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High-entropy alloy nanoparticles (HEA-NPs) are important class of materials with significant technological potential. However, the strategies for synthesizing uniformly dispersed HEA-NPs on granular supports such as carbon materials, γ-Al 2 O 3 , and zeolite, which is vital to their practical applications, are largely unexplored. Herein, we present a fast moving bed pyrolysis strategy to immobilize HEA-NPs on granular supports with a narrow size distribution of 2 nm up to denary (MnCoNiCuRhPdSnIrPtAu) HEA-NPs at 923 K. Fast moving bed pyrolysis strategy ensures the mixed metal precursors rapidly and simultaneously pyrolyzed at high temperatures, resulting in nuclei with a small size. The representative quinary (FeCoPdIrPt) HEA-NPs exhibit high stability (150 h) toward hydrogen evolution reaction with high mass activity, which is 26 times higher than the commercial Pt/C at an overpotential of 100 mV. Our strategy provides an improved methodology for synthesizing HEA-NPs on various supports. The large-scale application of extremely small, high-entropy alloy nanoparticles is limited by the phase separation and immobilization. Here, the authors develop a general method of fast-moving bed pyrolysis, uniformly dispersing high-entropy alloy nanoparticles on various granular supports.

Ag/γ-Al 2 O 3 is widely used for catalyzing various reactions, and its performance depends on the valence state, morphology and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al 2 O 3 remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al 2 O 3 are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al 2 O 3 can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al 2 O 3 . Density-functional-theory calculations confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al 2 O 3 , but not on microsized γ-Al 2 O 3 . The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts. Detailed atom-level anchoring mechanism of Ag species on γ-Al 2 O 3 is largely unknown for the widely used Ag/γ-Al 2 O 3 catalyst. Here, the authors demonstrate that single-Ag atom can be only anchored by the terminal hydroxyls on the (100) surfaces of γ-Al 2 O 3 through consuming two or three terminal hydroxyls.

Noble-metal alloys are widely used as heterogeneous catalysts. However, due to the existence of scaling properties of adsorption energies on transition metal surfaces, the enhancement of catalytic activity is frequently accompanied by side reactions leading to a reduction in selectivity for the target product. Herein, we describe an approach to breaking the scaling relationship for propane dehydrogenation, an industrially important reaction, by assembling single atom alloys (SAAs), to achieve simultaneous enhancement of propylene selectivity and propane conversion. We synthesize γ-alumina-supported platinum/copper SAA catalysts by incipient wetness co-impregnation method with a high copper to platinum ratio. Single platinum atoms dispersed on copper nanoparticles dramatically enhance the desorption of surface-bounded propylene and prohibit its further dehydrogenation, resulting in high propylene selectivity (~90%). Unlike previous reported SAA applications at low temperatures (<400 °C), Pt/Cu SAA shows excellent stability of more than 120 h of operation under atmospheric pressure at 520 °C. Enhancing the catalytic activity of noble-metal alloys is frequently accompanied by side reactions. Here, the authors describe an approach to break the scaling relationship for propane dehydrogenation, by assembling single atom alloys, to achieve simultaneous enhancement of propylene selectivity and propane conversion.

In its nanoparticulate form, corundum (α-Al₂O₃) could lead to several applications. However, its production into nanoparticles (NPs) is greatly hampered by the high activation energy barrier for its formation from cubic close-packed oxides and the sporadic nature of its nucleation. We report a simple synthesis of nanometer-sized α-Al₂O₃ (particle diameter ~13 nm, surface areas ~140 m² g−1) by the mechanochemical dehydration of boehmite (γ-AlOOH) at room temperature. This transformation is accompanied by severe microstructural rearrangements and might involve the formation of rare mineral phases, diaspore and tohdite, as intermediates. Thermodynamic calculations indicate that this transformation is driven by the shift in stability from boehmite to α-Al₂O₃ caused by milling impacts on the surface energy. Structural water in boehmite plays a crucial role in generating and stabilizing α-Al₂O₃ NPs.

Sintering of active metal species often happens during catalytic reactions, which requires redispersion in a reactive atmosphere at elevated temperatures to recover the activity. Herein, we report a simple method to redisperse sintered Cu catalysts via O 2 -H 2 O treatment at room temperature. In-situ spectroscopic characterizations reveal that H 2 O induces the formation of hydroxylated Cu species in humid O 2 , pushing surface diffusion of Cu atoms at room temperature. Further, surface OH groups formed on most hydroxylable support surfaces such as γ-Al 2 O 3 , SiO 2 , and CeO 2 in the humid atmosphere help to pull the mobile Cu species and enhance Cu redispersion. Both pushing and pulling effects of gaseous H 2 O promote the structural transformation of Cu aggregates into highly dispersed Cu species at room temperature, which exhibit enhanced activity in reverse water gas shift and preferential oxidation of carbon monoxide reactions. These findings highlight the important role of H 2 O in the dynamic structure evolution of supported metal nanocatalysts and lay the foundation for the regeneration of sintered catalysts under mild conditions. Redispersion of sintered metal species requires high temperatures in reactive atmospheres. Here, the authors report room temperature redispersion of supported Cu particles via formation of mobile hydroxylated Cu species induced by gaseous H 2 O and anchoring of the Cu species by surface OH groups.

