钯复合膜的制备及其在氢气氮气分离中的应用

Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.     

Coal liquefaction by the hydrogen produced from methanol

Methanol was used as an in-situ hydrogen source, following its decomposition over ZnO-Cr₂O₃, for the hydrogenation of coal. The reaction was carried out in a high pressure autoclave at ≈400–440 °C, in the presence of different hydrogenation catalysts. Stabilized nickel, stabilized Co and Ni-Cr-Cu catalysts gave excellent results. The maximum conversion was 100% for pyridine, 94.4% for benzene and 66.2% for straight-chain hexane.     

Hydrogenation of chalcones using hydrogen permeating through a Pd and palladized Pd electrodes

The hydrogenation of benzalacetone and benzalacetophenone was carried out using atomic hydrogen permeating through a palladium membrane. A two-compartment cell separated by a Pd sheet or a palladized Pd (Pd/Pd black) sheet electrode was employed. The reduction products were identified by (GC) gas chromatography, UV-vis absorption spectroscopy and NMR spectroscopy. The carbon-carbon double bond was hydrogenated and the benzylacetone and benzylacetophenone were obtained as products using palladium catalyst. The current efficiency for hydrogenation reaction increases when the current density for water electrolysis decreases and depends on the initial chalcone concentration. It is over 90% at the concentration of 10 mmol L⁻¹. The hydrogen absorption and diffusion into and through a palladium membrane electrode has been studied by using an electrochemical impedance spectroscopy method. The impedance results would indicate that the hydrogen permeated through the membrane is consumed by the chalcone during the hydrogenation process keeping as the permeable boundary condition in the outer side of the Pd membrane the hydrogen activity almost zero. The hydrogen entering the metal through an adsorbed state and the rate of hydrogen absorption is diffusion-controlled.     

Enantioselective Hydrogenation of N‐Acetyldehydroamino Acids over Supported Palladium Catalysts

The enantioselective hydrogenation of two N‐acetyldehydroamino acids over Cinchona alkaloid‐modified, supported palladium catalysts has been studied. Moderate enantioselectivities, up to 36 %, were obtained in the hydrogenation of 2‐acetamidocinnamic acid over cinchonidine‐modified Pd/TiO₂ under low hydrogen pressure. Increase in the pressure or use of benzylamine as additive led to a gradual decrease in the enantiomeric excess and eventually inversion of the sense of the enantioselectivity. On the contrary, the optical purity of the product resulting from the hydrogenation of 2‐acetamidoacrylic acid was significantly increased by addition of benzylamine to the reaction mixture. Enantiomeric excess values up to 58 % and 60 % were obtained over Pd/Al₂O₃ modified by cinchonidine and cinchonine, respectively. These optical purities are the best obtained in the hydrogenation of dehydroamino acid derivatives over chirally modified heterogeneous metal catalysts.     

Preparation of sorbitol from D‐glucose hydrogenation in gas–liquid–solid three‐phase flow airlift loop reactor

A new process for D ‐glucose hydrogenation in 50 wt% aqueous solution, into sorbitol in a 1.5 m³ gas–liquid–solid three‐phase flow airlift loop reactor (ALR) over Raney Nickel catalysts has been developed. Five main factors affecting the reaction time and molar yield to sorbitol, including reaction temperature (T_R), reaction pressure (P_R), pH, hydrogen gas flowrate (Q_g) and content of active hydrogen, were investigated and optimized. The average reaction time and molar yield were 70 min and 98.6% under the optimum operating conditions, respectively. The efficiencies of preparation of sorbitol between the gas–liquid–solid three‐phase flow ALR and stirred tank reactor (STR) under the same operating conditions were compared. Copyright © 2004 Society of Chemical Industry     

States of surface hydrogen under reaction conditions of the Fischer-Tropsch synthesis

The reaction of hydrogen with Fe surfaces was observed by the ellipsometric method at 77 K to 500 ° C under H₂ pressures of 10^–3 Torr (0.1 Pa) to 500 Torr (7×10⁴ Pa). The ellipsometric analysis reveals no existence of adsorbed hydrogen on the surface above 400 °C; hydrogen seems to be alternatively absorbed into the subsurface region of two to three atomic layers. It is concluded that the subsurface hydrogen is specific to the high temperature and the high pressure owing to strained and roughened Fe surfaces as well as the equilibrium with gas phase hydrogen. Absence of adsorbed hydrogen is indicated as well in the ellipsometric response to the hydrogenation reaction of surface carbon species on Fe surfaces.     

