Palladium nanoclusters supported on propylurea-modified siliceous mesocellular foam for coupling and hydrogenation reactions

This paper describes the synthesis, characterization and applications of palladium (Pd) nanoparticles supported on siliceous mesocellular foam (MCF). Pd nanoparticles of 2-3 nm and 4-6 nm were used in reactions involving molecular hydrogen (such as hydrogenation of double bonds and reductive amination), transfer hydrogenation of ketones and epoxides, and coupling reactions (such as Heck and Suzuki reactions). They successfully catalyzed all these reactions with excellent yield and selectivity. This heterogeneous catalyst was easily recovered by filtration, and recycled several times without any significant loss in activity and selectivity. The palladium leaching in the reactions was determined to be much less than the FDA-approved limit of 5 ppm. Furthermore, the catalyst can be stored and handled under normal atmospheric conditions. This immobilized catalyst allows for ease of recovery/reuse and minimization of waste generation, which are of great interest in the development of green chemical processes.     

Adsorption of CO2 on mesocellular siliceous foam iteratively functionalized with dendrimers

Melamine-type dendrimers are grafted to mesocellular siliceous foam (MCF) with ultralarge mesopores by stepwise alternating treatments of the substrate with 2,4,6-trichlorotriazine and ethylenediamine. MCF grafted dendrimers up to 4th generation are prepared and characterized. Very high organic loadings (55 wt% at the 4th generation) are achieved, with half of the initial substrate mesopores volume remaining unoccupied—leaving room for the rapid ingress and egress of small gas molecules. The product materials possess relatively high thermal stability—their decomposition starts at around 300 °C. Adsorption measurements suggest that only the primary amine groups of these melamine type structures are active for CO₂ chemisorption. The CO₂ adsorption capacities of these adsorbents are improved relative to the unfunctionalized MCF, especially when considered on a wt% substrate basis.     

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) .

     

Efficient heterogeneous asymmetric transfer hydrogenation of ketones using highly recyclable and accessible silica-immobilized Ru-TsDPEN catalysts

[reaction: see text] Chiral Ru-TsDPEN [N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine]-derived catalysts were first successfully immobilized onto amorphous silica gel and mesoporous silicas of MCM-41 and SBA-15 by an easily accessible approach. The catalyst immobilized on silica gel demonstrated remarkably high catalytic activities and excellent enantioselectivities (up to >99% ee) for the heterogeneous asymmetric transfer hydrogenation of various ketones. Particularly, the catalyst could be readily recovered and reused in multiple consecutive catalytic runs (up to 10 uses) with the completely maintained enantioselectivity.     

Magnetic nanoparticles entrapped in siliceous mesocellular foam: a new catalyst support

γ-Fe(2)O(3) nanoparticles were formed inside the cage-like pores of mesocellular foam (MCF). These magnetic nanoparticles showed a uniform size distribution that could be easily controlled by the MCF pore size, as well as by the hydrocarbon chain length used for MCF surface modification. Throughout the entrapment process, the pore structure and surface area of the MCF remained intact. The resulting magnetic MCF facilitated the immobilization of biocatalysts, homogeneous catalysts, and nanoclusters. Moreover, the MCF allowed for facile catalyst recovery by using a simple magnet. The supported catalysts exhibited excellent catalytic efficiencies that were comparable to their homogeneous counterparts.     

Asymmetric transfer hydrogenation in water with a supported Noyori-Ikariya catalyst

[reaction: see text] The poly(ethylene glycol)-supported ruthenium precatalyst shown above is highly effective for asymmetric transfer hydrogenation of unfunctionalized aromatic ketones by HCOONa in neat water, affording fast rates, good to excellent enantioselectivities, and outstanding reusability.     

