不同类型含铁分子筛上N2O催化分解反应

采用固态离子交换法制备了一系列Fe/Al摩尔比为0.33的Fe/分子筛(ZSM-35,ZSM-5,beta和mordenite (丝光沸石))样品,并利用紫外-可见漫反射光谱、原位红外光谱和可见拉曼光谱以及瞬态应答实验考察了分子筛种类对N₂O分解反应性能的影响.研究表明,经高温处理(HT)后分子筛的催化活性顺序为 Fe/ZSM-35 > Fe/beta > Fe/ZSM-5 > Fe/mordenite,与骨架外铝稳定的双核铁物种含量一致.这说明双核铁物种是高温处理后Fe/分子筛样品中N₂O分解的活性位,而它的形成与分子筛种类密切相关.Fe/ZSM-35分子筛十元环孔道中相邻两个α位和八元环孔道中相邻两个β位都能稳定两个Fe(II)离子而形成能高效分解N₂O的双核铁活性中心.Fe/beta和Fe/ZSM-5分子筛中只有落在相邻两个β位上的两个Fe(II)离子才能形成参与N₂O分解的高活性的双铁活性中心.Fe/mordenite-HT分子筛上的铁物种绝大部分以孤立Fe离子的形式存在,因此其催化N₂O分解反应活性很低.     

催化材料的紫外拉曼光谱研究

综述了在过去的几年中,我们研究组利用紫外拉曼以及共振拉曼光谱技术在含过渡金属的微孔和介孔材料中活性位结构的表征.分子筛合成机理以及氧化物表面相结构研究中取得的进展.微孔.介孔材料骨架中超低含量的孤立的过渡金属离子或氧化物包括TS-1,Ti-MCM-41,Fe-ZSM-5,Fe-SBA-15和V-MCM-41等能够通过紫外拉曼光谱可靠、准确地鉴别出来.利用紫外拉曼可避开荧光和增加灵敏度的特点,利用自行设计的可用于原位研究水热合成过程的原位紫外拉曼光谱池,对几种典型分子筛(X型分子和Fe-ZSM-5)的合成过程实现了拉曼光谱研究.结果表明,紫外拉曼光谱可以灵敏地检测出合成前体、中间物以及分子筛晶体的演化过程.此外.通过共振拉曼光谱研究了Fe/ZSM-5上的活性中心以及活性氧物种.结果表明,这种具有高活性的氧物种是一种双原子铁物种上的过氧离子,反应的中间物种类似于单加氧酶中的铁络合物.紫外拉曼光谱对氧化锆和氧化钛等氧化物的研究中发现,氧化物的表面与体相结构不同.这一发现对于催化材料的研究有着非常重要的意义,因为大多数的催化材料性质主要取决于它的表面结构.例如,在氧化钛体系中,将用紫外拉曼光谱鉴定出的表面物相信息与氧化钛光催化活性相关联,提出了"锐钛矿-金红石表面异相结增强光催化活性"的新概念.     

含铁骨架Fe-Al-EU-1分子筛的设计合成和晶化

以溴化六甲双铵(HMBr2)为模板剂,在HMBr2-Na2O-Al2O3-SiO2-Fe2O3-H2O体系中,采用水热法合成了高结晶度Fe-Al-EU-1分子筛,通过X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、热重-微分热重(TG-DTG)分析、N2吸附-脱附、固体核磁共振(NMR)、紫外-可见(UV-Vis)吸收光谱和X射线吸收谱的精细结构(XAFS)等测试手段对合成样品的物理化学性质、铁在分子筛骨架的成键状态进行表征.结果表明:随着原始溶胶中铁的质量分数增加,Fe-Al-EU-1分子筛的晶胞体积增大;铁掺杂使Al-EU-1分子筛的表面积(BET)从272m2·g-1增加到365m2·g-1;模板剂脱除和分解温度降低;铁离子加入溶胶,导致zeta电位降低,胶体粒子容易聚集,分子筛外形增大.UV-Vis结果显示:由于220-250nm处的分子筛骨架中氧原子的成键2p电子向骨架四配位铁原子的空d轨道产生p-d跃迁,导致其特征峰的吸收峰强度急剧增加,在373nm左右骨架位的四配位铁原子与相邻的硅氧基团配位键合,产生能级分裂的d-d电荷跃迁峰且峰强度增加.XAFS结果表明:随着晶化过程的进行,边前1s→3d吸收峰和1s→4p主吸收峰发生了明显变化,原始溶胶样品在形成四配位铁物种结构单元后,逐步转化形成四面体配位的铁-硅-氧骨架铁物种,铁-硅-氧离子键结构单元也随之转变为四面体配位共价键结构的骨架铁物种.     

