Effects of preparation variables on the activity of alumina-supported platinum catalysts for liquid phase cinnamaldehyde hydrogenation

Alumina-supported platinum catalysts were prepared through different metal loading and reduction procedures. The platinum precursors were loaded by impregnation and ion-exchange and then reduced by hydrogen at high temperatures and by sodium tetrahydroborate solution at a low temperature of 35 degrees C. The low-temperature reduced (LR) catalysts were found to produce cinnamyl alcohol in high selectivities in the liquid phase hydrogenation of cinnamaldehyde, irrespective of the method of metal loading. The high-temperature reduced (HR) catalysts prepared with ion-exchange produced hydrocinnamaldehyde and cinnamyl alcohol; the selectivity of the former was larger than that of the latter. In contrast, the HR catalysts prepared with impregnation produced large amounts of by-products and small amounts of hydrocinnamaldehyde and cinnamyl alcohol. When these HR catalysts were additionally treated with sodium tetrahydroborate solution, they indicated product distributions similar to the LR catalysts. (C) 1999 Elsevier Science B.V. All rights reserved.