-Orbit Couplings Computational Description of TADF 3: Vibrations Marcus Theory Franck-Condon Principle and Marcus-Levich-Jortner Theory Effective Modes and Huang-Rhys Factors from DFTB and FCF Computational Description of TADF 4: Solvent Effects Vibrational progression of an OLED phosphorescent emitter 1.
Optimize lowest singlet state S 0 2. Optimize lowest triplet state T 1 3. Dative bonding 2. Electron-sharing bonding 3. Fragment Calculation 2. Density SCF 3. Generate CD function Case 2: Dewar-Chatt-Duncanson bonding components in a transition metal complex NOCV-CD 1. Visualize NOCV deformation densities 3. Generate a CUBE file 4. CD functions for the NOCV deformation densities Case 3: Open-Shell CD in the HAT mechanism of the TauD-J intermediate 1.
Unrestricted Calculations 2. Generate CUBE files 3. Crystals and Surfaces ¶ This tutorial covers, for crystals : Periodic crystals in AMSinput k-space sampling and convergence Lattice optimizations , with an example Overview of crystal properties in AMS And for surfaces : Slabs vs. Files ¶ AMSinput can import and export coordinates in many different file formats, including. Unit cells ¶ In AMS, a 3D-periodic crystal can be represented as a periodic repetition of some unit cell.
There are infinitely many choices of unit cells. The two most important ones are: The primitive cell , which is the smallest possible unit cell containing only one lattice point , and The conventional cell , which follows guidelines outlined by the International Union for Crystallography.
The primitive and conventional cells are: Cu unit cell lattice points atoms angles between lattice vectors primitive 1 1 non-orthogonal conventional 4 4 orthogonal 90° Fig. xyz into AMSinput. Note The conventional Cu unit cell contains 4 lattice points in a crystallographic sense. When to use primitive cell, conventional cell, or supercell ¶ Always use the primitive cell for electronic or phonon band structure calculations.
For the calculation of phonon band structures, you should use the primitive cell but also specify the size of the supercell used internally by AMS. Always use the conventional cell when creating a surface slab from Miller indices. Use some suitable supercell when you do not have a perfect crystal, for example if you want to introduce a defect like a vacancy.
The size of the supercell then determines the defect concentration. Supercells can also be used for approximately modeling amorphous solids , if atoms are displaced from their crystal positions. Tip Whenever you change the lattice vectors or lattice parameters, use the periodic view tool to double-check that the periodic boundary conditions are what you expect.
Rotation of lattice vectors relative to cartesian axes ¶ The components of the lattice vectors are cartesian xyz coordinates in angstroms. Note ReaxFF runs slightly faster if the the first convention is used. k-space sampling ¶ With DFTB, BAND, Quantum ESPRESSO, and VASP via AMS, you must specify some k-point sampling for periodic calculations. In deep seawaters the isotope Th makes up to 0.
Uranium ores with low thorium concentrations can be purified to produce gram-sized thorium samples of which over a quarter is the Th isotope, since Th is one of the daughters of U. Thorium has three known nuclear isomers or metastable states , m1 Th, m2 Th, and m Th. This is so low that when it undergoes isomeric transition , the emitted gamma radiation is in the ultraviolet range. Different isotopes of thorium are chemically identical, but have slightly differing physical properties: for example, the densities of pure Th, Th, Th, and Th are respectively expected to be Two radiometric dating methods involve thorium isotopes: uranium—thorium dating , based on the decay of U to Th, and ionium—thorium dating , which measures the ratio of Th to Th.
Uranium—thorium dating is commonly used to determine the age of calcium carbonate materials such as speleothem or coral , because uranium is more soluble in water than thorium and protactinium, which are selectively precipitated into ocean-floor sediments , where their ratios are measured. The scheme has a range of several hundred thousand years.
A thorium atom has 90 electrons, of which four are valence electrons. Four atomic orbitals are theoretically available for the valence electrons to occupy: 5f, 6d, 7s, and 7p. This is due to relativistic effects , which become stronger near the bottom of the periodic table, specifically the relativistic spin—orbit interaction. Thorium is much more similar to the transition metals zirconium and hafnium than to cerium in its ionization energies and redox potentials, and hence also in its chemistry: this transition-metal-like behaviour is the norm in the first half of the actinide series.
