Effect of promoter in the oxidative coupling of methane over synthesized Mn/SiO2 nanocatalysts via incipient wetness impregnation

The M-Na-Mn/SiO2 nanocatalysts (M = W, Mo, Nb, V, Cr) were synthesized with the size of 12-92 nm by incipient wetness impregnation method to study the effect of different promoters on the catalytic performance in the oxidative coupling of methane. The results at 1 atm, 1048 K, 2500 ml h(-1) g(-1), and CH4/O-2/N-2 = 2/2/1 revealed that C-2 selectivity was significantly increased (31.6%) in the order of W > Mo > Nb > Cr > V whereas moderate enhancement (12.6%) was observed in the CH4 conversion in the order of W > Cr > Nb > Mo > V. The results of the characterization techniques (Raman, FT-IR, BET, TGA/DTA and XRD) demonstrated that Mn2O3 and alpha-cristobalite were the predominant species and active sites in the nanocatalyst surface and Na2MoO4, Na2WO4 and Mn2O3 crystalline phases contributed to achieving high selectivity of C-2 products. The redox mechanism involving two metal sites such as Mn3+/2+ and W6+/5+ or Mn3+/2+ and Mo6+/5+ was found to be the most compatible route with the OCM reaction path in which CH4 and O-2 adsorption was the controlling step. (C) 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.