CuO(x)/SBA-15 catalysts prepared by a grafting approach (denoted as CuO(x)/SBA-15-gra) have been characterized and studied for the selective oxidation of methane to formaldehyde by oxygen Our characterizations using XRD H(2)-TPR UV-vis and ESR suggest that Cu(2+) ions are almost isolated on the surface of SBA-15 at a Cu content <= 0 6 wt% The increase in the Cu content to >06 wt% decreased the fraction of isolated Cu(2+) ions and increased that of aggregated CuO(x) clusters On the other hand the fraction of isolated Cu(2+) ions was much smaller in the CuO(x)/SBA-15 catalyst prepared by the impregnation method (denoted as CuOx/SBA-15-imp) even with a lower Cu content (0 5 wt%) The CuO(x)/SBA-15-gra provided significantly higher HCHO selectivity in the selective oxidation of CH(4) than the CuO(x)/SBA-15-imp and the CuO(x)/SBA-15-gra catalyst with a Cu content of 0 6 wt% showed the best performance for HCHO formation In situ FT-IR spectroscopy of adsorbed CO and XPS measurements suggest the generation of Cu(+) after the reaction and the Cu(+) site is likely responsible for the activation of oxygen forming an active oxygen species for the selective oxidation of CH(4) to HCHO (C) 2010 Elsevier B V All rights reserved