Pablo C. L'Argentiere

A palladium tetra-coordinated complex as catalyst in the selective hydrogenation of 1-heptyne

Abstract Supporting on γ-Al2O3 a palladium complex with chloride and tridecylamine as ligands, it is possible to obtain an heterogeneous catalyst which is more active and selective for the 1-heptyne hydrogenation to 1-heptene than the classic Lindlar catalyst. At the same operational conditions, the supported palladium complex is also more active and selective than the same complex unsupported. The hydrogen pressure and the operational temperature showed to play an important role in the catalytic behavior of the catalysts under study. As determined by FTIR and X-ray photoelectron spectroscopy (XPS), the active species is the complex itself, which is stable under the reaction conditions. The obtained XPS results show that the palladium complex, supported or not, is tetra-coordinated, suggesting that its formula is [PdCl2(NH2(CH2)12CH3)2]. The highest activity and selectivity of the palladium supported complex can be attributed, at least partially, to electronic and geometrical effects.

On the deactivation of supported palladium hydrogenation catalysts by thiophene poisoning

The deactivation of supported palladium catalysts for ethylbenzene hydrogenation by thiophene was studied. The presence of Pdn+ species on the catalyst surface, in samples prepared from acid solutions of PdCl2, and reduced at temperatures below 450 °C, was evidenced by XPS. A correlation between the concentration of electron-deficient Pd species and the sulfur resistance was found. Thus, the higher the value of the Pdn+/Pd0 ratio, the higher the sulfur resistance. Catalysts prepared from Pd(NO3)2 or from PdCl2 reduced at 450 °C, which essentially contain Pd0, are more quickly deactivated. Furthermore, our results also suggest that while the influence of the metal dispersion on the stability of the palladium catalysts toward sulfur is not significant, the nature of the support, on the other hand, plays an important role.

Hydrolysis of chlorobenzene over Cu-promoted hydroxyapatites

Abstract The chlorobenzene hydrolysis to phenol over Cu-promoted and -nonpromoted hydroxyapatites at different operational conditions was studied in a flow equipment under atmospheric pressure. The by-product was benzene. The different Ca to P ratios did not affect the catalyst activity and selectivity or the oxidation state of Cu. Catalyst deactivation was produced by the loss of Cu, which was associated with the temperature of operation. Correlations between the loss of Cu as a function of time at different temperatures and the decrease of activity with the loss of Cu were derived. Considerations about the reaction mechanism and about the reaction through which benzene was produced are made.

[PdCl2(NH2(CH2)12CH3)2] supported on an active carbon: effect of the carbon properties on the catalytic activity of cyclohexene hydrogenation

Abstract The catalytic activity and poisoning resistance of [PdCl2(NH2(CH2)12CH3)2], supported on active carbons, have been studied, regarding the effect of some of the support properties, such as: porosity, surface chemistry and sulphur content. Commercial active carbons and almond-shell-derived carbons were used. Some of the commercial active carbons were submitted to different treatments to purify them or to modify the support surface chemistry. Active carbons were characterised by nitrogen adsorption at 77 K, carbon dioxide adsorption at 273 K, mercury porosimetry, elemental analysis and TPD. Catalysts were prepared supporting the metal complex by the incipient impregnation method, with a palladium content of ca. 0.3% wt. All the catalysts were analysed by XPS and nitrogen adsorption at 77 K. The catalytic activity and sulphur-poisoning resistance were determined in the cyclohexene hydrogenation to cyclohexane. Tetrahydrothiophene (THT) was used as the poisoning agent in a concentration of 300 ppm. Regarding the effect of support porosity, the catalytic activity increases with supermicropore (∅ from 0.7 to 2 nm) volume. With regard to the oxygen surface groups and sulphur content of the active carbons, no effect has been found. Catalyst poisoning by THT is found to be independent of the active carbon properties and lower than that observed for the unsupported metal complex and the complex supported on γ-Al2O3.

