Hydrogenation of cinnamaldehyde over an ionic cobalt promoted alumina-supported palladium catalyst

Nano -alumina-supported transition metal-based mono- (Pd 0 /γ-Al 2 O 3 or Co III /γ-Al 2 O 3 ) and bimetallic catalysts (Pd 0 Co III /γ-Al 2 O 3 ), were prepared by wet impregnation, oxidation and in situ reduction of the palladium. The palladium(II) acetate [Pd II 3 (OOCCH 3 ) 6 ], cobalt(II) acetate [Co II (OOCCH 3 ) 2 ]·4H 2 O and palladium, cobalt bridging tetraacetate [Pd II Co II (OOCCH 3 ) 4 ]·H 2 O·2CH 3 COOH, were used as catalyst precursors to prepare a 7.4 % mol catalyst/support loading. The oxidation states of these activated catalysts were studied by XPS. These catalysts were evaluated for hydrogenation of cinnamaldehyde in a biphasic reaction under 3MPa of hydrogen at 80 °C. The Pd 0 /γ-Al 2 O 3 selectively catalyzed the hydrogenation of C=C bond in cinnamaldehyde to formphenylpropanol (100 %). In contrast, catalysis with Pd 0 Co III /γ-Al 2 O 3 hydrogenated both C=C and C=O bonds consecutively, forming 65 % phenylpropanal and 35 % phenylpropanol with TOF = 47.2 h –1 . No reaction occurred when Co III /γ-Al 2 O 3 was used. KEYWORDS  Bimetallic heterogeneous catalyst, palladium, cobalt, hydrogenation, unsaturated aldehydes.