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.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We thank the NSFC program (21506111, 2017YFB0602204) and the CNPC Innovation Foundation (2014D-5006-0506) for their support. National Supercomputing Center in Shenzhen (Shenzhen Cloud Computing Center) was acknowledged for providing software package.