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.

Homogeneous alkaline catalysts are highly efficient for converting triglycerides to methyl esters under mild conditions. However, soap formation remains a significant limitation, reducing the yield and complicating separation. Shortening the reaction time is a key strategy to mitigate this issue. In this work, the effect of CH₃CO₂Na and CH₃CO₂K on the alkaline methanolysis of soybean oil catalyzed by sodium methoxide was investigated to reduce reaction time. A zero-order reaction kinetic model was employed. Observed rate constants (k _obs) were determined from online monitoring the refractive index of the reaction mixture. Experiments were conducted at temperatures of 40.0, 50.0, and 60.0 °C and stirring speeds of 400 and 800 rpm. Both salts provided an increase in k _obs values compared to those in biodiesel synthesis in the absence of them. CH₃CO₂K proved to be the most effective additive by increasing k _obs values by up to 90% for methanolysis at 800 rpm and 40.0 °C, while CH₃CO₂Na increased values by up to 60% at 800 rpm and 40.0 °C. The conversion of triglycerides to methyl esters was determined by ¹H nuclear magnetic resonance, and an increase in conversion of up to 2.9 and 2.6% was observed in the presence of CH₃CO₂K and CH₃CO₂Na, respectively, after 60 min of reaction. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis confirmed that Na and K levels in biodiesel were below 0.5 mg kg^-1, well within international fuel quality limits. These findings highlight the potential of sodium and potassium acetates as effective additives for reducing the time of reaction and improving biodiesel synthesis.