离子液中磷酸铝方英石的低温合成及表征

 在溴化 1-丁基-3-甲基咪唑离子液体中, 于低温 80 °C 反应 30 min 即可制得结晶完好的磷酸铝方英石. 详细考察了有机胺和 HF 的加入量、反应原料磷铝比和反应时间等对合成固体磷酸盐骨架结构的影响. 粉末 X 射线衍射和高分辨固体核磁共振结果表明, 合成的方英石晶体为 α 晶相, 磷铝物种大部分位于分子筛骨架上, 并以四配位的形式通过 Al–O–P 键相连.     

Fe（Ⅲ）APO分子筛在芳香族化合物氧化反应中的催化活性

 Fe取代系列磷酸铝分子筛（FeAlPO4－5，FeAlPO4－11和FeVPI－5）在催化氧化芳香族化合物反应（如苯酚和苯的羟化、苯乙烯的环氧化以及萘酚的氧化）中具有很高的活性．系统研究的数据显示，在苯酚和苯的羟化及苯乙烯的环氧化反应中，FeAlPO4－5及FeAlPO4－11的活性与TS－1催化剂相近；在大分子萘酚的氧化反应中，FeVPI－5具有较高的活性，而小孔的TS－1则没有活性．比较不同催化剂的活性结果表明，骨架中的Fe（Ⅲ）是催化剂的活性中心．     

不同钴含量CoAPO-5分子筛的合成、表征及其催化环己烷氧化性能

用水热法合成了一系列不同含量钴掺杂的磷酸铝分子筛CoAPO-5. 合成的样品用X射线衍射(XRD), 扫描电镜(SEM), 紫外可见漫反射光谱(UV-Vis DRS), 热重分析(TG)仪和电感耦合等离子体发射光谱(ICP-AES)等进行了表征. XRD表征显示, 合成的CoAPO-5分子筛具有较高的结晶度, 分子筛晶胞参数与Co含量之间存在较好的对应关系. UV-Vis漫反射光谱显示合成的CoAPO-5分子筛具有骨架钴的特征三重峰; 焙烧后峰的强度降低, 表明分子筛骨架中Co2+可被氧化成Co3+. SEM表明该分子筛具有典型的AlPO4-5分子筛形貌特征. TG结果也表明Co2+进入了分子筛骨架, 分子筛具有较好的稳定性. 在环己烷氧化反应中CoAPO-5具有较好的催化性能, 环己烷转化率与环己酮选择性均较高; 随着分子筛中钴含量的增加, 环己烷的转化率增加.     

SbAlPO_4-5的合成及性能研究

据文献报道现在已经合成二十余种磷酸铝系列的分子筛,其中三维结构的有十四种,二维结构的六种.为了改善磷酸铝分子筛的性能,沸石工作者把P、Al以外的其他原子引入了磷酸铝分子筛骨架.Be、Li、B、Ti、V、Fe、Co、Ge等杂原子磷酸铝分子筛的合成已见报道.本文探索了均相体系SbAlPO_4-5的合成方法并对其物化性能作了研究.     

Au负载SBA-15分子筛上葡萄糖氧化反应

探讨了金与铝改性的SBA-15分子筛催化剂(Au-Al/SBA-15)上活性中心与葡萄糖氧化制葡萄酸反应性能的关系. 通过固体核磁共振波谱(ssNMR)、 X射线光电子能谱(XPS)、 紫外-可见光谱(UV-Vis)和透射电子显微镜(TEM)等手段对不同Au及Al含量的Au-Al/SBA-15催化剂进行了结构表征. 发现Al 改性能够在SBA-15载体上产生四配位Al物种, Au主要以单质的形式存在; SBA-15上的四配位Al物种具有稳定Au颗粒大小的作用. 通过对比发现, 催化剂上的Au和骨架四配位Al物种间的相互协作促进了对葡萄糖氧化的活性, 而非骨架Al物种会导致副反应的发生, 降低葡萄糖酸产物的选择性. 通过固体¹³C NMR揭示了反应体系中的NaOH能够将强吸附的产物葡萄糖酸分子从催化剂表面解离, 保持活性位不被覆盖进而促进反应持续进行.     

