Decomposition of Hydrogen Peroxide Catalyzed by AuPd Nanocatalysts during Methane Oxidation to Methanol

Selective oxidation of methane into energy-dense liquid derivatives at low temperature and pressure is critical for enabling the use of vast natural gas reserves around the world. This has been recently achieved with AuPd nanocatalysts, but the process exhibits accelerated rates of deleterious H2O2 self-decomposition, which results in prohibitive industrial costs. We performed a multivariate analysis of 143 H2O2 decomposition rate measurements reported in the literature to quantify the effect of reaction conditions and catalyst properties in the decomposition of H2O2 at conditions used during methane upgrading. The results show that the reaction is first order in terms of H2O2 concentration and correlates with a larger particle size. The catalytic activity of colloidal AuPd is lower than that of supported AuPd. The effect of methane pressure is practically negligible, which is evidenced by an H2O2 decomposition rate only 42% smaller when the methane pressure is increased more than 6 log-units. Overall, the results indicate that methane oxidation occurs in a significant excess of H2O2, which contributes to its radical-based self-decomposition. Inhibiting the activity of AuPd nanocatalysts toward H2O2 self-decomposition is key to achieving high H2O2 efficiency use for the oxidation of methane to methanol. This can be done by decreasing the concentration of H2O2, using smaller AuPd nanocatalysts, increasing the Au/Pd ratio, using colloidal versus supported nanocatalysts, or increasing the pressure of methane in the reactor. The results of this study provide a path for targeted AuPd catalyst optimization for methane upgrading with improved H2O2 decomposition efficiency and high methane oxidation productivity.