An insight into the photo-generation of H2 and a carbon fuel additive from biomass-derived ethanol: boosting the bio-chemical economy

Abstract

Unifying the production of hydrogen (H₂) fuel with the production of value-added chemicals from biomass through semiconductor-mediated solar redox reaction is an extremely appealing and sustainable process to solve energy shortages and environmental issues, cooperatively boosting the chemical economy. Its phenomenal H₂ content and excellent chemical bond versatility make biomass-derived ethanol an indispensable feedstock for the production of green H₂ fuel with the synergistic synthesis of value-added chemicals or fuel additives. Herein, Pt/UCN/Nb₂O₅-(2) photocatalyst, an organic–inorganic heterostructure, was prepared and employed to promote the light-mediated co-production of H₂ and 1,1-di-ethoxyethane (DEE) as a fuel additive from biomass-derived ethanol solution via photocatalytic dehydrogenation (PD). As a consequence, the photocatalytic performance of the Pt/UCN/Nb₂O₅-(2) catalyst was scrutinized for DEE (506.6 μmol h⁻¹ g⁻¹) and H₂ (558 μmol h⁻¹ g⁻¹) production, initially for 6 h under solar simulator light irradiation. Additionally, the apparent quantum yield (AQE) for H₂ production (400 nm) and the solar-to-hydrogen (STH) conversion efficiency in 6 h were estimated to be 2.18% and 0.04%, respectively. The DEE selectivity was determined to be 72%, along with 28% acetaldehyde (CH₃CHO). The strong adsorption of ethanol over the active sites present in the photocatalyst's surface, such as nitrogen vacancies (Nv), Nb⁵⁺, and Nb–OH, resulted in feasible progression of the PD of ethanol, which was ascertained by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) studies. Ammonia (NH₃)-temperature programmed desorption (NH₃-TPD) desorption study revealed that the Pt/UCN/Nb₂O₅-(2) catalyst exhibits enhanced surface Lewis acidity (due to Nb⁵⁺), which is essential for DEE synthesis. With the help of experimental and analytical techniques, the mechanistic pathway was explored inquisitively where first ethanol was oxidized into CH₃CHO, which was further reacted with another ethanol molecule to produce DEE in the presence of a Lewis acid.