Modifiers versus Channels: Creating Shape‐Selective Catalysis of Metal Nanoparticles/Porous Nanomaterials

Multidimensionally ordered mesoporous intermetallics: Frontier nanoarchitectonics for advanced catalysis

Ordered intermetallics contribute to a unique class of catalyst materials due to their rich atomic features. Further engineering of ordered intermetallics at a mesoscopic scale is of great importance to expose more active sites and introduce new functions. Recently, multidimensionally ordered mesoporous intermetallic (MOMI) nanoarchitectonics, which subtly integrate atomically ordered intermetallics and mesoscopically ordered mesoporous structures, have held add-in synergies that not only enhance catalytic activity and stability but also optimize catalytic selectivity. In this tutorial review, we have summarized the latest progress in the rational design, targeted synthesis, and catalytic applications of MOMIs, with a special focus on the findings of our group. Three strategies, including concurrent template route, self-template route, and dealloying route, are discussed in detail. Furthermore, physicochemical properties and catalytic performances for several important reactions are also described to highlight the remarkable activity, high stability, and controllable selectivity of MOMI nanoarchitectonics. Finally, we conclude with a summary and explore future perspectives in the field to contribute to wider applications.

Metal-organic frameworks for organic transformations by photocatalysis and photothermal catalysis

Organic transformation by light-driven catalysis, especially, photocatalysis and photothermal catalysis, denoted as photo(thermal) catalysis, is an efficient, green, and economical route to produce value-added compounds. In recent years, owing to their diverse structure types, tunable pore sizes, and abundant active sites, metal-organic framework (MOF)-based photo(thermal) catalysis has attracted broad interest in organic transformations. In this review, we provide a comprehensive and systematic overview of MOF-based photo(thermal) catalysis for organic transformations. First, the general mechanisms, unique advantages, and strategies to improve the performance of MOFs in photo(thermal) catalysis are discussed. Then, outstanding examples of organic transformations over MOF-based photo(thermal) catalysis are introduced according to the reaction type. In addition, several representative advanced characterization techniques used for revealing the charge reaction kinetics and reaction intermediates of MOF-based organic transformations by photo(thermal) catalysis are presented. Finally, the prospects and challenges in this field are proposed. This review aims to inspire the rational design and development of MOF-based materials with improved performance in organic transformations by photocatalysis and photothermal catalysis.

Atomically Contacted Cs3Bi2Br9 QDs@UiO-66 Composite for Photocatalytic CO2 Reduction

Metal halide perovskite quantum dots (QDs) are widely studied in the field of photocatalytic CO2 due to their strong light absorption and long carrier migration length. However, it can not exhibit high catalytic performance because of the radiative recombination and the lack of effective catalytic sites. Metal organic frameworks (MOFs) encapsulated QDs can not only solve the aforementioned problems, but also maintain their own unique characteristics with ultra-high specific surfaces area and abundant metal sites. In this work, lead-free bismuth-based halide perovskite QDs are encapsulated into Zr-based MOF (UiO-66), which combines the advantages with high power conversion efficiency of QDs and the high surface area and porosity of UiO-66. In addition, benefiting from the close contact between the Cs3Bi2Br9 QDs and the UiO-66 enables the photogenerated electrons in the QDs to be rapidly transferred to the MOF. As a result, the Cs3Bi2Br9@UiO-66 composite exhibits a higher yield for photocatalytic CO2 reduction than that of the prepared large-sized composite of Cs3Bi2Br9 and UiO-66.

