Framework Of Zeolite Beta Research Articles

Influence of the nature and environment of cobalt on the catalytic activity of Co-BEA zeolites in selective catalytic reduction of NO with ammonia

The influence of cobalt environment on the catalytic properties of CoxSiBEA zeolite in selective catalytic reduction of NO with ammonia was studied. Catalysts were prepared by a two-step postsynthesis method which consists, in the first step, of dealumination of parent BEA zeolite to obtain aluminum-free SiBEA support and then, in the second step, of contacting the obtained material with an aqueous solution of cobalt nitrate. DR UV–Vis and XPS results showed that cobalt was successfully incorporated into zeolite beta framework as isolated mononuclear Co(II). The presence of only isolated framework mononuclear Co(II) was evidenced in CoxSiBEA with cobalt content lower than 2 wt % and both isolated framework mononuclear Co(II) and extra-framework octahedral Co(II) for Co3.0SiBEA catalyst. FTIR investigation of pyridine adsorption revealed that the incorporation of cobalt into zeolite framework led to a creation of new Lewis acidic sites which are responsible for high activity in SCR of NO with ammonia. The catalytic activity of CoxSiBEA in selective catalytic reduction of NO with ammonia as reducing agent strongly depends on the nature and environment of cobalt in BEA structure. The single-site Co2.0SiBEA zeolite catalyst was the most active among tested, with maximum NO conversion about 80% at 673 K. In contrast, Co3.0SiBEA catalyst containing a mixture of framework and extra-framework Co(II) had lower activity in SCR of NO process than Co2.0SiBEA at higher temperature due to a competitive reaction of ammonia oxidation to NO.

Synthesis of (h0l)-oriented zeolite Fe-beta membrane

The continuous and intergrown zeolite Fe-beta membrane was synthesized on the porous α-Al2O3 substrate by fluoride route in combination with a secondary seeded growth method. XRD and SEM results show that the synthesized zeolite Fe-beta membrane and all-silica zeolite beta membrane are (h0l)-oriented. The thickness of zeolite Fe-beta membrane is just 5.6μm, which is thinner than that of the all-silica zeolite beta membrane (8.5μm). Leaking tests confirm that non-zeolitic pores in the synthesized membranes are negligible. XRD patterns of the powdery samples which were collected from the bottom of the autoclave after secondary growth indicated that most of iron is incorporated in the zeolite beta framework.

Direct hydrothermal synthesis and characterization of framework-substituted Co(Mn)-Beta zeolites

Isomorphously substituted Co(Mn)-Beta zeolites were directly synthesized through a static hydrothermal approach. The silica-metal precursor was prepared by co-hydrolysis of tetraethylorthosilicate with cobalt or manganese nitrates in acidic media, which was adjusted to the strong basic condition by adding the structural directing agent (tetraethylammonium hydroxide) and Al source (sodium aluminate) for the subsequent hydrothermal crystallization. The products were characterized by X-ray diffraction, inductively coupling plasma elemental analysis, Brunauer–Emmett–Teller surface area, nitrogen sorption isotherm, FT-IR, UV–vis, and SEM. The results show that Co or Mn ions are incorporated into the framework of zeolite Beta, and the thus obtained Co(Mn)-Beta zeolites are nano-structured zeolite crystallites. The acidic co-hydrolysis/considention is proposed to facilitate the formation of metal-bearing nucleus for growing Co(Mn)-Beta crystals.

Effect of Al on Zeolite Beta Solid State Chemistry

Zeolite beta free of alkali has been prepared over a wide range of Al concentrations in the presence of tetraethylammonium (TEA+). The as obtained materials have been characterized by a combination of magic angle spinning nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermal gravimetric analysis. The results show that zeolite beta materials exchange [[≡SiO]− TEA+] ion pairs for [[AlO2]− TEA+] ion pairs upon addition of more Al into the synthesis solutions. The term [[AlO2]− TEA+] accurately describes the 4-connected structure of Al in the zeolite beta framework. On the other hand, the [[≡SiO]− TEA+] ion pair descriptor hides the fact that these ion pairs are accompanied by the presence of high concentrations of Q3-Si(3Si, OH) and Q3-Si(3Si, O−) units. The isomorphous substitution of Al into the zeolite beta framework leads to Bronsted acid sites in samples which have longer coherence length and higher connectivity. Upon removal of the structure director from high Al zeolite beta samples the unit cell contracts along the c-axis but not along other axes presumably due to geometric flexibility provided by the parallel rows of oxygen atoms present along a and b directions.

