Preparation and characterisation of supported palladium, platinum and ruthenium catalysts for cinnamaldehyde hydrogenation

Author
Mohamed Lashdaf
Year
2004
Abstract & Cover

Hydrocinnamaldehyde and cinnamyl alcohol are produced in cinnamaldehyde hydrogenation. Both are of great practical importance with wide application in the fine chemicals, pharmaceuticals and perfume industries. In addition, cinnamyl alcohol is an important building block in organic synthesis. In view of the importance of these products, work was undertaken to prepare selective hydrogenation catalysts. Palladium, platinum and ruthenium catalysts supported on alumina and silica were prepared by gas phase deposition in an atomic layer epitaxy (ALE) reactor and by impregnation techniques. For study of the effect of the acidity of the support, Ru/β zeolite and Pt/β zeolite catalysts were prepared solely by impregnation. The materials were characterised by a variety of techniques. The catalytic properties of the catalysts were studied in cinnamaldehyde hydrogenation. Particle sizes were smaller for the ALE-deposited palladium than the corresponding impregnated samples. For the platinum and ruthenium samples, they were essentially the same for the two methods of preparation. Metal particles were small if a ligand exchange reaction occurred between metal precursor and support. In the ALE deposition, ligand exchange reaction and metal formation occurred for Pd(thd)2 and (CH3)3(CH3C5H4)Pt both on alumina and on silica. Ligand exchange and metal formation also took place for impregnated Pt catalysts with (CH3)3(CH3C5H4)Pt on both supports. In impregnation the interaction of Pd(thd)2 and Ru(thd)3 with the supports was associative adsorption. Palladium catalysts were more active than ruthenium and platinum catalysts, and the palladium catalysts prepared by ALE showed the highest initial activity in cinnamaldehyde hydrogenation because of the small particle size of metals obtained by ALE. Ruthenium on β zeolites were more active than platinum on β zeolites. The acidity of β zeolites affected the reduction behaviour of ruthenium and the particle size, which subsequently influenced the activity. As acidity increased, particle size decreased and the activity increased. The adsorption of cinnamaldehyde was preferably via the C=C bond on palladium catalysts, via the C=C and C=O bonds on ruthenium and via the C=O bond on platinum catalysts. Hydrocinnamaldehyde was the main product with all Pd catalysts. Ruthenium catalysts differ in selectivity. Only hydrocinnamaldehyde and 3-phenyl-1-propanol were produced with Ru/SiO2 prepared by ALE. Ruthenium on β zeolites were selective to hydrocinnamaldehyde. The other ruthenium catalysts formed a variety of hydrogenated products. The best choice of catalysts for cinnamyl alcohol formation is the impregnated 1.2 wt-% Pt/SiO2 catalyst with particle size of 4 nm. With use of this catalyst the selectivity toward cinnamyl alcohol was as much as 90% at conversion of 15%. For the formation of hydrocinnamaldehyde, 4.9 wt-% Pd/SiO2 is the best catalyst that was selective only to hydrocinnamaldehyde at conversion below 10%.

Source of Information
FinALD40 exhibition material, http://www.aldcoe.fi/events/finald40.pdf
University
Helsinki University of Technology, Department of Chemical Technology, Laboratory of Industrial Chemistry
(Espoo, Finland)
Other notes
Oksana: Author writes about Atomic Layer Epitaxy
External Link
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