Low-temperature oxidation of dimethyl ether to methyl formate with high selectivity over MoO₃-SnO₂ catalysts

Low-temperature oxidation of dimethyl ether (DME) to methyl formate (MF) with high selectivity was realized in a continuous flow fixed-bed reactor over the multifunctional MoO₃-SnO₂ catalysts designed and prepared intentionally. The effect of the preparation methods including mechanical mixing, co-precipitation and co-precipitation-impregnation on the catalyst activity was investigated. The results showed that the selectivity to MF reaches 94.1% at 160 °C over the catalyst prepared by co-precipitation-impregnation, with DME conversion of 33.9% and absence of CO_x in the products. The results of NH₃-TPD, CO₂-TPD and H₂-TPR characterizations indicated that the catalysts prepared by various methods are also obviously different in the surface acidic, alkaline and redox properties. The results of Raman, XRD and TEM revealed that MoO₃ structure and particle sizes have a significant influence on the catalyst activity; small particle size and oligomeric MoO₃ may be responsible for the high activity of the MoO₃-SnO₂ catalysts from co-precipitation-impregnation in the selective oxidation of DME to MF at low temperature.