The mechanism of liquid-phase catalytic hydrogenation of the olefinic double bond on supported nickel catalysts

Abstract

The liquid-phase catalytic hydrogenation of several styrene derivatives, PhCHCHR (R = H, CH2OH, CHO, COMe, CO2H, and CO2Me), has been carried out at 293–333 K with 0.41 MPa of initial hydrogen pressure on nickel catalysts at 20 wt% supported on Al2O3, SiO2, and on two different types of AlPO4. The metal–support interaction effects as well as the substituent effects can be evaluated through several isokinetic parameters obtained due to the existence of a linear correlation between the activation parameters ΔH and ΔS(and between In A and Ea) known as the ‘compensation effect.’A correlation between the reaction rates and the σ-parameters of the substituents within the context of the Yukawa–Tsuno equation is also obtained. The results for R substituents indicate the activating effect of electron-releasing groups. The results obtained considering the values of (r) and ρ, close to zero, when the substituents R′ in PhCHCHCOR′ are considered, show the low dependence of the reaction rate on the electron-releasing or electron-withdrawing character of R′. On the basis of these results, we suggest a cis-concerted mechanism for the liquid-phase catalytic hydrogenation of the olefin double bond on supported nickel catalysts.