Correlation between reduction potential of vanadium-containing heteropolyacid (HPA) catalysts and their oxidation activity for cyclohexanol dehydrogenation

Vanadium-containing H_6+xP₂Mo_18−xV_xO₆₂ (x = 0, 1, 2 and 3) Wells-Dawson heteropolyacid (HPA) and H_3+xPMo_12−xV_xO₄₀ (x = 0, 1, 2 and 3) Keggin HPA catalysts were applied to the vapor-phase dehydrogenation of cyclohexanol. The catalytic oxidation activity showed a volcano-shaped curve with respect to vanadium substitution for both families of HPA catalysts. The Wells-Dawson HPA showed a better catalytic oxidation performance than the Keggin HPA at the same level of vanadium substitution.     

Tungsten-based catalysts for the oxidation of cyclohexanol: The effect of phase transfer catalysts

The oxidation of cyclohexanol with hydrogen peroxide in the presence of tungsten-based catalysts was studied in this paper. The effect of phase transfer catalysts was discussed and clarified. [CTA]₉[SbW₉O₃₃] showed the best activity and good recyclability with a conversion over 95%.     

Pillared clays as efficient catalysts for cyclohexanol oxidation

Summary Iron, aluminium and mixed iron aluminium pillared clays were prepared by partial hydrolysis method and doped with 10% V and Mo. The samples were characterised by XRD, FTIR and surface area and pore volume measurements. Oxidation of cyclohexanol with hydrogen peroxide was done as probe reaction to test catalytic activity. Iron pillared systems exhibited maximum activity. The effects of various reaction variables on the reaction were studied.     

Geometric and electronic factors in paraffin dehydrogenation on bimetallic platinum catalysts

Summary Relationships between specific activity of bimetallic platinum catalysts in paraffin dehydrogenation and atomic sizes of promoters (i) and enthalpies of alloying with platinum (ii) were considered. The leading role of the size (geometric) effect was demonstrated.     

异丁烷直接脱氢制异丁烯催化剂研究进展

从热力学和反应机理角度概述了异丁烷直接脱氢和氧化脱氢的差异;从活性中心性质、失活与再生、助催化剂以及载体方面,综述了目前广泛研究的异丁烷直接脱氢制异丁烯催化剂,包括PtSn-、CrOx-、GaOx基和金属硫化物催化剂,并分析了各类催化剂的优缺点及目前的研究方向;简述了其他类型的脱氢催化剂,包括Mo/MgAl2O4、碳基材料、Co-、Ni2P-、VOx基催化剂等;分析了目前脱氢技术面临的问题以及未来的研究方向。     

Effect of the physico-chemical properties of vanadia/praseodymia on cyclohexanol decomposition

Vanadia supported on praseodymia (2, 6 and 10 wt.% V₂O₅) were prepared by wet impregnation and characterized by energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), TGA/DTA and BET surface area measurements. Decomposition of cyclohexanol was conducted over these catalysts in the vapor phase. Acidity of the catalysts was measured by temperature programmed desorption using ammonia as a probe molecule. The structural and acidic properties were correlated to the total conversion and cyclohexene selectivity.     

Dehydration and dehydrogenation of cyclohexanol over AlPO4-5 based molecular sieves

The role of incorporated divalent metal (Mn, Mg, Co and Zn) incorporated into the framework of AlPO₄-5 in conversion of cyclohexanol has been examined. The influence of these metals to cyclohexene and cyclohexanone selectivities was correlated to the acidity and basicity properties of these molecular sieves. Possible mechanism for the dehydration and dehydrogenation for cyclohexanol was proposed.     

Cu-Mn-Si催化剂在环己醇脱氢和糠醛加氢耦合反应中的研究:沉淀pH值和焙烧温度的影响

采用共沉淀法制备了Cu-Mn-Si催化剂,并将其应用于常压气相环己醇脱氢和糠醛加氢耦合反应中,考察了沉淀pH值和焙烧温度对耦合反应的影响。沉淀pH值对糠醛加氢制2 甲基呋喃反应影响不大,但对环己酮的选择性影响较大。pH值在7.5~10.0制备的催化剂具有优良的反应性能。焙烧温度的提高,导致催化剂的比表面积减小,孔径变大,铜的比表面积下降,还原温度提高。在耦合一体化反应中,环己醇脱氢制备环己酮反应受焙烧温度影响不大,但糠醛转化率和2 甲基呋喃选择性随着焙烧温度的提高而减小。     

