Crystallographic studies on the site selectivity of Ca<Superscript>2+</Superscript>, K<Superscript>+</Superscript>, and Rb<Superscript>+</Superscript> ions within zeolite Y (Si/Al = 1.56)

The single-crystals of Ca²⁺, K⁺-exchanged zeolite Y, and Ca²⁺, Rb⁺-exchanged zeolite Y were prepared by using flow method with mixed ion-exchange solution, whose Ca(NO₃)₂:KNO₃ mole ratios were 1:1 (crystal 1) and 1:100 (crystal 2), and Ca(NO₃)₂:RbNO₃ mole ratios were 1:1 (crystal 3) and 1:100 (crystal 4), respectively, with a total concentration of 0.05 M. They were fully dehydrated by vacuum dehydration at 723 K and 1 × 10^?6 Torr for 2 days. Their crystals were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group \(Fd \overline{3}\) m, respectively, and were refined to the final error indices R ₁/wR ₂ = 0.057/0.196, 0.073/0.223, 0.055/0.188, and 0.049/0.175 for crystals 1, 2, 3, and 4, respectively. In the structure of crystal 1 (|Ca₂₃K₂₉|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 23 Ca²⁺ ions per unit cell occupy sites I, II′, and II; 29 K⁺ ions per unit cell are at sites II′, II, and III′. In the structure of crystal 2 (|Ca_18.5K₃₈|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 18.5 Ca²⁺ ions per unit cell occupy sites I, I′, and II; 38 K⁺ ions are at sites I′, II, and III′. In the structure of crystal 3 (|Ca₂₇Rb₂₁|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 27 Ca²⁺ ions per unit cell occupy sites I, II′, and II; 21 Rb⁺ ions per unit cell are at sites II′, II, and III. In the structure of crystal 4 (|Ca₁₈Rb₃₉|[Si₁₁₇Al₇₅O₃₈₄]-FAU), 18 Ca²⁺ ions per unit cell occupy sites I and II; 39 Rb⁺ ions per unit cell are at sites I′, II′, II, III, and III′. In the four crystals, the Ca²⁺ ion which has much smaller size and higher charge than other cations such as K⁺ and Rb⁺ energetically preferred at site I and so the first to be filled on it. Unlike Ca²⁺ ion, no K⁺ and Rb⁺ ions are found at site I, which are clearly less favorable for K⁺ and Rb⁺ ions.     

Preparation of excessively Ni2+-exchanged zeolite Y (FAU,Si/Al = 1.70) and its single-crystal structure

A single crystal of excessively Ni²⁺-exchanged zeolite Y (FAU, Si/Al = 1.70) was prepared by exchange of |Na₇₁|[Si₁₂₁Al₇₁O₃₈₄]-FAU with an aqueous stream 0.05 M Ni(NO₃)₂ at 293 K and pH 4.9, followed by vacuum evacuation at room temperature and 1.3 × 10^?4 Pa. Its crystal structure was determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{ 3}\) m and was refined to the final error indices R ₁/wR ₂ = 0.0554/0.1557 for |Ni_24.7(NiOH)_12.1(Ni₂O(OH)₂)_4.8(Ni₄AlO₄)_1.7Na_17.0(H₃O)_6.9|[Si₁₁₇Al₇₅O₃₈₄]-FAU. Crystal has about 53 Ni²⁺ ions per unit cell, indicating the uptake of excess Ni(OH)₂, perhaps as NiOH⁺ ions. Some dealumination of the framework occurred during Ni²⁺ exchange. In this structure, Ni²⁺ ions occupy sites I, I′, II′, II, and III′. The residual Na⁺ ions are found at sites II′ and II. Due to the low pH of the Ni²⁺ exchange solution, some H₃O⁺ ions are observed. Nonframework oxygen atoms as oxide and hydroxide ions and orthoaluminate coordinate to some of Ni²⁺ ions to give NiOH⁺, Ni₂O(OH)₂, and Ni₄AlO₄ ³⁺ groups.     

