Photoreforming of cellulose is a promising route for sustainable H 2 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/TiO 2 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 H 2 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 H 2 production. This work presents a mechanistic investigation of glucose photoreforming over TiO 2 and Pt/m-TiO 2 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/ TiO 2 and TiO 2 , with Pt/TiO 2 showing the lower selectivity to formic acid due to enhanced adsorption/conversion of formic acid over Pt/TiO 2 . 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-TiO 2 interfacial sites to be key for formic acid oxidation as TiO 2 was unable to convert adsorbed formic acid/formate. Isotopic studies of the photoreforming of formic acid in D 2 O (with different concentrations) showed that the source of the protons (to form H 2 at Pt sites) was determined by the relative surface coverage of adsorbed water and formic acid.

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