Insights into deactivation mechanism of sulfonated carbonaceous solid acids probed by cellulose hydrolysis

Abstract

Sulfonated carbonaceous solid acids are key heterogeneous catalysts and are widely used in acid-catalyzed reactions, especially in biomass transformation. In this work, the sulfonated carbonaceous solid acids were prepared and their stability was examined in cellulose hydrolysis at 170 °C. Their activity decreased largely after the hydrothermal treatment at 170 °C, as a result of the leaching of their SO3H species. Characterizations of the filtrates after the hydrothermal treatment of these solid acid catalysts by NMR and laser scattering demonstrated that the leaching of SO3H sites was not caused by the cleavage of CS bonds, but by the exfoliation of colloidal carbon particles with SO3H sites from the catalysts. Such leaching problem led to significant decrease in SO3H density for the carbon-based solid acids that synthesized by traditional sulfonation methods because of their uneven distribution of SO3H sites. To address this issue, carbon precursors with more free CH sites were applied to regulate the distribution of SO3H sites. As a consequence, the evenly distributed SO3H sites resulted in less change in acid density after the hydrothermal treatment, and maintenance of high SO3H density. This study could provide new guidance to further design of water-tolerant solid acid catalysts, and would promote the development of energetically efficient processes to convert cellulose.