Modulating inherent lewis acidity at the intergrowth interface of mortise-tenon zeolite catalyst

Abstract

The acid sites of zeolite are important local structures to control the products in the chemical conversion. However, it remains a great challenge to precisely design the structures of acid sites, since there are still lack the controllable methods to generate and identify them with a high resolution. Here, we use the lattice mismatch of the intergrown zeolite to enrich the inherent Lewis acid sites (LASs) at the interface of a mortise-tenon ZSM-5 catalyst (ZSM-5-MT) with a 90° intergrowth structure. ZSM-5-MT is formed by two perpendicular blocks that are atomically resolved by integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM). It can be revealed by various methods that novel framework-associated Al (AlFR) LASs are generated in ZSM-5-MT. Combining the iDPC-STEM results with other characterizations, we demonstrate that the partial missing of O atoms at interfaces results in the formation of inherent AlFR LASs in ZSM-5-MT. As a result, the ZSM-5-MT catalyst shows a higher selectivity of propylene and butene than the single-crystal ZSM-5 in the steady conversion of methanol. These results provide an efficient strategy to design the Lewis acidity in zeolite catalysts for tailored functions via interface engineering.

Atomic Imaging of Zeolites and Confined Single Molecules by iDPC-STEM

“…By comparing the intensities of these O atom columns in different areas, the defects which brought by the formation of local lattice mismatch can be quantified. 63 Introducing heteroatoms into zeolite frameworks or pore channels, thereby regulating their transportation performance, reaction activity, or introducing new active sites, is also a very important method in the field of zeolite applications. 87−89 Direct observation of heteroatoms in the zeolite structure by using iDPC-STEM imaging is an ideal way to understand such catalysts.…”

“…And the intensities of the O peaks can semiquantitatively reflect the number of atoms in these columns, thereby identifying defects. By comparing the intensities of these O atom columns in different areas, the defects which brought by the formation of local lattice mismatch can be quantified …”

“…85,86 In terms of ZSM-5, it can form an intergrown structure by rotating the crystallographic axes a and b by 90°around common c in space and connecting straight and sinusoidal channels as shown in Figure 5a. 63 And this structure is also called mortise−tenon architecture. Splicing two such units into one zeolite crystal will inevitably result in large interfaces.…”

“…Next, successful demonstrations on a few industrially important zeolites are introduced to show the powerful capability of iDPC-STEM in imaging local structures at the atomic scale, including surfaces, interfaces, defects, loaded and confined metal clusters, and even isolated metal motifs. So far, iDPC-STEM has proven to be able to realize direct imaging of zeolite materials in real space under ultralow-electron-dose conditions, which provides intuitive information for determining the detailed structural information on nanoporous materials, and has been widely used in atomic imaging of zeolite frameworks, analysis of local structures, and determination of confined or incorporated metal atom positions. ,,− …”

Copper-Based Sorbents and Catalysts for Elemental Mercury Removal from Gas Stream: A Review

“…Natural clay benefits from low cost and Earth abundance, nonetheless, it often suffers from very small specific surface area . Thus, zeolite with much bigger specific surface area has gained more research attention in catalysis and gas adsorption. − Fan et al developed a Cu/HZSM-5 catalyst for concurrent removal of Hg 0 and NO. Cu/HZSM-5 distinctly outperformed bare HZSM-5.…”