Synthesis of NaKCO3@(Mn-Na2 WO4/SiO2) core-shell catalyst for oxidative coupling of methane

Abstract

Oxidative Coupling of Methane (OCM) is a process to produce ethylene as one of the most widely used petrochemicals from methane natural gas. The core–shell nano-catalyst of NaKCO3@(Mn-Na2WO4/SiO2) was prepared with different ratios of Na/K, and its activity in the OCM process was investigated and its performance was compared with the conventional Mn-Na2WO4/SiO2 nano-catalyst. The effect of temperature and methane-to-oxygen ratio on nano-catalyst performance was investigated. The performance criteria included methane conversion, ethylene selectivity, and C2+ yield. The formation of the core–shell structure has been deliberated using XRD and FE-SEM characterization tests. The results of characterization and reactor experiments indicated that the best performance was related to the nano-catalyst prepared with a ratio ofNa/K = 2/2.4, operating conditions: 850 °C, atmospheric pressure, and CH4/O2 ratio = 2 in the reaction feed. The formation of the core–shell structure does not reduce the nano-catalyst activity, but rather increases the selectivity of the main product, ethylene, by improving the nano-catalyst performance even at 850 °C. Stability tests were performed to examine the catalytic activity under high temperatures.