With increases in availability, decreases in its production cost, and available infrastructure for bio-derived ethanol production, ethanol has become an attractive platform molecule for the production of value-added chemicals. Isobutene (IB) is a highly valued industrial chemical that can be used as solvents, fuel additives, and precursors for synthetic rubber. In order to become less dependent on finite fossil fuel resources, sources other than crude oil are needed for isobutene. Mixed metal oxides are promising catalysts due to their dual acid-base functionality for multi-sequential step reactions converting ethanol to IB. In our previous work, IB yield – as high as 83% – from bio-ethanol was achieved over ZnxZryOz catalysts. Further work revealed that weak Brønsted acid sites were responsible for increased IB yield. However, the ZnxZryOz catalyst prepared by a hard template method (ZnxZryOz-H) suffered from deactivation and produced undesired C4 isomers with the IB stream due Brønsted sites. To mitigate these two issues, a new catalyst (ZnxZryOz-I) with only Lewis sites was designed and synthesized. Steady state and kinetic experiments, and pyridine-infrared spectroscopy (Py-IR) have been used to correlate the acidic sites with the activity of ZnxZryOz catalysts. The redesigned ZnxZryOz-I catalyst, with only Lewis acid-base pairs, showed not only high selectivity to IB without other C4 isomer formation, but also high stability (no noticeable deactivation for &gt;200 hours of TOS) (Fig. 1). Reaction pathway studied using isotope labeling and characterization work to elucidate acidic sites roles of ZnxZryOz-I will be presented. Fundamental understanding of acidic site requirements can be applied to the rational design of catalysts for the conversion of other bio-derived compounds.

Rational design of ZnxZryOz catalysts for the conversion of ethanol to isobutene with improved selectivity and stability

251st National Meeting (2016)

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