Catalytic Combustion of Methane

Catalytic combustion is an environmentally benign technology which has recently reached the stage of commercialization. Palladium is the catalyst of choice when considering gas turbines fuelled with natural gas because of its superior activity for methane oxidation. Several fundamental issues are still open and their understanding would result in an improvement of the technology. Hence, the work presented in this thesis aims at the identification of some of the parameters which govern the combustion activity of palladium-based catalysts. The first part of this work gives a background to catalytic combustion and a brief comparison with other existing technologies. Paper I reviews some of the issues related to material development and combustor design. The second part of this thesis consists of an experimental investigation on palladium-based catalysts. The influence of the preparation method on the properties of these catalyst materials is investigated in Paper II. Paper III examines the activity of the following catalysts: Pd/Al2O3, Pd/Ba-Al2O3 and Pd/La-Al2O3. Specific attention is given to the metal-support interaction which strongly affects the combustion activity of palladium. The effect of doping of the support by addition of cerium is reported in Paper IV. Finally, the deactivation of combustion catalysts is considered. The various deactivation processes which may affect high temperature combustion catalysts are reviewed in Paper V. Paper VI focuses on the poisoning of supported palladium catalysts by sulphur species. Palladium exhibits a higher resistance to sulphur poisoning than transition metals. Nevertheless, the nature of the support material plays an important role and may entail a severe loss of activity when sulphur is present in the fuel-air mixture entering the combustion chamber.