A collection of Al-SBA-15 mesoporous catalysts (Si/Al = 13–174) was investigated to overcome typical accessibility constraints of microporous solids. ²⁷Al MAS NMR confirmed the existence of tetrahedrally coordinated Al in the catalyst’s framework, and the fraction of such species increased as the Si/Al ratio decreased. Brønsted acidity followed the same pattern found using n-propylamine thermodecomposition. Mesoporous catalysts with lower Si/Al ratios exhibited a higher affinity to water as quantitatively determined using water adsorption experiments. Those surface properties were correlated to the catalytic performance on oleic acid esterification. The introduction of Al into the SBA-15 framework significantly improved esterification activity, leading to conversions ranging from 70 to 93%. This was explained by the acidity engendered upon Si substitution by Al. However, a turning point from which activity started dropping was registered and it was proposed to be associated with catalyst hydrophilicity. The balance between acidity and hydrophilicity was unveiled to be of paramount importance to accomplish the best catalytic efficiency and uppermost biofuel yield. Catalyst activity was also assessed for the esterification of stearic and linoleic acids. Higher conversion rates were accomplished with unsaturated fatty acids (oleic acid > linoleic acid > stearic acid) due to the higher reactivity of the carboxylic acid moieties as a consequence of the polarity of the double bonds in the carbon chain.

Glucose is the most abundant monosaccharide as it is the primary unit of cellulose and starch, which are the more relevant feedstocks for biorefineries. Dehydration of glucose can lead to anhydroglucoses, whose interest has been increasing due to its potential industrial use. Commercial sulfonic polymer resins and a synthesized organic–inorganic mesoporous material were taken as Brønsted acid catalysts. High hexose conversion (up to 98%) and selectivity to anhydroglucoses (~80%) could be reached, turning this process into an alternative route to carbohydrate pyrolysis that presents an energy-intensive downstream. Hexose conversion to anhydroglucoses was related to the amount of acid sites, and the removal of one molecule of water from hexoses to produce anhydroglucoses was found as the preferential dehydration route over a bare Brønsted acid catalyst in anhydrous polar aprotic solvent (DMF) at mild conditions. Product distribution changed dramatically upon catalyst deactivation with HMF and fructose emerging as relevant products. It was suggested that an additional Lewis surface is produced during the deactivation process, probably arising from the formation of insoluble high molecular weight compounds in acidic media.