Quantification of critical particle distance for mitigating catalyst sintering

A self-regenerating Pt/Ge-MFI zeolite for propane dehydrogenation with high endurance

Supported noble metal cluster catalysts are typically operated under severe conditions involving switching between reducing and oxidizing atmospheres, causing irreversible transformation of the catalyst structure and thereby leading to permanent deactivation. We discovered that various platinum (Pt) precursors spontaneously disperse in a germanium-MFI (Ge-MFI) zeolite, which opposes the Ostwald ripening phenomenon, producing self-regenerating Pt/Ge-MFI catalysts for propane dehydrogenation. These catalysts reversibly switch between Pt clusters and Pt single atoms in response to reducing reaction and oxidizing regeneration conditions. This environmental adaptability allows them to completely self-regenerate over 110 reaction and regeneration cycles in propane dehydrogenation, and they exhibited unprecedented sintering resistance when exposed to air at 800°C for 10 days. Such spontaneous metal dispersion in a Ge-MFI zeolite is a robust and versatile methodology for fabricating various rhodium, ruthenium, iridium, and palladium cluster catalysts.

Metalloenzyme-Inspired Cluster Fabrication within Mesoporous Channels Featuring Optimized Catalytic Microenvironments for Efficient Neutral pH H2O2 Electrosynthesis

In nature, some metalloenzymes facilitate highly efficient catalytic transformations of small molecules, primarily attributed to the effective coupling between their metal cluster active sites and the surrounding microenvironment. Inspired by this, a thermotropic redispersion strategy to incorporate bismuth nanoclusters (Bi NCs) into mesoporous channels, mimicking metalloenzyme-like catalysis to enhance the two-electron oxygen reduction reaction (2e- ORR) for efficient neutral pH H2O2 electrosynthesis, is developed. This model electrocatalyst exhibits exceptional 2e- ORR performance with >95% H2O2 selectivity across 0.2-0.6 V vs RHE in neutral electrolyte. Notably, the system produces up to 7.2 wt% neutral H2O2 solution at an industrially relevant current density of ≈320 mA cm-2, with 90% Faradaic efficiency for H2O2 over 120 h in a flow cell, demonstrating significant practical potential. Mechanistic insights reveal that the introduction of Bi NCs enhances the adsorption of the *OOH intermediate, facilitating a highly active 2e- ORR process. Moreover, the mesoporous channels of the carbon support create a favorable catalytic microenvironment for O2 aeration and local alkalinity, further boosting H2O2 productivity. This catalyst design mimics metalloenzymes by optimal integration of the active site with the surrounding microenvironment, offering valuable insights for the rational design of nature-inspired small-molecule catalysts.

Ultrafine metal nanoparticles isolated on oxide nano-islands as exceptional sintering-resistant catalysts

Ultrafine nanoparticles (NPs) have attracted extensive research interest, especially in heterogeneous catalysis. However, the inherent sintering propensity of NPs has been a major obstacle to their catalytic stability. Here we report an isolation strategy to preserve highly dispersed ultrafine NPs under extremely harsh conditions. Oxide nano-islands were grafted between the catalyst support and metal NPs, serving as a general approach by following a charge attraction principle. Specifically, LaOx nano-islands were ideally suited for stabilizing Ru NPs among the synthetic library, exhibiting strong adhesion to minimize the chemical potential and disconnect the sintering path. Thus, ultrafine Ru NPs in Ru/LaOx-SiO2 were isolated, maintaining a mean size of 1.4 nm in CO- and H2-rich atmosphere during efficient catalysis for methane dry reforming at 800 °C for 400 h. This isolation strategy has proved effective for many other metals on various supports, paving a practical way for the design of sintering-resistant catalysts.

P-Doping Modulated RuIr Nanoparticles Anchored on Co/N/C Catalysts with Improved Alkaline Hydrogen Evolution Activity and Stability

Achieving efficient and stable hydrogen evolution reactions in alkaline conditions is crucial for hydrogen production. In this study, a RuIr/Co(SA)NC-P catalyst featuring RuIr alloys alongside P-doping and CoNx sites is developed. RuIr alloying optimizes the electronic structure between Ru and Ir, promoting electron transfer from Ru to Ir. P-doping further modulates the electronic properties of RuIr alloys, optimizing hydrogen binding energy and weakening Ru─OH binding energy, facilitating rapid H2 generation and OHad transfer. Meanwhile, CoNx promotes water dissociation, providing a fast proton delivery path for RuIr alloys. The catalyst exhibits enhanced HER activity with a low overpotential of 20 mV at 10 mA cm-2, a Tafel slope of 20.4 mV dec-1, and a turnover frequency of 19.5 H2 s-1 at 150 mV overpotential. Moreover, catalyst stability is improved 8 times by mitigating RuIr alloy dissolution/agglomeration via P-doping. This work introduces a promising approach for developing efficient and stable HER electrocatalysts.

