Hydrogenation catalysis of nanosized palladium supported by polymer/silica disupporter. II. Effects of the characteristics of the catalyst on hydrogenation

A series of nanosized palladium catalysts supported by silica and polymers, prepared by the complex transformation method, were used for catalytic hydrogenation of nitrobenzene. It was found that both the thickness of the polymer layer and the size of the palladium particles would affect the catalysis. The results indicated that the reaction rate would be optimal when a polymer supporter formed a single layer on the silica surface. The catalytic activity of the catalyst would not simply increase with the decrease of the size of palladium particles. The effects of other conditions on the catalytic properties, such as the order during preparation of the catalyst, solvent, and the pH values, were also discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3661–3665, 2003     

Highly porous catalytic materials with Pd and ionic liquid supported on chitosan

Chitosan was used to immobilize phosphonium‐based ionic liquids, combined with silica particles, to prepare catalytic materials in the form of highly porous monoliths. These catalytic materials were studied for the hydrogenation of 4‐nitroaniline into p‐phenylenediamine in the presence of formic acid as hydrogen donor in a column reactor. Experimental conditions for the elaboration of the materials were evaluated by their impact on palladium sorption, on the structure of the materials, and on their catalytic efficiency. The concentration of chitosan in the initial solution and the size and concentration of silica particles had to be carefully chosen to elaborate homogeneous materials, with good mechanical resistance and stability in water. The chitosan characteristics and the type of ionic liquid immobilized in the material did not significantly affect the structure of the materials but proved to be crucial for their catalytic efficiency. Higher catalytic performances were obtained using materials prepared from chitosan of high‐deacetylation degree and with Cyphos IL‐101. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Dendrimer–Palladium Complex Catalyzed Oxidation of Terminal Alkenes to Methyl Ketones

Silica‐supported polyamidoamine (PAMAM) dendrimers with different spacer lengths were prepared. After the introduction of diphenylphosphino groups, complexation to dibenzylidenepalladium(0) gave the desired silica‐supported dendrimer–palladium catalyst complexes G0 to G4‐C2‐Pd. These catalysts showed activity towards the oxidation of terminal alkenes to methyl ketones. A dependence of catalytic activity on the spacer length of the diamine in PAMAM was observed.     

Highly selective asymmetry transfer hydrogenation of prochiral acetophenone catalyzed by palladium–chitosan on silica

The chitosan–palladium catalyst supported on silica was prepared and used to catalyze an asymmetry transfer hydrogenation of prochiral acetophenone to alcohol with formate salts as a hydrogen donor at atmosphere. The results indicate that palladium coordinates with amino group in chitosan to form palladium–chitosan complex and its performance for an asymmetry transfer hydrogenation of acetophenone is affected greatly by the reaction temperature, hydrogen donor and solvent. For the hydrogenation of acetophenone over the palladium–chitosan–silica catalyst, the suitable solvent is ethanol and hydrogen donor is ammonium formate or sodium formate. Using ammonium formate as H-donor at atmosphere and 80 °C, an enantiomeric excess of R-1-phenylethanol reaches 68.9%.     

Improved Palladium and Nickel Catalysts Heterogenised on Oxidic Supports (Silica,MCM‐41, ITQ‐2, ITQ‐6)

Two series of solid catalysts in which a chiral palladium or nickel complex with Schiff bases as ligands have been immobilized on ordered mesoporous silica supports (MCM‐41), delaminated ITQ‐2, ITQ‐6 zeolites and amorphous silica have been prepared. Hydrogenation of alkenes and imines was studied with the homogeneous as well as with the counterpart heterogenized catalysts. The high accessibility introduced by the structure of the supports allows the preparation of highly efficient immobilized catalysts with TOFs of 1,000,000 h⁻¹. A moderate acidity in the support increases the catalytic activity considerably, and the easy recoverable immobilized catalysts can duplicate the activity of the homogeneous analogues. No deactivation of the catalysts was observed after repeated recycling.     

