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 redo x reaction and coimpregnation methods. A comparison between the preparation methods in the activity and selectivity for o-xylene and carvone hydrogena tion was done. FTIR studies showed that the Cu is deposited mainly in the l ow 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 cata lysts, were found to depending on the method of preparation used. For o-xyl ene hydrogenation in redox catalyst, the selectivity to trans-1,2-dimethylc yclohexane was lower than that obtained in the Pd/SiO2 reference catalyst, whereas in the coimpregnated catalyst, the trans isomer selectivity was hig her. In the redox preparation, the selective hydrogenation of carvone favor s the formation of carvotanacetone, whereas the coimpregnated catalyst favo rs the selectivity to carvomenthone. (C) 2000 Elsevier Science B.V. All rig hts reserved.