Abstract: A method is provided for oxidizing gases such as, for example, CO, aldehydes having carbon atoms in the range 1 to 5 (e.g. formaldehyde), ketones having carbon atoms in the range 3 to 5, and alcohols having carbon atoms in the range 1 to 5, wherein the gas at a relative humidity in the range 0 to 100% and an input temperature in the range -50.degree. to 150.degree. C. is contacted with a catalyst assembly comprising (a) a hydrophobic support having a surface area in the range 50 to 1,500 m.sup.2 /g and selected from the group consisting of silicalite, silylated silica, and styrene divinylbenzene polymers, and, on said support (b) a catalytically active metal selected from the group consisting of chromium, molybdenum, tungsten, manganese, rhenium, iron, ruthenium, osmium, cobalt, rhodium, platinum, iridium, nickel, copper and silver, said metal being present in an amount in the range 0.1 to 22 wt % of the total weight of the catalyst assembly.