The origins of multiple bands in the infrared spectra of carbon monoxide adsorbed on metal surfaces

Greenler, Robert G.; Brandt, Robert K.

doi:10.1016/0927-7757(95)03336-x

Cited by 24 publications

(34 citation statements)

References 7 publications

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“…The band attributed to ν(CO) bridge redshifts to 1835 cm –1 and increases in intensity . The decreasing intensity of ν(CO) top is attributed to the displacement and partial desorption of on-top CO induced by the competitive adsorption with the IL. − The redshift is mainly due to the local electric field at the IL/Pt(111) interface, giving rise to a Stark shift. , The peak at 2061 cm –1 , only visible at high IL coverage, may originate from CO adsorbed at Pt defect sites. ,, Due to the intensity transfer, this band is not observed at full CO coverage. , Because CO is most strongly adsorbed at defect sites, it may not be displaced by the IL from these sites. ,,, Lastly, the intensity of the ν(CO) bridge band increases with increasing IL coverage. ,,, In conclusion, the specific adsorption of [NTf 2 ] − at low coverage is prevented by strongly bound CO. On the (111) terraces, there is a preference for bridge-bonded CO in the presence of the IL …”

Section: Resultsmentioning

confidence: 98%

CO Permeability and Wetting Behavior of Ionic Liquids on Pt(111): An IRAS and PM-IRAS Study from Ultrahigh Vacuum to Ambient Pressure

et al. 2021

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Solid catalysts with ionic liquid layers (SCILLs) show improved performance as compared to ionic liquid (IL)-free catalysts. To realize the beneficial IL-induced modification, the IL layer should be stable under reaction conditions but also permeable for gaseous reactants entering through the IL phase. Herein, we applied (polarization modulation-) infrared reflection absorption spectroscopy ((PM-)IRAS) to investigate the CO permeability of model SCILL systems. We investigated three different IL model systems prepared by physical vapor deposition (PVD) in ultrahigh vacuum (UHV) on atomically clean Pt(111), namely, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4C1Pyr][NTf2]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2C1Im][NTf2]), and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([C4C1Pyr][OTf]). The adsorption geometries of the anions depend on the surface structure, IL coverage, and precoverage of CO. At room temperature, IL multilayers of randomly oriented species grow on top of strongly adsorbed wetting layers. Upon heating, a partial wetting transition induces the coexistence of an IL wetting monolayer film with three-dimensional droplets. Gas-phase CO does not permeate through IL multilayers, while it penetrates the IL wetting monolayer leading to mixed IL/CO films. The partial dewetting transition and the permeability differ drastically with the temperature and IL. Consequently, the morphology of the IL films could be a factor that determines the catalytic behavior of SCILLs to a significant extent.

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Section: Resultsmentioning

confidence: 98%

CO Permeability and Wetting Behavior of Ionic Liquids on Pt(111): An IRAS and PM-IRAS Study from Ultrahigh Vacuum to Ambient Pressure

et al. 2021

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“…Prior to preparation and characterization, it should be emphasized that the CO stretching vibration of Pt-chemisorbed CO is not only sensitive to the support characteristics but also to a large number of experimental parameters. According to literature, the loading, dispersion, particle size, and coordination number of Pt, 9,[15][16][17][18][19] the reduction temperature, 20,21 and CO exposure pressure 22,23 can affect the observed IR data, whereas sample pretreatment, 24 CO exposure temperature, 12 CO adsorption, 25 and CO interaction with support cations 7,26 may play a role as well. To prevent erroneous assignments and conclusions, special attention has been paid to keep all experimental parameters and instrumental settings the same.…”

