Tuning functionality of photocatalytic materials: an infrared study on hydrocarbon oxidation

The focus of the research described in this thesis was on the engineering and design of effective photocatalysts able to catalyze the oxidative conversion of hydrocarbons. The prepared catalysts were synthesized by using different procedures involving sol gel precursors, and impregnation or photo-deposition of metallic nanoparticles. The prepared materials were characterized by several techniques in order to identify the obtained composition and morphology. The photocatalytic performance of the prepared materials was investigated in different oxidative photocatalytic conversions such as methylcyclohexane (MCH) oxidation, ethanol oxidation, or simultaneous oxidation of mixtures of hydrocarbons. To evaluate performance of the synthesized materials, several techniques have been used such as ATR-FTIR, DRIFT, a multi reactor set-up, and a top illuminated batch reactor setup. In chapter 1, an introduction is given about the basic principles of photocatalysis. Furthermore, an introduction to the photocatalysts is given, as well as background on some general aspects of the mechanism of plasmonic enhancement of photocatalytic activity. In chapter 2, an overview of the experimental procedures is presented. An introduction is given to IR spectroscopy applying two different reaction cells, one for liquid (ATR), and another for gas phase analysis (DRIFT). Also a photocatalytic reactor system equipped with a gas chromatograph is described, as well as the use of a setup containing multiple reactors. Chapters 3, 4 and 5 are focused on oxidation of MCH as a model reaction for selective, photocatalytic oxidation of hydrocarbons in the liquid phase. In chapter 6, another model reaction was investigated, i.e. the conversion of ethanol, when present in the gas phase. Photocatalytic ethanol conversion is relevant for air purification. Pt/WO3 prepared by an impregnation method was found to be very effective in the oxidative dehydrogenation of ethanol to acetaldehyde and CO2, even in dark conditions. Finally, in chapter 7, two modifications of silica supported Ti catalysts were prepared to enhance performance in photocatalytic conversion of CO2. Adding ZnO nanoparticles, which were anticipated to increase the sorption of CO2, led to a smaller apparent rate in hydrocarbon production. Addition of visible light absorption functionality by CrOx, was even more detrimental to the observed production of hydrocarbons.