Aluminophosphate Molecular Sieves Research Articles

Detecting proximities between quadrupolar nuclei by double-quantum NMR.

A robust, easy to optimize, and efficient homonuclear correlation NMR experiment for half-integer quadrupolar nuclei in solids is described and has been experimentally tested on anhydrous Na2HPO4-(23Na, S= 3/2 nucleus) and as-synthesized AlPO4-14 (27Al, S= 5/2 nucleus), an aluminophosphate molecular sieve.

Synthesis and characterization of SAPO-15 molecular sieve using hexamethylenetetramine template

Silico aluminophosphate molecular sieve SAPO-15 was synthesized using hexamethylenetetramine template for the first time and characterized by various physico-chemical techniques such as XRD, SEM, TC/DTA, elemental analyses, FT-IR and 2 7 Al, 3 1 P and 2 9 Si MASNMR. The results were compared with AIPO 4 -15 molecular sieve of the same template. XRD and SEM show that the synthesized samples were highly crystalline. The structure is stable upto 250. TG/DTA reveals the presence of charge compensated templates. FT-IR spectrum of SAPO-15 shows the similarity of the framework with AIPO 4 -15. 2 7 Al MASNMR reveals the presence of aluminium in octahedral environment. 3 1 P MASNMR shows the presence of environmentally distinct two tetrahedral phosphorous species. 2 9 Si MASNMR indicates the presence of dominant Si : [4AI] species along with small Si : [4Si], Si : [3Si : Al], Si : [2Si : 2AI] and Si : [Si : 3AI] species.

Correlation of 129Xe NMR shielding data with the pore structures of various aluminophosphate molecular sieves

129Xe NMR spectra of two different amounts of xenon sealed inside sample tubes containing various microporous aluminophosphate (AlPO-5, -11, -31, and -41) and silicoaluminophosphate (SAPO-5, -11, -31, and -41) molecular sieves are recorded at different temperatures and analysed. For most cases, the 129Xe shielding tensor of adsorbed xenon is asymmetric and distinct spectral differences between circular and elliptical cross-sections, framework dimensions, and xenon loading levels of sieve channels are detected based on the powder pattern lineshape fittings. The roles of Xe–wall and Xe–Xe interactions and different adsorbant diffusion modes on spectral characteristics are discussed. The shielding tensor axes are associated with the sieve channel planes by comparing the data with previously published limiting case models of lineshapes. Shielding tensor span is found to be a promising indicator of sieve channel dimensions. Small differences between AlPO and SAPO molecular sieves belonging to the same framework structure type are also detected. In AlPO-31, fast exchange effects between Xe in the free intercrystallite volume and Xe physisorbed on the external crystallite surfaces are observed and the intercrystallite cavity sizes are estimated.

Large‐Pore FAPO‐36: Synthesis and Characterization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Nickel Amine Complexes as Structure-Directing Agents for Aluminophosphate Molecular Sieves: A New Route to Supported Nickel Catalysts

Open framework aluminophosphates (AlPOs) with the framework types CHA, AFI, AEI, SAS and SAV have been prepared using nickel complexes of linear and macrocyclic polyamines as structure-directing agents: The [Ni(diethylenetriamine)2]2+ complex has been used to prepare aluminophosphate-fluoride versions of the CHA and AFI topologies as well as substituted metalloaluminophosphates (MAPOs) and silicoaluminophosphates (SAPOs) with the CHA topology; the nickel complex of the macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) acts as a structure-directing agent for MAPO-18 (AEI topology), and the nickel complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,4,8,11-tetramethylcyclam direct the formation of STA-6 (SAS topology) or STA-7 (SAV topology) depending on the inorganic composition and the type of amine added as a cobase to control the synthesis pH. Magnesioaluminophosphate-5 (AFI topology) containing complexed nickel has been prepared using a novel mixed azamacrocycle-quinuclidinium cation as a structure-directing agent. Nickel complex-containing AlPOs and SAPOs with the CHA framework topology have been calcined and used as catalysts for the conversion of butane over the temperature range 375 – 575°C with a WHSV of 1.8 h-1. The inclusion of nickel increases the rate of conversion and also changes the composition of the products from the full C1–C4 range to pure methane. This behavior is attributed to the reduction of Ni(II) to finely dispersed supported nickel particles.

