DFT simulation of HCl leaching over cellulase-mimetic solid acid catalyst for possible application in biohydrogen production

Abstract

Cellulase-mimetic solid acid catalysts (CMSAC), having both cellulose-binding and catalytic sites, are known to have much lower activation energy and higher catalytic activity than traditional solid acid catalysts. It is an emerging greener and cost-friendly solution for producing biofuel, such as bio-hydrogen, from lignocellulose. However, in 2018 the widely used CMSAC, sulfonated chloromethyl polystyrene, was found to have its catalytic activity attributed to the in-situ release of HCl during catalytic hydrolysis, which is unexpected. An ab initio quantum calculation based on density functional theory (DFT) is performed to study its reaction mechanism. Results have shown that the most probable mechanism responsible for the in-situ release of HCl is through SN1 nucleophilic substitution. The simulation also predicted a surface reaction activation energy of 1.56 eV (35.97 kcal/mol), along the predicted minimum energy path (MEP). This is the first ab initio study to theoretically predict the HCl leaching mechanism from CMSAC before its industrial application.