The selective oxidation of methane to methanol using in situ generated H2O2 over palladium-based bimetallic catalysts

Abstract

The selective oxidation of methane to methanol, using H2O2 generated in situ from H2 and O2 has been investigated using a series of TS-1 supported bimetallic palladium-based catalysts. The alloying of Pd with Au exhibited improved performance compared to monometallic Pd analogues, with the optimal AuPd catalyst stable over multiple uses. Complementary studies into catalytic performance towards the direct synthesis and subsequent degradation of H2O2 indicated that catalysts that offered moderate activity toward H2O2 synthesis and degradation were the most active for CH4 oxidation, balancing the high activity of the Pd-only formulation, with the greater selectivity of the Au-only analogue. In particular, the ability of Au to promote the release of oxygen-based radical species from catalytic surfaces is considered to be crucial in achieving improved reactivity, compared to monometallic Pd analogues. The alloying of Pd with more abundant secondary metals was also explored with the NiPd/TS-1 catalyst exhibiting comparable activity to the AuPd analogue. However, unlike over AuPd/TS-1, where methanol is the primary product, the production of formic acid was found to be favoured by the NiPd/TS-1 catalyst.