OXIDATIVE COUPLING OF METHANE ON LITHIUM CALCIUM-PHOSPHATE CATALYSTS

The oxidative coupling of methane has been tested over a series of lithium-calcium phosphate catalysts at 700 and 775-degrees-C with and without the introduction of a small quantity of tetrachloromethane (TCM) to the feedstream. The selectivity to C2 and higher hydrocarbons and that to oxidation products have been shown to have a dependence on the cation/cation and cation/anion ratio. The highest yield of C2+ hydrocarbons has been obtained on the lithium phosphate catalyst at 775-degrees-C but the activity of this catalyst decreased rapidly at this temperature. In contrast, the lithium-calcium phosphate (Li:Ca:P = 4:1:2) has shown almost the same activity as the lithium phosphate catalysts while remaining stable at the same temperature for more than 10 h. The effect of the addition of TCM on the selectivity was dependent both on the nature of the catalyst employed as well as the reaction temperature. On lithium doped calcium phosphate catalysts the conversion of methane was enhanced by the introduction of TCM but the selectivity to C2 hydrocarbons was not changed while with the lithium-calcium phosphate catalysts the conversion of methane was suppressed by the presence of TCM.