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address: vvk@catalysis.ru (V.V. Kaichev). A B S T R A C TThe methanol oxidation over highly dispersed vanadium oxide supported on TiO 2 (anatase) has been investigated by in situ Fourier transform infrared spectroscopy (FTIR), near ambient pressure X-ray photoelectron spectroscopy (NAP XPS), X-ray absorption near edge structure (XANES), and temperature-programmed reaction spectroscopy. The data were complimented with kinetics measurements in a flow reactor. It was found that at low temperatures dimethoxymethane competes with methyl formate, whereas the production of formaldehyde is greatly inhibited. FTIR shows the presence of non-dissociatively adsorbed molecules of methanol, as well as adsorbed methoxy, dioximethylene, and formate species under reaction conditions. According to the NAP XPS and XANES data, the reaction involves the reversible reduction of V 5+ cations, pointing that the vanadia lattice oxygen participates in the methanol oxidation through the classical Mars-van Krevelen mechanism. The detailed mechanism of the methanol oxidation on vanadia catalysts is discussed.

Nanostructured doped ceria is a prospective material for catalytic applications such as the construction of membranes with mixed electronic and ionic conductivity for effective syngas production. In this article, the surface properties of nanostructured ceria doped with praseodymium have been studied by X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and Fourier transform infrared spectroscopy of adsorbed carbon monoxide. The effects of supporting 1.4 wt % Pt as well as structural changes upon the reduction of the samples with methane have been investigated. While in samples without supported platinum, mainly praseodymium cations are reduced in a methane atmosphere; stronger reduction of cerium cations was found in the case of surface modification with Pt. The structural differences correlate with results from temperature-programmed reaction experiments with methane. Explanations are discussed in terms of different reaction mechanisms.

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Two oxygen species, which are constituents of the active centers for ethylene epoxidation over silver, have been characterized by a number of physical methods sensitive to adsorbate electronic structure such as XPS, UPS, Auger and XANES spectroscopy. One of the species denoted as nucleophilic oxygen due to its activity in total oxidation only exhibits spectroscopic characteristics close to those of bulk Ag2O. This allows us to describe this species as atomically adsorbed oxygen in the structure of surface silver (I) oxide. Considerable extent of the covalency in bonding of this oxide-like oxygen with silver surface due to hybridization of O2p levels with Ag4d and Ag5sp orbitals should be also emphasized. Contrary to this only 5sp orbitals of silver hybridize with 2p levels of oxygen as the other oxygen species forms. As consequence, this species being also atomic oxygen is characterized by a lower oxygen-silver bonding interaction and lower charge on the oxygen. The latter causes the activity of this electrophilic species in epoxidation. Possible models of adsorption centers for these oxygen species are discussed.

High-pressure CO adsorption on Pd(111) was examined by X-ray photoelectron spectroscopy (XPS) and vibrational sum frequency generation (SFG) from 200 to 400 K, and in a pressure range from 10 -6 to 1 mbar. Even in the millibar regime both methods indicated that CO adsorbed in "regular" adsorption sites such as hollow, bridge, and on-top. By combination of XPS and SFG, a quantitative analysis of CO coverages at various pressures was performed. At high pressure, no CO structures different from those known from UHV studies were observed. Also, no indications of CO dissociation or carbonyl formation were found under the given experimental conditions, provided that the CO gas was sufficiently cleaned.

Methanol decomposition on Pd(111) at 300 and 400 K was studied in situ from 5 × 10 -7 to 0.1 mbar by combining vibrational sum frequency generation (SFG) and X-ray photoelectron spectroscopy (XPS). Two competing decomposition pathways, i.e., dehydrogenation of CH 3 OH to CO and H 2 and methanolic C-O bond scission, were observed by monitoring the time-dependent evolution of CO/CH x O and of carbonaceous deposits CH x (x ) 0-3) via their vibrational and photoemission characteristics. Quantification of carboncontaining species was performed by XPS, while the preferred binding site of CH x was determined by SFG using CO as probe molecule for postreaction adsorption. In contrast to previous reports, Pd(111) was found to be quite active for methanolic C-O bond scission. The CH x formation rate strongly increased with pressure and temperature, leading to immediate catalyst deactivation at 0.1 mbar and 400 K. The combined SFG/XPS data suggest that the carbonaceous residues are highly dehydrogenated, such as CH or carbon atoms bonded to hollow sites. Complete dehydrogenation of CH x species and partial dissolution of atomic carbon in the Pd bulk most likely occurred even at 300 K. On the other hand, the CH x species was found to be unexpectedly thermally stable (up to ∼600 K), until carbon dissolution and formation of carbon clusters take place. Regeneration with oxygen above 400 K was able to remove CH x deposits and to partially restore the initial adsorption properties. Corresponding experiments with CO did not produce any carbon signals, indicating that the cleavage of the C-O bond must occur via CH x O intermediates (and not within CO). Methanol decomposition at pressures up to 15 mbar and temperatures up to 550 K, followed by gas chromatography, did not produce measurable decomposition products, due to fast carbon poisoning under catalytic reaction conditions.