Synthesis of polyoxymethylene dimethyl ethers from dimethoxymethane and trioxymethylene over graphene oxide: Probing the active species and relating the catalyst structure to performance

摘要

Polyoxymethylene dimethyl ethers (PODE, with the formula of CH3O-(CH2O)(n)-CH3), as a promising environmentally benign diesel fuel or additive with an enormous potential in the reduction of soot and NIC, emissions, can be efficiently synthesized from methanol derivatives such as dimethoxymethane (DMM) and trioxymethylene (TOM), which requests a proper catalyst of high performance. In this work, the catalytic performance of graphene oxide (GO) in the synthesis of PODEn as well as its relation to the catalyst structure was thoroughly investigated. The results indicate that GO is an excellent catalyst in the synthesis of PODEn from DMM and TOM; a TOM conversion of 94.6% and selectivity of 86.0% to PODE2-8 are achieved under mild reaction conditions, which is superior to the majority of the state-of-the-art catalysts. Meanwhile, the active species and characteristic layer structure of GO sheets catalytically responsible for PODEn formation were discriminated through selectively removing certain surface functional groups, thermally annealing at different temperatures, and carefully comparing with a series of model compounds. The results illustrate that the superior catalytic performance of GO in the PODEn synthesis should be ascribed to a synergy between the surface sulfonyl, hydroxyl and carboxyl groups present on the GO surface and the unique layered structure of GO sheets, wherein the surface sulfonyl groups act as the main active sites. The insights shown in this work are beneficial to a deep understanding on the catalytic principle of GO and development of efficient catalyst for the synthesis of PODEn.