以磷钨杂多酸银盐为催化剂合成丁酮乙二醇缩酮

以磷钨杂多酸银盐(AgxH3-xPW12O40,0相似文献   

壳聚糖硫酸盐催化合成环己酮缩乙二醇

由酮（醛）和醇合成缩酮（缩醛），传统的催化剂是强质子酸（如浓硫酸、盐酸或磷酸），其特点是催化剂价廉易得，催化活性高，但设备腐蚀严重，产物的后处理中存在大量的废酸废水造成环境污染。一些其它的酸性物质如NH2-SO3H、NaHSO4、SnCl4、Bi（NO3）3、维生素C等也是催化合成缩酮（缩醛）的良好催化剂，但催化剂难以回收利用。新型固体酸如分子筛、铌酸、SO4^2- -TiO2、TiSiW12O40／TiO2等由于其良好的催化活性和稳定性，与产物分离简便，     

新固体超强酸的制备和缩酮的合成

报道了新型固体超强酸Fe2O3／S2O8^2-催化剂的制备及其催化合成缩酮的研究工作,探讨了Fe2O3／S2O8^2-的制备方法和合成缩酮的反应条件。结果表明：酮(醛)117mmol,苯为带水剂,催化剂Fe2O3／S2O8^2-用量为原料总质量的8．4％,酮醇摩尔比为1．0：3．0,回流反应时间为4h,缩酮平均产率高达95．5％。     

Keggin型多元杂多酸催化合成苯乙酮环乙二缩酮

合成了一系列具有Keggin结构的P-V-Mo-W四元杂多酸H3+xPVxMoyW12-x-yO40.nH2O(其中,x=1,2和3),采用傅里叶变换红外光谱和X射线衍射等方法表征了杂多酸的结构;以磷钒钼钨杂多酸为催化剂合成苯乙酮环乙二缩酮.考察了催化剂的种类、醇酮摩尔比、带水剂的种类和反应条件(催化剂用量、带水剂用量、反应温度、反应时间)对苯乙酮乙二醇缩酮反应的影响.在优化条件下,即苯乙酮0.1 mol、乙二醇0.14 mol、催化剂H6PV3MoW8O400.4 mmol、在110℃反应6 h、带水剂环己烷15 mL,苯乙酮的转化率达到84.1%、苯乙酮环乙二缩酮的选择性达到99.4%.     

1-丁基-3-甲基咪唑磷钨酸盐的制备及其对酯化反应的催化性能

以溴化1-丁基-3-甲基咪唑盐([bmim]Br)和磷钨酸(H3PW12O40)为原料制备了1-丁基-3-甲基咪唑磷钨酸盐([bmim]3PW12O40)催化剂,并用傅里叶变换红外光谱、热重分析-差示扫描量热法、正丁胺电位滴定及元素分析等技术对催化剂进行了表征,考察了催化剂对乙醇与乙酸酯化合成乙酸乙酯反应的催化活性.结果表明,[bmim]3PW12O40中有3个结晶水,并保持有H3PW12O40的Keggin结构和酸强度,[bmim]3PW12O40的酸量明显少于H3PW12O40的酸量.在乙醇与乙酸酯化合成乙酸乙酯反应中,[bmim]3PW12O40催化剂具有较高的催化活性和较好的重复使用性能.     

碘掺杂聚苯胺催化合成环己酮1,2-丙二醇缩酮

合成了聚苯胺-碘(PAn-I2)催化剂,并对其结构进行了表征。并通过环己酮与1,2-丙二醇合成环己酮1,2-丙二醇缩酮,探讨了PAn-I2对缩酮反应的催化活性。实验结果表明,PAn-I2是缩酮反应的良好催化剂,在环己酮100 mmol,n(环己酮)∶n(1,2-丙二醇)=1∶1.5,催化剂用量为反应物总质量的3%,环己烷12 mL,反应时间2 h的优化条件下,环己酮1,2-丙二醇缩酮的收率可达92.1%。     

