Superior performance of a nanostructured platinum catalyst in water: Hydrogenations of alkenes, aldehydes and nitroaromatics

The hydrogenations of >C=C<, >C=O and nitro groups in ArNO2, with a water-soluble, polymer [poly(diallyldimethylammonium chloride)] supported, platinum carbonyl cluster {[Pt-30(CO)(60)](2-)} derived catalyst 1, have been studied. The performance of I has been compared with that of two other platinum catalysts: catalyst 2 prepared by the hydrogen reduction of [PtCl6](2-) supported on the same water-soluble polymer, and 3, a commercial platinum catalyst (5% Pt on alumina). Our catalyst I has been found to be more active than 2 and 3, and by TEM it has been shown that the nanoparticles in 1. are much smaller than those in 2. In the hydrogenation of o-chloromtrobenzene both 1 and 2 were found to be more selective (no hydrodehalogenation) than 3. To evaluate the advantages of water as a solvent, comparative studies have been carried out in three different solvent systems: water, methanol and a 1:1 mixture of water and toluene. Hydrogenations in methanol have been found to be accompanied by induction times while no such induction time is observed in water. Both liquid (methyl pyruvate, benzaldehyde, safflower oil and styrene) and water-insoluble solid nitroaromatics (o- and m-chloronitrobenzene and p-aminonitrobenzene) have been tested as substrates, and for all the substrates the activity in water was found to be higher.