Section: Methodsmentioning

confidence: 99%

Promotion Effects in the Oxidation of CO over Zeolite-Supported Pt Nanoparticles

et al. 2005

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, and Ba 2+ ) cations have been used as model systems to investigate the effect of promotor elements in the oxidation of CO in excess oxygen. Time-resolved infrared spectroscopy measurements allowed us to study the temperatureprogrammed desorption of CO from supported Pt nanoparticles to monitor the electronic changes in the local environment of adsorbed CO. It was found that the red shift of the linear Pt-coordinated CtO vibration compared to that of gas-phase CO increases with an increasing cation radius-to-charge ratio. In addition, a systematic shift from linear (L) to bridge (B) bonded CtO was observed for decreasing Lewis acidity, as expressed by the Kamlet-Taft parameter R. A decreasing R results in an increasing electron charge on the framework oxygen atoms and therefore an increasing electron charge on the supported Pt nanoparticles. This observation was confirmed with X-ray absorption spectroscopy, and the intensity of the experimental Pt atomic XAFS correlates with the Lewis acidity of the cation introduced. Furthermore, it was found that the CO coverage increases with increasing electron density on the Pt nanoparticles. This increasing electron density was found to result in an increased CO oxidation activity; i.e., the T 50% for CO oxidation decreases with decreasing R. In other words, basic promotors facilitate the chemisorption of CO on the Pt particles. The most promoted CO oxidation catalyst is a Pt/K-Y sample, which has a T 50% of 390 K and a L:B intensity ratio of 2.7. The obtained results provide guidelines to design improved CO oxidation catalysts.

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Section: Methodsmentioning

confidence: 99%

Promotion effects in the oxidation of CO over zeolite-supported Pt nanoparticles

Lepage¹,

Visser²,

Soulimani³

et al. 2005

Molecular Sieves: From Basic Research to Industrial Applications, Proceedings of the 3rd International Zeolite Symposium (3rd F

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Well-defined Pt-nanoparticles with an average diameter of 1 nm supported on a series of zeolite Y samples containing different monovalent (H + , Na + , K + , Rb + , and Cs + ) and divalent (Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ ) cations have been used as model systems to investigate the effect of promotor elements in the oxidation of CO in excess oxygen. Time-resolved infrared spectroscopy measurements allowed us to study the temperatureprogrammed desorption of CO from supported Pt nanoparticles to monitor the electronic changes in the local environment of adsorbed CO. It was found that the red shift of the linear Pt-coordinated CtO vibration compared to that of gas-phase CO increases with an increasing cation radius-to-charge ratio. In addition, a systematic shift from linear (L) to bridge (B) bonded CtO was observed for decreasing Lewis acidity, as expressed by the Kamlet-Taft parameter R. A decreasing R results in an increasing electron charge on the framework oxygen atoms and therefore an increasing electron charge on the supported Pt nanoparticles. This observation was confirmed with X-ray absorption spectroscopy, and the intensity of the experimental Pt atomic XAFS correlates with the Lewis acidity of the cation introduced. Furthermore, it was found that the CO coverage increases with increasing electron density on the Pt nanoparticles. This increasing electron density was found to result in an increased CO oxidation activity; i.e., the T 50% for CO oxidation decreases with decreasing R. In other words, basic promotors facilitate the chemisorption of CO on the Pt particles. The most promoted CO oxidation catalyst is a Pt/K-Y sample, which has a T 50% of 390 K and a L:B intensity ratio of 2.7. The obtained results provide guidelines to design improved CO oxidation catalysts.

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The origins of multiple bands in the infrared spectra of carbon monoxide adsorbed on metal surfaces

Cited by 24 publications

References 7 publications

CO Permeability and Wetting Behavior of Ionic Liquids on Pt(111): An IRAS and PM-IRAS Study from Ultrahigh Vacuum to Ambient Pressure

CO Permeability and Wetting Behavior of Ionic Liquids on Pt(111): An IRAS and PM-IRAS Study from Ultrahigh Vacuum to Ambient Pressure

Promotion Effects in the Oxidation of CO over Zeolite-Supported Pt Nanoparticles

Promotion effects in the oxidation of CO over zeolite-supported Pt nanoparticles

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