Kinetics of Liquid-phase Hydrogenation of Aliphatic α,β-Unsaturated Aldehyde over Raney Cobalt Catalyst Modified with Co-, Mn-, Ni-, and PdCl2

Abstract

Abstract Kinetic studies were carried out on the hydrogenation of the α,β-unsaturated aldehyde, 2-methyl-2-pentenal (UD), over the Raney cobalt catalyst modified with various amounts of Co-, Mn-, Ni- and PdCl2 in n-hexane under atmospheric pressure at 40 and 20°C. Initial rates of formation of the saturated aldehyde (rSD), saturated alcohol(rSA) and unsaturated alcohol(rUA) were determined in the concentration range of UD((CUD) 0.018–0.263 mol/l. It was found that (rSD+rSA) obeyed a Langmuir-type rate equation and rUA a different one. The rate equations are as follows. r SD+rSA=\frack1·b1·CUD(1+b1·CUD)2, rUA=\frack2·b2·CUD(1+b2·CUD)2 where k and b denote the rate constant of the surface reaction and parameter for the adsorption of UD and hydrogen, respectively, the subscripts 1 and 2 representing the formation of SA and SD and that of UA, respectively. Kinetic parameters k1, k2, b1 and b2 were found to vary with the amount and kind of modifier. The variation of b1 and b2 was irregular. The rate constant k1 decreased with increasing amount of Co-, Mn- and NiCl2 added; it increased remarkably with the addition of PdCl2. The variation of k2 was more complicated. Addition of a small amount of the modifiers did not decrease k2. Further addition of Co- and MnCl2 made k2 decrease, while that of NiCl2 made it increase. Mechanism of the modification with these metal chlorides is discussed on the basis of the active site hypothesis.