Catalytic transfer hydrogenation of 2-butanone over oxide catalysts

Catalytic transfer hydrogenation of 2-butanone with 2-propanol was studied in gas phase over a series of oxides of different acid-base properties. Although the basic oxides (MgO, La₂O₃) gave high initial conversions, these oxides underwent deactivation during the reaction. This deactivation could be partially prevented by a previous treatment with chloroform of the oxide. The amphoteric oxides (TiO₂, ZrO₂, Al₂O₃) were also active in this reaction. Increasing the acidic character of the catalyst (Nb₂O₅, WO₃) led to a pronounced dehydration of 2-propanol. The results obtained over a series of rare earth oxides (La₂O₃, Sm₂O₃, Gd₂O₃, Dy₂O₃, Er₂O₃) revealed that beside the role of basic and acid sites a correlation seems to exist between the number of unpaired electrons of the metal ion and the catalytic activity, indicating the role of one electron donor sites.     

Transfer hydrogenation of cellulose to sugar alcohols over supported ruthenium catalysts

Ru/C catalysts are active for the conversion of cellulose using 2-propanol or H(2) of 0.8 MPa as sources of hydrogen, whereas the Ru/Al(2)O(3) catalyst is inactive in both reactions, indicating that the Ru/C catalysts are remarkably effective for the cellulose conversion.     

Asymmetric transfer hydrogenation of quinolines using tethered Ru(II) catalysts

The first report of an asymmetric transfer hydrogenation, in formic acid/triethylamine, of quinolines is described. Using a Ru(II) catalyst containing a 4-carbon tether, products of up to 73% ee were formed, whilst a Rh(III)-tethered catalyst gave products of up to 94% ee.     

Asymmetric transfer hydrogenation of benzaldehydes

A combined system of RuCl[(R, R)-YCH(C(6)H(5))CH(C(6)H(5))NH(2)](eta(6)-arene) (Y = NSO(2)C(6)H(4)-4-CH(3) or O) and t-C(4)H(9)OK catalyzes the asymmetric transfer hydrogenation of various benzaldehyde-1-d derivatives with 2-propanol to yield (R)-benzyl-1-d alcohols in 95-99% ee and with >99% isotopic purity. Reaction of benzaldehydes with a DCO(2)D-triethylamine mixture and the R,R catalyst affords the S deuterated alcohols in 97-99% ee.     

Asymmetric reduction and hydrogenation over heterogenous catalysts prepared by reacting nickel-boride with norephedrine

The reduction of acetophenone with borane–THF over heterogeneous catalysts prepared by reacting nickel-boride with (1R,2S)-(−)-norephedrine, afforded (R)-(+)-1-phenylethanol with high enantioselectivity (ee=90%). The catalysts can be recycled two times with little or no loss of performance. The excellent enantioselective properties resulted from the formation of 1,3,2-oxazaborolidine which is strongly anchored at the surface of the nickel-boride. Used for the hydrogenation of acetophenone, 4-methylpentan-2-one and isophorone, the catalyst hydrogenated with a slight predominance of the S configuration. The ee was poor but it remained constant when the catalyst was reused.     

Pd/Amberlyst-45催化剂催化水相中苯酚选择性加氢制环己酮(英文)

