Ultrasonic enhancement of the acidity, surface area and free fatty acids esterification catalytic activity of sulphated ZrO2–TiO2 systems

• Published in: Journal of catalysis Vol. 297; pp. 17 - 26
• Main Authors: Boffito, D.C., Crocellà, V., Pirola, C., Neppolian, B., Cerrato, G., Ashokkumar, M., Bianchi, C.L.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.01.2013; Elsevier; Elsevier BV
• Subjects: Acid catalysts; acidity; active sites; adsorption; Catalysis; catalysts; catalytic activity; Chemistry; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Esterification; Exact sciences and technology; Fourier transform infrared spectroscopy; Free fatty acids; General and physical chemistry; Heterogeneous catalysis; ion exchange; nitrogen; porosity; Sol–gel; Sulfur; Sulphated titania; Sulphated zirconia; surface area; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; titanium dioxide; transmission electron microscopy; Ultrasonic imaging; Ultrasonication; ultrasonics; X-ray diffraction; X-ray photoelectron spectroscopy; Ultrasonication; Heterogeneous catalysis; Sulphated titania; Sulphated zirconia; Sol–gel; Acid catalysts; Esterification; Free fatty acids; Binary compound; Catalytic reaction; Sol-gel; Transition element compounds; Acidity; Fatty acids; Zirconia; Zirconium oxide; Sol gel process; Surface area; Titanium oxide; Ultrasound; Catalyst
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2012.09.013

The use of ultrasound to assist the sol–gel synthesis of sulphated ZrO2 and TiO2–ZrO2 was investigated. Properties such as acidity and surface area can be enhanced by acoustic cavitation and tuned by choosing appropriate on/off ratios of ultrasound pulses and powers. [Display omitted] ► Sulphated ZrO2–TiO2 systems with enhanced acidity and surface area were obtained with ultrasound. ► Acoustic cavitation is responsible for the formation of catalytically active surface defects. ► The effect of different ultrasound on/off pulses ratios and powers was investigated. ► Tuning catalysts’ properties is possible selecting appropriate on/off pulses ratios and powers. Different samples of sulphated zirconia and mixed zirconia/titania (SO42-/ZrO2 and SO42-/80%ZrO2–20%TiO2) were prepared with traditional- and ultrasound (US)-assisted sol–gel synthesis and tested in the free fatty acids esterification. The catalysts were characterized through acid sites quantification by ion exchange, specific surface area and porosity measurements (N2 adsorption at 77K), XRD, XPS and FT-IR spectroscopy. SEM–EDX and TEM analyses were also used to investigate the morphology of the samples. The results of this study demonstrate the possibility of increasing the acidity and the surface area of sulphated zirconia through the addition of TiO2 and tune the same properties with the continuous or pulsed US. It is also demonstrated that it is necessary to combine specific values of both acidity and surface area and which type of active sites are essential to obtain better catalytic performances in the free fatty acids esterification.