Long-Chain Glucan Adsorption and Depolymerization in Zeolite-Templated Carbon Catalysts

Abstract

We demonstrate adsorption and depolymerization of long-chain β-glu strands derived from cellulose, within the microporous confines of a zeolite-templated carbon (ZTC) material. The ZTC adsorbs β-glu strands that have a radius of gyration several-fold larger than the ZTC micropore diameter and do so rapidly (less than 2 min) and in adsorbed β-glu coverages of up to 80% of the ZTC mass. Principles of supramolecular chemistry predict that such adsorption occurs inside of the ZTC based on its micropore size as host being nearly ideal for glucan guest. A comparative study of partially etched materials and nitrogen physisorption at −196 °C indeed demonstrates β-glu adsorption to occur within internal ZTC micropores rather than on the external surface. Such adsorption under micropore confinement is expected to place significant mechanical strain on the β-glu strand, and this strain can be in principle relieved by depolymerization via hydrolysis. This hypothesis motivated us to investigate depolymerization of adsorbed β-glu strands in ZTC, where the ZTC serves as a catalyst for adsorbed β-glu hydrolysis. After a 3 h treatment in water at 180 °C, adsorbed β-glu was converted to soluble glucose in 73% yield. This represents the highest glucose yield observed to date for a carbon catalyst without postsynthetic surface functionalization and speaks to the effectiveness of weak-acid sites for β-glu hydrolysis within a constrained micropore environment.