Rational Design of Metal Alloy Catalysts for Engine Emission Abatement and Biofuels Production

Metal alloy catalysts with high activity, selectivity and stability have found applications in numerous industrial processes; yet, the origins of their unique properties compared to their parent metals are not well understood. Recent developments in quantum theoretical calculations in combination with advanced experimental characterization techniques have significantly improved our understanding of the synergistic catalytic effects of alloying metals, which in turn drives the design of improved heterogeneous catalysts. In this dissertation, we focus on the applications of metal alloy catalysts in emissions control for low temperature combustion and diesel engines, and the production of clean and sustainable fuels from biomass feedstock. To design improved metal alloys for emission control, we initially used a combination of density functional theory and descriptor-based microkinetic modeling, and computationally screened promising binary alloys. A Pd-alloy was found to be a better CO oxidation catalyst in the presence of NO and hydrocarbons compared to the commonly used Pt and Pd alloys. It not only exhibits higher activity at reduced temperatures, but also overcomes the mutual inhibition effect between CO and NO oxidations. Moreover, we integrated the descriptor-based catalyst design with reactor models to further optimize the overall DOC efficiency and minimize catalyst loading. The results show that the overall diesel oxidation catalyst (DOC) performance can be improved by designing a DOC reactor with metal concentration gradients, where the local alloy formulation is optimized for the local temperature and exhaust gas compositions. For the Guerbet and related condensation reactions, which can convert biomass-derived short chain alcohols into higher molecular weight oxygenates for the production of bio-fuel and bio-chemicals, Pd-Cu alloys were found to exhibit exceptional activity and selectivity. Experimental evidence and computational results indicate that the origin of the remarkable properties of this bimetallic alloy catalyst stem from electronic structure modifications, segregation, coverage and particle size effects. Overall, our results show that the ability to fundamentally understand the catalytically active sites on metal alloys through a combination of computational and experimental characterization methods can be used to rationally design metal alloy catalysts applicable to a wide range of processes.