OXIDATIVE METHYLATION OF TOLUENE WITH METHANE OVER LEAD LITHIUM MAGNESIUM-OXIDE CATALYSTS

The selectivity of C8 compounds (ethylbenzene + styrene) of the Li/MgO catalyst in the methylation of toluene with methane could be improved by the addition of oxides of lead, nickel, and cerium. The Pb/Li/MgO (5:15:80 mol-%) catalyst showed the highest catalytic activity, without deactivation for 350 h, at a given standard reaction condition. The Pb/Li/MgO catalyst suffered from continuous losses of lithium and lead components during the reaction. The loss of lead was correlated with the loss of catalytic activity when a Pb/Li/MgO catalyst (1:20:79 mol-%) containing a smaller quantity of lead was used. The catalytic property of the Pb/Li/MgO catalyst was different from those of the Pb/MgO catalyst and the Li/PbO catalyst which showed very low activities and different C8 selectivities. It was suggested that the main role of the lead component in the Pb/Li/MgO catalyst is as an oxygen species supplier to the reaction site of Li/MgO for the re-oxidation of the catalyst.