Pd4S/SiO2: A sulfur-tolerant palladium catalyst for catalytic complete oxidation of methane

Abstract

Sulfur species (e.g., H2S or SO2) are the natural enemies of most metal catalysts, especially palladium catalysts. The previously reported methods of improving sulfur-tolerance were to effectively defer the deactivation of palladium catalysts, but could not prevent PdO and carrier interaction between sulfur species. In this report, novel sulfur-tolerant SiO2 supported Pd4S catalysts (5 wt. % Pd loading) were prepared by H2S–H2 aqueous bubble method and applied to catalytic complete oxidation of methane. The catalysts were characterization by X-ray diffraction, Transmission electron microscopy, X-ray photoelectron Spectroscopy, temperature-programmed oxidation, and temperature-programmed desorption techniques under identical conditions. The structural characterization revealed that Pd4S and metallic Pd0 were found on the surface of freshly prepared catalysts. However, Pd4S remained stable while most of metallic Pd0 was converted to PdO during the oxidation reaction. When coexisting with PdO, Pd4S not only protected PdO from sulfur poisoning, but also determined the catalytic activity. Moreover, the content of Pd4S could be adjusted by changing H2S concentration of H2S–H2 mixture. When H2S concentration was 7 %, the Pd4S/SiO2 catalyst was effective in converting 96% of methane at the 400 °C and also exhibited long-term stability in the presence of 200 ppm H2S. A Pd4S/SiO2 catalyst that possesses excellent sulfur-tolerance, oxidation stability, and catalytic activity has been developed for catalytic complete oxidation of methane.