Dimethyl Ether Hydrolysis over WO3/γ-Al2O3 Supported Catalysts

Abstract

Dimethyl ether (DME) is considered an alternative hydrogen carrier with potential use in fuel cells and automotive and domestic applications. Dimethyl ether hydrolysis to methanol is a thermodynamically limited reaction catalyzed by solid-acid catalysts, mainly Al2O3 and zeolites. Moreover, it is the rate-limiting step of the DME steam reforming reaction, which is employed for the production of hydrogen fuel for fuel cell feeding. In the present study, the performance of WO3/Al2O3 catalysts (0–44% wt. WO3) was tested in DME hydrolysis reaction. The catalysts were characterized by means of N2-physisorption, XRD, Raman spectroscopy, XPS, NH3-TPD and 2,6-di-tert-butylpyridine adsorption experiments. The reaction rate of DME hydrolysis exhibited a volcanic trend as a function of tungsten surface density, while the best-performing catalyst was 37WO3/Al2O3, with a tungsten surface density of 7.4 W/nm2, noting that the theoretical monolayer coverage for the specific system is 4–5 W/nm2. Brønsted acidity was directly associated with the catalytic activity, following the same volcanic trend as a function of tungsten surface density. Blocking of Brønsted acid sites with 2,6-di-tert-butylpyridine led to a dramatic decrease in hydrolysis rates by 40 times, proving that Brønsted acid sites are primarily responsible for the catalytic activity. Thus, the type and strength rather than the concentration of acid sites are the key factors influencing the catalytic activity.