Characterization of bimetallic Ru-Sn supported catalysts and hydrogenation of 1,4-cyclohexanedicarboxylic acid

The supported catalysts were prepared by coimpregnation with aqueous solutions of ruthenium and tin salt and characterized by temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), carbon monoxide (CO) and oxygen (O2) chemisorption measurements. The surface of the reduced Al2O3-based bimetallic catalysts would be composed of metallic ruthenium and Sn(II) species. No evidence for substantial amounts of Sn(0) is found on reduced catalysts by XPS measurement. Based on the available evidence from the various techniques, the authors suggested that the high selectivity of the bimetallic Ru-Sn/Al2O3 catalyst for production of 1,4-cyclohexanedimethanol would be due to the action not only of the promoter (Sn) but also of the support (alumina). Catalytic hydrogenation of 1,4-cyclohexanedicarboxylic acid to 1,4-cyclohexanedimethanol over Ru-Sn supported catalysts was studied as functions of catalyst composition as well as various catalyst preparation parameters. Hydrogenation activity was affected by the kind of tin compounds and supports used for the preparation of the Ru-Sn catalyst. Stannous chloride and alumina were found to be the appropriate materials for the hydrogenation of CO group over the Ru-Sn catalysts. The yield for the 1,4-cyclohexanedimethanol on Ru-Sn/Al2O3 catalyst increased with Sn/Ru atomic ratio, reaching a maximum at a value of Sn/Ru = 1:1, which suggested a promotion of the CO bond hydrogenation by particular bimetallic Ru-Sn ensembles. The Ru-Sn/Al2O3 catalysts without any calcination activated in a hydrogen stream at 550 °C were effective for the hydrogenation of 1,4-cyclohexanedicarboxylic acid. Finally, we verified the durability of our catalyst by carrying out a catalyst-recycling test over five cycles.