Preparation and characterization of WOx/ZrO2 nanosized catalysts with high WOx dispersion threshold and acidity

WOx/ZrO2 nanosized catalysts with high dispersion threshold were prepared via a novel two-phase interface hydrolysis (TPIH) method and characterized by N2 physisorption, X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy, Raman spectroscopy, and potentiometric titration with n-butylamine. It was found that the WOx/ZrO2 nanosized catalyst prepared by TPIH possessed a higher dispersion threshold (ca. 0.372 g WOx/g ZrO2) than that obtained by a conventional impregnation method, due to its higher specific surface area of 114 m2/g and tungsten surface density (6.2 W atoms/nm2). Significantly, the catalyst at dispersion threshold by TPIH has a remarkable number of strong acid sites with E > 400 mV and nearly double catalytic activity for n-pentane isomerization compared to that prepared by a conventional impregnation method. When this is combined with the results of spectral characterization, the high activity of the catalysts obtained by TPIH is ascribed to the abundant strong acidic polytungstate species on ZrO2 at their dispersion threshold. Challenges for future work would be developing the TPIH method with supports and exploring reaction conditions to reduce coke formation.