scholarly journals Unexpected contraction of a zeolite framework upon isomorphous substitution of Si by Al

1996 ◽  
pp. 425 ◽  
Author(s):  
Miguel A. Camblor ◽  
Suk Bong Hong ◽  
Mark E. Davis
Keyword(s):  
Isomorphous Substitution ◽  
Zeolite Framework

Precise control of density and strength of acid sites of MFI-type zeolite nanoparticles via simultaneous isomorphous substitution by Al and Fe

CrystEngComm ◽  
2020 ◽  
Vol 22 (44) ◽  
pp. 7556-7564
Author(s):  
Mizuho Yabushita ◽  
Hiroki Kobayashi ◽  
Atsushi Neya ◽  
Masafumi Nakaya ◽  
Sachiko Maki ◽  
...  
Keyword(s):  
Acid Sites ◽  
Linear Control ◽  
Isomorphous Substitution ◽  
Zeolite Framework ◽  
Precise Control ◽  
Type Zeolite ◽  
Catalyst Lifetime

The co-incorporation of Al and Fe at various relative ratios into the MFI-type zeolite framework enabled linear control of the density and strength of acid sites, and such well-tuned acidity led to a better catalyst lifetime.

Molecular Mechanics Studies on MFI Type Zeolites. 2. Isomorphous Substitution by Aluminium

1992 ◽  
Vol 57 (4) ◽  
pp. 681-686 ◽  
Author(s):  
Erik de Vos Burchart ◽  
Herman van Bekkum ◽  
Bastiaan van de Graaf
Keyword(s):  
Force Field ◽  
Molecular Mechanics ◽  
Mirror Symmetry ◽  
Organic Molecules ◽  
Unit Cell ◽  
Isomorphous Substitution ◽  
Zeolite Framework ◽  
Mm3 Force Field ◽  
Framework Energy

The molecular mechanics force field developed for all-silica structures is extended with parameters for tetrahedral aluminium. With this force field and the MM3 force field for organic molecules the effects of isomorphous substitution in the MFI framework are examined (4 Al/unit cell) with tetrapropyl ammonium (TPA) as the charge compensating cation. The results indicate a slight preference for the positions 2, 9, 5, 12, and 6 and the by mirror symmetry related positions. The differences in energy are mainly due to the differences in the zeolite framework energy.

Isomorphous replacement in electron diffraction of wet crystals of rat hemoglobin

1983 ◽  
Vol 41 ◽  
pp. 446-447
Author(s):  
William F. Tivol ◽  
Murray Vernon King ◽  
D. F. Parsons
Keyword(s):  
Electron Diffraction ◽  
Heavy Atom ◽  
Isomorphous Substitution ◽  
X Ray Diffraction ◽  
Salt Solutions ◽  
X Ray ◽  
Isomorphous Replacement ◽  
Structure Factors ◽  
Diffraction Structure ◽  
The Mean

Feasibility of isomorphous substitution in electron diffraction is supported by a calculation of the mean alteration of the electron-diffraction structure factors for hemoglobin crystals caused by substituting two mercury atoms per molecule, following Green, Ingram & Perutz, but with allowance for the proportionality of f to Z3/4 for electron diffraction. This yields a mean net change in F of 12.5%, as contrasted with 22.8% for x-ray diffraction.Use of the hydration chamber in electron diffraction opens prospects for examining many proteins that yield only very thin crystals not suitable for x-ray diffraction. Examination in the wet state avoids treatments that could cause translocation of the heavy-atom labels or distortion of the crystal. Combined with low-fluence techniques, it enables study of the protein in a state as close to native as possible.We have undertaken a study of crystals of rat hemoglobin by electron diffraction in the wet state. Rat hemoglobin offers a certain advantage for hydration-chamber work over other hemoglobins in that it can be crystallized from distilled water instead of salt solutions.

ION Exchange Characterisation of Modified Zeolite

1992 ◽  
Vol 26 (9-11) ◽  
pp. 2269-2272 ◽  
Author(s):  
Š Cerjan-Stefanovic ◽  
M. Kaštelan-Macan ◽  
T. Filipan
Keyword(s):  
Drinking Water ◽  
Ion Exchange ◽  
Anion Exchange ◽  
Natural Zeolite ◽  
Deionized Water ◽  
Isomorphous Substitution ◽  
Waste Waters ◽  
Modified Zeolite ◽  
Water Drinking

Isomorphous substitution of phosphorus into a natural zeolite affords the possibility to change the overall framework charge from negative to positive. The substances so created should be used for purification of waste waters. The work describes the preparation of phosphated zeolite, their characterisation and examples of their anion exchange of NO3 on observed in deionized water, drinking water and in the solution containing varying amounts of nitrate.

