Mercaptoamine‐assisted Post‐encapsulation of Metal Nanoparticles within Preformed Zeolites and their Analogues for Hydroisomerization and Methane Decomposition

Abstract

We report a general synthetic strategy for post-encapsulation of metal nanoparticles within preformed zeolites using post-synthetic modification. Both anionic and cationic precursors to metal nanoparticle are supported on 8-and 10membered ring zeolites and analogues during wet impregnation using 2-aminoethanethiol (AET) as a bi-grafting agent. Thiol groups are coordinated to metal centers, whereas amine moieties are dynamically attached to micropore walls via acid-base interactions. The dynamic acid-base interactions cause the even distribution of the metal-AET complex throughout the zeolite matrix. These processes encapsulate Au, Rh, and Ni precursors within the CHA, *MRE, MFI zeolite, and SAPO-34 zeolite analogues, for which small channel apertures preclude the post-synthesis impregnation of metal precursors. Sequential activation forms small and uniform nanoparticles (1-2.5 nm in diameter), as confirmed through electron microscopy and X-ray absorption spectroscopy. Containment within the small micropores protected the nanoparticles against harsh thermal sintering conditions and prevented the fouling of the metal surface by coke, thus resulting in a high catalytic performance in n-dodecane hydroisomerization and methane decomposition. The remarkable specificity of the thiol to metal precursors and the dynamic acid-base interaction make these protocols extendable to various metal-zeolite systems, suitable for shape-selective catalysts in challenging chemical environments.

Promoting Catalytic Performance Involving Hydrogen Spillover by Ion Exchange of Pt@A Catalysts to Regulate Reactant Adsorption

“…Transition metal nanocatalysts are widely used in hydrogenation of various unsaturated functional groups, such as alkenyl, alkynyl, phenyl, nitro, carbonyl, aldehyde, and cyanogen groups. − Nanosized metal catalysts, however, are prone to suffer from aggregation, coking, and poisoning, which lead to deactivation at high temperatures or after long-term reactions . Confining transition metal sites into microporous materials such as zeolites (metal@zeolite) can avoid metal sintering and poisoning to improve catalyst lifetime. − Moreover, the unique pore sizes of different zeolites make shape-selectivity of reactants. − In some cases, substrate molecules which have larger sizes than the zeolite pores cannot enter zeolite pores and hence have no opportunity to make contact with the active sites inside zeolites. For instance, in hydrogenation of aromatics, H 2 molecules with a kinetic diameter of 0.28 nm can diffuse into zeolite micropores as small as six-membered rings (0.28 nm × 0.28 nm) of sodalite (SOD) cages to reach metal sites encapsulated in zeolite channels, while benzene rings (0.53 nm) cannot pass through micropores smaller than MFI zeolite channels (0.56 nm × 0.53 nm) such as linde type A (LTA) zeolite pores (0.3–0.5 nm). , Nevertheless, activated H 2 molecules adsorbed on metal sites yield dissociated H atoms, which can migrate by a hydrogen spillover process to the zeolite surface where the adsorbed reactants can be hydrogenated without reaching metal sites inside micropores directly .…”