Structure Sensitivity of La<sub>2</sub>O<sub>2</sub>CO<sub>3</sub> Catalysts in the Oxidative Coupling of Methane

Methane is the main component of natural gas and shale gas. It is chemically stable, and its activation often requires high temperatures, which lead to its extensive transformation into undesirable products such as CO and CO<sub>2</sub>. Thus, the development of efficient catalysts for the selective transformation of methane represents a substantial challenge. In this work, we synthesized La<sub>2</sub>O<sub>2</sub>CO<sub>3</sub> samples with different morphologies (rod- and plate-shapes) at the nanometer scale. We observed that one of the rod-shaped samples exhibited the best catalytic properties among the investigated samples in the oxidative coupling of methane (OCM) at low temperatures (420–500 °C); in addition, its specific activity was 20 times greater than that of any of the other rod-shaped samples. This difference corresponded to the O<sub>2</sub>-TPD results and was attributed to the crystallographic facets exposed. Among the exposed facets, the (110), (12̅0), and (21̅0) facets had relatively loose atomic configurations that increased the conversion of methane in the OCM. Moreover, these facets were beneficial to the formation of the chemisorbed oxygen species and their moderately basic sites, which improve the selectivity in the OCM.