Despite the anomalous electron configuration for gaseous thorium atoms, metallic thorium shows significant 5f involvement. A hypothetical metallic state of thorium that had the [Rn]6d 2 7s 2 configuration with the 5f orbitals above the Fermi level should be hexagonal close packed like the group 4 elements titanium, zirconium, and hafnium, and not face-centred cubic as it actually is.
The actual crystal structure can only be explained when the 5f states are invoked, proving that thorium is metallurgically a true actinide. Thorium is a highly reactive and electropositive metal. In bulk, the reaction of pure thorium with air is slow, although corrosion may occur after several months; most thorium samples are contaminated with varying degrees of the dioxide, which greatly accelerates corrosion.
At standard temperature and pressure , thorium is slowly attacked by water, but does not readily dissolve in most common acids, with the exception of hydrochloric acid , where it dissolves leaving a black insoluble residue of ThO OH,Cl H. Most binary compounds of thorium with nonmetals may be prepared by heating the elements together. When heated in air, thorium dioxide emits intense blue light; the light becomes white when ThO 2 is mixed with its lighter homologue cerium dioxide CeO 2 , ceria : this is the basis for its previously common application in gas mantles.
It occurs because ThO 2 : Ce acts as a catalyst for the recombination of free radicals that appear in high concentration in a flame, whose deexcitation releases large amounts of energy. Several binary thorium chalcogenides and oxychalcogenides are also known with sulfur , selenium , and tellurium. All four thorium tetrahalides are known, as are some low-valent bromides and iodides:  the tetrahalides are all 8-coordinated hygroscopic compounds that dissolve easily in polar solvents such as water.
Thorium borides, carbides, silicides, and nitrides are refractory materials, like those of uranium and plutonium, and have thus received attention as possible nuclear fuels. Thorium germanides are also known. High coordination numbers are the rule for thorium due to its large size. Thorium nitrate pentahydrate was the first known example of coordination number 11, the oxalate tetrahydrate has coordination number 10, and the borohydride first prepared in the Manhattan Project has coordination number Many other inorganic thorium compounds with polyatomic anions are known, such as the perchlorates , sulfates , sulfites , nitrates, carbonates, phosphates , vanadates , molybdates , and chromates , and their hydrated forms.
In natural thorium-containing waters, organic thorium complexes usually occur in concentrations orders of magnitude higher than the inorganic complexes, even when the concentrations of inorganic ligands are much greater than those of organic ligands. In January , the aromaticity has been observed in a large metal cluster anion consisting of 12 bismuth atoms stabilised by a center thorium cation.
Most of the work on organothorium compounds has focused on the cyclopentadienyl complexes and cyclooctatetraenyls. Like many of the early and middle actinides up to americium , and also expected for curium , thorium forms a cyclooctatetraenide complex: the yellow Th C 8 H 8 2 , thorocene. It is isotypic with the better-known analogous uranium compound uranocene. The simplest of the cyclopentadienyls are Th C 5 H 5 3 and Th C 5 H 5 4 : many derivatives are known. The alkyl and aryl derivatives are prepared from the chloride derivative and have been used to study the nature of the Th—C sigma bond.
Other organothorium compounds are not well-studied. They decompose slowly at room temperature. Although one methyl group is only attached to the thorium atom Th—C distance Tetramethylthorium, Th CH 3 4 , is not known, but its adducts are stabilised by phosphine ligands. These violent events scattered it across the galaxy. Neutron capture is the only way for stars to synthesise elements beyond iron because of the increased Coulomb barriers that make interactions between charged particles difficult at high atomic numbers and the fact that fusion beyond 56 Fe is endothermic.
In the universe, thorium is among the rarest of the primordial elements, because it is one of the two elements that can be produced only in the r-process the other being uranium , and also because it has slowly been decaying away from the moment it formed. The only primordial elements rarer than thorium are thulium , lutetium , tantalum, and rhenium, the odd-numbered elements just before the third peak of r-process abundances around the heavy platinum group metals, as well as uranium.
