The effect of coke distribution (external versus internal coke) on the deactivation behavior was investigated in methane dehydroaromatization (MDA) using benchmark metal-modified HZSM-5 catalysts. A hollow HZSM-5 capsule zeolite (HC) was facilely prepared by a one-step hydrothermal strategy with the assistance of Na₂EDTA and n-butylamine, and a commercial HZSM-5 (CZ) with a similar Si/Al molar ratio was used as a reference support. Four catalysts (Mo/HC, W/HC, Mo/CZ, and W/CZ) were synthesized via an incipient wetness impregnation method, and tested in the MDA reaction. The properties of coke species were characterized by means of the TG, TPO, HRTEM, and UV-Raman techniques, and different locations of coking over the spent catalysts were obtained. The results showed that external coke can give rise to a more severe deactivation than internal coke owing to the blockage of the pore mouths with external coke that decreased the diffusion length of feed gas in the zeolite channels. This phenomenon could be explained by the excellent catalytic stability over the hollow Mo/HZSM-5 capsule catalyst during the MDA reaction, which is associated with the lower external coke formation rate. Finally, the evolution of Mo species and coke species over the coked Mo/HC catalyst was determined by in situ UV-Raman spectroscopy during the TPO process, and the regeneration by O₂ was conducted for the hollow Mo/HZSM-5 capsule catalyst.

中文翻译：

---

焦炭分布决定了中空Mo / HZSM-5胶囊催化剂在CH ₄脱氢芳构化中的寿命†

使用基准金属改性的HZSM-5催化剂，在甲烷脱氢芳构化（MDA）中研究了焦炭分布（外部焦炭与内部焦炭）对失活行为的影响。在Na ₂ EDTA和正丁胺的帮助下，通过一步水热法轻松制备了空心HZSM-5胶囊型沸石（HC），而Si / Al摩尔比相似的商用HZSM-5（CZ）为用作参考支持。通过以下方法合成了四种催化剂（Mo / HC，W / HC，Mo / CZ和W / CZ）一种初期湿润浸渍方法，并在MDA反应中进行了测试。通过TG，TPO，HRTEM和UV-Raman技术表征了焦炭的性质，并获得了在废催化剂上焦化的不同位置。结果表明，由于内部焦炭堵塞了孔口，减少了沸石通道中原料气的扩散长度，外部焦炭比内部焦炭的失活更为严重。这种现象可以通过在MDA反应期间对空心Mo / HZSM-5胶囊催化剂的出色催化稳定性来解释，这与较低的外部焦炭生成速率有关。最后，通过原位测定了焦化Mo / HC催化剂上Mo种类和焦炭种类的演变。在TPO过程中进行UV-拉曼光谱分析，并用O ₂对中空的Mo / HZSM-5胶囊催化剂进行再生。