Oxidative dehydrogenation of methanol to formaldehyde

Abstract

Thermochemical results from ab initio quantum chemical calculations (generalized valence bond) are used to examine the reactions mechanism for H 3COH + 1 2 O 2→H 2CO + H 2O as catalyzed by MoO 3. We find that surface dioxo sites ▪ are critical to activating the methanol, but we find that the single-site single-step proposal ▪ is not favorable (Δ H ≈ + 31.5 kcal). Our conclusion is that an important catalytic site involves two adjacent surface dioxo units (the dual dioxo site), with each dioxo site extracting one H in a sequence of steps. The required dual dioxo site exists on the (010) surface of MoO 3 but does not exist on the other low index surfaces. This mechanism is supported by atmospheric pressure experimental studies which indicate that MoO 3(010) is selective for CH 2O products. A detailed sequence of reaction steps and the associated thermochemistry is proposed.