Abstract
The oxidative coupling of methane (OCM) is a promising pathway for directly converting methane into higher hydrocarbons (C(2+)). This research investigated the influence of alkali metal promoters (Li, Na, K, or Rb) on Co/Al(2)O(3) catalysts prepared based on incipient wetness impregnation for the OCM reaction. The catalyst investigations demonstrated that the catalysts promoted with K and Rb had superior performance, with the 4.6K-Co/Al(2)O(3) catalyst achieving a maximum C(2+) yield of 8.1%, C(2+) selectivity of 24.0%, and CH(4) conversion of 32.1% at 640 °C. Catalyst characterization, based on XRD, HR-TEM, BET, XPS, CO(2)-TPD, and H(2)-TPR analyses, revealed the structural and physicochemical properties responsible for the enhanced catalytic activity. Specifically, K and Rb promoters increased surface basicity and enhanced the electron density of active sites, thereby promoting selective methane activation. In-situ DRIFTS and mechanistic studies highlighted the role of reactive oxygen species in promoting C(2+) hydrocarbon formation. These results should position K-Co/Al(2)O(3) as a promising catalyst for OCM and provide valuable guidance for designing more efficient catalytic systems for methane utilization.