Active state of tungsten oxides on WO3/ZrO2 catalyst for steam reforming of dimethyl ether combined with CuO/CeO2

Steam reforming of dimethyl ether (DME) was carried out over WO3/ZrO2–CuO/CeO2 catalysts. The effect of the method of preparation of WO3/ZrO2 on its activity was investigated. Three kinds of WO3/ZrO2 were prepared by impregnating ammonium paratungstate (APT), ammonium metatungstate (AMT), and tungsten hexachloride (WCl). Although these WO3/ZrO2 catalysts had different activities, no difference was observed in their acidic property. The TG-DTA analysis clarified that the different kinds of W precursors affected the crystallization process of zirconia differently. The interaction with zirconia during calcination gave specific properties to the surface W species that are different from those of the single component WO3. The XPS study on the surface W species showed that H2 production rate depended on the surface WO3 amount and on the W(V)/[W(VI) + W(V)] ratio. Excess WO3 loading brought about the decrease in H2 production due to the formation of inactive bulk WO3. The active surface tungsten species were originated from W(V) components interacting with ZrO2. The APT gave the highest W(V)/[W(VI) + W(V)] ratio and, thus, was the best W precursor among the three.