Temperature dependence (90–440 K) of the vibrational spectra of CO adsorbed on platinum(111) studied by sum-frequency generation

Härle, H.; Mendel, K.; Metka, U.; Volpp, Hans-Robert; Willms, L.; Wolfrum, J.

doi:10.1016/s0009-2614(97)01040-3

Cited by 35 publications

(20 citation statements)

References 22 publications

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“…[1][2][3][4][5][6], and more recently SFG [7][8][9][10][11]. The knowledge of adsorption behavior is essential to gain an understanding on the heat of adsorption and adsorption geometry, which are key elements of surface chemistry [12].…”

Section: Introductionmentioning

confidence: 99%

Heat of adsorption of CO on Pt(111) obtained by sum frequency generation vibrational spectroscopy—a new technique to measure adsorption isotherms

2005

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Section: Introductionmentioning

confidence: 99%

Heat of adsorption of CO on Pt(111) obtained by sum frequency generation vibrational spectroscopy—a new technique to measure adsorption isotherms

2005

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“…UHV studies have revealed a similar trend in resonant mode shifting, peak broadening, and amplitude reduction. [27] The temperature dependence of the peak width is explained by a dephasing model in which a rapid energy exchange between low-frequency modes of the metal surface and low-frequency modes of the adsorbate, which are anharmonically coupled to the higher frequency mode investigated in this study. However, comparison of the peak widths obtained in this study, ~15 cm -1 , to that of CO adsorbed on a well ordered Pt(111)…”

Section: Sum Frequency Generation Vibrational Spectroscopymentioning

confidence: 75%

High Pressure Scanning Tunneling Microscopy and High PressureX-ray Photoemission Spectroscopy Studies of Adsorbate Structure,Composition and Mobility during Catalytic Reactions on A Model SingleCrystal

Montano¹

2006

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Our research focuses on taking advantage of the ability of scanning tunneling microscopy (STM) to operate at high-temperatures and high-pressures while still providing real-time atomic resolution images. We also utilize high-pressure x-ray photoelectron spectroscopy (HPXPS) to monitor systems under identical conditions thus giving us chemical information to compare and contrast with the structural and dynamic data provided by STM.STM was employed to study the structures formed by cyclic C 6 hydrocarbon monolayers adsorbed on a platinum (111) crystal surface. Cyclohexane. cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene and benzene were exposed to the platinum surface in the 10 -6Torr pressure regime. Upon adsorption on Pt (111) both cyclohexane and cyclohexene produced the same (√7 x √7) R19.1° hexagonal structure, which corresponds to the partially dehydrogenated π-allyl (C 6 H 9 ). 1,3-cyclohexadiene and 2 benzene produced a (2√3 x 2√3) R30.0° structure composed of pure benzene. 1,4-cyclohexadiene forms a structure very different from the others, which we attributed to a (√43 x √43) R7.6° structure composed of molecular 1,4-cyclohexadiene.STM studies on catalytic reactions of cyclohexene and its poisoning with carbon monoxide on Pt (111) were also performed in the presence of hydrogen at pressures slightly below 1Torr in the 300K -350K temperature range. At room temperature in the presence of 20 mTorr hydrogen and 20 mTorr cyclohexene, the surface formed the (√7 x √7) R19.1° π-allyl structure and no products were detected. Increasing the hydrogen pressure to 200 mTorr caused the catalyst to begin producing cyclohexane and some benzene, while also causing the STM images to disorder. The addition of 5 mTorr of CO to the system stopped all catalysis and formed an ordered CO overlayer. At 353K with 200 mTorr H 2 and 20 mTorr C 6 H 10 , the surface was more catalytically active that at lower temperatures, and again the addition of CO stopped all catalysis. STM revealed a mobile disordered surface suggesting that, although mobile, the surface was dominated by CO, which blocked adsorption of reactants.Catalytic hydrogen/deuterium exchange on a platinum (111) XPS shows us however, that the amount of the CO on the surface is only ~10% less than at room temperature, and the surface structure is largely unchanged. As the temperature is increased the surface CO decreases while the activity increases. At around 370K XPS displays an abrupt change in the ratio of atop to bridge bound CO corresponding to a surface phase change. Cooling the sample back to room temperature restores the original structure as shown by both STM and XPS. From these data, a CO dominated, mobile and catalytically active surface model has been proposed.

