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The nature of the NO x species obtained on NO adsorption and its coadsorption with O 2 at room temperature on TiO 2 and MnO x /TiO 2 catalysts with two different manganese loadings has been studied by means of in situ Fourier transform infrared spectroscopy. In order to obtain information about the potentials of titania-supported manganese materials as catalysts for selective catalytic reduction (SCR) of NO by hydrocarbons, the stability and reactivity of the adsorbed NO x species toward decane has been investigated.

Adsorption of carbon monoxide on CuO/SiO, (1 wt.% CuO) and Cu-ZSM-5 (11 wt.% CuO) catalysts has been studied by IR spectroscopy. CO adsorption on CuO/SiO, leads to formation of: (i) three kinds of unstable Cu2+-C0 species detected only under equilibrium CO pressure and characterized by v(C0) at 2216, 2199 and 2180 cm-', respectively, and (ii) one kind of Cu+-CO carbonyl manifesting an IR band at 2126.5 cm-'. The latter carbonyls possess moderate stability, and some of them are removed upon evacuation. Water replaces CO preadsorbed on the Cu+ ions. Testing the surface of Cu-ZSM-5 with CO reveals the existence of two types of sites: (i) associated Cu+ cations, monitored by a CO band at 2137 cm-' whose intensity is reduced during evacuation, and (ii) isolated Cu+ sites, which form, at high CO equilibrium pressures, dicarbonyls (bands at 2177.5 and 2151 cm-'). Decrease in CO pressure leads to destruction of these species according to the reaction Cu+(CO), -+ Cu'-CO + CO and after evacuation only monocarbonyls are detected by a band at 2158.5 cm-'. These monocarbonyls are stable and resistant towards evacuation. Water is coadsorbed with CO on the isolated Cu' sites, which is accompanied by a ca. 30 cm-' red shift of the 2158.5 cm-' band. This shift is reversible and the original band position is restored after subsequent evacuation.The results show that the state of Cu+ is quite different in Cu-ZSM-5 and CuO/Si02 catalysts. It is assumed that the Cu' sites on CuO/SiO, have one coordinative vacancy each, which leads to formation, primarily, of Cu+-CO monocarbonyls after CO adsorption. On the contrary, the isolated Cu' ions on Cu-ZSM-5 each possess two vacancies, which determine their ability to form dicarbonyls or to coordinate water and CO simultaneously. On the basis of the results obtained it is concluded that the participation (underestimated up to now) of the CJ component in the Cu+-CO bond plays a decisive role with respect to the frequency of CO adsorbed on Cu+ ions and the stability of the corresponding carbonyls.

The nature of the NO x species produced during the adsorption of NO at room temperature and during its coadsorption with oxygen on pure and sulfated zirconia has been investigated by means of in situ FTIR spectroscopy. The adsorption of NO on both samples occurs through disproportionation leading to the formation of nitrous acid; water molecules; nitro species; and anionic nitrosyls, NO -. A mechanism for the formation of these adsorption forms is proposed. The NO -species are stable on the surface of zirconia, whereas on the sulfated sample, they are readily oxidized by the SO 4 2-groups. The process of NO disproportionation is favored by wet surfaces and occurs with participation of the tribridged (ZrO 2 ) and terminal (ZrO 2 -SO 4 2-) hydroxyl groups. Coadsorption of NO and O 2 on pure zirconia leads to the formation of various kinds of nitrate species. The presence of sulfate ions reduces the amount of surface nitrates and decreases their thermal stability. An analysis of the combination bands of the nitrate species shows that this spectral region can be used for structural identification of bidentate and bridged nitrates.

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Cobalt catalysts are prepared by impregnating zirconia and sulfated zirconia using an aqueous solution of cobalt(II) acetate. XRD results show that the catalysts with 5 wt% cobalt loading contain a small amount of Co 3 O 4 . Analysis of the FT-IR results on the adsorption of NO at room temperature reveals the formation of cobalt(II) mono-and dinitrosyls. It is shown that the nitrosyls formed on the sulfate-free catalyst with 5 wt% cobalt loading are unstable on prolonged contact with NO at room temperature due to the oxidation of adsorbed NO to NO 2 − (nitro) and NO 3 − species by cobalt(III) originating from the Co 3 O 4 phase. This process does not occur in the case of the sulfated catalyst containing the same amount of cobalt, for which the existence of a Co 3 O 4 phase is also detected. This experimental fact leads to the conclusion that the sulfate ions lower the reducibility of cobalt(III). Upon coadsorption of NO and O 2 at room temperature on the samples studied, various kinds of surface nitrates are observed differing in the modes of their coordination. In the case of CoO x /SO 4 2− -ZrO 2 catalysts, part of the bidentate nitrates transform to NO 2 − (nitro) species after evacuation at 373 K. The nitro-nitrato species on the sulfated catalysts are characterized by a lower thermal stability than that of the nitrates on the CoO x /ZrO 2 samples.  2004 Elsevier Inc. All rights reserved.

. The adsorption of CO at room temperature on the catalysts studied results in formation of formate, carbonate, and hydrogen carbonate structures as well. It is found that the formation of formate species is associated with the Mn 3+ ions and the possible mechanism is discussed. The stabilization of the hydrogen carbonates is favored by Mn 2+ ions. The reduction of the catalyst studied with hydrogen strongly suppresses the adsorption of CO and is indicative of the occurrence of a strong metal-support interaction.

The adsorption of NO2 on anatase and deuteroxylated TiO, is investigated by IR spectroscopy. It is established that NO, reacts with the surface hydroxyl (deuteroxyl) groups of anatase to give nitrates and water molecules (H20, HOD and D,O) weakly bonded to t h e nitrates, while on t h e surface Lewis acidic-basic pairs of sites, NO, disproportionates to NO+ and nitrates. The stability of the differevt adsorption forms is studied and their structures are discussed. Titania in its low-temperature modification, anatase, is widely used as a support for the modern DeNOx catalyst^.'-^