| Autor: |
Gurung, Kshitij, James, Travis H., Torres, Angel, Sinitskii, Alexander, Langell, Marjorie A. |
| Zdroj: |
The Journal of Physical Chemistry - Part C; October 2021, Vol. 125 Issue: 42 p23071-23084, 14p |
| Abstrakt: |
Oxygen availability, an important property of cerium oxide catalysts, has been investigated over a wide range of concentrations for the substitutional solid solution ZnxCe1–xO2in nanocrystalline (∼2.5 nm) form. X-ray diffraction data of the as-synthesized materials indicates ZnxCe1–xO2to be a single-phase system up to approximately x= 0.16, with the lattice parameter decreasing linearly with zinc concentration, signifying a homogeneous distribution of the Zn2+cation within the bulk of the nanoparticle. X-ray photoelectron spectroscopy (XPS) of the ZnxCe1–xO2samples shows stoichiometric to slightly enriched zinc surface concentrations accompanied by oxygen surface reduction and an increased ratio of Ce3+/Ce4+upon zinc incorporation, which correlate with increased oxygen surface reactivity. The ability of ZnxCe1–xO2to oxidize chemical reactants, taken here as a measure of oxygen availability, is measured by two different reactions, H2temperature-programmed reduction (H2-TPR) to measure total oxygen storage capacity and the oxidation of methanol by temperature-programmed desorption (MeOH-TPD), both of which show enhancement in total oxidation and lower peak reaction temperatures with increased zinc concentration. H2-TPR gives evidence of involvement of both the outermost surface and sub-surface lattice oxygens, whereas XPS of methanol adsorption indicates the presence of both molecular and dissociative methoxy adsorbates as well as formate and carbonate intermediates. Methoxy decomposes into the intermediate species, leading to both CO partial oxidation and total oxidation to CO2at higher zinc concentrations. Both H2-TPR and MeOH-TPD are sensitive to zinc concentration, indicating increasing oxygen availability as zinc is added up to the 16% miscibility limit. |
| Databáze: |
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