Several commercial silica samples showing different catalytic activities in the partial oxidation of methane (MPO) to formaldehyde have been investigated using FTIR technique. Two IR absorption bands at 893 and 909 cm(-1), observed upon dehydroxylation of the silica catalysts and assigned to reactive siloxane sites on the surface ("strained siloxane bridges"), were found to disappear upon heating in methane at high temperature. The catalytic activity increases together with the intensity of the bands due to such "strained" sites in the different SiO2 samples.