ZSM-35 分子筛的静态合成和晶化机理

 以环己胺为有机模板剂, 硅溶胶为硅源, 采用静态合成法在 220 ºC 的水热体系中制得了 ZSM-35 分子筛纯相. 当初始凝胶中含有一定量的 K+时, 在晶化过程中, K+与Na+的共同作用可以很好地抑制混晶丝光沸石的生成, 且当 n(K+)/n(K+ + Na+) = 0.3 时, 制得的 ZSM-35 分子筛晶化度最高. 利用 X 射线衍射和紫外拉曼光谱对分子筛形成的最佳条件以及晶化机理进行了研究. 发现合成初期前体中含有五元环和六元环的硅物种构筑单元. 通过水热晶化过程, 与硅酸盐的五元环或六元环有关的 450 cm–1 处紫外拉曼谱峰增强, 在晶化后期, 随着无定形凝胶逐渐被消耗, 在 421, 312 和 215 cm–1 处出现新的 ZSM-35 结构的特征拉曼谱峰, 说明这些环物种相互聚集最终形成了 ZSM-35 分子筛.     

MCM—41型含V分子筛的合成与表征

本文合成出具有ＭＣＭ—４１型结构的含Ｖ和Ｖ—Ｔｉ分子筛，骨架红外、顺磁共振、紫外漫反射、固体魔角核磷、拉曼光谱、电子能借等测试结果表明Ｖ在分子筛中主要以分散的不流动的Ｖ￣（４＋）离子形式四配位存在于骨架上，Ｔｉ的存在不排斥Ｖ的同时进入骨架；同时考察了合成条件，吸附性能和热稳定性能。     

高度隔离过渡金属催化剂及其烯烃环氧化研究

 介绍了过渡金属杂原子分子筛的骨架杂原子表征、用离子注入法和化学嫁接法制备高度隔离过渡金属催化剂及其催化烯烃环氧化研究的结果．基于共振拉曼原理,用紫外共振拉曼光谱明确鉴别了TS－1,Fe－ZSM－5和V－MCM－41等分子筛中的骨架杂原子．用离子注入法和化学嫁接法制得具有高度隔离过渡金属离子的非杂原子分子筛催化剂．烯烃环氧化反应结果表明,所制得的催化剂显示出优良的催化性能．     

Infrared, optical absorption, and EPR spectroscopic studies on natural gypsum

The natural gypsum has been investigated by infrared, Raman, X-ray diffraction, optical absorption and electron paramagnetic resonance spectroscopy. The fundamental stretching and bending vibrations observed in the infrared region for SO₄²⁻ and H₂O are compared with the near-infrared overtones and combinations of these vibrations. MIR and Raman spectral features are attributed to sulfate fundamentals and lattice vibrations of H₂O, SO₄²⁻. The charge transfer and ligand field transition bands were observed near 490, 630, and 800–900 nm and were compared to those of iron oxides. The optical absorption spectrum indicates the presence of ferric and ferrous ions in the mineral. The site symmetry of Fe(III) in the sample is tetragonally distorted. EPR results indicate the presence of the ferric ion in a tetragonally distorted state.     

Effect of aluminum on the nature of the iron species in Fe-SBA-15

We report the preparation of highly ordered mesoporous Fe-Al-SBA-15 with isolated extraframework Fe species under acidic conditions. The materials were characterized by means of UV resonance Raman spectroscopy, in conjunction with BET, XRD, TEM, UV-vis, H2-TPR, FT-IR, and 27Al MAS NMR spectroscopy. The addition of both Fe and Al to the synthesis gel of SBA-15 results in the formation of isolated extraframework Fe species located close to the framework Al ions and the Fe content an order of magnitude higher than that in Fe-SBA-15 synthesized without Al. The existence of anchored extraframework Fe species was confirmed by the presence of a strong absorption band at 270 nm, hydrogen reduction at relatively low temperature, and the presence of a resonance Raman band at 1140 cm(-1). The location of Fe in close proximity to framework Al nuclei is further supported by 27Al MAS NMR measurements. Two characteristic UV Raman bands at 510 cm(-1) and 1090 cm(-1) excited by 244-nm laser are assigned to Fe-O-Si symmetric and asymmetric stretching modes of isolated tetrahedral Fe ions in the silica framework for Fe-SBA-15. The resonance Raman band at 1140 cm(-1) excited by 325-nm laser is attributed to the asymmetric stretching mode of the isolated extraframework iron species in Fe-Al-SBA-15. The isolated Fe species close to framework Al species are stable in acidic HCl solution, whereas the majority of Fe species in Fe-SBA-15 can be easily removed.     

