La2O3助剂对Rh/SiO2催化CO加氢反应性能的影响

采用溶胶凝胶法制备了SiO_2和La_2O_3-SiO_2载体,再通过浸渍法分别引入Rh-La和Rh组分,研究考察了La引入方式对Rh/SiO_2催化CO加氢反应性能的影响。结果表明,La的添加有利于提高Rh的分散度,促进Rh+中心数的增加,有效地抑制产物中CO2的生成,提高含氧化合物选择性。此外,La的引入方式会影响La与Rh间的相互作用强弱,Rh和La共浸渍制得的2Rh-5La_2O_3/SiO_2催化剂中Rh-La相互作用较强,削弱的Rh-CO键有利于反应过程中CO的插入反应,使得产物以C_(2+)含氧化合物为主。而La以助剂形式掺入SiO_2制得的2Rh/5La_2O_3-SiO_2催化剂具有较弱的La-Rh相互作用,其产物则以甲醇、乙醇等低碳醇为主。

Effect of La2O3 addition on the catalytic performance of Rh/SiO2 for CO hydrogenation

SiO₂ and La₂O₃-SiO₂ were synthesized via sol-gel method and used as support to prepared Rh-La or Rh doped catalysts by iso-volumic impregnation. Effects of doping mode of La on the catalytic performance of Rh/SiO₂ for CO hydrogenation are investigated detailedly. The results reveal that the addition of La can improve the dispersion of Rh and increase Rh⁺ centers, which can effectively inhibit the formation of CO₂ and improve the selectivity of oxygenates. Furthermore, the doping mode of La can affect the interaction between La and Rh. A strong La-Rh interaction is achieved over the 2Rh-5La₂O₃/SiO₂ catalyst prepared by co-impregnation of Rh and La with SiO₂ support. The strong interaction between La and Rh can efficiently weaken the Rh-CO bonds and enhance the CO insertion reaction in the reaction process, which makes the product dominated by C₂₊ oxygenates. The 2Rh/5La₂O₃-SiO₂ catalyst prepared via La₂O₃-SiO₂ composite support exhibits a weak La-Rh interaction, and methanol, ethanol and other low-carbon alcohols are obtained as the main products.