共查询到20条相似文献,搜索用时 31 毫秒
1.
制备了V取代的磷钼酸H 3+xPMo 12-xV xO 40( x=0,1,2)及1-丁基-3-甲基咪唑溴盐离子液体([C 4mim]Br),并采用离子交换的方法制备了系列杂化材料([C 4mim]3+xPMo 12-xV xO 40, x=0,1,2);采用X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、紫外-可见漫反射光谱(UV-Vis DRS)对所制备样品进行了表征;以H 2O 2为氧化剂,考察了所得样品催化苯羟基化制苯酚的活性。结果表明,和相应的离子液体及杂多酸相比,杂化材料的催化活性得到了很大的提高,尤其是催化剂[C 4mim] 5PMo 10V 2O 40,在优化后的条件下,苯的转化率可达到21%,苯酚的选择性在99%以上。而且,该催化剂具有很好的可重复使用性,连续使用五次后,苯的转化率和苯酚的选择性没有明显降低。 相似文献
2.
为了解Cr3+离子在钙铝锗酸盐Ca 3Al 2Ge 3O 12:石榴石中的光谱性质, 合成了Ca 3Al 2Ge 3O 12:Cr 3+多晶材料;测量了其X射线衍射图, 漫反射光谱, 激发、发射光谱等;分析了Cr3+离子在钙铝锗酸盐中的发光特性;计算了其晶场强度(Dq/B), Stokes位移(ΔEs)及黄昆-里斯因子(S)等. 在450 nm激发下, Ca 3Al 2Ge 3O 12:Cr 3+室温发射光谱主要由三个宽带及附加其上的弱R线构成, 分别对应于Cr3+离子的4T1、 4T2、2T2到 4A2 能级跃迁. 低温时R线变得强而锐. 通过计算, Dq/B=2.43, ΔEs=1884 cm-1, S=5.21. 表明在Ca 3Al 2Ge 3O 12中Cr 3+离子处于较弱的晶场强度, 电子-声子耦合较强, 为发展可调谐激光材料提供重要线索. 相似文献
3.
采用高温固相反应,以NaF作助熔剂,在1000 ℃的温度下合成了锕系元素Pu的模拟固化体(Gd 1-xCe x) 2Zr 2O 7+x (0 ≤ x ≤ 0.7).研究了模拟固化体的物相、热膨胀系数(TEC)、热导率(TC)随温度及组成的变化规律.粉末X射线衍射(XRD)测试结果表明: Gd 2Zr 2O 7基质本身呈弱有序烧绿石结构,而用Ce 4+取代Gd 3+的模拟固化体都呈缺陷萤石结构. (Gd 1-xCe x) 2Zr 2O 7+x的Ce(3d) X射线光电子能谱(XPS)有六个峰,结合能分别位于881.7, 888.1, 897.8, 900.4, 907.1, 916.1 eV处,与CeO2的XPS图谱非常相似,说明Ce为四价.随着温度的升高,所有样品的热膨胀系数总体上呈增大趋势.在室温至750 ℃附近,大部分样品的热导率随温度的升高而降低,之后热导率又呈小幅上升.在相同温度下,固化体(Gd 1-xCe x) 2Zr 2O 7+x (0 ≤ x ≤ 0.7)的热膨胀系数及热导率随组成变化呈相同趋势:在0 ≤ x ≤ 0.1范围内随x的增大而增大,随后在 x = 0.1-0.7时逐渐减小. 相似文献
4.
