A Brّnsted solid acid synthesized from fly ash for vapor phase dehydration of methanol

A Brønsted solid acid was prepared from waste coal fly ash by acid treatment with concentrated H2SO4 at 473 K. The prepared solid acid was characterized by X-ray diffraction (XRD), Fourier-transform Infrared spectra (FT-IR), solid-state nuclear magnetic resonance (NMR) and scanning electron microscope (SEM). The characterization results show that the solid acid contains two types of Brønsted acid sites: weak acidic –OH groups and strong bridging Si–O(H)–Al groups. The acid strength of the strong acid sites is similar to that of zeolite HY (Si/Al = 3). The solid acid from fly ash exhibits excellent catalytic activity and stability in methanol dehydration reaction for dimethyl ether (DME) production. Our finding is a promising way of utilization of waste coal fly ash to prepare effective solid acid catalyst for industrial acid catalysis reactions.