Cr或V掺杂的HMS在甲酸溶液中的光催化产氢性能研究

本文以过渡金属离子M(M代表Cr或V)掺杂为改性手段,通过改变掺杂量,合成了一系列分子筛光催化剂M(x)-HMS(x代表M/Si摩尔投料比)。用X-射线荧光光谱(XRF)、低温 N2 吸附-脱附、X-射线衍射(XRD)和紫外-可见吸收漫反射光谱(UV-vis)对M(x)-HMS进行了表征和分析。以高压汞灯为光源,以甲酸分解产氢为探针反应,研究了M(x)-HMS的光催化性能,发现Cr(x)-HMS和V(x)-HMS的产氢速率随组成变化呈双峰规律(均在x＝0.01和0.05时出现两个极大值),并从光催化剂的组成和结构角度给予了解释。以过渡金属离子M (M代表Cr或V)掺杂为改性手段, 通过改变掺杂量, 合成了一系列分子筛光催化剂M(x)-HMS (x代表M/Si投料摩尔比). 用X射线荧光光谱(XRF)、低温N₂吸附-脱附、X射线衍射(XRD)、紫外-可见吸收漫反射光谱(UV-vis)、高分辨透射电子显微镜(HRTEM)和X射线能量散射谱(EDXS)对M(x)-HMS进行了表征和分析. 以高压汞灯为光源, 以甲酸分解产氢为探针反应, 研究了M(x)-HMS的光催化性能, 发现Cr(x)-HMS和V(x)-HMS的产氢速率随组成变化呈双峰规律(均在x＝0.01和0.05时出现两个极大值), 并从光催化剂的组成和结构角度给予了解释.     

微量Al对杂原子ZSM-5型沸石晶化的影响

在HMDA-Na₂O-MO_x/2-SiO₂-H₂O体系中(HMDA=1,6-己二胺,M=V(Ⅲ),V(Ⅳ),Fe(Ⅲ)和Ga),通过加Al对照实验、液相电子衍射结构分析、X射线光电子能谱(XPS)表面组成分析和晶化动力学计算等方法,考察了微量Al对杂原子ZSM-5型沸石形成与晶体生长的影响。结果表明,微量Al对这类沸石的形成起"助成核作用刀,从而加速其晶体生长。     

钒,铬对快速凝固Al-Ti-Fe合金的组织结构与显微硬度的影响

利用X射线衍射(XRD)和透射电镜(TEM)研究了V, CrAl-Ti-Fe合金组织及显微硬度的影响. 结果表明 Al-Ti-Fe-(V,Cr)合金急冷态组织均为过饱和Al基固溶体; 300 ℃×10 h处理后, Al-2.5Ti-2.5Fe-2.5Cr合金析出Al3Ti和Al13Cr2相; 400 ℃×10 h处理后, Al-Ti-Fe-(V,Cr)合金均析出Al13Fe4相.随退火温度的升高, 快速凝固Al-2.5Ti-2.5Fe-2.5V合金的显微硬度略有下降, 快速凝固Al-2.5Ti-2.5Fe-2.5Cr合金的显微硬度略有上升,表明V, Cr元素的加入有利于快凝Al-2.5Ti-2.5Fe合金显微硬度的增加.     

杂原子分子筛(Ⅸ)——Zr-Si Pentasil型分子筛的合成及其结构和性能的研究

以正硅酸乙酯((C_2H_5)_4SiO_4)、水玻璃、硅溶胶为硅源,四丙基氢氧化铵(TPAOH),四丁基溴化铵(TBABr)、四乙基氢氧化铵(TEAOH)和1,6-己二胺(HDA)为模板剂,使用氯氧化锆(ZrOCl_2)为锆源首次合成了Zr-Si Pentasil型分子筛,用X射线衍射、X射线电子探针、红外光谱等研究了它的结构,并在X射线衍射仪上用每阶梯0.01°的阶梯扫描方法测得Zr-Si Pentasil型分子筛的晶胞参数,结果表明Zr进入分子筛的骨架,研究了此分子筛的晶体形貌、吸附性能、憎水性、热稳定性、比表面以及表面酸性等。     