In the Earth's crust, thorium is much more abundant: with an abundance of 8. Common thorium compounds are also poorly soluble in water. Thus, even though the refractory elements have the same relative abundances in the Earth as in the Solar System as a whole, there is more accessible thorium than heavy platinum group metals in the crust. Thorium is the 41st most abundant element in the Earth's crust. Natural thorium is usually almost pure Th, which is the longest-lived and most stable isotope of thorium, having a half-life comparable to the age of the universe.
At the time of the Earth's formation, 40 K and U contributed much more by virtue of their short half-lives, but they have decayed more quickly, leaving the contribution from Th and U predominant. Thorium only occurs as a minor constituent of most minerals, and was for this reason previously thought to be rare.
Monazite chiefly phosphates of various rare-earth elements is the most important commercial source of thorium because it occurs in large deposits worldwide, principally in India, South Africa, Brazil, Australia, and Malaysia. It contains around 2. Thorium dioxide occurs as the rare mineral thorianite. Due to its being isotypic with uranium dioxide , these two common actinide dioxides can form solid-state solutions and the name of the mineral changes according to the ThO 2 content.
In , the Swedish chemist Jöns Jacob Berzelius analysed an unusual sample of gadolinite from a copper mine in Falun , central Sweden. He noted impregnated traces of a white mineral, which he cautiously assumed to be an earth oxide in modern chemical nomenclature of an unknown element. Berzelius had already discovered two elements, cerium and selenium , but he had made a public mistake once, announcing a new element, gahnium , that turned out to be zinc oxide. In , Morten Thrane Esmark found a black mineral on Løvøya island, Telemark county, Norway.
He was a Norwegian priest and amateur mineralogist who studied the minerals in Telemark, where he served as vicar. He commonly sent the most interesting specimens, such as this one, to his father, Jens Esmark , a noted mineralogist and professor of mineralogy and geology at the Royal Frederick University in Christiania today called Oslo.
Berzelius determined that it contained a new element. Berzelius made some initial characterizations of the new metal and its chemical compounds: he correctly determined that the thorium—oxygen mass ratio of thorium oxide was 7. and Lodewijk Hamburger.
In the periodic table published by Dmitri Mendeleev in , thorium and the rare-earth elements were placed outside the main body of the table, at the end of each vertical period after the alkaline earth metals. This reflected the belief at that time that thorium and the rare-earth metals were divalent. While thorium was discovered in its first application dates only from , when Austrian chemist Carl Auer von Welsbach invented the gas mantle , a portable source of light which produces light from the incandescence of thorium oxide when heated by burning gaseous fuels.
Thorium was first observed to be radioactive in , by the German chemist Gerhard Carl Schmidt and later that year, independently, by the Polish-French physicist Marie Curie.
It was the second element that was found to be radioactive, after the discovery of radioactivity in uranium by French physicist Henri Becquerel.
It was determined that these variations came from a short-lived gaseous daughter of thorium, which they found to be a new element. This element is now named radon , the only one of the rare radioelements to be discovered in nature as a daughter of thorium rather than uranium. After accounting for the contribution of radon, Rutherford, now working with the British physicist Frederick Soddy , showed how thorium decayed at a fixed rate over time into a series of other elements in work dating from to This observation led to the identification of the half-life as one of the outcomes of the alpha particle experiments that led to the disintegration theory of radioactivity.
In the s, thorium's radioactivity was promoted as a cure for rheumatism , diabetes , and sexual impotence. In , most of these uses were banned in the United States after a federal investigation into the health effects of radioactivity. Up to the late 19th century, chemists unanimously agreed that thorium and uranium were the heaviest members of group 4 and group 6 respectively; the existence of the lanthanides in the sixth row was considered to be a one-off fluke.
In , British chemist Henry Bassett postulated a second extra-long periodic table row to accommodate known and undiscovered elements, considering thorium and uranium to be analogous to the lanthanides. In , Danish physicist Niels Bohr published a theoretical model of the atom and its electron orbitals, which soon gathered wide acceptance. The model indicated that the seventh row of the periodic table should also have f-shells filling before the d-shells that were filled in the transition elements, like the sixth row with the lanthanides preceding the 5d transition metals.
Seaborg and his team had discovered the transuranic elements americium and curium, he proposed the actinide concept , realising that thorium was the second member of an f-block actinide series analogous to the lanthanides, instead of being the heavier congener of hafnium in a fourth d-block row. In the s, most applications that do not depend on thorium's radioactivity declined quickly due to safety and environmental concerns as suitable safer replacements were found.
