Catalytic conversion of glycerol by means of coupled dehydration and oxidation reactions over multifunctional heterogeneous catalysts

Abstract

The biodiesel production, which occurs by means of the transesterification of triglyceride molecules with methanol and in the presence of a basic catalyst, is growing annually. This reaction coproduces more than 10 wt.% of glycerol, which also stays in growth. Consequently, the supply of glycerol is much greater than the demand. Therefore, the current challenge is to convert glycerol into value-added products aiming to promote the biodiesel production chain and to offer the industry several compounds of renewable source. The selective conversion of glycerol into chemicals such as acrolein, acrylic acid and acetaldehyde by means of coupled reactions of dehydration and oxidation is a good example to reinforce the potential of the renewable glycerol. Both reactions can be conducted in a single reactor by using bifunctional catalysts containing acid and redox sites. The acid sites (Brønsted or Lewis) have strong influence on the performance of the catalyst, such as selectivity to acrolein and coke formation. Additionally, micro-mesoporous catalysts have a pronounce improvement in deactivation in comparison to purely microporous catalysts, which is due to the system of pores and to the relative proportions of Brønsted/Lewis sites that lead to the formation of two distinct families of coke (polyaromatics and polyglycols). The insertion or dispersion of active elements such as V, Mo and/or Cr may produce drastic changes in the deactivation of the catalysts at the same time in which other value-added products are formed, such as acrylic acid. For the worthy performance of these catalysts, there is, as a result, the need of joint contribution of the acid and redox active sites that should be prepared by an adequate catalyst design, i.e. adding the active elements in an appropriate porous matrix. It is also expected that the mixing of the elements in certain proportions can enhance the formation of oxygen vacancies in the catalyst and, consequently, improve the redox cycle needed in the oxidation of glycerol. This proposal aims the development and study of multifunctional catalysts, as well as the identification of the reasons for their deactivation under glycerol dehydration-oxidation reactions. To help to achieve the postulated target time resolved Synchrotron characterization techniques, X-ray diffraction and X-ray absorption spectroscopies will be used. (AU)