Abstract:

The properties of alumina supports are the key factors affecting the propane dehydrogenation performance of Pt?Sn/γ?Al₂O₃ catalysts.In this paper,γ?Al₂O₃ supports were prepared at three calcination temperatures of 450,650,850 ℃,and the structures and properties of the supports and supported catalysts were systematically studied by XRD,XRF,NH₃?TPD,Py?FTIR, CO?FTIR,OH?FTIR,and other characterization methods.The properties of the propane dehydrogenation reaction were evaluated by a fixed?bed micro?reaction evaluation device with online analysis,and the gas?phase product distribution and coking properties were analyzed.The results show that with the increase in calcination temperature,the surface acid content of γ?Al₂O₃ supports decreases,and calcination at 850 ℃ almost eliminates the weak L acid centers on the surface.This indicates that the number of coordinated unsaturated Al sites on the surface of γ?Al₂O₃ and surface hydroxyl groups decreases as the calcination temperature grows,which is not conducive to the high dispersion of metal active centers.Both CO?FTIR and TEM results confirm the formation of larger Pt clusters on Pt?Sn/γ?Al₂O₃?850,and more Pt active phase structure with saturated coordination can promote the occurrence of side reactions such as deep dehydrogenation and reduce the selectivity of propylene products.

Key words: Alumina, Surface properties, Supported catalyst, Propane Dehydrogenation, Calcination

摘要：

Al₂O₃载体的性质是影响丙烷脱氢Pt?Sn/γ?Al₂O₃催化剂性能的关键因素。采用450、650、850 ℃三种焙烧温度制备了γ?Al₂O₃载体，运用XRD、XRF、NH₃?TPD、Py?FTIR、CO?FTIR、OH?FTIR等表征手段系统研究了载体和其负载型催化剂的结构和性质，使用固定床在线分析微型反应装置评价了丙烷脱氢反应性能，并对气相产物分布和结焦性质进行了分析。结果表明，随着焙烧温度的升高，γ?Al₂O₃载体的表面酸量减少，850 ℃高温焙烧几乎完全消除了表面弱L酸中心，这说明γ?Al₂O₃表面配位不饱和Al位点和表面-OH数量随焙烧温度的升高而减少，这一特征不利于金属活性中心的高度分散；CO?FTIR和TEM表征结果均证实了在Pt?Sn/γ?Al₂O₃?850催化剂上形成了更大的Pt团簇，更多的饱和配位Pt活性相结构会促进深度脱氢等副反应的发生，降低丙烯产物的选择性。

关键词: 氧化铝, 表面性质, 负载型催化剂, 丙烷脱氢, 焙烧