苯选择加氢制环己烯非负载型和负载型Ru-Zn催化剂的比较

摘要

An unsupported Ru-Zn catalyst and a supported Ru-Zn@ZrO2 catalyst with the same Ru loading were prepared by a co-precipitation method and an impregnation-precipitation method, and the difference of their catalytic performance for selective hydrogenation of benzene to cyclohexene under the conditions of ZrO2 as the dispersant for the unsupported Ru-Zn catalyst and similar dosage for the supported Ru-Zn@ZrO2 catalyst was investigated.The catalysts before and after hydrogenation were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 physisorption, X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS).The results showed that the unsupported Ru-Zn catalyst could absorb much more Zn2+ from the slurry than the supported Ru-Zn@ZrO2 catalyst.The Zn2+ absorbed could transform electrons from the metallic Ru, which turned the metallic Ru into the electron-deficient Ruδ+ species suitable for the formation of cyclohexene.Moreover, the Zn2+ absorbed also could cover the strong Ru active sites unfavorable for the formation of cyclohexene.Meanwhile, the unsupported Ru-Zn catalyst with ZrO2 as a dispersant had an optimum Ru particle size of 4.0 nm good for the selective hydrogenation of benzene to cyclohexene, however, the supported Ru-Zn catalyst had a small particle size of 2.7 nm.Consequently, the unsupported Ru-Zn catalyst gave a better cyclohexene yield of 61.0%, and the supported Ru-Zn@ZrO2 catalyst only gave a cyclohexene yield of 42.7%.Moreover, the unsupported Ru-Zn catalyst with ZrO2 as a dispersant had a good stability and an excellent reusability.%采用共沉淀法和浸渍-沉淀法分别制备了Ru负载量相同的非负载型Ru-Zn催化剂和负载型Ru-Zn@ZrO2催化剂,并在ZrO2作非负载型Ru-Zn催化剂分散剂、且其用量与负载型Ru-Zn@ZrO2催化剂的载体ZrO2用量相同的条件下,考察了它们催化苯选择加氢制环己烯性能的差异.并通过X-射线衍射(XRD)、透射电镜(TEM)、N2-物理吸附、X-射线荧光光谱(XRF)和X-射线光电子能谱(XPS)等手段对加氢前后催化剂进行了表征.结果表明,ZrO2作分散剂时加氢过程中非负载型Ru-Zn催化剂可以比负载型Ru-Zn@ZrO2催化剂从浆液中吸附更多Zn2+.吸附的Zn2+可以转移金属Ru上的电子,使Ru变为有利环己烯生成的缺电子的Ruδ+物种,而且还可以占据不适宜环己烯生成的强Ru活性位.同时ZrO2作分散剂的非负载型Ru-Zn催化剂具有4.0 nm适宜苯选择加氢制环己烯的最佳Ru粒径,而负载型Ru-Zn@ZrO2催化剂的粒径仅2.7 nm.因此,ZrO2作分散剂的非负载型Ru-Zn催化剂得到了61.0%的最高环己烯收率,而负载型Ru-Zn@ZrO2催化剂的最高环己烯收率仅42.7%.实验表明,ZrO2作分散剂的非负载型Ru-Zn催化剂具有良好的稳定性和重复使用性.