Probing Ge Distribution in Zeolite Frameworks by Post-Synthesis Introduction of Fluoride in As-Made Materials

A new method has been developed to introduce fluoride in the structure of as-made germanium-containing zeolites prepared under pure alkaline media. Incorporation of fluoride species occurs without modification of the framework composition (Si/Ge ratio) and of the crystallinity, as evidenced by X-ray diffraction and electron microscopy. After incorporation, ¹⁹F solid-state NMR has been used to probe the location and distribution of Ge atoms in the framework. In the case of ITQ-13 and ITQ-17, which can be prepared from both hydroxide and fluoride routes, incorporated F anions are located in the same structural units as those occupied when zeolites are prepared in the presence of fluoride. In the case of ITQ-22 and ITQ-24, fluoride goes mainly in D4R units, which appear to be in the most energetically favorable positions for these zeolites. All experiments clearly show that zeolites prepared in the absence of fluoride in the synthesis medium are enriched in germanium, compared to the same materials obtained from F-containing gels. Moreover, Ge plays a strong structure-directing role by replacing Si atoms preferentially in D4R, leading to zeolites with mainly [4Si, 4Ge] units in the framework. In the particular case of ITQ-22, a new line observed around −2 ppm in ¹⁹F NMR spectra has been tentatively assigned to [3Si, 5Ge] D4R units, which corroborates the structural data obtained via X-ray diffraction

Diffusion-Driven Selectivity in Oxidation of CO in the Presence of Propylene Using Zeolite Nano Shell as Membrane

The selective oxidation of CO over C₃H₆ is achieved in yolk-shell Pt@Silicalite-1 catalysts in which Pt nanoparticles are encapsulated in hollow silicalite-1 single crystals. The thin shell operates as a permselective membrane which limits Pt surface poisoning by C₃H₆. From adsorption measurements, we conclude that the catalytic selectivity arises from the fastest diffusion of CO over C₃H₆ through the silicalite-1 membrane

High-Resolution Structural Characterization of Two Layered Aluminophosphates by Synchrotron Powder Diffraction and NMR Crystallographies

The syntheses and structure resolution process of two highly complex powdered aluminophosphates with an original 5:7 Al/P ratio are presented: [Al₅(OH)­(PO₄)₃(PO₃OH)₄] [NH₃(CH₂)₂NH₃]₂ [2H₂O], compound <b>1</b>, and [Al₅(PO₄)₅(PO₃OH)₂] [NH₃(CH₂)₃NH₃]₂ [H₂O], compound <b>2</b>. We have previously reported the structure of the periodic part of <b>1</b> by coupling synchrotron powder diffraction and solid-state nuclear magnetic resonance (NMR) crystallographies. With a similar strategy, that is, input of large parts of the building blocks determined by analysis of the ²⁷Al–³¹P correlation pattern of the two-dimensional (2D) NMR spectrum in the structure search process, we first determine the periodic structure of <b>2</b>, using the powder synchrotron diffraction data as cost function. Both <b>1</b> and <b>2</b> are layered materials, in which the inorganic layers contain five P and seven Al inequivalent atoms, with aluminum atoms that are found in three different coordination states, AlO₄, AlO₅, and AlO₆, and the interlayer space contains the amines and water molecules. In <b>1</b>, the inorganic layers are stacked on each other with a 4₂ element of symmetry along the <i>c</i>-axis, while they are stacked with a 180° rotation angle in <b>2</b>. By analysis of a set of high-resolution 1D and 2D NMR spectra (³¹P, ²⁷Al, ¹H, ¹⁵N, ¹³C, ²⁷Al–³¹P, ¹H–³¹P, and ¹H–¹⁴N), the structure analysis of <b>1</b> and <b>2</b> is extended beyond the strict periodicity, to which diffraction is restricted, and provides localization of the hydroxyl groups and water molecules in the frameworks and an attempt to correlate the presence of these latter species to the structural features of the two samples is presented. Finally, the dehydration/rehydration processes occurring in these solids are analyzed. The methodology of the structure determination for these dehydrated forms uses the same principles, combining X-ray powder diffraction and solid-state NMR data

High-Resolution Structural Characterization of Two Layered Aluminophosphates by Synchrotron Powder Diffraction and NMR Crystallographies

