Synthesis and Catalytic Properties of Metal Clusters Encapsulated within Small-Pore (SOD, GIS, ANA) Zeolites

Abstract

The synthesis protocols for encapsulation of metal clusters reported here expand the diversity in catalytic chemistries made possible by the ability of microporous solids to select reactants, transition states, and products on the basis of their molecular size. We report a synthesis strategy for the encapsulation of noble metals and their oxides within SOD (Sodalite, 0.28 nm × 0.28 nm), GIS (Gismondine, 0.45 nm × 0.31 nm), and ANA (Analcime, 0.42 nm × 0.16 nm) zeolites. Encapsulation was achieved via direct hydrothermal synthesis for SOD and GIS using metal precursors stabilized by ammonia or organic amine ligands, which prevent their decomposition or precipitation as colloidal hydroxides at the conditions of hydrothermal synthesis (<380 K) and favor interactions between metal precursors and incipient aluminosilicate nuclei during self-assembly of microporous frameworks. The synthesis of ANA requires higher crystallization temperatures (~415 K) and high pH (>12), thereby causing precipitation of even ligand-stabilized metal precursors as hydroxides. As a result, encapsulation was achieved by the recrystallization of metal clusters containing GIS into ANA, which retained these metal clusters within voids throughout the GIS-ANA transformation.

Maximizing the catalytic function of hydrogen spillover in platinum-encapsulated aluminosilicates with controlled nanostructures

“…The Pt/NaA-n samples showed the chemisorption values somewhat smaller than 1.0 (0.52o H/Pt or CO/Pt o0.67). This can be explained by the limited access of H 2 and CO to the Pt clusters tightly fitted in the small-pore zeolite structure 7,20 .…”

Immobilized Ru Clusters in Nanosized Mesoporous Zirconium Silica for the Aqueous Hydrogenation of Furan Derivatives at Room Temperature

“…This confinement allows metal clusters to activate reactants with small molecular sizes that are accessible to the pores. [3] Mesoporous silica provides an ideal support, owing to its large pore diameters, which are suitable for large-sized organic substrates and biomass derivatives.[4] Ligand-stabilized metal precursors are usually used to anchor the clusters within the mesoporous channel with a low loading of the metal.[5] Uniform mesoporous-silica-supported noble-metal clusters cannot be achieved by impregnation of the support in an aqueous solution of the metal salts because the pore diameter of mesoporous silica (> 2 nm) is larger than the size of the metal clusters. The metal clusters are easily grown into big particles with a broad size distribution.…”

“…This confinement allows metal clusters to activate reactants with small molecular sizes that are accessible to the pores. [3] Mesoporous silica provides an ideal support, owing to its large pore diameters, which are suitable for large-sized organic substrates and biomass derivatives.…”

“…This confinement allows metal clusters to activate reactants with small molecular sizes that are accessible to the pores. [3] Mesoporous silica provides an ideal support, owing to its large pore diameters, which are suitable for large-sized organic substrates and biomass derivatives. [4] Ligand-stabilized metal precursors are usually used to anchor the clusters within the mesoporous channel with a low loading of the metal.…”

Solventless green synthesis of sodalite zeolite using diatomite as silica source by a microwave heating technique

“…Sodalite is a type of zeolite having ultra-micropore size and is commonly used as a heterogeneous basic catalyst in specialty and fine chemical production, which is generally prepared by hydrothermal synthesis under autogenous pressure [3][4][5][6]. However, this hydrothermal route has several disadvantages.…”