Photoreforming of cellulose is a promising route for sustainable H₂ production. Herein, ball-milling (BM, with varied treatment times of 0.5–24 h) was employed to pretreat microcrystalline cellulose (MCC) to improve its activity in photoreforming over a Pt/TiO₂ catalyst. It was found that BM treatment reduced the particle size, crystallinity index (CrI), and degree of polymerization (DP) of MCC significantly, as well as produced amorphous celluloses (with >2 h treatment time). Amorphous cellulose water-induced recrystallization to cellulose II (as evidenced by X-ray diffraction (XRD) and solid-state NMR analysis) was observed in aqueous media. Findings of the work showed that the BM treatment was a simple and effective pretreatment strategy to improve photoreforming of MCC for H₂ production, mainly due to the decreased particle size and, specifically in aqueous media, the formation of the cellulose II phase from the recrystallization of amorphous cellulose, the extent of which correlates well with the activity in photoreforming.

Glucose is a key intermediate in cellulose photoreforming for H₂ production. This work presents a mechanistic investigation of glucose photoreforming over TiO₂ and Pt/m-TiO₂ catalysts. Analysis of the intermediates formed in the process confirmed the α-scission mechanism of glucose oxidation forming arabinose (C_n-1 sugar) and formic acid in the initial oxidation step. The selectivity to sugar products and formic acid differed over Pt/TiO₂ and TiO₂, with Pt/TiO₂ showing the lower selectivity to formic acid due to enhanced adsorption/conversion of formic acid over Pt/TiO₂. In situ ATR-IR spectroscopy of glucose photoreforming showed the presence of molecular formic acid and formate on the surface of both catalysts at low glucose conversions, suggesting that formic acid oxidation could dominate surface reactions in glucose photoreforming. Further in situ ATR-IR of formic acid photoreforming showed Pt-TiO₂ interfacial sites to be key for formic acid oxidation as TiO₂ was unable to convert adsorbed formic acid/formate. Isotopic studies of the photoreforming of formic acid in D₂O (with different concentrations) showed that the source of the protons (to form H₂ at Pt sites) was determined by the relative surface coverage of adsorbed water and formic acid.