Reaction process and kinetics of the selective hydrogenation of resorcinol into 1,3-cyclohexanedione

The reaction process and kinetics of the selective hydrogenation of resorcinol to 1,3-cyclohexanedione on Pd/C were studied. The optimized reaction conditions were as follows: mole ratio of sodium hydroxide to resorcinol, 1.1–1.2; catalyst loading, 15% (w/w); hydrogen pressure, 2 MPa; reaction temperature, 353 K; and stirring speed, >800 rpm. A kinetic model was then established based on a report that two hydrogenation pathways simultaneously control hydrogenation: one is the simultaneous addition of two hydrogen atoms while a van der Waals complex forms between the aromatic π-bond and the catalyst surface; the other is the sequential addition of a single hydrogen atom while a π/σ complex forms between a single double-bond and the catalyst surface. Subsequently, the model parameters and activation parameters were estimated. Results showed that the reaction was mainly controlled by the sequential pathway and that the addition of the first hydrogen atom was the rate-determining step. The activation energies for the sequential addition of two hydrogen atoms were 19.9 and 35.0 kJ/mol, whereas the activation energy for the simultaneous addition of two hydrogen atoms was 54.1 kJ/mol. The adsorption heats for resorcinol and 1,3-cyclohexanedione on the catalyst surface were 63.4 and 25.7 kJ/mol, respectively.