1416 almost complete elimination of CH4 from 0.1 vol% simulated VAM can be achieved with extended irradiation in the batch mode tests. The continuous flow mode tests also reveal that the low concentration methane in the air can be oxidized and eliminated at the ambient temperature whilst the conversion rate of CH4 into CO2 is decreased with an increase in the flow rate. While the complete oxidation of dilute VAM is feasible with photocatalytic oxidation, there will be a challenge for photocatalytic process to deal with such a large VA flow (normally over hundreds m3/s) in practical application based on the low photocatalytic reaction rate obtained so far. The photocatalyst material holds the key for boosting the reaction rate. Engineering new photocatalysts for VAM oxidation should aim to enhance the light absorption, improve charge separation and transfer and increase the surface activity. Figure 10. (a) Photocatalytic oxidation of simulated 0.1 vol% VAM over two developed photocatalysts tested in a batch mode, and (b) variations of methane oxidation efficiency tested with different VAM concentrations and flow rates in a continuous flow mode. With the specific advantage of treating very low concentration methane, the photocatalysis technology is promising for open cut fugitive methane abatement for which no abatement technology is available. It also holds great potential in destroying atmospheric methane with sunlight for carbon offset as a negative emission technology. Low-cost catalysts for VAM catalytic oxidation 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 fine-tuning 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 0 2 4 6 8 10 12 0.00 0.02 0.04 0.06 0.08 0.10 CH4 conentration (vol%) Irradiation time (hour) VAMO-1 A5-A-2 0 20 40 60 80 100 CH4 oxidised (%) 1 3 5 10 15 20 0 20 40 60 80 100 CH4 oxidised (%) VAM flow rate (sccm) 0.05% CH4 0.1% CH4 0.3% CH4
RkJQdWJsaXNoZXIy MTM0Mzk2