COLLOIDALLY SYNTHESIZED BIMETALLIC NANOPARTICLES FOR WELL-DEFINED HETEROGENOUS CATALYSTS IN ALKANE DEHYDROGENATION

Over the past decade there has been an increase in the production of natural gas from shale deposits, which has presented tremendous opportunity to develop efficient technologies for the production of chemicals and fuels. Shale deposits primarily consist of methane, but they can also contain up to 20% ethane and propane. These light alkanes are used in the production of olefins, which can then be converted into fuels and chemicals. In this thesis we describe efforts to develop novel catalyst synthesis methods to tune the morphology and composition of bimetallic nanoparticles in order to achieve selective and stable non-oxidative alkane dehydrogenation.

First, a multistep colloidal synthetic process was implemented to make well-defined Pt-In and Pt-Ga nanoparticles prior to being supported on SiO₂ for light alkane dehydrogenation. The obtained nanoparticles were stripped of their ligands in order to generate a uniform population of alloy catalysts in the absence of large excesses of In or Ga oxides. Control over bimetallic composition and morphology allowed us to elucidate the role that phase and composition play in tuning reactivity, selectivity, and stability of the catalysts under reaction conditions. The promoter rich nanoparticles with a PtIn₂ alloy structure displayed the best performance, which could be attributed to strong electronic modifications to Pt sites, observed by X-ray absorption spectroscopy at the Pt L^III-edge. In addition, X-ray diffraction, electron microscopy and catalytic tests after high temperature reduction, demonstrated that colloidally synthesized nanoparticles were more thermally robust than their incipient wetness impregnation analogs.

Beyond ascertaining the role that composition and morphology play in light alkane dehydrogenation, mitigating catalyst deactivation processes such as sintering and coking will be critical toward the development of high performance catalysts. Colloidally synthesized PtIn₂ nanoparticles were supported on Ca-doped SiO₂ to systematically study the role of alkali-earth additives in influencing Ostwald ripening processes that lead to nanoparticle sintering and deep dehydrogenation reactions that result in catalyst coking.

Together, the projects outlined in this thesis demonstrate how colloidal synthesis can serve as a powerful tool in the understanding of structure-activity relationships in alkane dehydrogenation. We anticipate that the insights derived from colloidal synthesis will advance the rational design of new high-performance catalysts