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Co2 conversion and oxalate stability on alkali promoted metal surfaces: sodium modified Al(100)
1988 (English)In: Catalysis Letters, ISSN 1011-372X, E-ISSN 1572-879X, Vol. 1, no 12, p. 445-455Article in journal (Refereed) Published
Abstract [en]

CO2 conversion on alkali promoted metals in aprotic systems has been followed with surface sensitive spectroscopies. New results on sodium modified aluminum(100) are presented and compared with previous studies on magnesium [1], aluminum [2], and bulk alkali metals [3]. Electron energy loss spectra reveal two different states of CO2 adsorption at 100 K and monolayer sodium coverage. Vibrational bands at 650 cm-1 and 2325 cm-1 correspond to weakly bound molecular CO2 and a multitude of bands between 2300 cm-1 and 460 cm-1 to oxalate ions with low, possibly unidentate, coordination. Gentle annealing increases the coordination as apparent by vibrational shifts. This corresponds to oxalate to carbonate conversion, a process which is completed around room temperature. CO desorption was detected at 285 K and Auger measurements reveal a 1:3 C/O stoichiometry after high temperature annealing. We observe no release of CO2 above 110 K but an additional weak state of CO desorption around 470 K. High temperature annealing causes decomposition of all intermediates and leaves the aluminum surface covered with an irreducible carbide and oxide overlayer. We suggest that CO2 reduction and dimerization to C2O4 -2 is a common path to yield carbon deposition on all alkali promoted surfaces in hydrogen deficient systems. In contrast, oxalate decomposition is related to the specific chemistry of each substrate.

Abstract [en]

CO2 conversion on alkali promoted metals in aprotic systems has been followed with surface sensitive spectroscopies. New results on sodium modified aluminum(100) are presented and compared with previous studies on magnesium [1], aluminum [2], and bulk alkali metals [3]. Electron energy loss spectra reveal two different states of CO2 adsorption at 100 K and monolayer sodium coverage. Vibrational bands at 650 cm–1 and 2325 cm–1 correspond to weakly bound molecular CO2 and a multitude of bands between 2300 cm–1 and 460 cm–1 to oxalate ions with low, possibly unidentate, coordination. Gentle annealing increases the coordination as apparent by vibrational shifts. This corresponds to oxalate to carbonate conversion, a process which is completed around room temperature. CO desorption was detected at 285 K and Auger measurements reveal a 1:3 C/O stoichiometry after high temperature annealing. We observe no release of CO2 above 110 K but an additional weak state of CO desorption around 470 K. High temperature annealing causes decomposition of all intermediates and leaves the aluminum surface covered with an irreducible carbide and oxide overlayer. We suggest that CO2 reduction and dimerization to C2O4 –2 is a common path to yield carbon deposition on all alkali promoted surfaces in hydrogen deficient systems. In contrast, oxalate decomposition is related to the specific chemistry of each substrate.

Place, publisher, year, edition, pages
1988. Vol. 1, no 12, p. 445-455
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Other Physics Topics
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Fysik
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URN: urn:nbn:se:ltu:diva-9888DOI: 10.1007/BF00766205Local ID: 8963aa10-388c-11dd-8721-000ea68e967bOAI: oai:DiVA.org:ltu-9888DiVA, id: diva2:982827
Note
Upprättat; 1988; 20080612 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved

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Paul, Jan

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