Catalytic Behavior of Flame-Made Pd/TiO2 Nanoparticles in Methane Oxidation at Low Temperatures

Abstract

A controlled one-step synthesis of titania-supported palladium (Pd/TiO2) nanoparticles is demonstrated by using a premixed stagnation swirl flame with an ultrafine spray feeding system. The new method produces well-dispersed palladium clusters on the surface of TiO2 particle. The low-temperature methane catalytic oxidation indicates that the flame-made Pd/TiO2 possesses activity apparently higher than that of the impregnated one under the same Pd loading. For the first time, we observe a special pinched hysteresis loop of catalytic activity of Pd/TiO2 nanoparticles from the curves of CH4 conversion versus temperature during heating–cooling cycles. Thermal stability analysis confirms the complex coexistence and transformation of metallic Pd and PdO in Pd/TiO2 particles. Further morphological characterization reveals the oxidation rate is controlled by the metallic Pd content on the particle surface, whereas the deactivation of the catalysts is mainly due to the Pd dispersion decrement. The competition between the Pd dispersion decrement and the PdO reduction at the surface may result in the pinched hysteresis loop of Pd/TiO2 catalysts during low-temperature methane combustion.