Regeneration of Pd/Al2O3 catalysts used for tetrachloroethylene hydrodechlorination

The deactivation of the Pd/Al₂O₃ catalyst used for the hydrodechlorination of tetrachloroethylene (TTCE) is caused by both the carbonaceous deposits and by the hydrogen chloride produced in the reaction. In this work, several regeneration procedures have been tested, concluding that the best procedure is the leaching with ammonia, followed by calcinations and reduction. This procedure leads to an important recovery of the initial activity. The catalyst regenerated with this treatment is even less prone to deactivation that the fresh catalyst.     

Pd/C-catalyzed Heck reaction in ionic liquid accelerated by microwave heating

Pd/C-catalyzed Heck reaction was conducted in ionic liquid 1-octanyl-3-methylimidazolium tetrafluoroborate ([OMIm]BF₄) in absence of phosphine ligand, which was promoted by microwave irradiation. The ionic liquid containing catalyst system can be used five times with a little loss of activity.     

Polyacrylonitrile fiber mat‐supported palladium catalyst for Mizoroki–Heck reaction in aqueous solution

A novel palladium catalyst immobilized on polyacrylonitrile fiber mats (Pd/PAN) was prepared by electrospinning. The catalytic activity and recyclability of the microwave‐assisted Pd/PAN fiber mats were examined for the Mizoroki–Heck cross‐coupling of aryl iodides with three different acrylates in aqueous solution. The morphology of the prepared Pd/PAN fiber mats was characterized by scanning electron microscopy. The large size of the PAN fiber mat‐supported palladium catalyst enables much easier separation from the reaction mixture by simple filtration. Density functional theory calculation indicates that the chelation energy of palladium chloride (PdCl₂) with propionitrile (model of PAN) is considerable smaller than that of PdCl₂ with water, suggesting that the stability and reactivity of the Pd/PAN fiber mats catalyst could be improved through the surface derivatization with polar functional groups. Copyright © 2011 John Wiley & Sons, Ltd.     

Catalytic oxidation of methane over Pd/Co3O4

The catalytic activity of Pd/Co₃O₄ toward methane oxidation has been examined in this study as a function of Pd loading, reaction temperature, space velocity and methane concentration in the reaction gas mixture. The bare oxide is quite active achieving a 100% methane conversion at 480°C under the reaction conditions used. The catalyst with the highest Pd loading tested of 10 wt.% yields the best activity curve, but the 5 wt.% Pd/Co₃O₄ catalyst performs nearly as well. Complete conversion for this catalyst is attained at 300°C and the activity remains stable over a 90-min test period.     

Application of a dimeric ortho‐palladated complex of tribenzylamine as an efficient catalyst in microwave‐assisted Hiyama coupling reactions

The activity of [Pd{C₆H₄(CH₂N(CH₂Ph)₂)}(μ‐Br)]₂ complex was investigated in cross‐coupling reactions of triethoxy(phenyl)silane with various aryl halides under microwave irradiation. This complex is an efficient and stable catalyst for the synthesis of substituted biphenyls that is non‐sensitive to air and moisture. The combination of dimeric complex as homogenous catalyst, microwave irradiation, DMF as microwave‐active polar solvent and TBAF as microwave‐active additive led to excellent yields in short reaction times. Copyright © 2012 John Wiley & Sons, Ltd.     

微波辐射对浆态床合成甲醇CuO/ZnO/Al2O3催化剂前驱体晶相转变的影响

在微波辐射条件下,对CuO/ZnO/Al2O3催化剂的沉淀母液进行老化,通过XRD、TG、H2-TPR,FTIR、HR-TEM和XPS对前驱体及催化剂微观结构的进行表征,探讨了CuO/ZnO/Al2O3催化剂前驱体晶相转变过程中微波辐射的作用。结果表明,微波辐射有利于Cu2+取代Zn5(CO3)2(OH)6中Zn2+的同晶取代反应。微波辐射的老化过程中,首先发生Cu2+取代Zn5(CO3)2(OH)6中Zn2+生成(Cu,Zn)5(CO3)2(OH)6的同晶取代反应,并于1.0 h内基本完成;随着老化时间继续延长,主要进行Zn2+取代Cu2(CO3)(OH)2中Cu2+生成(Cu,Zn)2(CO3)(OH)2的同晶取代反应,同时(Cu,Zn)5(CO3)2(OH)6进一步结晶。与常规老化1 h制备的前驱体相比,微波辐射老化1.0 h制备的前驱体含有较多的(Cu,Zn)5(CO3)2(OH)6物相,有助于增强焙烧后CuO/ZnO/Al2O3催化剂中CuO-ZnO协同作用,提高表面铜含量,进而提高CuO/ZnO/Al2O3催化剂在浆态床合成甲醇的催化活性和稳定性,在400 h浆态床合成甲醇评价期间,甲醇时空收率最大达318.9 g.kg-1.h-1,失活率仅为0.11%.d-1。     