双杂原子 Fe-V-β 沸石的合成、表征及催化性能

 采用水热合成法在 SiO2-Fe2O3-V2O5-(TEA)2O-H2O-NH4F 体系中合成了 Fe-V-β 沸石, 并用 X 射线衍射、红外光谱、固体漫反射光谱、热重-差热分析、扫描电镜-能量色散谱仪和等离子体发射光谱等技术对沸石样品进行了表征, 探讨了影响 Fe-V-β 沸石合成的因素. 结果表明, 按摩尔比组成SiO2:Fe2O3:V2O5:(TEA)2O:H2O:NH4F = 60:(0.1~0.75):(0.1~0.75):(17~18):(550~ 650):(30~50) 配制初始反应混合物, 可以制备出结晶良好的 Fe-V-β 沸石, 且 Fe 和 V 原子进入到沸石骨架. 所得 Fe-V-β (Si/(Fe+V) = 30) 沸石在 H2O2 氧化苯乙烯反应中表现出最高的催化活性, 苯乙烯转化率为 25.4%, 苯甲醛、苯乙醛和苯乙酮的选择性分别为 69.1%, 22.5% 和 4.1%.     

静电S+X-I+组装途径合成中孔杂原子分子筛

During the last years there has been an increas ing interest in new mesoporous molecular sieves con taining transition metal cations in their framework.Substitution of Si by Ti or V may provide zeolites with dramatic selective catalytic activity. The incor poration of titanium, vanadium and chromium into the silicate MCM-41 framework by electrostatic S+ I- assembly pathway under hydrothermal condi tions at 100～150 ℃ has been reported[1]. Here,we prepared some transition metal-containing meso porous molecular sieves Me-MCM-41 (Me= Ti, V,Cr, Mo, Mn, Zr, W) at ambient temperature through the halogen anion mediated S+ X I + as sembly pathway[2] (S+ -cationic quaternary ammo nium ion surfactants; X -halogen anion C1- or Br-; I+-cationic silicate precursors), by the hy drolysis of silicon source and transition metal source in strongly acidic medium, and in the presence of cetyl trimethyl ammonium bromide (CTMABr) as templating species.     

离子液体[BMIM]PF_6中铬的电沉积行为

以一氯丁烷、N-甲基咪唑和KPF6为原料,合成了1-丁基-3-甲基咪唑六氟磷酸盐离子液体([BMIM]PF6),用红外光谱(IR)对产物进行了结构分析.用循环伏安法测试该离子液体在85℃下的电化学窗口为4.7 V.考察了[BMIM]PF6-Cr(Ⅲ)电解液的电化学行为,结果表明,在85℃下Cr(Ⅲ)的还原过程是受扩散控制的一步还原不可逆过程,Cr(Ⅲ)的传递系数α=0.023,阴极扩散系数D0=1.142×10-6cm2/s.在85℃和-1.5 V条件下,用恒电势法在铜片上电沉积Cr(Ⅲ),并通过扫描电子显微镜(SEM)观察了铜片上镀层的表面结构,发现该镀层呈颗粒状,且颗粒的体积随沉积时间的延长而增大.X射线能量色散谱(EDS)和X射线粉末衍射(XRD)测试结果表明,该镀层为无定形的金属铬.     

具有高活性(001)晶面的Cr-TiO_2微球的制备及可见光催化性能

采用一步水热法制备了具有高裸露率(001)晶面的锐钛矿相Cr掺杂TiO2(Cr-TiO2)微球,利用场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)和X射线光电子能谱仪(XPS)等对样品进行了表征.结果表明,掺杂的Cr元素以Cr3+离子和CrO3团簇2种形式存在,Cr3+离子进入TiO2晶格,形成Cr3+→Ti4+电荷转移跃迁,Cr-TiO2在可见光区具有强烈吸收.少量的Cr掺杂有利于形成平整的高活性(001)晶面.以可见光降解酸性红染料作为探针反应研究了Cr-TiO2的催化活性.结果表明,具有(001)晶面的Cr-TiO2的催化效率明显优于普通的Cr-TiO2.     