磷钼酸催化合成DL-α-生育酚

以磷钼酸(H3PMo12O40)为催化剂,通过2,3,5-三甲基氢醌与异植醇在室温下缩合得到DL-α-生育酚(维生素E),发现H3PMo12O40是合成DL-α-生育酚的一种高活性、易于分离和能够重复使用的催化剂。     

硫酸镓催化法合成环己酮乙二醇缩酮

以环己酮和乙二醇为原料,硫酸镓为催化剂,在微波辐射和无溶剂条件下,合成了环己酮乙二醇缩酮．探讨了酮醇物质的量比、催化剂用量、微波功率和辐射时间对产品收率的影响．结果表明,环己酮乙二醇缩酮的最佳合成条件为：n（环己酮）：n（乙二醇）=1：3,催化剂用量为反应物总质量的2．0％,微波功率为375W,辐射时间为20min．在此条件下,缩酮收率可达96．3％,说明硫酸镓是一种合成环己酮乙二醇缩酮的优良催化剂．     

H_4SiW_(12)O_(40)/C催化合成丁酮1,2-丙二醇缩酮

以丁酮和1,2-丙二醇为原料,活性炭负载硅钨酸(H4S iW12O40/C)为催化剂,催化合成了丁酮1,2-丙二醇缩酮。正交试验筛选出最佳反应条件为:丁酮200 mmol,n(丁酮)∶n(1,2-丙二醇)=1.0∶1.4,w(催化剂)=1.2%(以反应物质量计),反应时间1 h。在此最佳反应条件下,丁酮1,2-丙二醇缩酮的收率可达71.13%。     

TiSiW12O40/TiO2催化合成苹果酯

以固载杂多酸盐TiSiW12O40/TiO2为多相催化剂，通过乙酰乙酸乙酯和乙二醇反应合成了苹果酯，探讨TiSiW12O40/TiO2对缩酮反应的催化活性，较系统地研究了原料量比，催化剂肜量，反应时间诸因素对产品收率的影响，实验表明：TiSiW12O40/TiO2是合成苹果酯的良好催化剂，在n(乙酰乙酸乙酯）：n(乙二醇）＝1：1．5，催化剂用量为反应物料总质量的1．0％，环己烷为带水剂，反应时间50min的优化条件下，苹果酯的收率可达84．1％。     

Mechanistic analysis of the electrocatalytic properties of dissolved alpha and beta isomers of [SiW12O40]4- and solid [Ru(bipy)3]2[alpha-SiW12O40] on the reduction of nitrite in acidic aqueous media

Voltammetric studies on the reduction of alpha and beta isomers of the Keggin polyoxometalate anion [SiW12O40]4- reveal a series of electrochemically reversible processes in acidic aqueous media. In the presence of NO2-, catalytic current is detected in the potential region of the [SiW12O40]4-/5- process. Electronic spectroscopy and simulation of voltammetric data undertaken at variable [NO2-] and [H+] allow the following mechanism to be postulated, [SiW12O40]4- + e- <-->[SiW12O40]5-, H+ + HNO2 <--> NO+ + H2O, NO+ + [SiW12O40]5- --> NO + [SiW12O40]4-. The second-order rate constant for the rate-determining step is faster for the alpha isomer than for the beta one. This may be attributed to the different reversible potentials of -0.144 V (alpha isomer) and -0.036 V vs Ag/AgCl (beta isomer) and, hence, smaller driving force for an assumed outer sphere electron-transfer reaction in the case of beta isomer. A stable, water-insoluble, thin-film [Ru(bipy)3]2[alpha-SiW12O40] chemically modified electrode was generated electrochemically via ion-exchange of [Ru(bipy)3]2+ with Bu4N+ in the [Bu4N]4[alpha-SiW12O40] solid. The first reduction process with this modified electrode gives rise to the reaction [Ru(bipy)3]2[alpha-SiW12O40](solid) + H+(soln) + e- <--> H[Ru(bipy)3]2[alpha-SiW12O40](solid). The need to transfer a proton from the solution to the solid phase for charge neutralization purposes introduces a hydrogen-ion concentration dependence into this reaction, which is not found in the solution-phase study. Nevertheless, the voltammetric catalytic activity with respect to nitrite reduction is retained with the chemically modified electrode. However, nitrite catalysis with the [Ru(bipy)3]2[alpha-SiW12O40]-modified electrode is now independent of concentration of H+, rather than exhibiting a first-order dependence, and full mechanistic details for this process are unknown.     

