Alkene selectivity enhancement in the oxidation of propane on calcium-based catalysts

The oxidation of propane has been investigated in the presence and absence of tetrachloromethane (TCM) on calcium hydroxyapatite (CaHAp), Ca-3(PO4)(2), CaSO4 and CaO at 723 K. In the absence of TCM, the conversion of C3H8 on CaHAp was 7.7-9.2% during 6 h on-stream while that on Ca-3(PO4)(2), CaSO4 and CaO was 0.6, 0 and 0.2-0.4%, respectively. The principal products on all catalysts in the absence of TCM were CO and CO2 with small selectivities to C3H6 and C2H4 (both 5-6%) observed on CaHAp. Upon addition of TCM, the selectivity to C3H6 on all catalysts and the conversion of C3H8 on CaSO4 increased while, with increasing time-on-stream, the changes in the conversion and selectivity were dependent upon the nature of the catalysts. XPS and XRD analyses provide evidence for the presence of chlorine in the surface and/or bulk of three of the catalysts, suggesting that chlorinated species on the solids play a role in the selectivity enhancement, but the absence of chlorine from the sulphate demonstrates the dissimilarities of the catalysts in their abilities to sorb and decompose TCM.