Encapsulation of Noble Metal Nanoclusters into Zeolites for Highly Efficient Catalytic Hydrogenation of Nitroaromatics
Restricting reactive metal nanoclusters into a microporous zeolite matrix (metal@zeolite) can not only prevent the sintering of metal species but can also regulate their catalytic selectivities to certain products. However, there are some problems with current synthesis methods for these structures, such as low metal utilization or/and low product yield. Herein, we report a general strategy to encapsulate different noble metal nanoclusters (e.g., Pd, Pt, Rh, and Ru) into various zeolites (e.g., S-1, ZSM-5, SSZ-13, NaA, and beta). The key point of this strategy is the soft gel precursor (H2O/Si < 4) in the posthydrolysis evaporation process, which significantly improves metal utilization. Combined with the high temperature crystallization process, the space-time yield has been significantly improved, simultaneously. As a typical example, the metal utilization and space-time yield of Pd@S-1 synthesized through this method were nearly 2 and 67 times higher than those of the typical hydrothermal route, respectively. Compared with a supported Pd/SiO2 nanocatalyst, Pd@S-1 exhibited higher catalytic activity and selectivity in hydrogenation of p-chloronitrobenzene (p-CNB).
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