Pd-based sol-gel catalysts for the enantioselective hydrogenation of (E)-2-methyl-2-butenoic acid

The enantioselective hydrogenation of the C=C double bond in (E)-2-methyl-2-butenoic acid was studied using Pd-based (5 wt.% on Al(2)O(3), SiO(2) or TiO(2)) catalysts, prepared by sol-gel methods and modified with cinchonidine (CD). The catalysts were characterized by XRD, NH(3)-TPD, H(2)-chemisorption analyses and N(2)-physisorption for BET surface area measurements. In the absence of CD, some catalysts showed a satisfactory hydrogenation capacity, with best values for those supported on silica. However, when CD was added, the enantiomeric excess values obtained were lower than those previously observed using analogous commercial catalysts. The influence of preparation conditions on support texture and metal dispersion was evidenced and tentatively correlated with activity and enantioselectivity