Kinetic Modeling and Quantum Yields: Hydrogen Production via Pd-TiO2 Photocatalytic Water Splitting under Near-UV and Visible Light

Abstract

A palladium (Pd) doped mesoporous titanium dioxide (TiO2) photocatalyst was used to produce hydrogen (H2) via water splitting under both near-UV and visible light. Experiments were carried out in the Photo-CREC Water-II Reactor (PCW-II) using a 0.25 wt% Pd-TiO2 photocatalyst, initial pH = 4 and 2.0 v/v% ethanol, as an organic scavenger. After 6 h of near-UV irradiation, this photocatalyst yielded 113 cm3 STP of hydrogen (H2). Furthermore, after 1 h of near-UV photoreduction followed by 5 h of visible light, the 0.25 wt% Pd-TiO2 photocatalyst yielded 5.25 cm3 STP of H2. The same photocatalyst, photoreduced for 24 h under near-UV and subsequently exposed to 5 h of visible light, yielded 29 cm3 STP of H2. It was observed that the promoted redox reactions led to the production of hydrogen and by-products such as methane, ethane, ethylene, acetaldehyde, carbon monoxide, carbon dioxide and hydrogen peroxide. These redox reactions could be modeled using an “in series-parallel” reaction network and Langmuir Hinshelwood based kinetics. The proposed rate equations were validated using statistical analysis for the experimental data and calculated kinetic parameters. Furthermore, Quantum yields (QYH•%) based on the H• produced were also established at promising levels: (a) 34.8% under near-UV light and 1.00 g L−1 photocatalyst concentration; (b) 8.8% under visible light and 0.15 g L−1. photocatalyst concentration following 24 h of near-UV.