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  • ZrO2-SiO2 composite  (2)
  • fluoride ion loading  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Fluoride treatment of AlPO4-Al2O3 catalysts. II. Poisoning experiments by bases for cyclohexene conversion and cumene cracking (1994)
    Springer
    Catalysis letters 24 (1994), S. 293-301 
    Details
    ISSN: 1572-879X
    Keywords: AlPO4-Al2O3 ; fluoride ion loading ; surface acidity ; cyclohexene conversion ; cumene cracking ; poisoning by bases ; pyridine ; 2,6-dimethylpyridine ; hexamethyldisilazane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Brønsted acid sites on fluoride-modified AlPO4-Al2O3 (2.5 wt% F; APAl-P-2.5F) catalyst are poisoned by the presence of 2,6-dimethylpyridine (DMPY) and hexamethyldisilazane (HMDS), thus decreasing the catalytic activity for cyclohexene and cumene reaction processes, while the effect of pyridine (PY) was scarce. Besides, the drop in activity for cyclohexene conversion was accompanied by a change in reaction selectivity so that hydrogen transfer sites are much more sensitive to base poisoning (getting greater as the poisoning effect increased) than isomerization sites. Moreover, surface trimethylsilyl (TMS) complexes (formed by covalent reaction of HMDS with surface hydroxyls) decomposed and thus, the activity progressively increased at increasing time intervals, thus reaching greater values (at ca. 4 h) than the unpoisoned APAl-P-2.5F catalyst. So, DMPY was more suitable than PY and HMDS for the poisoning of Brønsted acid sites on APAl-P-F catalyst.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811802
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetic study of zirconia crystallization from amorphous ZrO2-SiO2 composite precursors processed by sol-gel chemistry (1994)
    Springer
    Journal of sol gel science and technology 2 (1994), S. 353-357 
    Details
    ISSN: 1573-4846
    Keywords: ZrO2-SiO2 composite ; kinetics of crystallization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Powder precursor gels with composition xZrO2·(100−x)SiO2, with selected values of x=8, 24, 43 and 75 mol%, were processed by sol-gel chemistry. Differential thermal analysis (DTA) was used to study crystallization in (cubic/tetragonal)-ZrO2 during the heating of the reactive amorphous precursors. Kinetic parameters such as activation energy, Avrami's exponent and frequency factor have been simultaneously calculated from the computed DTA data using a previously reported kinetic model. The crystallization temperature decreases relative to the increase in the amount of ZrO2, the value of the kinetic parameter of the crystallization being related to the value of x.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486269
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Preparation and Characterization of Amorphous ZrO2-SiO2 Composite Powders Processed by Sol-Gel Chemistry (1997)
    Springer
    Journal of sol gel science and technology 10 (1997), S. 165-175 
    Details
    ISSN: 1573-4846
    Keywords: ZrO2-SiO2 composite ; zirconia ; silica ; processing ; sol-gel chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Composite ZrO2-SiO2 powders, with different ZrO2 contents, including pure ZrO2 powders, were prepared by precipitation in SiO2 suspensions, of zirconia gels from solutions of zirconyl chloride at pH = 11. These products were investigated in connection with the phase changes in ZrO2 caused by heat-treatments. ZrO2-SiO2 mixtures containing 0–100% mol ZrO2, were studied by differential thermal analysis (DTA), X-ray powder diffraction (XRD), temperature programmed desorption combined with mass spectroscopy (TPD-MS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), to obtain information on the morphological and structural features of the particles before and during the heat treatment up to 1200°C. Specific surface areas were determined using nitrogen adsorption by the BET method. The results offer an explanation about some of the factors which can be influencing on the stabilization of metastable-cubic/tetragonal (C/T) phase of ZrO2 and the evolution of surface areas (“vulcano” profile) observed in the composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018399529744
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    Paper (German National Licenses)
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