2.12. Methane combustion activity of Al2O3-supported Pd, Pt, and Pd-Pt catalysts: Experimental and theoretical studies

Public examination of a doctoral dissertation in the field of physical chemistry

Doctoral candidate: M.Sc. Niko Kinnunen 

Date and venue: 2.12.2011, at 12 noon, Auditorium F100, Joensuu campus

 

ABSTRACT 

Zeolites, perovskites, non-noble transition metals, and many other catalytic materials have been tested in methane combustion, but no reasonable low temperature activity has been observed. In addition, the resistance to catalyst poisons is poor, which severely limits their use in low temperature applications such as automotive converters. Thus, at the moment, the only feasible catalyst group is the metal oxide supported noble metal catalysts, or more exactly, supported palladium, platinum, and rhodium catalysts. The methane combustion activity of the noble metal catalysts used in catalytic converters is nevertheless low after extended use.

Monometallic palladium and platinum and bimetallic palladium-platinum catalysts were prepared by impregnation methods. Several combinations of Pd precursors and impregnation solutions were tested with the aim of finding new procedures for preparing methane combustion catalysts. Platinum was used as activity promoter in the catalysts. The end objective was to improve low temperature activity and durability of supported Pd-PdOx catalysts. In this respect, the effects of palladium and platinum on surface chemistry of the catalysts were of central interest. Bulk and surface properties were characterized to clarify the correlation between structure and activity.  

Low temperature activity and long-term durability of the Pd-PdOx catalyst were successfully improved by using carboxylic acid solutions in the preparation and adding Pt promoter. A clear correlation was observed between activity and surface chemistry of the supported catalyst. Study showed that palladium and platinum have distinct roles in the formation of the active phase of the supported noble metal catalyst: palladium forms metal and metal oxide active sites, whereas platinum is responsible only for metallic active sites. Density functional theory calculations revealed the importance of the Pd and PdO interface for low temperature activity of methane combustion catalysts. PdO crystallite size and thermal stability of the bulk PdO had no effect on the low temperature activity. 

The doctoral dissertation of M.Sc. Niko Kinnunen entitled Methane combustion activity of Al2O3-supported Pd, Pt, and Pd-Pt catalysts: Experimental and theoretical studies” will be examined at the Faculty of Science and Forestry. The opponent in the public examination is Professor Riitta Keiski from the University of Oulu and the custos is Professor Tapani Pakkanen of the University of Eastern Finland.

Photo available for download at http://www.uef.fi/vaitoskuvat

Contact: Niko Kinnunen, tel. +358 50 591 9852, niko.kinnunen@uef.fi

Publishing year: 2011

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