Improved activity of Pt/γ-Al2O3 catalysts for CH4-O2 reaction under lean conditions due to sulfation and catalyst loading

The catalytic oxidation of low concentration of methane (2000 ppmV) in excess oxygen was investigated over unsulfated and pre-sulfated Pt/gamma-Al2O3 catalysts. Over unsulfated samples, catalyst activity increased slightly with Pt concentration and with catalyst loading in the reactor. This enhancement was stronger over pre-sulfated catalyst relative to unsulfated samples. The results suggest that the new catalytic sites generated during sulfation (formed by the interaction between surface support sulfates and highly oxidized Pt atom at the edge of the platinum particle) may activate the almost non-polar C-H bonds of methane through a dissociate adsorption of CH4, thus the increase in the sulfated catalyst loading results in the increase in the number of the catalytic sites generated during sulfation. The probability of the initial C-H activation of CH4 increases and may lead to the observed increase in the oxidation rate for CH4-O-2 reaction. (C) 2008 Elsevier B.V. All rights reserved.