Novel Pd-BTP/SiO2 as an Effective Heterogeneous Catalyst for Heck Reactions

A highly efficient and reusable catalyst, palladium (II) complex supported on functionalized silica, was prepared by anchoring palladium (II) onto 2,6-bis(5,6-dimethyl-1,2,4-triazine-3-yl)pyridine [BTP]-modified mesoporous silica (labeled as Pd-BTP/SiO₂). The catalyst was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Brunauer Emmett Teller (BET) analysis. Its catalytic performance was tested for the Heck coupling reactions between aryl halides with acrylic acid or styrene, and good to excellent results (higher conversions 87–96% and yields 66–78%) were obtained. The catalyst system was stable under the reaction conditions and could be successfully reused more than five times without the loss of catalytic activity.     

An Efficient and Recyclable Catalyst for N‐Alkylation of Amines and β‐Alkylation of Secondary Alcohols with Primary Alcohols: SBA‐15 Supported N‐Heterocyclic Carbene Iridium Complex

A mesoporous silica (SBA‐15)‐supported pyrimidine‐substituted N‐heterocyclic carbene iridium complex was prepared and used as a catalyst for both environmentally friendly N‐alkylation of amines and β‐alkylation of secondary alcohols with primary alcohols. The structure of the supported iridium catalyst was characterized by Fourier transform infrared (FT‐IR), ¹³C and ²⁹Si solid‐state nuclear magnetic resonance (NMR), small‐angle X‐ray scattering (SAXS), transmission electron microscopy (TEM), iridium K‐edge X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine structure (EXAFS) spectroscopic analyses which demonstrated that the coordination environment of the iridium centre and the 3‐dimensional‐hexagonal pore structure of SBA‐15 were retained after the immobilization. The catalyst was found to be highly efficient for both kinds of reaction on a wide range of substrates under mild conditions. Moreover, the supported iridium catalyst was obviously superior to the unsupported one in the N‐alkylation of aniline and β‐alkylation of 1‐phenylethanol with benzyl alcohol as substrate, which indicated that not only the iridium complex moiety but also the support material contributed to the catalytic activity of the supported iridium catalyst in these reactions. The supported iridium catalyst can be easily recycled by simple washing without chemical treatment, and exhibited excellent recycling performance without notable decrease in catalytic efficiency even after twelve test cycles for N‐alkylation of aniline with benzyl alcohol, nine cycles for N‐alkylation of different amines with different alcohols, and eight cycles for β‐alkylation of 1‐phenylethanol with benzyl alcohol, respectively.     

Macrocyclic Palladium(II) Complexes in C?C Coupling Reactions: Efficient Catalysis by Controlled Temporary Release of Active Species

Stabilization of palladium species against agglomeration is essential for reasonable catalytic activity in C C coupling reactions. In contrast to common methods of palladium(0) complex or particle stabilization, a new concept is introduced here: it is demonstrated that a controlled release of palladium from an inactive precatalyst provides stability, too, and leads to high catalytic activity. This paper presents surprising catalytic results for Heck and Suzuki reactions with aryl chlorides and bromides, using three highly stable macrocyclic palladium complexes as catalyst precursors. Three different behaviour patterns for the macrocyclic complexes can be deduced from the evaluation of catalytic activities, UV‐Vis spectroscopy, recycling studies of immobilized complexes, and ligand addition experiments. (i) Palladium tetraphenylporphyrin reversibly releases only extremely low amounts of palladium during the reactions, and low coupling activities are observed. (ii) Release of palladium from its phthalocyanine complex is irreversible; cumulative release of palladium into the reaction mixtures leads to high catalytic activity. (iii) Extraordinary results were obtained with a Robson‐type complex of palladium, which reversibly releases effectual amounts of palladium into solution under reaction conditions. This controlled release prevents the formation of inactive palladium agglomerates under harsh conditions and leads to high catalytic performances. Even strongly deactivated electron‐rich aryl chlorides (4‐chloroanisole) can be completely and selectively converted by the in situ formed anionic palladium halide complexes; the addition of typical stabilizing additives (TBAB) was found to be unnecessary. The bimetallic palladium complex is regenerated at the end of the reaction. These results contribute to the current understanding of the active species in C C coupling reactions of Heck and Suzuki types.     

