Kinetics of Liquid-phase Hydrogenation of Aliphatic α,β-Unsaturated Aldehyde over Raney Cobalt Catalyst

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Kinetic studies on the hydrogenation of 2-methyl-2-pentenal (UD) over the Raney cobalt catalyst were performed at temperatures ranging from 10 to 40°C in n-hexane. The products were found to be 2-methylpentan-1-ol (SA), 2-methyl-2-penten-1-ol (UA) and 2-methylpentanal (SD). The initial rates of the formation of SA(rSA), SD(rSD), and UA(rUA) were determined in the concentrations of UD(CUD), 0.026–0.263 mol/l. It was found by kinetic analysis that (rSA+rSD) was represented by a Langmuir-type rate equation and rUA by another one. The rate equations which fitted the rate data are as follows. rSA+rSD=\frac1.1×1010e−15200⁄RTCUD(1+4.4×105e−7500⁄RTCUD)2 rUA=\frac1.2×108e−13500⁄RTCUD(1+9.3×103e−5600⁄RTCUD)2 A mechanism in which the formation of SA and SD and that of UA proceed through different types of adsorbed UD was proposed. The adsorbed species in enol form and that in keto form were considered with respect to the formation of SA and SD. Activation energies for the formation of SA plus SD and of UA were determined to be 7.7 and 7.9 kcal/mol, respectively. The selectivity defined as the ratio of rSA to (rSA+rSD) was found to increase with the increase of the surface coverage of hydrogen.
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