Preparation of a Carbon-Based Solid Acid Catalyst by Sulfonating Activated Carbon in a Chemical Reduction Process

Sulfonated (SO3H-bearing) activated carbon (AC-SO3H) was synthesized by an aryl diazonium salt reduction process. The obtained material had a SO3H density of 0.64 mmol.g(-1) and a specific surface area of 602 m(2).g(-1). The catalytic properties of AC-SO3H were compared with that of two commercial solid acid catalysts, Nafion NR50 and Amberlyst-15. In a 10-h esterification reaction of acetic acid with ethanol, the acid conversion with AC-SO3H (78%) was lower than that of Amberlyst-15 (86%), which could be attributed to the fact that the SO3H density of the sulfonated carbon was lower than that of Amberlyst-15 (4.60 mmol.g(-1)). However, AC-SO3H exhibited comparable and even much higher catalytic activities than the commercial catalysts in the esterification of aliphatic acids with longer carbon chains such as hexanoic acid and decanoic acid, which may be due to the large specific surface area and mesoporous structures of the activated carbon. The disadvantage of AC-SO3H is the leaching of SO3H group during the reactions.