Juhani Väyrynen

Ruthenium-modified MCM-41 mesoporous molecular sieve and Y zeolite catalysts for selective hydrogenation of cinnamaldehyde

Abstract Ru-modified MCM-41 mesoporous molecular sieve and Y zeolite catalysts were synthesised and characterised using XRD, electrochemical voltammetry, ESCA (XPS), nitrogen adsorption and H2-TPD. Selective liquid-phase hydrogenation of cinnamaldehyde to cinnamyl alcohol was investigated over these catalysts and compared to hydrogenation on a commercial Ru/C catalyst. The effect of support (MCM-41, Y and C), solvent (cyclohexane, hexane and 2-propanol) and catalyst pre-treatment (calcination) on the conversion of cinnamaldehyde and selectivity to cinnamyl alcohol was studied. The zeolite structure, pore size, acidity, catalyst pre-treatment as well as the solvent influenced the activity and selectivity. Non-calcined Ru/Y exhibited the highest selectivity to cinnamyl alcohol. The activity of Ru/Y was highest with 2-propanol as a solvent.

Gas-phase hydrogenation of o-xylene over Pt/alumina catalyst, activity, and stereoselectivity

Abstract The kinetics of the gas-phase hydrogenation of o -xylene over Pt/alumina catalysts was studied at 430–520 K, a hydrogen partial pressure of 0.19–0.36, and an o -xylene partial pressure of 0.04–0.10. The catalysts were characterized by H 2 / o -xylene TPD, H 2 chemisorption, energy-dispersive X-ray analysis, and XPS. The stereoisomers, cis- and trans -1,2-dimethylcyclohexane, were the only reaction products. A reversible maximum in the o -xylene hydrogenation activity vs temperature was observed; it was explained by a decrease in the surface concentration of o -xylene at higher temperatures. The hydrogenation rate was independent of the o -xylene concentration, whereas the reaction orders with respect to hydrogen varied from 0.9 to 3 in the temperature range investigated. The stereoselectivity of the products was found to depend on temperature, reactant concentrations, and platinum precursor. The catalyst prepared from a chlorine-containing precursor exhibited a lower hydrogenation activity and selectivity toward the trans isomer. Chlorine remained on the catalyst surface, even after reduction at 673 K. Dehydrogenation and configurational isomerization of cis - to trans -1,2-dimethylcyclohexane took place at the same time as hydrogenation. Dehydrogenation and configurational isomerization reactions are enhanced by the presence of residual chlorine on the catalyst surface. The reaction pathway is proposed.

Batchwise and continuous enantioselective hydrogenation of 1-phenyl-1,2-propanedione catalyzed by new Pt/SiO2 fibers

Abstract A new knitted silica fiber was investigated as a support material in enantioselective hydrogenation of 1-phenyl-1,2-propanedione in a pressurized batch reactor. The active metal was platinum and the catalyst was modified in situ with (−)-cinchonidine. The catalysts were prepared by impregnation method using hexachloroplatinic acid as metal precursor. The main experimental parameters were the support calcination temperature and the metal loading of the catalyst. The optimum catalyst dispersion, BET specific surface area and mean Pt particle size for enantio-differentiation were measured. A comparison of alumina and silica supports revealed that the main parameters in the enantio-differentiation were the mean metal particle size and the metal dispersion. Optimal metal particle size and dispersion were detected which optimize the enantioselection. Experiments with continuously operated fixed bed reactor demonstrated that continuous hydrogenation, over the new knitted silica fiber catalyst, gives equally high enantiomeric excesses compared to the batch operation. Continuous operation can be used as tool to study catalyst deactivation and reaction mechanisms in enantioselective hydrogenation.

Experimental study of resonant photoemission in the metals V, Cr, Mn and Co

We have studied the resonant photoemission of the valence band in V, Cr, Mn and Co transition metals using synchrotron radiation excitation near the 3p ionization thresholds. The effect of the 3p - 3d interaction reaches maximum strength in Cr and Mn. On the other hand, the contribution related to the atomic Fano resonance goes to a minimum in Mn and increases rapidly on moving to Co. This behaviour is also reflected in the values of the effective Coulomb hole - hole interaction which we have calculated from experimental spectra. Furthermore, we have investigated when the Auger transition appears in the vicinity of the 3p ionization thresholds. Our results reveal that V, Cr and Co do not show the so-called subthreshold Auger emission whereas it can possibly be observed in Mn. However, we attribute the unusual appearance of the Auger peak to the wide valence band of Mn rather than the 3p - 3d resonance.

