Preparation, characterization, activity and selectivity of highly loaded oxide promoted ruthenium catalysts for selective hydrogenation of benzene to cyclohexene

Summary The influence of promoters and precipitants of the catalyst precursor on the activity and selectivity of the hydrogenation of benzene to cyclohexene catalyzed by highly loaded oxide-promoted Ru/ZrO₂catalysts, carried out in a tetraphase reactor (in the presence of an aqueous solution of ZnSO₄), at 423 K and 5 Mpa, was studied. The effect of hydrogen diffusion on the reaction kinetics and on the selectivity has been taken into consideration, the internal pore diffusion being actually the limiting step. Hydrogen chemisorption measurements indicate that the catalyst activity is not influenced by the Ru dispersion, but rather by weakly chemisorbed species.     

The Modifiable Character of a Novel Ru-Fe-B/ZrO2 Catalyst for Benzene Selective Hydrogenation to Cyclohexene

A novel Ru‐Fe‐B/ZrO₂ catalyst for the selective hydrogenation of benzene to cyclohexene was prepared by the chemical reduction method. A yield of cyclohexene of 57.3% was achieved at benzene conversion of 80.6% on this catalyst. The activity and yield of cyclohexene were higher than those studied previously. The structural characterizations of the catalyst were performed by TEM‐SAED, XRD, and N₂‐physisorption. Moreover, cyclohexene selectivities on this catalyst increased and the activities decreased with the increase of the ZnO dosages, however, the activities increased and cyclohexene selectivities decreased with the increase of the H₂SO₄ dosages. Different feeding manners of H₂SO₄ or ZnO exerted definitely influence on the performances of this catalyst, but the degrees of influence were different due to the character of chemisorptions. Furthermore, the activity and cyclohexene selectivity on the catalysts could be reversibly modified by adding H₂SO₄ or ZnO into reaction slurry, which provides an easy method to recover the activity and selectivity of Ru‐Fe‐B/ZrO₂ catalysts during the process of producing cyclohexene. And the modifiable mechanisms involved were speculated.     

反应修饰剂ZnSO4和预处理对苯选择加氢制环己烯Ru-Zn催化剂性能的影响

共沉淀法制备了Ru-Zn催化剂,考察了反应修饰剂ZnSO₄和预处理对苯选择加氢制环己烯Ru-Zn催化剂性能的影响。结果表明,反应修饰剂ZnSO₄可以与Ru-Zn催化剂中助剂ZnO反应生成（Zn（OH）₂）₃（ZnSO₄）（H₂O）盐。随反应修饰剂ZnSO₄浓度增加,（Zn（OH）₂）₃（ZnSO₄）（H₂O）盐量的逐渐增加,Ru-Zn催化剂活性逐渐降低,环己烯选择性逐渐升高。因为（Zn（OH）₂）₃（ZnSO₄）（H₂O）盐中的Zn²⁺可以使Ru变为有利环己烯生成的缺电子的Ru^δ+物种,而且还可以占据不适宜环己烯生成的强Ru活性位。但当反应修饰剂ZnSO₄浓度高于0.41 mol·L^-1后,继续增加ZnSO₄浓度,由于Zn²⁺水解浆液酸性太强,可以溶解部分（Zn（OH）₂）₃（ZnSO₄）（H₂O）盐,Ru-Zn催化剂活性升高,环己烯选择性降低。但环己烯选择性却略微降低,这是由于ZnSO₄溶液中大量的Zn²⁺可以与生成的环己烯形成配合物,稳定生成的环己烯,抑制生成的环己烯再吸附到催化剂表面并加氢生成环己烷。在ZnSO₄最佳浓度0.61 mol·L^-1下对Ru-Zn催化剂预处理15 h,Ru-Zn催化剂中助剂ZnO可以与ZnSO₄完全反应生成（Zn（OH）₂）₃（ZnSO₄）（H₂O）盐,在该催化剂上25 min苯转化68.2%时环己烯选择性和收率分别为80.2%和54.7%。而且该催化剂具有良好的稳定性和重复使用性能。     

