Methane oxidation over catalytic copper oxides nanowires

Abstract

Copper oxide (CuO) is one of the promising catalysts for the catalytic oxidation of methane (CH 4). Previous studies have focused on CuO nanoparticles (NPs) dispersed on other supporting oxides. However, aggregation of CuO NPs under large loadings and solid state reactions between CuO and supports hinder the understanding and further improvement of the catalytic properties of CuO. Here, we report the first study of the catalytic oxidation of CH 4 over CuO nanowires (NWs). The CuO NWs were prepared by the thermal annealing of copper meshes and grew perpendicularly to the mesh surface with a high surface coverage density. The percentage of CH 4 converted to CO 2 over the CuO NWs was experimentally measured in a flow reactor over a range of temperatures. First, the conversion percentage of CH 4 over the catalytic CuO NWs is almost 40% (a total flow rate of 100 sccm with 1.5 vol.% of CH 4) at 500 °C, which is comparable to that measured over supported CuO NPs. Second, the conversion percentage of CH 4 increases with increasing CuO NW loading. Third, the catalytic activity of the CuO NWs remains constant for at least 24 h at 500 °C. Moreover, the CuO NWs can be easily regenerated in situ by thermal annealing. Finally, when the CuO NWs are briefly reduced in hydrogen RF plasma, their catalytic activity is enhanced, such that the CH 4 conversion percentage is increased by approximately 7% over the tested temperature range. The hydrogen plasma treatment changes the oxidation state of surface copper species from Cu(II) to Cu(I), suggesting that Cu(I) is more active than Cu(II) in the catalytic process. These CuO NWs have great potential to be economical and effective catalysts for the oxidation of CH 4 and, possibly, hydrocarbons as well.