稀土改性MoO3／SiO2催化剂上丙烯的歧化

本文系统考察了镧系14种稀土氧化物对烯烃歧化催化剂MoO_3/SiO_2的影响,发现其中多数均可使催化剂的寿命延长,并以Tb及Pr的效果最佳,其稳定时间可达未改性时的1.6倍。主要原因是稀土添加剂有抑制积炭的能力和缩短催化剂的增活期(为未改性的40％～75％)。通过ESR表征,从本质上阐明了Tb_4O_7的作用在于促进了歧化活性中心——挠动四棱锥结构的Mo~(5 )值的增长。在增活期过程中,活性物种前体的减少服从一级反应力学规律。

STUDY OF PROPENE METATHESIS ON MoO_3/SiO_2 CATALYST PROMOTED BY RARE EARTH OXIDES

The metathesis of propene has been carried out on the MoO_3/SiO_2 catalyst modifiedwith rare earth oxides. In is found that most of the Ln_2O_3 can prolong the life of thecatalysts and shorten the "break-in" period. Among them Tb_4O_7 and Pr_6O_(11) exhibiteda more marked effect. The stable duration of catalyst modified by Tb_4O_7 can be prolongedto approximately 1.6 times as long as that of the unmodified one. The "break-in" periodwas reduced to about 40% to 75%. From the results of the Tb_4O_7. MoO_3/SiO_2 catalyst, itcan be concluded that the role of Tb_4O_7 is in facilitating the formation of the activesurface site, i.e. the distorted square pyramidal Mo~(5 ). The reaction of active sitc formationis in first order with respect to the precurser of the active species.