A study by the Oak Ridge National Laboratory in the United States estimated that using a thorium gas mantle every weekend would be safe for a person,  but this was not the case for the dose received by people manufacturing the mantles or for the soils around some factory sites.
Thorium has been used as a power source on a prototype scale. The earliest thorium-based reactor was built at the Indian Point Energy Center located in Buchanan , New York, United States in In the s, India targeted achieving energy independence with their three-stage nuclear power programme. Alvin Radkowsky of Tel Aviv University in Israel was the head designer of Shippingport Atomic Power Station in Pennsylvania, the first American civilian reactor to breed thorium.
and Brookhaven National Laboratory in the United States, and the Kurchatov Institute in Russia. In the 21st century, thorium's potential for reducing nuclear proliferation and its waste characteristics led to renewed interest in the thorium fuel cycle. In February , Bhabha Atomic Research Centre BARC , in Mumbai , India, presented their latest design for a "next-generation nuclear reactor" that burns thorium as its fuel ore, calling it the Advanced Heavy Water Reactor AHWR.
In , the chairman of the Indian Atomic Energy Commission said that India has a "long-term objective goal of becoming energy-independent based on its vast thorium resources.
When gram quantities of plutonium were first produced in the Manhattan Project , it was discovered that a minor isotope Pu underwent significant spontaneous fission , which brought into question the viability of a plutonium-fueled gun-type nuclear weapon.
While the Los Alamos team began work on the implosion-type weapon to circumvent this issue, the Chicago team discussed reactor design solutions. Eugene Wigner proposed to use the Pu-contaminated plutonium to drive the conversion of thorium into U in a special converter reactor.
It was hypothesized that the U would then be usable in a gun-type weapon, though concerns about contamination from U were voiced. Progress on the implosion weapon was sufficient, and this converter was not developed further, but the design had enormous influence on the development of nuclear energy.
It was the first detailed description of a highly enriched water-cooled, water-moderated reactor similar to future naval and commercial power reactors. During the Cold War the United States explored the possibility of using Th as a source of U to be used in a nuclear bomb ; they fired a test bomb in Thorium metal was used in the radiation case of at least one nuclear weapon design deployed by the United States the W The low demand makes working mines for extraction of thorium alone not profitable, and it is almost always extracted with the rare earths, which themselves may be by-products of production of other minerals.
The common production route of thorium constitutes concentration of thorium minerals; extraction of thorium from the concentrate; purification of thorium; and optionally conversion to compounds, such as thorium dioxide. There are two categories of thorium minerals for thorium extraction: primary and secondary. Primary deposits occur in acidic granitic magmas and pegmatites. They are concentrated, but of small size. Secondary deposits occur at the mouths of rivers in granitic mountain regions.
In these deposits, thorium is enriched along with other heavy minerals. For the primary deposits, the source pegmatites, which are usually obtained by mining, are divided into small parts and then undergo flotation.
Alkaline earth metal carbonates may be removed after reaction with hydrogen chloride ; then follow thickening , filtration, and calcination. Magnetic separation follows, with a series of magnets of increasing strength. Industrial production in the 20th century relied on treatment with hot, concentrated sulfuric acid in cast iron vessels, followed by selective precipitation by dilution with water, as on the subsequent steps.
This method relied on the specifics of the technique and the concentrate grain size; many alternatives have been proposed, but only one has proven effective economically: alkaline digestion with hot sodium hydroxide solution. This is more expensive than the original method but yields a higher purity of thorium; in particular, it removes phosphates from the concentrate. Then, fuming sulfuric acid is added and the mixture is kept at the same temperature for another five hours to reduce the volume of solution remaining after dilution.
The concentration of the sulfuric acid is selected based on reaction rate and viscosity, which both increase with concentration, albeit with viscosity retarding the reaction.
Increasing the temperature also speeds up the reaction, but temperatures of °C and above must be avoided, because they cause insoluble thorium pyrophosphate to form. Since dissolution is very exothermic, the monazite sand cannot be added to the acid too quickly. Conversely, at temperatures below °C the reaction does not go fast enough for the process to be practical.
