Photocatalytic Reforming of Lignocellulosic Feedstocks for H2 Production using TiO2-based Catalyst

Abstract

The demand for energy has increased massively, mainly supplied by fossil fuels with significant carbon emissions. Hydrogen (H2) emerges as an efficient and clean energy carrier, having many promising characteristics (such as higher heating value and zero carbon emission after combustion) to replace fossil fuels. Solar-driven photocatalytic reforming (photoreforming, PR) of biomasses (such as cellulose and lignin) at ambient conditions presents a promising solution to produce renewable H2 due to the use of (i) biomass (widely abundant in nature, sustainable and theoretically carbon neutral) and (ii) solar energy (i.e., the sun as the largest energy resource driving the catalysis). Current PR processes mainly employ cellulose and bio-derived chemicals such as bioethanol. Comparatively, although it is very challenging, the direct use of lignin for H2 production via PR can be advantageous. This PhD thesis employed platinised TiO2 catalysts to study the PR of model aromatic compounds, purified and IonSolv-extracted lignin and cellulose, and raw biomass feedstocks to produce H2. While PR of aromatic compounds and lignin yields comparable and low levels of H2 production (4.8−6.6 μmol gcat−1 h−1) compared to cellulose (~62.8 μmol gcat−1 h−1) due to poisoning by intermediates, alternating between anaerobic and aerobic atmospheres resulting in a threefold enhancement in H2 production from the PR of lignin. In addition, Pt nanoparticles loaded on TiO2 using an in-situ photodeposition method enhanced the production of H2 significantly from the PR of lignin and aromatic substrates compared to ex-situ methods. The PR of isolated cellulose pulps from various bioenergy crops showed the highest H2 production, while derived lignin was the lowest. The variations in H2 production from bioenergy crops were found to be unrelated to the differing composition of cellulose, hemicellulose and lignin. The interaction strength of bioenergy crops with water, as observed by NMR relaxometry, was determined to influence H2 production, correlating with H2 production. In summary, this thesis investigates the challenges of lignin PR, proposes mitigation strategies, and identifies factors impacting the PR of lignocellulosic feedstocks for efficient H2 production.