Further evidence of incorporation of chromium ions into the framework of silicoaluminophosphate molecular sieves

Three different molecular sieves were synthesised and characterized using³¹P and²⁷Al magic angle spinning nuclear magnetic resonance (³¹P and²⁷Al MAS NMR) spectroscopy and acidity measurement techniques. The synthesized solids were: a silicoaluminophosphate (SAPO-11) sample, a chromium-substituted silicoaluminophosphate (CrAPSO-11) sample and a chromium-supported SAPO-11 (Cr/SAPO-11) sample. Significant differences were observed between the CrAPSO-11 MAS NMR spectra and the spectra for the other two solids. The differences can be understood in terms of a different chemical environment for the Al(III) and P(V) ions in the molecular sieve framework, as a result of a different type of interaction, probably with substituted chromium ions in the framework. The acidity measurements were in agreement with the MAS NMR spectroscopy results, providing further evidence for the incorporation of chromium ions into the molecular sieve framework.     

Structure of iron and manganese ions substituted in the framework of nanoporous AlPO-5 material

The structure of iron and managanese ions substituted in the framework of nanoporous AlPO-5 is determined by ex situ and in situ X-ray absorption spectroscopy. Fe K-edge XANES and EXAFS studies clearly indicate that iron ions are present as Fe(III) in octahedral coordination in the assynthesised material and tetrahedral coordination in the calcined material in both pure FeAlPO-5 and FeMnalPO-5. XANES and EXAFS results also indicate that reaction with hydrogen peroxide causes the removal of Fe(III) ions from the framework. Mn K-edge XANES and EXAFS of FeMnAlPO-5 samples indicate that Mn(II) ions are present in the framework, tetrahedrally coordinated, in the as-synthesised material but upon calcination it is found that the Mn(II) ions are removed from the framework, suggesting a different synthesis strategy is necessary to stabilise the Mn(II) ions in the framework simultaneously with Fe(III) ions.     

Isomorphous substitution of Mn(II), Ni(II) and Zn(II) in AlPO-31 molecular sieves and study of their catalytic performance

Isomorphously substituted molecular sieves, MAPO-31, NAPO-31 and ZAPO-31, were prepared under mild hydrothermal conditions from gels containing sources of aluminium, phosphorus, appropriate metal and dipropylamine (DPA), presumably acting as a structure-directing template. They were characterized by XRD, FTIR, TGA, inductively coupled plasma (ICP), ESR, Brunauer, Emmett, Teller (BET) and diffusion reflectance spectroscopy (DRS) techniques. In the XRD, the peak at 2θ = 16.7° of the metal substituted AlPO-31 is more intense than that of pure AlPO-31 suggesting preferential occupation of the plane corresponding to it as compared to other planes. The O-H stretch in the IR spectra of the metal-substituted molecular sieves is blue-shifted with respect to the parent AlPO-31 molecular sieves possibly due to metal substitution. Theg values obtained from the ESR spectra of MAPO-31 and NAPO-31 also substantiate framework substitution. Ethylation of toluene was carried out between 300 and 450°C over the above catalysts as a model test reaction. The high toluene conversion over metal-substituted molecular sieves proves the isomorphic substitution of metal ions in the AlPO-31 framework.     

Probing the local environment of Ti3+ ions in TiO2 (rutile) by 17O HYSCORE

Reduced states in TiO(2) : (17)O hyperfine sublevel correlation spectroscopy was used to monitor the local environment of stable Ti(3+) ions generated in a (17)O-enriched polycrystalline TiO(2) (rutile) sample. A hyperfine interaction of about 8 MHz is found, which is analogous to that observed for molecular Ti(3+) aqua complex cations and suggests a localized nature of the unpaired electron wave function for these centers at 4 K.     

New chemical evidence for the ability to generate radical molecular ions of polyenes from ESI and HR-MALDI mass spectrometry

We report here new chemical evidence for the generation of radical molecular ions of compounds with a conjugated pi-system (polyene) in ESI and HR-MALDI mass spectrometry. The oxidation potential of the neutral polyenes was calculated by cyclic-voltammetry and the results compared with those previously published for other complex conjugated compounds that have also been shown to form M*+ in ESI-MS. This study clearly demonstrates the correlation between the oxidation potential and the formation of the M*+ for the polyenes studied.     