反应修饰剂ZnSO_4和预处理对苯选择加氢制环己烯Ru-Zn催化剂性能的影响

共沉淀法制备了Ru-Zn催化剂,考察了反应修饰剂ZnSO_4和预处理对苯选择加氢制环己烯Ru-Zn催化剂性能的影响。结果表明,反应修饰剂ZnSO_4可以与Ru-Zn催化剂中助剂Zn O反应生成(Zn(OH)2)3(ZnSO_4)(H_2O)盐。随反应修饰剂ZnSO_4浓度增加,(Zn(OH)2)3(ZnSO_4)(H_2O)盐量逐渐增加,Ru-Zn催化剂活性逐渐降低,环己烯选择性逐渐升高。因为(Zn(OH)2)3(ZnSO_4)(H_2O)盐中的Zn2+可以使Ru变为有利环己烯生成的缺电子的Ruδ+物种,而且还可以占据不适宜环己烯生成的强Ru活性位。但当反应修饰剂ZnSO_4浓度高于0.41 mol·L-1后,继续增加ZnSO_4浓度,由于Zn2+水解浆液酸性太强,可以溶解部分(Zn(OH)2)3(ZnSO_4)(H_2O)盐,RuZn催化剂活性升高,环己烯选择性降低。环己烯选择性略微降低,是由于ZnSO_4溶液中大量的Zn2+可以与生成的环己烯形成配合物,稳定生成的环己烯,抑制环己烯再吸附到催化剂表面并加氢生成环己烷。在ZnSO_4最佳浓度0.61 mol·L-1下对Ru-Zn催化剂预处理15 h,Ru-Zn催化剂中助剂Zn O可以与ZnSO_4完全反应生成(Zn(OH)2)3(ZnSO_4)(H_2O)盐,在该催化剂上25 min苯转化68.2%时环己烯选择性和收率分别为80.2%和54.7%。而且该催化剂具有良好的稳定性和重复使用性能。     

Effect of Organic Additives on the Performance of Nano-sized Ru-Zn Catalyst

A novel Ru‐Zn catalyst was prepared by coprecipitation. The catalyst was characterized by XRF, XRD and TEM. The effects of organic additives on the performance of the Ru‐Zn catalyst for benzene selective hydrogenation to cyclohexene were investigated. The results showed that the catalyst was composed of Ru and Zn in molar ratio of 33.8:1, and the most probable value of the Ru crystallite size in the catalyst was 5.1 nm. The modification of Ru with Zn and the small size effect were the main cause why the catalyst exhibited the high activity and the excellent cyclohexene selectivity. When PEG (polyethylene glycol) was used as an additive, the activity of the catalyst decreased, and the cyclohexene selectivity increased with the increase of the PEG molecular weight. With the addition of PEG‐20000, a cyclohexene selectivity of 78.9% at a benzene conversion of 68.7% and a maximum cyclohexene yield of 61.4% were obtained. With diethanolamine and triethanolamine as additives, cyclohexene yields were as high as 58.9% and 58.2%, respectively.     

Ru/ZrO_2催化剂在苯部分加氢反应中的粒径效应

采用多元醇还原法将2.4~5.4 nm范围内粒径均一、尺寸可控的Ru纳米粒子负载在ZrO2上,研究了Ru的粒径对Ru/ZrO2催化剂上苯部分加氢性能的影响.采用紫外-可见吸收光谱(UV-Vis)、N2物理吸附、H2化学吸附、H2-程序升温脱附(H2-TPD)、粉末X射线衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等手段对催化剂进行了系统的表征.研究表明,用于还原的醇的种类及添加剂乙酸钠的浓度对Ru粒径有显著影响.在苯部分加氢反应中,Ru/ZrO2催化剂有明显的粒径效应.随着Ru粒径的增大,苯的转换频率(TOF)提高,环己烯初始选择性(S0)则呈火山型变化趋势,选择性最高时的Ru粒径为4.4 nm.1,2-丙二醇还原得到的Ru/ZrO2催化剂上S0及环己烯得率最高,分别可达82%和39%.结合催化剂的表征和加氢结果,讨论了Ru粒径影响苯部分加氢活性和选择性的原因.     

