【作者】 张一卫；

【导师】 周钰明；

【作者基本信息】 东南大学 ， 材料物理与化学， 2006， 博士

【摘要】 以ZSM-5分子筛为载体,分别制得Pt/ZSM-5、PtSn/ZSM-5、PtSnNa/ZSM-和PtSnNaLa/ZSM-5催化剂用于丙烷脱氢制丙烯反应,并利用多种手段对催化剂进行表征。1.确定了Pt/ZSM-5催化剂中的最佳Pt负载量和分子筛的最佳Si/Al比。Pt/ZSM-5催化剂尽管具有较高的初始反应活性,但反应稳定性和产物选择性较差。适量Sn助剂的添加可明显改善Pt/ZSM-5催化剂的丙烷脱氢反应性能,利用比表面积测定、XRD、氢化学吸附、H₂-TPD、TPR、TPO、热重等技术对催化剂的物理结构、Pt金属表面性质、金属-载体之间的相互作用以及催化剂的抗积炭性能进行表征。与PtSn/γ-Al₂O₃催化剂相比,PtSn/ZSM-5催化剂的“容炭”能力强,反应稳定性好。研究了Pt/ZSM-5催化剂的积炭失活历程,推导出该催化剂在反应初期的积炭量随反应时间的幂函数形式的关系式和积炭速率式。2.PtSnNa/ZSM-5催化剂中的最佳Na含量为1.0%。适量Na助剂的添加不仅降低了催化剂中的Br（o|¨）nsted酸中心和Lewis中/强酸中心,而且提高了催化剂表面的Pt金属裸露度,使PtSn/ZSM-5催化剂的金属功能和酸性功能得到较好的匹配。过量Na的添加,增加了催化剂中的Lewis弱酸中心,同时促进了催化剂中Sn组分的还原,不利于丙烷脱氢反应的进行。不同反应条件对PtSnNa/ZSM-5催化剂的丙烷脱氢反应性能影响明显。3. Al₂O₃粘结剂的加入明显提高了PtSnNa/ZSM-5催化剂的机械强度。²⁷Al MAS NMR表明Al₂O₃粘结剂中的部分可溶性Al物种经高温焙烧后可进入ZSM-5分子筛的骨架,从而产生部分中等强度的酸中心。PtSnNa/ZSM-5催化剂中的最佳Al₂O₃粘结剂含量为5%,此时粘结剂的加入明显提高了PtSnNa/ZSM-5催化剂的Pt金属分散度,使催化剂中的金属功能和酸性功能达到较好的匹配。在不同的反应条件下,Al₂O₃粘结剂对PtSnNa/ZSM-5催化剂丙烷脱氢反应性能的影响是不同的。4. PtSnNa/ZSM-5催化剂的最佳焙烧温度为500℃,此时Pt组分与载体及Pt、Sn之间的相互作用得到增强,催化反应的稳定性和丙烯选择性明显提高。继续提高焙烧温度,催化剂的比表面积和孔容降低明显。催化剂的表面酸性降低,Pt颗粒发生不同程度的烧结,不利于丙烷脱氢反应的进行。5.不同条件的水热处理对PtSnNa/ZSM-5催化剂脱铝程度的影响不同。当水热处理温度在更多还原

【Abstract】 Pt/ZSM-5、PtSn/ZSM-5、PtSnNa/ZSM-5 and PtSnNaLa/ZSM-5 catalysts were prepared on ZSM-5 zeolite for propane dehydrogenation and the catalysts were characterized by several techniques.The best Pt content and suitable Si/Al ratio of ZSM-5 zeolite were confirmed on Pt/ZSM-5 catalyst. Although the initial reaction activity of Pt/ZSM-5 catalyst was high, the reaction stability and selectivity to propene were poor. Suitable addition of Sn could improve the catalytic behavior of Pt/ZSM-5 catalyst for propane dehydrogenation obviously. In order to discuss the possible reasons, several techniques including BET surface area, XRD, hydrogen chemisorption, H₂-TPD, TPR, TPO and thermogravimetric analysis were used to get their physical structure, surface character of Pt, interactions between metal and carrier and anti-coking property. Comparing with PtSn/γ-Al₂O₃ catalyst, the capacity to accommodate the coke of PtSn/ZSM-5 catalyst was much better, which resulted in the improved reaction stability. Moreover, the deactivation process of Pt/ZSM-5 catalyst was studied and the formula between the carbon amount and reaction time of Pt/ZSM-5 catalyst at the beginning of reaction and the formula about the coke velocity were obtained.The best content of Na in PtSnNa/ZSM-5 catalyst was 1.0%. In this case, the addition of Na could not only reduce the Br（o|¨）nsted acid sites and moderate/strong Lewis acid sites, but also increase the fraction of bare metallic Pt on the surface of the catalyst, thus making the matching between acid functions and metal functions stand at the best state. However, the excessive addition of Na increased the amount of Lewis acid sites and promoted the reduction of Sn species, which was disadvantageous to the reaction. Different reaction conditions could have obvious impacts on the reaction performance of PtSnNa/ZSM-5 catalyst in the dehydrogenation of propane.The addition of alumina binder in PtSnNa/ZSM-5 catalyst could increase the particle intensity obviously. The results of ²⁷Al MAS NMR indicated that some Al species from the binder could migrate into the zeolite framework in calcination so as to produce some acid sites of moderate intensity. The best content of更多还原