Designing Hierarchically b-Axis Shortening for Enhanced Diffusion and Coke Accommodation in Efficient Methanol to Olefins
Enhancing light olefin selectivity and extending catalytic durability remain critical challenges for ZSM-5 zeolites in methanol-to-olefins (MTO) conversion, primarily due to inherent diffusion restrictions along the MFI b-axis and poor coke accommodation. Here, we report a hierarchically single-crystalline ZSM-5 sheet architecture featuring interconnected multiscale porosity and a remarkably reduced b-axis thickness (<50 nm), quantitatively verified by three-dimensional electron tomography. Real-time confocal laser scanning microscopy tracking demonstrated significantly enhanced molecular diffusivity compared to conventional micron-sized ZSM-5 (Micro-ZSM-5). This engineered structure distributes abundant aluminum sites on highly accessible diffusion pathways, achieving an enlarged coke accommodation of 16.31 wt% with a coke deposition rate of 0.59 mg g−1 h−1, only one third of that in Micro-ZSM-5. In continuous MTO operation, the hierarchical ZSM-5 sheet (Hier-ZSM-5-S) maintained an average ethylene and propene selectivity of 63.5% for 22.2 hours (WHSV = 3.6 h−1, T = 480°C), which was 19% higher and 6.5 times longer than Micro-ZSM-5, respectively. This hierarchically shortened b-axis structure establishes a generalizable paradigm for enhanced diffusion and coke accommodation in precisely designed pore systems, applicable to various reactions.