ZnSO4和La2O3作共修饰剂单金属Ru催化剂上苯选择加氢制环己烯

用沉淀法制备了单金属纳米Ru（0）催化剂,考察了ZnSO₄和La₂O₃作共修饰剂对该催化剂催化苯选择加氢制环己烯性能的影响,并用X射线衍射（XRD）、X射线荧光（XRF）光谱、X射线光电子能谱（XPS）、俄歇电子能谱（AES）、透射电镜（TEM）和N₂物理吸附等手段对加氢前后催化剂进行了表征. 结果表明,在ZnSO₄存在下,随着添加碱性La₂O₃量的增加,ZnSO₄水解生成的（Zn（OH）₂）₃（ZnSO₄）（H₂O）_x（x=1,3）盐量增加,催化剂活性单调降低,环己烯选择性单调升高. 当La₂O₃/Ru 物质的量比为0.075 时,Ru催化剂上苯转化率为77.6%,环己烯选择性和收率分别为75.2%和58.4%. 且该催化体系具有良好的重复使用性能. 传质计算结果表明,苯、环己烯和氢气的液-固扩散限制和孔内扩散限制都可忽略. 因此,高环己烯选择性和收率的获得不能简单归结为物理效应,而与催化剂的结构和催化体系密切相关. 根据实验结果,我们推测在化学吸附有（Zn（OH）₂）₃（ZnSO₄）（H₂O）_x（x=1,3）盐的Ru（0）催化剂有两种活化苯的活性位：Ru⁰和Zn²⁺. 因为Zn²⁺将部分电子转移给了Ru,Zn²⁺活化苯的能力比Ru⁰弱. 同时由于Ru和Zn²⁺的原子半径接近,Zn²⁺可以覆盖一部分Ru⁰活性位,导致解离H₂的Ru⁰活性位减少. 这导致了Zn²⁺上活化的苯只能加氢生成环己烯和Ru（0）催化剂活性的降低. 本文利用双活性位模型来解释Ru基催化剂上的苯加氢反应,并用Hückel分子轨道理论说明了该模型的合理性.     

一种新型Ru-Zn体系催化苯选择加氢制环己烯的研究

制备了一种新型苯选择加氢制环己烯Ru-Zn催化剂.研究表明,该催化剂不但具有较好的活性选择性,而且具有稳定的晶态结构,良好的沉降分离性能.Zn/Ru比为8/92时,15min环己烯的收率达48.3%.利用XRD和物理吸附仪等手段对催化剂进行了表征.XRD证实了Ru和Zn形成固溶体,并观察到金属锌物相的存在.     

串联双釜连续反应装置中Ru-Co-B/ZrO2上苯选择加氢制环己烯

采用化学还原法制备了苯选择加氢制环己烯催化剂Ru-B/ZrO₂,考察了Cr,Mn,Fe,Co,Ni,Cu和Zn等过渡金属的添加对Ru-B/ZrO₂催化剂性能的影响.结果表明,这些过渡金属的添加均可提高Ru-B/ZrO₂催化剂中的B含量.B的修饰及第二种金属或金属氧化物的集团效应和配位效应导致Ru-B/ZrO₂催化剂活性降低和环己烯选择性升高.当Co/Ru原子比为0.06时,Ru-Co-B/ZrO₂催化剂上反应25min苯转化率为75.8%时,环己烯选择性和收率分别为82.8%和62.8%.在双釜串联连续反应器中和优化反应条件下,Ru-Co-B/ZrO₂催化剂使用419h内苯转化率稳定在40%左右,环己烯选择性和收率分别稳定在73%和30%左右.     

