The catalytic performance in oxidative coupling of methane and the surface basicity of La2O3, Nd2O3, ZrO2 and Nb2O5☆

The catalytic performance in oxidative coupling of methane (OCM) of unmodified pure La2O3, Nd2O3, ZrO2 and Nb2O5 has been investigated under various conditions. The results confirmed that the activity of La2O3 and Nd2O3 was always much higher than that of the remaining two. The surface basicity/base strength distribution of pure La2O3, Nd2O3, ZrO2 and Nb2O5 was measured using a test reaction of transformation of 2-butanol and a temperature-programmed desorption of CO2. Both methods showed that La2O3 and Nd2O3 had high basicity and contained medium and strong basic sites (lanthanum oxide more and neodymium oxide somewhat less). ZrO2 had only negligible amount of weak basic sites and Nb2O5 was rather acidic. The confrontation of the basicity and catalytic performance indicated that in the case of investigated oxides, the basicity (especially strong basic sites) could be a decisive factor in determination of the catalytic activity in OCM. Only in the case of ZrO2 it was observed a moderate catalytic performance in spite of negligible basicity. The influence of a gas atmosphere used in the calcination of oxides (flowing oxygen, helium and nitrogen) on their basicity and catalytic activity in OCM had been also investigated. Contrary to earlier observations with MgO, no effect of calcination atmosphere on the catalytic performance of investigated oxides in OCM and on their basicity was observed.