A catalytic composite comprising a metal chelate mercaptan oxidation catalyst and a quaternary ammonium hydroxide impregnated on a solid adsorptive support is disclosed. The quaternary ammonium hydroxide is represented by the structural formula ##STR1## wherein R is a hydrocarbon radical containing up to about 20 carbon atoms and selected from the group consisting of alkyl, cycloalkyl, aryl, alkaryl and aralkyl, R.sub.1 is a substantially straight-chain alkyl radical containing from about 5 to about 20 carbon atoms, and R.sub.2 is selected from the group consisting of aryl, alkaryl, and aralkyl. The catalytic composite is particularly adapted to the oxidation of mercaptans contained in a sour petroleum distillate.