Immobilized Copper-Substituted Keggin POM on Graphene Oxide for Highly Selective Heterogeneous Catalysis of Starch Hydrolysis.

Polyoxometalates (POMs) are bifunctional acid-redox catalysts with significant potential for biomass valorization. Herein, we investigate the heterogeneous catalytic studies of an immobilized 4,4'-bipyridine Cu-substituted Keggin POM, (4,4'-bpyH2)2(4,4'-bpyH)-[PCuW11O39]·H2O (Bp-PCuW11), anchored onto graphene oxide (GO) via ball milling. The Bp-PCuW11/GO nanohybrid proved to be an efficient solid acid heterogeneous catalyst for starch hydrolysis, resulting in the formation of glucose as a variable compound. Under optimized hydrothermal conditions, a superior catalytic performance was achieved with 92% starch conversion, 82% glucose yields, and excellent selectivity of 95%, coupled with over five recyclability runs. The Density functional theory (DFT) simulation revealed that the enhanced performance is attributed to the synergistic acid-redox behavior of PCuW11 and GO, which enables efficient proton transfer and improved substrate accessibility. This work provides new insights into the rational design of POM-carbon hybrid catalysts for sustainable biomass valorization and other environmentally relevant catalytic transformations.