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

Abstract

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/Mobulk before HDO = 0.23 ± 0.02) on fresh Mo2C, compared to CO2 and H2O (O/Mobulk 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/Mobulk 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.