Solubility in the NdCl3-LnCl3-HCl-H2O systems (Ln = Sm, Gd) at 25°C

The solubility at 25°C in the NdCl₃-SmCl₃-HCl-H₂O and NdCl₃-GdCl₃-HCl-H₂O quaternary water-salt systems has been studied in 40% hydrochloric acid sections. The NdCl₃-SmCl₃-HCl-H₂O system represents a continuous series of solid solutions (type I solid solutions). The NdCl₃-GdCl₃-HCl-H₂O system is a system with peritonic discontinuity (type V solid solutions). The discontinuity point of the peritonic solution has the following composition (wt %): NdCl₃ · 6H₂O, 1.13; GdCl₃ · 6H₂O, 0.11; HCl, 39.5; H₂O, 59.26.     

Location of protons in anhydrous Keggin heteropolyacids H(3)PMo(12)O(40) and H(3)PW(12)O(40) by (1)H[(31)P]/(31)P[(1)H] REDOR NMR and DFT quantum chemical calculations

HeteroPolyAcids (HPA's) are a class of solid acids that have broad applications in many fields of science and technology, including catalysis and chemical engineering. The proton locations within the thermally stable and commonly known Keggin unit, which is the primary structure building unit/block, has remained undetermined in anhydrous HPAs, despite numerous theoretical and experimental efforts. However, Rotational Echo DOuble Resonance (REDOR) NMR and Density Functional Theory (DFT) quantum chemical calculations offer a new opportunity to determine the exact locations of protons within the Keggin unit. The crucial experimental evidence is provided for the basic and very extensively studied acidic form of H(8-n)X(n+)M(12)O(40), X = Si, P and M = Mo, W, belonging to the Keggin structure. While showing that the acidic protons are located in the bridging oxygen positions (R(P-H) = 520 +/- 20 pm) in H(3)PMo(12)O(40) and in the terminal oxygen positions (R(P-H) = 570 +/- 20 pm) in H(3)PW(12)O(40), REDOR measurements also provide for the first time the structural basis to consistently rank the acid strength for the important class of Keggin solid catalysts.     

PW/SBA-15负载型催化剂的性能研究

合成、表征了一系列SBA-15负载H₃PW₁₂O₄₀(PW)催化剂.负载量高达60%以上时,XRD仍未检测到催化剂上有PW晶相峰.负载后PW保持其Keggin结构,但与载体之间存在较强的相互作用.通过改变PW负载量可调变催化剂的酸性,制得适用于中强酸和弱酸性催化反应的介孔固体酸催化剂.     

杂多酸(盐)及单缺位磷钨杂多化合物在醇类氧化反应中的催化活性

在相转移条件下,研究了杂多化合物在苄醇,环己醇氧化反应中的催化活性.六种Keggin结构杂多酸的催化活性按GeMo~12(H~4GeMo~12O~40的简写,其余类推,PW~12,PMo~12,SiMo~12,GeW~12,SiW~12顺序下降,杂多酸中的质子可分别被其它阳离逐渐取代而达到酸性修饰. H~3PW~12O~40随着其质子逐步被Na^+取代,酸性下降,催化活性大大提高;杂多酸(盐)的催化活性随体系pH值的改变将发生奇妙剧烈的变化;单缺位杂多化合物显示出较饱和杂多酸(盐)更高催化活性.溶剂对催化活性有明显影响.     