Catalyst selection and solvent effects in the enantioselective hydrogenation of 1-phenyl-1,2-propanedione

1-Phenyl-1,2-propanedione was hydrogenated at 5 bar and 25°C over Pt/Al2O3 catalysts in the presence of cinchonidine. The effect of four different solvents, ethyl acetate, toluene, ethanol and dichloromethane in the enantioselective hydrogenation of the dione was tested. The highest enantiomeric excess of (R)-1-hydroxy-1-phenyl-2-propanone, 65%, was obtained in dichloromethane. Also toluene and ethyl acetate gave relatively high enantiomeric excesses. In ethanol, which highly interacts with Pt surface, the enantiomeric excess was only 12%. Two different alumina supports and Pt-precursors were investigated using ethyl acetate as solvent. The highest enantiomeric excesses of (R)-1-hydroxy-1-phenyl-2-propanone were obtained with α-Al2O3 supported Pt catalyst prepared from hydrogen hexachloroplatinate(IV)hydrate presursor. The highest Pt loadings in the catalyst preferred enantiodifferentiation. Higher enantiomeric excesses were obtained by increasing the mean metal particle size of Pt.

Inverse photoemission and photoemission spectra of the PbS(001) surface

Abstract The inverse photoemission spectra of lead sulphide have been investigated in the energy range 15 – 33 eV of normal incidence electrons. In addition the angle-resolved photoemission spectra have been studied using synchrotron radiation. The sample crystals have been cleaved in UHV and the crystal structure has been observed by LEED to correspond the (1×1) surface geometry. The band structure to the direction Γ - X has been determined below and above the Fermi-level from the photoemission and the inverse photoemission spectra. The prominent dispersion of one occupied band is clear but the others are markedly flat. The unoccupied bands show quite well behaving dispersion. There are no bands crossing the Fermi-level in the Γ - X direction displaying the band gap 3.6 eV. General shapes of the experimental band dispersions agree satisfactorily with those predicted by theoretical calculations, but the binding energies of the bands show clearly some disagreement, especially for the lowest bands.

Hydrogenation of xylose to xylitol on sponge nickel catalyst: a study of the process and catalyst deactivation kinetics

The kinetics of hydrogenation of xylose to xylitol on a sponge nickel catalyst (commonly referred to as Raney Ni catalyst) and of catalyst deactivation were studied. Plausible explanations for the decrease in catalytic activity by means of surface studies, nitrogen adsorption and thermogravimetric analyses of the fresh and spent catalysts are presented. The kinetic parameters of the process were estimated by the use of a semi-competitive model, which allows full competition between the organic species and the hydrogen atoms for the adsorption sites on the catalyst surface (competitive case). In the model, a competitiveness factor (a) is introduced to take into account that even after complete coverage of the surface by the organic species, interstitial sites remain for the adsorption of the hydrogen atoms.

Unoccupied electronic states of the FeS2(100) surface studied by inverse photoemission

Inverse photoemission spectra have been measured to study unoccupied electronic states from an FeS2(100) single crystal along the Γ-X symmetry line with normal incidence electrons at energies between 20 and 40 eV. Two main features of the spectra are found, corresponding to direct bulk transitions into unoccupied iron 3d(eg) and sulphur 3p(σ∗) states, respectively, followed by a prominent minimum and a onset of a band with a wide structure due to mainly transitions into Fe 4sp-S 3d bands. These peaks are located at 1.4 and 3.0 eV above the Fermi level for an initial electron energy of 19.8 eV. They disperse according to band-structure calculations. The onset of the Fe 4sp-S 3d bands is about 5.0 eV above the Fermi level. The experimental results obtained here are in a reasonable agreement with band-structure calculations for FeS2, and with previous results of optical, BIS and XAS measurements.

Hydrothermally Stable Catalysts for the Removal of Emissions from Small-Scale Biofuel Combustion Systems

Catalytic oxidation of model pollutants, simulating the emissions from small-scale biofuel combustion systems, was studied over different fresh, aged and sulfur poisoned Pd-MeO/γ-alumina (Me = Ni, Ce and La) catalysts. Release of chlorine and restructuring of PdO particles was believed to cause activation of the Pd-MeO supported catalysts.

Resonant photoemission in titanium metal

Abstract The photoionization cross section of the titanium 3d band, including the contributions from direct photoemission and autoionization, has been measured using synchrotron radiation on a wide photon energy range (21 – 110 eV). Particularly, we have concentrated on the resonant behavior of the valence band near the 3p and 3s threshold in which the influence of autoionization appears as drastic fluctuations of a resonant profile. In addition, we have examined subthreshold Auger emission that should already occur below the threshold energy.