Pd/SiO2 as Heterogeneous Catalyst for the Heck Reaction: Evidence for a Sensitivity to the Surface Structure of Supported Particles

The contact of Pd(AcO)₂ in solution with thiouric tethered to a silica led to the formation of supported nanoparticles (ca. 2 nm in size) active in the Heck reaction, quite sensitive to the palladium leaching. A stable supported phase was obtained by subsequent calcination, but the catalytic activity resulted strongly dependent on the calcination temperature. Such a behaviour was related to differences in the surface structure of the supported particles, as those monitored by IR spectroscopy of CO adsorbed on catalysts reduced at various temperatures.     

Effect of the promoter and support on the catalytic activity of Pd?CeO2‐supported catalysts for CH4 combustion

A series of palladium–ceria‐supported catalysts prepared by the sol–gel method are characterized and their catalytic results are reported. It was found that the addition of ceria to alumina produces a highly dispersed catalyst when compared with their zirconia counterparts. However, the catalytic activity of the ceria zirconia series is higher, essentially due to the larger particle size of palladium. This result can be attributed to the structure‐sensitive reaction of the combustion of methane. Copyright © 2004 Society of Chemical Industry     

Effect of hierarchical meso-macroporous silica supports on Fischer-Tropsch synthesis using cobalt catalyst

Hierarchical meso-macroporous (HS-X) silica with different mesopore diameters synthesized by using rice husk ash as a silica source and chitosan as a natural template were applied for the first time as the cobalt support for Fischer-Tropsch synthesis. Unimodal mesoporous silica (MS-X) supports with equivalent mesopore diameters to HS-X supports have also been prepared for comparison. Effects of diffusion in MS-X and HS-X supports of different particle sizes on the catalytic activity and hydrocarbon selectivity were investigated. The cobalt crystallite sizes were increased with increasing mesopore diameters, whereas the highest amount of H₂ chemisorbed was found for the catalyst with the medium mesopore diameter. The HS-X supports revealed lower surface area and higher macroporosity which led to the formation of larger cobalt crystallite size and less chemisorbed H₂. However, the catalytic activity was much higher for cobalt supported on HS-X silica of both small and large catalyst particle sizes. Moreover, with the large catalyst particle size, the C₅₊ selectivity of cobalt supported on HS-X silica was much higher than that on MS-X silica, indicating the influence of mass transfer of reactants and products in macropores of HS-X supports.     

Dimethylsilylbis(1‐indenyl) zirconium dichloride/methylaluminoxane catalyst supported on nanosized silica for propylene polymerization

A dimethylsilylene‐bridged metallocene complex, (CH₃)₂Si(Ind)₂ZrCl₂, was supported on a nanosized silica particle, whose surface area was mostly external. The resulting catalyst was used to catalyze the polymerization of propylene to polypropylene. Under identical reaction conditions, a nanosized catalyst exhibited much better polymerization activity than a microsized catalyst. At the optimum polymerization temperature of 55°C, the former had 80% higher activity than the latter. In addition, the nanosized catalyst produced a polymer with a greater molecular weight, a narrower molecular weight distribution, and a higher melting point in comparison with the microsized catalyst. The nanosized catalyst's superiority was ascribed to the higher monomer concentration at its external active sites (which were free from internal diffusion resistance) and was also attributed to its much larger surface area. Electron microscopy results showed that the nanosized catalyst produced polymer particles of similar sizes and shapes, indicating that each nanosized catalyst particle had uniform polymerization activity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enantioselective Hydrogenation of Aromatic Ketones Catalyzed by a Mesoporous Silica‐Supported Iridium Catalyst

