Molybdenum supported on zeolite HZSM-5 is the most studied catalyst for methane dehydroaromatization. However, the nature of its catalytic sites and their deactivation mechanisms remain unclear and controversial. Here, we report further insights into this system: first, the crystal size of HZSM-5 determines the form and location of the catalytic active MoC_x species, and thus the catalyst performance; second, MoC_x sites are preferentially deactivated over acid sites, when supported on nano-sized HZSM-5; third, MoC_x particles that are traditionally considered detrimental to the reaction can serve as active sites, if they are properly protected from coke deposition. These findings lead us to develop an “encapsulation” strategy, which reconciles the deactivation rates of the MoC_x and acid sites, enabling a full utilization of both sites, and consequently leading to a 10-fold increase in catalyst lifetime. Encapsulation also allows us to design experiments to confirm the catalytic role of the acid sites.

负载在沸石HZSM-5上的钼是甲烷脱氢芳构化研究最多的催化剂。然而，其催化位点的性质及其失活机理仍不清楚和有争议。在这里，我们报告了对该系统的进一步见解：首先，HZSM-5的晶体尺寸决定了催化活性MoC _x物种的形式和位置，从而决定了催化剂的性能；其次，当被纳米级HZSM-5所支持时，MoC _x位点比酸性位点优先失活。第三，MoC _x如果适当地保护它们免受焦炭沉积，传统上被认为对反应有害的颗粒可以用作活性位点。这些发现使我们开发出一种“包封”策略，该策略可以协调MoC _x和酸性位点的失活速率，使两个位点都能得到充分利用，从而使催化剂寿命延长10倍。包封还允许我们设计实验以确认酸性位点的催化作用。