Well-dispersed and ultrasmall Pd clusters in nanosized silicalite-1 (MFI) zeolite have been prepared under direct hydrothermal conditions using [Pd(NH2CH2CH2NH2)2]Cl2 as precursor. High-resolution scanning transmission electron microscopy studies indicate that the Pd clusters are encapsulated within the intersectional channels of MFI, and the Pd clusters in adjacent channels visually aggregate, forming nanoparticles (NPs) of ∼1.8 nm. The resultant catalysts show an excellent activity and highly efficient H2 generation toward the complete decomposition of formic acid (FA) under mild conditions. Notably, thanks to the further reduced Pd NP size (∼1.5 nm) and the additionally introduced basic sites, the Pd/S-1-in-K catalyst affords turnover frequency values up to 856 h(-1) at 25 °C and 3027 h(-1) at 50 °C. The easy in situ confinement synthesis of metal clusters in zeolites endows the catalysts with superior catalytic activities, excellent recyclability, and high thermal stability, thus opening new perspectives for the practical application of FA as a viable and effective H2 storage material for use in fuel cells.
Single‐atom catalysts are emerging as a new frontier in heterogeneous catalysis because of their maximum atom utilization efficiency, but they usually suffer from inferior stability. Herein, we synthesized single‐atom Rh catalysts embedded in MFI‐type zeolites under hydrothermal conditions and subsequent ligand‐protected direct H2 reduction. Cs‐corrected scanning transmission electron microscopy and extended X‐ray absorption analyses revealed that single Rh atoms were encapsulated within 5‐membered rings and stabilized by zeolite framework oxygen atoms. The resultant catalysts exhibited excellent H2 generation rates from ammonia borane (AB) hydrolysis, up to 699 min−1 at 298 K, representing the top level among heterogeneous catalysts for AB hydrolysis. The catalysts also showed superior catalytic performance in shape‐selective tandem hydrogenation of various nitroarenes by coupling with AB hydrolysis, giving >99 % yield of corresponding amine products.
Crystalline nanoporous materials with uniform porous structures, such as zeolites and metal–organic frameworks (MOFs), have proven to be ideal supports to encapsulate ultrasmall metal nanoparticles (MNPs) inside their void nanospaces to generate high‐efficiency nanocatalysts. The nanopore‐encaged metal catalysts exhibit superior catalytic performance as well as high stability and catalytic shape selectivity endowed by the nanoporous matrix. In addition, the synergistic effect of confined MNPs and nanoporous frameworks with active sites can further promote the catalytic activities of the composite catalysts. Herein, recent progress in nanopore‐encaged metal nanocatalysts is reviewed, with a special focus on advances in synthetic strategies for ultrasmall MNPs (<5 nm), clusters, and even single atoms confined within zeolites and MOFs for various heterogeneous catalytic reactions. In addition, some advanced characterization methods to elucidate the atomic‐scale structures of the nanocatalysts are presented, and the current limitations of and future opportunities for these fantastic nanocatalysts are also highlighted and discussed. The aim is to provide some guidance for the rational synthesis of nanopore‐encaged metal catalysts and to inspire their further applications to meet the emerging demands in catalytic fields.
Hybrid multi-metallic nanocatalysts have attracted increasing attention because of the synergistic effect of metal species and considerably improved catalytic performance, but they often suffer from severe sintering and poor stability. Here, we show a facile strategy for preparing subnanometric hybrid bimetallic clusters Pd-M(OH) 2 (M = Ni, Co) within silicalite-1 (S-1) zeolite via a hydrothermal synthesis method. The hybrid bimetallic nanocatalysts exhibit excellent shape-selective catalytic performance and superior thermal stability. The incorporation of secondary Ni(OH) 2 species in S-1 can considerably increase the catalytic activity of the Pd nanoclusters for the dehydrogenation of formic acid (FA) as a result of the electron-enriched Pd surface and bimetallic interfacial effect. Notably, the 0.8Pd0.2Ni(OH) 2 @S-1 catalyst affords the highest initial turnover frequency value, up to 5,803 hr À1 toward complete FA decomposition without any additives at 60 C. The superior catalytic properties and excellent stability of the subnanometric hybrid bimetallic clusters confined in zeolites create new prospects for their practical high-performance catalytic application.
Using an organosilane surfactant as the mesopore director, hierarchical porous silicoaluminophosphate SAPO-34 is obtained as an assembly of nanocrystallites intergrown into cubic micrometer-sized crystals, which show excellent performance in MTO reactions with a remarkably prolonged catalyst lifetime and enhanced selectivity of ethylene and propylene compared to the conventional microporous SAPO-34.
His research focuses on the design and synthesis of high-performance zeolites and nanopore-supported metal nanocatalysts, and their applications in methanol-to-olefin conversion, chemical hydrogen storage, and CO 2 hydrogenation.
Efficient light harvesting and charge separation are of great importance in solar‐energy conversion on photocatalysts. Herein, the synthesis of a novel hollow porous CdS photocatalyst with effectively restrained electron–hole recombination is reported. By using microporous zeolites as a host and a hard template, ultrasmall Pd and PdS nanoparticles can be anchored separately onto the inner and outer surfaces of a hollow CdS structure. The metallic Pd pulls the photoexcited electrons away from CdS while PdS pushes the holes for more thorough oxidation of the sacrificial agent. The final Pd@CdS/PdS product exhibits superior visible‐light‐driven photocatalytic H2 evolution rate of up to 144.8 mmol h−1 g−1. This is among the highest values of all the reported CdS‐based catalysts. This synthetic approach may be used to fabricate other highly efficient catalysts with spatially separated cocatalysts.
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