Large-Pore FAPO-36: Synthesis and Characterization

A large-pore iron-substituted aluminophosphate molecular sieve of structure type AlPO4-36 was synthesized. Pure and highly crystalline FAPO-36 crystallized hydrothermally from a gel with a molar composition of 0.2:0.9:1:2:50 FeO:Al2O3:P2O5:Pr3N:H2O at 125°C after 7 days. The effects of the crystallization time and temperature on the crystallinity and phase purity were examined. FAPO-36 is thermally stable up to 900 °C in air. Elemental analysis and thermogravimetry indicate isomorphous aluminum substitution by iron. X-ray absorption spectroscopic methods XANES and EXAFS confirm the presence of Fe(II) and Fe(III) in the as-synthesized and Fe(III) in the template-free sample on tetrahedral sites, which strongly indicates the incorporation of iron into the framework of AlPO4-36. The acidity of template-free FAPO-36 has been investigated using carbon monoxide adsorption−desorption FT-IR spectroscopy on the oxidized and on the reduced material, evidencing the redox behavior. The net charge of the framework can be tuned by adjusting the oxidation state of iron, thus controlling the presence or absence of Brønsted acid sites on the sample.

Synthesis of AlPO 4-31 from nonaqueous systems

The aluminophosphate molecular sieve AlPO 4-31 has been synthesized from a nonaqueous system in the presence of hexamethyleneimine as templating agent and has been characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), FT-IR, differential thermal analysis (DTA) and thermogravimetric analysis (TG) and 27Al and 31P MAS NMR techniques.

Reductive cleavage of azo dyes and reduction of nitroarenes over trivalent iron incorporated hexagonal mesoporous aluminophosphate molecular sieves

A novel, efficient and eco-friendly iron incorporated hexagonal mesoporous aluminiphosphate (FeHMA) catalyst is put forward for the reductive cleavage of azo functions as well as for the reduction of nitroarenes, including larger molecules, by catalytic transfer hydrogenation (CTH). The results indicate that the transformations occur in elegant and rapid manner with excellent yields. Furthermore, the catalyst can easily be recovered and reused without practically affecting the yields for up to six cycles.

In situ X-ray absorption spectroscopic study on the reducibility of cobalt-containing aluminophosphate molecular sieves

Real-time X-ray absorption spectra (XAS) during the course of temperature-programmed reduction (TPR) were recorded to investigate the reducibility of cobalt on aluminophosphate molecular sieve AlPO-5. When incorporated into the AlPO-5 framework via hydrothermal synthesis, cobalt exhibited high resistance to reduction by hydrogen. In contrast, cobalt could be fully reduced in the temperature range between 400 and 500 °C when supported on the surface of AlPO-5. The coordination number (NCo–Co) for the first shell was 8.5 on the reduced catalyst with a cobalt loading of ∼5 wt.%, corresponding to an average particle size of 35 Å.

Heterogeneous Catalytic Transfer Hydrogenation of Aromatic Nitro and Carbonyl Compounds over Cobalt(II) Substituted Hexagonal Mesoporous Aluminophosphate Molecular Sieves.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic Transfer Hydrogenation of Nitro and Carbonyl Compounds over Novel Fe(III) Substituted Hexagonal Mesoporous Aluminophosphates

Abstract Catalytic transfer hydrogenation (CTH) of aromatic nitro and carbonyl compounds over novel Fe(III) substituted hexagonal mesoporous aluminophosphate (FeHMA) molecular sieve catalyst showed excellent regioselectivity/chemoselectivity as well as superior recycling capability. Furthermore, the reduction occurs without affecting other functional groups such as –CN, –CHO, –Cl, –CH3, –OCH3 and –NH2.

Synthesis, Characterization and Catalytic Properties of Mesoporous Cobalt Aluminophosphate Molecular Sieves

Isomorphously substituted cobalt(II) hexagonal mesoporous aluminophosphate (CoHMA) molecular sieves were synthesized hydrothermally and characterized by various analytical and spectroscopic techniques. It was deduced that cobalt ions exhibit a divalent oxidation state in tetrahedral coordination in mesoporous aluminophosphates. Further, unlike cobalt-containing microporous aluminophosphate molecular sieves, Co(II) ions remain in a tetrahedral geometry even after calcination. The catalytic activity of CoHMA was tested for the cyclohexane oxidation reaction under mild conditions. Remarkable substrate conversion and product (cyclohexanol) selectivity were obtained compared to several previously reported heterogeneous catalysts.

Synthesis, characterization, and catalytic properties of chromium-containing hexagonal mesoporous aluminophosphate molecular sieves

Chromium-containing hexagonal mesoporous aluminophosphate molecular sieve materials were synthesized, characterized and evaluated for the oxidation of cyclohexane under mild conditions. The catalysts showed remarkable activity for the chosen reaction with very high substrate conversion and excellent product selectivity. In addition, recycling studies over the spent catalysts as well as studies on quenched solutions under the reaction conditions indicated no or very meager loss in activity; thus, the materials behaved truly as heterogeneous catalysts. This observation was well supported by ICP-AES analysis of the filtrates obtained from the washed catalysts where no leaching of active chromium species was detected. Furthermore, the reaction carried out using these filtrates confirmed the absence of active metal ions as it exhibited only a marginal activity.

