Ru/ZrO_2催化剂在苯部分加氢反应中的粒径效应

The size effect of the Ru/ZrO_2 catalyst on partial hydrogenation of benzene to cyclohexene

采用多元醇还原法将2.4~5.4 nm范围内粒径均一、尺寸可控的Ru纳米粒子负载在ZrO2上,研究了Ru的粒径对Ru/ZrO2催化剂上苯部分加氢性能的影响.采用紫外-可见吸收光谱（UV-Vis）、N2物理吸附、H2化学吸附、H2-程序升温脱附（H2-TPD）、粉末X射线衍射（XRD）、透射电子显微镜（TEM）和X射线光电子能谱（XPS）等手段对催化剂进行了系统的表征.研究表明,用于还原的醇的种类及添加剂乙酸钠的浓度对Ru粒径有显著影响.在苯部分加氢反应中,Ru/ZrO2催化剂有明显的粒径效应.随着Ru粒径的增大,苯的转换频率（TOF）提高,环己烯初始选择性（S0）则呈火山型变化趋势,选择性最高时的Ru粒径为4.4 nm.1,2-丙二醇还原得到的Ru/ZrO2催化剂上S0及环己烯得率最高,分别可达82%和39%.结合催化剂的表征和加氢结果,讨论了Ru粒径影响苯部分加氢活性和选择性的原因.

The particle size effect on partial hydrogenation of benzene to cyclohexene over Ru/ZrO2 catalysts is reported. Uniform Ru nanoparticles （NPs） with a tunable particle size from 2,4 to 5.4 nm were synthesized by a polyol reduction method and deposited on ZrO2. The catalysts were characterized by ultraviolet-visible absorption spectroscopy （UV-Vis）, N2 physisorption, H2 chemisorption, temperature-programmed desorption of H2 （H2-TPD）, powder X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and X-ray photoelectron spectroscopy （XPS）. It was found that the type of polyol and the concentration of additive （sodium acetate trihydrate） imposed remarkable effect on the particle size of Ru. A distinct particle size effect occurred in partial hydrogenation of benzene. With the size of the Ru NPs increasing, the hydrogenation activity of benzene increased, and the initial selectivity （So） to cyclohexene showed a volcanic-type variation tendency, which revealed that the optimal Ru size for obtaining the highest So is 4.4 nm. The Ru/ZrO2 catalyst reduced by 1,2-propanediol exhibited the highest So （82%） and the yield of cyclohexene （39%）. Based on the characterization results, the size effect of Ru on the activity and selectivity is discussed.