Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Hugo de Lasa

2nd Supervisor

Benito Serrano Rosales

Joint Supervisor

Abstract

The present PhD dissertation establishes that hydrogen can be produced using mesoporous TiO2 as a photocatalyst, doped with platinum atoms (Pt), in a slurry medium, under near-UV irradiation and with ethanol as a sacrificial reagent (scavenger). These mesoporous TiO2 photocatalysts were prepared using a sol-gel method. The mesoporous Pt-TiO2 photocatalyst displayed a reduced 2.34 eV band gap compared to the bare TiO2 (3.20 eV).

Photocatalytic hydrogen production experiments were performed in a Photo-CREC Water II Reactor (PCW-II Reactor). This novel unit provides both radial and axial symmetrical irradiation profiles. Furthermore, macroscopic energy balances developed in this unit, showed a maximum 96% light absorption efficiency.

Runs in the PCW-II Reactor showed that hydrogen molecules were formed through the coupling of H• radicals under oxygen-free conditions. The use of 2.00 v/v% ethanol as a sacrificial reagent enabled the production of significant amounts of hydrogen with the simultaneous formation of hydrogen peroxide, methane, ethane, acetaldehyde and carbon dioxide by-products. It was confirmed that the extent of hydrogen generation in the presence of ethanol is a function of the pH level and Pt loading on the mesoporous TiO2 photocatalyst.

Additionally, it was established that the reaction networks leading to hydrogen production, using the various photocatalysts, shared common reactivity features. For example, it was shown that under an inert gas atmosphere, ethanol consumption takes place sub-stoichiometrically. This points towards the simultaneous formation and consumption of ethanol. Regarding the consumption of the ethanol scavenger, experimental observations were supported by an “in series-parallel” reaction network. With respect to energy efficiencies, it was observed that the maximum 22.6 % Quantum Yields found for hydrogen generation indicates a very good degree of photon utilization (45.2%).

Thus, this PhD dissertation contributes to the development of novel semiconductors for hydrogen production via water dissociation. It is demonstrated that when using the synthesized mesoporous semiconductors with added Pt, in a Photo-CREC-Water II Reactor unit, encouraging Quantum Yields are achieved.

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