HZSM-5分子筛在甲醇制丙烯反应中的失活与再生

Deactivation and Regeneration of HZSM-5 Zeolite in Methanol-to-Propylene Reaction

研究了甲醇制丙烯(MTP)催化剂经过多周期反应后失活的本质原因,据此提出了一种简便易行的催化剂再生方法,即二次晶化法,并将其应用到失活MTP催化剂的再生中。采用X射线衍射(XRD)、X射线荧光光谱(XRF)、X射线光电子能谱(XPS)、N_2吸附、^(27)Al魔角旋转固体核磁共振(^(27)Al MAS NMR)、NH_3程序升温脱附(NH_3-TPD)、吡啶吸附红外(Py-IR)光谱等测试技术对再生前后HZSM-5分子筛催化剂的晶体结构、硅铝比、织构性质、酸性质等进行了表征。并在常压(甲醇分压为30 k Pa)、反应温度为470°C、甲醇质量空速(WHSV)为1 h^(-1)的条件下,研究了再生前后HZSM-5分子筛催化剂的催化性能。结果表明,分子筛晶体结构被破坏、活性位流失是多周期反应后HZSM-5分子筛催化剂活性下降的主要原因。经过二次晶化再生后,催化剂的相对结晶度、比表面积、孔容和酸量都明显提高,晶体结构和活性位得到了有效修复,再生催化剂在MTP反应中重新表现出优异的甲醇转化能力和丙烯选择性。

The cause of the deactivation of a methanol-to-propylene（MTP） catalyst after multiple reaction cycles was studied. On this basis, a facile and effective approach, i.e., secondary crystallization, was proposed and applied to the regeneration of the catalyst. The HZSM-5 zeolite catalysts before and after regeneration were characterized by a series of techniques, including powder X-ray diffraction（XRD）, X-ray fluorescence（XRF）,X-ray photoelectron spectroscopy（XPS）, N2 adsorption,^（27）Al magic-angle spinning nuclear magnetic resonance（^（27）Al MAS NMR）, temperature-programmed desorption of ammonia（NH3-TPD）, and infrared spectroscopy of adsorbed pyridine（Py-IR）. The physicochemical properties, such as framework, silica/alumina ratio, texture,and acidity, of the deactivated catalysts and the regenerated ones were investigated in detail. The catalytic performance of the zeolites in MTP conversion was tested under operating conditions of T = 470 ℃ p = 0.1MPa（pMe OH= 30 k Pa） and weight hourly space velocity（WHSV） = 1 h-1. The collapse of the zeolite structure and loss of active sites were found to be the essential reasons for the decline in catalyst activity after multiple reaction cycles. By regeneration via secondary crystallization, the relative crystallization, specific surface area, pore volume and acidity of the HZSM- 5 catalyst were increased prominently. Meanwhile, the destroyed crystal structure and acid sites of the deactivated catalyst were restored effectively. Thus, the regenerated catalyst again exhibited excellent methanol conversion capacity and propylene selectivity in the MTP reaction.