Acetone Hydrodeoxygenation over Bifunctional Metallic–Acidic Molybdenum Carbide Catalysts

Metallic–acidic bifunctionality of molybdenum carbidic catalytic formulations can be tuned by oxygen cofeed and reductive pretreatments to control carbonyl hydrodeoxygenation (HDO). Acetone is deoxygenated over activated Mo2C via sequential hydrogenation of acetone to equilibrium and subsequent dehydration of isopropyl alcohol (IPA). Dehydration to propylene occurs over Brønsted acid sites with an intrinsic activation energy of 103 ± 1 kJ mol–1 and a rate-determining step of β-hydrogen scission, as inferred from a kinetic isotope effect (KIE) of 1.85. HDO rate-determining dehydration rates were kinetically independent of H2 and oxygenate pressure from 10 to 82 kPa and from 0.05 to 4 kPa, respectively. Both the kinetics and the deoxygenation reaction pathway were shown to be similar for the aldehyde group of propanal. Oxygen treatment of activated carbides via 13.5 kPa O2 cofeed was shown to decrease the catalyst surface area from 68 to 9 m2 g–1 and to suppress metallic hydrogenation of acetone to IPA. IPA dehydration rates per gram of catalyst could be altered by a factor of ∼60; a longer activation time under H2 flow at 773 K increased dehydration activation energies from 103 to 140 kJ mol–1, decreased Brønsted acid site densities, and decreased 2,6-di-tert-butylpyridine-normalized dehydration turnover frequencies, indicative of a reduction-induced change in the number and nature of the acid sites.