Theoretical Investigations On Interfacial Effect In Heterogeneous Catalysis

Interfaces play an important role in heterogeneous catalysis,they usually exist in multicomponent catalysts.Because interfaces can provide unique active sites,multicomponent catalysts can break up energy scaling relationships of single component and achieve higher catalytic performance than corresponding single component.In general,interfaces are related with varied materials,such as conductor,semiconductor,insulator.Traditional experimental measurements,like Scanning Tunneling Microscope(STM),are not qualified for interfaces like conductor-semiconductor interface which is the interface between metal and metal oxides in catalysis.With computing resources increasing and the development of density functional theory calculations,we can use simulation methods to explore interface problems which cannot be handled easily through experiments.By theoretical computations like adsorption configuration,transition state search,reaction pathway analysis,charge density analysis,density of states,this thesis systematically investigates the interfacial effects in heterogeneous catalysis.To demonstrate the universality of interfacial effects in heterogeneous catalysis,this thesis chooses different types of interfaces in different reactions as followed:(1)metal/oxide interface: this chapter chooses Pd-Ti O2 as research objects and uses Ti O2 supported Pd nanorods to minic Pd-Ti O2 interfaces.Different combinations between Pd facets and Ti O2 surfaces lead to different catalytic performace,and these diversity origins in Pd's activities and varied ability to excite electrons of Ti O2.(2)metal/metal interface: this chapter investigates propane dehydrogenation on Pt-based catalysts and build two models which are Pt surface alloys and Pt(111)with metal adatoms.Within all metals adding to Pt,Sn shows the highest dispersibility and is not likely to accumulate on Pt(111),so Sn can isolate active Pt atoms efficiently.Meanwhile,Sn is inert in C-H activation and has weak propylene adsorption energy.Thus,the rate of side reaction is low and propylene is easy to leave the surface,improving selectivity of propane dehydrogenation.In Pt Sn interface,the electron transfer from Sn to Pt would charge Pt negatively,while propylene has ? electrons,resulting in weaker propylene adsorption than Pt(111).(3)oxide/oxide interface: this chapter investigates propane dehydrogenation on Zr O2/Ga2O3 and performes reaction pathway analysis on three relevant models(Zr O2/Ga2O3,Zr O2,Ga2O3).First-principles calculations show that 4 coordinated Zr atoms in the Zr-Ga oxide interfaces are the energetically favorable sites for the adsorption of propane molecules.The subsequent successive dehydrogenation steps are then catalyzed by the low(4)coordinated Zr atoms.Ga2O3,on the other hand,plays a key role in stabilization and adsorption of propyl radicals.More importantly,it promotes the diffusion of dissociated hydrogen atoms so that the low coordinated Zr atoms are not deactivated by the adsorption of the dissociated H to adjacent O lattice atoms.