The catalytic performance of FexMn1-xWO4 as novel wolframite-type nanocatalysts for the selective dehydration of methanol into dimethyl ether

Selective production of dimethyl ether (DME), as a second-generation biofuel, under mild green conditions is still a challenge. Herein, FexMn1-xWO4 wolframite-type materials were proposed for the first time as efficient, selective, and stable catalysts towards methanol dehydration into DME. A simple one-step co-precipitation approach was used to fabricate the nanocomposites, and their catalytic performances were evaluated in comparison to earlier studies and to the commercial gamma-Al2O3 in terms of activity. The catalysts' structure, morphology, and porosity were identified by XRD, XPS, FTIR, TEM, and N-2-sorption analyses. Results of XRD and XPS confirmed the successful synthesis of FexMn1-xWO4 catalysts. Acidity of these nanocomposites were greatly influenced with the variation in x-value, calcination temperature, and doping with SO42-. The Bronsted characters of the acid sites and their weak and medium strength were investigated from PY-FTIR, chemisorption of basic probes and pyridine-TPD. The variation of the catalytic activities of these nanocomposites was strongly correlated to the variation in the catalyst acidity. The catalytic activity results indicated that Fe0.5Mn0.5WO4 catalyst calcined at 500 degrees C and modified with 5 wt.% of SO42- is the most effective nanocomposite with conversion values of 86 and 90% at reaction temperatures of 250 and 275 degrees C, respectively and all of 100% DME selectivity. The remarkable enhancement in the catalytic activity due to the doping with SO42- is attributed to the inductive effect of S = O group created on the catalyst surface. This nanocomposite could be regenerated many times with nearly the same efficiency and selectivity. Moreover, it offered a long-term stability (similar to 120 h) towards DME production.