The mixture is then cooled to 70 °C and diluted with ten times its volume of cold water, so that any remaining monazite sinks to the bottom while the rare earths and thorium remain in solution.
Thorium may then be separated by precipitating it as the phosphate at pH 1. Too high a temperature leads to the formation of poorly soluble thorium oxide and an excess of uranium in the filtrate, and too low a concentration of alkali leads to a very slow reaction. These reaction conditions are rather mild and require monazite sand with a particle size under 45 μm.
Following filtration, the filter cake includes thorium and the rare earths as their hydroxides, uranium as sodium diuranate , and phosphate as trisodium phosphate.
This crystallises trisodium phosphate decahydrate when cooled below 60 °C; uranium impurities in this product increase with the amount of silicon dioxide in the reaction mixture, necessitating recrystallisation before commercial use. The rare earths again precipitate out at higher pH. The precipitates are neutralised by the original sodium hydroxide solution, although most of the phosphate must first be removed to avoid precipitating rare-earth phosphates.
Solvent extraction may also be used to separate out the thorium and uranium, by dissolving the resultant filter cake in nitric acid.
The presence of titanium hydroxide is deleterious as it binds thorium and prevents it from dissolving fully. High thorium concentrations are needed in nuclear applications. In particular, concentrations of atoms with high neutron capture cross-sections must be very low for example, gadolinium concentrations must be lower than one part per million by weight.
Previously, repeated dissolution and recrystallisation was used to achieve high purity. For example, following alkaline digestion and the removal of phosphate, the resulting nitrato complexes of thorium, uranium, and the rare earths can be separated by extraction with tributyl phosphate in kerosene.
Non-radioactivity-related uses of thorium have been in decline since the s  due to environmental concerns largely stemming from the radioactivity of thorium and its decay products.
Most thorium applications use its dioxide sometimes called "thoria" in the industry , rather than the metal. This compound has a melting point of °C °F , the highest of all known oxides; only a few substances have higher melting points. Energy, some of it in the form of visible light, is emitted when thorium is exposed to a source of energy itself, such as a cathode ray, heat, or ultraviolet light. This effect is shared by cerium dioxide, which converts ultraviolet light into visible light more efficiently, but thorium dioxide gives a higher flame temperature, emitting less infrared light.
During the production of incandescent filaments, recrystallisation of tungsten is significantly lowered by adding small amounts of thorium dioxide to the tungsten sintering powder before drawing the filaments.
The work function from a thorium surface is lowered possibly because of the electric field on the interface between thorium and tungsten formed due to thorium's greater electropositivity. Thanks to the reactivity of thorium with atmospheric oxygen and nitrogen, thorium also acts as a getter for impurities in the evacuated tubes. The introduction of transistors in the s significantly diminished this use, but not entirely. Thorium dioxide is found in heat-resistant ceramics, such as high-temperature laboratory crucibles ,  either as the primary ingredient or as an addition to zirconium dioxide.
When added to glass , thorium dioxide helps increase its refractive index and decrease dispersion. Such glass finds application in high-quality lenses for cameras and scientific instruments. Thorium dioxide has since been replaced in this application by rare-earth oxides, such as lanthanum , as they provide similar effects and are not radioactive. Thorium tetrafluoride is used as an anti-reflection material in multilayered optical coatings.
It is transparent to electromagnetic waves having wavelengths in the range of 0. Its radiation is primarily due to alpha particles, which can be easily stopped by a thin cover layer of another material. Mag-Thor alloys also called thoriated magnesium found use in some aerospace applications, though such uses have been phased out due to concerns over radioactivity.
The main nuclear power source in a reactor is the neutron-induced fission of a nuclide; the synthetic fissile [d] nuclei U and Pu can be bred from neutron capture by the naturally occurring quantity nuclides Th and U. When U undergoes nuclear fission, the neutrons emitted can strike further Th nuclei, continuing the cycle.
Thorium is more abundant than uranium, and can satisfy world energy demands for longer. Because of this, thorium is a potentially attractive alternative to uranium in mixed oxide fuels to minimise the generation of transuranics and maximise the destruction of plutonium.