The syntheses and structure resolution process of two highly complex powdered aluminophosphates with an original 5:7 Al/P ratio are presented: [Al₅(OH)­(PO₄)₃(PO₃OH)₄] [NH₃(CH₂)₂NH₃]₂ [2H₂O], compound <b>1</b>, and [Al₅(PO₄)₅(PO₃OH)₂] [NH₃(CH₂)₃NH₃]₂ [H₂O], compound <b>2</b>. We have previously reported the structure of the periodic part of <b>1</b> by coupling synchrotron powder diffraction and solid-state nuclear magnetic resonance (NMR) crystallographies. With a similar strategy, that is, input of large parts of the building blocks determined by analysis of the ²⁷Al–³¹P correlation pattern of the two-dimensional (2D) NMR spectrum in the structure search process, we first determine the periodic structure of <b>2</b>, using the powder synchrotron diffraction data as cost function. Both <b>1</b> and <b>2</b> are layered materials, in which the inorganic layers contain five P and seven Al inequivalent atoms, with aluminum atoms that are found in three different coordination states, AlO₄, AlO₅, and AlO₆, and the interlayer space contains the amines and water molecules. In <b>1</b>, the inorganic layers are stacked on each other with a 4₂ element of symmetry along the <i>c</i>-axis, while they are stacked with a 180° rotation angle in <b>2</b>. By analysis of a set of high-resolution 1D and 2D NMR spectra (³¹P, ²⁷Al, ¹H, ¹⁵N, ¹³C, ²⁷Al–³¹P, ¹H–³¹P, and ¹H–¹⁴N), the structure analysis of <b>1</b> and <b>2</b> is extended beyond the strict periodicity, to which diffraction is restricted, and provides localization of the hydroxyl groups and water molecules in the frameworks and an attempt to correlate the presence of these latter species to the structural features of the two samples is presented. Finally, the dehydration/rehydration processes occurring in these solids are analyzed. The methodology of the structure determination for these dehydrated forms uses the same principles, combining X-ray powder diffraction and solid-state NMR data

High-Resolution Structural Characterization of Two Layered Aluminophosphates by Synchrotron Powder Diffraction and NMR Crystallographies

The syntheses and structure resolution process of two highly complex powdered aluminophosphates with an original 5:7 Al/P ratio are presented: [Al₅(OH)­(PO₄)₃(PO₃OH)₄] [NH₃(CH₂)₂NH₃]₂ [2H₂O], compound <b>1</b>, and [Al₅(PO₄)₅(PO₃OH)₂] [NH₃(CH₂)₃NH₃]₂ [H₂O], compound <b>2</b>. We have previously reported the structure of the periodic part of <b>1</b> by coupling synchrotron powder diffraction and solid-state nuclear magnetic resonance (NMR) crystallographies. With a similar strategy, that is, input of large parts of the building blocks determined by analysis of the ²⁷Al–³¹P correlation pattern of the two-dimensional (2D) NMR spectrum in the structure search process, we first determine the periodic structure of <b>2</b>, using the powder synchrotron diffraction data as cost function. Both <b>1</b> and <b>2</b> are layered materials, in which the inorganic layers contain five P and seven Al inequivalent atoms, with aluminum atoms that are found in three different coordination states, AlO₄, AlO₅, and AlO₆, and the interlayer space contains the amines and water molecules. In <b>1</b>, the inorganic layers are stacked on each other with a 4₂ element of symmetry along the <i>c</i>-axis, while they are stacked with a 180° rotation angle in <b>2</b>. By analysis of a set of high-resolution 1D and 2D NMR spectra (³¹P, ²⁷Al, ¹H, ¹⁵N, ¹³C, ²⁷Al–³¹P, ¹H–³¹P, and ¹H–¹⁴N), the structure analysis of <b>1</b> and <b>2</b> is extended beyond the strict periodicity, to which diffraction is restricted, and provides localization of the hydroxyl groups and water molecules in the frameworks and an attempt to correlate the presence of these latter species to the structural features of the two samples is presented. Finally, the dehydration/rehydration processes occurring in these solids are analyzed. The methodology of the structure determination for these dehydrated forms uses the same principles, combining X-ray powder diffraction and solid-state NMR data

Hollow Beta Zeolite Single Crystals for the Design of Selective Catalysts

We present a Pt@Beta catalyst with a unique, well-controlled location of metal nanoparticles that allows more efficient use of this rare, expensive metal in catalysis. The zeolite crystal has an inner cavity, leaving a thin zeolite shell where the metal nanoparticles are encapsulated, thereby ensuring a relatively small diffusional path length and high selectivity. Hollow Beta is obtained by a controlled dissolution–recrystallization method. The location of the particles not only was revealed by electron tomography 3D reconstruction but was further confirmed by a model hydrogenation reaction of aromatics

Hollow Beta Zeolite Single Crystals for the Design of Selective Catalysts

We present a Pt@Beta catalyst with a unique, well-controlled location of metal nanoparticles that allows more efficient use of this rare, expensive metal in catalysis. The zeolite crystal has an inner cavity, leaving a thin zeolite shell where the metal nanoparticles are encapsulated, thereby ensuring a relatively small diffusional path length and high selectivity. Hollow Beta is obtained by a controlled dissolution–recrystallization method. The location of the particles not only was revealed by electron tomography 3D reconstruction but was further confirmed by a model hydrogenation reaction of aromatics