Influence of the surface SO3H groups on the performance of activated carbon catalyst for ethanolysis of furfuryl alcohol to ethyl levulinate

A series of sulfonated activated carbon catalysts (AC-SO 3 H- x ) were prepared by using sulfuric acid as the sulfating agent and used for the ethanolysis of furfuryl alcohol (FA) to ethyl levulinate (EL). The catalytic performance of AC-SO 3 H- x catalysts increased firstly and then decreased with introducing sulfuric acid and AC-SO 3 H-5 catalyst exhibited the highest activity with 95.3 % yield to EL and complete FA conversion, superior to that reported in the literature. Moreover, EL yield displayed the volcanic trend against with SO 3 H group concentration and the excellent catalytic performance of AC-SO 3 H-5 was attributed to appropriate surface acidity derived from the introduction of sulfonic acid groups (SO 3 H groups). Furthermore, it was firstly identified by the combination of FT-IR characterizations with Boehm's titration method that C-S bonds were formed through C atoms in phenolic hydroxyl groups of carbon surface bonding with SO 3 H groups. Additionally, the various sulfonation conditions and reaction conditions were optimized and it was found that low n FA /n EtOH (0.005) was very critical. This work provided a feasible strategy for the design of efficient carbon-based solid acid catalysts and innovatively elucidated the surface functional groups of carbon bonded to SO 3 H groups, which would drive the development of renewable FA to EL.