系列三核铬钒羧酸配合物的FAB-MS研究

进行了系列三核羧酸配合物 [M3O(O2 CCH3) 6(THF) 3]X (M3=Cr3,X =ClO4;M3=Cr2 V ,CrV2 ,V3,X =M Cl5(M 统计为 2 /3Cr+1 /3V) ,etc)的快原子轰击质谱 (FAB MS)研究 ,在V3和Cr3两个同三核配合物中 ,V配合物易脱RCO ,而Cr配合物更易脱RCO2 。在Cr2 V和CrV2 两个异三核配合物中观察到重组反应 :Cr2 V除 [Cr2 V]还生成含有 [Cr3]重组生成的碎片离子 ,CrV2 除 [CrV2 ]则生成含有 [Cr3],[Cr2 V],[V3]等其它三种重组碎片离子。充实了前文所探讨得重组原因和规律 ,根据重组反应 ,确定了金属离子反应速率顺序为Cr >V。根据所脱落的碎片 ,初步探讨了此类三核羧酸配合物催化羧酸脱羧成酮的机理。     

杂原子分子筛 Ⅷ.Ti-Si Pentasil型分子筛的结构研究

本文研究了Ti-Si Pentasil型分子筛的结构。红外光谱和拉曼光谱表明,Ti-Si分子筛骨架中存在Ti—O—Si键的振动;顺磁共振谱证实Ti~(4 )处在畸变四面体环境中;X射线光电子能谱进一步验证了该分子筛骨架中钛以钛氧四面体(TiO_4)~(4-)的形式存在;电子探针对分子筛晶体的微区分析结果表明,Ti原子位于分子筛骨架上;X射线衍射测定了Ti-Si Pentasil型分子筛的晶胞参数,将钛含量作为被测函数,与全硅分子筛相比,Ti-Si分子筛的单位晶胞体积是直线上升的,这与分子筛骨架中Ti对Si的取代相一致。     

Redox and complexation chemistry of the Cr(VI)/Cr(V)-D-galacturonic acid system

The oxidation of d-galacturonic acid by Cr(VI) yields the aldaric acid and Cr(III) as final products when a 30-times or higher excess of the uronic acid over Cr(VI) is used. The redox reaction involves the formation of intermediate Cr(IV) and Cr(V) species, with Cr(VI) and the two intermediate species reacting with galacturonic acid at comparable rates. The rate of disappearance of Cr(VI), Cr(IV) and Cr(V) depends on pH and [substrate], and the slow reaction step of the Cr(VI) to Cr(III) conversion depends on the reaction conditions. The EPR spectra show that five-coordinate oxo-Cr(V) bischelates are formed at pH < or = 5 with the uronic acid bound to Cr(V) through the carboxylate and the alpha-OH group of the furanose form or the ring oxygen of the pyranose form. Six-coordinated oxo-Cr(V) monochelates are observed as minor species in addition to the major five-coordinated oxo-Cr(V) bischelates only for galacturonic acid : Cr(VI) < or =10 : 1, in 0.25-0.50 M HClO(4). At pH 7.5 the EPR spectra show the formation of a Cr(V) complex where the vic-diol groups of Galur participate in the bonding to Cr(V). At pH 3-5 the Galur-Cr(V) species grow and decay over short periods in a similar way to that observed for [Cr(O)(alpha-hydroxy acid)(2)](-). The lack of chelation at any vic-diolate group of Galur when pH < or = 5 differentiates its ability to stabilise Cr(V) from that of neutral saccharides that form very stable oxo-Cr(V)(diolato)(2) species at pH > 1.     

