Investigation of the state of copper cations in CuCr2O4/Al2O3 catalysts based on the IR spectra of adsorbed carbon monoxide

The state of copper cations in samples of CuCr₂O₄ applied on A1₂O₃, has been investigated by means of the IR spectroscopy of adsorbed molecules. The IR spectra of carbon monoxide, adsorbed on CuCr₂O₄/Al₂O₃ catalysts and submitted to different treatments, have been studied. The separation of a Cr₂O₃ phase was observed during heating of the sample under reducing conditions with the formation of a copper-containing compound, in which the state of the copper ions was different from the state characteristic for chromite. A change in the phase composition of the active component was established in comparison with the original samples and a change in the phase composition of the support from -Al₂O₃ to -Al₂O₃ in catalyst samples, spent in catalytic heat generators.Translated from Teoreticheskaya i Éksperimental/naya Khimiya, Vol. 26, No. 5, pp. 633–637, September–October, 1990.The authors wish to express their gratitude to T. A. Gordymova and B. A. Bunimovich for their assistance in the experimental work.     

Nature of α-Fe2O3 surface centers

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 480–485, March, 1991.     

Forms of adsorption of methanol on anatase and directions of their transformation

The adsorption of methanol on titanium(IV) oxide in the anatase crystalline modification was investigated by IR spectroscopy and thermal desorption. It was established that coordinationally bonded alcohol and two types of methoxides are formed on the surface of the titanium dioxide (anatase). The adsorption centers of the methanol were found. The thermal stability and the degree of particípation in oxidation were determined for the surface structures of the adsorbed alcohol. The possibility of the conversion of the coordinationally bonded alcohol and the weakly bonded methoxyl into partial oxidation products and the strongly bonded methoxyl into total oxidation products was demonstrated. In the investigated system formate complexes at concentrations sufficient for detection by IR spectroscopy were only formed with the participation of the oxygen of the gas phase through further oxidation of the strongly bonded methoxyls.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 707–712, November–December, 1988.The authors thank V. A. Gerasimova and S. K. Anan'in for assistance in the production of the experimental results.     

Nature of the centers on the surface of oxide catalysts and the forms of adsorbed toluene

IR spectroscopy has been used to analyze the forms of toluene adsorbed on various oxides, differing in the nature of their surface centers: TiO₂, CuO, V₂O₅/Al₂O₃, V₂O₅. The form of adsorption is found to depend on the nature of the surface centers of the oxide. When coordinationally saturated cations are involved complexes of toluene are formed, while if surface oxygen is involved benzoate structures are produced. The temperature at which the latter begin to be formed depends on the strength of the bond between oxygen and the surface. It was shown that the presence of acidic hydroxyl groups on the surface of the oxide leads to proton transfer to the aromatic compound to give carbonium ions. The nature of the interaction is then determined by the mobility of the proton on the surface and the basic strength of the adsorbed molecule. The possibility of identifying such compounds spectroscopically is discussed.Translated from Teoreticheskie i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 710–715, November–December, 1990.     

Forms of adsorption of ethanol on anatase and paths of their transformation

The adsorption of ethanol on anatase was studied by IR spectroscopy and thermodesorption methods. It was found that three surface forms of the adsorbed alcohol are formed: a coordinatively bound alcohol to the oxide surface, and two types of ethylates. It was shown that a weakly bound surface ester participates in the formation of acetaldehyde, while the more strongly bound chemisorbed ester is responsible for the formation of ethylene and products of complete oxidation, depending on the content of oxygen in the gaseous phase.Irkutsk Institute. Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 27, No. 2, pp. 232–237, March–April, 1991. Original article submitted April 21, 1987.     

IR-spectroscopic investigation of the nature of surface centers and of the adsorption of methanol on an iron-molybdenum oxide catalyst

Molecular-probe IR spectroscopy was used to investigate the nature of surface centers on an iron-molybdenum oxide catalyst. The acid properties of Fe/Mo catalysts with stoichiometric composition and with an excess of molybdenum have been studied; the presence of Lewis (LAS) as well as Brönsted acid sites (BAS) on their surface has been detected. The concentration of BAS increases significantly in the presence of an excess of molybdenum; the amount of coordination-unsaturated cations on the surface of the samples decreases at the same time. The interaction of methanol and isopropanol with the surface of the investigated catalysts has been studied and the determining role of BAS in complex formation and the conversion of alcohols on the Fe/Mo-oxide catalyst established. A mechanism has been proposed for the conversion of methanol on the Fe/Mo-oxide catalyst.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 474–480, July–August, 1990.     

Study of characteristic features of the state of palladium cation in PdY zeolites according to IR spectra of adsorbed NO

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 49, No. 5, pp. 815–820, November, 1988.     

Study of the surface properties of a solid solution of vanadium in SnO2 by IR spectroscopy

IR spectroscopy has been used to study the surface properties of a solid solution of vanadium in SnO₂. Adsorption of ammonia and carbon monoxide showed that compounds are formed on the surface of the oxidized Sn/V-oxide sample, the composition of which differs significantly from the solid solution of vanadium. The acid properties of this compound have been studied. The presence of Lewis as well as strong Broensted sites on the surface of the investigated sample has been established.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 505–509, July–August, 1990.     

The Claus Reaction: VI. The Reaction Mechanism over a Sn–Mo Oxide Catalyst

Based on the comparison of reactant conversions in pulses on the stationary surface of the catalyst, the Claus reaction is found to occur via a stepwise mechanism. The nature of interaction of the SO₂ and H₂S molecules with the catalyst surface was studied by FTIR and UV–VIS spectroscopy and the reactivity of the adsorbed species was studied in situ. The intermediate adsorbed reactant species are determined. A scheme of the reaction mechanism over the Sn–Mo oxide catalyst is discussed.