Impact of aging on the structural, textural, and acid properties of WO3 - SO42− - SnO2 solid acids

Abstract

Aging of solid acid catalysts (SAC) appears to be a hidden factor impacting the textural properties as well as the performance of catalysts. In this work, aged WO3-SO42--SnO2 catalysts were prepared via sol-gel method using two different percentage loadings of WO3 (15 wt% and 35 wt%) followed by three different calcination temperatures (CT) (200 °C, 400 °C, and 650 °C). The 24 h aging at both ambient temperature as well as 50 °C were performed on SO42--SnO2 hydrogel mixture prior to loading with an appropriate percentage of WO3 and then calcined. The catalysts were characterized by thermogravimetric analysis (TG–DTA), powder x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), surface acidity, and N2 isothermal adsorption/desorption techniques. The structural and textural properties of the catalysts were compared with the previously prepared non-aged catalysts and found to be different. The catalysts calcined at 400 °C have poor crystalline structures whereas the 650 °C product has crystalline tetragonal cassiterite structure. The potentiometric titration with n-butylamine also indicated very strong acid sites for catalysts calcined at 400 °C but dependent on the aging method, and percentage loading of WO3. Generally, both the surface area and micro-pore volume decreased gradually with rising calcination temperature, whereas the total pore volume (VT) and a mean pore radius increased with rising CT.