Pilar Salagre

A new and efficient catalytic method for synthesizing isocyanates from carbamates

Abstract Operationally simple, recyclable and environmentally friendly montmorillonite efficiently catalyses dealcoholysis of a wide range of mono- and dicarbamates to isocyanates.

Characterization of several γ-alumina-supported nickel catalysts and activity for selective hydrogenation of hexanedinitrile

Studies of the Chemical preparation, Temperature-programmed reduction (TPR), powder X-ray diffraction (XRD), X-ray photoelectron (XP) spectra and catalytic activities of several Nickel/γ-alumina catalysts have been carried out for the catalytic hydrogenation of hexanedinitrile, in a continuous process at 1 atm pressure, 443 K, and in the absence of ammonia. The TPR measurements detect the inhibiting effect of γ-alumina on NiO reduction and also the formation of some kind of nickel aluminate at the NiO/γ-alumina interface at calcination temperatures > 623 K, which affects the final degree of reduction of the catalysts. The XRD detects the nickel phases present except that of the non-crystalline nickel aluminate. The XPS results indicate the presence of surface Ni2+ and reduced nickel, presumably in the form of nickel aluminate underneath the reduced surface nickel crystallites, particularly for higher nickel loadings. Catalytic conversions increase significantly with increase in nickel content and degree of reduction of the catalysts; the latter was highly resistant to metallic sintering. Selectivities of 100% towards azacycloheptane were obtained, where nickel aluminate may play a role in a decoration mechanism.

Heterogenised iridium complexes for the asymmetric hydrogenation of imines

Abstract A method for immobilising preformed chiral homogeneous catalysts to a clay support material has been developed. The observed asymmetric induction in the hydrogenation of imines with the supported species was greater than that with the corresponding homogeneous catalysts and, on re-use, the supported species increased their enantioselectivity.

Surface characterization and hydrogenation properties of several nickel/α-alumina catalysts

Studies of the chemical preparation, X-ray photoelectron spectra (XPS), activation energies of reduction, temperature-programmed reduction (TPR), X-ray diffraction (XRD) and catalytic activities of several nickel/α-alumina catalysts have been carried out for the catalytic hydrogenation of hexanedinitrile, in a continuous process at 1 atm pressure, 443 K, and in the absence of ammonia. XPS results show complete reduction of non-stoichiometric NiO on α-alumina at temperatures higher than 623 K and higher surface nickel dispersion with increasing nickel content and decreasing reduction temperatures. Activation energies of reduction for the α-alumina-supported non-stoichiometric NiO were higher than those of the unsupported non-stoichiometric NiO. TPR results show that the initial and final temperatures of reduction of the α-alumina-supported non-stoichiometric NiO are higher with unsupported NiO, confirming the inhibiting effect of α-alumina on NiO reduction. XRD measurements show the presence of α-alumina, NiO and Ni phases, and also the increase in crystallite size with increasing reduction temperature. Catalytic conversions increase with the nickel content and selectivities toward 6-aminohexanenitrile increase at lower nickel contents, high space velocities, and higher metallic sintering, probably owing to the presence of a higher content of specific crystal sites responsible for the production of 6-aminohexanenitrile. A mechanism is proposed.

Functionalization of amines by 'one pot-free solvent' reductive alkylation with a recyclable catalyst

Abstract The ability to attach a preformed rhodium and iridium homogeneous catalyst to a support would have a distinct advantage over the ‘one pot–free solvent’ reductive alkylation of primary amines to form IPPD and DMPPD.

Activity and surface characteristics of several alkali-doped iron catalysts for nttrile hydrogenation

Abstract A non-doped and several alkali (Na, K, Cs)-doped iron catalysts were prepared by reduction of the impregnated iron oxide. The surface characterization of the catalysts was accomplished by use of BET, XRD, XPS, and surface acid determination. The surface areas of the catalysts decrease with the increase of the alkali atomic volume (BET). Alkali migration towards the surface is always found (XPS). The surface acid determination shows an increase in the number of acid centres per m2 of catalyst with the atomic volume of the alkali promoter. The curves of base adsorption show the presence of acid sites of different strengths in all the reduced catalysts. The characterization results are correlated with those of catalytic activity for hydrogenation of adiponitrile at 200–250 °C. The results indicate correlations between conversion and the type and concentration of surface acid sites.

Use of Ni/Al-MCM-41 Catalysts for the Exhaustive Hydrodechlorination of 1,2,4-Trichlorobenzene

Several Ni/Al-MCM-41 catalysts were tested in the gas phase hydrodechlorination of 1,2,4-trichlorobenzene at atmospheric pressure. They showed high activity and selectivity towards benzene at reaction temperatures between 473 and 523 K with values of 100% conversion and 100% benzene selectivity at 523 K for all of them.

High efficiency and reusability of iridium complexes adsorbed in montmorillonite clay on catalytic hydrogenation of imines

Heterogenised homogeneous catalytic hydrogenation of aldimines by removable and reusable immobilised iridium complexes on montmorillonite clay.

Properties of sodium ions in zeolite materials: FT-IR study of the low temperature adsorption of carbon monoxide

The low temperature adsorption of CO has been investigated on NaX (Si/Al a. r. = 1.3), NaY (Si/Al a. r. = 2.4), NaMOR (Si/Al a. r. = 6.5) and NaFER (Si/Al a. r. = 25) zeolites by FT-IR spectroscopy. For comparison CO adsorption has also been investigated on Na-silica–alumina. Bands assigned to CO C-bonded and O-bonded to Na+ ions have been observed and discussed. A correlation between the position of the band and the siting and coordination state of Na+ ions has been observed for C-bonded species. Some effect of the cavity has been envisaged for O-bonded species. Low frequency bands corresponding to quite stable species have also been found and assigned to carbon monoxide bonded to two cations. This suggests that CO may also probe couples of the nearest Na+ ions, that may act in adsorption.

TPD study about the surface modification of some Ni/spinel catalysts in the hydrodechlorination of 1,2,4-trichlorobenzene. Influence on hydrogenation ability

NiAl2O4 supports and fresh and reactivated Ni/NiAl2O4 catalysts were tested in the gas phase hydrodechlorination of 1,2,4‐trichlorobenzene. Fresh catalysts hydrogenate 1,2,4‐trichlorobenzene to cyclohexane in the first 30 min of reaction at 523 K. An irreversible partial chlorination of the catalytic surface makes the hydrogenation of the aromatic ring difficult.