Dehydrogenation activity and structure of polyaniline supported heteropolyacid catalysts

Polyaniline(PAN) supported H₆P₂W₁₈O₆₂(PW) , H₃PMo₁₂O₄₀ (PMo) and H₄PMo₁₁VO₄₀(PMoV) catalysts were prepared and their activities for hexanol conversion were tested. IR, XRD, ICP and SEM measurements proved that the heteropolyacids (HPA) could be supported on this type of polymer. The PAN supported HPA catalysts exhibit higher redox activities and low acid-base activities for the hexanol conversion. The redox activities increase with increasing amount of the heteropolyacid. Substitution of Mo ion by V ion results in an increase of redox activities of the catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of additives on properties of vanadia-based catalysts for oxidative dehydrogenation of propane: Experimental and quantum chemical studies

Effect of additives (A) comprising main group elements (K, P) and transition metals (Ni, Cr, Mo) to VO_x/SiO₂ catalysts on their catalytic behavior in oxidative dehydrogenation (ODH) of propane are studied. The experimental findings are compared with results of quantum chemical calculations performed for a model O=V---O---V^* cluster in which V^* atom is replaced by an atom of A. The selectivities to propene found in experiments change on introducing the additives, decreasing in the sequence VK(64)>VCr(38)>VMo=VNi(32)>VP(28)V0(27). Quantum chemical calculations indicate the change in the electron density on the atoms of the active O=V---O groups for the clusters with the additives’ atoms. The extent of the electron transfer from A towards the active group (the increase in the centre basicity) follows the sequence of the decreasing selectivity to propene, confirming the role of acid–base properties in controlling the selectivity in ODH of propane. Results of calculations show also an exceptional behavior of the potassium (the most effective additive for the increase in the selectivity in experiments); in contrast to all other additivies, K transfers electrons towards both V and O atoms in the active group, and does not form a definite O---K bond, but is rather “adsorbed” on the cluster.     

乙醇蒸气预处理Cr基催化剂对丙烷脱氢性能的影响

丙烯是仅次于乙烯的重要有机化工基础原料,广泛应用于生产聚丙烯、丙烯醛、丙烯酸、甘油、异丙醇、聚丙烯氰、丁辛醇等化工产品.近年来,随着市场经济的发展,丙烯下游产品的需求量迅速上涨,极大地促进了全球对丙烯的需求.负载型氧化基催化剂因其良好的催化性能和低廉的生产成本而被广泛应用于低碳烷烃脱氢反应中,Catofin,Linde及FBD工艺使用的就是Cr2O3/γ-Al2O3催化剂.丙烷脱氢过程中,担载型氧化铬催化剂Cr物种的价态、配位结构及与载体之间的相1互作用会影响其催化性能.催化反应过程中,丙烷分子吸附在Cr-O上进行活化反应,因而研究清楚催化剂的活性物种是非常重要的.综合文献,一部分研究者认为Cr6+为反应的活性中心,在反应初期与丙烷接触立即被还原为活性比较弱的Cr3+.随着原位表征技术的发展,一些研究者认为,八面体配位结构的Cr3+物种为催化反应的活性中心,四面体配位结构的Cr6+仅仅是Cr3+活性物种的前驱体,而且Cr6+并没有被发现具有催化活性.但何种Cr物种是脱氢活性中心,至今仍没有一致结论,这是值得继续关注和解决的问题.同时,浸渍法制备催化剂的过程中,金属前驱体、浸渍溶剂、干燥时间、干燥温度及焙烧时间和温度等因素会影响所制备催化剂的催化活性.我们采用等体积浸渍法制备催化剂,并用饱和乙醇蒸气对其进行预处理,以丙烷脱氢为探针反应研究了预处理对催化剂脱氢反应性能的影响,采用X射线衍射(XRD)、透射电镜(TEM)、程序升温还原(H2-TPR)、X射线光电子能谱(XPS)和紫外-可见光谱(UV-Vis)等表征手段,揭示催化反应的活性中心及反应机理.在无氧脱氢反应中,经过乙醇蒸气预处理的催化剂CrH-Et催化活性稍高于原始催化剂CrH.在二氧化碳参与的反应中,催化剂CrH-Et催化活性远远高于CrH.当C3Hs∶CO2∶He=1∶5∶4时达到最佳效果,CrH-Et的丙烷转化率为41.4％,丙烯选择性为84.8％,同样条件下CrH的催化活性和丙烯选择性分别为28.0％和85.9％.但是乙醇作为浸渍溶剂,对催化剂并没有促进作用.XRD和TEM结果表明,Cr均匀分散在载体表面,Cr粒子簇的大小并不影响催化剂的催化活性.H2-TPR,XPS和UV-Vis结果说明,经过乙醇蒸气预处理后催化剂中的Cr6+被还原成低价Cr,因而可以证明Cr6+不是催化剂的活性中心.Cr3+作为活性中心而存在,Cr6+仅作为活性组分的前驱体而存在.而在反应过程中,Cr3+容易被反应中生成的H2还原成非活性组分.相对于催化剂CrH,经过乙醇蒸气预处理的催化剂(CrH-Et)上部分还原后的低价Cr更容易被CO2重新氧化成Cr6+.即在反应过程中,CrH-Et能保持相对CrH更多的活性组分,因而保持更高的催化活性.     