XPS studies of the effect of Mn on PdAl2O3

Abstract The effect of Mn on Pd Al 2 O 3 is studied by XPS. Mn decreases the electronic density of Pd and thus its sulfur adsorption capacity, producing a decrease in activity and selectivity during the selective hydrogenation of styrene to ethylbenzene.

High active, selective and sulfur resistant supported palladium tetra-coordinated complex as catalyst in the selective hydrogenation of styrene

Abstract The [PdCl2(CH3SOCH3)2] complex supported on γ-Al2O3 was studied as catalyst in the selective hydrogenation of styrene to ethylbenzene. This catalyst is considerably more active, selective and sulfur-resistant than a conventional catalyst obtained from an acid solution of PdCl2. As determined by XPS and IR, the active species is the complex itself, which is stable under the reaction conditions. The complex is destroyed, at least partially, by hydrogen treatments above 353 K, leading to a less active and less sulfur resistant catalyst. The highest sulfur resistance can be attributed to electronic and geometrical effects.

[PdCl2(NH2(CH2)12CH3)2] supported on γ-Al2O3 as catalyst for selective hydrogenation

The [PdCl2(NH2(CH2)12CH3)2] complex supported on γ-Al2O3 has proved to be a considerably more active, selective and sulfur-resistant catalyst in the selective hydrogenation of styrene to ethylbenzene than a traditional catalyst obtained from acid solutions of PdCl2, and even than the same complex unsupported. The active species is the complex itself and it is stable under the reaction conditions. Hydrogen treatments above 353K destroy the complex, at least partially, leading to a less active and sulfur resistant catalyst. The higher sulfur resistance, when compared to a conventional Pd/Al2O3 catalyst, can be attributed to electronic and geometrical effects.

Regeneration of a sulfur poisoned Pd/Al2O3 catalyst during the selective hydrogenation of styrene

Abstract Deactivation by thiophene and the regeneration of a commercial Pd/Al2O3 catalyst was studied with reference to the contribution of the support to the loss and subsequent recovery of catalyst selectivity. The selective hydrogenation of styrene to ethylbenzene was taken as a test reaction. The electronic state of palladium during the poisoning/regeneration process was followed by XPS (X-ray photoelectron spectroscopy). The catalyst was regenerated by eliminating the poison in the feed or by ex-situ treatments at different temperatures or hydrogen pressures. Sulfur is partially and irreversibly adsorbed on the metal and the catalyst activity could never be completely renewed. The XPS results suggest that the electronic properties of palladium are modified in the poisoning/regeneration process.

Activated-Carbon-Heterogenized [PdCl2(NH2(CH2)12CH3)2] for the Selective Hydrogenation of 1-Heptyne

The complex [PdCl2(NH2(CH2)12CH3)2] has been heterogenized on two different activated carbons and tested as a catalyst for the semihydrogenation of 1-heptyne. The results are compared with those previously reported with the γ-Al2O3-supported complex. An important effect of the support porosity has been found. The location of the complex in the narrow pores induces shape selectivity. The effect of the support in concentrating the substrate close to the active species has been observed. A very active and selective catalyst has been prepared using an essentially microporous carbon.

Low metal loading catalysts used for the selective hydrogenation of styrene

A series of Group VIII metal catalysts was obtained for the semi-hydrogenation of styrene. Catalysts were characterized by Hydrogen Chemisorption, TPR and XPS. Palladium, rhodium and platinum low metal loading prepared catalysts presented high activity and selectivity (ca. 98%) during the semi-hydrogenation of styrene, being palladium the most active catalyst. The ruthenium catalyst also presented high selectivity (ca. 98%), but the lowest activity. For the palladium catalyst, the influence of the precursor salt and of the reduction temperature on the activity and selectivity were studied. The following activity series was obtained: PdN-423 > PdCl-673 > PdCl-373> PtCl-673 > RhCl-673 >> RuCl-673. As determined by XPS, differences in activity could be attributed, at least in part, to electronic effects.