A mesoporous, silica‐supported, chiral iridium catalyst with a highly ordered dimensional‐hexagonal mesostructure was prepared by postgrafting the organometallic complex (1‐diphenylphosphino‐2‐triethylsilylethane)[(R,R)‐1,2‐diphenylethylenediamine]iridium chloride {IrCl[PPh₂(CH₂)₂Si(OEt)₃]₂[(R,R)‐DPEN] (DPEN=1,2‐diphenylethylenediamine)} on SBA‐15 silica. During the asymmetric hydrogenation of various aromatic ketones under 40 atm of hydrogen, the mesoporous, silica‐supported, chiral iridium catalyst exhibited high catalytic activity (more than 95% conversions) and excellent enantioselectivity (up to more than 99% ee). The catalyst could be recovered easily and used repetitively seven times without significantly affecting the catalytic activity and the enantioselectivity.     

Thiirane resins cured with polythiourethane hardeners as novel supports for metal complex catalysts

The application of thiirane resin cured with polythiourethane (PTU) hardeners as novel and efficient support for palladium complex catalyst is reported. Stability and activity efficiency in Heck reactions were determined. IR and X‐ray photoelectron spectroscopy provided information of metal coordination to the polymer matrix. Characterization of polymer supports and palladium catalysts has involved the measurements of the structural parameters in the dry state by the nitrogen BET adsorption, time‐of‐flight secondary ion mass spectrometry, scanning electron microscopy, and energy dispersive X‐ray analysis. The results of this study indicate that PTU used to cure thiirane resin can greatly affect the catalytic properties of the episufide resin‐supported palladium catalyst. These new type of polymer supports comparing to other organic carriers offers several practical advantages such as ability to control the crosslinking density, porosity and the chemical structure of the polymeric matrix, which influence the catalytic properties of the immobilized metal complex. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40330.     

A Chemoselective Hydrogenation of the Olefinic Bond of α,β‐Unsaturated Carbonyl Compounds in Aqueous Medium under Microwave Irradiation

A microwave‐assisted mild and ecofriendly catalytic transfer hydrogenation process was developed to reduce various α,β‐unsaturated carbonyl compounds into the corresponding saturated carbonyl compounds in the presence of silica‐supported palladium chloride as catalyst and a combination of MeOH/HCOOH/H₂O (1 : 2 : 3) as hydrogen source within 22–55 minutes in moderate to excellent yields with 100% chemoselectivity.     

An Amine‐, Copper‐ and Phosphine‐Free Sonogashira Coupling Reaction Catalyzed by Immobilization of Palladium in Organic–Inorganic Hybrid Materials

An immobilization of palladium in organic‐inorganic hybrid materials‐catalyzed Sonogashira coupling reaction has been described. Terminal alkynes reacted with aryl iodides and aryl bromides only in the presence of a 3‐(2‐aminoethylamino)propyl‐functionalized, silica gel‐immobilized palladium catalyst under amine‐, copper‐ and phosphine‐free reaction conditions. The reaction generates the corresponding cross‐coupling products in excellent yields. Furthermore, the silica‐supported palladium can be recovered and recycled by a simple filtration of the reaction solution and used for 30 consecutive trials without any decreases in activity.     

Preparation of silica‐supported late transition metal catalyst and ethylene polymerization

