丙烷脱氢PtSn/Al_2O_3催化剂积炭行为研究

通过HRTEM、XRD、FT-IR、Raman、~(13)C NM R、NH_3-TPD、DTG及元素分析等表征手段,研究了丙烷脱氢PtSn催化剂积炭性质及其对催化剂结构的影响,分析了催化剂的积炭失活过程。结果表明,积炭覆盖活性位并堵塞催化剂孔道是催化剂失活主要因素;与新鲜催化剂相比,催化剂积炭完全失活后,Pt颗粒粒径并没有明显变化;完全失活时,XRD谱图出现了无定形石墨炭的衍射峰;随着积炭量的增加,焦的石墨化程度越高,芳构化程度加深,难以消除的炭增多,再生难度加大。提出丙烷在Pt活性位深度脱氢形成积炭并向载体转移的历程,认为更为稳定的C_(24)H_(12)是积炭前驱体。

Study on the coke formation behavior on PtSn/Al2O3 propane dehydrogenation catalyst

The nature and effect of coke formation on PtSn dehydrogenation catalyst were investigated by various technologies, such as HRTEM, XRD, FT-IR, Raman, ¹³C NMR, NH₃-TPD, DTG and ultimate analysis. The deactivation process of the catalyst was also discussed. The results showed that the catalyst deactivation was mainly caused by deposited carbon, which covered active sites and blocked the pores of the catalyst. The diffraction peaks of the amorphous graphite carbon were observed in the XRD patterns of the fully deactivated catalyst. Furthermore, the degree of aromatization and graphitization of coke formed in the catalyst were enhanced. It was difficult to regenerate the deactivated catalyst through coke elimination. It is proposed that the carbon deposit proceeded on the Pt active site by propane deep dehydrogenation and the deposited carbon could transfer to the surface of the support. The coke precursor is probably C₂₄H₁₂ when the coke content was accumulated to a certain degree.