Preparation and structural study of fully dehydrated,highly Mg2+-exchanged zeolite Y (FAU,Si/Al = 1.56) from undried methanol solution

Single-crystal of fully dehydrated, Mg²⁺-exchanged zeolite Y, |Mg_34.5Na₆|[Si₁₁₇Al₇₅O₃₈₄]-FAU (Si/Al = 1.56), was successfully prepared from undried methanol solution (water concentration 0.02 M). A crystal of Na-Y was treated with 0.05 M MgCl₂ ·6H₂O in the solvent at 333 K, followed by vacuum dehydration at 723 K and 1 × 10^?6 Torr for 2 days. Its structure was determined by single-crystal synchrotron X-ray diffraction techniques, in the cubic space group \(Fd\overline{3} m\) at 100 K. It was refined to the final error indices R ₁/wR ₂ = 0.0587/0.2210 with 1,294 reflections for which F _o > 4σ(F _o). In the structure of |Mg_34.5Na₆|[Si₁₁₇Al₇₅O₃₈₄]-FAU, 34.5 Mg²⁺ ions per unit cell are found at four different crystallographic sites: 15 per unit cell are located at site I at the center of the hexagonal prism [Mg–O = 2.216(2) Å], two are at site I’ in the sodalite cavity near the hexagonal prism [Mg–O = 2.20(3) Å], only one is located at site II’ in the sodalite cavity [Mg–O = 2.197(23) Å], and the remaining 16.5 are at site II near single 6-oxygen rings in the supercage [Mg–O = 2.103(3) Å]. The residual 6 Na⁺ ions per unit cell are found at site II [Na–O = 2.218(7) Å]. No water molecules are found in this structure.     

Crystallographic studies of fully dehydrated partially Zn<Superscript>2+</Superscript>-exchanged zeolite Y (FAU,Si/Al = 1.56) depending on Zn<Superscript>2+</Superscript> concentration of aqueous solution during exchange

Four single crystals of fully dehydrated and partially Zn²⁺-exchanged zeolites Y (Si/Al?=?1.56) were prepared by the static ion-exchange method using a mixed ion-exchange solution in which Zn(NO₃)₂:NaCl mole ratios were 1:1 (crystal 1), 1:25 (crystal 2), 1:50 (crystal 3), and 1:100 (crystal 4), respectively, with a total concentration of 0.05 M, and followed by vacuum dehydration at 673 K. Their single-crystal structures were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd\(\bar {3}\)m and refined to the final error indices R₁/wR₂?=?0.0459/0.1454, 0.0449/0.1283, 0.0427/0.1284, and 0.0486/0.1680, respectively. Their unit-cell formulas are |Zn₂₅Na₂₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 1), |Zn_19.5Na₃₆|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 2), |Zn_19.5Na₃₆|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 3), and |Zn₇Na₆₁|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 4), respectively. The degree of Zn²⁺ exchange decreases from 67 to 19% as the initial concentration of Zn²⁺ decrease and the initial concentration of Na⁺ increases in given ion-exchange solutions.     

Behavior of cesium cation in zeolite Y (FAU,Si/Al = 1.56) and their single-crystal structures, |Cs<Subscript>75−x</Subscript>Na<Subscript>x</Subscript>|[Si<Subscript>117</Subscript>Al<Subscript>75</Subscript>O<Subscript>384</Subscript>]-FAU (x = 35 and 54)

To study the tendency of Cs⁺ exchange into zeolite Y (Si/Al = 1.56) dependence on Cs⁺ and Na⁺ concentration of aqueous solution during exchange, two single-crystals of fully dehydrated, Cs⁺-and Na⁺-exchanged zeolites Y were prepared by the flow method using a mixed ion-exchange solution whose CsNO₃:NaNO₃ mol ratios were 1:1 (crystal 1) and 1:100 (crystal 2), respectively, with a total concentration of 0.1 M, followed by vacuum dehydration at 723 K. Their crystals were determined by single-crystal synchrotron X-ray diffraction techniques in the cubic space group Fd \(\overline{ 3}\) m, respectively, and were refined to the final error indices R ₁/wR ₂ = 0.084/0.248 and 0.088/0.274 for crystals 1 and 2, respectively. In the structure of |Cs₄₀Na₃₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 1), 40 Cs⁺ ions per unit cell occupy five different equipoints; 3, 3, 14, 9, and 11 are at sites I, II′, II, IIIa and IIIb, respectively, whereas, the remaining 35 Na⁺ ions occupy three different sites: 9, 11, and 15 are at sites I, I′, and II, respectively. In the structure of |Cs₂₁Na₅₄|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 2), 21 Cs ⁺ ions per unit cell occupy three equipoints; 4, 6, and 11 are at sites II, IIIa, and IIIb, respectively. The residual 54 Na⁺ ions per unit cell are found at three different sites; 6, 20 and 28 are at sites I, I′, and II, respectively. The degrees of ion exchange are 53 and 28 % for crystals 1and 2, respectively. This result shows that the degree of Cs⁺ exchange decreased sharply by decreasing the initial Cs⁺ concentration and increasing the initial Na⁺ concentration in given ion-exchange solution.     

