Dehydrogenative coupling of methane over Pt/Al2O3 catalysts: effect of hydrogen co-feeding

Abstract

The dehydrogenative conversion of methane (DCM) is a promising technology for using natural gas as a chemical resource. However, direct methane conversion is challenging owing to the high stability of methane molecules. In this study, we developed a novel DCM system in which a typical dehydrogenation catalyst, Pt/Al₂O₃, steadily converted methane into C₂ hydrocarbons with the aid of H₂ co-feeding. The catalytic performance of Pt/Al₂O₃ in the non-oxidative coupling of methane (NOCM) was significantly affected by the presence of hydrogen. When pure methane was fed over the Pt/Al₂O₃ catalyst, the catalyst was quickly deactivated via coke deposition. In contrast, when H₂ was co-fed with methane, the deactivation of the catalysts was suppressed, and C₂ hydrocarbons were stably formed. X-ray photoelectron spectroscopy and thermogravimetric analysis showed that H₂ co-feeding suppressed coke deposition on the Pt surface. At a reaction temperature of 600 °C, the Pt/Al₂O₃ catalyst showed a C₂ hydrocarbon formation rate of >8 μmol min⁻¹ g_cat⁻¹ over 24 h in the presence of H₂. Furthermore, Pt loading significantly affected the DCM reaction. A low Pt loading was effective for producing hydrocarbons. Electron microscopy analysis showed that with increasing Pt loading, the proportion of coarse nanoparticles increased. Fourier transform infrared spectroscopy suggested that the well-coordinated Pt sites were likely to form coke and deactivate, whereas the highly under-coordinated Pt sites were less likely to form coke. Because Pt/Al₂O₃ with a low Pt loading contains under-coordination sites, the catalyst was stable for the NOCM.