Bottom-up approaches for the synthesis of nanostructured heterogeneous (electro-) catalysts, via the colloidal deposition route combined with nanostructured catalyst supports, have been investigated in this thesis. Colloidal gold nanoparticles have been selected as a case study in view of their promising catalytic properties for oxidation reactions, as well as their ability to convert carbon dioxide to carbon monoxide under electrocatalytic conditions. Benzyl alcohol aerobic oxidation was selected as a test reaction of choice to characterize the catalytic properties of the colloidal gold nanoparticles under investigation, in view of the extensive literature available on this topic. Furthermore, practical experience with this reaction and colloidal gold nanoparticles had already been gained in the Catalysis Engineering group, reflected by a previous publication involving dodecylamine-capped gold nanoparticles...

This thesis focused on iron-based Fischer-Tropsch catalysts. It deals with different iron phases that might play a role in the catalytic process. As the activation step takes place inside the reactor (in-situ at high temperature and pressure), studying the catalyst activation process is not trivial. In addition, since the working catalysts are air sensitive, also post analysis on activated and used catalysts is challenging. As a result, the identity of the real active phase is still unknown.

To gain more insight in Fischer-Tropsch catalysts, we used different techniques like (in-situ) TEM, TEM-EELS, ED and PXRD. TEM and ED are very suitable techniques since they provide very high spatial resolutions (in the Å range). Special TEM grids and TEM holders were designed for this research in order to mimic the activation conditions and / or avoid any exposure to air.

Our results indeed showed that it is essential to avoid any exposure to air prior to analysis. In fact, we can question the results of some older publications where catalysts were exposed. In contrast to literature data published so far, we found no carbon deposits on the outer rim of the iron carbides at high temperature conditions. Overall, we showed that carbon surface layers can change, or even form, during exposure to air. We also found evidence for what in the literature has been designated as “hypothetical q¥-Fe2C”. We proposed a structure model for which the carbon content is higher than in the pure c-Fe5C2 carbide. More research is required to elucidate the exact nature of working iron-based Fischer-Tropsch catalysts.

Electrocatalytic reduction of CO2 is one possibility to solve the electrical energy storage problem and decrease the amount of CO2. Copper is the only metal that has been reported to produce hydrocarbons in the electrochemical CO2 reduction at ambient pressure and temperature. External parameters (potential, temperature and electrolyte), copper catalyst morphology and purity and newly designed carbon-based electrodes were investigated. The highest Faraday efficiency towards hydrocarbons at 22°C was obtained at a fixed potential of -2.50 V vs. Ag/AgCl reference electrode. The best electrolyte solution is 0.1 M KHCO3. Methane is the dominant product. FE towards ethylene maximizes at -2.25 V. Up to 40°C, the total Faraday efficiency towards hydrocarbons is not influenced by temperature, but ethylene amount increases with increasing temperature. Above 40°C hardly any hydrocarbons are formed. Altering the surface structure of the copper catalyst by electrodeposition give different results for the electrocatalytic CO2 reduction. The rougher the surface, the less methane and the more ethylene was formed. The macroscopic smooth surfaces are related to the (001) orientation and a rough macroscopic surface is related to the (111) orientation. To increase the surface area, carbon-based catalyst supports (graphite plates, carbon nanofibers and carbon xerogels) were tested. They show promising results.