Thorium fuels result in a safer and better-performing reactor core  because thorium dioxide has a higher melting point, higher thermal conductivity , and a lower coefficient of thermal expansion. It is more stable chemically than the now-common fuel uranium dioxide, because the latter oxidises to triuranium octoxide U 3 O 8 , becoming substantially less dense. The used fuel is difficult and dangerous to reprocess because many of the daughters of Th and U are strong gamma emitters.
Thus it is a neutron poison : instead of rapidly decaying to the useful U, a significant amount of Pa converts to U and consumes neutrons, degrading the reactor efficiency. To avoid this, Pa is extracted from the active zone of thorium molten salt reactors during their operation, so that it does not have a chance to capture a neutron and will only decay to U.
The irradiation of Th with neutrons, followed by its processing, need to be mastered before these advantages can be realised, and this requires more advanced technology than the uranium and plutonium fuel cycle;  research continues in this area. Others cite the low commercial viability of the thorium fuel cycle:    the international Nuclear Energy Agency predicts that the thorium cycle will never be commercially viable while uranium is available in abundance—a situation which may persist "in the coming decades".
Natural thorium decays very slowly compared to many other radioactive materials, and the emitted alpha radiation cannot penetrate human skin. As a result, handling small amounts of thorium, such as those in gas mantles, is considered safe, although the use of such items may pose some risks. The decay products of Th include more dangerous radionuclides such as radium and radon.
Crystals and Surfaces ¶ This tutorial covers, for crystals :. To run the PLAMS python scripts, first go through the Python Scripting With PLAMS tutorial. In this tutorial, Zn atoms are colored brown for improved contrast the default color is white. Learn how to change the default color of atoms.
This tutorial covers only 3D-periodic crystals and their surfaces. Quasicrystals aperiodic crystals are not covered. AMSinput can import and export coordinates in many different file formats, including. cif and. pdb files. When exporting to. xyz format, AMS also writes the lattice vectors into the file. In AMS, a 3D-periodic crystal can be represented as a periodic repetition of some unit cell.
This is known as periodic boundary conditions PBC. The unit cell is defined by three lattice vectors. For example, copper is a cubic closed-packed ccp metal with a face-centered cubic fcc lattice.
The primitive and conventional cells are:. In AMSinput you can switch between primitive and conventional cells. All other possible unit cells can be generated as supercells from the primitive cell. You can also view some of the periodic images of the system, without generating a supercell. Click the periodic view tool. The conventional Cu unit cell contains 4 lattice points in a crystallographic sense. AMS does not recognize that all 4 Cu atoms at the lattice points are identical, but would treat them independently at an increased computational cost compared to the primitive cell.
You can also edit them, but make sure to tick the Adjust atoms when changing lattice vectors box if you want the fractional coordinates to stay the same if you want the atoms to move when you change the lattice. Whenever you change the lattice vectors or lattice parameters, use the periodic view tool to double-check that the periodic boundary conditions are what you expect. You may also specify fractional coordinates in the text input file.
The components of the lattice vectors are cartesian xyz coordinates in angstroms. The lattice vectors can be rotated in an infinite number of ways relative to the cartesian axes. In AMS it does in general not matter how the lattice vectors are rotated. Two common conventions are.
Tick the Adjust atoms when changing lattice vectors , and press the Align c to z-axis or Align a to x-axis buttons. ReaxFF runs slightly faster if the the first convention is used. With DFTB, BAND, Quantum ESPRESSO, and VASP via AMS, you must specify some k-point sampling for periodic calculations. ReaxFF, ForceField, and MLPotential do not use k-points. In DFTB and BAND , you can specify the k-space quality using the values GammaOnly , Basic , Normal , Good , VeryGood , and Excellent.
You can also manually specify the number of k-points along each reciprocal lattice vector, or for highly symmetric systems use a Symmetric k-space grid. In Quantum ESPRESSO and VASP via AMS , you must manually specify the dimensions of the Monkhorst-Pack grid. To determine suitable k-point settings for your method and system, you should do a k-point convergence study in which you systematically increase the quality of the k-space sampling until the quantity that you are interested in e.
See Example: lattice optimization of wurtzite ZnO with DFTB for an example. The NumericalQuality keyword for BAND affects the k-space sampling. If possible, avoid comparing energies calculated with nonidentical k-space sampling.