Structural/Texture Evolution During Facile Substitution of Ni into ZSM-5 Nanostructure vs. its Impregnation Dispersion Used in Selective Transformation of Methanol to Ethylene and Propylene

2020 ◽  
Vol 23 ◽  
Author(s):  
Parisa Sadeghpour ◽  
Mohammad Haghighi ◽  
Mehrdad Esmaeili
Keyword(s):  
High Temperature ◽  
Physicochemical Properties ◽  
Active Sites ◽  
Catalytic Performance ◽  
Fixed Bed Reactor ◽  
Light Olefins ◽  
Isomorphous Substitution ◽  
Impregnation Method ◽  
Hydrothermal Temperature ◽  
X Ray

Aim and Objective: Effect of two different modification methods for introducing Ni into ZSM-5 framework was investigated under high temperature synthesis conditions. The nickel successfully introduced into the MFI structures at different crystallization conditions to enhance the physicochemical properties and catalytic performance. Materials and Methods: A series of impregnated Ni/ZSM-5 and isomorphous substituted NiZSM-5 nanostructure catalysts were prepared hydrothermally at different high temperatures and within short times. X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray (EDX), Brunner, Emmett and Teller-Barrett, Joyner and Halenda (BET-BJH), Fourier transform infrared (FTIR) and Temperature-programmed desorption of ammonia (TPDNH3) were applied to investigate the physicochemical properties. Results: Although all the catalysts showed pure silica MFI–type nanosheets and coffin-like morphology, using the isomorphous substitution for Ni incorporation into the ZSM-5 framework led to the formation of materials with lower crystallinity, higher pore volume and stronger acidity compared to using impregnation method. Moreover, it was found that raising the hydrothermal temperature increased the crystallinity and enhanced more uniform incorporation of Ni atoms in the crystalline structure of catalysts. TPD-NH3 analysis demonstrated that high crystallization temperature and short crystallization time of NiZSM-5(350-0.5) resulted in fewer weak acid sites and medium acid strength. The MTO catalytic performance was tested in a fixed bed reactor at 460ºC and GHSV=10500 cm3 /gcat.h. A slightly different reaction pathway was proposed for the production of light olefins over impregnated Ni/ZSM-5 catalysts based on the role of NiO species. The enhanced methanol conversion for isomorphous substituted NiZSM-5 catalysts could be related to the most accessible active sites located inside the pores. Conclusion: The impregnated Ni/ZSM-5 catalyst prepared at low hydrothermal temperature showed the best catalytic performance, while the isomorphous substituted NiZSM-5 prepared at high temperature was found to be the active molecular sieve regarding the stability performance.

Study of Coke Distribution in HZSM-5 by 129-Xe NMR

1992 ◽  
Vol 57 (4) ◽  
pp. 733-738 ◽  
Author(s):  
Jean L. Bonardet ◽  
M. C. Barrage ◽  
Jack P. Fraissard ◽  
Ludmila Kubelková ◽  
Jana Nováková ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Zeolite Framework

The location of coke formed during conversion of methanol or acetone on HZSM-5 zeolites has been examined using 129-Xe NMR spectroscopy. The results show that the type of reaction and the method of regeneration have great importance for the location of carbonaceous residues inside or outside the zeolite framework.

scholarly journals Synthesis of Hierarchical MOR-Type Zeolites with Improved Catalytic Properties

Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4508
Author(s):  
Zeinab Mcheik ◽  
Ludovic Pinard ◽  
Joumana Toufaily ◽  
Tayssir Hamieh ◽  
T. Jean Daou
Keyword(s):  
Catalytic Activity ◽  
Amorphous Materials ◽  
Essential Role ◽  
Aluminum Content ◽  
Catalytic Properties ◽  
Hexadecyltrimethylammonium Bromide ◽  
Zeolite Framework ◽  
Ctab Concentration ◽  
Porous Volume ◽  
Synthesis Medium

Hierarchical MOR-type zeolites were synthesized in the presence of hexadecyltrimethylammonium bromide (CTAB) as a porogen agent. XRD proved that the concentration of CTAB in the synthesis medium plays an essential role in forming pure hierarchical MOR-type material. Above a CTAB concentration of 0.04 mol·L−1, amorphous materials are observed. These hierarchical mordenite possess a higher porous volume compared to its counterpart conventional micrometer crystals. Nitrogen sorption showed the presence of mesoporosity for all mordenite samples synthesized in the presence of CTAB. The creation of mesopores due to the presence of CTAB in the synthesis medium does not occur at the expense of zeolite micropores. In addition, mesoporous volume and BET surface seem to increase upon the increase of CTAB concentration in the synthesis medium. The Si/Al ratio of the zeolite framework can be increased from 5.5 to 9.1 by halving the aluminum content present in the synthesis gel. These synthesized hierarchical MOR-type zeolites possess an improved catalytic activity for n-hexane cracking compared to large zeolite crystals obtained in the absence of CTAB.

