Rh/nylon catalysts for partial hydrogenation of benzene to cyclohexene

Hydrogenation of benzene on Rh/nylon produced cyclohexene with a high selectivity. The influence of contact time, pretreatment of catalyst and rhodium salt precursors have been studied. Samples prepared from Rh(III) were found more selective than catalysts obtained from Rh(I). It is suggested that electron deficient metal sites are responsible for cycloolefin formation.

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Rh/ . , . , Rh(III) , , Rh(I). , .

     

Acetylene hydrogenation selectivity control using Pd/Cu catalysts

The hydrogenation of acetylene impurity in ethylene has been studied over 0.04 wt% Pd/Al₂O₃ catalysts modified by Cu. The undesired hydrogenation of ethylene could be suppressed by Cu.¹⁴C labelling proved that the intrinsic selectivity is always 95–98% of Cu or gaseous CO reduces the parallel hydrogenation of ethylene on the support, leaving the intrinsic selectivity unchanged.

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0,04 . % Pd/Al₂O₃, Cu. . 14C , 95–98% , , CO .

     

Preparation and catalytic performance of monolayer-dispersed Pd/Ni bimetallic catalysts for hydrogenation

Pd/Ni bimetallic catalysts were prepared by replacement reactions, characterized by X-ray diffraction, CO chemisorption and H₂ temperature-programmed desorption, and evaluated for hydrogenation of cyclohexene, styrene and acetone. The results show that Pd atoms are monolayer-dispersed on the Ni surface in these Pd/Ni catalysts. Consequently, Pd/Ni catalysts are much more active than Pd/Ni and Pd/c-Al₂O₃ with the same Pd loading prepared by the conventional impregnation method. __________ Translated from Chinese Journal of Catalysis, 2007, 28(8): 676–680 [译自: 催化学报]     

Pd/TiN nanocomposite catalysts for selective hydrogenation of phenol and its derivatives

Pd/TiN nanocomposite catalysts were fabricated for one-step selective hydrogenation of phenol to cyclohexanone successfully. High conversion of phenol (99%) and selectivity of cyclohexanone (98%) were obtained at 30℃ and 0.2 MPa H₂ for 12 h in the mixed solvents of H₂O and CH₂Cl₂. The Pd nanoparticles were stable in the reaction, and no aggregation was detected after four successive runs. The catalytic activity and selectivity depended on slightly the Pd particle sizes. The generality of the catalysts for this reaction was demonstrated by the selective hydrogenation of phenol derivatives, which showed that the catalyst was selective for the formation of cyclohexanone.     

Temperature dependence of benzene hydrogenation over sulfide catalysts

Non-Arrhenius temperature dependence of benzene hydrogenation was found for sulfide alumina-supported (Ni,Mo) and (Ni,W) catalysts under unsteady-state reaction conditions. It was shown that THE observed decrease in the catalyst activity at high temperature cannot be explained by the increasing role of the reverse reaction. The activity decrease was supposed to result from the catalyst reduction with the reaction mixture.     

Partial hydrogenation of benzene over platinum supported catalysts

Partial hydrogenation of benzene to cyclohexene has been studied on Pt/Nylon 66, Pt/MgO and Pt/TiO₂. An effect of the support on the selectivity to cyclohexene was observed, Pt/Nylon showing the highest selectivity, followed by Pt/MgO and Pt/TiO₂. An interaction of platinum with the more basic supports (Nylon, MgO) and a pretreatment under oxidizing conditions, results in a higher selectivity to cyclohexene.

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Pt/ 66, Pt/MgO PtTiO₂. , Pt/, Pt/MgO Pt/T,O₂. (, MgO) .

     

Chemoselective hydrogenation using molecular sieves-supported Pd catalysts: Pd/MS3A and Pd/MS5A

Palladium catalysts embedded on molecular sieves (MS3A and MS5A) were prepared by the adsorption of Pd(OAc)₂ onto molecular sieves with its in situ reduction to Pd⁰ by MeOH as a reducing agent and solvent. 0.5% Pd/MS3A and 0.5% Pd/MS5A catalyzed the hydrogenation of alkynes, alkenes, and azides with a variety of coexisting reducible functionalities, such as nitro group, intact. It is noteworthy that terminal alkenes of styrene derivatives possessing electron-donating functionalities on the benzene nucleus were never hydrogenated under 0.5% Pd/MS5A-catalyzed conditions, while internal alkenes of 1-propenylbenzene derivatives were readily reduced to the corresponding alkanes.     

XPS analysis of the effect of Pt addition to Pd catalysts for complete benzene oxidation

Pt-Pd bimetallic catalysts were prepared in order to develop and investigate catalysts having excellent activity and stability for benzene destruction. The effect of Pt addition to Pd catalysts is studied by XPS analysis. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electronic effect induced by variation of size for Pd clusters in 1,3-butadiene hydrogenation

The size of palladium aggregates is monitored with atomic beam technique condensed onto an SiO₂ amorphous substrate, by this way it is possible to define an average size that make explicit the intrinsic electronic size effect on a given reaction. The 1,3 hydrogenation of butadiene is followed and it is shown that intrinsic electronic properties observed by A.E.S. and U.P.S. spectroscopies can explain the variation of the turn over frequency.     

Deactivation of nickel catalysts by thiophene in benzene hydrogenation

Kinetic dependences of the catalyst deactivation rates and poison concentrations on the partial pressures of the main reactants have been established. Numerical values for the kinetic constants are given. Poison chemisorption is shown to take place on both unoccupied and occupied active centers and also on the adsorption centers not involved in the main process.

