磷钼酸对直接甲醇燃料电池阴极氧还原的促进作用

以磷钼酸(H₄PMo₁₂O₄0·xH₂O,PMo₁₂)为直接甲醇燃料电池(DMFC)阴极添加剂,制备了Pt-PMo₁₂/C复合催化剂.电化学测试表明,该添加剂对于DMFC阴极氧还原具有明显的促进作用,与常规的Pt/C催化剂相比,相同载量下极限扩散电流提高了56.3%.在单电池性能测试中,这种促进作用使电池的最大输出功率提高了28%.     

一些含钒杂多化合物的合成、表征及其在环己烷催化氧化反应中性能的比较

合成了一系列钒取代在不同位置的杂多化合物, 考察了它们在环己烷催化氧化反应中的活性及其过氧化氢的分解情况, 发现钒的配位环境是影响反应活性的重要因素. 其中以H₄PMo₁₁VO₄₀为代表的钒在配位原子位置上的磷钼钒酸, 不但显示了很好的催化环己烷氧化反应的活性, 而且H₂O₂的分解反应同时也得到了较好的抑制.     

氧化镁负载磷钼钒杂多酸催化剂的结构和催化性能

采用乙醇溶液中浸渍的方法制备了氧化镁负载的磷钼钒酸铜(Cu₂PMo₁₁VO₄0)催化剂,考察了正己醇选择氧化生成正己醛的催化反应性能.催化剂的IR,XRD,UV-DRS,NMR,DTA-TG和比表面积等测试结果表明,Cu₂PMo₁₁VO₄0在氧化镁表面单层分散,形成缺位型Keggin结构.反应后催化剂表面分散状态及结构未发生明显改变,Keggin型对称结构有所恢复,形成活化状态的缺位型Keggin结构.     

H3PMo12O40/MOF-808复合材料制备及其吸附性能研究

以Keggin型磷钼酸、1,3,5-均苯三甲酸和八水氯氧化锆为原料，通过一步原位溶剂热制备了复合型吸附剂，通过XRD、SEM、FT-IR和TGA等表征手段说明，将亲水性杂多酸固定在MOF-808金属有机骨架基体上，对水溶液中亚甲基蓝溶液的吸附能力得以提升。动力学实验表明，H₃PMo₁₂O₄₀/MOF-808对亚甲基蓝的吸附符合准二级动力学模型，吸附等温线遵循Langmuir等温线模型，表明MB均匀吸附在H₃PMo₁₂O₄₀/MOF-808表面。根据Langmuir模型，在pH值为8,T=303K,吸附剂吸附性能最好。热力学研究表明，吸附过程是一个自发的放热反应。此外，H₃PMo₁₂O₄₀/MOF-808在五个连续循环实验中从其水溶液中吸附MB分子，表现出较好地可重复使用性。     

一个钼钒二聚体簇合物的合成及其性能

以NH₄VO₃, H₃PMo₁₂O₄₀·xH₂O, Cu(NO₃)₂和哌嗪为主要原料,采用水热方法,合成了一个新的钼钒二聚体簇合物--(H₂NC₄H₈NH₂)₆［Mo^VI₁₆V^V₁₂P₂O₈₄］·5H₂O(1),其结构和性能经UV-Vis, IR, X-射线衍射、光电子能谱及热重分析表征。1属单斜晶系,P2(1)/c空间群, 晶胞参数a=20.450(4) , b=24.989(5) , c=20.450(4) , β=93.89 °, V=10 427(4) ³, Fw=4 159.18, Dc=2.650 g·cm^-3, μ=3.018 mm^-1, F(000)=7 952, Gof=1.029。晶体结构解析表明：1由两个单元Keggin型簇核［PMo₈V₆O₄₂］^7-聚合而成一个二聚体簇［P₂Mo_l6V₁₂O₈₄］^14-,该二聚体簇核和有机配体哌嗪之间通过复杂的氢键相互作用,展示三维超分子网络结构。     

P、As为中心原子的杂多钼酸盐的合成、热稳定性及还原性研究

在合成(NH₄)₃PMo₁₂O₄₀和K₃PMo₁₂O₄₀的基础上,用改进的方法合成了(NH₄)₃AsMo₁₂O₄₀和K₃AsMo₁₂O₄₀,以FTIR、XRD、TG-DTA、ESR和TPR等手段对其结构、热稳定性和还原性进行了考查,当中心原子由P换成As后,杂多钼酸盐热稳定性下降,还原性提高.     

