Direct synthesis of supported palladium catalysts for methane combustion by stagnation swirl flame

Abstract

The titania supported palladium nano catalysts (Pd/TiO2) are synthesized in one-step using a premixed stagnation swirl flame (SSF) with ultra-fine spray system. This novel SSF method, with features of short residence time and fast quenching, produces nanosized (<2.5nm) palladium particles being well dispersed on the 7–8nm TiO2 particle surface, with an overall specific surface area of 210–220m2/g. The X-ray photoelectron spectroscopy (XPS) results indicate that the collected palladium particles are a mixture of both Pd and PdO, whereas the TiO2 support is mainly in anatase phase by X-ray diffraction (XRD). A revised population balance model (PBM) by incorporating coagulation, sintering and scavenging of the binary system (Pd and TiO2) is developed to explain the in situ doping mechanism of Pd/TiO2 composites in the flame domain. Then, we use the synthesized nano catalyst to conduct the catalytic combustion of methane under 5–15% Pd loadings. It exhibits more excellent activity than those in the literature under identical temperatures. The T20, as 20% methane conversion temperature, can reduce to as low as 293°C at 15% Pd loading. It is because that the Pd/TiO2 catalysts made from the stagnation flame show a good dispersion of size-controlled palladium on TiO2 which may not be accessible by wet-chemistry and even other flame synthesis routes.