Enhancement of the selectivity to carbon monoxide with feedstream doping by tetrachloromethane in the oxidation of methane on stoichiometric calcium hydroxyapatite

Abstract

The oxidation of methane on the stoichiometric hydroxyapatite Ca₁₀(PO₄)₆(OH)₂(HAP) has been examined in the presence and absence of tetrachloromethane (TCM). In contrast to the previously observed effects of TCM on the oxidation of methane with other catalysts, the introduction of a small amount of TCM into the feedstream with stoichiometric HAP produced an increased selectivity to carbon monoxide and a decreased conversion of methane with increasing time-on-stream. The selectivity to C₂ compounds changed relatively little on addition of TCM. X-Ray analysis showed that the chlorided species was formed not only on the surface but also in the bulk phase and, at least in the latter, was identified as chlorapatite Ca₁₀(PO₄)₆Cl₂. Pretreatment experiments, in which the hydroxyapatite was exposed to a mixture of O₂ and TCM before use in the methane conversion process, showed that the chlorinated surface formed by this method possessed distinctly different catalytic properties from that produced during the methane conversion process in the presence of feedstream TCM.