Abstract The high activity and selectivity of zeolites in the cyclisation of unsaturated alcohols is reported for the first time; the details of a reaction mechanism based on quantum chemical calculations are also provided. The high efficiency of zeolites MFI, BEA and FAU in the cyclisation of unsaturated alcohols ( cis ‐decen‐1‐ol, 6‐methylhept‐5‐en‐2‐ol and 2‐allylphenol) to afford oxygen‐containing heterocyclic rings is demonstrated. The best catalytic performance is found for zeolites with the optimum concentration of Brønsted acid sites (ca. 0.2 mmol g −1 ) and the minimum number of Lewis acid sites. It is proposed that the efficiency of the catalysts is reduced by the existence of the so‐called dual site, at which a molecule of unsaturated alcohol can simultaneously interact with two acid sites (an OH group with one and the double bond with the other Brønsted site), which increases the interaction strength. The formation of such adsorption complexes leads to a decrease in the catalyst activity because of (i) an increase in the reaction barrier, (ii) an unfavourable conformation and (iii) diffusion limitations. A new procedure for the preparation of tetrahydrofurans and pyrans over zeolite catalysts provides important oxygen‐containing heterocycles with numerous applications.
The crystal structure of pseudojohannite from White Canyon, Utah, was solved by charge-flipping from single-crystal X-ray diffraction data and refined to an Robs = 0.0347, based on 2664 observed reflections. Pseudojohannite from White Canyon is triclinic, P1̄, with a = 8.6744(4), b = 8.8692(4), c = 10.0090(5) Å, α = 72.105(4)°, β = 70.544(4)°, γ = 76.035(4)°, and V = 682.61(5) Å3, with Z = 1 and chemical formula Cu3(OH)2[(UO2)4O4(SO4)2](H2O)12. The crystal structure of pseudojohannite is built up from sheets of zippeite topology that do not contain any OH groups; these sheets are identical to those found in zippeites containing Mg2+, Co2+, and Zn2+. The two Cu2+ sites in pseudojohannite are [5]- and [6]-coordinated by H2O molecules and OH groups. The crystal structure of the pseudojohannite holotype specimen from Jáchymov was refined using Rietveld refinement of high-resolution powder diffraction data. Results indicate that the crystal structures of pseudojohannite from White Canyon and Jáchymov are identical.
A series of supported catalysts is prepared by treatment of SBA-15-type mesoporous molecular sieve bearing [triple chemical bond]SiCH(2)CH(2)CH(2)NHCH(2)CH(2)NEt(2) groups with palladium(II) acetate. These catalysts are studied in Suzuki biaryl couplings and in Heck reactions to establish the influence of metal loading and innocent surface modifications (trimethylsilylation). The Suzuki reaction proceeded efficiently with model and practically relevant substrates; the catalyst performance increasing with an increasing degree of metalation (decreasing N/Pd ratio). Catalyst poisoning tests revealed that the reaction takes place in the liquid phase with the catalyst serving as a reservoir of active metal species and also as a stabilizing support once the reaction is performed. In the Heck reactions, on the other hand, the catalyst performance strongly changed with the reaction temperature and with the N/Pd ratio. The material with the lowest metal loading (0.01 mmol palladium per gram of material, N/Pd ratio ca. 100:1) proved particularly attractive in the Heck coupling, being highly active at elevated temperatures, recyclable, and capable of acting as a bifunctional catalyst (i.e., functioning without any external base.