Dinuclear chromium(V) amino acid complexes from the reduction of chromium(VI) in the presence of amino acid ligands: XAFS characterization of a chromium(V) amino acid complex

The first synthesis and characterization of Cr(V) complexes of non-sulfur-containing amino acids are reported. The reduction of Cr(VI) in methanol in the presence of amino acids glycine, alanine, and 2-amino-2-methylpropanoic acid (alpha-aminoisobutyric acid, Aib) yielded several Cr(V) EPR signals. For the reaction involving glycine, the only Cr(V) EPR signals detected were those of the Cr(V)-intermediate methanol complexes, which were also observed in the absence of amino acids. The reaction involving alanine yielded one Cr(V) signal with a g(iso) value of 1.9754 (a(iso) = 4.88 x 10(-4) cm(-1) and A(iso)(53Cr) = 17.89 x 10(-4) cm(-1)). However, a solid product isolated from the reaction solution was EPR silent and was characterized as a dioxo-bridged dimeric species, [Cr(V)2(mu-O)2(O)2(Ala)2(OCH3)2](2-), by multiple-scattering XAFS analysis and electrospray mass spectrometry. The EPR spectrum of the reduction reaction of Cr(VI) in the presence of Aib showed several different Cr(V) signals. Those observed at lower g(iso) values (1.9765, 1.9806) were assigned to Cr(V)-methanol intermediates, while the relatively broad six-line signal at g(iso) = 2.0058 was assigned as being due to a Cr(V) complex with coupling to a single deprotonated amine group of the amino acid. This was confirmed by simplification of the superhyperfine coupling lines from six to three when the deuterated ligand was substituted in the reaction. The reduction of Cr(VI) with excess alanine or Aib ligands resulted in the formation of tris-chelate Cr(III) complexes, which were analytically identical to complexes formed via Cr(III) synthesis methods. The fac-[Cr(Aib)3] complex was characterized by single-crystal X-ray diffraction.     

Stabilization of high-valent metals by corroles: oxo[tris(pentafluorophenyl)corrolato]chromium(V)

The aerobic reaction of Cr(CO)6 with tris(pentafluorophenyl)corrole (H3(TpFPC)) in toluene gives the dark red oxochromium(V) compound (TpFPC)Cr(O), which has been characterized by X-ray crystallography, electrochemistry, and EPR spectroscopy. Short Cr-N (1.927-1.943 A) bonds as well as relatively large 14N and small 53Cr coupling constants suggest that sigma (N-->Cr) donation is responsible for the unusual stability of chromium(V) in this complex. The CrV/IV reduction potential (0.11 V vs Ag/AgCl) is 0.65 V below that of oxo(tetramesitylporphinato)chromium(V).     

Chromium(V) peptide complexes: synthesis and spectroscopic characterization

A series of stable Cr(V) model complexes that mimic the binding of Cr(V) to peptide backbones at the C-terminus of proteins have been prepared for N,N-dimethylurea derivatives of the tripeptides Aib3-DMF, AibLAlaAib-DMF, and AibDAlaAib-DMF (Aib = 2-amino-2-methylpropanoic acid, DMF = N,N-dimethylformamide). The Cr(ll) precursor complexes were synthesized by the initial deprotonation of the amide and acid groups of the peptide ligands in DMF with potassium tert-butoxide in the presence of CrCl2. The Cr(II) intermediates thus formed were then immediately oxidized to Cr(V) using tert-butyl hydroperoxide. Spectroscopic and mass-spectrometric analyses of the Cr(V) complexes showed that a new metal-directed organic transformation of the ligand had occurred. This involved a DMF solvent molecule becoming covalently bound to the amine group of the peptide ligand, yielding a urea group, and a third coordinated deprotonated urea nitrogen donor. A metal-directed oxidative coupling has been proposed as a possible mechanism for the organic transformation. The Cr(V/IV) reduction potential was determined for the three Cr(V) complexes using cyclic voltammetry, and in all cases it was quasi-reversible. These are the first isolated and fully characterized Cr(V) complexes with non-sulfur-containing peptide ligands.     