Since the discovery of superconductivity in Sr 2CuO 2F 2+δ there has been an increased interest in ternary oxide-fluorides. Sr 2CuO 2F 2+δ is prepared via low temperature ( T = 220 °C) reaction routes. Low temperature fluorination induces an interesting structural rearrangement in the parent compound Sr 2CuO 3, which is a one-dimensional material containing linear chains of vertex sharing CuO 4 squares along the crystallographic b axis. Upon fluorination, one oxide is substituted by two fluorides and Cu 2+ becomes octahedrally coordinated by four oxides and two fluorides. The fluorinated compound Sr 2CuO 2F 2+δ displays the T-type structure (La 2CuO 4). Insertion of excess fluorine, δ, also takes place and this fluorine occupies interstitial sites in the T structure. Although the starting material Ca 2CuO 3 is isostructural to Sr 2CuO 3, Ca 2CuO 2F 2+δ displays the T′ (Nd 2CuO 4) structure due to the smaller radius of Ca 2+ compared to that of Sr 2+. The alkaline-earth palladates with the general formula A2PdO3 (A = Ba, Sr) are isostructural with the A2CuO3(A = Ca, Sr) materials. We prepared the Ba2−xSrxPdO3 (x = 0–2) series and performed low temperature fluorination, which led to the synthesis of the series Ba2−xSrxPdO2F2+δ (0 ≤ x ≤ 1.5). All the compounds in the Ba2−xSrxPdO2F2+δ series show T′ structure (Ca2CuO2F2+δ). Similarities and differences with Sr2CuO2F2+δ and Ca2CuO2F2+δ will be discussed. 相似文献
5.
Dibromoacetic anhydride was prepared by reacting dibromoacetic acid with phosphorus(V) oxide in carbon tetrachloride at 85°C for 11 h. It reacts with Bi 2O 3 and CrO 3 in CCl 4 on prolonged refluxing forming Bi(CHBr 2COO) 3 and Cr (CHBr 2COO) 3, respectively. These new compounds were characterized by elemental analyses, IR, 1H NMR and mass spectroscopy. 相似文献
6.
The oxidation state, the mobility and the molecular structure of chromium species present on CrO x–Al 2O 3 catalysts have been studied by combined diffuse reflectance spectroscopy, EPR and reduction–extraction by ethane 1,2 diol. CrO 42− species exist on the alumina surface in the form of loosely-interacting species on hydrated surface (species A) and in the form of strongly bonded species on dehydrated Al 2O 3 surface (species B). The CrO 42− species show high mobility and are probably responsible for the formation of CrO x clusters. 相似文献
7.
CrO x/La 2O 3 mixed oxides, prepared by impregnating La 2O 3 with appropriate aqueous solutions of (NH 4) 2CrO 4 and calcining at 600 °C for 4 h, have been investigated by means of XRD, TPR, XPS, DRIFTS, and Raman spectroscopy (RS). The formation of the compounds La 2CrO 6, La(OH)CrO 4 and LaCrO 4 under these conditions was evidenced. Strong peaks at 864, 884, 913, and 921 cm −1, as well as weak peaks at 136, 180, 354, 370, and 388 cm −1 in the RS spectrum of CrO x/La 2O 3 have been assigned to La 2CrO 6. 相似文献
8.
The complexes, M[M(C 2O 4) 3]· xH 2 O, where x=4 for M=Cr(III), x=2 for M=Sb(III) and x=9 for M=La(III) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR and electronic spectral data, conductivity measurement and powder X-ray diffraction (XRD) studies. The chromium(III)tris(oxalato)chromate(III)tetrahydrate (COT), Cr[Cr(C 2 O 4) 3]·4H 2O, released water in a stepwise fashion. Removal of the last trace of water was accompanied by a partial decomposition of the oxalate group. Thermal investigation using TG, DTG and DTA techniques in air produced Cr 2O 3 at 858°C through the intermediate formation of Cr 2O 3 and CrC 2O 4 at around 460°C. While DSC study in nitrogen up to 670°C produced a mixture of Cr 2O 3 and CrC 2O 4. In antimony(III)tris(oxalato)antimonate(III)dihydrate (AOD), Sb[Sb(C 2O 4) 3]·3H 2O the dehydration took place during the decomposition of precursor at 170–290°C and finally at ca. 610°C Sb 2 O 5 along with trace amounts of Sb 2O 4 were produced. Trace amount of Sb 2O 3 and Sb along with Sb 2O is proposed as the end product at 670°C of AOD in nitrogen. The oxide La 2O 3 is formed at 838°C from the study with TG, DTG and DTA in air of lanthanum(III)tris(oxalato)lanthanum(III)nonahydrate (LON), La[La(C 2O 4) 3]·9H 2O. Intermediate dioxycarbonate, La 2O 2CO 3 was generated at 526°C prior to its decomposition to lanthanum oxide in air; whereas in N 2 the formation of La 2(CO 3) 3 at 651°C was proposed. The thermal parameters have been evaluated for each step of the dehydration and decomposition of COT, AOD and LON using five non-mechanistic equations i.e. Flynn and Wall, Freeman and Carroll, Modified Freeman and Carroll, Coats–Redfern and MacCallum–Tanner equations. Kinetic parameters, such as, E*, ko, Δ H*, Δ S* etc. were also supplemented by DSC studies in nitrogen for all the three complexes. Some of the intermediate species have been identified by analytical and powder XRD studies. Tentative schemes has been proposed for the decomposition of all three compounds in air and nitrogen. 相似文献
9.
