The hydrogenolysis of the lignan hydroxymatairesinol (HMR), extracted from Norway spruce knots, to matairesinol (MAT) was done in a stainless steel autoclave using a 5% Pd/C. The influence of hydrogen pressure (4-40 bar) was studied and the hydrogenolysis reaction rate was proved to decrease at higher hydrogen pressure. This was explained by competitive adsorption of HMR and hydrogen, where HMR adsorbs on several Pd atoms. The kinetic results were described with a model applying multi-site adsorption for the reactant, where the number of Pd surface atoms needed for the adsorption of a single HMR molecule was determined to 20 using molecular modelling. The values of the rate and adsorption constants were estimated using a parameter estimation program. The kinetic model explained the experimental data well. (C) 2009 Elsevier B.V. All rights reserved.