| The increasing fuel consumption and COx emission have broken the natural balance of circulation,resulting in the unsustainability of energy and environment.Therefore,catalytic reduction of COx into value-added fuels and chemical by using CO2 hydrogenation and Fischer-Tropsch synthesis methods realize the strategic significance of recycling economy.However,the cost of C-O bond breakage,which is a necessary step,is high,and the activation mechansm is still controversial.Recently,researchers focus on the selection and preparation of the high-efficiency catalysts.Yet,most of these works are limited to phenomenological study.With the rapid development of quantum chemistry and computational science,theoretical simulation has become an important methods during catalytic filed.In this work,we will systematically study the correlation between catalysts microstructure regulation(i.e.control the surface structure,environment and surface state of support)and COx decomposition activity by using first principles calculations,which will provide performance information and guide the preparation of such materials.For the CO2 conversion,we first studied the adsorption and degradation process for CO2 on a single Zn2Ge04 catalyst.The purpose of this work is to explore the effects of characteristic of preadsorbed H2O and reciprocal action with oxygen defect on reactivity of C-O bond scission.Secondly,after studying the adsorption and nucleation of Ru cluster on Al2O3 support in detail,we considered the influence of carrier effect on the CO2 decomposition process.The results indicated that the thermodynamics and kinetics of such step are determined by the electronic structure of the catalyst,for example,charge polarization and d-band center.For CO conversion,in view of the impurity ions presented in the system,we chose the CO adsorption and degradation on Ru(0001)as a representative and revealed the influence of surface ions on the CO decomposition.Our main research content and conclusions are as follows:In the first chapter,we mainly discussed the background and significance of this dissertation,including the mechanism and research status of COx catalytic conversion,the status of single catalysts with controlled surface/environment as well as the supported catalysts with controlled carrier states.At the end of this section,we discussed the deficiencies of the current study and summarized our research work.The second chapter described the basic principle of density functional theory,the two approximation theory that dealing with exchange-correlation energy,and the self-consistent filed calculation.Based on this,we introduced two quantum computing package.In the third chapter,we performed density functional theory calculations to study the adsorption and decomposition of CO2 on perfect and defect Zn2GeO4(010)surface.It is found that these processes were depended on the properties of adsorbed water and the reciprocal action with oxygen vacancy.When a perfect surface was hydrated,the dissociative H2O was predicted to greatly promote the H-assisted C-O bond scission step.The perfect surface with bidentate binding H2O was energetically more favorable for CO2 dissociation than the surface with monodentate-binding H2O.Direct dissociation was energetically favored by the former,whereas monodentate H2O facilitated the H-assisted pathway in thermodynamically.The defective surface exhibited a higher reactivity for CO2 decomposition than the perfect surface because the generation of oxygen vacancies could disperse the product location.When the defective surface was hydrated,the reciprocal action for vacancy and surface H2O on CO2 dissociation was related to the vacancy type.The presence of H2O substantially decreased the reaction energy for the direct dissociation of CO2 on O2c1-and O3c2-defect surfaces,which converted the endoergic reaction to an exoergic reaction.However,the increased decomposition barrier made the step kinetically unfavorable and reduced the reaction rate.When H2O was present on the O2c2-defect surface,both the barrier and reaction energy for direct dissociation were invariable.These results provided a theoretical perspective for the CO2 decomposition process and the design of highly efficient catalysts.In the fourth chapter,we further studied the geometries and electronic structures for Run(n=I-4)clusters adsorbed on Al2O3 surfaces,as well as the adsorption and dissociation behavior for CO2 on Ru4/Al2O3.The results indicated that the Run deposition process was strongly sensitive to cluster size and surface structure.A single Ru atom preferred to be adsorbed on the(100)surface with small deformation energies,while small interaction energies led to the adsorption of Ru4 clusters on the(110)surface.When the surface was dehydrated,the adsorption of Run(n=2-4)clusters on the(110)surface was substantially more stable than that on the(100)surface,due to the stronger acceptor present on(110)increased the bidirectional electron transfer between the clusters and surface sites.When the surface was hydrated,the introduction of hydroxyl groups lowered the Run(n=2-4)clusters' adsorption ability on the hydrated(110)surface by decreasing the surface acidity and basicity.However,the surface hydroxyl groups increased the stability of the adsorption of the Run(n=1-4)clusters on the hydrated(100)surface as surface H acted as an adsorption site,receiving an electron from the Ru atom because of its strong Lewis acidity.Moreover,it is found that the CO2 adsorption and decomposition were sensitive to support surface structure and hydroxylation.The irregular(110)surface help separate dissociated products and raised the d-band center of Ru resulting in a lower barrier for direct C-O bond decomposition in interfacial site.For Ru4/Al2O3(100),the smaller charge polarization on reactants caused the HCOO*-mediated association pathway to be favored in high temperature while direct dissociation route in low temperature.Although this difference made the reaction thermodynamically more favorable,it reduced the cleavage rate.The presence of hydroxyls thermodynamically favored CO2 dissociation via a COOH*intermediate and kinetically preferred direct dissociation.Although the introduction of hydroxyls to the(110)support substantially decreased the distance between products and lowered the Ru d-band center.However,the opposite behavior was observed thermodynamically for the direct and COOH*-mediated routes,because less charge was transferred to the reactant.These results showed that the decomposition pathway of CO2 was related to the support states,which gave a reasonable explanation for the experimental controversy.In the fifth chapter,we mainly studied decomposition of CO on clean,the Cl-and S2-modified Ru(0001).The results showed that regardless of the surface,the HCO*-mediated associate route was energetically more stable than direct scission.However,the overall reaction potential had a strong surface dependence.Such difference was mainly caused by the surface electronic structure.Because the introduction of Cl-largely shifted the d-band to low energy,the decrease in the hydrogenation energy and activation barrier compensated for the increase in decomposition barrier for C-O bond,resulting in favored the reaction in thermodynamically.The opposite was observed for the introduction of S2-,in which the S2-decreased the reaction rate because the promotion of hydrogenation was less than the suppression of C-O bond scission.These results provided a theoretical basis for understanding the effects of ions on CO cleavage activity.Finally,in the sixth chapter,main conclusions and the innovation of this paper were summarized,and the future research direction was made. |
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