Using Ab Initio Molecular Dynamics To Study The Reaction Process Of CO₂ And H₂ On Cu（100） Catalytic Surface

The rapid consumption of fossil fuels has accelerated the energy shortage,which has forced us to develop new energy sources as soon as possible.Hydrogen energy is one of them,which has the advantages of clean and easy production.Methanol can dissociate to produce hydrogen,and is easier to store and transport than hydrogen.Methanol can be industrially produced from H₂,CO,and CO₂ through the catalysis of Cu/ZnO/Al₂O₃.This catalytic reaction can also reduce carbon pollution in the environment.Although many theoretical and experimental studies have been done on the reaction of CO₂ hydrogenation to produce methanol on the copper surface,the complete reaction mechanism of this reaction is not clear.We have used the ab initio molecular dynamics（AIMD）method to study the reaction mechanism of CO₂ on the Cu（100）surface through a step-by-step hydrogenation reaction to form methanol.This method does not assume any intermediate products and reaction steps in advance,so that all reactants have An initial state of free movement.In the ab initio study,we used two layers of AIMD calculations.The first layer was to place the maximum number of adsorbates on the Cu（100）surface to cover the entire surface.The purpose of this is to simulate the real state.It is well known that traditional reaction kinetics places only one adsorbate on the surface,but in reality there is not only one on the surface,but many reactants,and the entire surface can adsorb the maximum amount that can be accommodated.The second layer of kinetic studies only places an adsorbate on the surface in order to simulate and study the detailed changes of each elementary step.The purpose of the second layer is not only to verify the reaction mechanism found in the first layer,but also to study the properties of each intermediate product and the structural changes of each reaction step in a more detailed and convenient way.All in all,our research pays more attention to the simulation of the real environment,so that important molecules can completely and randomly collide,and the results are more convincing.In many previous studies,some people think that HCOO*is a key intermediate product,and some people think that COOH*is a key intermediate product.We used AIMD to simulate random and free molecular motion and found the intermediate product COOH*,which verified the COOH*path.More importantly,we have discovered a new intermediate product,HCOHOH*,which was previously found in theoretical calculations of methanol synthesis reactions on copper surfaces.After this new intermediate,we found two new reaction paths.These two paths follow the same first half,starting to become different from the new intermediate.The first is a step-by-step method of hydrogenation by H₂ continuously moving from the asymptotic region to the surface,and the second is a method in which two adjacent HCOHOH*adsorbed on the surface continue to react through proton transfer.Both new paths have the same highest energy barrier of 0.68eV（with zero point energy）,which limits the rate of reaction.In addition,it should be pointed out that although both pathways can produce the same intermediate products and can also synthesize methanol in the end,after the same first half,in the second half of the different paths,the second path is better than the first path have lower energy barriers.The research on the reaction mechanism of methanol synthesis on Cu surface is far from over,especially when there are oxides or impurities on Cu surface.In addition,there are various disputes as to whether the key intermediate product is HCOO*or COOH*.The mainstream research method in this field is the climbing image nudged elastic band method.Researchers use this method to connect the intermediate structure of a predetermined reaction process.We have used the two-layer AIMD method for the first time to study the reaction mechanism of methanol synthesis on the Cu（100）surface.The advantage of this method is to simulate the real environment without presupposing any reaction mechanism and intermediate products.The method of being able to randomly and randomly collide reactions in space,and covering the surface with reactants increases the probability of reaction,and it is easier to find some new reaction mechanisms.This also provides a new idea for future research in this field.