Mild Hydrothermal Treatment Research Articles

Improved selectivity to lower substituted methylamines using hydrothermally treated zeolite Rho

Zeolite Rho is of particular interest for the methanol ammination reaction. Reaction/regeneration cycles on Rho lead to improved activity and selectivity. This is shown to be caused by the combustion on the surface of residual methyl groups, which leads to in situ steaming of the catalyst. Mild hydrothermal treatment gives similar results. The results of both cases are attributed to physico-chemical changes within the catalyst.

Synthesis and characterization of microporous pillared α‐zirconium phosphate–biphenylenebis(phosphonate)

D. Medoukali, P. Hubert Mutin and A. Vioux, J. Mater. Chem., 1999, 9, 2553 DOI: 10.1039/A902929J

Spectroscopic and catalytic evidence for the incorporation of gallium in the AEL framework

71Ga MAS n.m.r. analysis and the catalytic behavior during the transformation of 1-butene and n-butane strongly suggest the incorporation of Ga into the AlPO4-11 (AEL) framework during the synthesis of GaAPSO-11. A unique clear signal at around +120 ppm is proposed to be associated with the presence of tetrahedral Ga in the AEL framework of the unmodified GaAPSO-11. Migration of structural Ga atoms to the silicon domain of the AEL framework seems to occur as a result of a mild hydrothermal treatment, giving rise to an additional signal at +156 ppm, previously associated with tetrahedral gallium in gallosilicates with the MFI topology. The fact that GaAPO-11 and GaAPSO-11 behaved in a way similar to their counterparts AlPO4-11 and SAPO-11 during the skeletal isomerization of n-butenes reinforces the idea of an isomorphous substitution of Al(III) by Ga(III) in the AEL framework. The transformation of n-butane was shown to be a valuable test for detecting the presence of small amounts of hydro-dehydrogenating extraframework gallium species (EFGS) in Ga-supported SAPO-11 (Ga/SAPO-11). The fact that the sample of GaAPSO-11 was completely inactive for this transformation leads us to believe that the incorporation of gallium into the tetrahedral positions of the AEL framework was almost complete.

Dealumination of HZSM-5 Zeolites: II. Methanol to Gasoline Conversion

Changes in the structure and properties of HZSM-5 zeolites used for extended periods as catalysts in the conversion of methanol to gasoline have been investigated. HZSM-5 samples were characterized using solid-state NMR spectroscopy (27Al and29Si MAS), infrared spectroscopy; chemical analysis, water and nitrogen adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, and129Xe NMR spectroscopy of adsorbed xenon. Use of HZSM-5 in methanol conversion was found to cause dealumination of the zeolite lattice. The catalyst lifetime, however, increased after repeated use in MTG cycles. The dealumination is caused by water produced during methanol conversion, although the extralattice aluminum species formed appear to differ from those produced by calcination or mild hydrothermal treatment. The increase in catalyst lifetime is attributed to a decreased rate of coke formation in catalysts containing lower densities of acid sites.

Surface cristobalite formation by mild hydrothermal treatment of silica gel and its effect on the deposition of tris(allyl)rhodium and subsequent reactivity of (silica)rhodium(allyl)2

Surface cristobalite formation by mild hydrothermal treatment of silica gel and its effect on the deposition of tris(allyl)rhodium and subsequent reactivity of (silica)rhodium(allyl)2

ChemInform Abstract: High Dispersion Metal Oxide/Molecular Sieves: New Bifunctional Shape Selective Catalysts

Highly dispersed metal oxide/molecular sieve catalysts can be prepared through modification of metallosilicate molecular sieves. The resulting materials have been shown to exhibit enhanced catalytic activities for selected reactions. The metallosilicates examined include the gallosilicates, iron (ferri-) silicates and cobalt silicates. The size of the metal oxide particles as well as their location (in the pores or on the surface) can be controlled through post-synthesis methods. Thermal or mild hydrothermal treatment of the metallosilicate produces a highly dispersed metal oxide phase, while higher temperatures or longer treatment causes the metal oxide to migrate and form larger agglomerates of the metal oxide phase. The size of these agglomerates are strongly dependent on the conditions of hydrothermal treatment. Dispersion, location and agglomeration of the metal oxide phase have been characterized for the iron silicates using both physical and catalytic techniques. The magnetic properties of the iron silicates are described.