具有Dawson结构的钼钒磷杂多酸氧化还原性质的研究

通过SnCl₂电位滴定、极谱和循环伏安方法,详细研究了2:18系列钼钒磷杂多酸H_(6+n)[P₂Mo^13-nV_nO₆₂]·xH₂O(n=1～3)和H^_4+n[P₂Mo_18-nV_nO₆₂H₂]·xH₂O(n=4,5)在溶液中的氧化还原性质,证实它们的还原为三步分别加合n,2,2个电子,同时加合n,2,2个质子的过程,总结了循环伏安峰电位与pH的关系,提出了还原机理。     

基于2-氨基吡啶的两个簇基超分子化合物的合成、 结构及催化性能

以磷钼酸、 2-氨基吡啶、 五氧化二钒、 氯化锌和氯化镍等为主要原料, 采用水热方法合成了2个簇基超分子化合物[H₃PMo₁₂O₄₀]₂[C₅H₆N₂]₆(1)和[H₂PMo₁₂V₂O₄₂][C₅H₆N₂]₅·3H₂O(2)(C₅H₆N₂=2-氨基吡啶). 通过元素分析、 红外光谱、 紫外-可见光谱、 X射线光电子能谱、 热重分析、 X射线单晶衍射及X射线粉末衍射等手段对化合物进行了结构表征. 结构分析显示, 簇单元不同的2个超分子化合物以各自独特的堆积方式形成三维超分子网络. 利用苯乙烯的环氧化反应研究了2个化合物的催化性能.     

一种新型直接甲醇燃料电池阳极添加剂的电化学研究

将磷钼酸(H₄PMo₁₂O₄₀·xH₂O,PMo₁₂)作为一种添加剂,制备了直接甲醇燃料电池阳极Pt-Ru/C-PMo₁₂复合催化剂,并对甲醇在含有此复合催化剂的阳极上的氧化进行了电化学研究.测试表明该添加剂降低了甲醇及其电氧化中间产物转化的活化能,改善了电极内部的质子传输状况,对甲醇的电化学氧化过程具有明显的促进作用,该复合催化剂与常规的Pt-Ru/C催化剂相比,甲醇的阳极氧化电流提高了46%.添加剂的这一效应可能与磷钼酸的Keggin结构有关.     

钒氧多酸桥联大环铜配合物的合成及其晶体结构

以大环铜配合物［CuL］(ClO₄)₂(L=5,7,7,12,14,14-六甲基-1,4,8,11-四氮杂环十四-4,11-二烯)与NH₄VO₃反应合成了一个新的钒氧多酸桥联大环铜配合物［CuL］₂［H₂V₁₀O₂₈］·7H₂O(1),其结构经IR,元素分析和X-射线单晶衍射表征。1（CCDC: 1510831）属单斜晶系,P2(1)/n空间群,晶胞参数a=11.512(3) , b=18.170(4) , c=14.534(3) , β=102.997(4)°, V=2 962.3(11) ³, Dc=1.986 mg·cm^-3, Z=2, μ=2.300 mm^-1, R₁=0.047 2, wR₂=0.118 2。     

Kinetics and Mechanism of Dehydration of Heteropolyacids

The kinetics and mechanism of the dehydration and decomposition of heteropolyacids of molybdenum, tungsten and vanadium (H3+xYx+M12O40·mH2O; Y=Si, P; M=Mo, W) were studied. The data obtained on the dehydration kinetic parameters correlate with the expected structures, of these crystal hydrates, the IR data and X-ray phase analysis. This revised version was published online in July 2006 with corrections to the Cover Date.     