Synthesis and single-crystal structures of fully dehydrated fully Sr2+-exchanged zeolite Y (FAU) and its benzene sorption complex, |Sr37.5|[Si117Al75O384]-FAU and |Sr37.5(C6H6)33(H2O)15|[Si117Al75O384]-FAU

Single crystals of zeolite Y, |Na₇₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU, were Sr²⁺ ion exchanged and fully dehydrated to generate |Sr_37.5|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 1) and next, benzene adsorbed to generate |Sr_37.5(C₆H₆)₃₃(H₂O)₁₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU (crystal 2, partially dehydrated). Crystal 1 was prepared by ion exchange in a flowing stream of aqueous 0.05 M Sr(ClO₄)₂ for 3 days followed by dehydration at 673 K and 1 × 10^?6 Torr for 2 days. To prepare the benzene sorption complex (crystal 2), another dehydrated |Sr_37.5|[Si₁₁₇Al₇₅O₃₈₄]-FAU crystal was exposed to 50 Torr of benzene for 3 days at 294 K followed by evacuation for 30 min. at this temperature and 5 × 10^?5 Torr. Their structures were determined crystallographically at 100(1) K using synchrotron X-radiation in the cubic space group Fd $ \bar{3} $ m. They were refined to the final error indices R ₁/wR ₂ = 0.051/0.125 and 0.057/0.154 using 598 and 590 reflections with F _o > 4??(F _o) for crystals 1 and 2, respectively. In crystal 1, about 37.5 Sr²⁺ ions per unit cell are found at an unusually large number of crystallographically distinct positions, six. Eight Sr²⁺ ions per unit cell are at the centers of the double 6-rings (D6Rs, site I). Five additional Sr²⁺ ions are near site I. The site-I?? positions (in the sodalite cavities opposite D6Rs) are occupied by 2.5 Sr²⁺ ions per unit cell. Two Sr²⁺ ions are located at site II?? in the sodalite cavity. The remaining twenty Sr²⁺ ions are found at two nonequivalent sites II (in the supercages) with occupancies of 9 and 11 ions per unit cell, respectively. Each of these Sr²⁺ ions coordinates to three framework oxygens. In this crystal, all sites are only sparsely occupied. In crystal 2, all Sr²⁺ ions are located at four crystallographic sites and 33 benzene molecules are found at two distinct sites within the supercages. One Sr²⁺ ion is at the center of the D6R. Fifteen Sr²⁺ ions are located at site I??. The remaining 21.5 Sr²⁺ ions are found at two nonequivalent sites II with occupancies of 19 and 2.5 ions per unit cell. Nineteen benzenes lie on threefold axes in the supercages, where they interact facially with the latter 19 site-II Sr²⁺ ions; occupancy = 19 molecules/32 sites. The remaining fourteen benzene molecules are found in 12-ring planes; occupancy = 14 molecules/16 sites. Each hydrogen of these 14 benzenes is ca. 2.9 Å from six 12-ring oxygens.     

Synthesis and single-crystal structure of lead oxide nanoclusters in zeolite Y, |Pb 15.5 2+ (Pb4O4(Pb 16/19 2+ Pb 3/19 4+ )4)4.75|[Si117Al75O384]-FAU

A single crystal of excessively Pb²⁺-exchanged zeolite Y (|Pb _15.5 ²⁺ (Pb₄O₄(Pb _16/19 ²⁺ Pb _3/19 ⁴⁺ )₄)_4.75|[Si₁₁₇Al₇₅O₃₈₄]-FAU) was prepared by exchange of Na–Y (|Na₇₅|[Si₁₁₇Al₇₅O₃₈₄]-FAU, Si/Al = 1.56) with an aqueous stream 0.05 M Pb(C₂H₃O₂)₂ at 294 K, followed by vacuum dehydration at 1 × 10^?6 Torr and 693 K. Its structure was determined at 100 K, by X-ray diffraction techniques in the cubic space group Fd $ \overline{3} $ 3 ¯ m and was refined to the final error indices R ₁/wR ₂ = 0.0639/0.1323. About 53.5 Pbⁿ⁺ ions per unit cell occupy three different equipoints; 26 are at site I′, 19 are at site II, and the remaining 8.5 are at another site II. Three Pb⁴⁺ ions at some of the positions must have higher oxidation states due to elevated dehydration temperature; Pb(IIa) is supposed to coexist with Pb²⁺ and Pb⁴⁺ ions assuming the charge balance of the zeolite framework. A distorted Pb₄O₄ cube, alternating Pb²⁺ at Pb(I′) and O^2? at O(5), coordinates with four Pb²⁺ and/or Pb⁴⁺ ions through its oxygen atoms to give a [Pb ₄ ²⁺ O ₄ ^2? (Pb _16/19 ²⁺ Pb _3/19 ⁴⁺ )₄]^176/19+ cluster in 4.75 of eight sodalite cavities per unit cell in zeolite Y.     

