炭黑颗粒及氟粒子辅助法合成多级结构MCM-22分子筛及其催化性能

以碳黑为第二模板剂在氟离子体系中一步水热合成了多级结构MCM-22分子筛组装体（简称为MCM-22-FC）。考察了碳黑和氟离子对MCM-22分子筛形貌和催化性能的影响。MCM-22-FC分子筛是由大量片状晶体交错生长形成的组装体结构，其中MCM-22的片层结构更薄，在其固有的微孔中存在的晶间孔呈现大孔和介孔的特征。MCM-22-FC负载Mo后得到的Mo/MCM-22-FC催化剂在甲烷无氧芳构化反应（MDA）中提高了苯收率和芳烃选择性，并且提高了催化剂的寿命。通过氨气程序升温脱附（NH₃-TPD）表征，吡啶红外（Py-IR）表征，结合热重（TG）分析，得出的结论是Mo/MCM-22-FC在MDA中优越的催化性能是由于氟离子进入到分子筛骨架当中，形成具有拉电子效应的结构单元，从而提高了分子筛的Brönsted酸量，较多的Brönsted酸性位将更多的Mo物种迁移至分子筛孔道内部，形成更多的MoC_x或MoO_xC_y活性物种以及更有利于大分子产物扩散的MCM-22薄片层的结构。少量过剩的Brönsted酸性位在成型后保留在Mo/HMCM-22-FC催化剂活性中心抑制了积碳的形成，也有助于改善芳烃的选择性。

Synthesis and catalytic performance of hierarchical MCM-22 zeolite aggregates with the assistance of carbon particles and fluoride ions

Hierarchical MCM-22 zeolite aggregates (MCM-22-FC) were prepared by one-pot hydrothermal synthesis with the assistance of carbon particles and fluoride ions. The effects of carbon particles and fluoride ions on the morphology and catalytic properties of the MCM-22 zeolite were investigated. The hierarchical MCM-22-FC zeolite aggregates were constructed by intergrown and stacked thin MCM-22 lamellas and possessed macro-/mesopores and inherent micropores. The MCM-22-FC zeolite was modified to form the Mo/MCM-22-FC catalyst, which exhibited an improved benzene yield and aromatic selectivity as well as catalyst life in the methane dehydroaromatization (MDA) reaction. Based on NH₃-TPD and pyridine-Fourier transform infrared spectroscopy measurements together with thermogravimetric analysis, we found that the improved MDA catalytic performance of Mo/MCM-22-FC resulted from the formation of more active MoC_x or MoO_xC_y species that evolved from increased amounts of Brönsted acids with the assistance of fluoride ions. This promoted the diffusion of large molecule products because of the thin MCM-22 lamellas. Less excess Brönsted acid sites were retained in the Mo/HMCM-22-FC catalyst because the formation of active centers inhibited the formation of coke, which contributed to its improved aromatic selectivity.