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Journal of Catalysis, Volume 297, January 2013, Pages 17-26
D.C. Boffito, V. Crocellà, C. Pirola, B. Neppolian, G. Cerrato, M. Ashokkumar, C.L. Bianchi
Università degli Studi di Milano, Dipartimento di Chimica, via Golgi 19, 20133 Milano, Italy
Università di Torino, Dipartimento di Chimica Inorganica, Chimica Fisica e dei Materiali, via P. Giuria 7, 10125 Torino, Italy
SRM Research Institute, SRM University, Kattankulathur, Chennai, India
The University of Melbourne, School of Chemistry, Melbourne, Parkville 3052, Australia
Abstract
Different samples of sulphated zirconia and mixed zirconia/titania ( and ) 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 77 K), 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.
Additional Information
The work described in the present manuscript was carried out at the School of Chemistry of The University of Melbourne (Australia). The authors are grateful to the Australian Government that recognized the importance of this work in its design phase and awarded the Endeavour Research Fellowship to the main author.
This work deals with the application of the ultrasound to the sol-gel synthesis of sulphated zirconia and titania. It is shown how acidity and surface area of these catalysts can be increased and tuned in general by using ultrasound pulses or different amounts of water for the syntheses. The authors performed different sol-gel experiments by changing the ultrasound pulse length and the amount of water (i.e. the ultrasound densities) in the sol-gel medium. A study on how the properties of such materials can be modulated with the use of ultrasound is provided. This study demonstrates that there is an an optimal pulse on and off times where maximum cavitation efficiency (maximum number of active bubbles ultrasonically generated) can be achieved. In fact, as the pulse on time is increased and pulse off time is decreased, more active bubbles are generated but degassing may occur resulting in a lower number of active bubbles.
The catalysts were tested in the free fatty acids esterification, a reaction of environmental interest. The achieved results are encouraging and were discussed in detail relating them to the properties of the catalysts and therefore to the ultrasound synthesis conditions adopted.
This study might be interesting also in view of the application of sulphated zirconias in other kinds of reactions, such as isomerizations, alkilations and esterifications of other kinds of carboxylic acids.