Titanium substituted hexagonal mesoporous aluminophosphates: Highly efficient and selective heterogeneous catalysts for the oxidation of phenols at room temperature

A remarkable para-selectivity was achieved, for the first time, for the oxidation of phenol over novel titanium substituted hexagonal mesoporous aluminophosphate molecular sieves at room temperature, and that the catalysts also showed excellent activity for alkyl substituted phenols.

Heterogeneous catalytic transfer hydrogenation of aromatic nitro and carbonyl compounds over cobalt(II) substituted hexagonal mesoporous aluminophosphate molecular sieves

Catalytic transfer hydrogenation of aromatic nitro and carbonyl compounds was carried out using novel cobalt(II) substituted hexagonal mesoporous aluminophosphate molecular sieves. The catalyst showed excellent yield with good recycling capability.

Synthesis, characterization and catalytic properties of trivalent iron substituted hexagonal mesoporous aluminophosphates.

Trivalent iron substituted hexagonal mesoporous aluminophosphate molecular sieve has been synthesized and characterized for the first time, which showed excellent catalytic activity and reusability for the cyclohexane oxidation reaction under mild conditions.

Template-free synthesis of AlPO 4-H1, -H2, and -H3 by microwave heating

Aluminophosphate molecular sieves (AlPO 4's) were prepared by microwave heating without using organic template reagents. The microwave heating enhanced the crystallization of aluminophosphate gels, and AlPO 4-H1, -H2(AHT), and -H3(APC) were successfully obtained as single phases in a relatively short reaction time. The reaction conditions used for the crystallization of the three kinds of AlPO 4's were very similar to each other, but the use of different aluminum sources resulted in different structures; amorphous aluminum hydroxide, gibbsite, and boehmite were used for the preparation of AlPO 4-H1, -H2, and -H3, respectively. The crystallization temperatures were 125, 118, and 90 °C, respectively. The addition of hydrochloric acid was needed for the crystallization of AlPO 4-H1 and -H2. The addition of seed crystals and stirring the gels were found to be essential for the crystallization of AlPO 4-H3. Nitrogen and water adsorption properties were also measured.

Electronic state and three-dimensional structure of Mn(III) active sites in manganese-containing aluminophosphate molecular sieve catalysts for the oxyfunctionalisation of alkanes.

Combined in situ X-ray absorption spectroscopy measurements and quantum mechanical calculations yield a quantitative three-dimensional structure of the tetrahedrally coordinated Mn(III) active sites in MnAlPO catalysts.

Spectral diffusion in solvent-filled AlPO 4-5 molecular sieves: modification of amorphous phase properties by spatial restrictions

We report on persistent spectral hole-burning studies of thiazine and oxazine dyes encapsulated in an AlPO 4-5 aluminophosphate molecular sieve. A non-photochemical hole-burning mechanism is provided by small additional solvent molecules, e.g. glassy ethanol or amorphous water, in the pore system. Hole-burning efficiency and spontaneous hole-filling are in the typical range of glassy bulk systems. However, spectral diffusion is reduced drastically in the solvent-filled molecular sieve compared to the corresponding bulk glass. Based on previous work by the Fayer group [J. Chem. Phys. 92 (1990) 4125; Chem. Phys. Lett. 168 (1990) 371] this finding is discussed as an example of spatial restrictions to the solvation shell around the dye molecules.

Alkylation of benzene with isopropyl alcohol over SAPO-5 catalyst in an integral pressure reactor

The alkylation of benzene with isopropyl alcohol was studied in an integral pressure reactor over silicon substituted aluminophosphate molecular sieves, SAPO-5. The influence of various process parameters such as temperature, pressure, time on stream, weight hourly space velocity, and mole ratio of reactants on cumene yield and selectivity were investigated. The activity of SAPO-5 was compared with that of Hbeta for this reaction under similar conditions and in the same reactor. At pressures higher than atmospheric, almost the theoretical maximum yields of cumene were achieved on this SAPO-5. Among the diisopropyl benzenes formed by the alkylation of cumene, the meta-isomer was found to form in a significant amount followed by the para-isomer. The ortho-isomer with relatively high strain energy of 4.26 kcal/mol was almost negligible. The cumene yield goes through a maximum in the temperature range 498-543 K studied. Cumene selectivity was found to decrease at higher temperatures, higher pressures and lower benzene to isopropanol mole ratios.