Selective oxidation of light alkanes over Mo-based oxide catalysts

A highly reduced Keggin-type heteropolymolybdophosphate, H₃PMo₁₂O₄₀(Py), which was formed by the heat-treatment of pyridinium salt of H₃PMo₁₂O₄₀, can catalyze the propane oxidation to acrylic acid and acetic acid selectively. We propose a possible reaction mechanism for alkane oxidation, where protons and electrons on the reduced H₃PMo₁₂O₄₀ catalyst cooperate for activating molecular oxygen to form electrophilic oxygen species for alkane oxidation. It is also reported that Anderson-type heteropolycompounds linked with vanadyl cations VO²⁺ were able to be synthesized by hydrothermal reaction and showed good catalytic activity for the ethene oxidation to acetic acid.     

GaxCs2.5-3xH0.5PW12O40的固相法制备及其催化正丁烷异构化反应的活性

利用室温固相法制备了一系列掺镓的钨磷酸铯盐催化剂GaxCs2.5-3xH0.5PW12O40(x=0.05,0.1,0.15).与钨磷酸铯盐相比,掺镓的钨磷酸铯盐催化剂的结构未产生变化,但其酸强度提高,在正丁烷异构化反应中催化活性增强,其中以Ga0.1Cs2.2H0.5PW12O40和Ga0.15Cs2.05H0.5P...     

Protonation of phosphovanadomolybdates H(3+x)PV(x)Mo(12-x)O40: computational insight into reactivity

Protonated phosphovanadomolybdates of the Keggin structure, H(3+x)PV(x)Mo(12-x)O(40) where x = 0, 1, 2, and derivatives with surface defects formed by loss of constitutional water were studied using high-level DFT calculations toward determination of the most stable species and possible active forms in oxidation catalysis in both the gas phase and in polar solutions. The calculations demonstrate that protonation at bridging positions is energetically much more favorable than protonation of terminal oxygen atoms. The preferential protonation site is determined by the stability of the metal-oxygen bond rather than the negative charge on the oxygen atom. In H(3)PMo(12)O(40), maximum distances between protons at bridging oxygen atoms are energetically favored. In contrast, for H(4)PVMo(11)O(40) and H(5)PV(2)Mo(10)O(40) protons prefer nucleophilic sites adjacent to vanadium atoms. Up to three protons are bound to the nucleophilic sites around the same vanadium atom in the stable isomeric forms of H(5)PV(2)Mo(10)O(40) that result in strong destabilization of oxo-vanadium(V) bonding to the Keggin unit. Such behavior arises from the different nature of the Mo-O and V-O bonds that can be traced to the different sizes of the valence d orbitals of the metals. Coordination of two protons at the same site yields water and an oxygen defect as a result of its dissociation. The energetic cost for the formation of surface defects decreases in the order: O(t) ? O(c) ? O(e) and is lower for the sites adjacent to vanadium atoms. Vanadium atoms near defects also have a significant contribution to the LUMO. Thus, vanadium-substituted polyoxometalates with defects near and, especially, between vanadium atoms present a plausible active form of polyoxometalates in oxidation reactions.     

A quantum chemical study of the decomposition of Keggin-structured heteropolyacids

Heterpolyacids (HPAs) demonstrate catalytic activity for oxidative and acid-catalyzed hydrocarbon conversion processes. Deactivation and thermal instability, however, have prevented their widespread use. Herein, ab initio density functional theory is used to study the thermal decomposition of the Keggin molecular HPA structure through the desorption of constitutional water molecules. The overall reaction energy and activation barrier are computed for the overall reaction HnXM12O40-->Hn-2XM12O39+H2O. and subsequently used to predict the effect of HPA composition on thermal stability. For example, the desorption of a constitutional water molecule is found to be increasingly endothermic in the order silicomolybdic acid (H4SiMo12O40)相似文献