Partial Oxidation of Methane to Syngas via Formate Intermediate Found for a Ruthenium–Rhenium Bimetallic Catalyst

Partial oxidation of methane (POM) is a potential technology to increase the efficiency of synthesizing a mixture of CO and H₂ called syngas, in comparison to steam reforming processes. Recently, supported metals modified with Re have emerged as active catalysts for POM. However, the role of Re in this reaction has been unclear. Here, we demonstrate that the addition of Re to a Ru/Al₂O₃ catalyst changes the reaction mechanism. The bimetallic catalyst oxidizes CH₄ to mainly CO via formate. After all of the O₂ is used, steam reforming and reverse water-gas shift take place to increase the yield of CO and H₂. This is in contrast to Ru/Al₂O₃, which catalyzes POM mostly by complete oxidation of CH₄ to CO₂ and H₂O and subsequent reforming reactions. In the bimetallic catalyst, the main role of Ru is to reduce Re species, and the reduced Re species produces formate from CH₄ and also accelerates the steam reforming reaction. The dual roles of Re increase the total catalytic performance. These results show that Re is a main player rather than a simple promoter in the catalytic reaction.