Hydrogenation versus hydrogenolysis in the reaction of cis-2-butene-1,4-diol over supported platinum catalysts: kinetic aspects

The liquid phase hydrogenation of cis-2-butene-1,4-diol has been studied in ethanol, using different platinum-supported catalysts, at a temperature ranging from 273 to 303 K and at a partial H2 pressure between 0.01 and 0.1 MPa. Formation of only hydrogenation and hydrogenolysis products was detected and their selectivity was found to depend on the acid–base characteristics of the support. Ayield of 96% to the fully hydrogenated product, butane-1,4-diol, at 303 K and 0.1 MPa H2 pressure was obtained on Pt/MgO. The experimental data, in presence of platinum supported on TiO2, was explained on the basis of a two paths mechanism: one leading to butane-1,4-diol, as usually, through a s-alkyl species and the other, affording cis-crotyl alcohol and 3-buten-1-ol, involving the same unique intermediate, h3-allyl. Reaction rates were described on the basis of a Langmuir–Hinshelwood type model, assuming a non-competitive adsorption of organic species and hydrogen on the platinum active sites. Kinetic parameters for individual reaction steps were determined by a non-linear regression analysis. Furthermore, an adsorption of the olefinic substrate in a tilted mode was discussed in order to explain the hydrogenolysis reaction.