We report the direct characterization of coke information in the clearly resolved (0 1 0) and (1 0 0) planes of various anisotropic MFI zeolites using EELS techniques, in a model reaction of methanol to hydrocarbons. For the first time, we found that the main coke species varied between different planes and depended on the crystal structure. The coke species was graphite carbon and polyaromatic hydrocarbon over MFI nanosheets and MFI with b-axis length 60 nm, respectively. The diffusion of aromatics out of conventional MFI zeolites was found only through the straight channels, while small molecules randomly diffused through both channels, resulting in different coke deposition on the (0 1 0) plane and the (1 0 0) plane from different precursors. As all product molecules diffused only through the straight channels, the MFI nanosheet showed a distinct crystal-plane selective effect of coke deposition, in contrast to nearly uniform coke distribution throughout the entire external surface for conventional zeolites. This anisotropic diffusion behavior influenced the gaseous and liquid products significantly, providing deep insight into the MFI catalyst for the selective control of products via crystal structure.

我们报告了在使用甲醇对碳氢化合物进行模型反应的过程中，使用EELS技术在各种各向异性MFI沸石的清晰分辨的（0 1 0）和（1 0 0）平面中焦炭信息的直接表征。我们首次发现主要焦炭种类在不同平面之间变化，并取决于晶体结构。焦炭种类是MFI纳米片上的石墨碳和聚芳烃以及带有b的MFI轴长度分别为60 nm。仅通过直通道发现芳烃从常规MFI沸石中扩散出来，而小分子通过两个通道随机扩散，导致不同前体在（0 1 0）平面和（1 0 0）平面上沉积出不同的焦炭。由于所有产物分子仅通过直通道扩散，因此MFI纳米片显示出焦炭沉积的独特晶面选择性效应，这与常规沸石在整个外表面上几乎均匀的焦炭分布形成鲜明对比。这种各向异性的扩散行为极大地影响了气态和液态产品，为通过晶体结构选择性控制产品的MFI催化剂提供了深刻的见识。