Reduction of Nitric Oxide by Acetylene on Ir Surfaces with Different Morphologies: Comparison with Reduction of NO by CO

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• 作者：Wenhua Chen ; Quantong Shen ; Robert A. Bartynski ; Payam Kaghazchi ; Timo Jacob
• 刊名：Langmuir
• 出版年：2013
• 出版时间：January 29, 2013
• 年：2013
• 卷：29
• 期：4
• 页码：1113-1121
• 全文大小：490K
• 年卷期：v.29,no.4(January 29, 2013)
• ISSN：1520-5827

文摘

Reduction of nitric oxide (NO) by acetylene (C₂H₂) has been investigated by temperature-programmed desorption (TPD) on planar Ir(210) and faceted Ir(210) with tunable sizes of three-sided nanopyramids exposing (311), (311虆), and (110) faces. Upon adsorption, C₂H₂ dissociates to form acetylide (CCH) and H species on the Ir surfaces at low C₂H₂ precoverage. For adsorption of NO on C₂H₂-covered Ir, both planar and faceted Ir(210) exhibit high reactivity for reduction of NO with high selectivity to N₂ at low C₂H₂ precoverage, although the reaction is completely inhibited at high C₂H₂ precoverage. Coadsorbed C₂H₂ significantly influences dissociation of NO. The N-, H-, and C-containing TPD products are dominated by N₂, H₂, CO, and CO₂ together with small amounts of H₂O. For adsorption of NO on C-covered Ir(210) at fractional C precoverage, formation of CO₂ is promoted while production of CO is reduced. Reduction of NO by C₂H₂ is structure sensitive on faceted Ir(210) versus planar Ir(210), but no evidence is found for size effects in the reduction of NO by C₂H₂ on faceted Ir(210) for average facet sizes of 5 nm and 14 nm. The results are compared with reduction of NO by CO on the same Ir surfaces. As for NO+C₂H₂, the Ir surfaces are very active for reduction of NO by CO with high selectivity to N₂ and the reaction is structure sensitive, but clear evidence is found for size effects in the reduction of NO by CO on the nanometer scale. Furthermore, coadsorbed CO does not affect dissociation of NO at low CO precoverage whereas coadsorbed CO considerably influences dissociation of NO at high CO precoverage. The adsorption sites of CCH+H on Ir are characterized by density functional theory.