Experimental Study Of Catalytic Combustion Of Lean Methane On Pd-based Catalysts

The methane (CH4) used as fuel possesses various advantages, such as high calorific value, high combustion efficiency, low pollutant emissions and wide availability of the raw materials. At the same time, CH4 is also a powerful greenhouse gas with a harmful effect approximately 20 times higher than that of CO2. Most of the CH4 emissions come from ventilation-air methane (VAM) with a low concentration of 0.1-1%. In addition, the release of unburned CH4 from gas turbines fueled with natural gas is also a serious problem for the environment. Nevertheless, the conventional flame combustion usually leads to the production of large amounts of nitrogen oxides and the decrease of energy utilization due to the optical radiation. As the catalytic combustion of CH4 has been considered an effective measure to reduce CH4 emissions and maximize the utilization of clean energy, the key to the development of catalytic combustion technology is to research the catalyst with highly active and thermally stable.Noble metal Pd-based catalyst is well-known to be active for CH4 catalytic combustion at low temperatures. Firstly, a series of single component Pd-based supported catalysts were prepared, and then, the activities of the catalysts for the catalytic combustion of CH4 were examined over the self-designed experimental platform. The influence of the oxide supports, calcination temperature, Pd content, and gas hourly space velocity on catalytic combustion of CH4 were investigated. Subsequently, to improve performance of the Pd-based catalyst, a series of core-shell nanoparticles that consists of a Pd metal core coated with a mesoporous oxide shell, Pd@Oxide (Oxide= CeO2, ZrO2, SiO2), were prepared using a self-assembly method, and then supported on Si-modified hydrophobic Al2O3 (referred as Si-Al2O3). For comparison, Pd/Si-Al2O3 catalyst was also synthesized. Next, techniques such as BET, TEM, XRD, and XPS were used to characterize the catalysts, and the activities of these catalysts, which were prepared directly from Pd nanoparticles, for the catalytic combustion of CH4 were evaluated.The results showed that, the activity of Pd-based catalysts was affected by the support, the amount of Pd loading, calcination temperature, space velocity, etc. The core-shell structure could help in the stabilization of the active phase compared to the uncoated Pd/Si-Al2O3 catalyst. And a balanced mixed phase of PdOx/Pd was the active phase of these Pd-based core-shell catalysts for CH4 catalytic combustion. The presence of water vapor could inhibit the activity of catalysts in different degrees; and the activity of the catalysts, which affected by water vapor, could be restored after calcination at high temperature. Therefore, the core-shell catalysts demonstrated the great potential for high-temperature catalytic application.