Abstract: Photothermocatalysis represents a promising, energy-efficient route for cellulose steam reforming (Cellu-SR); however, its practical implementation is severely limited by the undesired formation of byproducts—particularly tar. Herein, we report a Co nanoparticle catalyst supported on Sr-modified Al₂O₃ (Co/Sr_2.5Al_4.5) that achieves exceptional performance in photothermocatalytic Cellu-SR. Under illumination, this catalyst delivers remarkably high production rates of H₂ (5101.4 mmol g^-1 h^-1) and CO (3061.7 mmol g^-1 h^-1), accompanied by markedly suppressed byproduct formation—most notably, a tar selectivity below 20%. Systematic physicochemical characterizations reveal that the outstanding performance is attributed to the introduction of Sr significantly enhances the H₂O adsorption. The resulting surface-adsorbed H₂O readily dissociates to generate reactive oxygen species (O*), which efficiently oxidize cellulose-derived pyrolysis intermediates (CxHyOz) and carbon species (C*) to syngas. Crucially, illumination induces a pronounced photoactivation effect on weaking the surface Co-O bonds, facilitating the oxidation of C* by O* and promoting the active participation of H₂O in the reforming.

Key words: Photothermocatalysis, Cellulose steam reforming, Co-based catalyst, Sr modification, Photoactivation