Ethanol is a promising platform molecule for the economically viable production of a variety of fuels and chemicals and with reduced carbon footprint. With the aviation industry committed to reduce their carbon footprint in half within the next three decades, producing jet fuel blendstock from renewable- and waste-derived ethanol feedstock is of particular interest. However, new processes must be developed that are both carbon efficient and with robust catalysts. We have developed a metal-supported ZrO2/SiO2 catalyst system with specially tailored metal and Lewis acid sites for producing either butadiene or n-butene from ethanol, and with outstanding activity, selectivity, and stability. Initially developed for the conversion of ethanol to butadiene, a Ag-based catalyst was found in our lab to be active for the single-step conversion to n-butene-rich olefins. High selectivity toward the targeted product is obtained by tuning the process conditions, including feed gas composition (e.g., H2 vs. N2 co-feed). For example, with either N2 or H2 co-feed, butadiene (71% selectivity) or n-butene-rich olefins (88% selectivity), respectively, were produced from ethanol at near complete conversion (99%). Although butadiene catalysts typically deactivate within hours, remarkably stable production of either butadiene or n-butene rich olefins was demonstrated for 100+ hours, as illustrated in Figure 1. XPS measurements have indicated that the product composition depends on the oxidation state of Ag. While n-butene formation is favored over metallic Ag, butadiene formation is preferred over partially oxidized Ag. Reactivity measurements coupled with operando NMR experiments have shed light on the reaction mechanism. Over supported Ag catalysts, n-butenes are primarily formed because of intermediate butadiene hydrogenation, while a small portion is also produced from butyraldehyde intermediate. We have additionally found how the choice of metal promotion can also influence the catalytic mechanism thereby significantly affecting catalyst stability.

Single-step conversion of ethanol to n-butene-rich olefins or butadiene over metal supported on ZrO2/SiO2 catalysts with tailored metal and Lewis-acid sites

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