An efficient Stille cross‐coupling reaction catalyzed by ortho‐palladated complex of tribenzylamine under microwave irradiation

The catalytic activity of [Pd{C₆H₄(CH₂N(CH₂Ph)₂)}(μ‐Br)]₂ complex as an efficient, stable and catalyst that is non‐sensitive to air and moisture was investigated in the Stille cross‐coupling reaction of various aryl halides with phenyltributyltins under microwave irradiation. The substituted biaryls were produced in excellent yield in short reaction times using a catalytic amount of this complex in DMF at 100 C. The combination of dimeric complex as homogeneous catalyst and microwave irradiation and also DMF as microwave‐active polar solvent gave higher yields in shorter reaction times. Copyright © 2011 John Wiley & Sons, Ltd.     

树枝状钯纳米结构的控制合成及硝基苯加氢反应的催化活性

以氯钯酸为前驱体, 苯甲醇为还原剂和溶剂, 十六烷基吡咯烷酮(PVP)为稳定剂, 在微波辐射下制备了分散均匀、形貌均一的树枝状钯纳米结构. 产物用透射电子显微镜(TEM), X射线粉末衍射(XRD), X射线光电子能谱(XPS)进行了表征, 表明所制备的Pd纳米颗粒呈树枝状, 形貌单一, 分散均匀, 是由许多近似圆形的小颗粒自组装而成的二级结构. 对树枝状钯催化硝基苯加氢反应进行探究, 表明树枝状钯的催化活性比市售的钯碳催化剂的催化活性高.     

Catalytic hydrodechlorination reaction of chlorophenols by Pd nanoparticles supported on graphene

Chlorophenols are widely used as industrial chemicals such as herbicides, insecticides, wood preservatives, and disinfectants. However, chlorophenols are very toxic materials and they have become the cause of current environmental issues. Hydrodechlorination (HDC) reaction is a more environmentally friendly removal method of chlorophenols than other methods. In this paper, Pd–modified graphene was prepared and applied to HDC reaction. Pd supported on graphene (refer to Pd/G) was prepared using the recently reported microwave irradiation method. The Pd(II)/GO was made by impregnation methods of palladium precursors in solution phase and was subsequently reduced to Pd/G by microwave irradiation. The morphological and chemical structure of the Pd/G was characterized by XRD, SEM, ICP-MS, EDS, and TEM. It was found that the graphene-based Pd catalyst showed the highest catalytic performance among Pd/Y, Pd/MCM-41, and Pd/G catalysts. This is attributed to the smaller particle size and higher dispersions of Pd nanoparticles on the graphene surface. The catalytic HDC of chlorophenols was investigated. For HDC reaction, 100 ppm solution of chlorophenols such as 4-chlorophenol, six isomers of dichlorophenol, and 2,3,5-trichlorophenol in isopropanol was treated with catalyst and base, such as Na₂CO₃ and K₂CO₃, under a hydrogen gas at ambient pressure. The progress of the chlorophenol decomposition was analyzed with GC. All chlorophenols were completely decomposed within 2 h in the 3 % Pd/G catalyst. The reaction pathway of chlorophenols was elucidated from the conversion of chlorophenols and selectivities of products. The reuse of the catalyst was also studied. The performance of the recycled catalyst in HDC reaction up to six successive runs was observed.     

Methane Combustion over Pd/Al2O3 Catalyst: Effects of Chlorine Ions and Water on Catalytic Activity

The influences of residual chlorine ions and water on the performance of a Pd/Al₂O₃ catalyst in methane combustion have been studied. The results show that the catalyst containing Cl⁻ exhibits a relatively low activity, and the addition of water to the reaction system accelerates the deactivation process. The catalyst has been characterized by N₂ adsorption, X-ray fluorescence, Fourier transform infrared spectroscopy (FT-IR), and thermogravimetry (TG). The results show that the presence of Cl⁻ appears to strongly inhibit the total oxidation of methane and hinder the dispersion of Pd on Al₂O₃. The formation of Pd(OH)₂ during the reaction is the most likely reason for the inhibition effect of water, which is confirmed by FT-IR and TG analysis. The regeneration of the Pd/Al₂O₃ catalyst can be achieved by purging in nitrogen at 550 °C.     

