中空胶囊Mo/HZSM-5催化甲烷无氧芳构化的积炭研究

Coke Mechanism of Hollow Capsule Mo/HZSM-5 During Methane Dehydroaromatization

【目的】甲烷无氧芳构化反应是天然气化工领域的一个前沿研究课题。【方法】采用浸渍法制备Mo/商用HZSM-5、Mo/纳米HZSM-5和Mo/中空胶囊HZSM-5催化剂。采用ICP、XRD、N2物理吸附、SEM、TEM、NH_(3)-TPD和XPS表征技术研究了三种Mo基分子筛的物化性质,并考察其甲烷无氧芳构化性能。采用TG和TPO手段定性和定量分析了三种催化剂的积炭分布情况。通过周期^(12)CH_(4)/^(13)CH_(4)同位素切换脉冲技术追踪甲烷芳构化过程中Mo/中空胶囊HZSM-5上的碳循环路径。【结果】催化剂孔道内活性碳物种会参与到苯的形成中。Mo/中空胶囊HZSM-5催化剂具有较高的CH_(4)转化率和芳烃收率,以及良好的催化寿命。Mo/纳米HZSM-5和Mo/中空胶囊HZSM-5的分子筛晶粒尺寸和酸强度相近,而Mo/中空胶囊HZSM-5的失活速率最小,这可能归因于中空胶囊结构中反应物和产物传质更快。

【Purposes】Methane dehydroaromatization(MDA)is a frontier topic in the field of natural gas chemical industry.【Methods】Mo/commercial-HZSM-5,Mo/nano-HZSM-5,and Mo/hollow capsule HZSM-5 were synthesized by using a conventional wet impregnation strategy.The samples were characterized by ICP,XRD,BET,SEM,TEM,NH_(3)-TPD,and XPS,and tested in MDA reaction.The properties of carbonaceous species were measured by TG and TPO techniques.The carbon cycle path was investigated through periodic^(12)CH_(4)/^(13)CH_(4)isotope switch pulse experiment over Mo/hollow capsule HZSM-5 catalyst during MDA reaction.【Findings】The active carbonaceous species located inside the pores could take part in the formation of ben-zene.Among these three Mo-based catalysts,the Mo/hollow capsule HZSM-5 showed higher CH_(4)conversion and aromatic yield,as well as superior catalytic lifespan.Compared to Mo/nano-HZSM-5 in zeolite particle size and acidity,Mo/hollow capsule HZSM-5 with lower deactivation rate is attributed enhanced gas molecules diffusion in its hollow capsule structure.