The oxidative coupling of methane overBa/CO3LaOCl catalysts Original Research Article

The performance of LaOCl at 800°C was promoted by BaCO3 in OCM reaction. When 10 mol% BaCO3 was added, there was little change in CH4 conversion, but C2 selectivity was increased from 37% to 66%. With the increase in BaCO3 loading, the Ba/CO3LaOCl catalysts decreased in specific surface area. The improvement in C2 selectivity is partly due to surface area diminution. The addition of BaCO3 has also caused surface modification of LaOCl. In the absence of BaCO3, LaOCl in OCM reaction is capable of generating dioxygen species O22−, O2n− and O2−, which can cause deep oxidation of CH4, C2H6 and C2H4. With the addition of BaCO3, sites for the activation of oxygen molecules are depleted. The nearby Cl− ions have the ability of destabilizing the BaCO3, causing it to decompose at ca. 780°C, a decomposition temperature about 200°C lower than that of pure BaCO3. With the deprivation of dioxygen species, the CH4 oxidative dehydrogenation process is enhanced, while deep oxidation processes are suppressed. Compared with the deep oxidation reaction processes, the number of sites required in the H-abstraction process is a lot fewer. Hence, although the specific surface area of LaOCl was reduced with the addition of BaCO3, the conversion of CH4 over the Ba/CO3LaOCl catalysts did not drop significantly.