Two new three-dimensional twelve-ring zeolite frameworks of which zeolite beta is a disordered intergrowth

Treacy, M.M.J.; Newsam, J. M.

doi:10.1038/332249a0

Cited by 472 publications

(256 citation statements)

References 4 publications

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“…Based on the previously reported TPR study [1], five different species can be found in a Pt supported zeolite Beta, corresponding to: PtO (80 • C) and PtO 2 (160-180 • C) located in zeolite channels; Pt 2+ (250 • C) and Pt 4+ (320-350 • C) ions, located inside the zeolite formed through ion-exchange process (replacing H + ions which are produced by heating the NH 4+ ions containing zeolite beta, which were present as charge compensating species for the negative charge produced by substituting Al 3+ in place Si 4+ in the framework) [42,43]; and finally Pt 2+ ions coordinated to silanol groups forming Pt-(OSi≡) 2−y y species (430-450 • C) as described in the literature [44,45]. It must be noted that the Al-containing zeolite Beta prepared in a OH − medium (which is the typical commercial zeolite Beta) possess a large number of terminal silanol groups and defects of aluminium, generating the so-called hydroxyl nests composed of four adjacent OH − groups.…”

Section: Temperature-programmed Reduction (Tpr)mentioning

confidence: 99%

Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

Roldán

Beale²,

Sánchez‐Sánchez

et al. 2008

Journal of Catalysis

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A series of mono-and bi-metallic (Pt and/or Pd) impregnated zeolite Beta samples have been prepared, characterized using a number of experimental techniques and catalytically tested for the hydroisomerization of a mixture of light paraffins. In particular, the effect of the order of Pt and Pd impregnation on the type/structure of the metallic species of the zeolite support and on the catalytic activity has been studied. Studied samples included a zeolite Beta in which both Pt and Pd (0.5 wt% of each) were simultaneously impregnated (and subsequently calcined and reduced) and two equally metal-loaded samples where the metals were sequentially impregnated (samples Pt*-Pd/Beta and Pd*-Pt/Beta, in which Pt and Pd were impregnated first, respectively). Mono-metallic samples were also prepared for comparison. TPR, DR-UV-visible, TEM, and XAS studies confirm that the order of impregnation plays a key role in the formation of metallic particles, influencing aspects as decisive in their catalytic behavior as their size, their dispersion and their composition (e.g., mono-or bi-metallic). The initial impregnation of Pd and subsequently of Pt produces a higher number of hetero-metallic (Pt-Pd) bonds than the simultaneous co-impregnation and especially for the impregnation in reverse order, which does not produce Pt-Pd bonds in a detectable amount. Based on the results from the different characterization techniques, a model of the metal distribution and composition of the particles was proposed for each bi-metallic sample. In good agreement, the order of the catalytic activity was found to be Pd*-Pt/Beta > Pd-Pt/Beta > Pt/Beta > Pt*-Pd/Beta > Pd/Beta, making clear that not only the presence of both metals, but also an adequate preparation method generating a high number of hetero-metallic bonds must be taken into account to improve the catalytic properties in relation to the mono-metallic samples.

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Section: Temperature-programmed Reduction (Tpr)mentioning

confidence: 99%

Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

Roldán

Beale²,

Sánchez‐Sánchez

et al. 2008

Journal of Catalysis

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“…The large pore beta zeolite is structurally disordered and its framework structure was described as a three-dimensional intersecting channel system [20][21][22]. The beta crystalline structure is an intergrowth of two or three polymorphs and has high density of stacking defects due to partially coordinated aluminum [23].…”

