In situ preparation of bimetallic ReOx-Pd/TiO2 catalysts for selective aqueous-phase hydrogenation of succinic acid to 1,4-butanediol

TiO2-supported Re-Pd catalysts were evaluated for the selective hydrogenation of succinic acid (SUC) to 1,4-butanediol (BDO) in aqueous solution at 160 degrees C under 150 bar of H-2. Rhenium immobilized on Pd/TiO2 catalysts by ex situ preparation methods, namely successive impregnation (SI) or deposition by catalytic reduction (CR), was partially leached after handling in air and introduction into the SUC aqueous solution in the batch reactor; it was then re-deposited under H-2 pressure. It was demonstrated in this study that Re can be deposited by CR on a monometallic Pd catalyst directly in situ in the autoclave under hydrogen pressure before the catalytic test. The Re loading and the activation time under reducing atmosphere in the autoclave were optimized. Finally, the best bimetallic catalysts synthesized in situ demonstrated an intermediate selectivity to BDO compared to the systems prepared ex situ from the same parent monometallic catalyst, in the following order: ex situ CR < in situ CR < ex situ SI.