Theoretical Study Of The Structure And Performance Of Nano-catalytic Materials In Real Reaction Environment

As the frontier of chemistry and materials science,heterogeneous catalysis has a wide range of applications in the fields of chemical synthesis,pollution control,petroleum smelting,energy storage and utilization.Here,the structure morphology and element distribution of the catalytic material have a decisive influence on the performance of the catalyst.However,with the development and progress of scientific research,people have gradually realized that the structure and performance of nano-catalytic materials may dynamically change in the reaction.Therefore,studying the dynamic changes of nano-catalytic materials during the reaction process is crucial for a thorough understanding of their micro-reaction mechanisms.Fully analyzing these relationships is a prerequisite for screening catalysts and catalytic conditions,and even for designing new types of catalysts and reactors.Since the catalytic process is a complex process involving multiple factors,it is difficult for the most advanced characterization instruments to clearly study the dynamic structure and performance of the catalyst under the reaction conditions.Aimed at this key scientific problem,combining the development of the all-atom kinetic Monte Carlo（KMC）model,the specific experimental system,and the density functional theory（DFT）calculations,This thesis theoretically studied dynamic behavior of different kinds of metal-based nanocatalytic materials in real reaction,as following:（1）Combining the DFT calculations and the self-developed Monte Carlo model of all-atom dynamics,the effect of temperature on the structure of non-equilibrium nanocrystals is studied.The structural evolution of Pt hollow cube was consistent with the experimental observation results of Xia et al.,which verifies the accuracy of the model.Further analysis of the results revealed that the structural instability of the hollow nanocrystals originated from the imbalance of the coordination number of the atoms on the inner and outer surfaces,which resulted in the reconstruction speed of the outer surface being higher than that of the inner surface.And then,the design of a high-stability hollow Wulff was proposed.The strategy of nanocrystal structure has been verified in the three hollow nanocrystals of Au,Pt and Pd.Furtherly,the model was extended to different reaction environments.The surface structure and performance of the catalytic material were studied in the nanocatalytic reaction.The effect of the simulated CO environment on the surface structure of Pt（332）and Pt（557）was consistent with the experimental results of Tao et al.,which verifies the reliability and scalability of this model.By studying the Pt-catalyzed CO oxidation reaction under different conditions,the relationship between the morphology and performance of nano-catalytic materials was revealed on the atomic scale.（2）Combined the DFT calculations and in-situ experimental observations,the influence of the water vapor and water gas reaction environment on the surface structure of the reconstructed nano-anatase Ti O₂（001）-（1×4）was studied.Through a large number of structural screening and theoretical infrared Vibrational spectrum calculation and reaction path search,etc.,for the first time analyzed the‘twin-protrusion’structure found in the experiment,and revealed the reason for the unstable‘twin-protrusion’phenomenon observed in the experiment;studied the effects of oxygen and carbon monoxide oxidation environment on gold The influence of nanoparticle-nano anatase Ti O₂（001）interface.It was found that when the oxygen adsorption at the interface increases or decreases,the rotation of Au nanoparticles makes the combination with the substrate more stable.The proposed strategy of adjusting the interface by changing the gas environment and temperature has been verified by experiments.The effect of carbon dioxide hydrogenation reaction on the structure and performance of the nickel-gold core-shell catalyst was studied under the action of different adsorbed species,which explained the surface alloying phenomenon of the Ni-Au core-shell catalyst during the reaction.Through the search and analysis of the reaction network,the reasons for the high CO selectivity and low methane selectivity of the Ni Au bimetallic catalyst observed in the experiment were revealed.In short,this thesis introduces our self-developed all-atom KMC model,which can simulate and predict the influence of different temperatures and reaction environments on the structure and performance of nanocrystals.Combined with the experimental observation results of in-situ TEM,the nature of the influence of different reaction environments on the structure and performance of the catalyst was explored.These research works not only confirm that the study of the dynamic process of the catalyst in the reaction has outstanding significance for many catalytic processes in the reaction environment,but also show that the study of the process is expected to become a key direction for the design of high-efficiency catalysts.