助剂前体ZnSO_4浓度对苯选择加氢制环己烯Ru-Zn催化剂性能的影响

共沉淀法制备了Ru-Zn催化剂,在ZrO_2作分散剂下考察了助剂前体ZnSO_4浓度对苯选择加氢制环己烯Ru-Zn催化剂性能的影响.并用X-射线衍射(XRD)、X-射线荧光光谱(XRF)、N_2-物理吸附、透射电镜(TEM)和X-射线光电子能谱(XPS)等手段对催化剂进行了表征.结果表明,当ZnSO_4前体浓度低于0.10 mol/L时,Ru-Zn催化剂中Zn以ZnO形式存在,在加氢过程中ZnO可以与反应修饰剂ZnSO_4反应生成(Zn( OH)_2)_3(ZnSO_4)(H_2O)_3盐.继续增加ZnSO_4前体浓度,催化剂中Zn以ZnO和NaZn_4(SO_4)(Cl)(OH)_6·6H_2O盐存在,在加氢过程中ZnO和NaZn_4(SO_4)(Cl)(OH)_6·6H_2O盐可以与反应修饰剂ZnSO_4反应生成(Zn( OH)_2)_3(ZnSO_4)(H_2O)_5.(Zn( OH)_2)_3(ZnSO_4)(H_2O)_x(x=3或5)盐的Zn~(2+)可以转移金属Ru的部分电子.因此,随ZnSO_4前体浓度的增加,(Zn( OH)_2)_3(ZnSO_4)(H_2O)_x的量逐渐增加,金属Ru失电子越多,催化剂活性越低,环己烯选择性越高.0.08 mol/L ZnSO_4前体制备Ru-Zn催化剂给出了59.1%的环己烯收率,而且该催化剂具有良好的重复使用性能和稳定性.     

Enhancing the selective hydrogenation of benzene to cyclohexene over Ru/TiO_2 catalyst in the presence of a very small amount of ZnO

Highly efficient and greener hydrogenation of benzene to cyclohexene is of great importance but is challenging.In this work,Ru/Ti O2 catalyst was prepared by a simple chemical-reduction method.The catalyst was characterized by transmission electron spectroscopy(TEM),X-ray powder diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),and nitrogen adsorption-desorption techniques.It was shown that the Ru nanoparticles with average size of about 2.2 nm were dispersed uniformly on the surface of the Ti O2 support.The effect of a very small amount of Zn O in Na OH solution on the selectivity to cyclohexene was investigated under different conditions by using Ru/Ti O2 catalyst.It was found that the addition of a small amount of Zn O to the Na OH solution could effectively enhance the selectivity to cyclohexene and that the yield of cyclohexene could reach 41.5%.Control experiments revealed that the main reason for the enhancement of the selectivity to cyclohexene was the presence of Zn O in the form of Na2Zn(OH)4 in the alkaline solution,which effectively retarded the further hydrogenation of cyclohexene.A recycling experiment showed that the yield of cyclohexene was not obviously decreased after four reuses.     

Encapsulation of a binuclear manganese(II) complex with an amino acid-based ligand in zeolite Y and its catalytic epoxidation of cyclohexene

A Schiff base ligand was synthesized by the condensation of salicylaldehyde with l-tyrosine. Interaction of this ligand with Mn(II)-exchanged zeolite Y leads to encapsulation of the ligand within the zeolite and complexation of the metal. The encapsulated complex has been characterized by spectroscopic studies and chemical analyses. This material serves as a catalyst for the oxidation of cyclohexene to cyclohexene epoxide and 2-cyclohexene-1-ol using H₂O₂ as oxidant. The reaction conditions have been optimized for solvent, temperature and amount of oxidant and catalyst. The catalyst shows high activity and selectivity toward production of cyclohexene epoxide in acetonitrile at 60 °C with [H₂O₂]/[C₆H₁₀] = 2.5 molar ratio. Comparison of the encapsulated catalyst with the corresponding homogeneous catalyst showed that the heterogeneous catalyst had higher activity and selectivity than the homogeneous catalyst.     

