An investigation of platinum group metals for environmental catalysis

• Main Author: Rioche, Cyrille Christophe
• Published: Queen's University Belfast 2009
• Subjects: 541.39
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492038

Environmental concerns and more stringent regulations have stimulated the development of new cleaner technologies to decrease the emissions of greenhouse gases and other hazardous gas emissions. In this study, the steam reforming of biooil as well as NOx storage and reduction catalysts were investigated. The production of hydrogen by steam reforming of bio-oils obtained from the fast pyrolysis of biomass requires the development of efficient catalysts able to cope with the complex chemical nature of the reactant. Steam reforming of a few model compounds and that of an actual bio-oil was investigated in the temperature range 650-900°C over Pt, Pd and Rh supported on alumina and a ceria-zirconia sample. The use of ceria-zirconia led to higher H2 yields. The supported Rh and Pt catalysts were the most active, while palladium-based catalysts performed poorly. Temperatures close to, or higher than, 800°C were required to achieve significant conversions to COx and H2 (e.g., H2 yields around 70%) ofthe bio-oil. NOx Storage and Reduction (NSR) catalysts are considered to be one of the most promising solutions to meet the upcoming NOx exhaust emission regulations. However, despite the high level of activity in this area, it is surprising that most studies have been conducted under conditions that are far from realistic. A fast transient apparatus has been developed to study these catalysts under realistic temporal conditions. The performance of a typical Pt/Ba/y-Ah03 NSR catalyst was studied as a function ofthe temperature, rich phase duration, reductant concentration, the type of reductant and the space velocity and the importance of the regeneration step in the NSR process was highlighted. The regeneration step was further investigated over Pt and/or Rh based catalysts by coupling of fast transient kinetic switching and the use of 15NO. An unexpected double peak in the evolution of nitrogen was revealed. The first peak occurred immediately on switching from lean to rich conditions, while the second peak started at the point at which the gases switched from rich to lean. Rh/Ba/Ah03 trap was found to be dependent on the rate of NOx storage, since the rate of regeneration was sufficient to remove the NOx stored in the lean phase. pt/Ba/Al203 was found to be limited by the rate of regeneration.