For example, if you create a supercell from the primitive cell and introduce an interstitial defect, calculate the insertion energy with respect to the energy of the nondefective supercell , not with respect to a multiple of the energy of the primitive cell.
See also: Surface energy calculations. Recommendations for k-space. It is common in computational chemistry to optimize the lattice vectors of a crystal before constructing a supercell or surface. It is necessary to first optimize the lattice before calculating phonons or the elastic tensor.
ReaxFF is not reliable for lattice optimizations of small crystal unit cells. For ReaxFF we recommend creating a larger supercell at least 8x8x8 angstrom before running a lattice optimization. The first three are defined as for normal geometry optimizations. The maximum stress energy per atom is used as a convergence criterion for the components of the stress tensor. This example uses the znorg DFTB parameter set.
You can also run the example with ForceField UFF , BAND, or Quantum ESPRESSO. Table 3 gives the a and c lattice parameters for different k-space qualities. This is an example of a k-point convergence test. k-point convergence tests can be scripted with the PLAMS Python module. Download a PLAMS python script and xyz file to generate the above table. The rest of this tutorial only covers slab models , which are the most common type of surface model. AMS includes a kinetics module for modeling reactions on surfaces.
Surfaces are often defined based on Miller indices. A surface plane is denoted hkl. The Miller indices give the inverse fractional intercepts along the lattice vectors in the conventional unit cell.
If an index is 0, the surface lateral plane is parallel to that direction. A negative index is denoted by a bar. Example 1 : The Cu surface is parallel to the second and third lattice vectors of Cu in the conventional unit cell. Example 2 : The Cu surface is formed by the plane slicing all lattice vectors of the Cu conventional unit cell at the maximum coordinates for the unit cell. Example 3 : The Cu surface is formed by the plane slicing the second and third lattice vectors of the Cu conventional unit cell at the maximum coordinates for the unit cell, but slicing the first vector at one fifth.
This forms a stepped surface. For hexagonal crystals e. Zn or ZnO , four Miller indices hkil are often used. For hexagonal crystals with a rhombohedral lattice e. α-Al 2 O 3 or calcite CaCO 3 , the Miller indices can refer to either the rhombohedral primitive cell or the hexagonal conventional cell. You need to know which convention is used; when publishing or communicating with others, you should explicitly state which convention you use.
This direction is not necessarily perpendicular to the plane hkl. For hexagonal lattices, crystal directions can either be given using three indices as above, or a special four-index [hkil] notation. How to convert between the two types of notation is described in materials science or crystallography text books. Crystal directions are almost always given with respect to the conventional cell.
This will generate a Cu slab as in Fig. See also the Building Crystals and Slabs tutorial. The slab is rotated such that the surface normal direction is parallel to z. If you have the , , , or panel active, the periodicity will be automatically changed to Slab 2D. For the other engines, 3D periodicity Bulk is retained, and a vacuum gap is introduced. It is more common to use an angle of °. The above definition of hkl Miller indices was based on intercepts in the conventional unit cell, but any plane that is parallel to that plane is also a hkl surface, but with a potentially different surface termination.
In general, you should carefully look at the generated surface structure to see if it is reasonable. Generate 3 layers of a ZnO for hexagonal crystals, ignore the third index so type in 0 , 0 , 1. First generate the slab with the Zn 1 atom selected, then with the O 3 atom selected. The surface terminations are different. In the first case, the surface atoms become 3-coordinated, which is favorable.
In the second case, the surface atoms become 1-coordinated, which is much less stable. Create a thicker slab than you need , and manually remove atoms until the surface terminations are correct. Sometimes it is very difficult to create ideal slabs, especially if the crystal contains composite ions like carbonate, nitrate, sulfate, or phosphate. Surface passivation is often accomplished by adding H atoms that are coordinated by the surface atoms.
Such H atoms can passivate dangling bonds. Example : The diamond surface is terminated by two-coordinated sp 3 C atoms. This is very unstable. By passivating the surface with H, the dangling bonds at the surface become passivated. The DOS is high at the Fermi level The Fermi level lies in the band gap diamond is an insulator.
The Add Hydrogens function does not add H atoms to the most energetically favored positions. Randomly move the H atoms a little, and perform a geometry optimization, to find more suitable positions for the H atoms.
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