Crystallinity of large single crystals of FAU-type zeolites with a wide range of Si/Al ratios

Large colorless single crystals of FAU-type zeolites were synthesized from gels with the composition xSiO₂ : 2.0NaAlO₂ : 7.5NaOH : 454H₂O : 5.0TEA, where x = 2.0–6.0. FAU-type zeolite with Si/Al = 1.26(4) was nearly pure and the maximum size of the single crystals was ca. 150 μm. In case of FAU-type zeolites with Si/Al = 1.54(5), the maximum size of single crystals was ca. 200 μm and the ratio of FAU/impurity was 0.07. The framework Si/Al ratio of the as-synthesized FAU-type zeolite tended to increase with the Si/Al ratio of gel composition. All of the large single crystals had good crystallinities for single-crystal X-ray diffraction, leading to enough numbers of significant reflections which have strong intensity. The structure of a single crystal of dehydrated zeolite Na-X (Si/Al = 1.41(4)) with composition |Na₈₀|[Si₁₁₂Al₈₀O₃₈₄]-FAU per unit cell was determined by X-ray diffraction methods in the cubic space group \( Fd \bar{3} m; \) a = 24.9434(6) Å at 294 K. The structure was refined by using all intensities to the final error indices (using only the 771 reflections for which F _o > 4σ(F _o)), R ₁ = 0.048 (based on F) and R ₂ = 0.188 (based on F ²). In the crystallographic studies, the Si/Al ratio of the synthetic FAU-type zeolite is 1.41(4) which is quite consistent with the SEM–EDS analysis.     

Complete Li+ exchange into zeolite X (FAU, Si/Al = 1.09) from undried methanol solution

Complete exchange of Li⁺ into zeolite Na-X, |Na₉₂|[Si₁₀₀Al₉₂O₃₈₄]-FAU, was accomplished using undried methanol solvent (water concentration 0.02 M). A crystal of Na-X was treated with 0.1 M LiNO₃ in the solvent at 333 K, followed by vacuum dehydration at 673 K and 1 × 10^?6 Torr for 2 days. Its structure was determined by single-crystal synchrotron X-ray diffraction techniques, in the cubic space group $ Fd\overline{3} $ at 100(1) K. The 92 Li⁺ ions per unit cell are found at three different crystallographic sites. The 32 Li⁺ ions occupy at site I’ in the sodalite cavity: these Li⁺ ions are recessed 0.28 Å into the sodalite cavity from their 3-oxygens plane [Li–O = 1.903(5) Å and O–Li–O = 117.8(3)°]. Another 32 Li⁺ ions are found at site II in the supercage, being recessed 0.26 Å into the supercage [Li–O = 1.968(5) Å and O–Li–O = 118.3(3)°]. The remaining 28 Li⁺ ions are located at site III in the supercage [Li–O = 2.00(8) Å].     

Introducing copper ions into zeolite Y by the thallous ion exchange method: single crystal structure of |Cu21.6Tl39.2|[Si121Al71O384]–FAU

