Effect of Fe/Zn ratio in composite catalyst for synthesizing polyoxymethylene dimethyl ethers

Abstract

Polyoxymethylene dimethyl ethers (PODE n ) are extremely effective diesel additives to reduce soot formation during combustion. We introduce a series of Fe-Zn composite solid acid catalysts (SO 4 2− /xFe 2 O 3 -yZnO), for the condensation reaction of methanol and paraformaldehyde (PF) with a cheap and feasible route to efficiently synthesize PODE n . These catalysts were characterized by different characterization techniques, namely BET, XRD, SEM, EDS, FTIR, and NH 3 -TPD and the results showed that Fe/Zn molar ratios strongly influenced the physicochemical characteristics of catalysts, thus affecting the methanol conversion and PODE 1-6 and PODE 3-6 selectivity. Accordingly, the methanol conversion was decreased and the selectivity of PODE 3-6 was increased after increasing the Zn molar content. Comparatively, SO 4 2− /Fe 2 O 3 -2ZnO exhibited superior catalytic activity among the various investigated catalysts due to the high acid density of strong acid sites. The optimal reaction conditions were observed to be at a 3.0 wt% catalyst loading (catalyst/reactant mass ratio), 2.5 hours ours of reaction time, a reaction temperature of 403 K, and a molar ratio of 3:1 of CH 2 O to methanol, achieving a high selectivity of 99.09% PODE 1-6 and 28.23% PODE 3-6 with 55.16% methanol conversion during the reaction. K E Y W O R D S acid sites, composite catalyst, polyoxymethylene dimethyl ethers, SO 4 2− /xFe 2 O 3 -yZnO