Reaction performance of partial oxidation of methane over Ni/SiO_2 catalysts using monodisperse silica sol as supporting precursor

摘要

The reaction performance of partial oxidation of methane (POM) by air over Ni/SiO_2 catalysts was investigated using monodisperse silica sol [H.E.Bergna,in:H.E.Bergna (Ed.),The Colloid Chemistry of Silica,Adv.Chem.Ser.234,The American Chemical Society Press,Washington,DC,1994,p.1.] as supporting precursor in a fixed micro-reactor at atmospheric pressure.The distribution of SiO_2 particles in silica sol was imaged by transmission electron microscopy (TEM).Ni/silica-sol catalyst has an excellent performance during partial oxidation of methane,and methane oxidation greatly depends on the concentration of O_2.At 800 deg C,when the CH4/O_2 molar ratio is ca.2,about 96% of CH4 conversion is achieved,and the selectivities of H_2 and CO are above 98% and 95%,respectively.The reaction products are mainly H_2,H_2O and CO_2 at low temperature;a large amount of heat is released to sustain the POM reactions for a long time while the temperature of the surroundings is close to room temperature.The facts indicate that the catalyst has high activity and that the POM reaction can be ignited by H_2 injection at low temperature.The structure and the reducing properties of these catalysts were characterized by BET,temperature programmed reduction (TPR) and powder X-ray diffraction (XRD) methods.XRD patterns also indicate that oxygen is completely consumed on the top layer of the catalysts;and the active species of catalyst can fully sustain Ni~° phase under low reaction temperature in water-rich product mixtures.