Investigation of metal oxide additives onto Na2WO4-Ti/SiO2 catalysts for oxidative coupling of methane to value-added chemicals

Abstract The oxidative coupling of methane (OCM) is a closely related reaction process involving the transformation of methane (CH4) and O2 mixtures into value-added chemicals such as ethylene and ethane (i.e. C2+). This work presents the effects of metal oxide additives into the Na2WO4-Ti/SiO2 catalyst on the performance of the OCM reaction. Several metal oxide additives—including oxides of Co, Mn, Cu, Fe, Ce, Zn, La, Ni, Zr, Cr, and V—were investigated with the Na2WO4-Ti/SiO2 catalyst. All of the catalysts were prepared using co-impregnation and the catalyst activity test was performed in a plug flow reactor at a reactor temperature range of 600–800 °C and atmospheric pressure. The physicochemical properties of the prepared catalysts relating to their catalytic activity were discussed by using the information of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) measurements. Na2WO4-Ti/SiO2 added Mn was found to be the most active catalyst, involving shifts of binding energies of W 4f and Ti 2p toward lower binding energies. Moreover, a variety of operating conditions—including reactant- to-nitrogen gas ratio, catalyst mass, reactor temperature, and total feed flow rate—were intensively examined for the OCM reaction using the Na2WO4-Ti-Mn/SiO2 catalyst. The maximum C2+ yield was subsequently discovered at 22.09% with 62.3% C2+ selectivity and 35.43% CH4 conversion. Additionally, the stability of the Na2WO4-Ti-Mn/SiO2 catalyst was also monitored with time on stream for 24 h.