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Deactivation of silica supported Pd catalysts during liquid-phase hydrogenation

Summary Large pore MCM-41 was found to provide a better stabilization of Pd particles than amorphous SiO₂ during liquid phase hydrogenation. Pd/large pore MCM-41 exhibited higher hydrogenation activities as well as lower amount of metal loss by Pd leaching.     

Characterization and performance of Pd/Ni(Zn)-aluminate catalysts for acetylene hydrogenation

Research on Chemical Intermediates - 0.03 wt% Pd catalysts on nickel and zinc aluminate supports were prepared by impregnation. The samples were characterized by XRD, BET, ICP, SEM, EDS,...     

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.     

Crystallite size determination for supported metal catalysts by single X-ray profile fourier analysis

An X-ray diffraction method is presented capable of determining the average particle size, microstrains, the probability of faults as well as a particle size distribution function in crystalline materials. The method is based on the Fourier analysis of a single X-ray diffraction profile. Results obtained on supported platinum catalysts used in H/D isotopic exchange reactions are reported. On the basis of experimental spectra and our XRLINE1 code all structural parameters could be obtained.     

Pd cluster nanowires as highly efficient catalysts for selective hydrogenation reactions

Palladium is a key catalyst invaluable to many industrial processes and fine-chemical synthesis. Although recent progress has allowed the synthesis of Pd nanoparticles with various shapes by using different techniques, the facile synthesis of Pd nanocrystals and turning them into a highly active, selective, and stable catalyst systems still remain challenging. Herein, we report the highly selective one-pot synthesis of monodisperse Pd cluster nanowires in aqueous solution; these consist of interconnected nanoparticles and may serve as highly active catalysts because of the enrichment of high index facets on the surface, including {443}, {331}, and {221} steps. For the first time, carbon nanotube and γ-Al(2)O(3) immobilized Pd cluster nanowires showed highly enhanced catalytic performance in the liquid-phase selective hydrogenation of cinnamaldehyde and gas-phase hydrogenation of 1,3butadiene relative to immobilized Pd icosahedra and nanocubes, as well as commercial Pd catalysts.     

Activity of some crystal faces of supported palladium catalysts for benzene hydrogenation

Using known coverages of preadsorbed carbon monoxide as a specific poison on supported polycrystalline Pd, the degree of benzene conversion into cyclohexane was measured and compared with the conversion over a CO-free catalyst surface. Palladium crystal faces adsorbing carbon monoxide in various manners are uniformly active for benzene hydrogenation, which appears to be a structure insensitive reaction.

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Crystallite size determination for supported metal catalysts by single X-ray profile fourier analysis

An X-ray diffraction method is presented capable of determining the average particle size, microstrains, the probability of faults as well as a particle size distribution function in crystalline materials. The method is based on the Fourier analysis of a single X-ray diffraction profile. Results obtained on supported platinum catalysts used in H/D isotopic exchange reactions are reported. On the basis of experimental spectra and our XRLINE1 code all structural parameters could be obtained.     

低碱度共沉淀法制备苯选择加氢Ru-Zn催化剂

在低碱度下采用共沉淀法成功制备了非负载型Ru-Zn催化剂,用于苯选择加氢制环己烯反应.固定氢氧化钠沉淀剂的量,考察了不同氯化锌加入量对催化剂结构和催化性能的影响,采用N2吸附、X射线衍射和程序升温还原等手段对催化剂进行了表征.同时考察了选用具有最佳锌含量的Ru-Zn催化剂时搅拌速度和硫酸锌添加剂等对催化反应性能的影响,最后考察了催化剂多次使用时的反应性能.研究表明, Zn含量16.7%(质量分数)的Ru-Zn催化剂具有最佳的催化性能;在ZnSO4水溶液(0.45 mol/L)中,优化反应条件(哈氏合金釜,1200 r/min,150oC, H2压5 MPa)下反应45 min,苯转化率57%时环己烯选择性可达80%(收率超过45%).钌催化剂中ZnO晶体对于环己烯选择性达到80%非常重要.催化剂回收循环反应5次时反应性能基本不变,表明低碱度下制备的催化剂具有良好的稳定性,显示了工业化应用前景.     

低碱度共沉淀法制备苯选择加氢Ru-Zn催化剂

在低碱度下采用共沉淀法成功制备了非负载型Ru-Zn催化剂,用于苯选择加氢制环己烯反应.固定氢氧化钠沉淀剂的量,考察了不同氯化锌加入量对催化剂结构和催化性能的影响,采用N2吸附、X射线衍射和程序升温还原等手段对催化剂进行了表征.同时考察了选用具有最佳锌含量的Ru-Zn催化剂时搅拌速度和硫酸锌添加剂等对催化反应性能的影响,最后考察了催化剂多次使用时的反应性能.研究表明, Zn含量16.7%(质量分数)的Ru-Zn催化剂具有最佳的催化性能;在ZnSO4水溶液(0.45 mol/L)中,优化反应条件(哈氏合金釜,1200 r/min,150oC, H2压5 MPa)下反应45 min,苯转化率57%时环己烯选择性可达80%(收率超过45%).钌催化剂中ZnO晶体对于环己烯选择性达到80%非常重要.催化剂回收循环反应5次时反应性能基本不变,表明低碱度下制备的催化剂具有良好的稳定性,显示了工业化应用前景.     

Enhanced selectivity in acetylene hydrogenation by ligand modified Pd/TiO2 catalysts

Modification of Pd/TiO(2) catalyst by adsorption of triphenylphosphine and phenyl sulfide leads to markedly enhanced selectivity for acetylene hydrogenation in the presence of ethylene and excess hydrogen. Similar selectivities were maintained in cases where ligand decomposition took place and sulfur was retained on the catalyst surface.