**Acknowledgements**

composite catalysts had slightly better catalytic properties than the commercial Pd catalysts,

In the tests of selective hydrogenation of terminal alkynes to terminal alkenes, the activity of the catalysts 0.3PdAl, 0.3PdCNR, 0.3PdUTAl, and Lindlar were evaluated using 1-heptyne as reactant. It was seen that at 180 min, Lindlar and 0.3PdUTAl achieved total conversion of the alkyne, with selectivity to 1-heptene of 85% in the case of the Lindlar catalyst and 97% in the case of 0.3PdUTAl. The 0.3PdAl and 0.3PdCNR catalysts suffered in this strong reaction deactivation. This was more noticeable from 1-heptyne conversion values of 10–20%.The 0.3PdUTAl catalyst had a similar activity as the commercial Lindlar catalyst. Some advantages of the new materials were evident. The Lindlar catalyst was available in powder form and was very expensive due to the high metal content (5 wt% Pd).The Pd/composites were pelletized

The good results of conversion and selectivity obtained during the reaction of hydrogenation of 3-hexyne, a nonterminal alkyne, to 3-hexene, over the 0.3PdUTAl catalyst, indicates that

The reactions of hydrogenation presented were also favored by the use of composite supports because of their lower acid strength. This is an advantage for suppressing undesirable reactions, such as the oligomerization of alkenes and alkynes, leading to the formation of carbon deposits or gums over the catalysts. These and other reactions affect the selectivity and

In the case of the reaction of synthesis of 3-hydroxybutane-2-one from 2,3-butanedione, which is of commercial interest for the perfume industry, it was seen that the Pd/composite catalysts could be used with values of conversion and selectivity close to 100%.The use of composites in the slurry reactors enabled sparing the filtering of the liquid phase at the end of the reaction. The difference in activity found between the PdBTAl and PdUTAl catalysts could be due to the differences in metal dispersion or to differences in the electronic properties of the surface

During the enantioselectivity hydrogenation reaction of ethyl pyruvate using cinchonidineas a quiral modifier, both PtUTAl and PtBTAl composite catalysts were active and selective to (R)-Ethyl Lactate. PtUTAl catalyst had higher total conversion than PtBTAl but had less enantiomeric excess (ee). This activity and enantioselectivity behavior could be related, at least partly due to the electronic effects of the presence of chloride species that prevents the adsorption of the quiral modifier causing a decrease in the enantiomeric excess (ee), although

OxCly species could not be discarded.

The advantage of the egg-shell catalysts that makes them to be preferred over other catalyst types is that they have smaller intraparticle mass transfer limitations. Having most of the metal phase on the outer surface layer, makes also the heat transfer more efficient, enabling a better

A last advantage is related to the mechanical properties. The composites displayed higher values of diametrical and longitudinal resistance than alumina and silica and also suffered less

these composite catalysts can also be used in reactions comprising consecutive steps.

a fact pointing to the possibility of industrial use of these new materials.

202 New Advances in Hydrogenation Processes - Fundamentals and Applications

and only had 0.25 wt% Pd content.

lifetime of the catalysts.

geometrical effects of Ptδ+

control of the reaction and the reactor temperature.

Pd species.

The experimental assistance of F. Coloma-Pascual is greatly acknowledged. The financial assistance of CAI+D (UNL), CONICET (PIP 410), and ANPCyT are also acknowledged.
