Preparation and characterization of mesoporous Zr-WOx/SiO2 catalysts for the esterification of 1-butanol with acetic acid

Zr-WOx clusters on WOx/ZrO2 catalysts are known to be active sites for the acid catalyzed reactions, such as dehydration of alcohols and alkane isomerization reactions. However, synthetic methods for producing high density of Zr-WOx clusters with high surface areas are not currently available. Herein, a facile method for preparing mesoporous Zr-WOx/SiO2 is proposed and the effect of Zr/W ratio on its structure and acidity was examined. Results showed that the sequential hydrolysis of zirconium and tungsten via soft-templating resulted in the formation of Zr-WOx clusters with uniform mesopore structures and a high acidity. The prepared Zr-WOx/SiO2 was characterized by N2 physisorption, XRD, TEM, XPS, UV-Vis spectroscopy, NH3-TPD and in situ FTIR. Catalytic performance for the esterification of 1-butanol with acetic acid was evaluated. The materials had a high surface area of over 500 m2 g−1 and ordered cylindrical pores with a uniform size of ca. 5 nm. Below a Zr/W ratio of ∼0.5, the zirconium was primarily associated with tungstate rather than SiO2, which indicates the formation of Zr-WOx clusters. The highest density of Zr-WOx clusters was obtained at a Zr/W ratio of 0.3 with a strong Brønsted acidity. Consequently, Zr-WOx/SiO2, as a Zr/W ratio of 0.3, exhibited the highest activity with a significantly improved performance compared to HZSM-5 and WOx/ZrO2 catalysts.