Hydrothermal Synthesis of La2O2CO3 and La2O3 Catalysts: Influence of Alkaline Solution on Low-Temperature OCM Performance

The oxidative coupling of methane (OCM) offers a direct route to produce value-added C 2 hydrocarbons; however, achieving high activity and selectivity at low temperatures remains challenging. In this experimental study, La 2 O 2 CO 3 and La 2 O 3 nanowire catalysts were synthesized hydrothermally using different alkaline precipitants under identical conditions. Structural and surface analyses (XRD, FE-SEM, BET) demonstrate the decisive role of the precipitant in controlling phase composition, morphology, and surface area. The ammonia-derived La 2 O 2 CO 3 catalyst (A-500) demonstrated stable OCM activity at temperatures as high as 350 °C, yielding a C 2+ yield of 12.3%. This finding indicates that the reported onset temperature for OCM is among the lowest documented to date. As the temperature increased, the A-500 demonstrated a maximum C 2+ yield of 13.1% at 500 °C, exhibiting suppressed COx formation. Over the duration of 50 h, the system maintained approximately 31% CH₄ conversion and 44% C 2+ selectivity without any discernible deactivation. The results suggest that OCM performance is governed by a coupled structural parameter space in which crystallite size, morphology, and surface area act synergistically to determine catalytic efficiency. Consequently, the integration of hydrothermal synthesis with a judicious selection of precipitant agents has yielded La-based catalysts that exhibit remarkably low-temperature activity and prolonged durability. This approach provides a set of pragmatic design principles for the development of catalysts in the context of low-temperature OCM.