Mechanistic Studies on the Oxidative Dehydrogenation of Methanol over Polycrystalline Silver Using the Temporal-Analysis-of-Products Approach

Abstract

The temporal-analysis-of-products approach was used to study the mechanism of the oxidative dehydrogenation of methanol over an unsupported polycrystalline silver catalyst. Pulse experiments revealed a distinct influence of the state of the silver surface on the adsorption of oxygen and on reactivity toward methanol. The surface-embedded oxygen species O γ, which is stable at high temperatures, was found to provide a highly selective reaction pathway for the oxidation of methanol to formaldehyde above 550 K. A comparison of the pulse responses of formaldehyde, water, and hydrogen to methanol pulses showed that water is a primary gas-phase product and that only small amounts of hydrogen are formed. Furthermore, it was found that the O γ species is not active in the oxidation of hydrogen or carbon monoxide. In contrast, the much more active adsorbed oxygen species O α was observed to be involved in the nonselective deep oxidation of methanol at lower temperatures, yielding carbon dioxide at high coverages. However, at low coverages O α also causes the selective formation of formaldehyde.