K4H2[PMo9V3O40]·10H2O的合成及其晶体结构

采用低温技术,用X射线单晶衍射法测定了标题化合物的结构。晶体属P4/mnc空间群,=12.515(3),c=17.636(7)A,Z=2.用788个独立可观测反射精修所有结构参数得R=0.061.钼钒磷杂多酸阴离子中,PO4四面体是无序的,P-O键长1.54A.M(Mo,V)是6配位,M-O键长1.62-2.48A,K是7配位,K-O键长2.84-3.10A。     

Novel charge transfer supramolecular assemblies with Keggin anions and 2-amino-5-nitropyridine

Several novel compounds with the non-linear optical chromophore 2-amino-5-nitropyridine (2A5NP) and Keggin polyoxoanions (alpha-isomers), having the general formula (2A5NP)(m)H(n)[XM12O40].xH2O, M = Mo, W, were synthesised. Compounds were obtained with X = P, n = 3, m = 3 and 4 and X = Si, n = m = 4 (x = 2-6). Thus, for each of the anions [PMo12O40]3- and [PW12O40]3- two different compounds were obtained, with the same anion and organic counterpart but with a different stoichiometric ratio. These presented different charge transfer properties and thermal stability. All compounds were characterised by spectroscopic and analytical techniques. The single crystal X-ray diffraction structure of (2A5NP)4H3[PMo12O40].2.5H2O.0.5C2H5OH showed that the water solvent molecules and the organic chromophores are assembled via infinite one-dimensional chains of hydrogen bonds with formation of open channels, which accommodate [PMo12O40]3- and ethanol solvent molecules.     

Formation of p-phenylenediamine-crown ether-[PMo12O40]4- salts

Electron transfer from the electron donor of p-phenylenediamine (PPD) to the electron acceptor of (H+)3[PMo12O40]3- forms a one-electron-reduced Keggin cluster of [PMo12O40]4-, bearing a S = 1/2 spin, while proton transfer from the proton donor of (H+)3[PMo12O40]3- to the proton acceptor of PPD yielded mono- and diprotonated cations of 4-aminoanilinium (HPPD+) and p-phenylenediammonium (H2PPD2+). By introduction of crown ether receptors during the crystallization process, supramolecular cations of (HPPD+)(crown ethers) and/or (H2PPD2+)(crown ethers) were successfully introduced into three new alpha-[PMo12O40]4- salts of (H2PPD2+)2([12]crown-4)4[PMo12O40]4- (1), (HPPD+)4([15]crown-5)4[PMo12O40]4- (2), and (HPPD+)2(H2PPD2+)([18]crown-6)4[PMo12O40]4- (3) as the countercation. The protonated states of PPD and molecular-assembly structures of the supramolecular cations depended on the size of the crown ethers. In salt 3, a novel mixed-protonated state of HPPD+ and H2PPD2+ was confirmed to be complexed in the cation structure. According to the changes in the cation structures, the anion arrangements were modulated from those of the two-dimensional layer for salt 1 to the isolated cluster for salts 2 and 3. The temperature-dependent magnetic susceptibilities of salts 1-3 were consistent with the isolated spin arrangements of [PMo12O40]4-. The electronic spectra of salts 1-3 indicated the intervalence optical transition from pentavalent Mo(V) to hexavalent Mo(VI) ions within the [PMo12O40]4- cluster. Temperature-dependent electron spin resonance spectra of salt 2 revealed the delocalization-localization transition of the S = 1/2 spin at 60 K. The spin on the [PMo12O40]4- cluster was localized on a specific Mo(V) site below 60 K, which was thermally activated with an activation energy of 0.015 eV.     

