Carbon supported precious metal-based single metal site heterogeneous catalysts

Single metal site heterogeneous catalysts (SMSHCs) are catalysts that have efficient use of metal as (nearly) every metal atom is involved during a reaction. The synthesis of these materials can be quite challenging as single metal species tend to agglomerate and form nanoparticles. An example of a SMSHC is the Au/C catalyst that is used in the acetylene hydrochlorination reaction. This catalyst is synthesised using a wet impregnation with aqua regia. In this study, an alternative method to synthesise a Au/C SMSHC has been developed. This catalyst, prepared using dry acetone as a solvent, is more environmentally friendly and has the potential to be scaled-up. It is demonstrated that this method can be used to prepare other precious-metal-based SMSHCs such as platinum, palladium and ruthenium catalysts. The state of gold in the two Au/C catalysts are very comparable; both consist of well-dispersed cationic gold species. However, the two catalysts have significantly different surface functionalities which are a result of the impregnation solvent. The influence of these surface functionalities was studied by testing the catalysts in a Suzuki-type homocoupling reaction. Chlorine bound to carbon (C-Cl), which was generated by the aqua regia solvent, was vital for the reaction to take place, and results indicate that C-Cl is consumed during the reaction. The last part of the thesis contains an XPS study on the distribution and oxidation state of palladium and gold in catalysts that are used for the gas phase direct synthesis of hydrogen peroxide. The presence of gold in the bimetallic catalyst altered the degree of palladium oxidation after calcination compared to that of the monometallic catalyst. In addition, gas phase hydrogen peroxide synthesis had an overall reducing effect on the metal in the catalysts. Complete reduction was observed for monometallic catalysts, whereas only partial reduction was observed for bimetallic catalysts. This indicates that the presence of gold alters the electronic properties of palladium