The role of C1 species in the methanol-to-hydrocarbons reaction: Beyond merely being reactants

Abstract

In the methanol-to-hydrocarbons (MTH) process, C1 species, including methanol, dimethyl ether, and surface methoxy species (SMS), play crucial roles in the evolution of organic species and the construction of reaction networks. Understanding the roles of C1 species throughout the entire MTH process is both essential and challenging. Herein, the dynamic evolution of organic species and unique variation of C1 species during the real-time MTH process were observed by operando diffused reflectance Fourier transform infrared spectroscopy and ex-situ ¹³C cross polarization/magic-angle spinning nuclear magnetic resonance experiments. Importantly, density functional theory calculations thoroughly illustrated that methanol and SMS serve as key C1 species, in the form of not only methylation agents but also hydride acceptors, and their contributions vary across different reaction periods. Initially, SMS acts as the preferential C1 surface intermediate, methylating with hydrocarbons to propagate C–C bond, while also accepting hydrides to generate precursors for active hydrocarbon pool species. As reaction progresses, the role of SMS gradually diminishes, and thereby methanol becomes the predominant C1 species, in methylation for efficient product formation, meanwhile in hydride-transfer causing catalyst deactivation. Additionally, it was demonstrated that the confined zeolite microenvironment modified by large organics affects methanol adsorption and SMS formation, also accounting for the absence of SMS during the later period of reaction. This work provides a comprehensive and systematic understanding of the dynamic roles of C1 species throughout the MTH process, beyond the role as reactants.