Ionic Liquid Encapsulated in MIL-100(Fe): A Green Catalyst for Synthesis of Polyoxymethylene Dimethyl Ethers from Methanol and Trioxane

Polyoxymethylene dimethyl ether (PODEn) is a promising ether fuel. Especially PODE3–5 can be directly mixed into diesel without modification of the diesel engine’s infrastructure for improving thermal efficiency, and significant reduction in particulate matter (PM) and nitrogen oxides (NOx) emissions. In this paper, a series of heterogeneous catalysts, the imidazole sulfonate ionic liquids (ILs) encapsulated in the cages of metal–organic frameworks (MOFs) MIL-100(Fe), were used successfully and efficiently in the synthesis of polyoxymethylene dimethyl ethers (PODEn) from methanol and trioxane (TOX). These catalysts have exhibited excellent catalytic properties because of strong Brønsted acid sites. MIL-100(Fe)@[BSO3HIm][CF3SO3] shows the best catalytic activity with 96.98% conversation of TOX and 47.49% selectivity of the desired product PODE3–5 under a mild reaction condition. Of importance is that the catalyst is recovered easily and reused.