Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces

Water dissociation and the energetics of the WGS reaction on a bulk MgO, an Ag supported MgO thin film and Au/MgO/Ag surfaces is studied based on the density functional theory. The literature results for water splitting on MgO and MgO/Ag surfaces with a step type defect are repeated and further anal...

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Päätekijä: Nevalaita, Janne
Muut tekijät: Matemaattis-luonnontieteellinen tiedekunta, Faculty of Sciences, Fysiikan laitos, Department of Physics, University of Jyväskylä, Jyväskylän yliopisto
Aineistotyyppi: Pro gradu
Kieli:eng
Julkaistu: 2011
Aiheet:
Linkit: https://jyx.jyu.fi/handle/123456789/37046
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author Nevalaita, Janne
author2 Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Fysiikan laitos Department of Physics University of Jyväskylä Jyväskylän yliopisto
author_facet Nevalaita, Janne Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Fysiikan laitos Department of Physics University of Jyväskylä Jyväskylän yliopisto Nevalaita, Janne Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Fysiikan laitos Department of Physics University of Jyväskylä Jyväskylän yliopisto
author_sort Nevalaita, Janne
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description Water dissociation and the energetics of the WGS reaction on a bulk MgO, an Ag supported MgO thin film and Au/MgO/Ag surfaces is studied based on the density functional theory. The literature results for water splitting on MgO and MgO/Ag surfaces with a step type defect are repeated and further analysis on the origin of the energetically favored dissociative water adsorption are made. The reactivity towards water dissociation on the stepped MgO and MgO/Ag surfaces is attributed to four contributing factors: 1. The change in the interlayer distance of the surface in dissociative adsorption is diminished on the stepped surfaces compared to the flat surfaces. On the flat surfaces the dissociative adsorption of water leads to an increased interlayer distance between the first and second MgO layer while the molecular adsorption does not change the distance. 2. A surface OH group is formed in the H adsorption. On the stepped surface the adsorbed OH and surface OH form aligned dipoles. On the flat surface the adsorbed OH and the surface OH group do not align. 3. The density difference analysis shows that the charge transfer in the co-adsorption of H and OH on the stepped MgO/Ag surface is mainly between the adsorbed H and OH. This leads to an at- tractive Coulomb interaction between the adsorbed species. 4. The p-band center of the edge O atoms show a strong shift towards the Fermi energy compared to the average surface O atoms. On the bulk MgO surfaces the p-band center of the O atom at the H adsorption site is shown to correlate with the H adsorption energy. Similar trend is seen in the MgO/Ag surfaces. The energetics of a WGS reaction on a surface with large Au clusters deposited on an Ag supported MgO thin film is studied. The large Au cluster is modeled with an Au stripe set with the periodic boundary conditions to produce similar distances between the Au atoms as for a large Au cluster. The Bader charges of the edge atoms of the Au stripe are similar to the charges for the edge atoms of a large Au cluster. Water dissociation at the edge of the Au stripe is not deemed probable due to the weak binding of OH to the Au/MgO/Ag surface.
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The literature results for\nwater splitting on MgO and MgO/Ag surfaces with a step type defect are\nrepeated and further analysis on the origin of the energetically favored\ndissociative water adsorption are made. The reactivity towards water\ndissociation on the stepped MgO and MgO/Ag surfaces is attributed to\nfour contributing factors:\n 1. The change in the interlayer distance of the surface in dissociative\n adsorption is diminished on the stepped surfaces compared to the\n flat surfaces. On the flat surfaces the dissociative adsorption of\n water leads to an increased interlayer distance between the first\n and second MgO layer while the molecular adsorption does not\n change the distance.\n 2. A surface OH group is formed in the H adsorption. On the stepped\n surface the adsorbed OH and surface OH form aligned dipoles. On\n the flat surface the adsorbed OH and the surface OH group do not\n align.\n 3. The density difference analysis shows that the charge transfer in\n the co-adsorption of H and OH on the stepped MgO/Ag surface\n is mainly between the adsorbed H and OH. This leads to an at-\n tractive Coulomb interaction between the adsorbed species.\n 4. The p-band center of the edge O atoms show a strong shift towards\n the Fermi energy compared to the average surface O atoms. On\n the bulk MgO surfaces the p-band center of the O atom at the H\n adsorption site is shown to correlate with the H adsorption energy.\n Similar trend is seen in the MgO/Ag surfaces.\nThe energetics of a WGS reaction on a surface with large Au clusters\ndeposited on an Ag supported MgO thin film is studied. The large Au\ncluster is modeled with an Au stripe set with the periodic boundary\nconditions to produce similar distances between the Au atoms as for a\nlarge Au cluster. The Bader charges of the edge atoms of the Au stripe\nare similar to the charges for the edge atoms of a large Au cluster. 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spellingShingle Nevalaita, Janne Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces DFT water dissociation water-gas shift Au cluster MgO surface MgO thin film Fysiikka Physics 4021 fysiikka energetiikka
title Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces
title_full Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces
title_fullStr Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces
title_full_unstemmed Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces
title_short Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces
title_sort water dissociation and water gas shift energetics on mgo mgo ag and au mgo ag surfaces
title_txtP Water dissociation and water-gas shift energetics on MgO, MgO/Ag and Au/MgO/Ag surfaces
topic DFT water dissociation water-gas shift Au cluster MgO surface MgO thin film Fysiikka Physics 4021 fysiikka energetiikka
topic_facet 4021 Au cluster DFT Fysiikka MgO surface MgO thin film Physics energetiikka fysiikka water dissociation water-gas shift
url https://jyx.jyu.fi/handle/123456789/37046 http://www.urn.fi/URN:NBN:fi:jyu-2011120711768
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