High-Pressure Carbon Monoxide Adsorption on Pt(111) Revisited:  A Sum Frequency Generation Study

Abstract

The adsorption of CO on Pt(111) was studied by picosecond infrared-visible sum frequency generation (SFG) vibrational spectroscopy in a pressure range from 10 -7 to 500 mbar and in a temperature range of 160-400 K. At low pressure the experiments were complemented by TPD, LEED, and AES. Terminally bonded (on-top) CO was the only species observed between 160 and 400 K, independent of gas pressure. The CO stretching frequency was blue-shifted by about 15 cm -1 with increasing pressure (up to 2097 cm -1 ), but no evidence for high-pressure CO species or surface roughening was found. The influence of defects was also investigated. CO adsorption on a defective (nonannealed) Pt( 111) surface yielded peaks that were slightly broadened but otherwise identical to the defect-free surface. At 160 K, a second peak at 2085 cm -1 evolved above 50 mbar of CO. TPD revealed that under these conditions residual (contaminant) water adsorbs on the surface. The coadsorption of water and CO red-shifted the terminal CO peak by about 15 cm -1 , resulting from the substrate-mediated interaction of CO and water.

Reactivity of a gas/metal/metal-oxide three-phase boundary: CO oxidation at the Pt(111)–c(4×2)-2CO/α-PtO2 phase boundary

“…2a suggests that for ambient partial pressures at room temperature (and even higher), the c(4 · 2)-2CO overlayer forms on the metallic part of the Pt surface. This structure is the well-characterized low-pressure, room-temperature equilibrium structure [5] of CO at Pt (1 1 1). The GGA-PW91 based phase diagram depicted in Fig.…”

“…The application of in situ experimental techniques, including high-pressure scanning tunneling microscopy [1,2], X-ray diffraction [3], sum frequency generation [4,5], and high resolution transmission electron microscopy [6] have shown that catalytic surfaces often undergo structural transitions under reaction conditions. In the case of oxidation reactions at transition metal surfaces it has been suggested that high coverage oxygen chemisorption phases, surface oxide phases, or bulk oxide phases are the relevant reaction states of the surfaces.…”

CO adsorption and dissociation on iron oxide supported Pt particles

“…It was generally believed that Pt does not appreciably dissociate CO, although controversial results were reported [5][6][7][8][13][14][15][16]. Somorjai and co-workers first showed that CO dissociation on Pt is, in fact, a surface structure sensitive reaction [13].…”

“…Using sum frequency generation spectroscopy at 40 Torr of CO and Auger electron spectroscopy (AES) McCrea et al showed that CO dissociation occurs on Pt(111), Pt(557) and Pt(100) at 673, 548 and 500 K, respectively [17]. The authors suggested that dissociation proceeds via CO-induced surface roughening at high pressures and temperatures, but this mechanism was revisited in the more recent work by Rupprechter et al [16].…”

Surface science under reaction conditions: CO oxidation on Pt and Pd model catalysts

“…This complex behavior was contradicted by a more recent study by Freund and coworkers. 61 After correcting the data for the gas-phase IR absorption, the peak ascribed to CO adsorbed on atop sites was found not to be suppressed. In fact, it increased in intensity corresponding to a coverage of B0.…”