Crystallization behavior of zeolite beta from acid-leached metakaolin

Well-crystallized zeolite beta was synthesized by using acid-leached metakaolin as the silica-alumina source and tetraethylammonium hydroxide structure-directing agent. The influence of the composition of the reaction mixture on product crystallinity was investigated, and the crystallization process was studied by examining solid samples obtained at different synthesis times. Results showed that the acid-leached metakaolin was fully converted into soluble aluminum and silicon species, which is crucial for the formation of well-crystallized zeolite beta. At the beginning of the crystallization process, these soluble aluminum and silicon species formed a aluminum-rich intermediate structure with layer morphology. With the crystallization proceeding, more silicon species were incorporated into the zeolite beta framework and the layered structure was changed into spherical particles of zeolite beta with high SiO2/Al2O3 ratio and crystallinity.

Water Resistant, Catalytically Active Nb and Ta Isolated Lewis Acid Sites, Homogeneously Distributed by Direct Synthesis in a Beta Zeolite

Nb and Ta solid Lewis acids able to work in the presence of water have been prepared by incorporating these elements in the framework of zeolite Beta by a direct synthesis procedure. Characterization of the samples by extended X-ray absorption fine structure and X-ray absorption near edge structure indicate that the calcined samples contain tetracoordinated Nb5+ (or Ta5+) with three siloxane bridges and one Nb═O (or Ta═O) bonds. The presence of Lewis acidity has been characterized by IR of adsorbed pyridine and cyclohexanone. The Nb- and Ta-Beta samples are catalytically active for the Meerwein−Ponndorf−Verley reduction of cyclohexanone with 2-butanol and the etherification of 2-butanol with p-methoxybenzalcohol. Both reactions can be successfully combined in a domino reaction to obtain the ether starting with p-methoxybenzaldehyde. The catalytic activity of Nb- and Ta-Beta has been compared with that of the homogeneous counterparts (NbCl5 and TaCl5) reported in the literature for the intramolecular carbo...

Crystallization behavior of zeolite beta with balanced incorporation of silicon and aluminum synthesized from alkali metal cation-free mixture

Zeolite beta with the SiO 2/Al 2O 3 ratios ranging from 20 to 60 is synthesized from alkali metal cation-free aluminosilicate gel under basic condition. MTW-type zeolite is crystallized as an impurity phase at higher SiO 2/Al 2O 3 ratios. The presence of sodium cations also induces the formation of impurity phases. The total amount of tetraethylammonium cations occluded in the crystals are related to the crystalline phases of the obtained products; that is, the amount of tetraethylammonium cations are the same in all of the zeolite beta products while smaller amounts are occluded in the MTW products. The SiO 2/Al 2O 3 molar ratios of the obtained zeolites are almost the same as those of the initial mixtures, which is an unusual phenomenon in hydrothermally crystallized zeolite beta in hydroxide media, indicating balanced incorporation of silicon and aluminum. Since the reactivity of aluminum species strongly affects the incorporation of aluminum into the framework of zeolite beta, balance of yields of silicon and aluminum could be tuned. In other words, the SiO 2/Al 2O 3 ratios could be adjusted by balancing the reactivity of aluminum and silicon sources. Acylation of 2-methoxynaphthalene with acetic anhydride is carried out as a test reaction. The zeolite beta synthesized from alkali metal cation-free gel shows a higher catalytic activity for acylation of 2-methoxynaphthalene than that synthesized with alkali metal cation.

Preparation and characterization of zeolite beta with low SiO2/Al2O3 ratio

Zeolite beta with a low SiO2/Al2O3 ratio was synthesized by a novel two-step process. The synthesized sample was characterized with XRD, SEM, FTIR, and N2 adsorption-desorption and solid-state MAS NMR. The results showed that aluminium species were inserted into the framework of zeolite beta. The BET surface area, volume, and particle size of the zeolite beta sample decreased with decreasing SiO2/Al2O3 ratio. Our process was proved an efficient route to synthesize zeolite beta with a low SiO2/Al2O3 ratio.

