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

• Published in: Journal of catalysis 2013-03, Vol.299, p.119-128
• Main Authors: Song, Kunshan, Zhang, Hongbin, Zhang, Yahong, Tang, Yi, Tang, Kangjian
• Format: Article
• Language: English
• Subjects: acidity; Catalysis; catalysts; catalytic activity; Chemistry; Dispersion threshold; Exact sciences and technology; General and physical chemistry; hydrolysis; Isomerization; Nanosized catalyst; nitrogen; Raman spectroscopy; reflectance spectroscopy; surface area; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; titration; transmission electron microscopy; tungsten; Two-phase interface hydrolysis; WOx/ZrO2; X-ray diffraction
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2012.11.011

The WOx/ZrO2 catalysts prepared by the two-phase interface hydrolysis method possess much more polytungstate species with strong acidity as a result of a higher WOx loading at dispersion threshold and double catalytic activity for the isomerization of n-pentane compared with that prepared by conventional impregnation method. [Display omitted] ► WOx/ZrO2 catalysts prepared by TPIH possess a higher surface and W surface density. ► The TPIH method can make WOx/ZrO2 catalysts achieve higher dispersion threshold. ► TPIH endows WOx/ZrO2 catalysts with double catalytic activity as impregnation method. ► Polytungstate species with E>400 mV are suggested to be the active sites. 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. 0.372g WOx/g ZrO2) than that obtained by a conventional impregnation method, due to its higher specific surface area of 114m2/g and tungsten surface density (6.2W atoms/nm2). Significantly, the catalyst at dispersion threshold by TPIH has a remarkable number of strong acid sites with E>400mV 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.