Transformation of Birnessite to Buserite, Todorokite, and Manganite under Mild Hydrothermal Treatment

AbstractInvestigations were conducted to determine the hydrothermal transformations of synthetic birnessite exchanged with different metal ions. Autoclaving in a Teflon-lined stainless steel pressure vessel at 155°C for 24 hr of Mg-, Ca-, La-, and Co-saturated birnessite yielded manganese minerals having 10-Å X-ray powder diffraction (XRD) spacings. The autoclaved Mg-birnessite yielded a mineral identical to natural todorokite in its infrared (IR) spectrum and XRD patterns. High-resolution transmission electron microscopy (HRTEM) provided images having 10-, 12.5-, 15-, and 20-Å wide fringes indicating heterogeneous channel widths in the crystallographic a direction, and IR spectroscopy produced bands at 757, 635, 552, 515, 460, and 435 cm-1, confirming the product obtained by autoclaving Mg-birnessite to be todorokite. Prolonged autoclaving of Mg-birnessite yielded manganite (γ-MnOOH) as a by-product; manganite did not form when the autoclaving time was shortened to 8 hr. Also, when Ca-saturated samples were autoclaved, the product gave d-values of 10 Å, but the XRD lines were broad and heterogeneity of the channel sizes was evident from HRTEM observations. The Ca-derivative had an IR spectrum similar to that of natural todorokite. Images showing 10-Å lattice fringes were observed by HRTEM for the Ni-saturated sample, which also produced an XRD pattern similar to that of the Mg-saturated sample. Co- and Lasaturated samples did not form todorokite, although HRTEM of La-saturated samples indicated some 10-Å lattice fringes that were unstable in the electron beam. Birnessite saturated with Na, K, NH4, Cs, Ba, or Mn(II) gave products having 7-Å spacings upon autoclaving.

High Dispersion Metal Oxide/Molecular Sieves: New Bifunctional Shape Selective Catalysts

AbstractHighly dispersed metal oxide/molecular sieve catalysts can be prepared through modification of metallosilicate molecular sieves. The resulting materials have been shown to exhibit enhanced catalytic activities for selected reactions. The metallosilicates examined include the gallosilicates, iron (ferri-) silicates and cobalt silicates. The size of the metal oxide particles as well as their location (in the pores or on the surface) can be controlled through post-synthesis methods. Thermal or mild hydrothermal treatment of the metallosilicate produces a highly dispersed metal oxide phase, while higher temperatures or longer treatment causes the metal oxide to migrate and form larger agglomerates of the metal oxide phase. The size of these agglomerates are strongly dependent on the conditions of hydrothermal treatment. Dispersion, location and agglomeration of the metal oxide phase have been characterized for the iron silicates using both physical and catalytic techniques. The magnetic properties of the iron silicates are described.

ChemInform Abstract: A NEW METHOD FOR THE PREPARATION OF ZEOLITE ZSM‐5 BY USING SODIUM N‐DODECYLBENZENE SULFONATE

Zeolite ZSM-5 was easily synthesized by using sodium n-dodecylbenzene sulfonate (SDBS) in place of organic ammonium and/or phosphonium ions. A well-crystallized ZSM-5 was obtained by the mild hydrothermal treatment of a reaction mixture composed of SDBS and alumina-silica gel at about 180 °C and PH2O ≈10 kg/cm2 for 4 h.

A NEW METHOD FOR THE PREPARATION OF ZEOLITE ZSM-5 BY USING SODIUM n-DODECYLBENZENE SULFONATE

Abstract Zeolite ZSM-5 was easily synthesized by using sodium n-dodecylbenzene sulfonate (SDBS) in place of organic ammonium and/or phosphonium ions. A well-crystallized ZSM-5 was obtained by the mild hydrothermal treatment of a reaction mixture composed of SDBS and alumina-silica gel at about 180 °C and PH2O ≈10 kg/cm2 for 4 h.

New data on Sepiolite and Attapulgite

AbstractHydrothermal studies have failed to yield synthetic attapulgite or sepiolites in the system MgO-Al2O3-SiO2-H2O. However, the natural minerals can be decomposed to yield mont-morillonoids by mild hydrothermal treatment as low as 200°C and probably as low as 100°C. These data indicate that they are metastable and probably could not have formed at these temperatures.Dry dehydration at 400° and 750°C gave no evidence for the presence of “zeolitic water” in these minerals and failed to establish the existence of “anhydride” phases. The field study of relationships in one sepiolite locality suggests the importance of structural control in the formation of these minerals.