Mo₂C Modification by CO₂, H₂O, and O₂: Effects of Oxygen Content and Oxygen Source on Rates and Selectivity of m-Cresol Hydrodeoxygenation

Vapor-phase m-cresol hydrodeoxygenation rates on oxygenate-modified Mo₂C catalysts prepared by pretreating fresh Mo₂C catalysts in 1 kPa of O₂, H₂O, and CO₂ at 333 K showed that (i) molecular oxygen has a higher propensity to deposit oxygen (O/Mo_bulk before HDO = 0.23 ± 0.02) on fresh Mo₂C, compared to CO₂ and H₂O (O/Mo_bulk before HDO ≠0.036), as assessed from temperature-programmed surface reaction with H₂, and (ii) oxygen adsorbed in amounts exceeding ∼0.06 ± 0.01 of O/Mo_bulk poisons the metal-like sites for toluene synthesis as inferred from a 10-fold decrease in toluene synthesis rate per gram on the O₂-1 kPa (333 K)-Mo₂C compared to that on fresh Mo₂C, H₂O-1 kPa (333 K)-Mo₂C, and CO₂-1 kPa (333 K)-Mo₂C catalysts. Invariant turnover frequencies of toluene synthesis measured from in situ CO titration among the O₂-, H₂O-, and CO₂-modified samples demonstrate that the effect of adsorbed oxygen is independent of the oxygen source.