J. Raskó

An infrared study of the influence of CO adsorption on the topology of supported ruthenium

The interaction of CO with alumina-supported ruthenium, reduced at different temperatures, was investigated by following the development of infrared bands due to adsorbed CO. It was concluded that the adsorption of CO on Ru at 170–350 K leads to the oxidative disruption of Ru clusters as indicated by the slow transformation of the band at 2020–2040 cm−1 due to RuxCO to bands at 2140 and 2075 cm−1 attributed to Run+(CO)2 species (n = 1–3). This process occurred more slowly under dry conditions, and in the presence of hydrogen, whereas it was accelerated by H2O addition. Analysis of spectral features suggested the involvement of the isolated OH groups on the alumina support in the oxidative disruption process. It was demonstrated that at higher temperatures, namely at around 500 K, the presence of CO causes the reductive agglomeration of Run+ sites, i.e., the reformation of Rux clusters.

An infrared study on the formation of isocyanate in the NO + CO reaction on supported Ir catalyst

The formation of isocyanate surface species in the NO + CO reaction was investigated on supported iridium catalyst as a function of temperature and composition of the reacting gas mixture. On reduced IrAl2O3 samples absorption bands due to isocyanate were observed at 2260-2240 cm−1. The isocyanate band was first detected at 200 °C, and its maximum intensity was registered at 280–300 °C. It is stable below 200 °C but decomposes rapidly above 300 °C in vacuo producing CO2, CO, and N2. Isocyanate species was also formed on oxidized surfaces but with considerably lower intensities. The reaction between preadsorbed NO and gaseous CO also resulted in the formation of isocyanate, but it was not identified when NO was admitted onto preadsorbed CO. During the surface interaction of NO and CO a large downscale shift of the NO band occurred which was explained by the perturbing effect of adsorbed CO. It is assumed that the primary step in the formation of isocyanate is the dissociation of NO on the reduced centers. It is postulated that isocyanate formed on the iridium migrates to the acceptor sites of the support. This explanation is backed by the observations that the different supports markedly influence the location, formation, and stability of the isocyanate band.

Catalytic decomposition and oxidation of CH3Cl on Cr2O3-doped SnO2

Abstract The adsorption, decomposition and oxidation of CH 3 Cl have been investigated on pure and chromiadoped SnO 2 catalysts by means of infrared spectroscopy, mass spectrometric and gas chromatographic analysis. Catalyst samples have been characterized by X-ray photoelectron spectroscopy. It was found that the Cr 3+ ions incorporated in the surface layer of SnO 2 are oxidized to higher valent chromium ions. In harmony with the determination of active oxygen content, samples calcined at 873–973 K contained the largest concentration of higher valent chromium ions. Infrared spectroscopy showed that CH 3 Cl interacts with the OH groups of SnO 2 at 200–300 K to form H-bridge-bonded alkyl chloride. The decomposition of CH 3 Cl occurred slowly on pure SnO 2 above 573 K to give CH 4 , H 2 O, CO and HCl. The oxidation of CH 3 Cl on SnO 2 proceeded at a measurable rate at 400–440 K. Incorporation of a small amount of chromium ions into the SnO 2 increased the rate of both the decomposition and the oxidation by a factor of 10–16. The enhanced activity of chromia-doped SnO 2 is attributed to the high reactivity of chromium ions in the surface layer of SnO 2 .

The effect of chemisorbed oxygen on the stability of NCO on platinum, rhodium and palladium supported by silica

Abstract The stability of NCO species bonded to Pt, Rh and Pd produced by isocyanic acid (HNCO) adsorption has been investigated by infrared spectroscopy. Adsorption of HNCO on supported metals at 190 K produced an intense band at 2180 cm −1 which is attributed to the asymmetric vibration v a of NCO formed in the dissociative adsorption of HNCO on the metals. This band started to attenuate above 200 K, partly due to the decomposition of NCO into adsorbed CO and N, and partly due to the migration of NCO from the metals onto silica. These processes are indicated on the ir spectra by the appearance of absorption bands due to Si-NCO and M-CO species. The 2180 cm −1 band indicative of the presence of metal-NCO species was completely eliminated at 350 K on Pd, 400 K on Pt and 425 K on Rh. Oxygen treatment of the supported metals, however, greatly enhanced the stability of NCO on the metals.

FTIR study of the photoinduced dissociation of CO2 on titania-supported noble metals

AbstractThe effect of illumination on the activation and dissociation of CO2 was investigated at 190 and 300 K on titania-supported noble metals by means of Fourier transform infrared spectroscopy. The photoinduced dissociation of CO2 (through the formation of

FTIR study of the rearrangement of adsorbed CO species on Al2O3-supported rhodium catalysts

CO_{2(a)}^ - )

NO + CO interaction and NCO formation on PdY zeolite studied by infrared spectroscopy

resulting in CO(a) occurred on Pt/TiO2, Rh/TiO2 and Ir/TiO2; no CO(a) formation, however, was observed on Pd/TiO2 and Ru/TiO2. It is assumed that the CO2 on supported noble metals is bonded to the surface with both C (linked to a noble metal atom) and one of the O atoms (linked to the oxygen vacancy of the supports), and an extended charge transfer induced by illumination leads to the cleavage of a C–O bond.

Infrared spectroscopic detection of Rh(1) by CO in supported Rh catalyst

Methyl radicals, produced by the high temperature pyrolysis of azomethane, were adsorbed on Rh/SiO2. The reaction between adsorbed CH3 and gaseous CO2 has been followed by determining the intensity changes of the asymmetric stretch of CH3 and the composition of the gas phase. It was found that adsorbed CH3 reacts with CO2 at and above 373 K. It is assumed that similar processes may also take place in the dry reforming of methane, and that they are responsible for the lack of carbon deposition on supported Rh catalysts.