Experimental demonstration of enhanced hydrogen permeation in palladium via a composite catalytic‐permselective membrane

A composite catalytic‐permselective (CCP) membrane comprised of a 500‐μm Cu(II)O/Al₂O₃ catalyst film washcoated overtop a 27‐μm electroless‐plated dense palladium thin film was constructed on a porous less‐steel substrate. Hydrogen purification experiments performed under ideal (H₂–Ar) nonreactive mixtures and simulated reformate (5% CO, 7.5% H₂O, 15% H₂, 1.5% CO₂, and balance Ar) over a range of residence times at 623–773 K confirm up to 30% enhancement in observed hydrogen permeance of the palladium film, achieved using the CCP membrane design in which the catalyst layer modifies the gas‐phase composition in direct contact with the permselective Pd film. Scanning electron microscopy analysis of the palladium film after ～10‐h exposure to reaction conditions and Cu(II)O catalyst confirm no corrosion of the film, while observed hydrogen permselectivities remained in excess of 10,000:1. These experimental results confirm that the CCP membrane design is capable of significantly improving palladium membrane performance. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1627–1634, 2013     

Catalytic wood liquefaction using a hydrogen donor solvent

Direct wood liquefaction of pine sawdust (Pinus radiata) in a hydrogen donor solvent (tetralin), was studied in a 0.5 L autoclave using Co-Mo/γ-Al₂O₃ and Pt/γ-Al₂O₃ supported catalysts. Uncatalyzed as well as Raney Nickel catalyzed runs were also performed for comparison purposes. Reaction temperature was kept at 673 K and total system pressure at 10 MPa in all cases. Weight ratio of solvent to solid loaded was 2:1, the gas phase being either H₂ or N₂. Independent runs were also performed with cellulose and lignin which are the main wood constituents. Reaction products were characterized by means of gas chromatography and solvent fractionation using specific solvents.     

Hydrocarbon conversions with some intermetallic catalysts

The intermetallic pseudo-binary alloys of the general type ZrRh_3-xPd_x and ZrRh_3-xRu_x (0 < × < 3) have been prepared by argon arc melting and melt quenching of the constituent elements. The alloys were powdered and employed as catalysts for (i) hydrogenation of oct-1-yne in the liquid phase at 101.32 kPa total pressure and 70°C, (ii) hydrogenation of buta-1,3-diene in the gas phase at 101.32 kPa total pressure in the temperature range 45–225°C, and (iii) hydrogenolysis of n-pentane in the gas phase at 101.32 kPa total pressure and in the temperature range 200–400°C. Activity and selectivity measurements were made with respect to (i) alkene formation for the hydrogenation reactions, and (ii) C₂ + C₃-alkane formation for the hydrogenolysis reaction. The activity of the alloy series appears to correlate to some degree with the electronic properties and hydrogen sorption capacity of the intermetallic alloys. Auger electron spectroscopy measurements revealed that for ZrRh_3-xPd_x alloys both the surface and bulk compositions were in good agreement; this behaviour is contrasted briefly with that of CeRh_3-xPd_x alloys which, unlike ZrRh_3-x alloys, suffered significant oxygen interaction in the surface and sub-surface layers, although this did not affect Rh:Pd ratios. Catalysts that were active for hydrogenation were inactive for hydrogenolysis and vice versa. However, selectivity values for the hydrogenation reactions generally reflected the behaviour of the predominant noble transition metal. Again, the behaviour of ZrRh_3-xPd_x and CeRh_3-x alloys is contrasted, since the latter were more selective for butene formation from buta-1,3-diene, and attributed to the oxygen Contamination of the surface. Further more, the selectivity of both ZrPd and CePd, for 1-octyne and butu-l j-dene hydrogenation was significantly greater than that of palladium by virtue of the fact that the intermetallics were found to be largely inactive for alkene hydrogenation.     

Rate and oxygen activity oscillations during hydrogen oxidation on nickel films in a CSTR

The catalytic oxidation of hydrogen on polycrystalline nickel films was studied in a CSTR at 510-681°K and atmospheric pressure. The technique of Solid Electrolyte Potentiometry (SEP) was used to monitor the thermodynamic activity of oxygen adsorbed on the catalyst surface. To this end the reaction was studied in an yttria-stabilized zirconia solid electrolyte cell. Both steady state kinetics and potentiometric results indicate formation and reduction of a surface nickel oxide. In a certain range of temperature and gas composition sustained oscillatory phenomena were observed on both the reaction rate and the surface oxygen activity. A dynamic model of six differential equations that takes into account transient changes of the gas phase concentration of H₂, O₂ and H₂O as well as of the surface coverage of adsorbed hydrogen, oxygen and nickel oxide has been developed. The model explains quantitatively the stable steady state kinetic and SEP results. The same model predicts oscillatory behavior and explains qualitatively the observed unsteady state phenomena.     

