Colloidal Synthesis of Well-Defined Bimetallic Nanoparticles for Nonoxidative Alkane Dehydrogenation

Precise synthesis and characterization of bimetallic nanoparticles are critical toward understanding structure–activity relationships in alkane dehydrogenation catalysis. Traditional synthetic methods for Pt alloy catalysts involve impregnation of two metal salts onto high surface area supports followed by thermal reduction to form an alloy, which frequently results in inhomogeneous alloying and phase segregation of excess metal oxides in the material. In this work, we utilize colloidal methods to synthesize supported Pt–In and Pt–Ga nanoparticles with controlled bimetallic composition. The supported colloidal nanoparticles display phase uniformity while eliminating large excesses of In and Ga oxides, which allows us to ascertain the role that the bimetallic phase and composition play in tuning the reactivity, selectivity, and stability of the catalyst in both ethane and propane dehydrogenation. Indeed, the promoter-rich PtIn2 phase shows the highest turnover rate for ethane dehydrogenation, which we attribute to both the strong electronic perturbation to Pt sites observed in Pt LIII-edge X-ray absorption spectroscopy and the major geometric change at the surface upon formation of the CaF2 crystal structure adopted by PtIn2. Finally, we show that the promoter-rich colloidal nanoparticles are more thermally robust than incipient wetness impregnation catalysts of the same composition because they eliminate two deactivation pathways—reduction and vaporization of unalloyed promoter atoms—that only occur on the structurally nonuniform impregnated catalyst.