Lanthanum based catalysts for oxidative coupling of methane: Effect of morphology and structure

La2O3 and La2O2CO3 catalysts with the nanoparticle, nanorod, flower-like, nanofiber, and nanosphere morphologies were synthesized and tested for the oxidative coupling of methane. It was determined that La2O3 catalysts were sensitive and La2O2CO3 catalysts were stable under atmospheric conditions. Thus, the amounts of oxygen from water and the ratio of complex hydroxyl-carbonate oxygen species (OA) to lattice oxygen (OL) were higher on La2O3 than La2O2CO3 catalysts. Obtained results showed that the activity and selectivity of the catalysts mainly depend on the surface oxygen type, and then the surface area and basicity. The stable carbonate formation was found detrimental to activity and selectivity, thus La2O3 catalysts were more active and selective than La2O2CO3 catalysts. The catalyst morphology greatly affected the reaction performances, and La2O3 with nanorod and nanofiber morphology could initiate the reaction even at 450 °C and the highest C2 yield was 11.7 % obtained with nanofiber morphology at this temperature.