Three-phase catalytic hydrogenation of α-methylstyrene in supercritical carbon dioxide

The three-phase catalytic hydrogenation (TPCH) of α-methylstyrene using supercritical carbon dioxide (scCO₂) in a slurry reactor is reported. Kinetic data are presented for the reaction at 323 K over the range of pressure from 7.0 to 13.0 MPa using a carbon-supported palladium catalyst. The experimental data are fitted to a first-order power-law model. A detailed explanation of the methodology used to isolate the effect of CO₂ on the rate of reaction is presented. Particular attention is given to the phase behaviour of the reaction system and the volumetric expansion of the liquid phase with CO₂. It is shown that scCO₂ significantly enhances the rate of reaction. This effect is attributed to the enhancement of the solubility of hydrogen in the liquid phase.     

Ni//Mo synergism via hydrogen spillover,in pyridine hydrodenitrogenation

The pyridine hydrodenitrogenation (HDN) over physically separated stacked Ni//Mo beds was investigated using a continuous-flow high pressure (3 MPa) stainless steel microreactor. Results prove the existence of synergism between physically separated beds of Ni-/γ-Al₂O₃ and Mo/γ-Al₂O₃ catalysts for the pyridine hydrodenitrogenation reaction. This synergism is explained by the formation of hydrogen spillover. Product analysis of the pyridine hydrodenitrogenation over Ni//Mo stacked beds suggested that the hydrogen spillover modified the active sites of the MoS₂ by increasing the hydrogenation sites.     

An overview of aqueous-phase catalytic processes for production of hydrogen and alkanes in a biorefinery

In this overview we discuss how aqueous-phase catalytic processes can be used to convert biomass into hydrogen and alkanes ranging from C₁ to C₁₅. Hydrogen can be produced by aqueous-phase reforming (APR) of biomass-derived oxygenated hydrocarbons at low temperatures (423–538 K) in a single reactor over supported metal catalysts. Alkanes, ranging from C₁ to C₆ can be produced by aqueous-phase dehydration/hydrogenation (APD/H). This APD/H process involves a bi-functional pathway in which sorbitol (hydrogenated glucose) is repeatedly dehydrated by a solid acid (SiO₂–Al₂O₃) or a mineral acid (HCl) catalyst and then hydrogenated on a metal catalyst (Pt or Pd). Liquid alkanes ranging from C₇ to C₁₅ can be produced from carbohydrates by combining the dehydration/hydrogenation process with an upstream aldol condensation step to form C–C bonds. In this case, the dehydration/hydrogenation step takes place over a bi-functional catalyst (4 wt.% Pt/SiO₂–Al₂O₃) containing acid and metal sites in a specially designed four-phase reactor employing an aqueous inlet stream containing the large water-soluble organic reactant, a hexadecane alkane sweep stream, and a H₂ inlet gas stream. The aqueous organic reactant become more hydrophobic during dehydration/hydrogenation, and the hexadecane sweep stream removes these species from the catalyst as valuable products before they go on further to form coke.     

Magnetically Stabilized Bed for Selective Hydrogenation of Benzene

The characteristics of a magnetically stabilized bed (MSB) were studied by cold‐model experiments, using water as liquid phase, hydrogen as gas phase, and γ‐Fe₂O₃ magnetic powder as solid phase. The fluidized state of different bed positions was investigated by testing the transmissible laser current. Effects of magnetic field intensity and gas flow rate on layer expansion states of the MSB were analyzed by color diagrams. A Ru‐Zn‐B amorphous alloy was prepared by chemical reduction. Selective hydrogenation of benzene was carried out in the MSB by adjusting the contact time between the catalysts and reactants through variations of reaction temperature, magnetic field current, and liquid hourly space velocity.     

Transfer hydrogenation and transfer hydrogenolysis: XII. Selective hydrogenation of fatty acid methyl esters by various hydrogen donors

The selective hydrogenation of methyl linoleate was studied using various organic compounds as hydrogen sources in the presence of homogeneous and metallic palladium catalysts. Complete selectivity to monoenes and relatively little formation of isolatedtrans double bonds were realized by the hydrogen transfer from L-ascorbic acid at 47% conversion of starting material to hydrogenation products. The hydrogenation bytrans-1,2-cyclohexanediol catalyzed by RuH₂(PPh₃)₄ also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH₂(PPh₃)₄, also showed rather high selectivity tocis-monoenes. In the reaction catalyzed by RuH₂(PPh₃)₄, the presence of these hydroxy compounds increased the isomerization of methyl elaidate tocis-monoenes.     

Hydrodenitrogenation reaction of quinoline with nascent hydrogen generated from water gas shift reaction

The HDN of quinoline was investigated for the purpose of utilizing the hydrogen which could be generated from the water gas shift reaction (WGSR). The optimum concentration of hydrogen were produced under 1.5 of water to carbon monoxide mole ratio and 6 hr^-1 of space velocity at 390°C of temperature during WGSR over Co-Mo/γ-Al₂O₃ catalyst. The HDN reactions were compared by using the pure hydrogen and the nascent hydrogen which was produced by a WGSR. The pure hydrogen gave much higher activity in the overall HDN reaction than the nascent hydrogen. However, kinetic study on the hydrogenation, hydrogenolysis and cracking reaction steps showed that only at the cracking reaction step the nascent hydrogen gave the superiority to the pure hydrogen. This inferiority of the nascent hydrogen in overall HDN reaction could be resulted from the negative effect of water which should be accompanied during WGSR. The conversion of the HDN reaction was maximized at the water pressure of 150 kpa.     

