Promoting effect of Co addition on the catalytic partial oxidation of methane at short contact time over a Rh/MgO catalyst

In catalytic partial oxidation of methane under isothermal conditions, a 0.3 wt% Rh/MgO catalyst modified with Co at a molar ratio of Co/Rh = 1 gave greater CH₄ conversion and selectivity to CO and H₂ than unmodified 0.3 wt% Rh/MgO. Characterization results using temperature-programmed reduction, extended X-ray absorption fine structure, and transmission electron microscopy demonstrated alloy formation between Rh and Co. In catalytic partial oxidation of methane without N₂ dilution, the Rh-Co/MgO catalyst with Co/Rh = 1 suppressed the temperature increase near the catalyst bed inlet and yielded a flat temperature profile. This behavior can be interpreted as greater selectivity in the direct partial oxidation route in the presence of gas-phase oxygen and lower activity in the steam reforming of methane in the absence of gas-phase oxygen. The better performance of Rh-Co/MgO (Co/Rh = 1) compared with Rh/MgO may result from greater methane dissociation and reduction degree during the partial oxidation of methane.