Please cite this article in press as: A. Cubo, et al., Appl. Catal. A: Gen. (2016), http://dx.doi.org/10.1016/j.apcata.2016.10.029 ARTICLE IN PRESS G Model APCATA-16045; No. of Pages 10 Applied Catalysis A: General xxx (2016) xxx–xxx Contents lists available at ScienceDirect Applied Catalysis A: General jou rn al hom ep age: www.elsevier.com/locate/apcata Feature Article Dehydration of sorbitol to isosorbide in melted phase with propyl-sulfonic functionalized SBA-15: Influence of catalyst hydrophobization A. Cubo, J. Iglesias ∗ , G. Morales, J.A. Melero, J. Moreno, R. Sánchez-Vázquez ESCET, Universidad Rey Juan Carlos, C/Tulipán s/n, E28933, Mostoles, Madrid, Spain a r t i c l e i n f o Article history: Received 28 July 2016 Received in revised form 17 October 2016 Accepted 28 October 2016 Available online xxx Keywords: Isosorbide Sorbitol dehydration Sulfonic acids Heterogeneous catalysis Organic fucntionalization a b s t r a c t Propyl sulfonic acid functionalized mesostructured SBA-15 silicas have been used to promote the dehy- dration of sorbitol to isosorbide, in melted phase, under atmospheric pressure. These materials were prepared with different acid capacities and modified with different types of methylsilane functionalities, looking for an enhancement of the catalytic activity of these solid acids in the studied reaction. These two strategies seemed not only to condition the way in which reactants interact with the surface and the cat- alytic acid sites, i.e. through variations in the hydrophilic/hydrophobic balance, but a change in the acid strength of the catalytic sites is also influenced. Results indicate that increasing the acid loading slowed down the first reaction stage (sorbitol to sorbitan) but boosted the second one (sorbitan to isosorbide), because the interaction of the same sorbitol molecule with more than one acid site difficult its conversion, but increase acid strength, favoring the second dehydration step. Similarly, the organic modification of the solid acid SBA-15-based materials with hydrophobic methylsilane functionalities moieties reduced the affinity of the sorbitol substrate for the catalyst surface, but it also enhanced acid strength as well as the accesibility of sulfonic acids, slowing down the first step, but enhancing the second one. Despite of the influence of both assayed strategies on the catalytic performance of the tested materials is opposite in both dehydration steps, the positive influence of the same on the second reaction stage was proved to be dominant, because of being the limiting step on the conversion of sorbitol to isosorbide. In this way, using highly acid loaded sulfonic acid functionalized SBA-15 modified with surface grafted methylsilanes can be considered the right combination to maximize isosorbide production using these catalysts. © 2016 Published by Elsevier B.V. 1. Introduction Sorbitol is a sugar alcohol, currently derived from hydrolysed starch, which can be easily obtained via hydrogenolysis of glu- cose. Sorbitol is an important platform molecule used as a starting point in the synthesis of a large variety of chemicals [1]. One of these routes is the dehydration of sorbitol to produce anhydrosugar alcohols, such as mono-anhydrosorbitol and di-anhydrosorbitol. Sorbitan, a food additive, and isosorbide, an organic diol, are good examples of sorbitol-derived alcohols. Both products have multiple commercial applications and they can be used to synthesize numer- ous final products and chemical intermediates such as surfactants, polymers, drugs and cosmetics [2,3]. ∗ Corresponding author. E-mail addresses: jose.iglesias@urjc.es, jose.iglesias.moran@me.com (J. Iglesias). Isosorbide is conventionally obtained by sequential dehydra- tion of sorbitol to sorbitan, and from this to isosorbide (Scheme 1). This transformation requires the presence of strong acids such as sulfuric or hydrochloric acid as catalysts [4–6], but the use of such mineral acids involves several drawbacks such as a dif- ficult separation of isosorbide from the reaction mixture, or equipment corrosion, as far as the environment and safety are con- cerned. Therefore, several heterogeneous alternatives have been addressed, including zeolites in acid form [7–9], cation exchange resins [10–12], sulfonated carbons [13], or sulfated metal oxides [14–17], among many others [19,20]. All these studies are focused on developing a heterogeneous catalytic system suitable for sor- bitol conversion, but most of them require applying severe reaction conditions -high temperatures, low pressures, and long reaction times-, thus compensating the lack of enough catalytic activity to provide satisfactory isosorbide yields. Therefore, the development of an efficient solid acid catalyst capable to operate under milder http://dx.doi.org/10.1016/j.apcata.2016.10.029 0926-860X/© 2016 Published by Elsevier B.V.