A series of chromium(III) complexes [Cr(bipy)(HC 2O 4) 2]Cl·3H 2O (1), [Cr(phen)(HC 2O 4) 2]Cl·3H 2O (2), [Cr(phen) 2(C 2O 4)]ClO 4 (3), [Cr 2(bipy) 4(C 2O 4)](SO 4)·(bipy) 0.5·H 2O (4) and [Mn(phen) 2(H 2O) 2] 2[Cr(phen)(C 2O 4) 2] 3ClO 4·14H 2O (5) were synthesized (bipy=4,4′-bipyridine, phen=1,10-phenanthroline), while the crystal structures of 1 and 3–5 have been determined by X-ray analysis. 1 and 3 are mononuclear complexes, 4 contains binuclear chromium(III) ions and 5 is a 3D supromolecule formed by complicated hydrogen bonding. 1–3 are potential molecular bricks of chromium(III) building blocks for synthesis heterometallic complexes. When we use these molecular bricks as ligands to react with other metal salts, unexpected complexes 4 and 5 are isolated in water solution. The synthesis conditions and reaction results are also discussed. 相似文献
10.
The stabilities of the hydrated uranyl phosphates (UO 2) 3(PO 4) 2 · 4 H 2O, UO 2HPO 4 · 4 H 2O, and UO 2(H 2PO 4) · 3 H 2O have been reinvestigated. The compounds identified by thermal analysis have been prepared isothermally and characterized by their strongest X-ray reflections. During dehydration, oxygen was not evolved and the crystalline compounds (UO 2) 3(PO 4) 2, (UO 2) 2P 2O 7, UO 2(PO 3) 2, and probably (UO 2) 3P 4O) 13 were found. At still higher temperatures, the uranyl phosphates are reduced. The decomposition products lose phosphorus oxide above 1300–1400°C. The present results are summarized in a tentative pseudo-binary phase diagram UOx(x = 3 to 2)—UO2(PO3)2. 相似文献
11.
A potentially decadentate ligand, 1,1,4,7,10,10-hexakis(3,5-dimethyl-1-pyrazolylmethyl)-1,4,7,10-tetraazadecane (tthd), has been synthesized from the reaction of tri-ethylenetetramine with six equivalents of N-hydroxymethyl-3,5-dimethylpyrazole. The tthd ligand forms coordination compounds, M 2(tthd)(ClO 4) 4(H 2O) x, when M is Co, Ni, Cu, Zn and Cd and x = 4–8; and M 2(tthd)(A) 2(ClO 4) 2(H 2O) x when M is Co and Ni, A is NCS or Cl, and x = 4–8. The cobalt compound, Co 2(tthd)(ClO 4) 2(H 2O) 2(MeOH) 1.75, crystallizes in the triclinic space group P1, a = 1.959(2), b = 1.5657(3), c = 2.1244(3) nm, = 105.5(1), β = 96.9(1), γ = 112.1(1). Due to severe disorder of the anions the structure could only be refined to an Rw, value of 0.099. The ligand acts as a decadentate, dinucleating ligand. The cobalt ions are distorted octahedrally surrounded by five N-atoms of the tthd ligand and an O-atom of water occupying the sixth coordination place. The other perchlorate compounds have very similar structures, as can be concluded from spectroscopic data. In the thiocyanate and chloride compounds the anions have replaced the coordinated water molecules, resulting in octahedral Ni compounds. With Co thiocyanate, however, tthd acts as an octadentate ligand, resulting only in five-coordinated compounds. 相似文献
12.
