Synthesis gas production from partial oxidation of methane over highly dispersed Pd/SiO2 catalyst

Pd/SiO2 catalyst prepared by impregnation method using (NH4)2PdCl4, Pd(NO3)2 and Pd(acac)2 as precursors was used for the synthesis gas production by partial oxidation of methane (POM). Compared to the catalysts prepared from other two precursors, the catalyst prepared from Pd(acac)2 demonstrated better activity and stability for the reaction at 700 °C. Methane conversion above 90% with H2 yield higher than 80% was achieved during 7 h on stream. The catalysts were characterized by N2 physical adsorption, CO chemisorption, Transmission electron microscopy and in situ X-ray diffraction techniques. The Pd/SiO2 catalyst prepared from Pd(acac)2 was found to have a superior performance against sintering during air-calcination at 800 °C. The size of Pd particles remained at 4–5 nm even after the POM reaction at 700 °C for 7 h. The results of mass spectroscopy characterization on the thermal decomposition of a SiO2 supported Pd(acac)2 sample under air suggest that formation of highly dispersed (SiOs)2Pd intermediate through the H-transfer from silica surface hydroxyl groups to the acac ligand of Pd(acac)2 followed by a fast reduction of the (SiOs)2Pd at ∼200 °C by acacH species plays an important role in the formation of highly dispersed Pd particles on SiO2 with excellent thermal stability.