Zinc oxide nanowires in chemical bath on seeded substrates: Role of hexamine |
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Authors: | Abhilash Sugunan Hemant C Warad Mats Boman Joydeep Dutta |
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Institution: | (1) Universidad Autónoma Metropolitana-Iztapalapa, Area de Ingeniería Química; Av. San Rafael Atlixco 186, Col. Vicentina, México, D.F., 09340;(2) Instituto Mexicano del Petróleo, Ingeniería Molecular, Eje Lázaro Cárdenas 152, México D.F., 07730 |
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Abstract: | Ceria-doped alumina sol-gel materials were obtained by two synthesis methods at low temperature; using method A, 2-propanol-diluted
cerium precursor was slowly added at the time of the aluminum sol formation in acidic environment; using method B, the cerium
salt was mixed with the aluminum alkoxide before sol formation in a basic environment. The supports were characterized by
N2 physisorption, thermogravimetric and thermal differential analyses (TGA and DTA), X-ray diffraction (XRD), 27Al Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR), 2-propanol reactions, and ammonia temperature-programmed desorption
(NH3-TPD). The samples obtained by Method B present similar values in properties such as specific areas, pore volumes, pore size
distribution, and acidity compared to those of pure alumina; the alumina structure was not modified, but segregated crystallites
of CeO2 were found in samples calcined at 1000 ∘C, as observed by XRD. The ceria-containing materials synthesized by method A show a thermal behavior similar to that of alumina,
with no appreciable segregation of CeO2 detected by XRD and modifications in the amounts of tetra, penta, and octa-hedral aluminum coordination as determined by
NMR. 2-propanol reactions showed a good correlation with acid density determined by NH3-TPD. As the percentage of ceria in the material increases, surface area, pore volume, and acidity decrease. These changes
can be correlated with an increase of pentacoordinated aluminum content. The results indicate that CeO2 is well dispersed in the alumina framework when method A is used, but synthesis method B does not have the same effect on
the CeO2incorporation. |
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Keywords: | alumina ceria 2-propanol dehydration mixed oxides thermal analysis N2 Physisorption XRD 27Al MAS-NMR NH3-TPD acidity |
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