In situ investigations of structure-activity relationships in heteropolyoxomolybdates as partial oxidation catalysts

The structural evolution of Keggin-type heteropolyoxomolybdates (HPOM) during thermal treatment in propene and in propene and oxygen in the temperature range from 300 to 773 K was investigated by in situ X-ray diffraction (XRD) and in situ X-ray absorption spectroscopy (XAS) combined with mass spectrometry. During treatment in propene or hydrogen and at reaction temperatures above 673 K, the initially triclinic H(3)[PMo(12)O(40)].13 H(2)O is transformed quantitatively into a cubic HPOM (Pn$\bar 3$m, a=11.853 A) exhibiting a long-range structure similar to that of the corresponding cesium salts. The treatment described constitutes the first readily available preparation route for a cubic HPOM without alkali metal ions in the structure. For both H(3)[PMo(12)O(40)] and Cs(2)H[PMo(12)O(40)] migration of molybdenum from the Keggin ion onto interstitial sites is proposed to occur in propene or hydrogen at temperatures above about 573 K to give thermally stable, partially reduced lacunary Keggin ions. During activation in propene and oxygen the onset of catalytic activity of H(3)[PMo(12)O(40)] and Cs(2)H[PMo(12)O(40)] at about 573 K correlates with partial reduction of Mo and characteristic changes in the local structure of the Keggin ion. The structural changes observed indicate that, similar to the treatment of the HPOM in propene, migration of molybdenum from the Keggin ions onto interstitial sites and formation of lacunary Keggin ions take place. Moreover, the formation of these partially reduced lacunary Keggin ions appears to be a prerequisite for the material to become an active heterogeneous catalyst. Evidently, the undistorted Keggin ion in the as-prepared HPOM has to be regarded as a precursor of the active catalyst.     

Na_3H_2[PMo_(10)V_2O_(40)]·16H_2O的合成与晶体结构

标题化合物的晶体属P2_1/m空间群,α=13.821(2),b=15.355(3),c=11.597(2),β=107.50(2)°,V=2347.2~3,M_r=2091.46,Z=2,D_c=2.959 g·cm~(-3),μ(MoK_o)=30.77cm~(-1),F(000)=1992。用4049个独立可观测衍射精修结构,R=0.033。杂多酸阴离子[PMo_(10)V_2O_(40)]~(5-)具有准Keggin结构,12个金属原子呈无序分布,中心原子P与两个齿顶原子M(Mo/V)在对称面上。P—O平均键长1.541(2),M—O键长1.671(2)-2.432(2)。除一个Na—O配位多面体为畸变三方锥外,其余四个Na—O配位体均为六配位。讨论了Na~+离子呈无序分布的晶体结构特征并初步总结[PMo_(10)V_2O_(40)]~(5-)在不同晶相中的构型。     

Synthesis and characterizations of cyclic octanuclear mixed-valence vanadium(IV,V) clusters with polyoxometalate counterions

Hydrothermal reaction of Na2WO4, VOSO4, 2,2'-bpy and H3PO4 has afforded in high yield the compound [V(IV)2V(V)6O14(bpy)8(PO4)2][PW11V(V)O40](bpy).12H2O (1). Compound 1 contains a novel octanuclear mixed valence V(IV,V) cluster, [V(IV)2V(V)6O14(bpy)8(PO4)2]4+, with [PW11V(V)O40]4- as counterion. In the vanadium cluster, four V(V) centers are localized and the remaining two V(IV) and two V(V) ions are disordered over four crystallographically equivalent positions. The isostructural compound [V(IV)2V(V)6O14(bpy)8(PO4)2][PMo11V(V)O40](bpy).3H2O (2) has also been synthesized. Thermodiffractometry experiments indicate that 2 is stable up to 360 degrees C. Redox activities for both the vanadium and molybdenum centers have been observed by solid-state electrochemical measurements performed on mechanically attached microparticles of 2. Magnetic measurements performed on have shown the occurrence of weak ferromagnetic interactions between the V(IV) centres (J = +0.34 cm(-1), H(ex) = -JS1 x S2), and combined with DFT calculations, have allowed to propose a localization of the two V(IV) centers on two of the four equivalent crystallographic sites. Finally high field electron paramagnetic resonance has evidenced the magnetic axial anisotropy of the paramagnetic centers (g(x) = g(y) = 1.975(3); g(z) = 1.939(4)).     

