Effect of the introduction of tetrachloromethane into the feedstream for methane oxidation with oxygen and nitrous oxide on thermally stable strontium hydroxyapatites

Abstract

Thermally stable strontium hydroxyapatite (SrHAp) was prepared with a variety of stoichiometries and employed as catalysts for the oxidation of methane with oxygen and nitrous oxide in the presence and absence of tetrachloromethane (TCM) as a gas‐phase additive. In contrast to the oxidation of methane on thermally unstable SrHAp, non‐selective oxidation to CO and CO₂ at 873 K proceeded with oxygen while the selectivity to CO increased with increasing time‐on‐stream in the presence of TCM and was higher than 90% at 6 h on‐stream, regardless of the Sr/P ratios in the catalysts. However, with nitrous oxide the selectivity to CO in the presence of TCM was strongly influenced by the Sr/P ratio with smaller values producing higher CO selectivity. In the presence of TCM, the catalyst consists of a complex mixture of the hydroxyapatite, the corresponding chlorapatite, phosphate, chloride and oxychloride, each of which contributes dissimilarly to the catalytic process.