ABSTRACT
Catalytic hydrogenation of cinnamaldehyde received a keen interest because of the applications in the field of flavor and fragrances, and as building block in organic synthesis. The carbon-carbon double bond in the a, (3-unsaturated aldehyde is more easily hydrogenated than the carbonyl double bond. Therefore, the chemoselectivity is a very important factor in this reaction. Several studies stressed that this reaction can be improved by modifying the surface properties of the catalyst ( 1 ). Most reported cases refer to the use of the various promoters such as metal chloride (2), or heteropolyacids (3). But the dispersion and the reduction state of the metal also are important factors in this reaction, both determining changes of the electronic state. Gallezot and Richard (1) underlined the necessity to have low dispersion. Arai and co-workers brought evidence for the fact that a metal surface is more selective for this reaction when it exhibits high Miller index planes ( 4, 5). In addition to the preparation conditions, the support is another key factor in controlling these properties. Titania (6), zirconia (7), and also microporous zeolites (8, 9) proved to have a good effectiveness. In all these cases, the improvement factor seems to be related with the presence of Lewis acidity, and not eventual shape selectivity effects induced by the microporous texture. The selective hydrogenation of the carbonyl bond can be achieved by the proper activation of dihydrogen into a hydride-proton pair (10). Strong Lewis sites would have a profound impact by the way of generating this.
