(20b) Selective Butene Formation in Direct Ethanol to C3+ Olefin Valorization over Zn-Y/Beta and Single-Atom Alloy Pt-Cu Composite Catalysts Using in Situ Generated Hydrogen

The identification of catalytic pathways for generating renewable fuels and fuel additives from biomass-derived feedstocks is of critical importance to achieve carbon-neutral operations. Here, we present our latest work on designing a catalyst combination consisting of multifunctional bimetallic Zn-Y/Beta zeolites and “single-atom alloy” (SAA) Pt-Cu supported metal catalysts for ethanol upgrading into butene-rich olefins as precursors to jet-range hydrocarbons. Ethanol conversion to 1,3-butadiene and subsequent hydrogenation to butene isomers occurs through a complex reaction network consisting of dehydrogenation, aldol condensation, dehydration, and selective hydrogenation reactions where each reaction step requires unique active site requirements for efficient conversion. The development of multifunctional catalysts through the incorporation of multiple transition metals (e.g. Zn, Y, Cu, Pt) onto a single support (e.g. Beta, Al₂O₃) is investigated using a suite of in situ and ex situ characterizations (e.g. XAS, HAADF-STEM, pyridine DRIFTS) to identify both Lewis and Brønsted acid sites. These site configurations and mixed metal center identities are correlated to specific reaction steps at 588 K and are evaluated at both high (>95%) and low (<10%) ethanol conversions. High conversion product distributions indicate improved ethanol valorization to butene-rich olefin streams (65% butenes, 78% C₃₊ olefin selectivity at 94% conversion) while avoiding further hydrogenation to butanes or other saturated hydrocarbons. This ethanol-to-olefins (ETO) reaction network is accomplished without cofed hydrogen using a SAA Pt-Cu catalyst capable of catalyzing butadiene hydrogenation at stoichiometric hydrogen and butadiene partial pressures and reflects a significant step towards economically viable renewable olefins generation from bioethanol.