Rietveldite (IMA2016-081), Fe(UO 2 )(SO 4 ) 2 •5H 2 O, is a new uranyl sulfate mineral described from three localities: Giveaway-Simplot mine (Utah, USA), Willi Agatz mine (Saxony, Germany) and Jáchymov (Western Bohemia, Czech Republic).The mineral rarely occurs in blades up to 0.5 mm long, in association with other post-mining supergene uranyl sulfates and U-free sulfates.Rietveldite is orthorhombic, space group Pmn2 1 , a = 12.9577( 9), b = 8.3183(3), c = 11.2971(5)Å, V = 1217.7(1)Å 3 and Z = 4. Thin blades are elongated on [001] and flattened on {010}.Rietveldite is brownish yellow; powdery aggregates have yellowish beige color; and it has a white streak.It does not exhibit fluorescence under either long-or short-wave UV.It is transparent to translucent with a vitreous luster.Crystals are brittle, with curved fracture and Mohs hardness ~2.Cleavage is good on {010}, and fair on {100} and {001}.Rietveldite is easily soluble in room-temperature H 2 O.The density is 3.31 g/cm 3 .Rietveldite is optically biaxial (+), with α = 1.570(1), β = 1.577(1) and γ = 1.586(1) (white light); 2V calc.= 83.3°,2V meas.= 82(1)°.Dispersion is very strong (r > v).Rietveldite exhibits barely noticeable pleochroism in shades of light brownish yellow color, Y < X ≈ Z.The optical orientation is X = b, Y = a, Z = c.Chemical analyses for rietveldite from Giveaway-Simplot (WDS, 4 spots on 2 crystals) provided FeO 9.56, ZnO 1.06, MgO 0.14, MnO 0.10, SO 3 26.99,UO 3 47.32,H 2 O (calc.) 15.39, total 100.56 wt.%, which yields the empirical formula (Fe 0.79 Zn 0.08 Mg 0.02 Mn 0.01 ) Σ0.90 (UO 2 ) 0.99 (SO 4 ) 2.01 •5.10H 2 O (based on 15 O apfu).Prominent features in the Raman and infrared spectra include the O-H stretching vibrations, symmetric and antisymmetric stretching vibrations of (UO 2 ) 2+ ion, and stretching and bending vibrations of symmetrically non-equivalent (SO 4 ) 2-groups.The eight strongest powder X-ray diffraction lines are [d obs Å (I rel. ) (hkl)]: 8.309(34)(010), 6.477(100) (200), 5.110(58)(210), 4.668(48) (012), 4.653(36)(211), 3.428(41)(013), 3.341(33)(221), 3.238(49)(400).The crystal structure of rietveldite (R 1 = 0.037 for 2396 reflections with I obs > 2σ[I]) contains infinite uranyl sulfate chains of composition [(UO 2 )(SO 4 ) 2 (H 2 O)] 2-along [001].The adjacent chains are linked in the [100] direction by FeO 6 octahedra, which share vertices with SO 4 tetrahedra resulting in a heteropolyhedral sheet parallel to {010}; adjacent sheets are linked by hydrogen bonding only.The uranyl sulfate chains are the same as those in the structures of several other uranyl sulfate minerals.Rietveldite is named for Hugo M. Rietveld (1932Rietveld ( -2016)).
Abstract Catalysis is undergoing a major transition resulting from significant changes in chemical and energy production. To honor the 50th anniversary of establishing the Jerzy Haber Institute of Catalysis and Surface Chemistry, this Essay discusses, from a forward‐looking, personal and somewhat provocative perspective, the needs and gaps of catalysis to address the ongoing transition in chemistry and energy from a sustainability perspective. The focus is on a few selected aspects identified as crucial: i) The precise synthesis of catalytic materials, particularly focusing on mesoporous molecular sieves, metal–organic frameworks, and zeolites (particularly two‐dimensional type); ii) advanced catalyst characterization methods; iii) new concepts and approaches needed in catalysis to meet the demands of a field of energy and chemistry in transition.
Supergene mineralization of the hydrothermal vein uranium deposit Medvědín (Krkonoše Mts., northern Bohemia) is rather varied both in number of the mineral phases and their chemical variation.The supergene minerals agardite-(Y), autunite/metaautunite, dewindtite, churchite-(Y), kasolite, new unnamed phase Pb(Ce,REE) 3 (PO 4 ) 3 (OH) 2 .nH 2 O, parsonsite, phosphuranylite, plumbogummite, pseudomalachite, pyromorphite, saléeite, torbernite/metatorbernite and uranophane were studied using powder XRD, EPMA, IR-spectroscopic and thermal analysis, contributing significantly to the clarification of their crystal chemistry.The alteration mineral assemblage consisting mostly of uranyl phosphates and silicates exhibits relatively high contents of REE and Pb.Minerals with a composition corresponding to pure mineral end-members have not been observed; instead most of the studied phases represent members of isomorphic series.Studied mineral assemblage is a stable association in surface conditions resulting apparently from a long-term alteration of the primary uranium mineralization.
Enhanced 4-aryltetrahydropyran yields are correlated with the relative concentration of medium-strength Brønsted acid sites on the mesopore surface in hierarchical zeolites.
