N-Doped Carbon–Silica Composite Confined Pd Nanoparticles for Abatement of Methane Emission From Automobiles

Natural gas vehicles, as well as some other engines in automobiles, emit methane, which is a potent greenhouse gas. Developing advanced catalysts that can oxidize methane with good and stable activity is required for new emission standards of automobiles. We report here a N-doped carbon–silica composite that can well disperse Pd nanoparticles and preserve part of active Pd nanoparticles (< 8 nm) under typical conditions of exhaust gas from a working engine. Comparative studies indicate a stronger metal-support interaction between Pd nanoparticle and N-doped carbon (NC) than none N-doped carbon. A facile silica coating is formed from SiCl4 in water vapor. The silica coating encapsulates Pd/NC and prevents extreme Pd sintering. The Pd catalyst with N-doped carbon–silica composite, i.e. (Pd/NC)@SiO2, performs stable and complete conversion of 5000 ppm CH4 to CO2 and H2O at 350 °C with a space velocity of 40,000 cm3 per gram of catalyst per hour. This research illustrates the advantage of using N-doped carbons supported catalyst for methane oxidation. Future optimization could be attempted by improving the thermal stability of carbons at the reaction conditions.