Selective Hydrogenation of Cinnamaldehyde over Salt-Promoted Pd-Based Catalysts

The effect of salt additives (alcl3, sncl2, fecl3) on the catalytic behavior of pd3%/al2o3 catalyst in the selective liquid-phase hydrogenation of cinnamaldehyde in i- propanol was investigated at 25ºc and 4 bar h2 for salt concentrations in the range 4.5×10^-5-5.0×10^-3 m. the effect of added metal salts on the catalytic behavior of pd/al2o3 is rather complex. in the case of alcl3, a significant enhancement of the c=o bond hydrogenation could be achieved, accompanied by a strong suppression of the c=c bond hydrogenation. the selectivity towards cinnamyl alcohol formation could be raised from 26% to 70% by introducing small concentrations of alcl3 (~2.0×10-3 m) into the reaction mixture. selectivity improvement was also observed upon the addition of sncl2 (up to 67%) and fecl3 (up to 70%), however, at the expense of activity which is believed to be due to poisoning of the pd surface by metallic fe and sn. the mecha- nisms of the additives effects on the catalytic behavior of pd/al2o3 are discussed.