Catalytic hydrogenation of propene over polymer supported rhodium complexes

Hydrogenation of propene and other substrates has been studied in flow and batch reactors using various rhodium catalysts. The results show that in some cases rhodium metal is probably formed, but only if solvent is present. A possible explanation is given.     

Kinetics of phenol hydrogenation over supported palladium catalyst

Kinetics of vapor phase hydrogenation of phenol to cyclohexanone over Pd/MgO system has been studied in a flow microreactor under normal atmospheric pressure. The reaction rate is found to be negative order with respect to the partial pressure of phenol and has increased from −0.5 to 0.5 with increasing temperature (473 to 563 K). The apparent activation energy (E_a) of the process is found to be close to 65 kJ per mol. On the basis of kinetic results a surface mechanism is proposed.     

Promotion effects in the hydrogenation of propanal and acetone over palladium

The hydrogenation of acetone and of propanal have been studied over Pd and Gapromoted Pd catalysts. The main effect of the promoter is to create new sites bearing the more reactive adsorption mode of propanal and acetone. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

Catalyst support effects: gas-phase hydrogenation of phenol over palladium

The catalytic action of 10% w/w Pd supported on two forms of graphitic carbon nanofibers (GCN) has been assessed and compared with the performance of 10% w/w Pd on SiO(2), Ta(2)O(5), activated carbon (AC), and graphite. Palladium nitrate served as metal precursor in each case but the role of the starting metal salt was also considered by examining the action of palladium acetate impregnated SiO(2). The activated catalysts have been characterized by hydrogen chemisorption, high-resolution transmission electron microscopy, and scanning electron microscopy. Phenol hydrogenation served as the test reaction, which proceeds in a stepwise fashion involving the partially hydrogenated cyclohexanone as a reactive intermediate. The occurrence and ramifications of Pd/support interaction(s) are related to hydrogenation activity and selectivity. The effects of contact time and reaction temperature (398-448 K) are reported and discussed in terms of phenol/catalyst interaction(s). Hydrogenation kinetics have been adequately represented by a standard pseudo-first-order approximation. The specific activities exhibited the following sequence of increasing values: Pd/AC相似文献   

Influence of the ligand structure on SLP-catalysed hydroformylation of propene

Hydroformylation of propene was studied at 90–120°C and 3–10 atm. The catalyst was hydrido-(carbonyl)tris(triphenylphosphine)rhodium [H(CO)Rh(PPh₃)₃] supported on silica, in an excess of a liquid phosphine (P) ligand as solvent. The following series of ligands (P) was synthesized and studied in this application: CH₃(CH₂)_nPPh₂ (n = 3, 7, 17), (c – C₆H₁₁)_xPPh_3?x (x = 0, 1, 2) and also unsaturated allyl- and poly(butadienyl)-diphenylphosphines. The activity and regioselectivity of the catalysts are discussed in terms of the mobility and coordination ability of the ligands used. With the same electron density of the phosphorus atom, the activity of the catalysts increases with the mobility of the ligands. On the other hand, given the same mobility of the ligand, a lower electron density on phosphorus results in increased catalytic activity.     

Formation of aromatic hydrocarbons in CO hydrogenation over silica gel-supported palladium

It has been established that several aromatic hydrocarbons are formed in CO hydrogenation over silica gel-supported palladium catalysts. A mechanism for the formation of reaction products is suggested.

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High-throughput kinetic study of hydrogenation over palladium nanoparticles: combination of reaction and analysis

The hydrogenation of 1-acetylcyclohexene, cyclohex-2-enone, nitrobenzene, and trans-methylpent-3-enoate catalyzed by highly active palladium nanoparticles was studied by high-throughput on-column reaction gas chromatography. In these experiments, catalysis and separation of educts and products is integrated by the use of a catalytically active gas chromatographic stationary phase, which allows reaction rate measurements to be efficiently performed by employing reactant libraries. Palladium nanoparticles embedded in a stabilizing polysiloxane matrix serve as catalyst and selective chromatographic stationary phase for these multiphase reactions (gas-liquid-solid) and are coated in fused-silica capillaries (inner diameter 250 microm) as a thin film of thickness 250 nm. The palladium nanoparticles were prepared by reduction of palladium acetate with hydridomethylsiloxane-dimethylsiloxane copolymer and self-catalyzed hydrosilylation with methylvinylsiloxane-dimethylsiloxane copolymer to obtain a stabilizing matrix. Diphenylsiloxane-dimethylsiloxane copolymer (GE SE 52) was added to improve film stability over a wide range of compositions. Herein, we show by systematic TEM investigations that the size and morphology (crystalline or amorphous) of the nanoparticles strongly depends on the ratio of the stabilizing polysiloxanes, the conditions to immobilize the stationary phase on the surface of the fused-silica capillary, and the loading of the palladium precursor. Furthermore, hydrogenations were performed with these catalytically active stationary phases between 60 and 100 degrees C at various contact times to determine the temperature-dependent reaction rate constants and to obtain activation parameters and diffusion coefficients.     