Nanocavity in hollow sandwiched catalysts as substrate regulator for boosting hydrodeoxygenation of biomass-derived carbonyl compounds

Hydrodeoxygenation of oxygen-rich molecules toward hydrocarbons is attractive yet challenging in the sustainable biomass upgrading. The typical supported metal catalysts often display unstable catalytic performances owing to the migration and aggregation of metal nanoparticles (NPs) into large sizes under harsh conditions. Here, we develop a crystal growth and post-synthetic etching method to construct hollow chromium terephthalate MIL-101 (named as HoMIL-101) with one layer of sandwiched Ru NPs as robust catalysts. Impressively, HoMIL-101@Ru@MIL-101 exhibits the excellent activity and stability for hydrodeoxygenation of biomass-derived levulinic acid to gamma-valerolactone under 50°C and 1-megapascal H2, and its activity is about six times of solid sandwich counterparts, outperforming the state-of-the-art heterogeneous catalysts. Control experiments and theoretical simulation clearly indicate that the enrichment of levulinic acid and H2 by nanocavity as substrate regulator enables self-regulating the backwash of both substrates toward Ru NPs sandwiched in MIL-101 shells for promoting reaction with respect to solid counterparts, thus leading to the substantially enhanced performance.

Heteroatom-Doped Ag25 Nanoclusters Encapsulated in Metal-Organic Frameworks for Photocatalytic Hydrogen Production

Atomically precise metal nanoclusters (NCs) with unique optical properties and abundant catalytic sites are promising in photocatalysis. However, their light-induced instability and the difficulty of utilizing the photogenerated carriers for photocatalysis pose significant challenges. Here, MAg24 (M=Ag, Pd, Pt, and Au) NCs doped with diverse single heteroatoms have been encapsulated in a metal-organic framework (MOF), UiO-66-NH2, affording MAg24@UiO-66-NH2. Strikingly, compared with Ag25@UiO-66-NH2, the MAg24@UiO-66-NH2 doped with heteroatom exhibits much enhanced activity in photocatalytic hydrogen production, among which AuAg24@UiO-66-NH2 presents the best activity up to 3.6 mmol g-1 h-1, far superior to all other counterparts. Moreover, they display excellent photocatalytic recyclability and stability. X-ray photoelectron spectroscopy and ultrafast transient absorption spectroscopy demonstrate that MAg24 NCs encapsulated into the MOF create a favorable charge transfer pathway, similar to a Z-scheme heterojunction, when exposed to visible light. This promotes charge separation, along with optimized Ag electronic state, which are responsible for the superior activity in photocatalytic hydrogen production.

Exfoliation of Metal-Organic Frameworks to Give 2D MOF Nanosheets for the Electrocatalytic Oxygen Evolution Reaction

The structure and properties of materials are determined by a diverse range of chemical bond formation and breaking mechanisms, which greatly motivates the development of selectively controlling the chemical bonds in order to achieve materials with specific characteristics. Here, an orientational intervening bond-breaking strategy is demonstrated for synthesizing ultrathin metal-organic framework (MOF) nanosheets through balancing the process of thermal decomposition and liquid nitrogen exfoliation. In such approach, proper thermal treatment can weaken the interlayer bond while maintaining the stability of the intralayer bond in the layered MOFs. And the following liquid nitrogen treatment results in significant deformation and stress in the layered MOFs' structure due to the instant temperature drop and drastic expansion of liquid N2, leading to the curling, detachment, and separation of the MOF layers. The produced MOF nanosheets with five cycles of treatment are primarily composed of nanosheets that are less than 10 nm in thickness. The MOF nanosheets exhibit enhanced catalytic performance in oxygen evolution reactions owing to the ultrathin thickness without capping agents which provide improved charge transfer efficiency and dense exposed active sites. This strategy underscores the significance of orientational intervention in chemical bonds to engineer innovative materials.

Promoting Catalytic Performance Involving Hydrogen Spillover by Ion Exchange of Pt@A Catalysts to Regulate Reactant Adsorption

