A new approach for methane oxidation: photocatalytic ozonation over noble metal decorated zinc oxide nanocatalysts

Abstract

We designed a new approach to oxidize methane, a potent greenhouse gas. In this approach, the synergistic effect of photocatalytic ozonation is utilized to oxidize methane at low concentrations. Using ZnO nanomaterials modified with noble metals (i.e., Au, Pt, and Pd), results show that the catalytic oxidation of methane is generally significantly improved by the synergistic system approach. More specifically, the efficiency of photocatalytic ozonation was at least two times higher than the sum of the contributions from individual sub-processes (i.e., photocatalysis, catalytic ozonation, and ozone photolysis), and the synergistic effect was effectively utilized. The durability of the catalysts is another highlight, with no decrease in activity over ten cycles. Based on the experimental results, combined with the characterization, and taking Au/ZnO as an example, it can be seen that Au/ZnO with high specific surface area and high adsorption capacity is more conducive to ozone adsorption and activation, enhances the formation of active radicals (·O2- and 1O2) and promotes the synergistic effect. Meanwhile, we believe that the larger Au nanoclusters and the zero-valent stabilized Au are important reasons for the durability of the catalyst. This work provides a novel approach to removing low-concentration methane and guides further development of a practical photocatalytic ozonation system.