Effect of different Mn salt precursors on Mn-H 4SiW 12O 40/SiO 2 used for dimethoxymethane synthesis from dimethyl ether oxidation

Abstract

Mn-H 4SiW 12O 40/SiO 2 heteropolyacid catalysts were prepared by impregnation method from different Mn salt precursors, such as MnSO 4, Mn(NO 3) 2, MnCl 2 and Mn(CH 3COO) 2. The catalytic oxidation reaction of dimethyl ether (DME) to dimethoxymethane (DMM) was carried out in a continuous flow type fixed-bed reactor with a ratio of N DME/ N O 2 = 1:1. It is found that the sequence of catalytic activity for DMM synthesis is MnCl 2-H 4SiW 12O 40/SiO 2>Mn(NO 3) 2-H 4SiW 12O 40/SiO 2>MnSO 4-H 4SiW 12O 40/SiO 2>Mn(AC) 2-H 4SiW 12O 40/SiO 2. The effects of reaction temperature (573 −633 K) on the catalysts were also investigated. With the increase of reaction temperature, the DME oxidation reaction is more exquisite over MnSO 4-H 4SiW 12O 40/SiO 2 catalyst. 42.4% of DME conversion and 0.9% of DMM selectivity have also been obtained at 613 K. However, MnCl 2 modified H 4SiW 12O 40/SiO 2 catalyst obtains higher DMM selectivity (37.5%, at 593 K) than other three catalysts at mild reaction conditions. H 2-TPR profiles show that MnSO 4 modification demonstrates stronger oxidative performance at high temperature than other catalysts, while MnCl 2-H 4SiW 12O 40/SiO 2 catalyst exhibits better oxidative performance at low temperature. XRD patterns of the catalysts show that the diffraction peaks are strong and MnO 2 diffraction peak is also found over the MnCl 2 modified catalyst.