Sulfur-Tolerant NOx Storage Traps: An Infrared and Thermodynamic Study of the Reactions of Alkali and Alkaline-Earth Metal Sulfates |
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Authors: | JP Breen M Marella C Pistarino JRH Ross |
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Affiliation: | (1) Centre for Environmental Research, Dept. CES, University of Limerick, Limerick, Ireland;(2) Present address: Catalysis Research Group, School of Chemistry, Queens University Belfast, Belfast, BT9 5AG, N. Ireland;(3) VeneziaTecnologie., 39 Via Delle Industrie, 30175 Porta Marghera, Italy;(4) Dept. of Chem. and Proc. Eng., University of Genoa, Ple JF Kennedy, Genoa, Italy |
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Abstract: | The sulfur tolerance of a barium-containing NOx storage/reduction trap was investigated using infrared analysis. It was confirmed that barium carbonate could be replaced by barium sulfate by reaction with low concentrations of sulfur dioxide (50 ppm) in the presence of large concentrations of carbon dioxide (10%) at temperatures up to 700 °C. These sulfates could at least be partially removed by switching to hydrogen-rich conditions at elevated temperatures. Thermodynamic calculations were used to evaluate the effects of gas composition and temperature on the various reactions of barium sulfate and carbonate under oxidizing and reducing conditions. These calculations clearly showed that if, under a hydrogen-rich atmosphere, carbon dioxide is included as a reactant and barium carbonate as a product then barium sulfate can be removed by reaction with carbon dioxide at a much lower temperature than is possible by decomposition to barium oxide. It was also found that if hydrogen sulfide was included as a product of decomposition of barium sulfate instead of sulfur dioxide then the temperature of reaction could be significantly lowered. Similar calculations were conducted using a selection of other alkaline-earth and alkali metals. In this case calculations were simulated in a gas mixture containing carbon monoxide, hydrogen and carbon dioxide with partial pressures similar to those encountered in real exhausts during switches to rich conditions. The results indicated that there are metals such as lithium and strontium with less stable sulfates than barium, which may also possess sufficient NOx storage capacity to give sulfur-tolerant NOx traps. |
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Keywords: | sulfur tolerance NOx storage barium sulfate decomposition thermodynamics alkali and alkaline-earth metals SO2 H2S |
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