On the hydrogenation of CO and CO2 over copper/zirconia and palladium/zirconia catalysts

Summary Zirconia-supported hydrogenation catalysts were obtained by activation of the amorphous precursors Cu₇₀Zr₃₀ and Pd₂₅Zr₇₅ under CO₂ hydrogenation conditions. Catalysts of comparable compositions prepared by co-precipitation and wet impregnation of zirconia with copper- and palladium salts, respectively, served as reference materials. The catalyst surfaces under reaction conditions were investigated by diffuse reflectance FTIR spectroscopy. Carbonates, formate, formaldehyde, methylate and methanol were identified as the pivotal surface species. The appearance and surface concentrations of these species were correlated with the presence of CO₂ and CO as reactant gases, and with the formation of either methane or methanol as reaction products. Two major pathways have been identified from the experimental results. i) The reaction of CO₂/H₂-mixtures on Cu/zirconia and Pd/zirconia primarily yields surface formate, which is hydrogenated to methane without further observable intermediates. ii) The catalytic reaction between CO and hydrogen yields -bonded formaldehyde, which is subsequently reduced to methylate and methanol. Interestingly, there is no observable correlation between absorbed formaldehyde or methylate on the one hand, and gas phase methane on the other hand. The reactants, CO₂ and CO, can be interconverted catalytically by the water gas shift reaction. The influence of the metals on this system of coupled reactions gives rise to different product selectivities in CO₂ hydrogenation reactions. On zirconia-supported palladium catalysts, surface formate is efficiently reduced to methane, which consequently appears to be the principal CO₂ hydrogenation product. In contrast, there is a favorable reaction pathway on copper in which CO is reduced to methanol without C-O bond cleavage; surface formate does not participate significantly in this reaction. In CO₂ hydrogenations on copper/zirconia, methanol can be obtained as the main product, from a sequence of the reverse water gas shift reaction followed by CO reduction.     

Structure sensitivity of selective acetylene hydrogenation over the catalysts with shape-controlled palladium nanoparticles

The structure sensitivity of acetylene hydrogenation on catalysts with controlled shape of palladium nanoparticles was studied. Palladium particles of cubic (Pd_cub), cuboctahedral (Pd_co) and octahedral (Pd_oct) shapes were obtained by a colloidal method. Poly(N-vinyl)pyrrolidone (PVP) was used as the stabilizer of colloidal solutions. In order to eliminate the effect of the polymer on the properties of the catalyst, PVP was removed from the surface of the particles after their transfer to the support by simultaneous treatment with ozone and UV radiation. This allowed complete cleaning of the catalyst surface from the organic stabilizer without any change in the morphology of particles. The effectiveness of this treatment method was confirmed by X-ray photoelectron spectroscopy and scanning electron microscopy. It was found experimentally that the shape of nanoparticles does not influence the catalyst selectivity, but the activity decreases in the order Pd_oct > Pd_co > Pd_cub. Since octahedrons consist of (111) faces, the cubes contain only (100) faces, and the cuboctahedrons are composed of faces of both types, Pd₁₁₁ is more active than Pd₁₀₀. Calculations with the use of a statistical method showed that the ～3-nm Pd octahedrons are nanoparticles with optimum shape and size, giving maximum catalyst activity.     

Selective hydrogenation of unprotected indole to indoline over N-doped carbon supported palladium catalyst

Mesoporous N-doped carbon supported palladium catalyst Pd@CN0.132 was able to efficiently catalyze unprotected indole to indoline under mild conditions.In the aqueous system,a selectivity of 100% and conversion of 96% was achieved under 313 K and atmospheric hydrogen gas.     