A Correction has been published for this article in Polymer International 51(6) 2002, 561 The late transition metal catalyst 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron(II) chloride was supported on silica. Fourier transform infrared spectroscopy, scanning electronic micrograph and X‐ray photoelectron spectroscopy measurements were utilized to examine the process of supporting catalyst on silica and investigate the possible mechanism of support. Furthermore, ethylene polymerizations with the supported catalysts were carried out in various conditions such as different reaction temperatures and Al/Fe molar ratios. The results showed that MAO first reacted with the hydroxyl of silica forming Si? O? Al bonds and then the catalyst was bridged through MAO on the surface of silica. Compared with homogeneous catalysts, the supported catalysts show some decrease in catalyst activity. However, they can show good activity at a lower Al/Fe molar ratio with MAO as co‐catalyst and give rise to higher molecular weight and melting temperature of the polymer. Better morphology of polyethylene was obtained by a supported catalyst than by its corresponding homogeneous catalyst. The late transition metal catalyst 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine iron(II) chloride was supported on silica. Fourier transform infrared spectroscopy, scanning electronic micrograph and X‐ray photoelectron spectroscopy measurements were utilized to examine the process of supporting catalyst on silica and investigate the possible mechanism of support. Furthermore, ethylene polymerizations with the supported catalysts were carried out in various conditions such as different reaction temperatures and Al/Fe molar ratios. The results showed that MAO first reacted with the hydroxyl of silica forming Si? O? Al bonds and then the catalyst was bridged through MAO on the surface of silica. Compared with homogeneous catalysts, the supported catalysts show some decrease in catalyst activity. However, they can show good activity at a lower Al/Fe molar ratio with MAO as co‐catalyst and give rise to higher molecular weight and melting temperature of the polymer. Better morphology of polyethylene was obtained by a supported catalyst than by its corresponding homogeneous catalyst. © 2002 Society of Chemical Industry     

聚酰胺-胺树状分子锡配合物催化性能研究

通过固相合成的方法将聚酰胺-胺树状大分子PAMAM担载于大孔硅胶上,并对其外围分别用对羟基苯甲醛、2,4-二羟基苯甲醛和邻羟基苯甲醛进行修饰,再与SnCl2.2H2O反应形成三类共计9种不同代数树状高分子锡配合物。将该类配合物用作质量分数30%双氧水氧化酮的Baeyer-Villiger(B-V)反应的催化剂,考察其催化活性,结果表明,在该类配合物作用下,2-金刚烷酮、环戊酮、环己酮、4-甲基环己酮、4-叔丁基环己酮、3-甲基-2-戊酮和4-甲基-2-戊酮都可以发生B-V氧化反应而转化为相应的酯和内酯,底物的转化率(75%～99%)和产物选择性(95%～100%)都较高。比较了不同载体(氯球、纤维素、壳聚糖、硅胶)、不同配体的金属锡配合物对B-V催氧化反应的催化效果,研究发现,载体、配体和金属担载量对配合物的催化活性均有不同程度的影响。其中,硅胶为最好的载体,而邻羟基苯甲醛为最好的配体。     

A Simple and Efficient Route to Active and Dispersed Silica Supported Palladium Nanoparticles

Various mesoporous silica supported Pd materials were prepared by different methodologies in order to control and optimize the metal nanoparticle sizes for catalytic applications. The catalytic activities (conversion, mol% and selectivity to methyl-cinnamate) of the supported palladium catalysts were investigated in the Heck reaction under microwave irradiation using various haloarenes. Pd materials prepared by co-precipitation exhibited a very poor activity in the Heck reaction compared to that of Pd impregnated samples. Impregnated materials prepared without the use of a specific reducing agent had comparable activities to those of APTS-NaBH₄ reduced Pd materials, validating the simplicity of the methodology. High selectivities to methylcinnamate were obtained for all materials.     

Diethanol amine‐functionalized polymer‐supported palladium (0) complex as catalyst for Suzuki cross‐coupling reaction in water

Diethanol amine‐functionalized polymer‐supported palladium (0) complex as catalyst for Suzuki cross‐coupling reaction in water was synthesized and characterized. The catalyst exhibits excellent catalytic activity and stability in the Suzuki cross‐coupling reaction. Various aryl bromides were coupled with aryl boronic acids in water, under air, and in the presence of 0.5 mol % of the catalyst to afford corresponding cross‐coupled products in high yields at 100°C. Furthermore, the heterogeneous catalyst can be readily recovered by simple filtration and reused for several times only with a slight decrease in its activity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011