Surface Self-Diffusion Induced Sintering of Nanoparticles

Despite the critical role of sintering phenomena in constraining the long-term durability of nanosized particles, a clear understanding of nanoparticle sintering has remained elusive due to the challenges in atomically tracking the neck initiation and discerning different mechanisms. Through the integration of in situ transmission electron microscopy and atomistic modeling, this study uncovers the atomic dynamics governing the neck initiation of Pt-Fe nanoparticles via a surface self-diffusion process, allowing for coalescence without significant particle movement. Real-time imaging reveals that thermally activated surface morphology changes in individual nanoparticles induce significant surface self-diffusion. The kinetic entrapment of self-diffusing atoms in the gaps between closely spaced nanoparticles leads to the nucleation and growth of atomic layers for neck formation. This surface self-diffusion-driven sintering process is activated at a relatively lower temperature compared to the classic Ostwald ripening and particle migration and coalescence processes. The fundamental insights have practical implications for manipulating the morphology, size distribution, and stability of nanostructures by leveraging surface self-diffusion processes.

Reaction-Driven Migration Dynamics of Nano-Metal Particles Unraveled by Quantitative Electron Microscopies

The stability of supported nano-metal catalysts holds significant importance in both scientific and economic practice, beyond the long pursuit of enhanced activity. While previous efforts have concentrated on augmenting the interaction between nano-metals and carriers, in the thermodynamic macro-perspective, to achieve optimized repression upon particle migration coalescence and Ostwald ripening, nevertheless, the microscale kinetics of migrating catalyst particles driven by the reaction remains unknown. In this work, the migration of nano-copper particles is investigated during hydrogen oxidation reaction by utilizing high spatiotemporal resolution of environmental transmission electron microscopy. It is shown that there exists a delicate correlation between the migration dynamics of nano-copper particles and the evolution of asymmetrically distributed Cu and Cu2O phases over the particle surface. It is found that the interplay of reduction and oxidation near the surface areas filled with Cu and Cu2O phases can facilitate the pressure gradient, which drives the migration of nano-particles. A driving force model is therefore established which is capable of qualitatively explaining the influences of reaction conditions such as temperature and hydrogen-to-oxygen ratio on the reaction-driven particle migration. This work adds a potential yet critical perspective to understanding particle migration and thus the nano-metal catalyst particle sintering in heterogeneous catalysis.

Rationally Designed L12-Pt2RhFe Intermetallic Catalyst with High CO-Tolerance for Alkaline Methanol Electrooxidation

It is a grand challenge to deep understanding of and precise control over functional sites for the rational design of highly efficient catalysts for methanol electrooxidation. Here, an L12-Pt2RhFe intermetallic catalyst with integrated functional components is demonstrated, which exhibits exceptional CO tolerance. The Pt2RhFe/C achieves a superior mass activity of 6.43 A mgPt -1, which is 2.23-fold and 3.53-fold higher than those of PtRu/C and Pt/C. Impressively, the Pt2RhFe/C exhibits a significant enhancement in durability owing to its high CO-tolerance and stability. Density functional theory calculations reveal that high performance of Pt2RhFe intermetallic catalyst arises from the synergistic effect: the strong OH binding energy (OHBE) at Fe sites induce stably adsorbed OH species and thus facilitate the dehydrogenation step of methanol via rapid hydrogen transfer, while moderate OHBE at Rh sites promote the formation of the transition state (Pt-CO···OH-Rh) with a low activation barrier for CO removal. This work provides new insights into the role of OH binding strength in the removal of CO species, which is beneficial for the rational design of highly efficient catalysts.

Real-Time Simulation of the Reaction Kinetics of Supported Metal Nanoparticles

A common issue with supported metal catalysts is the sintering of metal nanoparticles, resulting in catalyst deactivation. In this study, we propose a theoretical framework for realizing a real-time simulation of the reactivity of supported metal nanoparticles during the sintering process, combining density functional theory calculations, microkinetic modeling, Wulff-Kaichew construction, and sintering kinetic simulations. To validate our approach, we demonstrate its feasibility on α-Al2O3(0001)-supported Ag nanoparticles, where the simulated sintering behavior and ethylene epoxidation reaction rate as a function of time show qualitative agreement with experimental observation. Our proposed theoretical approach can be employed to screen out the promising microstructure feature of α-Al2O3 for stable supported Ag NPs, including the surface orientation and promoter species modified on it. The outlined approach of this work may be applied to a range of different thermocatalytic reactions other than ethylene epoxidation and provide guidance for the development of supported metal catalysts with long-term stability.