Kinetics and mechanism of propene hydroformylation catalyzed by rhodium complexes with a diphosphite ligand

The kinetics of propene hydroformylation in the presence of the catalytic system Rh(acac)(CO)₂/nL (L = 2,2′-bis[(1,1′-diphenyl-2,2′-diyl)phosphito]-3,3′,5,5′-tetra-tert-butyl-1,1′-diphenyl, 0.5 < n < 20) in para-xylene at 90°C is reported. At n ≥ 2, the rate and regioselectivity of the process are independent of the L concentration. The reaction is of positive fractional order with respect to propene and hydrogen and of negative order with respect to CO. The molar ratio between the linear product and the branched product decreases with an increasing CO pressure and increases with an increasing H₂ pressure. The kinetic data are consistent with a process mechanism involving irreversible propene addition to the unsaturated hydride complex HRh(CO)L with the formation of the π-complex HRh(CO)L(C₃H₆). The insertion of coordinated propene into the H-Rh bond of this complex is reversible in the linear aldehyde formation route and is quasi-equilibrium in the branched isomer formation route. The conclusions as to the character of these reaction steps are corroborated by the compositions of the but-1-ene and but-2-ene hydro-formylation products.     

Mechanism of isoprene hydrogenation on palladium

Conclusions The reaction for the selective hydrogenation of isoprene on a palladium catalyst at low temperatures is accomplished mainly on a small portion of the surface via the rapid formation of the surface isoprene compound in the undissociated form, with the subsequent slow steps of its conversion to the semihydrogenated form, and then to isopentenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 949–951, April, 1975.     

INDOLPhos: novel hybrid phosphine-phosphoramidite ligands for asymmetric hydrogenation and hydroformylation

Hybrid bidentate phosphine-phosphoramidite ligands are prepared in a modular 2-step sequence and their rhodium complexes display high selectivity in rhodium catalysed hydrogenation and hydroformylation reactions.     

On the mechanism of auto-oscillations in CO hydrogenation on supported palladium catalysts

A mechanism accounting for the occurrence of auto-oscillations in the formation rates of CH₃Cl and (CH₃)₂O during CO hydrogenation on chlorine-containing supported palladium catalysts is proposed.

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, CH₃Cl (CH₃)₂O CO .

     

Polymer-supported palladium and platinum species as hydrogenation catalysts

The synthesis of new hydrogel copolymers and their use for anchoring Pd and Pt species is described. The supported catalysts are effective for the reduction of alkenes, dienes, alkynes, and nitroaromatics under mild conditions. The catalysts have been characterized by chemical analysis, particle size measurement, IR, TGA, and x-ray photoelectron spectra. Relative reactivities and the effects of substrate structure, solvents, catalyst loading, particle size of the catalysts, and partial pressure of hydrogen have been determined. The kinetics of hydrogenation have been analyzed using concepts useful under slurry reaction conditions. The recycling efficiencies of the catalysts and product analysis to establish selectivities have been assessed. © 1992 John Wiley & Sons, Inc.     

Polymer-supported palladium and rhodium species as hydrogenation catalysts

The synthesis of new copolymers containing amino and heterocyclic ligands and their use for anchoring Pd and Rh species is described. The supported catalysts are effective for the hydrogenation of alkenes, dienes, alkynes, and nitrobenzene under very mild conditions. The catalysts have been characterized by chemical analysis, particle size measurement, IR, and x-ray photoelectron spectroscopy. Relative reactivities and the effects of substrate structure, solvents, catalyst loading, anchoring ligands, metal species, and particle size on the rates of hydrogenation have been determined using a wide variety of substrates. The kinetics of hydrogenation have been analyzed using concepts suitable under slurry reaction conditions. Comparisons between different oxidation states of the same metal and between different metal species have also been made. The recycling efficiencies of the catalysts have been determined and found to be very good. © 1997 John Wiley & Sons, Inc.     

Ethylene hydroformylation over a nafion-supported rhodium catalyst

Ethylene hydroformylation over a Nafion-supported rhodium catalyst has been studied under atmospheric pressure in the temperature range of 100–135 °C, using the transient response method.

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, , 100–135°C, .

     

Gas-phase propene epoxidation over coinage metal catalysts

Propene oxide (PO) is a very important bulk chemical and is produced on a scale of about 7.5 million tons per year. In industry, PO is produced via multiple reaction steps in the liquid phase, using hazardous chlorine or costly organic hydroperoxides as oxidants. Accordingly, development of a simple and green process to produce PO has been desired. This paper presents an overview of one-step propene epoxidation in the gas phase over coinage metal catalysts with a mixture of O₂ and H₂ or with molecular O₂ alone as oxidant. Silver (Ag) and gold (Au) catalysts can catalyze propene epoxidation with a mixture of O₂ and H₂, with high selectivity, whereas copper (Cu) catalysts cannot. In this reaction Au catalysts are much more active than Ag catalysts. All the coinage metals can catalyze propene epoxidation by molecular O₂, but with selectivity usually below 60%. The valence states of Cu species and the sizes of Ag particles and Au particles are of crucial importance in PO synthesis.