Theoretical investigation on transformation of Cr(II) to Cr(V) complexes bearing tetra-N-heterocyclic carbene and group transfer reactivity

The mechanism for the transformation among a series of Cr(II) to Cr(V) complexes bearing tetra-N-heterocyclic carbene macrocycle is investigated. The oxidation and aziridination of Cr(II) monomer are studied by local density functional M06L. The former generates Cr(IV) oxo and further oxidizes to cationic Cr(V) oxo. The latter proceeds via two paths with different multiplicity, forming Cr(IV) imide. The Cr(IV) oxo cannot transfer its oxygen atom neither to phosphine nor to alkene because of the high energy barrier and endothermic process. The group transfer reactions are explored for Cr(V) oxo and Cr(IV) imide. The doublet Cr(V) oxo can also exist as quartet Cr(IV)-oxyl radical and promote oxygen transfer to phosphine, resulting in phosphine oxide in one exergonic step. The macrocyclic ligand effect of imido group transfer from Cr(IV) imide is verified by Multiwfn analysis. For 18-ringed imide, the matched orbital type and same-phase overlap reduce the barrier of its 16-ringed analog and facilitate the formation of phosphorus imine.     

Charge distribution in chromium and vanadium catecholato complexes: X-ray absorption spectroscopic and computational studies

Transition-metal complexes with redox-active catecholato ligands are of interest as models of bioinorganic systems and as potential molecular materials. This work expands our recent X-ray absorption spectroscopic (XAS) studies of Cr(V/IV/III) triscatecholato complexes (Levina, A.; Foran, G. J.; Pattison, D. I.; Lay, P. A. Angew. Chem., Int. Ed. 2004, 43, 462-465) to a Cr(III) monocatecholato complex, [Cr(tren)(cat)]+ (tren = tris(2-aminoethyl)amine, cat = catecholato2-), and its oxidized analogue, as well as to a series of V(V/IV/III) triscatecholato complexes ([VL3]n-, where L = cat, 3,5-di-tert-butylcatecholato2-, or tetrachlorocatecholato2-, and n = 1-3). Various oxidation states of these complexes in solutions were generated by bulk electrolysis directly in the XAS cell. Increases in the edge energies and pre-edge absorbance intensities in XANES spectra, as well as decreases in the average M-O bond lengths (M = Cr or V) revealed by XAFS data analyses, are consistent with predominantly metal-based oxidations in both the Cr(V/IV/III) and V(V/IV/III) triscatecholato series, but the degree of electron delocalization between the metal ion and the ligands was higher in the case of Cr complexes. By contrast, oxidation of [Cr(III)(tren)(cat)]+ was mainly ligand-based and led to [Cr(III)(tren)(sq)]2+ (sq = semiquinonato-), as shown by the absence of significant changes in the pre-edge and edge features and by an increase in the average Cr-O bond length. The observed differences in electron-density distribution in various oxidation states of Cr and V mono- and triscatecholato complexes have been discussed on the basis of the results of density functional calculations. A crystal and molecular structure of (Et3NH)2[V(IV)(cat)3] has been determined at 25 K and the same complex with an acetonitrile of crystallization at 150 K.     

New insights on the mechanism of oxidation of D-galacturonic acid by hypervalent chromium

The pollutant Cr(VI) is known to be very carcinogenic. In conditions of excess of Cr(VI), oxidation of D-galacturonic acid (Galur), the major metabolite of pectin, yields d-galactaric acid (Galar) and Cr(III). The redox reaction takes place through a multistep mechanism involving formation of intermediate Cr(II/IV) and Cr(V) species. The mechanism combines one- and two-electron pathways for the reduction of Cr(IV) by the organic substrate: Cr(VI)→ Cr(IV)→ Cr(II) and Cr(VI)→ Cr(IV)→ Cr(III). This is supported by the observation of the optical absorption spectra of Cr(VI) esters, free radicals, CrO(2)(2+) (superoxoCr(III) ion) and oxo-Cr(V) complexes. Cr(IV) cannot be directly detected; however, formation of CrO(2)(2+) provides indirect evidence for the intermediacy of Cr(II/IV). Cr(IV) reacts with Galur much faster than Cr(V) and Cr(VI) do. The analysis of the reaction kinetics via optical absorption spectroscopy shows that the Cr(IV)-Galur reaction rate inversely depends on [H(+)]. Nevertheless, high [H(+)] still does not facilitate accumulation of Cr(IV) in the Cr(VI)-Galur mixture. Cr(VI) and the intermediate Cr(V) react with Galur at comparable rates; therefore the build-up and decay of Cr(V) accompany the decay of Cr(VI). The complete rate laws for the Cr(VI), Cr(V) and Cr(IV)-Galur redox reaction are here derived in detail. Furthermore, the nature of the five-co-ordinated oxo-Cr(V) bischelate complexes formed in Cr(VI)-Galur mixtures at pH 1-5 is investigated using continuous-wave and pulsed electron paramagnetic resonance (EPR) and density functional theory (DFT).     