环己酮是重要的有机化工原料和工业溶剂,是制造尼龙、己内酰胺和己二酸的主要中间体,环己酮的绿色生产工艺受到人们关注.目前全世界环己酮年产量接近900万吨,但环己酮生产仍主要以环己烷为原料,采用富氧空气氧化为环己基过氧化氢,再在铬酸叔丁酯催化剂作用下分解为环己醇和环己酮的混合物,然后经一系列蒸馏精制后得到环己酮、工艺复杂、能耗高,而且设备腐蚀、环境污染及安全问题严重.因此,大量工作正致力于新工艺和新催化剂研究,其中光催化氧化、分子筛催化氧化和金属氧化物催化氧化等都有相关报道,同时还有学者开发了其它环己酮制备新方法,如环己烯水合法、苯加氢法、环己醇氧化法和苯酚加氢法等.苯酚直接选择性加氢合成环己酮研究具有重要意义.苯酚加氢通常有两种工艺,气相加氢和液相加氢,由于液相加氢具有无需将反应物汽化、能耗较低和催化剂反应活性高等优势而受到广泛关注.但是目前大量文献报道的苯酚加氢过程仍需要高温条件且较易产生环己醇和环己烷等副产物,大部分催化反应需在有机溶剂中进行,因此如何提高环己酮选择性,减小环境影响成为近年来的热门课题.在过去数年中,人们筛选了大量催化剂,其中Pd催化剂具有较高活性和目的产物选择性,因为其对羰基表现出较低的催化活性.研究还发现,催化剂载体对苯酚加氢产物分布有重要影响,酸性载体或酸性助剂的加入均能提高苯酚转化率和环己酮选择性,可能的原因是催化剂表面可与苯酚羟基形成O-H…π强相互作用,使苯酚分子更容易吸附在载体表面,而一旦苯酚经催化加氢生成环己酮,由于失去羟基与载体表面相互作用,环己酮更容易从载体表面脱附,从而避免过度加氢生成环己醇,同时酸性位点可以增强Pd的电子密度,提高催化加氢活性.另外,通过添加助剂也可有效改善催化剂性能.然而,到目前为止,通过单一的一种催化剂仍然很难同时实现苯酚的高转化率和环己酮的高选择性.因此,开发新催化剂和简便的生产工艺对环己酮高效高质量生产具有重要意义.本文使用一种多孔、不易溶解的酸性离子交换树脂Amberlyst-45(A-45)为载体,采用简单的浸渍工艺制备了一系列不同Pd负载量的Pd/A-45催化剂,详细考察了催化剂在水相中对苯酚选择性加氢制环己酮的催化活性和选择性,包括反应温度、催化剂用量、反应时间和Pd负载量等对反应活性的影响及催化剂重复使用情况,并且与传统的SiO_2,ZnO,MgO,Al_2O_3和活性炭负载的Pd催化剂进行对比.研究发现,Pd/A-45催化剂在温和反应条件(40-100℃,0.2-1 MPa)下具有极高的催化活性和选择性,在适宜的反应条件下苯酚转化率达到100%,环己酮选择性高于89%.进一步分析由不同活性金属负载量制备的不同粒径Pd/A-45催化剂的活性规律发现,苯酚加氢生成环己酮是一个结构敏感型反应,其中Pd颗粒尺寸为12-14 nm时更有利于环己酮生成.     

Stereoselective hydrogenation of 11-hexadecyne-l-ol on supported copper catalysts

Hydrogenation of 11-hexadecyne-l-ol on 5–30 % copper catalysts supported on -A1₂O₃ and MgCO₃ results incis-11-hexadecyne-1-ol in 100 % yield. Hydrogenation does not occur on 5–30 % Cu/ZnO catalysts. The difference in behavior of the catalysts is connected with the valent state of copper on the surface and different hydrogen chemisorption.Positive conclusion on the application No. 930071.1 of 16.06.93 for the Kazakhstan preliminary Patent (A. M. Pak, O. 1. Kartonozhkina, and G. T. lzdebskaya).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1147–1150, May, 1996.     

Gas phase hydrogenation of o-xylene on Ru supported catalysts

The gas phase hydrogenation of o-xylene on supported ruthenium catalysts has been studied. Metal dispersity, acidity of the support and carbonaceous residues modified the stereoselectivity of Ru. Following the rollover model for the reaction, the results are explained in terms of the residence time of the reactive species on the metal surface.     

Efficient and chemoselective reduction of carbonyl compounds with supported gold catalysts under transfer hydrogenation conditions

A new heterogeneous catalytic transfer hydrogenation (CTH) system, consisting of a non-flammable supported Au catalyst along with 2-propanol as the hydrogen donor, was proven to be effective for chemoselective reduction of a wide range of aromatic ketones and aldehydes to the corresponding alcohols.     

High-selectivity hydrogenation of cinnamaldehyde over platinum supported on aluminosilicates

This work studies liquid-phase hydrogenation of cinnamaldehyde to cinnamylalcohol over Pt/K-10 and ion-exchanged Pt/Na-Y. The experiments show the highest selectivity of 78% for Pt/K-10 and 92% for the Pt/Na-Y. By careful analysis, characterisation and changing reaction conditions it was attempted to cover key parameters possibly responsible for the high selectivity. The parameters are described and discussed in detail.     

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.     

Hydrodesulfurization and hydrogenation activities of carbon supported bimetallic catalysts

Carbon-supported noble metals are tailored for hydrodesulfurization reaction by adding iron, in such a manner that undesirable hydrogenation reactions are prevented without decrease of the catalytic activity.

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