Acid properties of M-SBA-15 and M-SBA-15-SO3H (M = Al, Ti) materials and their role on esterification of oleic acid

The acidity of SBA-15 was tuned with the incorporation of Al+3, Ti+4, and -PrSO3H groups through sol-gel, employing molar ratios of Si/M = 10 (M = Al, Ti) and Si/S = 10. This results in mesoporous materials with the typical hexaonal structure of SBA-15, large surface areas, and great pore diameter. The incorporation of Al+3 and Ti+4 mainly leads to catalysts with both Bronsted and Lewis acid sites. The addition of sulfonic groups to these samples enhanced their surface acidity, creating preferentially Bronsted acid sites. Among the evaluated catalysts, the SBA-15-SO3H showed the highest catalytic activity, which was related to the high concentration of Lewis acid sites, and a remarkable resistance to deactivation, probably due to its low hydrophilicity. A first order kinetic equation fits well the experimental data and an activation energy of 31.5 kJ/mol similar to other reports for this reaction was calculated for the SBA-15-SO3H catalyst.