Section: Introductionmentioning

confidence: 99%

“…For carrying out various kinds of organic transformations zeolite catalysts of different acid strengths and textural properties are required. Zeolite beta is a right candidate due to its optimal pore dimensions and higher surface area [20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Dealumination of Zeolite Beta Catalyst Under Controlled Conditions for Enhancing its Activity in Acylation and Esterification

et al. 2009

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This work deals with the dealumination of zeolite beta (HBEA) under different conditions to optimize its catalytic performance. The dealumination was carried out either using oxalic or tartaric acid solution of different pH values or steaming up to 500˚C. The dealuminated zeolite samples were characterized using X-ray diffraction (XRD), N 2 -physisorption, ICP, 27 Al NMR and NH 3 -TPD. Their catalytic activities were studied for acylation reaction of 2-methoxy naphthalene or naphthalene with acetic anhydride and esterification of benzyl alcohol with hexanoic acid. Among the dealuminated samples examined, those treated with oxalic acid or tartaric acid at pH 2 showed high activity. The high activity can be correlated with the relative increase in the amount of strong acid sites and with the enhanced accessibility of the reactants to the active sites, which are caused by removal of extra-framework Al species on the acid treatments.

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“…By combining the results of many different experimental methods [8][9][10] , the zeolite structure database 2 was established. Some insight into the aluminium distribution was obtained by NMR and neutron diffraction and by replacing aluminium with atoms such as Ti, Fe, Ga and B (refs 11-16).…”

mentioning

confidence: 99%

Determining the aluminium occupancy on the active T-sites in zeolites using X-ray standing waves

et al. 2008

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Zeolites are microporous crystalline materials that find wide application in industry, for example, as catalysts and gas separators, and in our daily life, for example, as adsorbents or as ion exchangers in laundry detergents 1 . The tetrahedrally coordinated silicon and aluminium atoms in the zeolite unit cell occupy the so-called crystallographic T-sites. Besides their pore size, the occupation of specific T-sites by the aluminium atoms determines the performance of the zeolites 2 . Despite its importance, the distribution of aluminium over the crystallographic T-sites remains one of the most challenging, unresolved issues in zeolite science. Here, we report how to determine unambiguously and directly the distribution of aluminium in zeolites by means of the X-ray standing wave technique 3 using brilliant, focused X-rays from a thirdgeneration synchrotron source. We report in detail the analysis of the aluminium distribution in scolecite, which demonstrates how the aluminium occupancy in zeolites can systematically be determined.Zeolites are widely used materials with a very wide range of applications. They are used in households in laundry detergents and in industry as catalysts for petrochemical refining and they have become increasingly important in fine-chemical production and in environmental applications; they are used as air and water purifiers and in heating and refrigerating, and they are used in agriculture as selective absorbents. With natural zeolites being discovered more than 200 years ago, intensive research is nowadays aimed at developing new, synthetic zeolites with tailored properties for specific tasks. The functionality of a zeolite is determined basically by just a few parameters: the size and connectivity of the pores and cages, the Si/Al ratio and the placement of the trivalent aluminium atoms at specific crystallographic T-sites. Among them, the placement of aluminium is still unknown for many zeolites because no generally applicable experimental method has been reported to solve this problem. This seriously hampers the understanding of the function of some technologically important zeolites and hinders the development of new zeolites with novel functionalities.In a zeolite, the replacement of a tetravalent silicon atom by a trivalent aluminium atom on a T-site places a negative charge on the framework, which is compensated by non-framework cations. These charge-compensating cations are loosely held in the pores and cages of a zeolite and can be exchanged by other cations. This property makes zeolites good cation exchangers, which are useful in water softening and in the removal of nuclear waste. When the charge-compensating species are protons or elements that are involved in oxidation or reduction reactions, zeolites become catalytically active in Brønsted and redox reactions, respectively. The Si/Al ratio and the aluminium distribution over the framework T-sites thus determine the species and the positions of the chargecompensating cations in a zeolite, which strongly affect its cata...

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Two new three-dimensional twelve-ring zeolite frameworks of which zeolite beta is a disordered intergrowth

Cited by 472 publications

References 4 publications

Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

Effect of the impregnation order on the nature of metal particles of bi-functional Pt/Pd-supported zeolite Beta materials and on their catalytic activity for the hydroisomerization of alkanes

Dealumination of Zeolite Beta Catalyst Under Controlled Conditions for Enhancing its Activity in Acylation and Esterification

Determining the aluminium occupancy on the active T-sites in zeolites using X-ray standing waves

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