Catalytic destruction of halogenated volatile organic compounds

Abstract

The interaction of nitric oxide with carbon monoxide on the surface of the Cu-containing catalysts Cu-AlPO4, Cu-AlPO-5, Cu-MnAlPO-5, Cu-SAPO-5, Cu-CoAPSO-11 and Cu-ZSM-5 has been studied by the transient response technique. In the temperature region studied (60–300°C), the catalysts Cu-AlPO4, Cu-MnAlPO-5, Cu-CoAPSO-11, Cu-AlPO-5 and Cu-SAPO-5 start to interact first with carbon monoxide above a definite temperature. High reduction degrees (over 30%) for the supported CuO are attained after treatment with a NO + N2O + CO + Ar gas mixture at 60–300°C. Nevertheless, only the last two catalysts exhibit activity towards conversion of nitric oxide to nitrogen (above 100°C) which is comparable to that of aCuO/γ-Al2O3 catalyst. The heat-treated in an inert (agron) atmosphere Cu-ZSM-5 catalyst exhibits activity towards the reduction of NO by CO to N2O and N2. A competition between the CO + NO and CO + O(surface) interactions is observed at a definite temperature under the conditions of a NO + N2O + CO + Ar gas mixture. Competitive carbon monoxide adsorption occurs, depending on the temperature and degree of surface reduction, which poisons the catalyst surface with respect to the reduction of nitric oxide to nitrogen. The surface of heat-treated Cu-ZSM-5 catalyst possesses centres active in the decomposition of nitrous oxide and nitric oxide to nitrogen from a NO + N2O + Ar gas mixture. During temperature-programmed desorption (TPD) experiments, a nitric oxide desorption peak with Tmax = 180°C is observed. The species to which this peak belongs are suggested as precursors for the nitric oxide decomposition reactions. The difference in catalytic behaviour of the catalysts studied is explained by the hypothesis (proposed by W.K. Hall) about the dependence of the catalyst activity on the ability of the catalyst surface to stabilize various intermediates during adsorption of nitric oxide and its interaction with carbon monoxide.