Atom-glue stabilized Pt-based intermetallic nanoparticles

Pt-based nanoparticles (NPs) have been widely used in catalysis. However, this suffers from aggregation and/or sintering at working conditions. We demonstrate a robust strategy for stabilizing PtCo NPs under high temperature with strong interaction between M-N-C and PtCo NPs with Pt-M-N coordination, namely, "atom glue." Such atom glue for stabilizing Pt-based NPs can be extended to Zn, Mn, Fe, Ni, Co, and Cu, being a versatile strategy for stabilizing PtCo NPs, which substantially promotes the performance toward oxygen reduction reaction (ORR) and fuel cell. Impressively, the mass activity (MA) reaches 2.99 A mgPt-1 for ORR over g-Zn-N-C/PtCo, and 79.3% of the initial MA is maintained after 90K cycles in fuel cell. This work provides a versatile strategy for stabilizing Pt-based NPs via atom glue, which is likely to spark widespread interest across various fields.

Engineering Asymmetric Strain within C-Shaped CeO2 Nanofibers for Stabilizing Sub-3 nm Pt Clusters against Sintering

Ultrafine noble metals have emerged as advanced nanocatalysts in modern society but still suffer from unavoidable sintering at temperatures above 250 °C (e.g., Pt). In this work, closely packed CeO2 grains were confined elegantly in fibrous nanostructures and served as a porous support for stabilizing sub-3 nm Pt clusters. Through precisely manipulating the asymmetry of obtained nanofibers, uneven strain was induced within C-shaped CeO2 nanofibers with tensile strain at the outer side and compressive strain at the inner side. As a result, the enriched oxygen vacancies significantly improved adhesion of Pt to CeO2, thereby boosting the sinter-resistance of ultraclose sub-3 nm Pt clusters. Notably, no aggregation was observed even after exposure to humid air at 750 °C for 12 h, which is far beyond their Tammann temperature (sintering onset temperature, below 250 °C). In situ HAADF-STEM observation revealed a unique sintering mechanism, wherein Pt clusters initially migrate toward the grain boundaries with concentrated stain and undergo slight coalescence, followed by subsequent Ostwald ripening at higher temperatures. Moreover, the sinter-resistant Pt/C-shaped CeO2 effectively catalyzed soot combustion (over 700 °C) in a durable manner. This work provides a new insight for developing sinter-resistant catalysts from the perspective of strain engineering within nano-oxides.

Stabilizing ultra-close Pt clusters on all-in-one CeO2/Al2O3 fibril-in-tubes against sintering

Metal sintering poses significant challenges for developing reliable catalytic systems toward high-temperature reactions, particularly those based on metal clusters with sizes below 3 nm. In this work, electrospun dual-oxide fibril-in-tubes consisting of CeO2 and Al2O3 are rationally designed in an all-in-one manner, to stabilize 2.3 nm Pt clusters with a Tammann temperature (sintering onset temperature) lower than 250 °C. The abundant pores and channels effectively stabilize the Pt clusters physically, while the strong support, CeO2, with high adhesion, pins Pt clusters firmly, and the adjacent weak support, Al2O3, with low adhesion, provides energy barriers to prevent the clusters and emitted Pt atom(s) from moving across the support. Therefore, the ultra-close 2.3 nm Pt clusters, featuring an average nearest neighboring distance of only 2.1 nm, were carefully stabilized against sintering at temperatures exceeding 750 °C, even in oxidative and steam-containing environments. In addition, this catalytic system can efficiently and durably serve in diesel combustion, a high-temperature exothermic reaction, showing no activity decline after 5 cycles. This work provides a comprehensive understanding of sinter-resistant catalytic systems, and presents new insights for the development of advanced nanocatalysts.

