Spatiotemporal investigation of the temperature and structure of a Pt/CeO2oxidation catalyst for co and hydrocarbon oxidation during pulse activation

Abstract

Reductive treatments with pulses of CO-rich atmosphere have been used to increase and maintain the low temperature activity of a Pt/CeO2-based oxidation catalyst. A combination of operando infrared thermography and spatiotemporalresolved quick scanning extended X-ray absorption fine structure spectroscopy on a fixed bed microreactor unraveled that, apart from the pulse length, the reaction atmosphere, and the reactor temperature, also the emerging reaction heat during such activating pulses has a strong influence on the structure and catalytic performance of CO and propylene conversion in the axial direction of a fixed-bed and a monolithic reactor. The reductive pulse activation led to an increase of the integral catalyst activity as well as to the generation of zones of different particle sizes along the catalyst bed. In the case of an activation temperature between 250 and 350 °C and pulse lengths between 5 and 30 s, a hotspot of more than 80 K was observed at the beginning of the catalyst bed. Spatially resolved X-ray absorption spectroscopy indicates that larger and more reduced Pt particles are formed particularly at the beginning of the catalyst bed, whereas its subsequent part is less affected. Both the length of the reductive pulses and activation temperature have a distinct influence on the noble metal particle size. On the basis of these results, a Pt/CeO2 based honeycomb shaped substrate was activated in a similar manner. Spatially resolved gas phase profiling showed different reaction rates at the beginning of the reactor, which indicates that the concept can be transferred also to industrially relevant catalysts. In the future, such an activation procedure might open up the door to a new class of operation strategies, by which individual zones generated in the catalyst bed could be assigned for removal of specific pollutants in the exhaust stream.