Oxidative dehydrogenation of ethane with carbon dioxide over sulfated zirconia supported metal oxides catalysts

Several metal oxides supported on sulfated zirconia catalysts were tested for the oxidative dehydrogenation of ethane into ethylene by carbon dioxide. It is found that the catalytic behavior of supported oxide catalysts differ depending on the nature of metal oxides. Chromium oxide-sulfated zirconia exhibits the highest ethane conversion and medium level of ethylene selectivity, producing 38% ethylene yield at 50% ethane conversion at 650°C.     

Effects of the preparation method and calcination temperature on Cu–Cr–Mg–Al catalysts for the dehydrogenation of cyclohexanol

Novel dioxomolybdenum(VI) complexes bearing bis(ferrocenylcarbaldimine) ligands were prepared in good yield and characterized by spectroscopy and elemental analysis. The complexes were found to be excellent catalysts for the homogeneous epoxidation of cyclohexene and styrene using tert-butyl hydroperoxide (TBHP) as oxidant. The complexes can be recovered and reused.     

Understanding the dehydrogenation mechanism over iron nanoparticles catalysts based on density functional theory

The conversion of chemical feedstock materials into high value-added products accompanied with dehydrogenation is of great value in the chemical industry.However,the catalytic dehydrogenation reaction is inhibited by a limited number of expensive noble metal catalysts and lacks understanding of dehydrogenation mechanism.Here,we report the use of heterogeneous non-noble metal iron nanoparticles(NPs) incorporated mesoporous nitrogen-doped carbon to investigate the dehydrogenation mechanism based on experiment observation and density functional theory(DFT) method.Fe NPs catalyst displays excellent performance in the dehydrogenation of 1,2,3,4-tetrahydroquinoline(THQ)with 100% selectivity and 100% conversion for 10-12 h at room temperature.The calculated adsorption energy implies that THQ prefers to adsorb on Fe NPs as compared with absence of Fe NPs.What is more,the energy barrier of transition state is relatively low,illustrating the dehydrogenation is feasible.This work provides an atomic scale mechanism guidance for the catalytic dehydrogenation reaction and points out the direction for the design of new catalysts.     

Sulfate additives generate robust and highly active palladium catalysts for the cyanation of aryl chlorides

The use of sulfate additives such as H₂SO₄ greatly increases the reactivity of palladium catalysts for the cyanation of aryl and heteroaryl chlorides and renders them more robust toward adventitious air. Using this method, a wide variety of aromatic and heteroaromatic nitriles were prepared in high yield.     

Effect of different additives on the performance of V?Mg?O catalysts in the oxidative dehydrogenation of propane

The addition of K₂O, Cr₂O₃, Sm₂O₃ or Nb₂O₅ to V–Mg–O catalyst decreased both activity and selectivity in propane oxydehydrogenation. By comparing these results with the characterization data, a relationship between propylene selectivity and catalyst reducibility was revealed. The most easily reduced catalyst was the most selective.     

The catalytic activity of a cyclometalated ruthenium(III) complex for aerobic oxidative dehydrogenation of benzylamines

The ruthenium(III) complex bearing benzo[h]quinoline as a cyclometalated ligand was synthesized and characterized by ESI-MS, elemental analysis, cyclic voltammetry and crystallography. The complex serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzylamines to the corresponding benzonitriles under mild conditions.