Abstract
The kinetics of NO reduction by methane over Pd catalysts supported on 8 mol% yttria-stabilised zirconia (YSZ) has been studied at atmospheric pressure in the 620–770 K temperature range. Langmuir–Hinshelwood type kinetics are found with characteristic rate maxima reflecting competitive adsorption of NO and methane: NO adsorption is much more pronounced than that of methane within the temperature range of this investigation. Pd is an effective catalyst: 100% selectivity towards N 2 can be achieved at 100% conversion of NO over this wide temperature range. Sodium causes strong poisoning of the reaction. The response of the system to variations in NO and methane concentrations, temperature, and sodium loading indicate that this is due to the Na-induced enhancement of NO chemisorption and dissociation relative to methane adsorption, i.e. sodium enhances oxygen poisoning of the catalyst. These results stand in revealing contrast to the strong promotional effect of sodium in the reduction of NO by propene over the same catalysts. The very different response of the two hydrocarbon reductants to Na doping of the Pd catalyst receives a consistent explanation.
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