PVP-stabilized heteropolyacids as reusable self-assembling catalysts for alcoholysis of cellulosic saccharides

Abstract

Polyvinylpyrrolidone-stabilized heteropolyacids (PVP–HPAs) are synthesized by self-assembling in alcohol. The structure of PVP–HPAs is determined by various characteristic techniques. HPAs can protonate PVP to form polymeric cations. In turn, the protonated PVP interacts strongly with the heteropolyanion by forming an ionic liquid (IL)-like structure. The self-assembling separation and recyclability characteristics are related to the PVP's IL-like structure. The catalyzing performance of PVP–HPAs varies with the species of HPA and the content of PVP. The optimized PVP–H₄SiW₁₂O₄₀·5H₂O (HSiW) (1/5 : 3/4) gives more than 60% conversion of cellulose and complete conversion of highly selective cellobiose into butylglucosides. The optimized PVP–HSiW is separated directly by centrifugation and retains the activity without any post-treatment during recycling. The deactivation of PVP–HPAs is related to the loss of the catalyst during recycling. The functional mechanism of the IL-like structure is explored in this control experiment.