Theory Study Of Support Effect In Supported Gold Catalysts And The Performance Of O₂ Adsorption

Since Haruta et al.disclosed the excellent activity of supported gold for CO oxidation at low temperature,supported gold catalysts were proved to exhibit good activity and selectivity in various reactions,such as propylene oxidation,water-gas shift reaction and alcohol oxidation and so on.Gold catalysts show different catalytic activity for various reactions when adsorbed on different supports.For example,Au nanoparticles supported on TiO₂ are more active for CO and propylene oxidation than supported on other supports,while CeO₂ for water-gas shift reaction and HT for alcohol oxidation under mild reaction conditions.Certain supports are experimentally reported for specific reactions,but there exists no detailed information for the relationship between supports and the catalytic activity and selectivity.Therefore,density functional theory calculations were performed here to shed light on the mechanism of catalytic performance of Au₁₀ cluster dispersed on different supports including HT,ZnO,ZrO₂,CeO₂,Al₂O₃,TiO₂,graphene and SiO₂.All of the calculations in this work were conducted using CP2K software package and the interaction mechanism between Au₁₀and the supports,the electronic structure and charge distribution were explored.It was found that Au₁₀ favors planar structures and prefers the sites that match its own geometry structure.The adsorption energies increase as SiO₂?0001??graphene?TiO₂?110??Al₂O₃?0001??CeO₂?111??ZrO₂-mono?111??Zn0?10 0??HT.The larger value of adsorption energy indicates the stronger interaction between Au₁₀ and the supports.Au-Au bond length is also related to the supports,Au-Au bond length is lengthened when supported on supports compared to the bond length of Au-Au of Au₁₀ in gas phase.And with the increasing value of adsorption energy,the Au-Au bond length increases.The results of electron density difference indicate that there exists binding interaction between Au atoms and the metal atoms of the supports.The electrons transfering from the supports to Au₁₀0 clusters lead to negatively charged Au₁₀0 cluster except Au₁₀0 on SiO₂ and TiO₂.The positively charged Au₁₀ clusters on these two supports can be attributed to the O-dominated surface of SiO₂ and TiO₂.As for support effect in O₂ adsorption on supported gold catalysts,Au₁₀/ZnO,Au₁₀/ZrO₂,Au₁₀/TiO₂ and Au₁₀/SiO₂ are selected as the model systems to explore the O₂ adsorption configurations on those models.Whether O₂ prefers to locate at Au₁₀ clusters or at the interface between Au₁₀ and the surface was studied.The binding mechanism and charge distribution were also discussed.The results are as follows:O₂ prefers the interface structure when adsorbed on Au₁₀/ZrO₂ and Au₁₀/SiO₂ while O₂ on Au₁₀/ZnO and Au₁₀/TiO₂ favors to locate at Au₁₀ clusters.O₂ in Au₁₀/ZrO₂ interacts with the surface Zr atom while O₂ adsorbed on others only interact with Au atoms.O₂ behaves as electron acceptor in all structures,and the electrons are mainly from Au atoms except Au₁₀/ZrO₂.O₂ on Au₁₀/ZrO₂ gets electrons from not only Au atoms but also the surface Zr atom.