The “terminal hydroxyl group anchoring mechanism” has been studied on metal oxides (Al 2 O 3 , CeO 2 ) as well as a variety of noble and transition metals (Ag, Pt, Pd, Cu, Ni, Fe, Mn, and Co) in a number of generalized studies, but there is still a gap in how to regulate the content of terminal hydroxyl groups to influence the dispersion of the active species and thus to achieve optimal catalytic performance. Herein, we utilized AlOOH as a precursor for γ-Al 2 O 3 and induced the transformation of the exposed crystal face of γ-Al 2 O 3 from (110) to (100) by controlling the calcination temperature to generate more terminal hydroxyl groups to anchor Ag species. Experimental results combined with AIMD and DFT show that temperature can drive the atomic rearrangement on the (110) crystal face, thereby forming a structure similar to the atomic arrangement of the (100) crystal face. This resulted in the formation of more terminal hydroxyl groups during the high-temperature calcination of the support (Al-900), which can capture Ag species to form single-atom dispersions, and ultimately develop a stable and efficient single-atom Ag-based catalyst. Terminal hydroxyl groups on γ-Al 2 O 3 surfaces serve as anchoring sites for Ag. Based on the surface energy of different crystal planes of γ-Al 2 O 3 at various temperatures, the authors propose a high-temperature-induced crystal plane transformation method to construct terminal hydroxyl anchoring sites.

The design and synthesis of robust sintering-resistant nanocatalysts for high-temperature oxidation reactions is ubiquitous in many industrial catalytic processes and still a big challenge in implementing nanostructured metal catalyst systems. Herein, we demonstrate a strategy for designing robust nanocatalysts through a sintering-resistant support via compartmentalization. Ultrafine palladium active phases can be highly dispersed and thermally stabilized by nanosheet-assembled γ-Al 2 O 3 (NA-Al 2 O 3 ) architectures. The NA-Al 2 O 3 architectures with unique flowerlike morphologies not only efficiently suppress the lamellar aggregation and irreversible phase transformation of γ-Al 2 O 3 nanosheets at elevated temperatures to avoid the sintering and encapsulation of metal phases, but also exhibit significant structural advantages for heterogeneous reactions, such as fast mass transport and easy access to active sites. This is a facile stabilization strategy that can be further extended to improve the thermal stability of other Al 2 O 3 -supported nanocatalysts for industrial catalytic applications, in particular for those involving high-temperature reactions. The design and synthesis of robust sintering-resistant nanocatalysts for high-temperature oxidation reactions remains challenging, even though the strategy of metal-support interactions has been extensively used. Here, the authors demonstrate an alternative strategy for designing robust nanocatalysts through a sintering-resistant support.

Although Cu/ZnO-based catalysts have been long used for the hydrogenation of CO 2 to methanol, open questions still remain regarding the role and the dynamic nature of the active sites formed at the metal-oxide interface. Here, we apply high-pressure operando spectroscopy methods to well-defined Cu and Cu 0.7 Zn 0.3 nanoparticles supported on ZnO/Al 2 O 3 , γ-Al 2 O 3 and SiO 2 to correlate their structure, composition and catalytic performance. We obtain similar activity and methanol selectivity for Cu/ZnO/Al 2 O 3 and CuZn/SiO 2 , but the methanol yield decreases with time on stream for the latter sample. Operando X-ray absorption spectroscopy data reveal the formation of reduced Zn species coexisting with ZnO on CuZn/SiO 2 . Near-ambient pressure X-ray photoelectron spectroscopy shows Zn surface segregation and the formation of a ZnO-rich shell on CuZn/SiO 2 . In this work we demonstrate the beneficial effect of Zn, even in diluted form, and highlight the influence of the oxide support and the Cu-Zn interface in the reactivity. The nature of the active species over Cu/ZnO catalysts for methanol synthesis remains elusive. Here, the authors shed light on the evolution of the nanoparticle/support interface and correlate its structural and chemical transformations with changes in the catalytic performance.

Reducing the size of metal nanoparticles down to the single-atom level has been actively pursued to maximize the use of precious metals. Recently, single-atom catalysts, in which all the metal atoms are isolated on a support with 100% dispersion, have received much attention. However, the lack of ensemble sites prevents valuable surface reactions that require metal proximity to occur. Here, we present metal (Pt, Pd and Rh) ensemble catalysts with 100% dispersion and a reduced metallic surface state. More specifically, nanoceria particles were anchored on Al 3+ penta sites of activated γ-alumina, and then metal was deposited and reduced. The ensemble catalysts are highly durable: their structure was maintained even after hydrothermal ageing at 900 °C for 24 h or after long-term reaction. These catalysts have superior activity and durability for three-way catalytic reactions and can provide insights beyond single-atom catalysts for heterogeneous catalysis. Supported single atoms can minimize metal utilization in catalysis, although reactivity restrictions exist. Here, fully exposed Pt, Pd and Rh ensembles localized on CeO 2 islands anchored onto partially reduced γ-Al 2 O 3 are introduced as a superior and durable alternative for three-way catalysis.

Ni/γ-Al2O3 catalysts can effectively improve the selectivity during the hydrogenation of mixed nitroaniline and m-nitrochlorobenzene and can inhibit the dechlorination phenomenon. In this paper, different crystal types of Ni/Al2O3 were prepared, and the carrier surface morphology, crystal structure, specific surface area, and pore volume and pore size of the catalysts were characterized by SEM, BET, XRD, etc. The prepared catalysts were used for the catalytic hydrogenation for the synthesis of o- and p-phenylenediamine and m-chloroaniline, and by comparing the catalysts with the nickel catalysts with a skeleton, we obtained better catalytic performance and inhibition of dechlorination for the catalysts of Ni/γ-Al2O3.