Effect of the nature of quaternary ammonium surfactants on the structure and properties of mesoporous molecular sieves

The influence of the nature of surfactant cations (dodecyltrimethylammonium bromide and tosylate and ethonium chloride) on the structure and adsorbent properties of mesoporous molecular sieves has been studied. The possibility of spatial self-organization of silica-surfactant systems without hydrothermal treatment has been observed. The influence of the surfactant counterions on the structure formation process has also been noted. L. V. Pisarzhevskii Institute of Physical Chemistry, Ukrainian Academy of Sciences, Ukraine, 252039 Kiev, Science Prosp., 31. Translated from Teoreticheskiya i éksperimental’naya Khimii, Vol. 33, No. 1, pp. 53–57, January–February, 1997.     

The formation of [CH5O]+ and ions from the molecular ions of isobutyl alcohol

On the basis of field ionization kinetic and deuterium labelling experiments, it is shown that the molecular ions of isobutyl alcohol generate [CH₅O]⁺ ions at 10^?11 s via a 1,4-shift of a hydrogen atom from one of the methyl groups to the oxygen atom, followed by a 1,2-elimination of protonated methanol with a hydrogen atom of the other methyl group. At times > 10^?11 s two distinct interchange processes between hydrogen atoms appear to compete with this reaction, as shown from field ionization kinetic experiments and metastable decompositions. Ion cyclotron resonance experiments on the long-lived [CH₅O]⁺ ions further demonstrate that they are protonated methanol ions. Arguments are put forward that the ions, generated by a specific 1,3-elimination of a molecule of water from metastable decomposing molecular ions, have an isobutene structure.     

The production and spectroscopy of molecular ions isolated in solid neon

Studies of the molecular spectra of small polyatomic molecular ions are stlll in therr infancy. The availability of survey spectra would facilitate the search for individual vibrational and vibronic bands of gas-phase ion species using sophisticated, highly sensitive laser techniques. Deeectable concentrations not only of simpee ions such as CO⁺ ₂ and H⁺ ₂ but also of dimer cations and anions such as O⁺ ₄ and O^- ₄ have been stabilized in solid neon when the parett molecule is codeposited with a beam of excited neon atoms. The vibrational fundamentals heretofore observed for the simpee ions isolated in solid neon lie very close to the positions of the corresponding gas-phase band centers. Molecular spectroscopic data are not yet available for the gas-phase dimer ions. Therefore, it is difficutt to estimate how closely the neon-matrix vibrational frequencies here reported for a numbrr of dimer ions correspond to the gas-phase band centers. Some guidance is available from comparison of the argon-matrix spectra of small molecules hydrogen-bonded to HF with the gasphaee spectra of theee hydrogen-bonded species [55]. In theee studies, the effect of the argon matrix is to enhance the apparent hydrogen-bond strength; the HF stretching frequency is lowered by 1 to 5% from the gas-phase value, and the absorptions contributed by the flexing of the HF with respect to the other molecule are raised by 5% or more. Since neon matrices are generally less perturbing than argon matrices, the deviation from the gas-phase frequencies shoudd be somewhat less in neon-matrix studies. In the present experiments, only the high frequency stretching fundamentals have been observed, suggesting that matrix shifss shoudd amoutt to less than 3 or 4%. Therefore, matrix isolation studies such as theee promise to provide a valuable new tool for the detection and spectroscopic characterization of small molecular ions and cluster ions.     

Application of the attached proton test technique in 31P NMR spectroscopy

Intensity modulated ³¹P NMR spectra were obtained using the pulse sequence published by Patt and Shoolery. This attached proton test (APT) technique for signal assignment could be applied to systems with long-range heteronuclear couplings in P? O? C? H fragments. In a model system derived from the alcoholysis of P₄S₁₀ the six reaction products were assigned to the six signals in the ³¹P NMR spectrum.     