MXene是一种新型的二维析氢催化材料,其表面容易被亲水基团O和OH混合覆盖。我们基于第一性原理计算的方法,研究了M_2XO_(2-2x)(OH)_(2x)(M=Ti,V;X=C,N)的析氢催化活性。计算结果显示,M_2XO_(2-2x)(OH)_(2x)的析氢催化活性与其表面OH覆盖率(X)密切相关。对Ti_2CO_(2-2x)(OH)_(2x)来说,OH覆盖率不超过1/3时,具有优异的析氢催化活性。对Ti_2NO_(2-2x)(OH)_(2x)、V_2CO_(2-2x)(OH)_(2x)和V_2NO_(2-2x)(OH)_(2x)来说,OH覆盖率分别达到4/9、1/3和5/9时,才具有最佳的析氢催化活性。接着,电荷分析显示OH覆盖率会显著影响M_2XO_(2-2x)(OH)_(2x)活性位点O基团的电荷量。最后,我们从态密度的角度揭示了析氢催化活性变化的原因,即活性位点O基团的氧化性随OH覆盖率的增大而被削弱。因此,本文提出了调节表面OH覆盖率来获取M_2XO_(2-2x)(OH)_(2x)最佳析氢催化活性状态的方法,这在工业制氢生产过程中具有重要的应用价值。 相似文献
13.
Two novel complexes of calcium croconate Ca(μ 3-C 5O 5)(H 2O) 3 (I) and calcium oxalato-croconate Ca 2(μ 4-C 5O 5)(μ 6-C 2O 4)(H 2O) (II) have been synthesized by soft chemical routes and their crystal structures have been solved from single-crystal data. Croconates I and II crystallize in orthorhombic space groups Pbca and Pnma, respectively. Their crystal structures evidence the versatile character of the croconate anion in the framework design. The calcium croconate I displays a 2D structure with corrugated sheets formed by croconate dianions and eightfold coordinated calcium atoms within [Ca 2O 14] dimers. The sheets develop eight-member apertures made of four dimers and four croconate dianions. The structure of II displays a 3D open-framework built from layers connected to each other by croconate dianions. This arrangement generates rectangular cavities free of water molecules. Seven- and eightfold coordinated calcium atoms with oxalate dianions constitute the layers. In both structures, the connecting modes of croconates are unusual. The thermal behaviour study has demonstrated that II is stable until 380 °C. 相似文献
14.
The preparation and characterization by X-ray crystallography of transition metal sulfur dioxide hexafluoroarsenates of the general formula [M(SO 2) x](AsF 6) 2 1 (1a: M=Mn, x=2; 1c: M=Co, x=4; 1e: M=Cu, x=4) and the hexafluoroantimonate [Co(SO 2) 2](SbF 6) 2 3 is reported. The structural features of the compounds mentioned are compared with those of [Fe(SO 2) 4](AsF 6) 2 (1b) and [Ni(SO 2) 6](AsF 6) 2 (1d), reported previously. The structural diversity of transition metal sulfur dioxide complexes is discussed. 相似文献
15.
Synthesis of the Y xGd 1−xBa 2Cu 4O 8 phases ( x=1; 0.5; 0.75) by special method from nitrates is described in this paper. Dissolution enthalpies of YBa 2Cu 4O 8, Y 0.5Gd 0.5Ba 2Cu 4O 8, Y 0.75Gd 0.25Ba 2Cu 4O 8, Y 2O 3, Gd 2O 3, CuO, BaCO 3 were measured in 6 N HCl at 323 K. On the basis of obtained experimental data, the enthalpies of some reactions with Y xGd 1−xBa 2Cu 4O 8 were determined. It was established that the above-mentioned 1 : 2 : 4 superconductors were thermodynamically more favourable than mixtures including CuO, YBa 2Cu 3O x. It was also established that, according to the obtained data, these phases can react with CO 2. 相似文献
16.
The applicability of positron annihilation spectroscopy for chemical structural problems is demonstrated by two examples: For the swelling dynamics of an amphiphilic polymer network, very quick structural changes were indicated by positronium lifetime parameters at very low swelling ratios and a hydration mechanism was proposed accordingly. For the series [Fe xZn 1−x(propyltetrazole) 6](BF 4) 2( x=1, 0.6, 0.4, 0.1, 0), changes in the dynamic structure were revealed by positronium lifetime spectroscopy. For compounds of x>0, temperature-induced spin-crossover was detected. 相似文献
17.
