Siting and Distribution of Framework Aluminium Atoms in Silicon-Rich Zeolites and Impact on Catalysis

Dědeček, Jiřı́; Sobalı́k, Zdenĕk; Wichterlová, Blanka

doi:10.1080/01614940.2012.632662

Cited by 388 publications

(264 citation statements)

References 123 publications

Supporting

Mentioning

256

Contrasting

Unclassified

Order By: Relevance

“…Also the hydrophilic/hydrophobic features, controlled by varying the SiO 2 /Al 2 O 3 ratio (SAR), can influence the behaviour of zeolites towards polar/non-polar reactants and products in adsorption and catalytic processes. In fact, the roles played both by calcination and by SAR on catalytic activity of beta zeolites received great attention [25,26]. However there are only few works dealing with the effects of both chemical the composition and thermal treatments of beta on the adsorption properties toward solutes from water solutions.…”

Section: Introductionmentioning

confidence: 99%

Effect of Silica Alumina Ratio and Thermal Treatment of Beta Zeolites on the Adsorption of Toluene from Aqueous Solutions

et al. 2017

View full text Add to dashboard Cite

Abstract:The adsorption of toluene from aqueous solutions onto hydrophobic zeolites was studied by combining chromatographic, thermal and structural techniques. Three beta zeolites (notated BEAs, since they belong to BEA framework type), with different SiO 2 /Al 2 O 3 ratios (i.e., 25, 38 and 360), before and after calcination, were tested as adsorbents of toluene from aqueous media. This was performed by measuring the adsorbed quantities of toluene onto zeolites in a wide concentration range of solute. The adsorption data were fitted with isotherms whose models are based on surface heterogeneity of the adsorbent, according to the defective structure of beta zeolites. The thermal treatment considerably increases the adsorption of toluene, in the low concentration range, on all BEAs, probably due to surface and structural modifications induced by calcination. Among the calcined BEAs, the most hydrophobic zeolite (i.e., that with SiO 2 /Al 2 O 3 ratio of 360) showed the highest binding constant, probably due to its high affinity for an organophilic solute such as toluene. The high sorption capacity was confirmed by thermogravimetric analyses on BEAs, before and after saturation with toluene.

show abstract

Section: Introductionmentioning

confidence: 99%

Effect of Silica Alumina Ratio and Thermal Treatment of Beta Zeolites on the Adsorption of Toluene from Aqueous Solutions

et al. 2017

View full text Add to dashboard Cite

show abstract

“…The a-and b-sites restrict the FER cavity from perpendicular directions and represent sites for accommodation of bare divalent cations. 1,29 Our model structure is composed of a-and b-sites containing silicon/aluminum atoms forming the two 6-rings and O atoms connected to the T-sites, shown in Fig. 2(b) and (c).…”

mentioning

confidence: 99%

“…1 The Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) spectroscopy of 29 Si represents a standard method to address the Si-Al connectivity, however, not providing information about the absolute position of aluminum and silicon atoms inside the framework. 27 Al MAS NMR is sensitive to the averaged Al-O-Si angle and therefore partially yields aluminum occupation.…”

mentioning

confidence: 99%

Distribution of aluminum over different T-sites in ferrierite zeolites studied with aluminum valence to core X-ray emission spectroscopy

