Sustainable cellulose nanocrystal hybrid platforms for catalysis and CO2 conversion

• CNCs emerge as a sustainable alternative to conventional catalyst supports. • The surface functionalisation of CNCs enhances catalytic activity and stability. • CNC catalysts enhance the electron transport, inhibit aggregation and improve durability. • CNC-based hybrids are efficient at converting CO2 into fuels and value-added chemicals. • CNC allow electrocatalytic, thermocatalytic, and photocatalytic CO2 reduction using metals. Cellulose nanocrystals (CNCs) provide a sustainable, high-surface-area system of hybrid catalysts; however, their mechanistic contributions to CO 2 conversion and their potential for use in decentralised, renewable-powered systems are fragmented across disciplines. The review points out the fundamental issue: a deficiency in coherent design requirements that bridge CNC interfacial chemistry, catalyst architecture, and system-level performance, and fills that void by synthesising evidence from materials, electrochemistry, and life-cycle studies. The review recapitulates the most important conductive and control mechanisms and selectivity by CNCs (hydrogen bonding, covalent anchoring, 3D coupling, electrostatic modulation, and nanoconfinement) and demonstrates the ability of CNC-derived carbons to enhance charge transport, stability, and electrocatalytic rate. Representative case studies show reduced overpotentials, increased Faradaic selectivity toward C 1 products, and increased stability upon cycling of catalysts with optimised CNC motifs. Lastly, material-level strategies to cradle-to-gate life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA) considerations, and describe how waste-biomass feedstocks and point-of-use reactors operated by IoT and powered by renewable energy could enable the conversion of CO 2 into low-impact, scalable solutions. This is followed by a practical design guide, schematic outlines, and a mechanistic table to inform future pilot-scale demonstrations.