Unbounding the Future: Designing NiAl-Based Catalysts for Dry Reforming of Methane

Dry reforming of methane (DRM), the catalytic conversion of CH4 and CO2 into syngas (H2+CO), is an important process closely correlated to the environment and chemical industry. NiAl-based catalysts have been reported to exhibit excellent activity, low cost, and environmental friendliness. At the same time, the rapid deactivation caused by carbon deposition, Ni sintering, and phase transformation exerts great challenges for its large-scale applications. This review summarizes the recent advances in NiAl-based catalysts for DRM, particularly focusing on the strategies to construct efficient and stable NiAl-based catalysts. Firstly, the thermodynamics and elementary steps of DRM, including the activation of reactants and coke formation and elimination, are summarized. The roles of Al2O3 and its mixed oxides as the support, and the influences of the promoters employed in NiAl-based catalysts over the DRM performance, are then illustrated. Finally, the design of anti-coking and anti-sintering NiAl-based catalysts for DRM is suggested as feasible and promising by tailoring the structure and states of Ni and the modification of Al-based supports including small Ni size, high Ni dispersion, proper basicity, strong metal-support interaction (SMSI), active oxygen species as well as high phase stability.

Synergistic Modulation of Multiple Sites Boosts Anti-Poisoning Hydrogen Electrooxidation Reaction with Ultrasmall (Pt0.9Rh0.1)3V Ternary Intermetallic Nanoparticles

Promoting the hydrogen oxidation reaction (HOR) activity and poisoning tolerance of electrocatalysts is crucial for the large-scale application of hydrogen-oxygen fuel cell. However, it is severely hindered by the scaling relations among different intermediates. Herein, lattice-contracted Pt-Rh in ultrasmall ternary L12-(Pt0.9Rh0.1)3V intermetallic nanoparticles (~2.2 nm) were fabricated to promote the HOR performances through an oxides self-confined growth strategy. The prepared (Pt0.9Rh0.1)3V displayed 5.5/3.7 times promotion in HOR mass/specific activity than Pt/C in pure H2 and dramatically limited activity attenuation in 1000 ppm CO/H2 mixture. In situ Raman spectra tracked the superior anti-CO* capability as a result of compressive strained Pt, and the adsorption of oxygen-containing species was promoted due to the dual-functional effect. Further assisted by density functional theory calculations, both the adsorption of H* and CO* on (Pt0.9Rh0.1)3V were reduced compared with that of Pt due to lattice contraction, while the adsorption of OH* was enhanced by introducing oxyphilic Rh sites. This work provides an effective tactic to stimulate the electrocatalytic performances by optimizing the adsorption of different intermediates severally.

Thermal-Driven Dispersion of Bismuth Nanoparticles among Carbon Matrix for Efficient Carbon Dioxide Reduction

The poor electrocatalytic stability and rapid deactivation of metal electrocatalysts are always present in the electrocatalytic conversion of carbon dioxide (CO2) due to the harsh reduction condition. Herein, we demonstrate the controllable dispersion of ultrafine bismuth nanoparticles among the hollow carbon shell (Bi@C-700-4) simply by a thermal-driven diffusion process. The confinement effect of nitrogen-doped carbon matrix is able to low the surface energy of bismuth nanoparticles against the easy aggregation commonly observed for the thermal treatment. On the basis of the synergistic effect and confinement effect between bismuth nanoparticles and carbon matrix, the highly dispersed active sites render the obviously improved electrocatalytic activity and stability for CO2 reduction into formate. The in situ experimental observations on the reduction process and theoretical calculations reveal that the incorporation of bismuth nanoparticles with nitrogen-doped carbon matrix would promote the activation of CO2 and the easy formation of key intermediate (*OCHO), thus leading the enhanced electrocatalytic activity, with a Faradaic Efficiency (FE) of formate about 94.8 % and the long-time stability. Furthermore, the coupling of an anode for 5-hydroxymethylfurfural oxidation reaction (HMFOR) in solar-driven system renders the high 2,5-furandicarboxylic acid (FDCA) yield of 81.2 %, presenting the impressive solar-to-fuel conversion.

The Importance of Sintering-Induced Grain Boundaries in Copper Catalysis to Improve Carbon-Carbon Coupling

Syngas conversion serves as a gas-to-liquid technology to produce liquid fuels and valuable chemicals from coal, natural gas, or biomass. During syngas conversion, sintering is known to deactivate the catalyst owing to the loss of active surface area. However, the growth of nanoparticles might induce the formation of new active sites such as grain boundaries (GBs) which perform differently from the original nanoparticles. Herein, we reported a unique Cu-based catalyst, Cu nanoparticles with in situ generated GBs confined in zeolite Y (denoted as activated Cu/Y), which exhibited a high selectivity for C5+ hydrocarbons (65.3 C%) during syngas conversion. Such high selectivity for long-chain products distinguished activated Cu/Y from typical copper-based catalysts which mainly catalyze methanol synthesis. This unique performance was attributed to the GBs, while the zeolite assisted the stabilization through spatial confinement. Specifically, the GBs enabled H-assisted dissociation of CO and subsequent hydrogenation into CHx*. CHx* species not only serve as the initiator but also directly polymerize on Cu GBs, known as the carbide mechanism. Meanwhile, the synergy of GBs and their vicinal low-index facets led to the CO insertion where non-dissociative adsorbed CO on low-index facets migrated to GBs and inserted into the metal-alkyl bond for the chain growth.

