Scheme 1 . Synthetic Strategy for Fe immobilized hierarchical single-crystalline MEL zeolites.
and P-MEL@Fe in the region of 3~4.5 nm, which were attributed to the formation of mesoporous. The above TEM images, N2 adsorption data combined with textural properties of zeolites (Table S2) verified that the H-MEL-31 and H-MEL@Fe-xzeolites encompassed a significant amount of mesoporosity, possibly arising from the orientated crystal transformation process:i) the silica source (TEOS) and template (TBAOH) assembled with Ferric citrate through the electrostatic and dispersion interactions between zeolite precursor and solvated ligand-stabilized Fe species22, inducing the formation of Fe containing silicate-2; ii) these Fe containing silicate-2 underwent the targeted corrosion towards silicon extraction by interactions between Si–OH groups on the surface of silicate-2 and TBA+, resulting in the generation of voids in the silicate-232. Simultaneously, the Fe containing silicate-2 finished crystal transformation via directional control of crystallization process combined with leached silicate oligomers and additional aluminum isopropoxide species, guiding the formation of acid-redox co-functionalized single crystalline mesoporous MEL zeolites, as schematically illustrated in Scheme 1. These mesopores were enclosed by a series of low-index facets like [011] and [010] as clearly observed in HRTEM images from an “edge-on” projection (Fig. 2b and 2c). After correcting the defocus effects (Fig. 2d), The HRTEM images of the crystalline pore walls also well matched the simulated projected potential and structural projections of a MEL zeolite along the [100] direction.