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.