积碳对MCM-22分子筛催化剂上1-丁烯骨架异构化反应的影响

Coke-Deposition on MCM-22 Molecular Sieve Catalyst During Isomerization of 1-Butene

采用氨程序升温脱附、热重-差热分析、气相色谱-质谱、元素分析、氮吸附及扫描电镜对1-丁烯骨架异构化反应中 MCM-22分子筛催化剂(简称催化剂)表面的积碳进行了表征和分析。结合催化剂活性的变化,对积碳的种类、位置、影响因素以及积碳对反应机理的影响进行了探讨。分析结果表明,适量的积碳有益于改进催化剂的催化性能,催化剂的酸中心强度、浓度和孔结构对积碳的形成均有很大的影响。反应初期积碳主要在催化剂的外表面形成,并导致外表面的大量酸中心被覆盖,而后在其内表面缓慢积碳。在反应过程中,催化剂表面形成的脂肪烃类积碳逐渐向不饱和的芳香烃类积碳转变。1-丁烯骨架异构化反应主要通过单分子机理进行。

Coke-deposition on external surface of MCM-22 molecular sieve catalyst, formed during isomerization of 1-butene to isobutene, was characterized by means of NH3-TPD, TG-DTA, GC-MS, elementary analysis, N2 adsorption and SEM. Influences of types and location of coke-deposition on performance of MCM-22 molecular sieve catalysts were studied in detail. Suitable amount of coke-deposition could＇ improve activity of MCM-22 molecular sieve catalyst. Pore structure and acidity of MCM-22 molecular sieves played important roles in isomerization. Coke-deposition of aliphatic hydrocarbon type formed first on surface of MCM-22 molecular sieves and then gradually transited to polyaromatics during reaction. Coke-deposition first occurred on acidic sites on external surface of catalysts, covered the surface acid sites, and then formed gradually on acidic sites on surface of internal pores of MCM-22 molecular sieves along with reaction time. The skeletal isomerization of 1-butene mainly carried out via mono-molecular mechanism.