Fischer-Tropsch synthesis over Ru/Al2O3 catalysts

Fischer-Tropsch syntheses (FTS) were carried out in a slurry phase over Ru/Al₂O₃ catalysts using hexadecane as a solvent. The outcome of the FTS was dependent on the oxide support, calcination temperature, synthesis gas composition and sulfur content. The addition of Mn/Na to Ru/Al₂O₃ was effective in raising the initial activity and C5+ selectivity, but after 20 hours, the performance of the modified catalyst was similar to that of the unmodified catalyst. An additional investigation involving the use of fresh vs used catalysts demonstrated that an agglomeration of the metallic Ru, at least in part, does occur during the reaction.     

Role of ZnNb2O6 in ZnO-promoted amorphous-Nb2O5 supported Ru catalyst for the partial hydrogenation of benzene

Ruthenium catalysts supported on zinc-promoted amorphous-niobium mixed oxides were prepared, characterized, and studied in the additive-free partial hydrogenation of benzene reaction. The amorphous matrix of Nb₂O₅ was responsible for a highly active Ru/Nb₂O₅ catalyst, although less selective than those containing zinc. The ZnO-containing supports were prepared by wet impregnation technique, followed by incipient wetness of ruthenium chloride salt. The catalysts were characterized by textural analysis, X-ray fluorescence, X-ray diffraction, H₂ chemisorption, temperature-programmed reduction (TPR), Scanning electron microscopy, H₂ temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS) of the calcined-reduced samples. Chlorine retention was observed on zinc-containing samples. An unexpected ZnNb₂O₆ oxide phase, ascribed to a selectivity increase with less activity loss, was obtained for the supports at lower temperatures than those related on the literature. A very complex electronic environment of Ru- and Zn-containing species interactions was observed by TPR. The presence of surface-reduced (Ru⁰) and partially reduced (Ru^δ+) Ru species observed by XPS justified well, respectively, the activity and selectivity achieved with every catalyst. The addition of water as a solvent resulted in very constant yield to cyclohexene, as expected, despite activity diminution due to low solubility of the reactants.     

ZnSO_4和La_2O_3作共修饰剂单金属Ru催化剂上苯选择加氢制环己烯

用沉淀法制备了单金属纳米Ru(0)催化剂,考察了ZnSO4和La2O3作共修饰剂对该催化剂催化苯选择加氢制环己烯性能的影响,并用X射线衍射(XRD)、X射线荧光(XRF)光谱、X射线光电子能谱(XPS)、俄歇电子能谱(AES)、透射电镜(TEM)和N2物理吸附等手段对加氢前后催化剂进行了表征.结果表明,在ZnSO4存在下,随着添加碱性La2O3量的增加,ZnSO4水解生成的(Zn(OH)2)3(ZnSO4)(H2O)x(x=1,3)盐量增加,催化剂活性单调降低,环己烯选择性单调升高.当La2O3/Ru物质的量比为0.075时,Ru催化剂上苯转化率为77.6%,环己烯选择性和收率分别为75.2%和58.4%.且该催化体系具有良好的重复使用性能.传质计算结果表明,苯、环己烯和氢气的液-固扩散限制和孔内扩散限制都可忽略.因此,高环己烯选择性和收率的获得不能简单归结为物理效应,而与催化剂的结构和催化体系密切相关.根据实验结果,我们推测在化学吸附有(Zn(OH)2)3(ZnSO4)(H2O)x(x=1,3)盐的Ru(0)催化剂有两种活化苯的活性位:Ru0和Zn2+.因为Zn2+将部分电子转移给了Ru,Zn2+活化苯的能力比Ru0弱.同时由于Ru和Zn2+的原子半径接近,Zn2+可以覆盖一部分Ru0活性位,导致解离H2的Ru0活性位减少.这导致了Zn2+上活化的苯只能加氢生成环己烯和Ru(0)催化剂活性的降低.本文利用双活性位模型来解释Ru基催化剂上的苯加氢反应,并用Hückel分子轨道理论说明了该模型的合理性.     

