Super Ambient Gas-Phase Photocatalysis

Semiconductor photocatalysis is emerging as a significant new photochemical process for creating innovative commercial products, such as: self-cleaning glass, concrete and tiles. However, to date, attention has been restricted to ambient temperature applications of the technology and in this project we explore its application at elevated temperatures. In particular, we will use semiconductor photocatalysis to mediate gas phase reactions of commercial significance, at lower temperatures than the conventional thermal catalytic reactions. For instance, alcohol reforming with steam will be explored. Reforming of alcohols to produce hydrogen has many potential commercial applications. Hydrogen can be used in a wide variety of applications such as hydrogen fuel cells and synthesis. The by-products of this photocatalytic process are carbon dioxide and carbon monoxide primarily which can also be utilised for synthesis of important industrial chemicals. The primary alcohol for photocatalytic reforming research is currently methanol. Ethanol reforming will also be studied due to widespread production and use of bio-ethanol, leading to a possible renewable method of hydrogen production. This reforming process will be primarily carried out using platinum group metal modified titanium dioxide catalysts such as Pt/TiO2 and Au/TiO2 with various metal loadings.

Environmental clean-up reactions will also be explored using photocatalysis, such as NOx and ozone removal. NOx is formed in many thermal combustion processes and in internal combustion engines. NO is toxic and can cause irritation of the eyes and respiratory system. NO2 is a highly reactive gas that is highly toxic and hazardous to humans as it can cause delayed chemical pneumonitis and pulmonary edema. It is estimated that the effects of NO2 pollution is equivalent to 23,500 deaths each year in the UK. NO2 is also responsible for corrosive acid rain in the form of nitric acid. NO also contributes to lower atmosphere ozone levels by reacting with oxygen in the air. Ozone is also a health hazard as it can cause respiratory problems. The ability of semiconductor photocatalysts to remove NOx and ozone from gas streams will be explored.

This project will utilise the techniques of not only photocatalysis and thermal catalysis, but also analytical techniques such as DRIFT-MS, BET, SEM, TEM and laser-driven, time resolved transient adsorption spectroscopy.

Some of these reactions have been investigated at a lower temperature using semiconductor photocatalysis, however, this project will investigate the use of photocatalysis at higher temperatures which will allow reactions which are limited by kinetics at low temperature and thermodynamics at high temperature, for example, water-gas shift processes to circumvent this issue and operate with sufficient activity in the thermodynamically favourable regime. This is a new and exciting area of research and so is open to a wide array of discoveries and challenges.