Faculty of Science and Technology
University of Twente
P.O. Box 217
7500 AE Enschede
supervisor: Prof. Dr. Guido Mul
period: May. 2007 – Apr. 2011
The project is aimed at an efficient use of photons to improve efficiency in the highly desired conversion of CO2 and H2O into fuel molecules, such as CH4, CH3OH, or even Fisher Tropsch-like products. From the viewpoint of energy and environment, the conversion of CO2 to hydrocarbons by solar energy is the ultimate solution for CO2 emission and renewable energy. The reactions can be summarized as follows
CO2 +H2O → CH4 + O2
CO2 +H2O → CH3OH + O2
XCO2 + ½ yH2O → CxHy + (x+2y)O2
The research comprises catalyst development, CO2 reduction mechanism investigation, and photoreactor design, all aiming at highly efficient light harvesting. The photocatalysts should have well designed characteristics, such as large absorption of, preferably, visible light photons, a long lifetime of activated states, a good adsorption of reactants CO2 and H2O, and a relatively easy desorption of products (the fuel molecules).
Ti-based mesoporous materials (e.g. Ti-SBA-15) and Ti-nanotube have been reported in the literature to be more efficient in the CO2 reduction reaction than dense phase TiO2 particles.
Mechanism investigation (in-situ DRIFTS technique)
In-situ DRIFTS (Diffuse and Reflectance Infrared Fourier Transform Spectroscopy) experiments are means to obtain mechanistic information and can be carried out by using a three-window cell. Two windows (ZnSe) allow IR transmission, and the third (Quartz) the introduction of UV/Vis light into the reactor. IR signals can thus be collected when catalysts in presence of CO2 and water vapor. Carbonyl, (bi)carbonates and carboxylates can be during UV/Vis illumination (100Watt Hg lamp, λ: 280-650nm).
Fig. 1 (a) three-window cell; (b) time profiled DRIFT spectra of Cu/TiO2 in presence of CO2 during 80mins illumination
Photoreactor development (combinatorial photoreactors for catalyst screening)
Different semiconductors, porous materials with isolated metal centers, and Ti-nanotubes have been tested in the target reaction and described in the literature. It is still difficult to compare the catalyst performance, since they have typically been tested under specific reaction conditions. In particular, comparison on basis of the quantum efficiency is impossible. We have developed a photocatalyst screening device for heterogeneous photocatalysis application (such as CO2 reduction and H2O oxidation). A multi-batch reactor coupled to a compact gas chromatograph, and fully automated sampling program, enables photocatalyst screening, quick product analysis and fair comparison of photo-activity performance.
Fig. 2 Principle of the combinatorial photoreactors for CO2 reduction or H2O oxidation