Enhanced Catalytic Performance through In Situ Encapsulation of Ultrafine Ru Clusters within a High-Aluminum Zeolite

Abstract

Zeolite-encapsulated metal clusters have been shown to be an effective bifunctional catalyst for tandem catalysis. Nevertheless, the efficient encapsulation of nanometric metal species into a high-aluminum ZSM-5 zeolite still poses a significant challenge. In this contribution, we have prepared well-dispersed and ultra-small Ru clusters encapsulated within a high-aluminum ZSM-5 zeolite (with a Si/Al ratio of ∼30–40) via an in situ two-stage hydrothermal synthesis method. Small Ru clusters with an average size of ∼1 nm have been identified by scanning transmission electron microscopy and hydrogen chemisorption. Shape-selective hydrogenation experiments with different probe molecules reveal a predominant encapsulation (∼90%) of metal clusters within the MFI zeolite cavities, which significantly enhances thermal stability of metal clusters against sintering. 27Al magic angle spinning nuclear magnetic resonance and Brønsted acid site (BAS) titration experiments show the successful incorporation of aluminum species (>99%) into the zeolite framework and build-up of intimacy between the Ru clusters and BASs at a sub-nanometric level. The resulting Ru@H-ZSM-5 shows an enhanced activity and stability for the crucial hydrodeoxygenation (HDO) of phenol to cyclohexane, in biomass valorization. This synthesis strategy could be of great help for the rational design and development of zeolitic bifunctional catalysts and could be extended to other crystalline porous materials.

Highly Efficient Decarboxylation of L-Lysine to Cadaverine Catalyzed by RuO2 Encapsulated in FAU Zeolite

“…with FAU, RuO2@FAU exhibited an obvious decrease in the micropore volume from 0.217 to 0.177 cm 3 •g −1 and surface area from 506 to 424 m 2 •g −1 (Table 1). It indicated that ruthenium particles were successfully encapsulated into FAU cages [19]. The hydrogen temperature-programmed reduction result of RuO2@FAU was given in Figure 1C.…”

“…RuO 2 clusters have been successfully encapsulated in LTA (8 MR) for methanol oxidation [16], in MFI (10 MR) for phenol hydrodeoxygenation [17] and in FAU (12 MR) for aerobic alcohol oxidation [18]. Yang et al [19] found that metal-acid intimacy played an essential role in enhancing the production of cyclohexane. Particularly, few works have been reported on the application of encapsulated RuO 2 clusters in the decarboxylation of L-lysine.…”

Influence of Brønsted acid sites on the product distribution in the hydrodeoxygenation of methyl laurate over supported Ru catalysts

“…kinds of CO adsorption at 2090, 1994-2011, and 1890 cm −1 , which is attributed to multi-coordinated Ru n+ −CO, linear Ru 0 −CO, and bridging Ru 0 −CO species, respectively. [34][35][36] The main adsorption is linear Ru 0 −CO, and it showed a blue shift on Ru/H-Z5 (1997-2011 cm −1 ) compared with that on Ru/SiO 2 and Ru/Al 2 O 3 (1994 cm −1 ). The relatively high transition energy of adsorbed CO species on Ru/H-Z5 resulted from the strong interaction between Ru and H-Z5, which caused an electron-deficient Ru metal as the electron of Ru was extracted by H-Z5 with more Brønsted acid sites, and consequently induced a larger blue shift of CO adsorption on the catalyst.…”

Zeolite confinement-catalyzed cleavage of C–O/C–C bonds in biomass

“…The greater number of OSDAs could interact strongly with metal precursors, hindering the successful construction of the zeolite structure. It is gratifying that a two-step hydrothermal synthesis method of low-temperature nucleation and high-temperature crystallization was used, and metal precursors were added after nucleation to successfully achieve the encapsulation of ultrasmall Ru clusters in high aluminum ZSM-5 (Si/Al = 30–40) 85 (Fig. 9a).…”

“…85 27 Al MAS NMR spectra of (b) H-ZSM-5, (c) Ru/ H-ZSM-5-IP and (d) Ru@H-ZSM-5. 85 (e) Content distribution of different Al species for different samples. 85 able catalyst sources.…”