From Molecular Fragments to Crystals: A UV Raman Spectroscopic Study on the Mechanism of Fe‐ZSM‐5 Synthesis

The nucleation process of iron‐exchanged zeolite Fe‐ZSM‐5, from the assembly of distorted tetrahedrally coordinated iron species and silicate rings in the precursor to the final Fe‐ZSM‐5 crystals, as well as variations in the coordination environment of iron, were studied by UV resonance Raman spectroscopy and complementary techniques.

     

Studies on the Structure, Properties of Ferroaluminophosphate Molecular Sieve (FAPO-5) and Chemical State of Iron in the FAPO-5 Molecular Sieve

The pure Ferroaluminophosphate molecular sieve(FAPO-5) was synthesized by hydrothermal crystallization. The crystal structure of FAPO-5 was studied via XRD, electron probe energy dispersion analysis, Mossbauer spectroscopy, EPR, XPS and IR, the parameters of unit cell and chemical composition of FAPO-5 were determined. The result has that the structure of FAPO-5 is AlPO -5 type and Fe2+ Fe3+ are incorporated into the framework of FAPO-5 molecular sieve. In addition, the chemical state of iron in FAPO-5 molecular sieve were studied and the adsorption properties, surface acidity and thermal stability were also investigated.     

Electronic, vibrational, and structural properties of a spin-crossover catecholato-iron system in the solid state: theoretical study of the electronic nature of the doublet and sextet states

As a functional model of the catechol dioxygenases, [(TPA)Fe(Cat)]BPh4 (TPA = tris(2-pyridylmethyl)amine and Cat = catecholate dianion) exhibits the purple-blue coloration indicative of some charge transfer within the ground state. In contrast to a number of high-spin bioinspired systems, it was previously shown that, in the solid state, [(TPA)Fe(Cat)]BPh4 undergoes a two-step S = 1/2 = S = 5/2 spin-crossover. Therefore, the electronic and vibrational characteristics of this compound were investigated in the solid state by UV/Vis absorption and resonance Raman spectroscopies over the temperature range of the transition. This allowed the charge-transfer transitions of the low-spin (LS) form to be identified. In addition, the vibrational progression observed in the NIR absorption of the LS form was assigned to a five-membered chelate ring mode. The X-ray crystal structure solved at two different temperatures, shows the presence of highly distorted pseudo-octahedral ferric complexes that occupy two nonequivalent crystalline sites. The variation of the molecular parameters as a function of temperature strongly suggests that the two-step transition proceeds by a successive transition of the species in the two nonequivalent sites. The thermal dependence of the high-spin fraction of metal ions determined by M?ssbauer experiments is consistent with the magnetic data, except for slight deviations in the high temperature range. The optimized geometries, the electronic transitions, vibrational frequencies, and thermodynamic functions were calculated with the B3LYP density functional method for the doublet and the sextet states. The finding of a ground state that possesses a significant mixture of Fe(III)-catecholate and FeII-semiquinonate configurations is discussed with regard to the set of experimental and theoretical data.     

有机胺在离子热合成 LTA 型磷酸铝分子筛中的助模板作用

 在 1-丁基-3-甲基溴化咪唑 ([bmim]Br) 离子液体中引入有机胺合成了 LTA 型磷酸铝分子筛 (AlPO4-42), 采用热重分析、核磁共振光谱、红外光谱以及荧光光谱对所得晶化产物进行了表征, 并考察了体系的晶化动力学. 结果表明, 有机胺以特定的聚集形态协同离子液体阳离子起到助模板剂的作用, 并填充在 AlPO4-42 分子筛孔道中. 晶化产物随晶化时间的演变表明, 体系中有机胺浓度的变化改变了动力学路径. 高浓度有机胺所形成的聚集体组装周围的无机物种, 促进了 sod 或 lta 笼结构的形成, 并导致立方相的 LTA 骨架晶化.     