Thermolyse de mélanges de chromates et d'oxalates de métaux alcalino-terreux II. Composés du magnésium

The thermolysis of mixtures of chromates and oxalates of magnesium has been studied combining thermal analysis and electron paramagnetic resonance. It is found that both the reduction of Cr(VI) to Cr(III) and that of Cr(VI) to Cr(V) are spontaneous and occur at about 600 and 250°C, respectively, under vacuum. Highly dispersed Cr(V) species are present after activation below 400°C while dispersed Cr(II) species, either as Cr₂O₃ or as Cr(III) in solid solution in the MgO lattice, are observed above 350 and 550°C, respectively. CO evolved during the decomposition of the oxalate is found to play a major role in the reduction of Cr(V) in Cr(III). Contrarily to the observation on the Ba and Sr homologues, no effect of the carbonate has been found.     

EPR spectroscopic studies of the reduction of chromium(VI) by methanol in the presence of peptides. Formation of long-lived chromium(V) peptide complexes

The synthesis and characterization of the first Cr(V) complexes with non-sulfur-containing peptides, which may mimic the chemistry of the intermediates in the formation of Cr-induced peptide-DNA cross-links in vivo, are reported. The reduction of Cr(VI) with methanol in the presence of a number of non-sulfur-containing peptides produced relatively stable Cr(V)-peptide complexes, which were characterized by EPR spectroscopy and electrospray mass spectrometry. The reaction of Cr(VI) with methanol alone (in the absence of peptide ligands) resulted in the formation of two Cr(V)-methanol intermediates, with giso values of 1.9765 and 1.9687. The methanol reduction of Cr(VI) in the presence of the glycine peptides, triglycine, tetraglycine, and pentaglycine resulted in the formation of both Cr(V)-methanol and Cr(V)-peptide intermediates, while only the Cr(V)-peptide complexes were detected in the reactions with the alanine peptides trialanine, tetraalanine, and pentaalanine. Similar EPR signals were observed for all of the Cr(V)-peptide complexes with giso values between approximately 1.986 and approximately 1.979, and AN values of (2.1-2.6) x 10(-4) cm-1.     

Adsorption of metal anions of vanadium(V) and chromium(VI) on Zr(IV)-impregnated collagen fiber

The metal anions of vanadium (V) and chromium (VI) in aqueous solution can be effectively adsorbed by Zr(IV)-impregnated collagen fiber (ZrICF). The maximum adsorption capacity of V(V) takes place within the pH range of 5.0 to 8.0, while that of Cr(VI) is within the pH range of 6.0 to 9.0. When the initial concentration of metal ions was 2.00 mmol L⁻¹ and the temperature was 303 K, the adsorption capacity of V(V) on Zr-ICF was 1.92 mmol g⁻¹ at pH 5.0, and the adsorption capacity of Cr(VI) was 0.53 mmol g⁻¹ at pH 7.0. As temperature increased, the adsorption capacity of V(V) increased, while that of Cr(VI) was almost unchanged. The adsorption isotherms of the anionic species of V(V) and Cr(VI) can be fit by the Langmuir equation. The adsorption rate of V(V) follows the pseudo-first-order rate model, while the adsorption rate of Cr(VI) follows the pseudo-second-order rate model. Furthermore, ZrICF shows high adsorption selectivity to V(V) in the mixture solution of V(V) and Cr(VI). Practical applications of ZrICF could be expected in consideration of its performance in adsorption of V(V) and Cr(VI).