FT-IR studies on partial oxidation of methane over ferric molybdate catalysts.

摘要

The reactions of methane on Fe{dollar}sb2{dollar}O{dollar}sb3{dollar}, MoO{dollar}sb3{dollar} and ferric molybdate catalysts were studied in situ using the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) technique. The ferric molybdate catalysts were prepared by coprecipitation of ferric nitrate and ammonium paramolybdate solutions. The experiments were carried out at the temperatures of 673, 703 and 743 K, and at the pressure of 1 and 3 MPa. This study revealed that MoO{dollar}sb3{dollar} is the active catalyst for the partial oxidation of methane to formaldehyde and Fe{dollar}sb2{dollar}O{dollar}sb3{dollar} gives carbon dioxide. Both methanol and formaldehyde can be obtained from the ferric molybdate catalysts. The formation of methoxy (OCH{dollar}sb3{dollar}), adsorbed formaldehyde, dioxymethylene (OCH{dollar}sb2{dollar}O), and formate (OCHO) species were observed on the catalyst surface. A mechanism based on the reaction of methane with the surface of the ferric molybdate catalysts to produce methoxy groups which are further oxidized to dioxymethylene was proposed. The formation of carbon oxides is attributed to either the decomposition of dioxymethylene or to the formation of formate species. The kinetic parameters of the elementary reactions in the proposed mechanism were determined.