四氢糠醇合成吡啶催化剂MoO_3-NiO/γ-Al_2O_3的失活和再生

Deactivation and Regeneration Behaviors of MoO_3-NiO/γ-Al_2O_3 for the Synthesis of Pyridine from Tetrahydrofurfuryl Alcohol

采用新鲜的及再生的MoO_3-NiO/γ-Al_2O_3催化剂,催化生物质四氢糠醇合成吡啶,考察其催化性能的差异及催化剂失活的原因,并通过氮气物理吸附测试(BET)、元素分析仪(EA)、场发射扫描电子显微镜(SEM)、场发射透射电子显微镜(TEM)、X射线衍射分析仪(XRD)、激光拉曼光谱仪(LRS)、X射线光电子能谱仪(XPS)、热重分析仪(TG)以及吡啶原位红外吸收光谱仪(PY-IR)对失活催化剂进行表征分析。发现失活催化剂有两种形态的碳,即无定形碳和石墨化碳,催化剂失活的原因不是活性组分的变化或流失,而是由积碳引起的。积碳堵塞了催化剂的孔道和比表面积,并且覆盖了活性组分以及酸性位,降低了活性位点的有效利用率。针对催化失活,尝试了在线燃烧的方法使失活催化剂在空气中再生,发现再生后的催化剂与新鲜催化剂的催化活性基本一致,并且也可以保持50 h内吡啶收率大于80%。

The fresh and regenerated catalysts MoO_3-NiO/γ-Al_2O_3 were applied for the conversion of biomass tetrahydrofurfuryl alcohol( THFA) into pyridine( PY). The differences of catalytic performances between the fresh and regenerated catalysts and the reason of the deactivation behaviors of the catalysts were investigated by nitrogen adsorption,elemental analysis( EA),scanning electron microscope( SEM),transmission electron microscope( TEM),X-ray diffraction analyzer( XRD),Laser Raman spectroscopy( LRS),X-ray photoelectron spectrometer( XPS),thermogravimetric analyzer( TG) and Fourier transformed infrared spectroscopy of chemisorbed pyridine( PY-IR). Characterization of deactivated catalysts identified two types of carbonaceous species deposited on the catalysts,the amorphous carbon and the graphitic carbon. The reason of catalyst deactivation was not caused by the change or loss of active com-ponents,but by the carbon deposition. The pores and surfaces of the deactivation catalysts were blocked by carbon deposition,which resulted in the decline of effective utilization rate of active components and acidic sites. For the catalyst deactivation,online burning method was employed for the regeneration of deactivation catalyst in the air. The activity of the regenerated catalysts could be restored mostly and remained stable in the first 50 h with pyridine yield more than 80% compared with the fresh catalysts.