Ph-SO3H-modified mesoporous carbon as an efficient catalyst for the esterification of oleic acid

Mesoporous carbon materials with thin pore walls (∼1.7 nm) were synthesized using low-cost γ-Al2O3 as a hard template and in situ polymerized resorcinol–furfural resin as the carbon precursor. Compared with sugar, resin, a widely used carbon precursor, has higher carbon yield and simplifies the synthetic process. Ph-SO3H modified mesoporous carbon was synthesized by covalent grafting of Ph-SO3H groups on mesoporous carbon via the diazonium salt. The resulting materials were characterized by means of nitrogen adsorption analysis, TEM, 13C NMR, XRD, FTIR and sulfur elemental analysis. The modified carbons were shown to possess high surface area (∼1000 m2/g), a bimodal pore size distribution and high strong acid density (1.86 mmol H+/g). These sulfonated carbons were used as solid acid catalysts in the esterification of oleic acid and methanol, a key reaction in biodiesel production. Compared with the traditional solid acid Amberlyst-15, the optimized carbon catalyst exhibited much higher activity with a rate constant (1.34 h−1) three times to that of Amberlyt-15 and a turnover frequency (TOF) of 128 h−1 eight times that of Amberlyst-15. The efficient catalytic ability was attributed to the high surface area and a proper mesopore texture. This carbon catalyst could then be easily separated from the product by filtration. The catalyst was reused six times, and no distinct activity drop was observed after the initial deactivation.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (135 K)Download as PowerPoint slideHighlights► Ph-SO3H-modified mesoporous carbon catalysts were synthesized by Al2O3 and RF resin. ► Such catalysts have thin carbon walls (∼1.7 nm) and high BET area (∼1000 m2/g). ► Such carbon catalysts were tested in the esterification of oleic acid and methanol. ► TOF of optimal catalyst was 128 h−1, eight times that of Amberlyst-15. ► Such carbon catalysts were a type of stable solid acid.