Natural gas, composed primarily of methane, is an abundant resource worldwide. Natural gas vehicles (NGVs) produce less CO2, NOx, and SOx per unit energy than gasoline or diesel. However, incomplete combustion of methane in natural gas engines results in emission of methane, and this is a much more potent greenhouse gas than CO2.
To reduce the CH4 concentration in exhaust, we have developed four types of nanostructured catalysts for low temperature methane combustion. For noble metal catalysts, we have prepared nanostructured PdO/CeO2 supported on mesoporous silica for methane oxidation with high catalytic activity and improved hydrothermal stability. We have also synthesized metal oxide aerogel supported PdO, which exhibited excellent activity. The hydrothermal stability, sulfur tolerance, and deactivation mechanism of these catalysts were also studied.
Furthermore, to decrease the cost of catalysts, we have explored different types of non-noble metal catalysts such as spinel-based catalysts. These catalysts exhibit good catalytic activity, comparable to Pd-based catalysts. In addition, these precious metal-free catalysts show outstanding hydrothermal stability and SO2 tolerance, and have potential to be used for natural gas vehicles.