磁性纳米Pd/Fe3O4催化剂的制备及其在Heck反应中的应用

通过使用聚乙烯吡咯烷酮作为稳定剂,合成了磁性Pd/Fe₃O₄纳米颗粒催化剂。对该催化剂进行粉末X射线衍射、透射电子显微镜、感应耦合等离子体和磁性表征。将Pd/Fe₃O₄催化剂用于Heck反应,检测其催化性能。测试结果表明Pd纳米颗粒负载在Fe₃O₄纳米颗粒上,而且催化剂的尺寸<20 nm,并在Heck反应中表现了极好的催化性能。此外,催化剂可以通过磁场回收利用, 且催化活性没有显著的降低。     

FeOx Coating on Pd/C Catalyst by Atomic Layer Deposition Enhances the Catalytic Activity in Dehydrogenation of Formic Acid

Hydrogen generation from formic acid (FA) has received significant attention.The challenge is to obtain a highly active catalyst under mild conditions for practical applications.Here atomic layer deposition (ALD) of FeO_x was performed to deposit an ultrathin oxide coating layer to a Pd/C catalyst,therein the FeO_x coverage was precisely controlled by ALD cycles.Transmission electron microscopy and powder X-ray diffraction measurements suggest that the FeO_x coating layer improved the thermal stability of Pd nanoparticles (NPs).X-ray photoelectron spectroscopy measurement showed that deposition of FeO_x on the Pd NPs caused a positive shift of Pd3d binding energy.In the FA dehydrogenation reaction,the ultrathin FeO_x layer on the Pd/C could considerably improve the catalytic activity,and Pd/C coated with 8 cycles of FeO_x showed an optimized activity with turnover frequency being about 2 times higher than the uncoated one.The improved activities were in a volcanoshape as a function of the number of FeO_x ALD cycles,indicating the coverage of FeO_x is critical for the optimized activity.In summary,simultaneous improvements of activity and thermal stability of Pd/C catalyst by ultra-thin FeO_x overlayer suggest to be an effective way to design active catalysts for the FA dehydrogenation reaction.     

Effect of Au loading, H2O and CO concentration on the stability of Au/ZnO catalysts for room-temperature CO oxidation

Catalytic decomposition of ethanol in the presence of steam over Pd supported on a porous carbonaceous material was studied. XPS and TEM were used for the catalyst characterization. Experiments were performed under atmospheric pressure, temperature of 320-360°C and H₂O/C₂H₅OH molar ratio 8.1. It was found that the catalyst exhibited a high activity and long-term stability for the ethanol decomposition into a gas mixture containing carbon oxides, methane and hydrogen.     

Synthesis and comparative study of catalytic activity between Pd-metallodendrimer and Pd/Cu-bimetallodendrimer nanoparticle-based on triazine

Triazine-based heterogeneous Pd/Cu-bimetallodendrimer Nanoparticle (Pd/Cu-BMDNP) has been synthesized by sequential loading method from palladium containing metallodendrimer (Pd-MD) which was prepared by the reaction of 2,4,6-Triamine-1,3,5-triazine (melamine) with substituted benzoyl chloride using (Ph₃P)₂PdCl₂ in DMSO at 90 °C. SEM and EDX of Pd/Cu-BMDNP showed the nanosized aggregated spherical surface morphology and the presence of Palladium and copper of the NP. Also, the phase was detected as Face Centered Cubic (FCC) structure by XRD analysis. In addition, the average particle size of Pd/Cu bimetallic catalyst was identified as 12–13 nm by TEM investigation. Greater thermal stability of Pd/Cu-BMDNP than Pd-MD was detected from TG and DSC experiments. The Pd-metallodendrimer has been also characterized by IR, ¹H NMR, ¹³C NMR, SEM, EDX, Mass, TG and DSC techniques. The simple recoverability, high reusability, low amount of catalyst loading, negligible amount of catalyst leaching of the heterogeneous Pd/Cu-BMDNP have made more effective catalyst than homogeneous Pd-metallodendrimer for the C–C cross-coupling reaction such as Heck, Glaser, Sonogashira and Suzuki-Miyaura in excellent yields.     

