The addition of Triton X-100 slows down the crystallization rate of TS-1, while the rota-crystallization accelerates the incorporation rate of Ti.

A facile strategy affording high-quality single-crystalline MFI-type nanozeolites (10–55 nm) with hexagonal prism morphology, good monodispersity, high crystallinity, and high product yield (above 97%) has been developed. This is achieved by synergistically using an l-lysine-assisted approach and a two-step crystallization process in a concentrated gel system (H2O/Si = 9). The morphological evolution of nanosized silicalite-1 is monitored by high-resolution transmission electron microscopy (HRTEM). In this process, metastable irregular nanoparticles are initially obtained at 80 °C as the first step. Consequently, a rearrangement in morphology toward equilibrium crystal shape and without excessive growth for the metastable nanoparticles occurs at 170 °C as the second step. Throughout the whole process, l-lysine acts as an inhibitor to effectively limit the crystal growth of zeolites. Thanks to the high-quality nanosized crystals, the as-prepared ZSM-5 catalysts exhibit superior performance in methanol-to-propylene (MTP) reactions, which deliver a prolonged lifetime of 54 h with a total light olefin selectivity of 74% and a high propylene selectivity of 49% at 470 °C at a high methanol weight hourly space velocity (WHSV) of 7.2 h–1. This synthetic route provides a general strategy for preparing other types of zeolites with good monodispersity, nanosize, high yield, and high crystallinity.

The incorporation of secondary metal ions into Cuexchanged SSZ-13 zeolites could improve their catalytic properties in selective catalytic reduction of NO x with ammonia (NH 3 -SCR), but their essential roles remain unclear at the molecular level. Herein, a series of Cu-Sm-SSZ-13 zeolites have been prepared by ion-exchanging Sm ions followed by Cu ions, which exhibit superior NH 3 -SCR performance. The NO conversion of Cu-Sm-SSZ-13 is nearly 10% higher than that of conventional Cu-SSZ-13 (175−250 °C) after hydrothermal ageing, showing an enhanced low-temperature activity. The Sm ions are found to occupy the sixmembered rings (6MRs) of SSZ-13 by X-ray diffraction Rietveld refinement and aberration-corrected scanning transmission electron microscopy. The Sm ions at 6MRs can facilitate the formation of more active [ZCu 2+ (OH)] + ions at 8MRs, as revealed by temperature-programmed reduction of hydrogen. X-ray photoelectron spectroscopy and density functional theory (DFT) calculations indicate that there exists electron transfer from Sm 3+ to [ZCu 2+ (OH)] + ions, which promotes the activity of [ZCu 2+ (OH)] + ions by decreasing the activation energy of the formation of intermediates (NH 4 NO 2 and H 2 NNO). Meanwhile, the electrostatic interaction between Sm 3+ and [ZCu 2+ (OH)] + results in a highreaction energy barrier for transforming [ZCu 2+ (OH)] + ions into inactive CuO x species, thus enhancing the stability of [ZCu 2+ (OH)] + ions. The influence of the ion-exchanging sequence of Sm and Cu ions into SSZ-13 is further investigated by combining both experiments and theoretical calculations. This work provides a mechanistic insight of secondary ions in regulating the distribution, activity, and stability of Cu active sites, which is helpful for the design of high-performance Cu-SSZ-13 catalysts for the NH 3 -SCR reaction.

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