Nitrous oxide as oxidant for the oxidation of methane on barium hydroxyapatites in the presence and absence of tetrachloromethane

The oxidation of methane with nitrous oxide on PO4-deficient barium hydroxy apatite (BaHAp) has been investigated in the presence and absence of tetrac hloromethane (TCM) and compared to that with oxygen in order to obtain poss ible activities for the partial oxidation of methane using hydroxyapatite c atalysts. In the absence of an external oxidant, the addition of TCM suppre ssed the formation of oxidation products with the essential elimination of CO and CO2, in favor of an increased selectivity to C2H6 while that to C2H4 changed relatively Little, indicating that TCM directly contributes to an activation of structural oxygen of the catalyst. In the absence of TCM and with nitrous oxide as the oxidant, the maximum selectivity to the coupling products reached approximately 80% at a conversion of methane of 4.5% at 0. 5 h on-stream although calcium hydroxyapatites mainly afforded CO, under th e corresponding conditions. However, carbon oxides, primarily CO2, were the predominant products with oxygen. With nitrous oxide and in the presence o f TCM with increasing time-on-stream carbon monoxide became the only signif icant product. The formation of barium chlorapatite is demonstrated and the relative effects of nitrous oxide and TCM are compared. (C) 2001 Elsevier Science B.V. All rights reserved.