Catalytic dehydrogenation of isobutane over supported MoOx/K-Al2O3.

[Display omitted] • Sub-monolayer Mo oxides are demonstrated as stable alkane dehydrogenation catalysts. • Partially reduced Mo4+ sites are the active species for dehydrogenation. • Catalyst structure is stable under reaction conditions regardless of Mo loading. • Deactivation is due to coke formation, not continual catalyst restructuring. • Mo reduction to oxidation states lower than Mo4+ correlates with increased coking. Potassium-promoted, alumina-supported molybdenum oxide is investigated for non-oxidative isobutane dehydrogenation, with an emphasis on sub-monolayer coverages. After pre-reduction in H 2 , initial isobutene turnover frequencies are largely independent of Mo loading, but deactivation rate constants increase by >100-fold as loadings increase to monolayer, leading to a >13-fold difference in reaction rates at extended time on stream. Mo oxidation state by in situ X-ray absorption spectroscopy is stable with time on stream, arguing against continued catalyst restructuring as the origin of deactivation. Across the set of loadings, isobutane dehydrogenation and coke formation are correlated with partially reduced Mo4+ and deeply reduced Moδ+ sites, respectively. Given the stable dehydrogenation activity of low-loaded Mo, in contrast to the rapid deactivation of high-loaded Mo, sub-monolayer metal oxides may warrant further investigation as light alkane dehydrogenation even when their bulk counterparts may not. [ABSTRACT FROM AUTHOR]