Tin oxide surfaces. Part 9.—Infrared study of the adsorption of CO, NO and CO + NO mixtures on tin(IV) oxide gels containing ion-exchanged CrIII, MnII, FeIII, CoII, NiII and CuII

Abstract

Infrared transmission spectroscopy has been used to study the adsorption of CO, NO and CO + NO mixtures on tin(Iv) oxide gels containing CrlIr, Mn", FelI1, CoII, Nil1 and CuII as ion-exchanged cations. Exposure to CO results in the formation of linear physisorbed CO species exhibiting a single absorption band in the range 2200-2180cm-I for all the oxidised gels (except the FelIrexchanged sample). The increase in absorption frequency above that of the gas phase value (2143 cm-l) is rationalised by considering the strong electric field due to the transition metal ion, and it was concluded that the carbon monoxide is adsorbed perpendicular to the surface, probably via carbon, at a cationic transition metal site, except for CulI exchanged gel which was bonded via oxygen. Bands due to bidentate carbonate complexes associated with transition metal sites were also observed for the oxidised Mn", FelI1 and Coll samples. In contrast, exposure of CO-reduced Mn", FerI1, CoI1 and NiI1 samples to CO+Oz mixtures resulted in the formation of unidentate carbonate complexes bound to transition metal ion sites. Nitric oxide is chemisorbed on all gels except the Mnrl-exchanged sample, but the nature of the chemisorbed species varies. All the samples catalysed the CO-NO reaction, and physisorbed C 0 2 was present in the Mn", FelI1, ColI and NilI samples as well as physisorbed N20 in the case of Mn". All samples showed spectra due to carbonate species consistent with a redox mechanism for the CO-NO reaction catalysed by these oxides.Additionally, those oxides with exchanged cations which adsorb NO from CO + NO mixtures (CoII, NiiI and FerlI) show a marked selectivity for reduction of NO to N20, whereas the Cu"exchanged gel, which preferentially adsorbs CO, exhibits a similar selectivity for reduction to Nz.

Infrared studies of the surface acidity of oxides and zeolites using adsorbed probe molecules

“…The blue shift increases with increasing strength of electron donation from the CO molecule to the acid site. For a given type of site (nature of the acid site, hardness) the shift usually increases with in-creasing positive charge at the acid site [133][134][135][136][137][138][139]. This is well supported by theoretical calculations which suggest that the CO stretching frequency increases monotonously with the electric field strength of the cation [132].…”

In situ DRIFTS study of the NO + CO reaction on Fe–Co binary metal oxides over activated semi-coke supports

“…Besides these peaks, the spectrum of Fe 0.8 Co 0.2 /ASC in Fig. 3(a) showed bands at 1740 cm À1 , 1679 cm À1 , 1587 cm À1 cm À1 , 1430 cm À1 , and 1526 cm À1 , assigned to n(C]O), n as (CO 3 2À ) in bidentate coordination, the n of CO 3 2À species adsorbed on Fe 3+ in bidentate (1590 cm À1 ) 51,52 and monodentate coordination (1435 cm À1 ), 30,37 and n as (COO À ), respectively. Moreover, the intensity of these peaks decreased continuously with increasing temperature.…”

Spectroscopic Investigation of Species Arising from CO Chemisorption on Titania-Supported Manganese

“…However, only a few studies (10,(13)(14)(15)(16)(17)(18)(19)(20) (compared, for example, to those devoted to the catalytic performance) have appeared on the characterization of manganese oxide catalysts by this method. The reason for this could be the fact that manganese forms very complex species with oxygen, making characterization of manganese catalysts very difficult.…”