Synthesis, crystal structure of α-Keggin heteropolymolybdates with pyridine-2,6-dicarboxylate based frameworks, and associated RhB photocatalytic degradation and 2D-IR COS tests

Three α-Keggin heteropolymolybdates with the formula [(C(5)H(4)NH)COOH](3)[PMo(12)O(40)] 1, {[Sm(H(2)O)(4)(pdc)](3)}{[Sm(H(2)O)(3)(pdc)]}[SiMo(12)O(40)]·3H(2)O 2 and {[La(H(2)O)(4)(pdc)](4)}[PMo(12)O(40)]F 3 (H(2)pdc = pyridine-2,6-dicarboxylate), have been synthesized under hydrothermal condition and characterized by single crystal X-ray diffraction analyses, elemental analyses, inductively coupled plasma atomic emission spectroscopy (ICP-AES), IR, thermal gravimetric analyses, thermal infrared spectrum analyses and powder X-ray diffraction (PXRD) analyses. Single crystal X-ray diffraction indicates all three compounds comprise ball-shaped Keggin type [XMo(12)O(40)](n-) polyoxometalates (POMs) (n = 3, X = P; n = 4, X = Si, respectively) with different types of carboxylic ligands derived from H(2)pdc, and these cluster anions are isostructural. In order to explore structural characteristics, Rhodamine B photocatalytic (RhB) degradation and two-dimensional infrared correlation spectroscopy (2D-IR COS) tests, are investigated for 1, 2 and 3. In RhB degradation, all compounds show good photocatalytic activity. For 1, the activity mainly comes from POMs. While in 2 and 3, POMs' photocatalytic activity is enhanced by the Ln(iii)-pdc metal-organic frameworks. Structural properties like POM's stability and magnetic sensitivity are discussed by 2D-IR COS under thermal/magnetic perturbations.     

Electrochemical Properties and ESR Characterization of Mixed Valence alpha-[XMo(3)(-)(x)()V(x)()W(9)O(40)](n)()(-) Heteropolyanions with X = P(V) and Si(IV), x = 1, 2, or 3

Electrochemical behavior of the alpha-[SiMo(3)(-)(x)()V(x)()W(9)O(40)]((4+)(x)()())(-) and alpha-[PMo(3)(-)(x)()V(x)()W(9)O(40)]((3+)(x)()())(-) anions with x = 1, 2, or 3 were studied. Electrochemical reduction of each compounds was consistent with its Mo/V ratio, reduction of vanadium and molybdenum atoms occurring in the +0.6 to -0.6 V potential range. The one-electron-reduced species were prepared by electrolysis and then characterized by ESR spectroscopy. The g and A values for V(4+)ions appeared to depend on the nature of the surrounding atoms (Mo(VI), W(VI), and V(V)). In solution at 330 K, the ESR spectrum of the protonated alpha-H[SiMoV(IV)VW(9)O(40)](6)(-) anion displayed 29 superhyperfine lines which were related to the partial localization of the electron on one vanadium nucleus. The ESR spectra at room temperature for the divanadium-substituted anions showed a strong anisotropy of the A tensor which would be related to the electron transfer along a preferential axis. An isolated V(4+) signal was not observed, even at 12 K, indicating that the electron is never firmly trapped on one single vanadium atom.     

A New Supramolecular Compound Based on Cd（II）-Schiff-base and Keggin-type [PMo_（12）O_（40）]~3

A new supramolecular compound, {[Cd(L)2]2[PMo12O40NO3]·CH3CN·2H2O}n 1 (L is 1,4-bis(4-imidazolyl)-2,3-diaza-1,3-butadiene), based on Cd(II)-Schiff-base and Keggin- type [PMo12O40]3- was synthesized via self-assembly and structurally characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction analysis. The crystal is of triclinic, space group P1 with a = 12.0128(11), b = 13.6196(13), c = 13.9995(13) , α = 103.868(2), β = 95.225(2), γ = 101.024(2)°, V = 2160.0(3) 3, Z = 1, C34H39N26O45Cd2Mo12P, Mr = 2938.96, Dc = 2.259 g/cm3, μ = 2.276 mm-1, F(000) = 1400, the final R = 0.0565 and wR = 0.1613 for 4973 observed reflections with I 2σ(I). The crystal structure can be described by the packing of Keggin anionic and Metal-Schiff-base cationic layers.