离子液体[Bmim]BF4中单分散Ru纳米粒子的制备及选择加氢性能

采用化学还原法在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([BMim]BF₄)中制备了单分散纳米金属Ru粒子。采用X射线衍射(XRD)、透射电镜(TEM)、傅里叶红外光谱(FTTR)及热重(TG)对所制备样品的形貌和结构进行了表征。XRD表征结果显示：在[BMim]BF₄中制备的Ru具有六方紧密堆积结构,无氧化物峰出现;TEM结果显示：采用正滴法制备的Ru纳米粒子为球形颗粒,呈现良好的单分散状态,粒径分布窄,为2~5 nm,而采用反滴法制备的Ru纳米粒子则发生了严重的团聚,团聚体粒径大于10 nm;FTIR表征表明：Ru纳米粒子表面存在[BMim]BF₄液体层,分析二者之间存在较强的物理吸附作用,[BMim]BF₄在Ru纳米粒子的制备中起到了修饰剂和保护剂的双重作用,这一推论通过TG分析得到了进一步验证。将分散于[BMim]BF₄的Ru纳米粒子作为催化剂应用于苯选择加氢反应,结果分析表明：Ru-离子液体-苯反应体系中,苯转化率仅有0.3%;Ru-离子液体-苯-水反应体系中加氢活性较高,但环己烯选择性较低,在一定条件下,加氢30 min,苯转化率为27.3%,环己烯选择性仅为14.5%。     

Zn4Si2O7(OH)2H2O盐修饰的纳米Ru催化剂催化苯选择加氢制环己烯

利用沉淀法制备了纳米Ru催化剂,在ZnSO₄存在下考察了Na₂SiO₃·9H₂O和二乙醇胺作反应修饰剂对Ru催化剂催化苯选择加氢制环己烯性能的影响,并用X-射线衍射(XRD)、X-射线荧光光谱(XRF)和透射电镜-能量散射谱(TEM-EDS)等物理化学手段对加氢前后Ru催化剂进行了表征。结果表明,在水溶液中Na₂SiO₃与ZnSO₄可以反应生成Zn₄Si₂O₇(OH)₂H₂O盐、H₂SO₄和Na₂SO₄,化学吸附在Ru催化剂表面上的Zn₄Si₂O₇(OH)₂H₂O盐起着提高Ru催化剂环己烯选择性的关键作用。Na₂SiO₃·9H₂O量的增加,生成的Zn₄Si₂O₇(OH)₂H₂O盐逐渐增加,Ru催化剂的活性降低,环己烯选择性逐渐升高。向反应体系中加入二乙醇胺,它可以中和Na₂SiO₃与ZnSO₄反应生成的硫酸,使化学平衡向生成更多的Zn₄Si₂O₇(OH)₂H₂O盐的方向移动,导致Ru催化剂环己烯选择性增加。当Ru催化剂与ZnSO₄·7H₂O、Na₂SiO₃·9H₂O和二乙醇胺、分散剂ZrO₂的质量比为1.0:24.6:0.4:0.2:5.0时,2 g Ru催化剂上苯转化73%时环己烯选择性和收率分别为75%和55%,而且该催化剂体系具有良好的重复使用性和稳定性。     

Catalytic properties of Ru nanoparticles embedded on ordered mesoporous carbon with different pore size in Fischer-Tropsch synthesis

