Photoreforming with Cu/TiO2 and Ni/TiO2 photocatalysts: production of hydrogen and revalorization of biomass substrates

To produce hydrogen and revalorize lignocellulosic residues, Cu/TiO 2 and Ni/TiO 2 photocatalysts (metal loading 1 or 5 wt%), as-prepared and after thermal reduction treatment, were tested for the photoreforming of cellulose and almond shell derived-substrates. Net photoreforming contributions were quantified by subtracting the individual contributions of photodegradation and photocatalyzed water splitting. Only milled cellulose (MC) and the liquid from the hydrothermal carbonization of milled almond shell (HMAS-L2) substrates proved effective for photoreforming, yielding significantly higher hydrogen productions than those obtained from substrates photodegradation and water splitting. As-prepared Cu/TiO 2 showed efficient photocatalytic activity due to the facile in-situ reduction of Cu species. Conversely, Ni/TiO 2 photocatalysts became active only after the reduction treatment, when partial formation of Ni 0 species enhanced charge separation. The presence of reduced metals significantly improved photoactivity by decreasing charge recombination. The highest hydrogen productions reached were 2320 μmol·g cat −1 · h −1 and 2440 μmol·g cat −1 ·h −1 with MC_5Ni-P25-r and HMAS-L2_5Cu/P25-r, respectively, surpassing previously reported literature values. The H 2 /CO 2 molar ratios, with values close to the theoretical stoichiometric ratio (≈2), confirmed the predominant photoreforming pathway, while deviations indicated concurrent photodegradation and/or photoinduced water splitting. Tests with scavengers confirmed the effective photoreforming with MC and HMAS-L2 substrates, in contrast to milled almond shell and its derived solids. • Cu/TiO 2 and Ni/TiO 2 tested for photoreforming of almond shell derivatives. • Cellulose and HT-carbonization liquid (HMAS-L2) are effective PR substrates. • As-prepared Cu/TiO 2 is active via in situ Cu 2+ →Cu + /Cu 0 reduction on TiO 2 . • Ni/TiO 2 becomes highly active only after thermal reduction to Ni 0 species. • Up to 2440 μmol·gcat −1 ·h −1 H 2 achieved, surpassing previously reported value.