Surface-Diffusion-Induced Amorphization of Pt Nanoparticles over Ru Oxide Boost Acidic Oxygen Evolution

Phase transformation offers an alternative strategy for the synthesis of nanomaterials with unconventional phases, allowing us to further explore their unique properties and promising applications. Herein, we first observed the amorphization of Pt nanoparticles on the RuO2 surface by in situ scanning transmission electron microscopy. Density functional theory calculations demonstrate the low energy barrier and thermodynamic driving force for Pt atoms transferring from the Pt cluster to the RuO2 surface to form amorphous Pt. Remarkably, the as-synthesized amorphous Pt/RuO2 exhibits 14.2 times enhanced mass activity compared to commercial RuO2 catalysts for the oxygen evolution reaction (OER). Water electrolyzer with amorphous Pt/RuO2 achieves 1.0 A cm-2 at 1.70 V and remains stable at 200 mA cm-2 for over 80 h. The amorphous Pt layer not only optimized the *O binding but also enhanced the antioxidation ability of amorphous Pt/RuO2, thereby boosting the activity and stability for the OER.

Water-assisted oxidative redispersion of Cu particles through formation of Cu hydroxide at room temperature

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 O2-H2O treatment at room temperature. In-situ spectroscopic characterizations reveal that H2O induces the formation of hydroxylated Cu species in humid O2, pushing surface diffusion of Cu atoms at room temperature. Further, surface OH groups formed on most hydroxylable support surfaces such as γ-Al2O3, SiO2, and CeO2 in the humid atmosphere help to pull the mobile Cu species and enhance Cu redispersion. Both pushing and pulling effects of gaseous H2O 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 H2O in the dynamic structure evolution of supported metal nanocatalysts and lay the foundation for the regeneration of sintered catalysts under mild conditions.

Hydrogenated borophene enabled synthesis of multielement intermetallic catalysts

Supported metal catalysts often suffer from rapid degradation under harsh conditions due to material failure and weak metal-support interaction. Here we propose using reductive hydrogenated borophene to in-situ synthesize Pt/B/C catalysts with small sizes (~2.5 nm), high-density dispersion (up to 80 wt%Pt), and promising stability, originating from forming Pt-B bond which are theoretically ~5× stronger than Pt-C. Based on the Pt/B/C module, a series (~18 kinds) of carbon supported binary, ternary, quaternary, and quinary Pt intermetallic compound nanocatalysts with sub-4 nm size are synthesized. Thanks to the stable intermetallics and strong metal-support interaction, annealing at 1000 °C does not cause those nanoparticles sintering. They also show much improved activity and stability in electrocatalytic oxygen reduction reaction. Therefore, by introducing the boron chemistry, the hydrogenated borophene derived multielement catalysts enable the synergy of small size, high loading, stable anchoring, and flexible compositions, thus demonstrating high versatility toward efficient and durable catalysis.

Ferric Single-Site Catalyst Confined in a Zeolite Framework for Propane Dehydrogenation

Non-oxidative dehydrogenation of propane is a highly efficient approach for industrial preparation of propene that is commonly catalyzed by noble Pt or toxic Cr catalysts and suffers from coking. In this work, ferric catalyst confined in a zeolite framework was synthesized by a hydrothermal procedure. The isolated Fe in the framework formed distorted tetrahedra, which were beneficial for the selective dehydrogenation of propane and reached over 95 % propene selectivity and over 99 % total olefins selectivity. This catalyst had a silanol-free structure and was oxygen tolerant, hydrothermally stable, and coke free, with a deactivation constant of 0.01 h-1 . This study provided guidance for the synthesis of structural heteroatomic zeolite and efficient propane non-oxidative dehydrogenation over early transition metals.

