Catalytic oxidation of methane to C2-C4 hydrocarbons over CeO2 promoted W-Mn/SiO2 catalysts at higher pressure

CeO2-promoted Na-Mn-W/SiO2 catalyst has been studied for catalytic oxidation of methane in a microstainless-steel reactor at elevated pressure. The effect of operating conditions, such as GHSV, pressure and CH4/O-2 ratio, has been investigated. 22.0% CH4 conversion with 73.8% C-2-C-4 selectivity (C-2/C-3/C-4 = 3.8/1.0/3.6) was obtained at 1003 K, 1.5 x 10(5) h(-1) GHSV and 1.0 MPa. The results show: Elevated pressure disadvantages the catalytic oxidation of methane to C-2-C-4 hydrocarbons. Large amounts of C-3 and C-4 hydrocarbons are observed. The unfavorable effects of elevated pressure can be overcome by increasing GHSV; the reaction is strongly dependent on the operating conditions at elevated pressure, particularly dependent on GHSV and ratio of CH4/O-2. Analyses by means of XRD, XPS and CO2-TPD show that CO2 produced from the reaction makes a weakly poisoning capacity of the catalyst; information of changeful valence on Ce and Mn was detected over the near-surface of the Ce-Na-W-Mn/SiO2 catalyst; the existence of Ce3+/Ce4+ and Mn2+/ Mn3+ ion couple supported that the reaction over the catalyst followed the Redeal-Redox mechanism. Oxidative re-coupling of C2H6 and CH4 in gas phase or over surface of catalyst produces C-3 or C-4 hydrocarbons.