Zeolite-encapsulated metal nanoparticle systems have exhibited interesting catalytic performances via the hydrogen spillover process, yet how to further utilize the function of zeolite supports to promote catalytic properties in such a process is still challenging and has rarely been investigated. Herein, to address this issue, the strategy to strengthen the adsorption energy of reactant onto the zeolite surface via a simple ion exchange method has been implemented. Ion-exchanged linde type A (LTA) zeolite-encapsulated platinum nanoclusters (Pt@NaA, Pt@HA, Pt@KA, and Pt@CaA) were prepared to study the influence of ion exchange on the catalytic performance in the model reaction of hydrogenation of acetophenone to 1-phenylethanol. The reaction results showed that the Pt@CaA catalyst exhibited the best catalytic activity in the series of encapsulated catalysts, and the selectivity of 1-phenylethanol approached 100%. As revealed by density functional theory (DFT) calculations and acetophenone temperature-programmed desorption (acetophenone-TPD) experiments, in comparison with introduced cations of Na+, H+, and K+, ion-exchanged Ca2+ on the zeolite maximumly enhanced the adsorption of carbonyl groups in acetophenone, playing a critical role in achieving the highest activity and excellent catalytic selectivity among the Pt@A catalysts.

Selectivity Control in the Direct CO Esterification over Pd@UiO-66: The Pd Location Matters

The selectivity control of Pd nanoparticles (NPs) in the direct CO esterification with methyl nitrite toward dimethyl oxalate (DMO) or dimethyl carbonate (DMC) remains a grand challenge. Herein, Pd NPs are incorporated into isoreticular metal-organic frameworks (MOFs), namely UiO-66-X (X=-H, -NO2 , -NH2 ), affording Pd@UiO-66-X, which unexpectedly exhibit high selectivity (up to 99 %) to DMC and regulated activity in the direct CO esterification. In sharp contrast, the Pd NPs supported on the MOF, yielding Pd/UiO-66, displays high selectivity (89 %) to DMO as always reported with Pd NPs. Both experimental and DFT calculation results prove that the Pd location relative to UiO-66 gives rise to discriminated microenvironment of different amounts of interface between Zr-oxo clusters and Pd NPs in Pd@UiO-66 and Pd/UiO-66, resulting in their distinctly different selectivity. This is an unprecedented finding on the production of DMC by Pd NPs, which was previously achieved by Pd(II) only, in the direct CO esterification.

Electronic State and Microenvironment Modulation of Metal Nanoparticles Stabilized by MOFs for Boosting Electrocatalytic Nitrogen Reduction

Modulation of the local electronic structure and microenvironment of catalytic metal sites plays a critical role in electrocatalysis, yet remains a grand challenge. Herein, PdCu nanoparticles with an electron rich state are encapsulated into a sulfonate functionalized metal-organic framework, UiO-66-SO₃ H (simply as UiO-S), and their microenvironment is further modulated by coating a hydrophobic polydimethylsiloxane (PDMS) layer, affording PdCu@UiO-S@PDMS. This resultant catalyst presents high activity toward the electrochemical nitrogen reduction reaction (NRR, Faraday efficiency: 13.16%, yield: 20.24 µg h^-1 mg_cat. ^-1 ), far superior to the corresponding counterparts. Experimental and theoretical results jointly demonstrate that the protonated and hydrophobic microenvironment supplies protons for the NRR yet suppresses the competitive hydrogen evolution reaction reaction, and electron-rich PdCu sites in PdCu@UiO-S@PDMS are favorable to formation of the N₂ H* intermediate and reduce the energy barrier of NRR, thereby accounting for its good performance.

Discovery of a low-temperature Fe2O3 reduction route to Fe with carbon via Fe-MOF-74 decomposition

Fe₂O₃ reduction to Fe with carbon requires a high temperature of 1200 °C in a blast furnace process. We have discovered a novel low-temperature reduction route from γ-phase Fe₂O₃ to Fe with carbon. The reduction temperature was 430 °C, which is the lowest recorded up to now.

