Concerted Bimetallic Nanocluster Synthesis and Encapsulation via Induced Zeolite Framework Demetallation for Shape and Substrate Selective Heterogeneous Catalysis

Abstract

Bimetallic nanoparticle encapsulation in microporous zeolite crystals is a promising route for producing catalysts with unprecedented reaction selectivities. Herein, a novel synthetic approach was developed to produce PtZn nanoclusters encapsulated inside zeolite micropores by introducing Pt cations into a zincosilicate framework via ion exchange, and subsequent controlled demetallation and alloying with framework Zn. The resulting zeolites featured nanoclusters with sizes of approximately 1 nm, having an interatomic structure corresponding to a PtZn alloy as confirmed by pair distribution function (PDF) analysis. These materials featured simultaneous shape and substrate specificity demonstrated by the selective production of p-chloroaniline from the competitive hydrogenation of p-chloronitrobenzene and 1,3-dimethyl-5-nitrobenzene.

Recent developments in the control of selectivity in hydrogenation reactions by confined metal functionalities

“…The selective hydrogenation of 4-nitrochlorobenzene was also studied over PtZn x clusters confined in MFI by host-guest assembly method. 51 In a similar fashion as in the previous study, 4-nitrochlorobenzene molecules reached the active sites with the nitro functional group pointing towards the metallic clusters, thus ensuring the selective hydrogenation of nitro functionality without cleaving the C-Cl bond. The importance of Zn species in modulating the selectivity was investigated by running the reaction over monometallic (Pt) and bimetallic (PtZn) catalysts supported on silica; a far higher selectivity was observed for the bimetallic catalyst compared to the mono-metallic one.…”

“…Host-guest assembly. Host-guest assembly allows facile incorporation of metallic cations or complexes into/onto the zeolite by ion-exchange 50,51 or incipient wetness impregnation. 52 While the ion-exchange capacity is highly dependent on the number of countercations per unit cell, the quantity of metal introduced by wetness impregnation is limited by the pore size and volume.…”

Selective steam reforming of n‐dodecane over stable subnanometric NiPt clusters encapsulated in Silicalite‐1 zeolite

“…Encapsulation confers active sites with the ability to contact only certain reactants and products based on their molecular sizes and shapes as shown inFigure 3b. These results further prove that the nickel and platinum particles are encapsulated inside the zeolite crystals instead of located on the crystal surface 1,72. Figures S15-S18 display the relationship of n-dodecane conversion and gas formation rate on reaction temperature over preparedcatalysts after reaction for an hour.…”

“…Encapsulation confers active sites with the ability to contact only certain reactants and products based on their molecular sizes and shapes as shown in Figure 3b. These results further prove that the nickel and platinum particles are encapsulated inside the zeolite crystals instead of located on the crystal surface …”

Ultrafast Encapsulation of Metal Nanoclusters into MFI Zeolite in the Course of Its Crystallization: Catalytic Application for Propane Dehydrogenation

“…[1c, 3] Encapsulation of metal nanoclusters into zeolites enables a synergistic effect in heterogeneous catalysis that combines superior activity of the nanoclusters with high stability and unique shape selectivity of the zeolites. [4] The fabrication of such metal-nanocluster-encapsulated zeolites, however, is not straightforward. Due to high surface free energy of the metal species, they tend to agglomerate and precipitate very fast, in particular, under harsh conditions of zeolite synthesis (e.g., strong alkalinity and high temperature); [5] whereas the crystallization of zeolites typically takes a much longer time.…”