Influence of Pd-Ce interaction and chlorine ion on hydrodesulfurization reaction: The activity and sulfur tolerance of the Pd-Ceo2/Al2O3 catalyst

CeO₂ promoted palladium catalysts supported on Al₂O₃ were prepared using the impregnation (IM) and the deposition-precipitation (DP) methods. The activities and sulfur tolerance of the catalysts for hydrodesulfurization (HDS) were detected with thiophene HDS as probe reaction. H₂ adsorption, XRD, FTIR, NH₃-TPD, XPS were used to characterize the catalysts. The Pd-CeO₂/Al₂O₃ (IM) catalyst was highly active for the HDS reaction, and it had much stronger sulfur tolerance than the Pd/Al₂O₃ catalyst. Pd-CeO₂/Al₂O₃ (DP) showed excellent sulfur tolerance while its initial activity decreased. It was observed that with the chlorine bridge, the interfacial structure of Pd-Cl⁻¹-Ce³⁺ was responsible for the high activity of the Pd-CeO₂/Al₂O₃ (IM) catalyst, at the same time the interaction of Pd with Ce was weakened by Cl₋₁ ions. The enhanced sulfur tolerance over the Pd-CeO₂/Al₂O₃ (IM) catalyst was attributed to the weakened Pd-S bond caused by the competitive adsorption of H₂S on Ce³⁺ ions. As to the Pd-CeO₂/Al₂O₃ (DP) catalyst, a strong interaction of Pd with Ce put Pd at an electron-deficient state, the creation of sulfided palladium was therefore inhibited.     

Microwave-assisted Stille and Hiyama cross-coupling reactions catalyzed by ortho-palladated complexes of homoveratrylamine

The activity of dimeric [Pd{C₆H₂(CH₂CH₂NH₂)-(OMe)₂-3,4}(μ-Br)]₂ and monomeric [Pd{C₆H₂(CH₂CH₂NH₂)-(OMe)₂-3,4}Br(PPh₃)] complexes as efficient, air, and moisture tolerant catalysts was investigated in Stille and Hiyama cross-coupling reactions of various aryl halides. Substituted biaryls were produced in excellent yields in short reaction times using these complexes. The monomeric complex had been demonstrated to be more active than the corresponding dimeric catalyst for the cross-coupling of some of aryl bromides and unreactive aryl chlorides. The combination of homogenous metal catalyst, microwave irradiation, and microwave-active polar solvents gave high yields of products in short reaction times.     

PdCl2-CuCl2/Al2O3催化剂低温催化CO氧化的失活机理

采用X射线衍射、N₂吸-脱附、X射线光电子能谱分析、氢气-程序升温还原和原位红外漫反射等方法对新鲜和失活的PdCl₂-CuCl₂/Al₂O₃低温催化CO氧化催化剂进行表征,研究了高相对湿度(100%)下催化剂的失活机理.结果表明,催化剂表面沉积的水使得活性铜物种容易从催化剂表面向载体孔道内部迁移,由于Pd、Cu相互作用弱化从而减弱了Pd与Cu物种间的相互作用,使得催化剂的氧化还原性能受到影响,抑制了Pd⁰再氧化为Pd²⁺的过程,从而因CO氧化反应中催化剂氧化还原循环受阻而导致失活.     

H3PW12O40–[bmim][FeCl4]: A novel and green catalyst-medium system for microwave-promoted selective interconversion of alkoxymethyl ethers into their corresponding nitriles, bromides and iodides

In the present work, the catalytic activity of 12-tungstophosphoric acid immobilized on [bmim][FeCl₄] ionic liquid as a highly efficient and eco-friendly catalytic system for rapid and chemoselective direct conversion of MOM- or EOM-ethers into their corresponding nitriles, bromides and iodides under microwave irradiation is reported. In these reactions, the products are obtained in high yields. The catalyst exhibited remarkable reactivity and was reused several times.     

Accelerated Heck reaction using ortho‐palladated complex with controlled microwave heating

Palladium‐catalyzed Heck couplings utilizing [Pd{C₆H₂(CH₂CH₂NH₂)‐(OMe)₂,3,4} (µ‐Br)]₂ palladacycle catalyst and microwave irradiation lead to formation of different coupling products. This complex is an active and efficient catalyst for the Heck reaction of aryl iodides, bromides and even less reactive chlorides. The cross‐coupled products were produced in excellent yields. The reaction time was reduced from hours to minutes and full conversion was achieved under microwave irradiation. Copyright © 2009 John Wiley & Sons, Ltd.     

SBA-15负载Pd催化剂的制备及其在Heck反应中的应用研究

利用水热反应制备了表面离子液体功能化的SBA-15介孔材料,在丙酮溶液中与氯化钯反应,然后使用水合肼在乙醇中还原.测试了这种催化剂在Mizoroki-Heck反应中的催化活性.与直接负载在SBA-15上的钯催化剂相比,这种表面修饰的介孔SBA-15负载催化剂表现出更高的催化活性、可回收性和反应稳定性.氮气吸脱附实验和小角XRD衍射实验表明,在合成中,材料的介孔性能并没有被破坏.透视电镜也表征了该材料的表面形貌.最后,Mizoroki-Heck反应表明该催化剂具有很高的催化活性,且循环五次后,其催化活性降低并不明显.