A series of 3 wt% Ru embedded on ordered mesoporous carbon (OMC) catalysts with different pore sizes were prepared by autoreduction between ruthenium precursors and carbon sources at 1123 K. Ru nanoparticles were embedded on the carbon walls of OMC. Characterization technologies including power X-ray diffraction (XRD), nitrogen adsorption-desorption, transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H₂-TPR) were used to scrutinize the catalysts. The catalyst activity for Fischer-Tropsch synthesis (FTS) was measured in a fixed bed reactor. It was revealed that 3 wt% Ru-OMC catalysts exhibited highly ordered mesoporous structure and large surface area. Compared with the catalysts with smaller pores, the catalysts with larger pores were inclined to form larger Ru particles. These 3 wt% Ru-OMC catalysts with different pore sizes were more stable than 3 wt% Ru/AC catalyst during the FTS reactions because Ru particles were embedded on the carbon walls, suppressing particles aggregation, movement and oxidation. The catalytic activity and C₅₊ selectivity were found to increase with the increasing pore size, however, CH₄ selectivity showed the opposite trend. These changes may be explained in terms of the special environment of the active Ru sites and the diffusion of products in the pores of the catalysts, suggesting that the activity and hydrocarbon selectivity are more dependent on the pore size of OMC than on the Ru particle size.     

蜂窝陶瓷整体反应器内苯选择加氢制环己烯

 研究了Ru/ZrO2蜂窝陶瓷整体催化剂对苯液相选择加氢制环己烯反应的催化性能,考察了催化剂载体、活性组分含量、预处理条件、反应温度、反应压力、水和硫酸锌水溶液等对该反应的影响. 结果表明,整体催化剂不经预还原就可以直接进行苯液相加氢反应; 反应物中不加水或其它无机添加剂时环己烯的选择性为0,水或硫酸锌水溶液的加入大大降低了反应活性,但环己烯的选择性显著提高,约达到20%; 反应物中水和苯有最优配比,以保证最佳的环己烯选择性和收率; 反应温度在413～443 K,反应压力为3～4 MPa,硫酸锌浓度为0.1 mol/L时,反应结果较好.     

Zn4Si2O7(OH)2H2O盐修饰的纳米Ru催化剂催化苯选择加氢制环己烯

利用沉淀法制备了纳米Ru催化剂, 在ZnSO₄存在下考察了Na₂SiO₃·9H₂O和二乙醇胺作反应修饰剂对Ru催化剂催化苯选择加氢制环己烯性能的影响, 并用X-射线衍射(XRD)、X-射线荧光光谱(XRF)和透射电镜-能量散射谱(TEM-EDS)等物理化学手段对加氢前后Ru催化剂进行了表征。结果表明, 在水溶液中Na₂SiO₃与ZnSO₄可以反应生成Zn₄Si₂O₇(OH)₂H₂O盐、H₂SO₄和Na₂SO₄, 化学吸附在Ru催化剂表面上的Zn₄Si₂O₇(OH)₂H₂O盐起着提高Ru催化剂环己烯选择性的关键作用。Na₂SiO₃·9H₂O量的增加, 生成的Zn₄Si₂O₇(OH)₂H₂O盐逐渐增加, Ru催化剂的活性降低, 环己烯选择性逐渐升高。向反应体系中加入二乙醇胺, 它可以中和Na₂SiO₃与ZnSO₄反应生成的硫酸, 使化学平衡向生成更多的Zn₄Si₂O₇(OH)₂H₂O盐的方向移动, 导致Ru催化剂环己烯选择性增加。当Ru催化剂与ZnSO₄·7H₂O、Na₂SiO₃·9H₂O和二乙醇胺、分散剂ZrO₂的质量比为1.0:24.6:0.4:0.2:5.0时, 2 g Ru催化剂上苯转化73%时环己烯选择性和收率分别为75%和55%, 而且该催化剂体系具有良好的重复使用性和稳定性。