Production of H2 and organic acids by cellulose photo-reforming with TiO2-bimetallic(CuNi) co-catalysts: Metal loading and photodeposition sequence effects

Cellulose photo-reforming using TiO₂ modified with non-noble metals as photocatalysts to produce hydrogen and organic acids via the valorization of lignocellulosic residues is an attractive strategy towards renewable energy. Non-noble metals such as Cu and Ni photodeposited on commercial TiO₂ play an important role as mono or bimetallic co-catalysts that strongly improve the photo-reforming of cellulose producing both H₂ and valuable organic acids in solution. In this study, preparation variables like the total metal loading (nominal 1 and 5 wt%, with a weight ratio Cu:Ni = 1:1) and different Cu-Ni photodeposition sequence (consecutive (first Cu and then Ni and vice versa), or simultaneous) were studied, resulting in a set of twelve photocatalysts. All the metal-loaded photocatalysts exhibit enhanced H₂ production with respect to bare TiO₂ with total H₂ generation and product selectivity influenced by the metal content, the interaction between both metals, and the state of the deposited species. The last two properties have shown to be highly dependent on the photodeposition sequence. The higher metal loadings lead to the less active photocatalysts, mainly attributed to an excessive coverage of the TiO₂ surface. Notably, the stepwise incorporation of Cu and Ni leads to more active photocatalysts than the simultaneous photodeposition. The photocatalyst with 1 wt% metal loading prepared via sequential NiCu deposition provides the highest hydrogen generation, 489 μmol/h · g_cat. This value is among the highest reported up to now for noble-metal-free photocatalysts.