UNIQUE HYDROGENATION ACTIVITY OF SUPPORTED TIN CATALYST - SELECTIVE HYDROGENATION CATALYST FOR UNSATURATED ALDEHYDES

Selective hydrogenation of unsaturated aldehydes, crotonaldehyde (CH3C H=CHCH=O) and cinnamaldehyde (C6H5CH=CHCH=O), has been studied over Si O2-supported monometallic Sn and bimetallic Rh-Sn catalysts in the liq uid phase. Over a silica-supported monometallic Rh catalyst, Rh/SiO2, no unsaturated alcohol (crotyl alcohol or cinnamyl alcohol) was formed , whereas considerable amounts of the corresponding saturated aldehyde and saturated alcohol were obtained. The selectivity to the unsaturat ed alcohol was improved over the Rh-Sn bimetallic catalyst. The select ivity to the corresponding unsaturated alcohol attained ca. 65% over t he Rh-Sn bimetallic catalysts. On the other hand, The supported Sn cat alyst showed markedly high selectivity to the unsaturated alcohols. Th e selectivity of the Sn/SiO2, attained 95% to crotyl alcohol and 100% to cinnamyl alcohol, respectively. Although the conversion of each uns aturated aldehyde over Rh-Sn/SiO2 catalysts was greater than that over Sn/SiO2 catalysts, the selectivity of Sn/SiO2 catalysts to the corres ponding unsaturated alcohols was superior to that over Rh-Sn/SiO2. The selectivity of Sn/SiO2 was also compared with that of Rh-Sn/SiO2 at a similar conversion of the unsaturated aldehydes. The selectivity of S n/SiO2 was significantly greater than that of the Rh-Sn bimetallic cat alyst. These results indicate that the high selectivity over Sn/SiO2 w as ascribed not to low conversion but to intrinsic selectivity of the Sn catalyst.