Light-Induced Selective Hydrogenation over PdAg Nanocages in Hollow MOF Microenvironment

Selective hydrogenation with high efficiency under ambient conditions remains a long-standing challenge. Here, a yolk-shell nanostructured catalyst, PdAg@ZIF-8, featuring plasmonic PdAg nanocages encompassed by a metal-organic framework (MOF, namely, ZIF-8) shell, has been rationally fabricated. PdAg@ZIF-8 achieves selective (97.5%) hydrogenation of nitrostyrene to vinylaniline with complete conversion at ambient temperature under visible light irradiation. The photothermal effect of Ag, together with the substrate enrichment effect of the catalyst, improves the Pd activity. The near-field enhancement effect from plasmonic Ag and optimized Pd electronic state by Ag alloying promote selective adsorption of the -NO₂ group and therefore catalytic selectivity. Remarkably, the unique yolk-shell nanostructure not only facilitates access to PdAg cores and protects them from aggregation but also benefits substrate enrichment and preferential -NO₂ adsorption under light irradiation, the latter two of which surpass the core-shell counterpart, giving rise to enhanced activity, selectivity, and recyclability.

Metal-based nano-delivery platform for treating bone disease and regeneration

Owing to their excellent characteristics, such as large specific surface area, favorable biosafety, and versatile application, nanomaterials have attracted significant attention in biomedical applications. Among them, metal-based nanomaterials containing various metal elements exhibit significant bone tissue regeneration potential, unique antibacterial properties, and advanced drug delivery functions, thus becoming crucial development platforms for bone tissue engineering and drug therapy for orthopedic diseases. Herein, metal-based drug-loaded nanomaterial platforms are classified and introduced, and the achievable drug-loading methods are comprehensively generalized. Furthermore, their applications in bone tissue engineering, osteoarthritis, orthopedic implant infection, bone tumor, and joint lubrication are reviewed in detail. Finally, the merits and demerits of the current metal-based drug-loaded nanomaterial platforms are critically discussed, and the challenges faced to realize their future applications are summarized.

Metal-Organic Framework-Based Nanoheater with Photo-Triggered Cascade Effects for On-Demand Suppression of Cellular Thermoresistance and Synergistic Cancer Therapy

Nanomedicine with stable light-heat conversion and spatiotemporally controllable drug activation is crucial for the success of photothermal therapy (PTT). Herein, a metal-organic framework (MOF)-based nanoheater with light-triggered multi-responsiveness is engineered to in-situ and on-demand sensitize cancer cells to local hyperthermia. Well-dispersed platinum nanoparticles synthesized inside nanospaces of the MOF are employed as the near-infrared (NIR)-harvesting unit with stable and high light-heat conversion performance. A conformation switchable polymer shell is constructed as a secondary light-responding unit to gate the targeted activation of a molecular inhibitor against thermoresistance. By cascade transformation of light stimuli to downstream signals, the nanoheater enables inhibitor release to go with local heating at the same time restricted in lesion sites to maximize efficacy and minimize systemic toxicity. The efficient photothermal conversion and the blockage of cellular heat-protective pathways provide a dual-mode of action which selectively sensitizes cancer cells to hyperthermia in a spatiotemporally controlled manner. With NIR as the remote switch, the MOF-based nanosystem demonstrates localized and boosted PTT efficacy against cancer both in vitro and in vivo. These results present nanosized MOFs as tailorable and versatile platforms for synergistic and precise cancer therapy.

Significantly lowered activation energy in proton conductor by Mg substitution in a layered Ni metal-organic framework

Designs and developments of proton conductors are highly important in chemistry and energy fields. In this study, a novel metal-organic framework H₂DAB-MgNi(ox)₃ was synthesized. X-ray powder diffraction, scanning transmission electron microscopy, and scanning transmission electron microscopy-energy-dispersive X-ray mapping measurements demonstrated that the H₂DAB-MgNi(ox)₃ had a solid-solution structure, with the homogeneous distribution of Mg and Ni elements. The proton conductivity of H₂DAB-MgNi(ox)₃ was enhanced from that of H₂DAB-Ni₂(ox)₃ at 95% relative humidity by Mg substitution.

Size-controlled, hollow and hierarchically porous Co2Ni2 alloy nanocubes for efficient oxygen reduction in microbial fuel cells

Schematic illustration of the fabrication of CoxNiy alloy nanocubes (ANCs) and hollow CoxNiy alloy nanocubes (HANCs).

