Acid site densities and reactivity of oxygen-modified transition metal carbide catalysts

Acidic properties of beta-Mo2C, alpha-Mo2C, W2C, and WC were quantified by assessing the kinetics of isopropanol (IPA) dehydration at 415 K either (i) under inert He/Ar atmosphere or (ii) with 13 kPa O-2 co-feed. Dehydration kinetics were zero-order with respect to IPA for all catalysts and under all reaction conditions. Intrinsic activation energies were similar across all catalysts (89-104 kJ mol(-1)). Acid site densities calculated via in situ 2,6-di-tert-butylpyridine (DTBP) titration were used to normalize dehydration turnover frequencies (TOF). O-2 co-feed increased dehydration rates per gram by an order of magnitude for all catalysts tested, but TOF remained invariant within a factor of similar to 2. Mo- and W-based carbides showed similar dehydration kinetics regardless of O-2 co-feed, and O-2 co-feed did not alter bulk carbidic structure as noted by X-ray diffraction. Bronsted acid site provenance results from the oxophilicity of Mo and W carbides. (C) 2016 Elsevier Inc. All rights reserved.