The thallous ion exchange (TIE) method was used for the first time in an attempt to introduce copper ions into zeolite Y (FAU, Si/Al = 1.69). |Cu _10.9 ⁺ Cu _10.7 ²⁺ Tl _39.2 ⁺ |[Si₁₂₁Al₇₁O₃₈₄]–FAU was prepared by reacting fully dehydrated and fully Tl⁺-exchanged zeolite Y (Tl₇₁–Y) with CuCl₂(g) and its decomposition products CuCl(g) and Cl₂(g) at 673 K under anhydrous conditions. Its structure was determined using single-crystal crystallography with synchrotron X-radiation and was refined in the space group ${Fd}\bar{3}$ m (a = 24.769(1) Å) with all 903 unique data; the final error index, R ₁ = 0.075, was calculated using only the 858 reflections with F _o > 4σ(F _o). About 45 % of the Tl⁺ ions were replaced by 21.6 copper ions per unit cell at the following sites (distances to nearest framework oxygen atoms are given): 10.7 Cu²⁺ at site I′ in the sodalite cavity opposite double 6-rings (Cu²⁺–O = 2.093(9) Å), 3.5 Cu⁺ at site II opposite single 6-rings in the supercage (Cu⁺–O = 2.24(3) Å), and 7.4 Cu⁺ at site III near 12-rings in the supercage (Cu⁺–O = 2.45(7) Å). All Cu⁺ ions are in supercages where they are easily accessible to guest molecules. The remaining ca. 39 Tl⁺ ions per unit cell occupy three distinct positions: 12 are at a second site I′ (Tl⁺–O = 2.571(9) Å), 23 are at a second site II (Tl⁺–O = 2.732(10) Å), and 4 are at site III′ (Tl⁺–O = 2.871(16) Å) near triple 4-rings in the supercages.     

Single crystal structure of fully dehydrated partially Co-exchanged zeolite X: Comparison with partially dehydrated partially Co-exchanged zeolites X

The crystal structure of the fully dehydrated Co, Na–X zeolite (Na₁₆Co₃₈Al₉₂Si₁₀₀O₃₈₄) is investigated and compared to that of three partially hydrated zeolites. In the fully dehydrated crystal, cobalt ions almost entirely occupy Site I, and partially Site II while the residual sodium cations partly occupy Site II and Site III. The dehydration induces a migration of Co²⁺ cations from Site I′ to Site I and severely affects the structure, the structural strain being released by changes of framework valence angles or, to a less extent, by distortions of TO₄ tetrahedra. Comparison with dehydrated M–X zeolite structures (M = Ba, Na, Ca, Tl, Li) confirms the relation between the size of the charge compensating cation and the stresses on the skeleton that are mainly explained by cation–oxygen electrostatic interactions.     

Synthesis and structural refinement of fully dehydrated fully Zn<Superscript>2+</Superscript>-exchanged zeolite Y (FAU), |Zn<Subscript>35.5</Subscript>|[Si<Subscript>121</Subscript>Al<Subscript>71</Subscript>O<Subscript>384</Subscript>]-FAU

The single-crystal structure of |Zn_35.5|[Si₁₂₁Al₇₁O₃₈₄]-FAU per unit cell, a = 24.794(1), dehydrated at 673 K and 1 × 10^?6 Torr, has been determined by single-crystal X-ray diffraction techniques in the space group \( Fd\bar{3}m \) at 294(1) K. The structure was refined using all intensities to the final error indices (using the 930 reflections for which F _o > 4σ(F _o)) R ₁ = 0.0448 (based on F) and wR ₂ = 0.1545 (based on F ²). About 35.5 Zn²⁺ ions per unit cell are found at an unusually large number of crystallographic distinct positions, six. The 0.5 Zn²⁺ ion per unit cell is located at the center of double 6-ring (D6R, site I; Zn(I)-O(3) = 2.642(3) Å and O(3)-Zn(I)-O(3) = 81.23(12) and 98.77(12)°). Two different site-I′ positions (in the sodalite cavities opposite D6Rs) are occupied by 14 and 3 Zn²⁺ ions per unit cell, respectively; these Zn²⁺ ions are recessed 0.67 Å and 1.02 Å, respectively, into the sodalite cavities from their 3-oxygens plane (Zn(I′a)-O(3) = 2.094(3) Å, Zn(I′b)-O(3) = 2.23(5) Å, O(3)-Zn(I′a)-O(3) = 110.32(12)°, and O(3)-Zn(I′b)-O(3) = 100.9(30)°). Site-II′ positions (in the sodalite cavities opposite S6Rs) are occupied by 6 Zn²⁺ ions, each of which extends 0.63 Å into the sodalite cavities from their 3-oxygens plane (Zn(II′)-O(2) = 2.164(3) Å and O(2)-Zn(II′)-O(2) = 112.00(12)°). Twelve Zn²⁺ ions are found at two nonequivalent sites II (in the supercage) with occupancies of 7 and 5 ions, respectively; these Zn²⁺ ions are recessed 0.52 Å and 0.96 Å, respectively, into the supercage from their 3-oxygens plane (Zn(IIa)-O(2) = 2.138(12) Å, Zn(IIb)-O(2) = 2.28(4) Å, O(2)-Zn(IIa)-O(2) = 114.2(10)°, and O(2)-Zn(IIb)-O(2) = 103.7(25)°).     