In Situ and Emerging Transmission Electron Microscopy for Catalysis Research

Catalysts are the primary facilitator in many dynamic processes. Therefore, a thorough understanding of these processes has vast implications for a myriad of energy systems. The scanning/transmission electron microscope (S/TEM) is a powerful tool not only for atomic-scale characterization but also in situ catalytic experimentation. Techniques such as liquid and gas phase electron microscopy allow the observation of catalysts in an environment conducive to catalytic reactions. Correlated algorithms can greatly improve microscopy data processing and expand multidimensional data handling. Furthermore, new techniques including 4D-STEM, atomic electron tomography, cryogenic electron microscopy, and monochromated electron energy loss spectroscopy (EELS) push the boundaries of our comprehension of catalyst behavior. In this review, we discuss the existing and emergent techniques for observing catalysts using S/TEM. Challenges and opportunities highlighted aim to inspire and accelerate the use of electron microscopy to further investigate the complex interplay of catalytic systems.

Does Cluster Encapsulation Inhibit Sintering? Stabilization of Size-Selected Pt Clusters on Fe3O4(001) by SMSI

The metastability of supported metal nanoparticles limits their application in heterogeneous catalysis at elevated temperatures due to their tendency to sinter. One strategy to overcome these thermodynamic limits on reducible oxide supports is encapsulation via strong metal-support interaction (SMSI). While annealing-induced encapsulation is a well-explored phenomenon for extended nanoparticles, it is as yet unknown whether the same mechanisms hold for subnanometer clusters, where concomitant sintering and alloying might play a significant role. In this article, we explore the encapsulation and stability of size-selected Pt5, Pt10, and Pt19 clusters deposited on Fe3O4(001). In a multimodal approach using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and scanning tunneling microscopy (STM), we demonstrate that SMSI indeed leads to the formation of a defective, FeO-like conglomerate encapsulating the clusters. By stepwise annealing up to 1023 K, we observe the succession of encapsulation, cluster coalescence, and Ostwald ripening, resulting in square-shaped crystalline Pt particles, independent of the initial cluster size. The respective sintering onset temperatures scale with the cluster footprint and thus size. Remarkably, while small encapsulated clusters can still diffuse as a whole, atom detachment and thus Ostwald ripening are successfully suppressed up to 823 K, i.e., 200 K above the Hüttig temperature that indicates the thermodynamic stability limit.

Alloying Matters for Ordering: Synthesis of Highly Ordered PtCo Intermetallic Catalysts for Fuel Cells

Porous carbon-supported atomically ordered intermetallic compounds (IMCs) are promising electrocatalysts in boosting oxygen reduction reaction (ORR) for fuel cell applications. However, the formation mechanism of IMC structures under high temperatures is poorly understood, which hampers the synthesis of highly ordered IMC catalysts with promoted ORR performance. Here, we employ high-temperature X-ray diffraction and energy-dispersive spectroscopic elemental mapping techniques to study the formation process of IMCs, by taking PtCo for example, in an industry-relevant impregnation synthesis. We find that high-temperature annealing is crucial in promoting the formation of alloy particles with a stoichiometric Co/Pt ratio, which in turn is the precondition for transforming the disordered alloys to ordered intermetallic structures at a relatively low temperature. Based on the findings, we accordingly synthesize highly ordered L1₀-type PtCo catalysts with a remarkable ORR performance in fuel cells.

High entropy alloy nanoparticles encapsulated in graphitised hollow carbon tubes for oxygen reduction electrocatalysis

High entropy alloys (HEAs) with a tunable alloy composition and fascinating synergetic effects between various metals have attracted significant attention in the field of electrocatalysis, but their potential is limited by inefficient and unscalable fabrication methodologies. This work proposes a novel solid-state thermal reaction method to synthesise HEA nanoparticles encapsulated in an N-doped graphitised hollow carbon tube. This facile method is simple and efficient and involves no use of organic solvents during the fabrication process. The synthesized HEA nanoparticles are confined by the graphitised hollow carbon tube, which is possibly beneficial for preventing the aggregation of alloy particles during the oxygen reduction reaction (ORR). In a 0.1 M KOH solution, the HEA catalyst FeCoNiMnCu-1000(1 : 1) exhibits an onset and half-wave potential of 0.92 V and 0.78 V (vs. RHE), respectively. We assembled a Zn-Air battery with FeCoNiMnCu-1000 as a catalyst for the air electrode, and a power density of 81 mW cm^-2 and a long-term durability of >200 h were achieved, which is comparable to the performance of the state-of-the-art catalyst Pt/C-RuO₂. This work herein offers a scalable and green method for synthesising multinary transition metal-based HEAs and highlights the potential of HEA nanoparticles as electrocatalysts for energy storage and conversion.

