147 Noble-metal catalysts reported for the complete oxidation of methane include palladium (Pd), platinum (Pt), gold (Au), etc. Among them, the most active catalyst materials are supported Pd catalyst materials like Pd supported on alumina (Pd/Al2O3) and its modification by ceria, Pd/SiO2, Pd/ZrO2, Pd/SnO, Pd/zeolites. The supported Pd (Pd-based) catalysts are considered to be the most active catalyst materials, which have been widely reported to achieve approximately 100% conversion CH4 to CO2 at relatively low temperatures of 350-500 oC. The high cost of noble metals has driven the search for catalyst materials made of earth-abundant elements. Metal oxides, particularly transition metal oxides have been investigated as the catalyst for the complete oxidation of methane due to their higher stability and significantly lower cost. Transition metal oxides are effective in catalytic oxidation due to multiple valence states of metal elements, and the active lattice oxygen in metal oxides. The recent advancement in nanomaterials and theory calculations has opened new opportunities to increase the catalytic activity of metal oxides and improve their stability against temperature and water vapor by finetuning their chemical compositions and nanostructures, aided by novel tools such as advanced catalyst synthesis, in-situ characterization and theoretical computational calculations. Over recent years, the CSIRO team has been focusing on the development of low-cost transition metal oxide catalysts through controlling composition, nanostructures and crystallin facets to tune catalytic activity and water resistance for catalytic VAM oxidation. We have demonstrated enhanced catalytic activity of CuO by synthesizing shape-controlled CuO nanocrystals with well-defined active surface crystal facets [10]. As shown in Figure 11, the newly developed CuO nanobelt (NB) catalyst comprised of predominantly (001) active surface exhibits the best catalytic performance compared to CuO nanowire (NW) and CuO nanoparticle (NP) and comes closest to that of Pd-based catalyst as a comparison. NB performance is even close to that of the Pd-based catalyst (1% Pd supported on Co3O4). Figure 11. CuO nanobelts (NB) catalyst for CH4 oxidation: (a) TEM image of CuO NBs, (b) CH4 catalytic oxidation activity of CuO NB, CuO nanowires (NW) and CuO nanoparticles (NP). A new type of low-cost precious-metal-free catalysts have been developed based on spinel oxides exhibiting outstanding catalytic activity for VAM oxidation and notably exceptional catalytic stability with wet VAM [12]. As shown in Figure 12a, they are highly
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