## 1 Introduction  
Cellulose is one of the major polymers in the plant cell wall. Deconstruction of cellulosic biomass is a critical step in the production of sugars and biofuels, as an alternative to depleting fossil fuels [1; 2; 3; 4; 5; 6; 7]. In the biochemical platform of biomass conversion, a pretreatment step is required to open up the biomass structures, relocate lignin, or to partially hydrolyze hemicelluloses [8; 9; 10; 11]. Dilute acid pretreatment is one of the leading technologies, among several other approaches [12; 13; 14]. The disadvantages of the dilute acid pretreatment include the high equipment cost, and the detrimental effect on the environment with regard to acid disposal and recycling. The pretreated lignocellulosic biomass is typically further hydrolyzed to monomeric sugars using an enzyme cocktail [15; 16]. However, enzymatic conversion is slow and expensive [17]. Cel48F is a widely used cellulase to catalyze cellulose hydrolysis [18; 19]. The mechanism involved in the Cel48F hydrolysis involves two reaction steps. The first step is to break the intermolecular hydrogen bonds formed between cellulose chains, followed by the second step of hydrolyzing the individual cellulose chain to glucose and shorter oligosaccharides. Earlier studies using classical molecular dynamics (MD) simulations have gained insights into the catalytic mechanisms of cellulases such as TmCell2A [20], Cel7A [21], and Cel48F [18; 19]. Amino acid residues on cellulases play important roles in adapting their conformations for the entry, breakage, and exit of cellulose chains in the catalytic tunnel, as well as in transferring water molecules into the hydrolysis site for breaking down the glycosidic bond. The microenvironment in the catalytic tunnel inside cellulase is partially dehydrated. Previously, we have performed ab initio molecular dynamics simulations coupled with metadynamics (CPMD-MTD) simulations [22; 23; 24; 25; 26; 27; 28; 29; 30; 31] to elucidate the energetics and mechanisms of acid-catalyzed catalytic conversions, including cellulose hydrolysis, glucose ring opening, glucose dehydration, and isomerization reactions. The barriers of these reactions are found to strongly affect by the solvent. A partially dehydrated environment could potentially reduce the activation barrier and facilitate the hydrolysis reaction. Inspired by action of cellulase enzymes, a polymeric solid acid catalyst consisting of two adjacent nanostructures was synthesized and immobilized on a porous membrane substrate to mimic the function of cellulase. The poly(styrene sulfonic acid) (PSSA) chain hydrolyzes the \(\beta\)-1\(A\)-glycoside bonds, whereas the neighboring poly(vinyl imidazolium chloride) ionic liquid (PIL) chain enhances the solvation of the PSSA chain and facilitates the dissolution of cellulose by breaking the intermolecular hydrogen bonds between the neighboring cellulose chains. The schematic interaction between the polymeric acid catalyst and cellulose is shown in Figure 1. The polymeric acid catalyst can operate at higher temperatures than cellulase enzymes, overcoming the limitations of biocatalysts to speed up the reaction rates significantly [32; 33]. This designed polymeric acid catalyst was successfully synthesized and studied [34; 35; 36]. More than 97% total reduction of sugar (TRS) yield was obtained in 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) solution using cellulose as a substrate at a mild temperature of 130 \({}^{\circ}\)C. More recently, the depolymerization of lignocellulosic corn over the biomass was conducted using the optimized polymeric catalyst. Near-quantitative TRS yields were obtained in IL and IL/H\({}_{2}\)O mixed solvents for dilute acid, base, and stream-pretreated samples obtained from the National Renewable Energy Laboratory [35]. In addition, over 50% glucose yield was obtained for acid-pretreated wheat straw in mixed solvents consisting of ionic liquid and \(\gamma\)-valerolactone (GVL) [36].