Selective hydrogenation of carvone and o-xylene on Pd-Cu catalysts prepared by surface redox reaction

A series of Pd and Pd-Cu bimetallic catalysts were prepared by surface redox reaction and coimpregnation methods. A comparison between the preparation methods in the activity and selectivity for o-xylene and carvone hydrogenation was done. FTIR studies showed that the Cu is deposited mainly in the low coordination Pd sites when the catalyst was prepared by redox, whereas a random distribution of Cu on the Pd surface was obtained for the catalyst prepared by coimpregnation. The activity and selectivity of bimetallic catalysts, were found to depending on the method of preparation used. For o-xylene hydrogenation in redox catalyst, the selectivity to trans- 1,2-dimethylcyclohexane was lower than that obtained in the Pd/SiO₂ reference catalyst, whereas in the coimpregnated catalyst, the trans isomer selectivity was higher. In the redox preparation, the selective hydrogenation of carvone favors the formation of carvotanacetone, whereas the coimpregnated catalyst favors the selectivity to carvomenthone. (C) 2000 Elsevier Science B.V.