Ru/氧化物催化剂在甲苯部分加氢反应中的载体效应

Effect of the Support on Partial Hydrogenation of Toluene over Ru/Oxide Catalysts

采用浸渍-化学还原法制备了一系列负载型Ru催化剂,考察了一些常见的氧化物载体(Si O_2、mZr O_2、t-Zr O_2、g-Al2O3和P25)对甲苯部分加氢制甲基环己烯催化性能的影响。采用N_2物理吸附、X射线粉末衍射(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,载体通过影响Ru的粒径,进而影响甲苯部分加氢催化性能。当Ru纳米粒子的粒径由2.6 nm增大到17.3 nm时,甲苯的转换频率(TOF)以及甲基环己烯初始选择性(S0)先增加,然后降低,呈火山型变化趋势,二者的最大值均在Ru粒径为3.0 nm时出现。在催化性能最优的Ru/P25催化剂上,进一步考察了修饰剂的种类和浓度、反应温度、反应压力等条件的影响。当反应温度为423 K、H_2压力为5.0 MPa,以0.25 g七水合硫酸锌为修饰剂时,Ru/P25催化剂上的初始加氢速率(r0)为26 mmol?g^(-1)?min^(-1),S0为57%,甲基环己烯得率可达36%。

The supported Ru catalysts were prepared by the impregnation-chemical reduction method to investigate the effect of some conventional oxide supports（Si O2, m-Zr O2, t-Zr O2, γ-Al2O3, and P25） on the partial hydrogenation of toluene to methylcyclohexenes. The catalysts were characterized by N2 physisorption, powder X-ray diffraction（XRD）, transmission electron microscopy（TEM）, and X-ray photoelectron spectroscopy（XPS）.It was found that the supports influenced the size of the Ru nanoparticles（NPs） and consequently the catalytic performance. With the increase in the size of the Ru NPs from 2.6 to 17.3 nm, the turnover frequency（TOF）of toluene and the initial selectivity（S0） to methylcyclohexenes increased first, reached the maximum, and then decreased, following a volcano-like curve. At the Ru particle size of 3.0 nm, both TOF and S0 reached the highest values. Reaction conditions, such as the type and concentration of the modifiers, the temperature, and the pressure, were optimized over the best Ru/P25 catalyst among the supported Ru catalysts investigated herein.Under the reaction conditions of 423 K, H2 pressure of 5.0 MPa, and using 0.25 g zinc sulfate heptahydrate as the modifier, the initial hydrogenation activity（r0） of 26 mmol.g^（-1）.min^（-1）, the S0 of 57%, and the methylcyclohexenes yield of 36% were obtained.