Browsing by Author "Harrison, Philip G."

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Tin oxide surfaces. Part 4.—Infrared study of the adsorption of oxygen and carbon monoxide + oxygen mixtures on tin(IV) oxide, and the adsorption of carbon dioxide on ammonia-pretreated tin(IV) oxide
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Harrison, Philip G.; Thornton, Edward W.
The transmission infrared technique has been used to study the adsorption of oxygen and carbon monoxide + oxygen mixtures on tin(IV) oxide. Adsorption of oxygen results in the appearance of two weak bands at 1155 and 1020 cm–1 which did not shift using 18O-enriched oxygen. No assignment of the species responsible for these bands was made, but the accompanying broad intense band below 900 cm–1 is associated with surface Sn—O—Sn bridges. Surface carbonate and bicarbonate species are formed slowly when the oxide is exposed to carbon monoxide + oxygen mixtures, essentially independent of the gas mixture composition in the range 10–70 % CO. No bulk reduction of the oxide was observed, in contrast to the behaviour previously observed with carbon monoxide alone. Hydration of the oxide surface prior to treatment with adsorbent severely inhibits the adsorption of carbon dioxide and carbon monoxide + oxygen mixtures. Preadsorbed ammonia has a similar inhibiting effect with carbon dioxide, but leads to the formation of a low stability carbamate salt of the unsubstituted carbamic acid, H2NCO2H.
Tin oxide surfaces. Part 8.—Infrared study of the mechanism of formation of a surface isocyanate species on SnO2· 0·55 CuO during catalysis of the oxidation of carbon monoxide by nitric oxide
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Harrison, Philip G.; Thornton, Edward W.
An experimental study has been carried out on the mechanism of formation of a surface isocyanate species on the mixed oxide catalyst SnO2· 0·55 CuO during the initial stages of catalysis of the CO + NO reaction at ≈470 K. Using infrared spectroscopy, the isotopic shifts of the 2189 cm–1 pseudo-antisymmetric stretching vibration have been measured for 13C, 15N and 18O substitution. The oxygen atom of the surface isocyanate has been shown to originate from NO rather than CO as was previously assumed. This observation has been interpreted in terms of a mechanism involving initial dissociative chemisorption of CO followed by the formation of a fulminate via reaction of NO with the surface carbon atom and subsequent rapid isomerisation to the isocyanate: [graphic omitted].
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
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Harrison, Philip G.; Thornton, Edward W.
Infrared transmission spectroscopy has been used to study the adsorption of CO, NO and CO + NO mixtures on tin(IV) oxide gels containing CrIII, MnII, FeIII, CoII, NiII 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 2200–2180 cm–1 for all the oxidised gels (except the FeIII exchanged sample). The increase in absorption frequency above that of the gas phase value (2143 cm–1) 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 CuII exchanged gel which was bonded via oxygen. Bands due to bidentate carbonate complexes associated with transition metal sites were also observed for the oxidised MnII, FeIII and CoII samples. In contrast, exposure of CO-reduced MnII, FeIII, CoII and NiII samples to CO + O2 mixtures resulted in the formation of unidentate carbonate complexes bound to transition metal ion sites. Nitric oxide is chemisorbed on all gels except the MnII-exchanged sample, but the nature of the chemisorbed species varies. All the samples catalysed the CO–NO reaction, and physisorbed CO2 was present in the MnII, FeIII, CoII and NiII samples as well as physisorbed N2O in the case of MnII. 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 FeIII) show a marked selectivity for reduction of NO to N2O, whereas the CuII- exchanged gel, which preferentially adsorbs CO, exhibits a similar selectivity for reduction to N2.