tive coupling of methane have been studied in our labora-The oxidation of methane on near-stoichiometric strontium tories with a wide variety of heterogeneous catalysts hydroxyapatites pretreated at 873, 1048 and 1123 K in O 2 has (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Although with the latter process the enhancement been examined in the presence and absence of tetrachloromethof the conversion of methane and the selectivities to C 2Ο© ane (TCM) as a gas-phase additive at 973 K. Under these hydrocarbons are generally obtained, recent results show conditions, strontium hydroxyapatite, regardless of its stoichithat on stoichiometric and nonstoichiometric calcium hyometry, is converted, at least in part, to Sr 3 (PO 4 ) 2 . On introducdroxyapatites the selectivities to carbon monoxide were tion of TCM to the feedstream, the selectivities to carbon monincreased (18-20). oxide, ethane, and ethylene are increased while the conversion Calcium hydroxyapatites [Ca 10Οͺz (HPO 4 ) z (PO 4 ) 6Οͺz of methane is decreased. Qualitatively similar effects of TCM (OH) 2Οͺz ; 0 Υ
Z Υ
1] are bifunctional catalysts, with acidic on the oxidation were observed on Sr 3 (PO 4 ) 2 prepared by an or basic properties, depending on their compositions (21independent procedure. Strontium chlorapatite, formed from 26). Recently, calcium (27, 28), strontium (29), and leadthe apatites and phosphate during the oxidation in the presence of TCM, as shown from XRD, contributes to the increased calcium (30-32) hydroxyapatites have been studied in our selectivity to CO and decreased conversion of methane. Β© 1996 laboratories as catalysts for the conversion of methane in Academic Press, Inc.
the absence of TCM. Lead-calcium hydroxyapatites were found to catalyze the selective coupling (30-32) while with calcium (27, 28) and strontium (29) hydroxyapatites the on the oxidation of methane in the presence and absence of TCM over Sr 3 (PO 4 ) 2 .