Hydrothermal synthesis attempts of dawsonite-type hydroxymetalocarbonate precursor compounds for catalytic Ho, Sm, and La oxides

Journal Article · Tue Jan 08 00:00:00 EST 2008 · Materials Research Bulletin

DOI:https://doi.org/10.1016/j.materresbull.2007.07.026· OSTI ID:21068171

Ali, Asma A; Hasan, Muhammad A ^[1]

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1. Chemistry Department, Faculty of Science, Kuwait University, P.O. Box 5969, Safat 13060 (Kuwait)

Chemical interactions in mixed, aqueous solutions of NH{sub 4}HCO{sub 3} and M(NO{sub 3}){sub 3}.9H{sub 2}O, where M stands for Ho, Sm, or La, were facilitated under various hydrothermal treatment conditions (pH 8-12 and temperature = 75-135 deg. C). The solution chemistry established did not make available necessary concentrations of soluble HCO{sub 3}{sup -} and MO(OH){sub 2}{sup -} species for the formation of dawsonite-type ammonium hydroxymetalocarbonates, NH{sub 4}M(CO{sub 3})(OH){sub 2}, but, alternatively, high concentrations of soluble CO{sub 3}{sup 2-}, and M(H{sub 2}O){sub n}{sup 3+} or M(H{sub 2}O){sub n-1}(OH){sup 2+} facilitating, respectively, precipitation of corresponding hydrated carbonate, M{sub 2}(CO{sub 3}){sub 2}.2H{sub 2}O, or carbonate hydroxide, MCO{sub 3}(OH). X-ray powder diffractometry, infrared spectroscopy, and thermal analyses proved alternative formation of Ho{sub 2}(CO{sub 3}){sub 3}.2H{sub 2}O or LaCO{sub 3}(OH) under the whole set of hydrothermal treatment conditions probed, and Sm{sub 2}(CO{sub 3}){sub 3}.2H{sub 2}O at pH < 10 or SmCO{sub 3}(OH) at pH {>=} 10, thus implying dependence of the composition of the product carbonate compound on the hydrolysability of the initial M(H{sub 2}O){sub n}{sup 3+} species and, hence, the metal ionic size (La > Sm > Ho). Calcination of the various hydrothermal treatment products at {>=}600 deg. C resulted in the thermal genesis of the corresponding sesqui-oxides (M{sub 2}O{sub 3}). Bulk and surface characterization studies of the product oxides, employing N{sub 2} sorptiometry and scanning electron microscopy, in addition to the above analytical techniques, revealed overall strong crystallinity, large average crystallite size, and well-defined particle morphology. They revealed, moreover, surfaces, though of limited accessibilities ({<=}13 m{sup 2}/g), exposing OH groups of various coordination symmetries and, hence, acid-base properties, thus furnishing promising surface catalytic attributes.

• OSTI ID: 21068171
• Journal Information: Materials Research Bulletin, Vol. 43, Issue 1; Other Information: DOI: 10.1016/j.materresbull.2007.07.026; PII: S0025-5408(07)00334-0; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION SPECTROSCOPY
AQUEOUS SOLUTIONS
CALCINATION
CARBONATES
DAWSONITE
HOLMIUM OXIDES
HYDROTHERMAL SYNTHESIS
HYDROXIDES
INFRARED SPECTRA
LANTHANUM OXIDES
MICROSTRUCTURE
PH VALUE
PRECIPITATION
SAMARIUM OXIDES
SCANNING ELECTRON MICROSCOPY
SURFACES
TEMPERATURE RANGE 0400-1000 K
THERMAL ANALYSIS
X-RAY DIFFRACTION