scholarly journals Ultrasound-Assisted Preparation of Mo/ZSM-5 Zeolite Catalyst for Non-Oxidative Methane Dehydroaromatization

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 313
Author(s):  
Heidy Ramirez-Mendoza ◽  
Mafalda Valdez Lancinha Pereira ◽  
Tom Van Gerven ◽  
Cécile Lutz ◽  
Ignacio Julian
Keyword(s):  
Catalytic Activity ◽  
Ion Exchange ◽  
Active Sites ◽  
Chemical Properties ◽  
Successful Implementation ◽  
Metal Dispersion ◽  
Zeolite Framework ◽  
Dispersed Catalysts ◽  
Methane Dehydroaromatization ◽  
Ultrasound Assisted

The activity and selectivity of Mo/ZSM-5, benchmarking catalyst for the non-oxidative dehydroaromatization of methane, strongly depend on the cluster size, spatial distribution, and chemical environment of the Mo-based active sites. This study discloses the use of an ultrasound-assisted ion-exchange (US-IE) technique as an alternative Mo/ZSM-5 synthesis procedure in order to promote metal dispersion along the zeolite framework. For this purpose, a plate transducer (91.8 kHz) is employed to transmit the ultrasonic irradiation (US) into the ion-exchange reactor. The physico-chemical properties and catalytic activity of samples prepared under the said irradiation procedure and traditional impregnation (IWI) method are critically evaluated. Characterization results suggest that US neither affects the crystalline structure nor the particle size of the parent zeolite. However, US-IE promotes molybdenum species dispersion, avoids clustering at the external fresh zeolite surface and enhances molybdate species anchoring to the zeolite framework with respect to IWI. Despite the improved metal dispersion, the catalytic activity between catalysts synthesized by US-IE and IWI is comparable. This suggests that the sole initial dispersion enhancement does not suffice to boost the catalyst productivity and further actions such ZSM-5 support and catalyst pre-conditioning are required. Nevertheless, the successful implementation of US-IE and the resulting metal dispersion enhancement pave the way toward the application of this technique to the synthesis of other dispersed catalysts and materials of interest.

scholarly journals Theoretical Study of Zirconium Isomorphous Substitution into Zeolite Frameworks

Molecules ◽  
2019 ◽  
Vol 24 (24) ◽  
pp. 4466
Author(s):  
Duichun Li ◽  
Bin Xing ◽  
Baojun Wang ◽  
Ruifeng Li
Keyword(s):  
Acid Site ◽  
Density Functional ◽  
Theoretical Study ◽  
Atomic Radius ◽  
Acid Sites ◽  
Isomorphous Substitution ◽  
Dispersion Correction ◽  
Brønsted Acidity ◽  
Functional Theory ◽  
Brönsted Acidity

Systematic periodic density functional theory computations including dispersion correction (DFT-D) were carried out to determine the preferred location site of Zr atoms in sodalite (SOD) and CHA-type topology frameworks, including alumino-phosphate-34 (AlPO-34) and silico-alumino-phosphate-34 (SAPO-34), and to determine the relative stability and Brönsted acidity of Zr-substituted forms of SOD, AlPO-34, and SAPO-34. Mono and multiple Zr atom substitutions were considered. The Zr substitution causes obvious structural distortion because of the larger atomic radius of Zr than that of Si, however, Zr-substituted forms of zeolites are found to be more stable than pristine zeolites. Our results demonstrate that in the most stable configurations, the preferred favorable substitutions of Zr in substituted SOD have Zr located at the neighboring sites of the Al-substituted site. However, in the AlPO-34 and SAPO-34 frameworks, the Zr atoms are more easily distributed in a dispersed form, rather than being centralized. Brönsted acidity of substituted zeolites strongly depends on Zr content. For SOD, substitution of Zr atoms reduces Brönsted acidity. However, for Zr-substituted forms of AlPO-34 and SAPO-34, Brönsted acidity of the Zr-O(H)-Al acid sites are, at first, reduced and, then, the presence of Zr atoms substantially increased Brönsted acidity of the Zr-O(H)-Al acid site. The results in the SAPO-34-Zr indicate that more Zr atoms substantially increase Brönsted acidity of the Si-O(H)-Al acid site. It is suggested that substituted heteroatoms play an important role in regulating and controlling structural stability and Brönsted acidity of zeolites.

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