Methanol Oxidation over Co- and/or Ag-Based Catalysts: Effect of Impurities (H₂O and CO)

The methanol oxidation reaction was investigated on Co- and/or Ag-based γ-Al2O3 catalysts, which were prepared by different methods and further doped with noble metals (Pd, Pt). During the present study, three different reaction pathways were revealed. Complete oxidation of methanol to CO2 and H2O was achieved over Pd-doped catalysts (Pd-Co/Al-SI and Pd-Ag/Al-SI), while partial oxidation to intermediates, such as formaldehyde, was observed for Ag/Al catalysts. The dehydration reaction of methanol to dimethyl ether took place over Co/Al, Ag-Co/Al and Pt-Co/Al catalysts. The 0.5wt.% Pd-5wt.% Co/γ-Al2O3 catalyst, prepared via the spray impregnation (SI) method, exhibited the highest methanol oxidation efficiency (T50: 43°C) and was further evaluated in the presence of H2O and CO in the feed, for several hours on stream. Initially, the activity of the catalyst was decreased, while over time complete oxidation of methanol was achieved. Characterization of the used catalyst revealed that in addition to the Co3O4 phase initially formed in the fresh catalyst, a CoO phase was also formed, concluding that the active phase of the 0.5Pd-5Co/Al-SI catalyst for the methanol oxidation reaction is a mixture of Co3O4 and CoO phases.