Screening of single and binary catalysts for oxidative coupling of methane to value-added chemicals

Abstract

A combinatorial approach was applied to explore active binary catalysts for oxidative coupling of methane (OCM) to value-added hydrocarbons (C2+). A screening of 25 selected single components on SiO2 for OCM reaction identified the top-14 single active components as follows: La > Ce > Ga > Al > Ca > Cr > Ba > Na2WO4 > Mn > Cu > Ti > Zn > Rb > Ni. Binary catalyst screening was then performed and resulted in a combination of Na2WO4 and Mn producing the most active binary catalyst. X-ray powder diffraction measurement of the Na2WO4-Mn/SiO2 catalyst revealed that the presence of α-cristobalite phase was essential for the activation of methane. Moreover, the X-ray photoelectron spectroscopy spectrum of the Na2WO4-Mn/SiO2 catalyst showed that the binding energy of W4f and Mn 2p shifted toward a lower binding energy, thereby enhancing the catalytic activity. Optimization of C2+ production of the catalyst by varying Na2WO4:Mn weight ratios, total metal loadings, catalyst weights, and feeding gas compositions, achieved maximum C2+ yield of 23.54% with 60.5% selectivity and 39.67% methane conversion. Furthermore, the activity of the Na2WO4-Mn/SiO2 catalyst was monitored with time-on-steam for 50 h, revealing good catalyst stability.