Synthesis of rhodium intermetallic catalysts by enlarging the inter-particle distance on high-surface-area carbon black supports

Here, we report a "critical distance" method for the synthesis of 9 kinds of sub-5 nm rhodium (Rh)-based intermetallic catalysts. Enlarging the distance between intermetallic particles on high-surface-area carbon black supports could significantly suppress the metal sintering in high-temperature annealing. The prepared Rh₂Sn intermetallic catalysts exhibited enhanced activity in catalyzing the hydrogenation of nitrobenzene.

Small molecule-assisted synthesis of carbon supported platinum intermetallic fuel cell catalysts

Supported ordered intermetallic compounds exhibit superior catalytic performance over their disordered alloy counterparts in diverse reactions. But the synthesis of intermetallic compounds catalysts often requires high-temperature annealing that leads to the sintering of metals into larger crystallites. Herein, we report a small molecule-assisted impregnation approach to realize the general synthesis of a family of intermetallic catalysts, consisting of 18 binary platinum intermetallic compounds supported on carbon blacks. The molecular additives containing heteroatoms (that is, O, N, or S) can be coordinated with platinum in impregnation and thermally converted into heteroatom-doped graphene layers in high-temperature annealing, which significantly suppress alloy sintering and insure the formation of small-sized intermetallic catalysts. The prepared optimal PtCo intermetallics as cathodic oxygen-reduction catalysts exhibit a high mass activity of 1.08 A mg_Pt^-1 at 0.9 V in H₂-O₂ fuel cells and a rated power density of 1.17 W cm^-2 in H₂-air fuel cells.

Ordered Intermetallic PtCu Catalysts Made from Pt@Cu Core/Shell Structures for Oxygen Reduction Reaction

Platinum-based ordered intermetallic compounds are promising low-Pt catalysts toward the oxygen reduction reaction (ORR) for high-performance fuel cells. However, the synthesis of ordered intermetallic catalysts usually requires high-temperature annealing to overcome the energy barrier for atom diffusion, which leads to inevitable sintering of catalysts and greatly reduced mass-specific activity. Herein, we developed a new strategy to synthesize PtCu-ordered intermetallic catalysts by the generation of the Pt@Cu core/shell nanoparticles (Pt@Cu NPs) by Pt-assisted H₂ reduction of Cu²⁺ with subsequent annealing at 500-1000 °C. Compared to the commonly used wet-impregnation method, the core/shell structure starts to form ordered PtCu alloys at a lower annealing temperature (500 °C). The Pt@Cu core/shell structure avoids the necessary process of Cu atoms diffusing to Pt NPs across the carbon supports occurred during high-temperature annealing in the wet-impregnation method, which ensures the formation of PtCu NPs with higher ordering degree while annealing at the same temperature. The highly ordered small-sized PtCu catalysts prepared by the core/shell strategy exhibit higher mass activity and specific activity compared to those prepared by the wet-impregnation method. Moreover, a positive correlation between the ORR activity and the ordering degree of the intermetallic PtCu NPs is identified, which could be associated with the increase of compressive strain with the ordering degree.

Intermetallic PtFe Electrocatalysts for the Oxygen Reduction Reaction: Ordering Degree-Dependent Performance

Platinum-based atomically ordered alloys (i.e., intermetallic compounds) have distinct advantages over disordered solid solution counterparts in boosting the cathodic oxygen-reduction reaction (ORR) in proton-exchange-membrane fuel cells. Nevertheless, the pivotal role of ordering degree of intermetallic catalysts in promoting ORR performance has been ignored heavily so far, probably owing to the lack of synthetic routes for controlling the ordering degree, especially for preparing highly ordered intermetallic catalysts. Herein, a family of intermetallic PtFe catalysts with similar particle size of 3-4 nm but varied ordering degree in a wide range of 10-70% are prepared. After constructing the PtFe/Pt core/shell structure with around 3 Pt-layer skin, a positive correlation between the ordering degree of the intermetallic catalysts and their ORR activity and durability is identified. Notably, the highly ordered PtFe/Pt catalyst exhibits a high mass activity of 0.92 A mg_Pt ^-1 at 0.9 V_iR-corrected as cathode catalyst in H₂ -O₂ fuel cell, with only 24% loss after accelerated durability tests. The ordering degree-dependent performance can be ascribed to the compressive strain effect induced by the intermetallic PtFe core with smaller lattice parameters, and the more thermodynamically stable intermetallic structure compared to disordered alloys.