Determination of coordination modes and estimation of the 31P-31P distances in heterogeneous catalyst by solid state double quantum filtered 31P NMR spectroscopy

To overcome the separation difficulty of the palladium-based homogeneous catalyst, the palladium complex can be anchored on various supports such as silica. However, it is difficult to determine the amounts of the two coordination modes of the Pd nucleus, that is, Pd coordinates with one phosphorus atom and Pd coordinates with two phosphorus atoms. Here a (31)P double-quantum filtered (DQ-filtered) method in solid-state NMR is introduced for the palladium-based heterogenous catalyst system. With the DQ-filtered method, we can not only determine the amounts of the two different kinds of palladium coordination modes, we can also estimate the interatomic distance of two (31)P nuclei bonded to a palladium nucleus. With the help of this method, we can quickly estimate interatomic distances in our designed system and accurately re-design the palladium system to accommodate either one (31)P or two (31)P.     

New type of ring-chain tautomerism. Direct evidence from 1H NMR spectroscopy

A new type of ring-chain tautomerism consisting in the reversible transformation of 4-(5-)haloalkanecarboxylic acid dialkylamides into dialkyl(tetrahydrofuran-2-ylidene)- and dialkyl(tetrahydropyran-2-ylidene)ammonium halides, respectively, was found and studied by ¹H NMR spectroscopy.     

含镓ZSM-5分子筛的制备及其在甲醇芳构化反应中的催化性能

用三种不同方法(水热合成法、浸渍法、离子交换法)制备了含Ga的ZSM-5分子筛,采用XRD、SEM、FT-IR、NH₃-TPD、ICP、XPS和氮吸附等多种技术对其进行了表征,并考察了硅源、Ga含量和Ga的存在状态等对该分子筛结构、酸性及其在甲醇芳构化反应中催化性能的影响。结果表明,硅源种类(硅溶胶、白炭黑、正硅酸乙酯)显著影响分子筛的形貌、晶粒粒径大小及杂原子Ga的存在状态,进而决定其在甲醇制芳烃反应中的芳构化催化活性和稳定性。分子筛中Ga物种主要有骨架Ga、骨架外表面游离态(与分子筛无相互作用)的Ga₂O₃以及与分子筛有相互作用的非骨架Ga三种不同的存在状态。骨架Ga物种以四配位形式存在,提供酸性位点;非骨架Ga作为芳构化活性中心,主要起脱氢芳构化作用。适量的非骨架Ga中心与酸中心协调匹配能有效促进芳烃产物的生成。     

Determination of 3J(31P31P) and 13C31P coupling constants in 1,6-diphosphatriptycene from carbon-13 n.m.r. lone pairs effects on 13C31P couplings

The ³¹P? ³¹P and ¹³C? ³¹P coupling constants in 1,6-diphosphatriptycene have been obtained from analysis of its proton decoupled ¹³C n.m.r. spectra. More accurate data, however, resulted from simultaneous analysis of the proton decoupled ¹³C spectra and ³¹P(¹³C) satellite spectra. The ¹³C? ³¹P couplings are strongly influenced by the proximity and orientation of the phosphorus lone pair electrons. The first ³¹P? ³¹P coupling in an aromatic diphosphine is reported.     

Synthesis of Schiff's bases from furylacroleins and aminopyridines in the presence of molecular sieves

We have studied the reactions of (hetero)aromatic aldehydes with 2-aminopyridines. The results obtained suggest that molecular sieves play a role in these processes not only as a dehydrating agent but also as an acid catalyst. We have synthesized a series of novel heterocyclic azomethines.Dedicated to Professor M. A. Yurovskaya on her Jubilee.Latvian Institute of Organic Synthesis, Riga LV-1006 Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 324–335, March, 2000.     