Synthesis of granulated binder-free LTA zeolite from metakaolin using ultrasonic treatment

It was studied the influence ultrasonic treatment (22 kHz) of an aqueous suspension of metakaolin on the synthesis of the granulated binder-free LTA zeolite. Mixtures with a molar ratio of the solid ingredients of 6Al₂Si₂O₇:12NaOH (stoichiometric) and 6Al₂Si₂O₇:12NaOH:2Al₂O₃ have been investigated. XRD, SEM, FT-IR and rotational viscosimetry have been used for testing. It was established that in the mixture with an Al₂O₃ excess after the ultrasonic treatment, sodium aluminates of cubic syngony were synthesized. Moulding pastes have been prepared from the sonicated suspensions and pellets of 3 mm diameter have been formed by extrusion. It is shown that sodium aluminates increased both the strength of coagulation structure of pastes and the mechanical strength of the pellets. It was found that after the thermal treatment of the granules at 650 °C, Na₆Al₄Si₄O₁₇ was formed. In the mixture with an Al₂O₃ excess, Na₈Al₄Si₄O₁₈ was also detected. The zeolitization of sodium aluminosilicates and unreacted metakaolin during hydrothermal crystallization in the NaOH solution with concentration of 2 mol l^?1 allowed synthesizing the LTA zeolite. The pellets from the stoichiometric mixture contained 91 wt% zeolite and the remainder was unreacted Na₆Al₄Si₄O₁₇ and other byproducts. The pellets from the mixture with an Al₂O₃ excess contained 97 wt% LTA.     

Production of Propylene from Ethanol Over ZSM-5 Zeolites

In this work, we studied the conversion of ethanol to propylene over ZSM-5 zeolites. The catalytic performance of H-ZSM-5 (Si/Al₂ = 30, 80, and 280) and ZSM-5 (Si/Al₂ = 80) modified with various metals was investigated. H-ZSM-5(Si/Al₂ = 80) afforded high propylene yield, which indicates that a moderate surface acidity favored propylene production. Zr-modified ZSM-5(80) gave the highest yield (32%) of propylene at 773 K. Furthermore, the catalytic stability of the zeolite was improved by the modification of zirconium. The surface acidity and the presence of metal ions played important roles on the production of propylene.     

Layered nanocomposites based on molybdenum disulfide and hydroxy-NiAl oligocations: characterization and catalytic activities in oxidation of sulfide

A series of layered nanocomposites constructed from MoS₂ and hydroxy-NiAl oligocations with various Ni/Al ratios were prepared. The interlayer expansions of 8.11–9.03 Å with Ni/Al ≤ 0.8 indicate that the intercalated species should mainly be [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ or substituted [Al_13?x Ni _x O₄(OH)₂₄(H₂O)₁₂]^(7?x)+ Keggin oligocations. In the presence of molecular oxygen, the composites exhibit good catalytic activities in the oxidization of sulfide ions into thiosulfate ions, and their catalytic activities have been enhanced upon irradiation with visible light.     

Structure of a methylamine sorption complex of fully dehydrated Cd-exchanged zeolite X, Cd46(CH3NH2)16[Si100Al92O384]-FAU

The structure of a methylamine sorption complex of fully dehydrated, fully Cd²⁺-exchanged zeolite X, Cd₄₆(CH₃NH₂)₁₆[Si₁₀₀Al₉₂O₃₈₄]-FAU (a = 24.863(4) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group at 21(1) °C. An aqueous exchange solution 0.05 M in Cd²⁺ was allowed to flow past the crystal for 5 days. The crystal was then dehydrated at 480 °C and 2 × 10⁻⁶ Torr for 2 days (colorless), and exposed to 160 Torr of methylamine gas at 21(1) °C for 2 h (yellow). Diffraction data were then gathered in this atmosphere and were refined using all data to the final error indices (based upon the 524 reflections for which F_o > 4σ(F_o)) of R₁ = 0.069 and wR₂ = 0.200. In this structure, Cd²⁺ ions occupy three crystallographic sites. The octahedral sites I at the centers of the hexagonal prisms are filled with 16 Cd²⁺ ions per unit cell (Cd–O = 2.369(8) Å). The remaining 30 Cd²⁺ ions are located at two non-equivalent sites II with occupancies of 14 and 16. The 16 methylamine molecules per unit cell lie in the supercage where each interacts with one of the latter 16 site-II Cd²⁺ ions: N–Cd = 2.11(8) Å. The imprecisely determined N–C bond length, 1.49(22) Å, agrees with that in gaseous methylamine, 1.474 Å. The positions of the hydrogen atoms were calculated. It appears that one of the amino hydrogen atoms hydrogen bonds to a 6-ring oxygen, and that the other forms a bifurcated hydrogen bond to this and another 6-ring oxygen. The methyl group is not involved in hydrogen bonding.     