Kinetic diffusion-controlled synthesis of twinned intermetallic nanocrystals for CO-resistant catalysis

Intermetallic catalysts are of immense interest, but how heterometals diffuse and related interface structure remain unclear when there exists a strong metal-support interaction. Here, we developed a kinetic diffusion-controlled method and synthesized intermetallic Pt₂Mo nanocrystals with twin boundaries on mesoporous carbon (Pt₂Mo/C). The formation of small-sized twinned intermetallic nanocrystals is associated with the strong Mo-C interaction-induced slow Mo diffusion and the heterogeneity of alloying, which is revealed by an in situ aberration-corrected transmission electron microscope (TEM) at high temperature. The twinned Pt₂Mo/C constitutes a promising CO-resistant catalyst for highly selective hydrogenation of nitroarenes. Theoretical calculations and environmental TEM suggest that the weakened CO adsorption over Pt sites of Pt₂Mo twin boundaries and their local region endows them with high CO resistance, selectivity, and reusability. The present strategy paves the way for tailoring the interface structure of high-melting point Mo/W-based intermetallic nanocrystals that proved to be important for the industrially viable reactions.

Synthesis of a Spatially Confined, Highly Durable, and Fully Exposed Pd Cluster Catalyst via Sequential Site-Selective Atomic Layer Deposition

Bottom-up synthesis based on site-selective atomic layer deposition is a powerful atomic-scale processing approach to fabricate materials with desired functionalities. Typical selective atomic layer deposition (ALD) can be achieved using selective activation of a growth area or selective deactivation of a protected area. In this work, we explored the site selectivity based on the difference of the inherent surface reactivity between different materials and within the same materials. By sequentially applying two site-selective atomic layer deposition, the ALD Pd catalyst is spatially confined on ALD SnO₂ modified h-BN substrate Pd/SnO₂/h-BN shows improved catalytic activity and stability due to strong metal-support interactions and spatial confinement. The results reveal that sequential site-selective ALD is a feasible and effective synthesis strategy that provides an attractive path toward designing and developing highly stable catalysts.

Recent Progress on Sulfated Nanozirconia as a Solid Acid Catalyst in the Hydrocracking Reaction

Zirconia has advantageous thermal stability and acid–base properties. The acidity character of ZrO2 can be enhanced through the sulfation process forming sulfated zirconia (ZrO2-SO4). An acidity test of the catalyst produced proved that the sulfate loading succeeded in increasing the acidity of ZrO2 as confirmed by the presence of characteristic absorptions of the sulfate group from the FTIR spectra of the catalyst. The ZrO2-SO4 catalyst can be further modified with transition metals, such as Platinum (Pt), Chromium (Cr), and Nickel (Ni) to increase catalytic activity and catalyst stability. It was observed that variations in the concentrations of Pt, Cr, and Ni produced a strong influence on the catalytic activity as the acidity and porosity of the catalyst increased with their addition. The activity, selectivity, and catalytic stability tests of Pt/ZrO2-SO4, Cr/ZrO2-SO4 and Ni/ZrO2-SO4 were carried out with their application in the hydrocracking reaction to produce liquid fuel. The percentage of liquid fractions produced using these catalysts were higher than the fraction produced using pure ZrO2 and ZrO2-SO4 catalyst.

High-Temperature Synthesis of Carbon-Supported Bimetallic Nanocluster Catalysts by Enlarging the Interparticle Distance

Supported bimetallic nanoparticle catalysts with small size have attracted wide research attention in catalysis but are difficult to synthesize because high-temperature annealing required for alloying inevitably accelerates metal sintering and leads to larger particles. Here, we report a simple and scalable "critical interparticle distance" method for the synthesis of a family of bimetallic nanocluster catalysts with an average particle size of only 1.5 nm by using large-surface-area carbon black supports at high temperatures, which consist of 12 diverse combinations of 3 noble metals (Pt, Ru, and Rh) and 4 other metals (Cr, Fe, Zr, and Sn). In this strategy, high-temperature treatments ensure the formation of alloyed bimetallic nanoparticles and enlargement of the interparticle distance on high-surface-area supports significantly suppresses metal sintering. The prepared ultrafine Pt₂Sn and RuSn nanocluster catalysts exhibited enhanced performance in catalyzing the synthesis of aromatic secondary amines and the selective hydrogenation of furfural, respectively.

Sabatier principle of metal-support interaction for design of ultrastable metal nanocatalysts

[Figure: see text].