State of phosphorus in sorbents based on titanium and zirconium phosphates from 31P NMR spectroscopy data

A ³¹P NMR method has been used to study sorbents based on titanium and zirconium phosphates synthesized by bulk mixing the reagents and treatment of x-ray amorphous TiO₂, rutile and ZrO₂ by phosphoric acid. In the bulk titanium and zirconium phosphates the phosphorus occurs in four different states, phosphate groups bonded through cross-linking oxygen atoms with one, two, and three atoms of the metal and molecules of phosphoric acid trapped in the matrix of the sorbent in the synthesis process. It is established that the method of grafting the phosphate groups to the surfaces of the hydrated TiO₂ and ZrO₂ is determined by the crystalline and chemical properties of the surfaces.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 633–636, September–October, 1988.     

Sandia octahedral molecular sieves (SOMS): structural and property effects of charge-balancing the M(IV)-substituted (M = Ti, Zr) Niobate framework

Sandia octahedral molecular sieves (SOMS) is an isostructural, variable composition class of ion exchangers with the general formula Na(2)Nb(2-x)M(IV)(x)O (6-x)(OH)(x).H(2)O (M(IV) = Ti, Zr; x = 0.04-0.40) where up to 20% of the framework Nb(V) can be substituted with Ti(IV) or Zr(IV). This class of molecular sieves is easily converted to perovskite through low-temperature heat treatment (500-600 degrees C). This report provides a detailed account of how the charge imbalance of this Nb(V)-M(IV) substitution is compensated. X-ray powder diffraction with Rietveld refinement, infrared spectroscopy, thermogravimetric analysis, (23)Na MAS NMR, and (1)H MAS NMR were used to determine how the framework anionic charge is cation-balanced over a range of framework compositions. All spectroscopic evidence indicated a proton addition for each M(IV) substitution. Evidences for variable proton content included (1) increasing OH observed by (1)H MAS NMR with increasing M(IV) substitution, (2) increased infrared band broadening indicating increased H-bonding with increasing M(IV) substitution, (3) increased TGA weight loss (due to increased OH content) with increasing M(IV) substitution, (4) no variance in population on the sodium sites (indicated by Rietveld refinement) with variable composition, and (5) no change in the (23)Na MAS NMR spectra with variable composition. Also observed by infrared spectroscopy and (23)Na MAS NMR was increased disorder on the Nb(V)/M(IV) framework sites with increasing M(IV) substitution, evidenced by broadening of these spectral features. These spectroscopic studies, along with ion exchange experiments, also revealed the effect of the Nb(V)/M(IV) framework substitution on materials properties. Namely, the temperature of conversion to NaNb(1-x)M(IV)(x)O(3) (M = Ti, Zr) perovskite increased with increasing Ti in the framework and decreased with increasing Zr in the framework. This suggested that Ti stabilizes the SOMS framework and Zr destabilizes the SOMS framework. Finally, comparing ion exchange properties of a SOMS material with minimal (2%) Ti to a SOMS material with maximum (20%) Ti revealed the divalent cation selectivity of these materials which was reported previously is a function of the M(IV) substitution in the framework. A thorough investigation of this class of SOMS materials has revealed the importance of understanding the influence of heterovalent substitutions in microporous frameworks on material properties.     

New chiral organophosphorus derivatizing agent for the determination of enantiomeric composition of chloro- and bromohydrins by 31P NMR spectroscopy

The synthesis of a new chiral organophosphorus derivatizing agent prepared from (S)-2-anilinomethylpyrrolidine 1 and its successful use in the determination of enantiomeric composition of various halohydrins by ³¹P NMR spectroscopy is described.     

晶种和溶剂对复合分子筛形成的影响

采用包埋法合成ZSM-5/SAPO-5核壳结构复合分子筛,研究了凝胶组成对该材料性能的影响,并利用X射线衍射和扫描电镜等手段对其进行了表征。结果表明,合成的分子筛是以ZSM-5为核,SAPO-5为壳的双结构复合分子筛。通过向凝胶中加入晶种或者调节溶剂性质可以明显改变复合材料的结晶度和颗粒形貌。引入晶种合成材料的颗粒形貌以椭圆型为主,分子筛的结晶度增加;以醇和水混合物为溶剂合成分子筛的颗粒仍以球形为主,分子筛的结晶速率降低,结晶度的最高值降低。