Study On The Catalytic Properties Of Supported Amorphous Ru-B Alloy Catalysts For Benzene Selective Hydrogenation To Cyclohexene

Bezene selective hydrogenation to cyclohexene was selected as the probe reaction to study the catalytic properties of supported amorphous Ru-B alloy catalyst. The effects of reaction conditions, rare earths (RE) and supports including sepiolite (Sep), acid modified sepiolite(Sep-A), ion exchanged sepiolite (Sep-I), bentonite, A1₂O₃, TiO₂/Sep-A and TiO₂/Al₂O₃ composite supports on the catalytic properties of Ru-B alloy were studied. The Ru loading and composition of the alloys were analyzed by means of inductively coupled plasma optical emission spectroscopy (ICP), special surface area and pore distribution of the catalysts were measured by nitrogen adsorption method. The surface properties of the catalysts were characterized by temperature programmed reduction (TPR) and temperature programmed desorption (TPD) of hydrogen, cyclohexane and cyclohexene, respectively.It is found that the optimal reaction conditions for the reaction catalyzed by Ru-B/Sep are as follows:initial reaction temperature 393K, hydrogen pressure 3.5MPa, water/benzene ratio 1:1, amount of catalyst 0.1g, reaction time 20 minutes, amount of ZnSO₄ ? 7H₂O 0.3g.Ru-B/Sep-A exhibits higher activity and selectivity than Ru-B/Sep. This is attribute to that the higher special surface area of Sep-A is in favor of well dispersion of Ru and that the lager pore diameter of Sep-A facilitates the diffusion of cyclohexene. Additionally, cyclohexene desorbs at lower temperature for Ru-B/Sep-A than that for Ru-B/Sep. Ion exchange can change the composition and surface properties of Sep, which affects the interaction between Ru-B alloy and supports. Therefore, the catalytic properties are changed. Ru-B/Sep-Zn and Ru-B/Sep-Fe exhibit higher activity and selectivity than Ru-B/Sep. Ru-B/Sep-Ti shows higher activity but lower selectivity. Proper amount of TiO₂ added to Sep-A by impregnation method can improve the activity but decrease the selectivity to cyclohexene. It can be explained by that proper amount of TiO₂ can improve special surface area of the catalysts, and that Ru⁶⁺ oxides on the surface of the catalysts reduced more easily owing to the...