Vapor phase hydrodeoxygenation of furfural to 2-methylfuran on molybdenum carbide catalysts

Vapor phase hydrodeoxygenation (HDO) of furfural over Mo₂C catalysts at low temperatures (423 K) and ambient pressure showed high/low selectivity to CO bond/C-C bond cleavage, resulting in selectivity to 2-methylfuran (2MF) and furan of ~50-60% and <1%, respectively. Efficient usage of H₂ for deoxygenation, instead of unwanted sequential hydrogenation, was evidenced by the low selectivity to 2-methyltetrahydrofuran. The apparent activation energy and H₂ order for 2MF production rates were both found to be invariant with furfural conversion caused by catalyst deactivation, suggesting that (1) the measured reaction kinetics are not influenced by the products of furfural HDO and (2) the loss of active sites, presumably by formation of carbonaceous species observed by TEM analysis, is the reason for the observed catalyst deactivation. The observed half order dependence of 2MF production rates on H₂ pressure at different furfural pressures (~0.12-0.96 kPa) and the 0-0.3 order dependence in furfural pressure support the idea of two distinct sites required for vapor phase furfural HDO reactions on Mo₂C catalysts. The invariance of 2MF production rates normalized by the number of catalytic centers assessed via ex situ CO chemisorption suggests that metal-like sites on Mo₂C catalysts are involved in selective HDO reactions.