Enhancing Hydrogen Production from the Photoreforming of Lignin

Photoreforming of lignocellulose biomass is widely recognised as a challenging but key technology for producing value‐added chemicals and renewable hydrogen (H2). In this study, H2 production from photoreforming of organosolv lignin in a neutral aqueous solution was studied over a 0.1 wt % Pt/TiO2 (P25) catalyst with ultraviolet A (UVA) light. The H2 production from the system employing the lignin (~4.8 μmol gcat−1 h−1) was comparable to that using hydroxylated/methoxylated aromatic model compounds (i. e., guaiacol and phenol, 4.8–6.6 μmol gcat−1 h−1), being significantly lower than that from photoreforming of cellulose (~62.8 μmol gcat−1 h−1). Photoreforming of phenol and reaction intermediates catechol, hydroquinone and benzoquinone were studied to probe the mechanism of phenol oxidation under anaerobic photoreforming conditions with strong adsorption and electron transfer reactions lowering H2 production from the intermediates relative to that from phenol. The issues associated with catalyst poisoning and low photoreforming activity of lignins demonstrated in this paper have been mitigated by implementing a process by which the catalyst was cycled through anaerobic and aerobic conditions. This strategy enabled the periodic regeneration of the photocatalyst resulting in a threefold enhancement in H2 production from the photoreforming of lignin. Lignin and aromatic model compounds (phenol and guaiacol) show low activity in the production of H2 by photoreforming. Strong adsorption of intermediates (partial oxidation products) and electron transfer reactions inhibit the photocatalytic reactions under anaerobic conditions. Cycling between an anaerobic and a regenerative aerobic stage enhanced H2 production from lignin.