Abstract
<jats:p>This study investigates the critical role of carbon catalyst surface architecture in the direct ("onepot") ethanolysis of microcrystalline cellulose to ethyl levulinate. Three sulfonated carbon matrices were synthesized and evaluated: pristine graphite, nanostructured mesoporous graphite obtained via thermal exfoliation, and amorphous micro/mesoporous hemp hurd-derived biochar. The materials were characterized using XRD, SEM, and nitrogen adsorption-desorption, while the density of grafted -SO3H groups was quantified via Boehm titration. Catalytic testing revealed that the efficiency of the solid-solid system is primarily governed by the surface morphology and pore size rather than the amount of -SO3H group. The pristine graphite sample exhibited the lowest ethyl levulinate yield due to its dense, non-porous structure, which minimizes the effective reactant contact area. Despite possessing a specific surface area comparable to nanostructured graphite, the amorphous biochar showed poor activity because its narrow micropores physically restrict the diffusion of bulky cellulose macromolecules. In contrast, the nanostructured graphite demonstrated the highest catalytic activity (achieving at a 20 mg/mL cellulose-to-ethanol ratio a maximum yield of ~15% in comparison with 1% and 2.4% for the graphite and biochar samples, respectively). Its exfoliated, mesoporous network successfully overcomes diffusion limitations, providing unhindered access of the solid substrate to the active acid sites. These findings demonstrate that the nanostructuring of crystalline graphite is a highly effective strategy for designing efficient solid acid catalysts for biomass valorization.</jats:p>