Gas phase hydrogenation of ortho-chloronitrobenzene (O-CNB) to ortho-chloroaniline (O-CAN) over unpromoted and alkali metal promoted-alumina supported palladium catalysts

A series of alkali metals (Li, Na, K and Cs) promoted alumina-supported palladium catalysts were prepared by a wet impregnation method and characterized by X-ray diffraction (XRD) and CO chemisorption measurements. The samples were tested for the gas phase hydrogenation of ortho-chloronitrobenzene (O-CNB) to ortho-chloroaniline (O-CAN) in a fixed-bed micro reactor at 250 °C under normal atmospheric pressure. The promoted-Pd/Al₂O₃ catalysts show higher conversion for O-CNB and the hydrogenation activity of O-CNB per site decreases with the increasing ionic radius of the alkali metal promoter ions. However, the selectivity for O-CAN remains more or less the same in both unpromoted and promoted catalysts and also irrespective of the nature of the alkali metal promoter ions used for promotion of alumina support. Despite, similar activity and selectivity observed between Li- and Na-promoted Pd/Al₂O₃ catalysts, the Na-promoted showed higher resistance for coke formation than a Li-promoted catalyst. The increase in the intrinsic activity of palladium site on alkali promotion has been attributed to the increase in hydrogenation activity over promoted catalysts.     

Identification of the state of palladium in various hydrogenation catalysts by XPS

Various commercial supported palladium hydrogenation catalysts were studied by XPS and treated at ambient pressure with hydrogen and air. Unused catalysts exhibit a significant fraction of divalent Pd (oxide) which is reduced by hydrogen treatment at room temperature. Exposure to air in systems with carbonate, alumina, silica or active carbon as support causes the formation of a solid solution of oxygen in Pd characterized by a Pd 3d chemical shift of ca. + 0.4 eV. The absolute binding energy of Pd depends strongly on the matrix, indicating a significant contribution of extra-atomic screening, which prevents a direct comparison of reference samples and supported catalysts. Using the oxidation of CO to CO₂ at 300 K as in situ chemical probe it was confirmed that Pd supported on carbonate, silica and alumina exists in the same metallic state which could be activated for the test reaction irrespective of the variation in XPS binding energies.     

The effects of modes of hydrogen input and reactor configuration on reaction rate and H2 efficiency in the catalytic hydrogenation of alkynol to alkenol

Hydrogenation often involves three phases where hydrogen-on-demand is the typical mode of operation in industrial scale reactors. In research labs and publications, however, continuous hydrogen flow has been used. This paper investigates the effect of such modes of operation on reaction rate using a selective hydrogenation of 3-butyn-2-ol over Pd/Al₂O₃ to obtain 3-buten-2-ol as the model reaction. The two modes of operation were first tested in a commercial PARR stirred tank reactor and then repeated in an oscillatory baffled reactor (OBR) in order to validate the experimental results. Our investigation demonstrates that an enhanced reaction performance and 10 times better H₂ efficiency were obtained when the pressure was maintained constant during the reaction by feeding gas as required, ie hydrogen-on-demand mode. The method of a continuous flow of hydrogen in hydrogenation means that excess hydrogen is vented out when operating at ambient pressures or builds up at elevated pressures. Our work also enables a comparison of reactor designs on reactor performance, and three times higher H₂ efficiency and 2.3 times shorter residence time were achieved when using the OBR instead of the PARR due to its enhanced and uniform mixing, regardless of the mode of operation.     

Kinetics of Liquid‐Phase Hydrogenation of Iso‐valeraldehyde to Iso‐amyl Alcohol Over A Ru/Al2O3 Catalyst

The liquid‐phase catalytic hydrogenation of iso‐valeraldehyde to iso‐amyl alcohol was studied in a slurry reactor. The kinetics of liquid‐phase hydrogenation of iso‐valeraldehyde over a 5% Ru/Al₂O₃ catalyst was studied in the range of temperature 373‐393 K and H₂ pressure 0.68‐2.72 MPa using 2‐propanol as the solvent. The selectivity to iso‐amyl alcohol was 100%. The kinetic data were analyzed using a simple power law model. A single site Langmuir‐Hinshelwood type model suggesting dissociative adsorption of hydrogen and surface reaction as the rate‐controlling step provided the best fit of the experimental data. The catalyst could be reused thrice without any loss in activity.