The influence of volatile organic compound structure on conditions required for total oxidation

The reactivity of a range of volatile organic compounds with differing functional groups has been assessed over platinum catalysts supported on β-zeolite, mordenite, silica or alumina. Alcohols, ketones, carboxylic acids, aromatics and alkanes were included in the range. In general, the reactivity pattern observed was alcohols > aromatics > ketones > carboxylic acids > alkanes, although some overlap was observed in that the more reactive alkanes were more readily oxidized than the less reactive carboxylic acids. The same order of reactivity was observed for all the catalysts studied here. A kinetic isotope effect was observed when deuterated acetone was compared to normal acetone, consistent with C-H bond cleavage being the slow step in the catalytic oxidation of this substrate. A correlation was found between the reactivity of the individual substrates and the strength of the weakest C-H bond in the structure. A single weak C-H bond in the substrate led to a high reactivity. It is postulated that catalytic oxidation on platinum catalysts proceeds via initial rupture of the weakest C-H bond in the substrate followed by further reaction steps which involves free radical chemistry.