An octanuclear complex containing the [Fe3O]7+ metal core: structural, magnetic, Mössbauer, and electron paramagnetic resonance studies

A new asymmetrically coordinated bis-trinuclear iron(III) cluster containing a [Fe(3)O](7+) core has been synthesized and structurally, magnetically, and spectroscopically characterized. [Fe(6)Na(2)O(2)(O(2)CPh)(10)(pic)(4)(EtOH)(4)(H(2)O)(2)](ClO(4))(2).2EpsilontOH (1.2EpsilontOH) crystallizes in the P space group and consists of two symmetry-related {Fe(3)O](7+) subunits linked by two Na(+) cations. Inside each [Fe(3)O](7+) subunit, the iron(III) ions are antiferromagnetically coupled, and their magnetic exchange is best described by an isosceles triangle model with two equal (J) and one different (J ') coupling constants. On the basis of the H = -2SigmaJ(ij)S(i)S(j) spin Hamiltonian formalism, the two best fits to the data yield solutions J = -27.4 cm(-1), J ' = -20.9 cm(-1) and J = -22.7 cm(-1), J ' = -31.6 cm(-1). The ground state of the cluster is S = (1)/(2). X-band electron paramagnetic resonance (EPR) spectroscopy at liquid-helium temperature reveals a signal comprising a sharp peak at g approximately 2 and a broad tail at higher magnetic fields consistent with the S = (1)/(2) character of the ground state. Variable-temperature zero-field and magnetically perturbed M?ssbauer spectra at liquid-helium temperatures are consistent with three antiferromagnetically coupled high-spin ferric ions in agreement with the magnetic susceptibility and EPR results. The EPR and M?ssbauer spectra are interpreted by assuming the presence of an antisymmetric exchange interaction with |d| approximately 2-4 cm(-1) and a distribution of exchange constants J(ij).     

Low-frequency mode activity of heme: femtosecond coherence spectroscopy of iron porphine halides and nitrophorin

The low-frequency mode activity of metalloporphyrins has been studied for iron porphine-halides (Fe(P)(X), X = Cl, Br) and nitrophorin 4 (NP4) using femtosecond coherence spectroscopy (FCS) in combination with polarized resonance Raman spectroscopy and density functional theory (DFT). It is confirmed that the mode symmetry selection rules for FCS are the same as for Raman scattering and that both Franck-Condon and Jahn-Teller mode activities are observed for Fe(P)(X) under Soret resonance conditions. The DFT-calculated low-frequency (20-400 cm (-1)) modes, and their frequency shifts upon halide substitution, are in good agreement with experimental Raman and coherence data, so that mode assignments can be made. The doming mode is located at approximately 80 cm (-1) for Fe(P)(Cl) and at approximately 60 cm (-1) for Fe(P)(Br). NP4 is also studied with coherence techniques, and the NO-bound species of ferric and ferrous NP4 display a mode at approximately 30-40 cm (-1) that is associated with transient heme doming motion following NO photolysis. The coherence spectra of three ferric derivatives of NP4 with different degrees of heme ruffling distortion are also investigated. We find a mode at approximately 60 cm (-1) whose relative intensity in the coherence spectra depends quadratically on the magnitude of the ruffling distortion. To quantitatively account for this correlation, a new "distortion-induced" Raman enhancement mechanism is presented. This mechanism is unique to low-frequency "soft modes" of the molecular framework that can be distorted by environmental forces. These results demonstrate the potential of FCS as a sensitive probe of dynamic and functionally important nonplanar heme vibrational excitations that are induced by the protein environmental forces or by the chemical reactions in the aqueous phase.     

Vibrational spectroscopy of the multi-anion mineral zykaite Fe4(AsO4)(SO4)(OH)·15H2O-implications for arsenate removal

Some minerals are colloidal and are poorly diffracting. Vibrational spectroscopy offers one of the few methods for the assessment of the structure of these types of minerals. Among this group of minerals is zykaite with formula Fe(4)(AsO(4))(SO(4))(OH)·15H(2)O. The objective of this research is to determine the molecular structure of the mineral zykaite using vibrational spectroscopy. Raman and infrared bands are attributed to the AsO(4)(3-), SO(4)(2-) and water stretching vibrations. The sharp band at 3515 cm(-1) is assigned to the stretching vibration of the OH units. This mineral offers a mechanism for the formation of more crystalline minerals such as scorodite and bukovskyite. Arsenate ions can be removed from aqueous systems through the addition of ferric compounds such as ferric chloride. This results in the formation of minerals such as zykaite and pitticite (Fe(3+), AsO(4), SO(4), H(2)O).