Supporter Regulation Of Catalytic Activity Of Noble Metal Nanoparticles

The catalytic materials constructed by precious metal nanoparticles supported on the surface of materials with large specific surface area are widely used in chemical reactions in many fields such as chemical medicine,energy conversion,and environmental protection.Improving its activity through proper material design is the core theme unchanged in this field,and the traditional strategy is mainly to modify the metal components.In recent years,with the strengthening of the understanding of the metal-support interface interaction,it has become an important research topic to improve the overall performance of catalytic materials through modification of support oxides.This thesis focuses on the influence of TiO2 support on the electronic structure of supported precious metals.The electronic structure of Pd nanoparticles is adjusted by adjusting the Fermi level of TiO2 semiconductors,and the relationship between the electronic structure of Pd and its catalytic hydrogenation performance is explored.The main findings obtained are as follows:1.Pd/CrxTi-xO2(x=0.00,0.01 and 0.05)catalytic materials were successfully prepared by gel hydrothermal method and sedimentation precipitation method.The CrxTi1-xO2 support is a hollow spherical anatase structure,and no Cr oxidation It indicates that Cr enters the TiO2 lattice by doping.Energy spectrum analysis showed that Pd,Cr and Ti elements were uniformly distributed in the catalyst.2.Electronic structure analysis shows that Ti exists in the form of Ti4+ and Ti3+,O exists in the form of lattice oxygen and surface adsorbed hydroxyl species,Cr exists in the form of Cr3+ and Cr6+,and Pd exists in the form of Pd2+and Pd0.As the doping amount of Cr increases,the proportion of Cr6+ in the carrier increases,the amount of Pd2+ decreases,and the amount of Pd0 increases.At the same time,the flat band potential of the CrxTi1-xO2 carrier gradually shifted toward the low potential direction with the increase of Cr content,and the Fermi level moved up.It is confirmed that Cr6+ doping is the main reason for changing the Fermi level of the carrier.Cr6+introduces electrons into the carrier,which increases the Fermi level of the carrier and transfers the electrons in the carrier to Pd,thereby increasing the amount of Pd0.Pd0 as the active site of hydrogenation reaction,the increase in the number of active sites,accelerate the hydrogenation reaction rate of phenylacetylene and benzaldehyde,and improve the catalytic activity of the catalyst.3.Pd/AlxTi1-xO2 was prepared by sol hydrothermal method and sedimentation method,which is an anatase hollow sphere structure.Al exists in the form of Al3+,and the binding energy of Pd is shifted to a high energy direction.With the increase of Al doping,the flat band potential of TiO2 is shifted forward,and the Fermi level is shifted downward.Therefore,when Pd is in contact with the AlxTi1-xO2 support,the amount of electrons transferred from the support to Pd decreases,which reduces the negative charge of the Pd band.In the acetylene hydrogenation reaction,Pd reduces the carbon-carbon double bond and the adsorption strength of hydrogen atoms on its surface,inhibits the carbon-carbon double bond hydrogenation and thereby improves the reaction selectivity.