Abstract
Taking advantage of the synergetic effect of confined ultrasmall metal clusters and zeolite frameworks is an efficient strategy for improving the catalytic performance of metal nanocatalysts. Herein, it is demonstrated that the synergetic effect of ultrasmall ruthenium (Ru) clusters and intrinsic Brønsted acidity of zeolite frameworks can significantly promote the hydrogen generation of ammonia borane (AB) hydrolysis. Ultrasmall Ru clusters are embedded onto the silicoaluminophosphate SAPO‐34 (CHA) and various aluminosilicate zeolites (MFI, *BEA, and FAU) with tunable acidities by a facile incipient wetness impregnation method. Evidenced by high‐resolution scanning transmission electron microscopy, the sub‐nanometric Ru clusters are uniformly distributed throughout the zeolite crystals. The X‐ray absorption spectroscopy measurements reveal the existence of Ru‐H species between Ru clusters and adjacent Brønsted acid sites of zeolites, which could synergistically activate AB and water molecules, significantly enhancing the hydrogen evolution rate of AB hydrolysis. Notably, the Ru/SAPO‐34‐0.8Si (Si/Al = 0.8) and Ru/FAU (Si/Al = 30) catalysts with strong acidities afford high turnover frequency values up to 490 and 627 min−1, respectively. These values are more than a 13‐fold enhancement than that of the commercial Ru/C catalyst, and among the top level over other heterogeneous catalysts tested under similar conditions.
Highlights
Taking advantage of the synergetic effect of confined ultrasmall metal clusters and zeolite frameworks is an efficient strategy for improving the catalytic performance of metal nanocatalysts
When the reaction temperature increased up to 50 °C, about 4.8 mL H2 could be generated from pure SAPO-34-0.2Si zeolite within 10 min, which was fourfold improvement than that of pure AlPO-34 zeolite (1.2 mL) (Figures S15 and S16, Supporting Information), confirming that the Brønsted acid sites of SAPO-34 zeolite are beneficial for the decomposition of ammonia borane (AB)
The physical mixture of Ru/AlPO-34 and SAPO34-0.2Si catalysts exhibited no improvement for the H2 generation rate as compared with the pure Ru/AlPO-34 catalyst (Figure 4B), indicating that the synergistic effect between Ru clusters and adjacent Brønsted acid sites of zeolite supports is responsible for enhancement of the catalytic activity for the H2 evolution
Summary
Taking advantage of the synergetic effect of confined ultrasmall metal clusters and zeolite frameworks is an efficient strategy for improving the catalytic performance of metal nanocatalysts. When the reaction temperature increased up to 50 °C, about 4.8 mL H2 could be generated from pure SAPO-34-0.2Si zeolite within 10 min, which was fourfold improvement than that of pure AlPO-34 zeolite (1.2 mL) (Figures S15 and S16, Supporting Information), confirming that the Brønsted acid sites of SAPO-34 zeolite are beneficial for the decomposition of AB.
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