A Dft Study On Partial Process In Catalytic Purification Of Auto Exhaust Over Pd, Pt, Rh And Their Alloy Catalysts

At present, the automobile exhaust pollution control has become a topic of concern at home and abroad, the three-way catalyst composed by Pd/Pt/Rh and catalytic carrier has been proved to be the best choice in Catalytic Purification of Auto Exhaust because of the better catalytic properties and anti-toxic. So it is become important to improve the catalytic properties and develop the alternative products by study the catalytic mechanism. Also the metal surface adsorption and desorption has been an important subject of surface science in the past several decades.The adsorption of H2, NO, CO and H2O, CO2, N2 molecule on a set of metal surfaces such as Pd(111), Pt(111), Rh(111), PdRh(111) and PtRh(111) has been studied with periodic slab model by Perdew-Burke-Emzerh(PBE) approach of GGA within the framework of density functional theory(DFT). PdRh and PtRh has a same proportion. Several consequences are discussed.The DOS of PdRh(111) and PtRh(111) are calculated and compared with pure metal surface Pd(111) and Pt(111), analyze the changes of DOS and reasons for the changes. Optimized geometries and adsorption properties for every gas on four adsorption sites, namely top, bridge, fcc hollow and hcp hollow sites of different metal surfaces are presented. The results show the doping of Rh effect on the adsorption properties. H2 and NO molecule are studied by two kinds of adsorbed forms on the metal catalyst:linear complex and the bridge complex adsorption mode. The optimized results indicate that the bridge complex adsorption of H2 is dissociative adsorption while NO turns to the tilted state.The translation states of the dissociation of NO and the former of CO2 and N2 are found by using LST/QST. The results indicate that the dissociation activation energy of NO decrease on PdRh(111) and PtRh(111) compared with Pd(111) and Pt(111), while the activation energy of the formation of CO2 and N2 increased.The processes of the adsorption and dissociation of automobile exhaust on different translate metal surfaces are systematically investigated in this paper. The work in this paper will supply guidance in theory for future research.