Removal of Fluoride from Water by Metal Ions (Al3+, La3+ and ZrO2+) Loaded Natural Zeolite

Abstract

In this study, the ion exchange of metal ions (Al³⁺, La³⁺ and ZrO²⁺) on modified zeolites was carried out using batch method. Fluoride removal from water using Al³⁺‐, La³⁺‐ and ZrO²⁺‐ exchanged zeolite was subsequently investigated to evaluate the fluoride sorption characteristics of the sorbents. Natural zeolite samples (<45 µm) were pre‐conditioned with HNO₃ solution (ZEO‐1), NaNO₃ solution (ZEO‐2), and deionized water (ZEO‐3) before loading Al³⁺, La³⁺, and ZrO²⁺ on zeolite. ZEO‐1 type zeolite had a higher capacity than ZEO‐2 and ZEO‐3 type zeolites. Metal exchange capacities are 0.233, 0.089, 0.090 mmol/g for ZrO²⁺‐, La³⁺‐, and Al³⁺‐ exchanged zeolite (ZEO‐1), respectively. Equilibrium isotherms fitted well to Langmuir and Freundlich models. Percent removal of fluoride from aqueous solution containing 2.5 mg F/L was 94% using metal loaded zeolite (ZEO‐1 type) at an adsorbent concentration of 6.00 g/L.     

Co2+ Ion Exchange in Zeolite NaA

Abstract

⁶⁰Co²⁺ ion exchange at room temperature (20°C) from aqueous cobalt chloride solution with zeolite NaA either hydrated or heated at 150 and 600°C has been studied. In all samples a fast Co²⁺ uptake is found in which 2 meq Na⁺ ions/g of zeolite are replaced by cobalt ions. This process is stable and no desorption is observed. These results are quite different from those obtained in previous work with zeolite NaY which showed that sorption was followed by a desorption process.     

Immobilization of Cs,Cd, Pb and Cr by synthetic zeolites from Spanish low-calcium coal fly ash

This report describes a study of the immobilization of Cs⁺, Cd²⁺, Pb²⁺ and Cr³⁺ by synthetic zeolites formed as a result of the hydrothermal treatment of Spanish class F coal fly ash in a 1 M solution of NaOH. The majority zeolite formed at 150 °C was a gismondine-type P1-Na species (Na₆Al₆Si₁₀O₃₂·12H₂O), which at 200 °C transformed into analcime-C zeolite (Na(Si₂Al)O₆H₂O). The shift in pore size distribution towards pores with diameters of about 2.2 nm observed after the zeolites were washed entailed an increase in the specific surface area, to values nearly double the figures recorded prior to washing. With a high selectivity for Cs, the gismondine type Na zeolite P was found to be the best candidate for immobilizing radioactive waste. Gismondine and analcime-C zeolites also exhibited high Cd selectivity.     

Effects of Modified Beta Zeolites with Acid on Anisole Acetylation in a Fixed Bed Reactor

A beta zeolite sample (Si/Al = 30) was modified by citric acid, tartaric acid, and hydrochloric acid. The catalytic performances of these zeolite together with another beta zeolite (Si/Al = 12.5) were tested in the anisole acetylation in a fixed-bed configuration. The zeolites were characterized by powder X-ray diffraction, FT-IR of adsorbed pyridine, and temperature programmed desorption of ammonia. The ratios of Si/Al, the specific surface areas, and the pore sizes were also measured. The results showed that the most active and stable behavior was achieved on the HCl treated zeolite. The strong acid sites as many as possible but with an appropriate concentration and strength were needed in order to obtain an optimum activity and stability.