High-pressure study on the adsorption and oxidation of CO on gold/titania model catalysts

Coadsorption of Hydrogen and CO on Hydrogen Pre‐Covered PtRu/Ru(0001) Surface Alloys

“…[41] In brief, the experiments were carried out in a UHV system (base pressure~1 10 À10 mbar) equipped with facilities for TPD, infrared reflection absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The Ru(0001) single crystal (8 mm diameter), used as substrate for the preparation of the bimetallic samples, was cleaned before each experiment by standard procedures described elsewhere.…”

“…The Ru(0001) single crystal (8 mm diameter), used as substrate for the preparation of the bimetallic samples, was cleaned before each experiment by standard procedures described elsewhere. [2,10,41] To prepare the PtRu/Ru(0001) surface alloys, sub-monolayer amounts of Pt were deposited on the Ru(0001) substrate (substrate temperature 300 K, deposition rate~0.1 ML s À1 ) and subsequently annealed to 1300 K. Bulk dissolution of Pt atoms during annealing is negligible for Pt coverages up to~0.8 ML, while at 1 ML Pt a loss of~10 % of the Pt atoms is observed. [8] The Pt concentrations in the present study were determined by AES measurements crosscalibrated to the results of the previous STM study (see ref.…”

“…In addition, a shift of the vibrational peak is observed upon coadsorption on pure Ru(0001), which was already discussed in detail earlier. [41] For the surface alloys with 25 and 47 % Pt, the presence of the second band at 2090 cm À1 indicates the occupation of Pt sites on the D ad pre-saturated surfaces, while on the clean surfaces Ru sites are occupied exclusively at the corresponding CO coverages (in the range between 0.2-0.3 ML). This finding can be explained by partial blocking of the energetically more favorable Ru sites by pre-adsorbed D ad and implies a comparable probability for CO adsorption on both types of sites (at least as long as the D ad saturation coverage does not decrease substantially below 1 ML).…”

“…Instead, as already shown previously for a surface alloy with 35 % Pt, a displacement of CO molecules from Pt sites to Ru sites is initiated only at a temperature where D 2 desorption already sets in. [41] This means in other words that D 2 desorption after coadsorption is initiated by D ad displacement to Pt-rich ensembles of the surface alloys followed by rapid D 2 desorption from these adsorption ensembles. For Pt-rich surface alloys (Pt concentrations > 60 %), the high CO coverages obtained by the chosen dosing sequence, prevent the observation of similar effects in the respective IR spectra, since coadsorption-induced changes are masked by dipole coupling effects.…”

Planar Au/TiO2 Model Catalysts: Fabrication, Characterization and Catalytic Activity

“…In the first reactor, turn-over frequencies (TOF) of about 0.14 AE 0.04 site À1 s À1 have been observed for Au nanoparticles with different sizes on TiO 2 films (initial Au coverage: ranging from 0.2 to 0.6 ML) at 80 8C [27,39,40] (total pressure: 20 mbar, CO:O 2 = 2:1). This type of model catalysts [0.5 ML Au on TiO 2 films on Ru(0001)] has also been investigated in the microflow reactor and a CO 2 concentration of (3.3 AE 0.2) % was measured in the gas stream behind the reactor.…”