Jozsef Petro

Palladium-cobalt catalysts: Phase structure and activity in liquid phase hydrogenations

Pd-Co catalysts on activated graphite support are more active in some liquid phase hydrogenations than any of the unalloyed metals. The bimetallic catalysts consisted of (i) unalloyed Pd phase detected by x-ray diffraction and thermogravimetric measurements, and (ii) alloy phase detected by thermogravimetric measurements.AbstractКатализаторя Pd−Co на активированном графите более активны в некоторых жидкофазных гидрованиях, чем любые несплавленные металлы. Биметаллические катализаторы состоят из 1) несплавленной Pd фазы, детектированной рентγеновой диффракцией и термогравиметрическими измениями, и 2) фазы сплава, детектированной термогравиметрическими исследованиями.

The role of lead in the selectivity of palladium-lead (lindlar type) catalysts

Abstract Surface structures and selectivities of lead-poisoned Pd or Pd/graphite catalysts were studied. Two types of surface species, adsorbed lead and bulk lead, were identified by XRD or the potential sweep method. It was found that the use of oxygen covered Pd for lead acetate poisoning and the removal of excess lead acetate before hydrogenation is of crucial importance for preparing selective Lindlar-type catalysts.

EFFECT OF THE CONDITIONS IN HETEROGENEOUS CATALYTIC HYDROGENATION ON ASYMMETRIC INDUCTION.

Abstract In the hydrogenation of optically active Schiff bases the effect of reaction-parameters, i.e. catalyst dispersion, mass and solvent polarity, on the asymmetric induction was studied. Increasing the catalysts dispersion and amount decreases the asymmetric induction. The influence of solvent polarity on the ratio of diastereoisomers produced depends on whether the more or the less polar substituents of the molecules are attached to the prochiral carbon atom. The asymmetric induction also depends on the catalysts pretreatment, i.e. whether it was saturated with hydrogen before the reaction or its surface was covered with oxygen. On the basis of our observations and of the structure of Dreiding models, the following reaction course was proposed: the most stable adsorbed conformers reacting with the H atoms adsorbed on neighbouring Pd atoms give the diastereoisomers produced in excess.

Real and apparent dispersion of carbon supported palladium—cobalt catalysts

Abstract Activated carbon supported Pd Co catalysts of 10–4 wt.-% Pd and 0–6 wt.-% Pd and 0–6 wt.-% Co loading were examined by hydrogen chemisorption, electrochemical polarization, transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. Unreduced cobalt or cobalt-rich phases raised difficulties in the determination of real (conventional) dispersion. Apparent dispersion (number of active surface sites/total number of metal atoms) was calculated from hydrogen chemisorption or electrochemical polarization data. Apparent dispersion was used for the interpretation of reaction rates in the liquid phase hydrogenation of propionitrile or benzaldehyde.

Stereoselective hydrogenation of thymol

Abstract The stereoselective hydrogenation of thymol and menthone was studied in gas and liquid-phase reactions with palladium, rhodium, nickel and copper catalysts. The gas-phase hydrogenation of thymol and menthone on nickel and copper catalysts results in equilibrium mixtures of menthol isomers. On palladium, thymol gives menthone isomers. In the liquid phase, hydrogenation menthols are formed via menthones, in non-equilibrium ratios: smaller percentages of isomenthol and neo-isomenthol are formed, and the menthol: neomenthol ratios change with pH. On the basis of these observations, we proposed a reaction course for the hydrogenation of thymol and menthone.

Synthesis and pKa determination of new enantiopure dimethyl‐substituted acridino‐crown ethers containing a carboxyl group: Useful candidates for enantiomeric recognition studies

New enantiopure dimethyl-substituted acridino-18-crown-6 and acridino-21-crown-7 ethers containing a carboxyl group at position 9 of the acridine ring [(S,S)-8, (S,S)-9, (R,R)-10] were synthesized. The pKa values of the new crown ethers [(S,S)-8, (S,S)-9, (R,R)-10] and of an earlier reported macrocycle [(R,R)-2] were determined by UV-pH titrations. Crown ether (S,S)-8 was attached to silica gel by covalent bonds and the enantiomeric separation ability of the newly prepared chiral stationary phase [(S,S)-CSP-12] was studied by high-performance liquid chromatography (HPLC). Homochiral preference was observed and the best separation was achieved for the enantiomers of 1-NEA. Ligands (S,S)-9 and (R,R)-10 are precursors of enantioselective sensor and selector molecules for the enantiomers of protonated primary amines, amino acids, and their derivatives.

Palladium as catalyst in polycondensed matrix, Part III

In this part we aim at elucidating the chemical state of palladium in the polymer cages. It was established that in samples both the adduct and the polymer exist in the forms of Pd0, Pdox and metallic Pd. Their ratio depends on the reaction conditions. Conclusions of the three parts are also given.

Palladium as a Catalyst in a Polycondensed Matrix, Part 1

Adducts of palladium and organic amines were polycondensed. The catalysts formed were studied in liquid-phase hydrogenations of simple organic molecules. Their activities and specific selectivities were compared with these of a palladium/carbon catalyst.

Factors influencing activity and selectivity of Palladium Catalystst

Abstract The most important factors effecting hydrogenating catalytic activity and selectivity are 1. The metal hydrogen system which could be varied by the way of catalyst preparation and reaction variables 2. Dispersion of the metal and 3. Applying promoters. Examples are given for the effects of factors mentioned above.

Reduction of propionitrile to propionaldehyde on supported palladium catalysts. II. Optimum in selectivity

Abstract The transformation of propionitrile to propionaldehyde via the corresponding methyl acetal was studied on a commercial 10 wt.-% palladium-on-carbon catalyst. Hydrogen sorption characteristics of the catalyst and the effect of purification were studied by an electrochemical polarization method. Good yields (approx. 80%) could be achieved under circumstances in which hydrogen availability was poor. Amine formation (hydrogenation of aldimine intermediate) was promoted by metal ion poisoning.