Construction of Inverse Metal-Zeolite Interfaces via Area-Selective Atomic Layer Deposition

The spatial confinement at metal-zeolite interfaces offers a powerful knob to steer the selectivity of chemical reactions on metal catalysts. However, encapsulating metal catalysts into small-pore zeolites remains a challenging task. Here, we demonstrate an inverse design of metal-zeolite interfaces, "metal-on-zeolite," constructed by area-selective atomic layer deposition. This inverse design bypasses the intrinsic synthetic issues associated with metal encapsulation, offering a potential solution for the fabrication of task-specific metal-zeolite interfaces for desired catalytic applications. Infrared spectroscopy and several probe reactions confirmed the spatial confinement effects at the inverse metal-zeolite interfaces.

High Loading of Air-Sensitive Guest Molecules into Polycrystalline Metal-Organic Framework Hosts

Loading air-sensitive guest molecules inside polycrystalline metal-organic framework (MOF) hosts is currently a challenging process. In this study, the air-sensitive guest molecule magnesocene (MgCp₂) was loaded into two porous MOF hosts, polycrystalline Ni-MOF-74 and NH₂-MIL-101(Al), using a gas-phase infiltration process. X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning transmission electron microscopy, and scanning transmission electron microscopy-energy-dispersive X-ray mapping measurements demonstrated that MgCp₂ was successfully loaded inside the three-dimensional pores of NH₂-MIL-101(Al) with a maximum loading of 43.1 wt %. MgCp₂ was found to cover the outside of Ni-MOF-74 owing to the small one-dimensional channels.

Zeolite Fixed Metal Nanoparticles: New Perspective in Catalysis

ConspectusLoading metal nanoparticles on the surface of solid supports has emerged as an efficient route for the preparation of heterogeneous catalysts. Notably, most of these supported metal nanoparticles still have shortcomings such as dissatisfactory activity and low product selectivity in catalysis. In addition, these metal nanoparticles also suffer from deactivation because of nanoparticle sintering, leaching, and coke formation under harsh conditions. The fixation of metal nanoparticles within zeolite crystals should have advantages of high activities for metal nanoparticles and excellent shape selectivity for zeolite micropores as well as extraordinary stability of metal nanoparticles immobilized with a stable zeolite framework, which is a good solution for the shortcomings of supported metal nanoparticles.Materials with metal nanostructures within the zeolite crystals are normally denoted as metal@zeolite, where the metal nanoparticles with diameters similar to those of industrial catalysts are usually larger than the micropore size. These metal nanoparticles are enveloped with the zeolite rigid framework to prevent migration under harsh reaction conditions, which is described as a fixed structure. The zeolite micropores allow the diffusion of reactants to the metal nanoparticles. As a result, metal@zeolite catalysts combine the features of both metal nanoparticles (high activity) and zeolites (shape selectivity and thermal stability), compared with the supported metal nanoparticles.In this Account, we describe how the zeolite micropore and metal nanoparticle synergistically work to improve the catalytic performance by the preparation of a variety of metal@zeolite catalysts. Multiple functions of zeolites with respect to the metal nanoparticles are highlighted, including control of the reactant/product diffusion in the micropores, the adjustment of reactant adsorption on the metal nanoparticles, and sieving the reactants and products with zeolite micropores. Furthermore, by optimizing the wettability of the zeolite external surface, the zeolite crystals could form a nanoreactor to efficiently enrich the crucial intermediates, thus boosting the performance in low-temperature methane oxidation. Also, the microporous confinement weakens the adsorption of C₁ intermediates on the metal sites, accelerating the C-C coupling to improve C₂ oxygenate productivity in syngas conversion. In particular, the zeolite framework efficiently stabilizes the metal nanoparticles against sintering and leaching to give durable catalysts. Clearly, this strategy not only guides the rational design of efficient heterogeneous catalysts for potential applications in a variety of industrial chemical reactions but also accelerates the fundamental understanding of the catalytic mechanisms by providing new model catalysts.