Composites Li1-xVxCryFe1-yPO4/C(x=0.01, 0.02; y = 0.01, 0.02) were synthesized by solid-state reaction method. The influence of the content of doping vanadium and chromium on the structure of Li1-xVxCryFe1-yPO4/C was investigated by XRD, while the morphology of powders was observed by SEM. The investigation of the electrochemical performances showed that the Li0.99V0.01Cr0.02Fe0.98PO4/C material has a higher capacity. At 0.1 C discharging rate, it is capable of delivering reversible specific capacity of 163.8 mAh/g with fairly stable cycleability. 相似文献
18.
A series of Ce xPr 1−xO 2−δ mixed oxides were synthesized by a sol–gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO, CH 3OH and CH 4 on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO 2 was observed. The samples were greatly crystallized in the range of the value x from 0.99 to 0.80, which is due to the formation of solid solutions caused by the complete insertion of Pr into the CeO 2 crystal lattices. Raman bands at 465 and 1150 cm −1 in Ce xPr 1−xO 2−δ samples are attributed to the Raman active F 2g mode of CeO 2. The broad band at around 570 cm −1 in the region of 0.3 ≤ x ≤ 0.99 can be linked to oxygen vacancies. The new band at 195 cm −1 may be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies. The TPR profile of Pr 6O 11 shows two reduction peaks and the reduction process is followed: . The reduction temperature of Ce xPr 1−xO 2−δ mixed oxides is lower than those of Pr 6O 11 or CeO 2. TPR results indicate that Ce xPr 1−xO 2−δ mixed oxides have higher redox properties because of the formation of Ce xPr 1−xO 2−δ solid solutions. The presence of the oxygen vacancies favors CO and CH 3OH oxidation, while the activity of CH 4 oxidation is mostly related to reduction temperatures and redox properties. 相似文献
19.
铬铁电化学氧化法是一种新的制备铬酸钠的方法,然而高碳铬铁在NaOH水溶液中的电化学氧化过程尚不明确。 采用循环伏安法(CV)、稳态极化法(LSV)等电化学测试方法对金属铬、高碳铬铁在NaOH水溶液中的电化学氧化过程进行研究,通过扫描电子显微镜(SEM)、能量散射谱(EDS)和X射线光电子能谱(XPS)对高碳铬铁电解后固相产物表征,判断固相产物的组成。 结果表明,高碳铬铁不同于金属铬的电氧化过程,它在NaOH溶液中通过Cr(0)→Cr(Ⅵ)的电氧化方式生成铬酸钠,中间产物Cr(OH) 3和Fe(0)发生电化学反应生成稳定的FeCr 2O 4。 随着NaOH浓度的增加,电势较低时,受高碳铬铁中Fe(0)的影响,高碳铬铁容易在NaOH水溶液中发生钝化;当电势足够正时,钝化膜溶解,生成铬酸钠、氢氧化铁和亚铬酸亚铁,同时,阳极表面有氧气析出。 高碳铬铁电化学氧化制备铬酸钠的适宜条件:碱浓度≥2 mol/L,阳极电势≥1.6 V( vs.SCE)。 相似文献
20.
用热分解法制得不同混合比例的二元金属氧化物催化剂Co xCr 1-xO 3/2(x = 0,0.2,0.4,0.6,0.8,1),使用SEM、XRD和XPS观察表征催化剂形貌、晶型和价态,使用线性扫描伏安、阶梯波伏安和恒电位测试电极活性、过电位和稳定性. 结果表明,该Co 3O 4和绿铬矿型Cr 2O 3混合物形成固溶体Co xCr 1-xO 3/2. x = 0.2时,Co 0.2Cr 0.8O 3/2电极性能较单一Co 3O 4和Cr 2O 3电极好,在高电位(1.0 V vs. Ag/AgCl),其电流强度是Co 3O 4的3.75倍,Cr 2O 3的15.2倍,其过电位(η = 0.0703 V)也较Co 3O 4(η = 0.6109 V)和Cr 2O 3(η = 0.435 V)小,催化性能最好,在强碱性溶液(pH=13)中有良好的稳定性. 相似文献
|