Direct hydrogen production by cellulose aqueous phase reforming over NiMgAl hydrotalcite-derived catalyst: the counterintuitive effect of the addition of H2

Aqueous-phase reforming (APR) of cellulose is a process for sustainable hydrogen production and was investigated in this study using hydrotalcite-derived NiMgAl catalysts under optimized reaction conditions. Waste cellulose from the paper industry was employed as feedstock, highlighting the relevance of this approach within a circular economy and waste-to-hydrogen framework. Among the investigated Ni0/Mg(Al)O formulations, Ni24Mg56Al20 exhibited the best performance, providing an optimal balance between nickel loading, metal dispersion, and textural properties. The results indicate that hydrogen productivity is primarily governed by the availability and dispersion of metallic Ni species. In addition, different to previous studies, reaction conditions were investigated and the analysis of both gaseous and liquid products enabled the proposal of a reaction mechanism involving dehydration and hydrogenation/dehydrogenation pathways, which allowed to conceive effective strategies to increase hydrogen production. For instance, a notable and counterintuitive outcome of this work is the beneficial effect of a moderate initial H2 atmosphere. Controlled H2 addition significantly enhanced hydrogen yields, reaching up to 40%, by promoting hydrogenolysis and reforming reactions while limiting condensation pathways associated with humin formation. In contrast, excessive H2 partial pressure shifted the reaction network toward hydrogenation reactions, decreasing net hydrogen production. These findings highlight the crucial role of the reaction atmosphere in determining APR pathways. The synthetized catalyst was compared with a benchmark Pt/Al2O3 catalyst tested under identical conditions, achieving superior hydrogen productivity and favouring reaction routes involving formic and levulinic acid intermediates, further contributing to hydrogen generation. Overall, the results demonstrate that properly engineered LDH-derived NiMgAl catalysts, combined with controlled reaction atmospheres, offer a cost-effective and sustainable alternative to noble-metal systems for hydrogen production from biomass and industrial waste streams.