Effect of Na-addition on catalytic activity of Pt-ZSM-5 for low-temperature NO–H2–O2 reactions |
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Authors: | M Machida T Watanabe |
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Affiliation: | Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan |
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Abstract: | The effect of additives on Pt-ZSM-5 catalysts was studied for the selective NO reduction by H2 in the presence of excess O2 (NO–H2–O2 reaction) at 100 °C. The reaction of NO in a stream of 0.08% NO, 0.28% H2, 10% O2, and He balance yielded N2 with less than 10% selectivity, which could not be increased by changing Pt loading or H2 concentration in the gas feed. Co-impregnation of NaHCO3 and Pt onto ZSM-5 decreased the BET surface area and the Pt dispersion. Nevertheless, the Na-loaded catalyst (Na-Pt-ZSM-5) exhibited the higher NOx conversion (>90%) and the N2 selectivity (ca. 50%). Such a high catalytic activity even at high Na loadings (≥10 wt.%) is completely contrast to other Na-added Pt catalyst systems reported so far. Further improvement of N2 selectivity was attained by the post-impregnation of NaHCO3 onto Pt-ZSM-5. In situ DRIFT measurements suggested that the addition of Na promotes the adsorption of NO as NO2?-type species, which would play a role of an intermediate to yield N2. The introduction of Lewis base to the acidic supports including ZSM-5 would be applied to the catalyst design for selective NO–H2–O2 reaction at low temperatures. |
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Keywords: | Additive Na NO–H2–O2 reaction Platinum ZSM-5 |
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