Supported Metal Nanoparticles Stability Under Reaction Condition Investigated By Density Functional Theory

Recent progress in the precise synthesis and in situ characterization provides evidence and understanding of nanocatalysts and the relation between catalytic performance and local structures.Improving the stability against different deactivation mechanisms under reaction conditions is essential for better sustainment of catalysts.In this thesis,we studied the growth and disintegration of supported metal nanoparticles under reaction conditions with the influence of the metal/reactant composition,temperature,reactant pressure,and defects by using density functional theory(DFT)calculations and kinetic simulations of ripening.1.The gaseous Ostwald ripening(OR)under reaction conditions has been studied with kinetics simulation and thermodynamics calculations.Using the gaseous PtO2 as the ripening intermediate,the effect of particle distributions,reaction conditions,and intermediates adsorption-desorption are evaluated.Results of different particle size distribution simulations show that larger and more unified particles are more ripeningresisted.Higher reactant pressure and pressure both accelerate the ripening.2.Competition of oxygen-induced disintegration and OR have been studied for Ni,Cu,Pt,Pd,and Ag nanoparticles on TiO2(110).The binding between different metals and supports and reactants leads to different behaviors.Cu shows strong binding with oxygen and favors oxidation.The strong binding between NiO and support induces the disintegration of Ni into the supported NiO complex.Pt forms volatile gaseous PtO2 and favors gaseous OR.Ag and Pd have moderate interactions with support and weak interaction with oxygen,hence surface OR occurs through surface Ag/Ag-O complex and Pd atoms.3.Disintegration of Ni,Cu,Ag,Au,Pt,Rh,Ru,and Ir nanoparticles under CO and H2O conditions have been studied thermodynamically.Compared to OH,CO shows strong binding with Ni,Rh,Ru,and Ir and can disperse these particles.Metals-reactant complexes with higher cohesive energies generally have higher aggregation resistance due to stronger binding with reactant and support.Support defects can greatly stabilize the metal adatoms,but have only a minor effect on the metal-reactant complex.