Characterization of zeolite Beta grown in microgravity

Zeolite Beta was grown in the microgravity environment (10 −3–10 −5 g) of the International Space Station from the precursor solutions held unmixed until activation on orbit. The space-grown product had the same spheroidal and truncated square bipyramidal particle morphology, and close to identical “surface” and framework Si/Al ratio, and the same unit cell dimensions as the terrestrial/control product. However, the flight particles were ∼10% larger on average. The less intense terminal silanol infrared band acquired for the flight particles was consistent with their larger average size, but may also indicate a more uniform or “smoother” surface. The Meerwein–Ponndorf–Verley reduction of 4- tert-butylcyclohexanone with 2-propanol performed using the heat-treated flight samples showed lower catalyst activity and higher tr-4- tert-butylcyclohexanol selectivity when compared with the terrestrial/controls. This suggests smaller amounts of aluminum partially coordinated to the framework (as characterized by the ∼3670 cm −1 infrared band), and more space being available in the straight channels of the flight zeolite Beta for hydrogen transfer (i.e., no steric hindrances). This is consistent with a higher degree of perfection and order in the space-grown zeolite Beta framework, and higher degree of thermal stability of the flight product.

Characterization of Ga-substituted zeolite Beta by X-ray absorption spectroscopy

The incorporation of Ga into the framework of zeolite Beta has been evidenced by X-ray absorption spectroscopy. Analysis of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) data reveals the atomic environment of Ga in zeolite Beta. Both techniques provide evidence that calcination and dehydration of the synthesized zeolites provokes changes in the Ga atomic environment, which can be understood as due to the migration of Ga from framework sites to extra-framework positions. The XANES results allow calculation of the atomic fraction at both positions.

A new and simple method for the preparation of active Ti-? zeolite catalysts

Incorporation of titanium into the framework of zeolite beta was achieved by simply treating Al-β zeolite with an ammonium titanyl oxalate solution followed by air calcinations; the material obtained is a very active catalyst for the epoxidation of olefins.

Acidity and catalytic activity of B-A1 beta zeolite

Boron atoms incorporated into the framework of zeolite beta during synthesis are nearly quantitatively removed from the solid after activation by thermal/hydrothermal treatments followed by ion exchange. Boron extraction is accompanied by the removal of small amounts of aluminium and silicon and results in the creation of isolated defect sites. The acidity and the cracking properties of the activated zeolite are governed by the aluminium content, independently of the composition of the parent material.

Synthesis of titanoaluminosilicates isomorphous to zeolite Beta, active as oxidation catalysts

Isomorphous replacement of Si by Ti in the low aluminum-containing zeolite Beta framework has been achieved by direct synthesis. The crystallization must be carried out in the absence of alkali cations, as they promote the precipitation of amorphous titanosilicate. The incorporation of Ti to the framework has been characterized by XRD, i.r., and thermal analysis. Ti is believed to perform a stabilizing role of the Beta framework similar to that of Al. The large pores of [Al, Ti]-Beta compared to TS-1 allow the use of this material as a catalyst in the selective oxidation of cyclododecane with hydrogen peroxide.

Synthesis and characterization of gallosilicates and galloaluminosilicates isomorphous to zeolite Beta

Partial and total replacement of Al by Ga in the zeolite Beta framework has been achieved by synthesis. This causes the acid strength of the zeolite Bro¨nsted acid centers to decrease as reflected in the increase in the wavenumber of the acid OH infrared band (3615–3625 cm −1). Modifications on crystal habit, crystal size, effective free-pore volume, and thermal stability of T III atoms in the framework are also discussed. The efficiency in the incorporation of Si to the zeolite Beta is shown to be higher in the Ga system than in the Al system.

Synthesis of a titaniumsilicoaluminate isomorphous to zeolite beta and its application as a catalyst for the selective oxidation of large organic molecules

The isomorphous substitution of Si by Ti in the zeolite Beta framework by direct hydrothermal synthesis gives rise to useful catalysts for the selective oxidation of small and large organic compounds.

Mössbauer spectroscopic study of ferrisilicate analog of zeolite BETA

Mössbauer spectroscopic studies on an as-synthesized sample of ferrisilicate analog of zeolite BETA, which was substantially free from Al (SiO2/Al2O3 > 2000) have been carried out at rt, 4.2 K, and in the presence of an externally applied field (4.13 T) at 4.2 K. The broadness of the sole peak in the spectra recorded at rt. and at 4.2 K, isomer shift (IS) of 0.22 mm/s at rt. and 0.32 mm/s at 4.2 K, and the quite narrow and sharp hyperfine sextet in the spectrum of 4.2 K with externally applied field (4.13 T), clearly demonstrate that most of the Fe3+ ions, if not all, are well dispersed and present in the tetrahedral framework of zeolite BETA.