Tuning Pd Nanoparticle Size for Sustainable Cellulose Conversion to C₂ Alcohols over Pd/WOx Catalysts

The sustainable conversion of cellulose to C2 alcohols (ethylene glycol and ethanol) represents a promising sustainable pathway to reduce reliance on fossil resources. However, achieving an effective balance between hydrolysis, C–C bond cleavage, and hydrogenation has remained a challenge. In this study, Pd/WOx catalysts with tunable Pd nanoparticle sizes (1.81–4.46 nm) were developed to investigate the structure–performance relationship. Catalytic evaluations revealed a volcano-type correlation between Pd particle size and C2 alcohol selectivity, with the 3Pd/WOx catalyst, featuring Pd nanoparticles averaging ∼3.0 nm, achieving a maximum selectivity of 78.5% under mild conditions (water solvent, 230 °C, 5 MPa H2, 4 h). Structural and chemical analyses revealed that smaller Pd clusters retained excess oxygen vacancies but lacked hydrogenation capacity, while larger Pd nanoparticles reduced accessible hydrogenation sites and acidity. Mechanistic studies showed that WOx oxygen vacancies promoted cellulose hydrolysis, Pd–O(H)–W sites facilitated glucose adsorption and C–C cleavage to glycolaldehyde, and adjacent Pd0 sites enabled efficient hydrogenation. This work highlights the critical role of Pd particle size in optimizing acid–hydrogenation synergy, providing a green and efficient strategy for biomass valorization without additives or toxic solvents.