Bohinc

Hoszowska

Dousse

et al. 2017

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

The potential of valence to core Al X-ray emission spectroscopy to determine aluminum distribution in ferrierite zeolites was investigated. The recorded emission spectra of four samples prepared with different structure directing agents exhibit slight variations in the position of the main emission peak and the intensity of its low energy shoulder. Theoretical calculations indicate that an increased intensity of the Kb x shoulder in the Al emission spectra can be linked to a predominant occupation of the T3 site by a single aluminum atom. This study thus suggests that valence to core X-ray emission spectroscopy can be applied to help determine the occupation of aluminum at crystallographic T-sites in zeolites.Zeolites are microporous crystalline aluminosilicates whose frameworks are composed of corner sharing TO 4 tetrahedra (T = either silicon or aluminum). The mutual arrangement of these subunits defines the framework structure which is characterized by periodical pores and channels. Replacing silicon atoms with aluminum atoms at the T-sites introduces a local negative charge to the framework which can be stabilized by protons or cations, which confer the catalytic activity to the zeolite. The catalytic activity is therefore directly related to the positioning of aluminum atoms within the zeolite framework.The determination of both the location of aluminum atoms at individual T-sites (aluminum sitting) and the mutual arrangement of several aluminum atoms (aluminum distribution) remains an open question in zeolite structural analysis.1 The Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR) spectroscopy of 29Si represents a standard method to address the Si-Al connectivity, however, not providing information about the absolute position of aluminum and silicon atoms inside the framework.27 Al MAS NMR is sensitive to the averaged Al-O-Si angle and therefore partially yields aluminum occupation. sequences, where at least one aluminum atom is located in the second coordination shell of another aluminum atom, has been determined. Due to a large penetration depth of X-rays, X-ray-based techniques are suited for the characterization of catalysts under reaction conditions. X-ray absorption fine structure (EXAFS) analysis combined with DFT simulations showed a preference of aluminum for the T sites in the 4-ring of zeolite beta. 7 X-ray absorption near-edge structure spectroscopy (XANES) was successfully applied to monitor aluminum coordination as a function of temperature and gas composition. 8 X-ray diffraction (XRD) techniques are, in general, not suitable for distinguishing silicon and aluminum atoms because of their similar scattering power. The structural changes induced by introducing aluminum, mainly an elongation of the T-O distance by ca. 0.1 Å, can in some cases indicate the position of aluminum. 9 However, this difference is obscured by the low Al/Si proportion at that specific T-site. Using the X-ray standing waves, the location of aluminum in scolecite (NAT framework type) has been determined. 10 Alt...

show abstract

“…The fi ndings on the sitespecifi c distribution of Al on T sites of the silicate framework were transferred then into synthesis recipes with the aim to direct Al on distinct T sites [ 81 , 82 ]. In catalytic experiments, the impact of distinct Al distribution pattern on the performance and product distribution was exemplifi ed [ 83 ]. Similarly, studies on SCR catalysis (selected catalytic reduction) using MFI-type materials with distinct Al distribution and, therefore, specifi c cation sites were published [ 84 ].…”

Section: Heteroatom Localization and The Problem Of Reactive Centers mentioning

confidence: 99%

Structure Analysis in Zeolite Research: From Framework Topologies to Functional Properties

Gies

Marler

2016

Green Chemistry and Sustainable Technology

View full text Add to dashboard Cite

The solution and the refi nement of crystal structures of microporous materials are of prime interest for the synthesis and application community in porous solid research. The structure of a material reveals not only the geometry of the bonding network of the rigid framework but also the location of the nonframework constituents responsible for the porosity of the material. Analyzing the structure, therefore, unveils the synthesis protocol including nucleation and growth. The properties related to the porous net correspond to the local structure, i.e., the composition and the geometry of local confi gurations. It thus inspires ideas about possible properties and modifi cations to improve functionality.The chapter is intended to highlight the contribution of crystallographic analysis of microporous materials and in particular porous silicates to the success of this class of materials. It does not survey the continuous growth of materials in the fi eld but show how the insight gained from crystallographic studies acted as catalyst in the further development of the fi eld.

show abstract

Siting and Distribution of Framework Aluminium Atoms in Silicon-Rich Zeolites and Impact on Catalysis

Cited by 388 publications

References 123 publications

Effect of Silica Alumina Ratio and Thermal Treatment of Beta Zeolites on the Adsorption of Toluene from Aqueous Solutions

Effect of Silica Alumina Ratio and Thermal Treatment of Beta Zeolites on the Adsorption of Toluene from Aqueous Solutions

Distribution of aluminum over different T-sites in ferrierite zeolites studied with aluminum valence to core X-ray emission spectroscopy

Structure Analysis in Zeolite Research: From Framework Topologies to Functional Properties

Contact Info

Product

Resources

About