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“…It was explained that this red shift was most likely due to anharmonic coupling to the frustrated translation mode. 27,28 This model explains that a temperature dependent red shift could result from vibrational dephasing, which is due to a rapid energy exchange between low frequency modes of the adsorbed molecule and substrate that are anharmonically coupled to the top site vibrational mode. Essentially, because of the mobility of CO molecules at high-temperatures, dephasing of the harmonic coupling occurs.…”

Section: Discussionmentioning

confidence: 99%

“…These results are very similar to results obtained on Pt(111) under 400 Torr of CO pressure and it is believed that the frequency shift is due to anharmonic coupling to the frustrated translational mode. 27,28 At 673 K, the SFG spectra changed as a function of time with the top site peak red shifting to 2052 cm -1 and becoming broader. The CO top-site frequency observed is very similar to platinum carbonyls (Pt(CO), Pt(CO) 2 , Pt(CO) 3 , which have been observed to exhibit CO stretching frequencies near 2055 cm -1 .…”

Section: Pt(111)mentioning

confidence: 99%

“…A similar shift in the CO top site frequency is observed up to 523 K as observed on Pt(111) which is attributed to anharmonic coupling to the frustrated translational mode. 27,28 The difference between Pt(557) and Pt(111) is that once the Pt(557) surface is heated to 548 K, the top site CO frequency no longer shifts below 2077 cm -1 , but the amplitude of the peak decreases over time. The SFG spectrum evolves differently for Pt(557) at the dissociation temperature as compared to Pt (111) and there does not appear to be any evidence for the production of platinum carbonyls as observed on Pt(111).…”

Section: Pt(557)mentioning

confidence: 99%

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Effect of surface structure on catalytic reactions: A sum frequency generation surface vibrational spectroscopy study

McCrea¹

2001

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Using Sum Frequency Generation (SFG) and gas chromatography (GC), molecular level investigations of catalytic reactions were performed on platinum single crystal surfaces. The SFG spectra and GC data was correlated to elucidate the nature of active species present on the surface under high-pressure catalytic reactions.The effect of structure sensitivity and insensitivity of several catalytic reactions were investigated. Ethylene hydrogenation, a structure insensitive reaction, was performed over both Pt(111) and Pt(100). The reaction rate was the same on both surfaces (11 molecules/site/sec 300 K), although the relative concentrations of surface species were observed to be different. Both ethylidyne and di-σ bonded ethylene, strongly adsorbed species, were present on the surface under reaction conditions. These species were not responsible for catalytic turnover. Weekly adsorbed species 2 such as π-bonded ethylene and ethyl intermediates are responsible for surface turnover as revealed by SFG.Cyclohexene hydrogenation and dehydrogenation were also performed on Pt(100) and Pt(111). Cyclohexene dehydrogenation is structure sensitive and it was found that the rate of dehydrogenation was higher on the (100) surface of platinum.From SFG results, it was concluded that dehydrogenation can proceed through both 1,3-and 1,4-cyclohexadiene intermediates, although, the rate proceeds faster through the 1,3-intermediate. The rate dehydrogenation on Pt(100) was higher because there was a higher concentration of 1,3-cyclohexadiene on the Pt(100) surface as compared to the (111) surface.By exposing Pt(111), Pt(100), and Pt(557) single crystal surfaces to high pressures of CO, it was found that Pt-carbonyls could be produced leading to the dissociation of CO. In addition, it was found that CO dissociation was structure sensitive when the crystals were exposed to 40 Torr of CO. The Pt(100) surface was the most active and showed dissociation at 500 K, while the Pt(111) surface was the least active with a dissociation temperature of 673 K. Pt(557) exhibited a dissociation temperature at 548 K, between the two other surfaces. Surface roughness was found to affect the temperature of dissociation and Pt-carbonyls were responsible for roughening of the surface. Pt(100) was the most active because the surface reconstructs and roughens at a lower temperature than the other two surfaces. In addition, CO oxidation experiments were performed on all three surfaces and the ignition temperature followed 3 the same trend observed for CO dissociation. This indicates that CO dissociation is important for the onset of ignition.An in depth study of CO oxidation on Pt(557) was performed on both clean and carbon-covered prepared surfaces. Under excess O 2 and excess CO conditions, a clean prepared platinum surface will remain carbon free below and above ignition. It was found that a carbon oxide species was formed on carbon covered platinum surfaces.The carbon oxide species was also found to form on clean prepared platinum below ignition when it was e...

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Temperature dependence (90–440 K) of the vibrational spectra of CO adsorbed on platinum(111) studied by sum-frequency generation

Cited by 35 publications

References 22 publications

Heat of adsorption of CO on Pt(111) obtained by sum frequency generation vibrational spectroscopy—a new technique to measure adsorption isotherms

Heat of adsorption of CO on Pt(111) obtained by sum frequency generation vibrational spectroscopy—a new technique to measure adsorption isotherms

High Pressure Scanning Tunneling Microscopy and High PressureX-ray Photoemission Spectroscopy Studies of Adsorbate Structure,Composition and Mobility during Catalytic Reactions on A Model SingleCrystal

Effect of surface structure on catalytic reactions: A sum frequency generation surface vibrational spectroscopy study

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