RATIONAL DESIGN OF MULTIFUNCTIONAL ZEOLITES FOR BIOMASS CONVERSION

Abstract

Biomass conversion to long-chain hydrocarbons is imperative to producing sustainable feedstock for the transportation sector's decarbonization. The complexity of biomass composition requires hybrid conversion technology where the rational design of multifunctional catalysts is indispensable for the efficient downstream process towards platform molecules. Conversion of biomass-derived ethanol or butanediol to C3+ olefins via heterogeneous catalysis is a promising pathway for generating platform hydrocarbon molecules. Zeolite is crystalline microporous material with a framework of silicate tetrahedron (SiO4) and AlO4 tetrahedra. The unique porous structure provides shape selectivity for both reactants and products, and isomorphous heteroatom substitution can form Brønsted or Lewis acidic sites (LAS) with tunable acidity, creating the capability of catalyzing the critical reaction steps in biomass conversion. This dissertation starts with titrating mesopore interconnectivity within pillared MFI and MWW zeolites by atomic layer deposition of titania to get proper candidates with improved diffusion conditions. The results indicate better mesopore connectivity in PMFI than PMWW. Afterward, bifunctional Cu/PMFI was synthesized to catalyze 2,3-butanediol conversion to C3+ olefins, with alkaline-treated mesoporous Cu/ZSM-5 as reference material. It is demonstrated that better mesopore connectivity plays a crucial role in depressing coke formation. For ethanol conversion, the creation of new types of Lewis acidic sites within the BEA zeolite framework was done by incorporating rare-earth and other transition metals. The as-synthesized catalysts can achieve over 80% C3+ olefins yield in one-process-step ethanol conversion. Characterizations and further kinetic study demonstrate the acidity and isolated status of loaded metal species as well as their functionalities. Also, the corresponding reaction network from ethanol to C3+ olefins was revealed. A similar synthesis procedure was applied to other silica supports. However, the as-formed isolated sites showed strongly support-dependent activity. Further improvement focuses on reducing external hydrogen input by utilizing the intrinsically generated H2 in the ethanol dehydrogenation step. A composition of Lewis acid Beta zeolite and single-atom alloy catalyst was studied with a two-bed configuration, which can achieve over 70% C3+ olefins yield without external H2 input. This work provides new types of supports, acid sites, and system designs to overcome the challenges of biomass-derived alcohols upgrading.