Supported Bimetallic Cluster Catalysts

Bimetallic Nanoalloy Catalysts for Green Energy Production: Advances in Synthesis Routes and Characterization Techniques

Bimetallic Nanoalloy catalysts have diverse uses in clean energy, sensing, catalysis, biomedicine, and energy storage, with some supported and unsupported catalysts. Conventional synthetic methods for producing bimetallic alloy nanoparticles often produce unalloyed and bulky particles that do not exhibit desired characteristics. Alloys, when prepared with advanced nanoscale methods, give higher surface area, activity, and selectivity than individual metals due to changes in their electronic properties and reduced size. This review demonstrates the synthesis methods and principles to produce and characterize highly dispersed, well-alloyed bimetallic nanoalloy particles in relatively simple, effective, and generalized approaches and the overall existence of conventional synthetic methods with modifications to prepare bimetallic alloy catalysts. The basic concepts and mechanistic understanding are represented with purposely selected examples. Herein, the enthralling properties with widespread applications of nanoalloy catalysts in heterogeneous catalysis are also presented, especially for Hydrogen Evolution Reaction (HER), Oxidation Reduction Reaction (ORR), Oxygen Evolution Reaction (OER), and alcohol oxidation with a particular focus on Pt and Pd-based bimetallic nanoalloys and their numerous fields of applications. The high entropy alloy is described as a complicated subject with an emphasis on laser-based green synthesis of nanoparticles and, in conclusion, the forecasts and contemporary challenges for the controlled synthesis of nanoalloys are addressed.

Electrospun CuCoN0.6 coating necklace-like N-doped carbon nanofibers for high performance lithium-sulfur batteries

Freestanding electrodes with high energy density and cycle stability have attracted attention on the development of lithium-sulfur (Li-S) batteries. However, both severe shuttle effect and sluggish conversion kinetics hinder their practical applications. Herein, we employed the electrospinning and subsequent nitridation processes to prepare a necklace-like structure of CuCoN_0.6 nanoparticles anchored on N-doped carbon nanofibers (CuCoN_0.6/NC) as freestanding sulfur host for Li-S batteries. Such bimetallic nitride boosts chemical adsorption and catalytic activity throughout detailed theoretical calculation and experimental electrochemical characterization. The three-dimensional conductive necklace-like framework could provide abundant cavities for realizing high sulfur utilization and alleviating the volume variation, as well as fast lithium-ions diffusion and electron transfer. The Li-S cell with the S@CuCoN_0.6/NC cathode delivers a stable cycling performance with a capacity attenuation rate of 0.076% per cycle after 150cycles at 2.0C and an exceptional capacity retention of 657 mAh g^-1 even at a high sulfur loading of 6.8 mg cm^-2 over 100cycles. The facile and scalable method can help promote the widespread application of fabrics.

Nested Metal Catalysts: Metal Atoms and Clusters Stabilized by Confinement with Accessibility on Supports

Supported catalysts that are important in technology prominently include atomically dispersed metals and metal clusters. When the metals are noble, they are typically unstable-susceptible to sintering-especially under reducing conditions. Embedding the metals in supports such as organic polymers, metal oxides, and zeolites confers stability on the metals but at the cost of catalytic activity associated with the lack of accessibility of metal bonding sites to reactants. An approach to stabilizing noble metal catalysts while maintaining their accessibility involves anchoring them in molecular-scale nests that are in or on supports. The nests include zeolite pore mouths, zeolite surface cups (half-cages), raft-like islands of oxophilic metals bonded to metal oxide supports, clusters of non-noble metals (e.g., hosting noble metals as single-atom alloys), and nanoscale metal oxide islands that selectively bond to the catalytic metals, isolating them from the support. These examples illustrate a trend toward precision in the synthesis of solid catalysts, and the latter two classes of nested catalysts offer realistic prospects for economical large-scale application.

Comprehensive Model for the Synthesis of γ-Al2O3 Microsphere-Supported Bimetallic Iron- and Copper Oxide Materials

The effects of incipient wetness impregnation synthesis conditions on the macro- and microscopic properties of bimetallic iron oxide/copper oxide@γ-Al₂O₃ microspheres were elucidated. The key steering factors for the macroscopic distribution of the metals throughout the support, and for the metal nanoparticle sizes, were the pH of the impregnation solution, the counterions present in the metal precursor, the amount of negatively charged groups on the alumina, the complexation of iron, the impregnation strategy (simultaneous or sequential) and, in the latter case, the order of impregnation. The interactions taking place during impregnation are identified as competitive adsorption of charged dissolved species (Fe/Cu cations, protons, and additional anions) in the impregnation solution. Adsorption can take place on either charged alumina sites or previously deposited metal (i.e., iron on iron, copper on copper, iron on copper, and copper on iron) and is affected by counterion shielding. Modeling of these interactions via simulation on an in-house-developed python code allowed quantification of the adsorption constants for each of the above-mentioned processes, where iron adsorbs much faster than copper on all surfaces, and adsorption of iron on both alumina surface groups and previously deposited copper contributes majorly to the final iron distribution. The findings in this work will allow for better prediction and control over bimetallic materials synthesized via the simple and scalable impregnation procedure.

Cu-Mo Bimetal Modulated Multifunctional Carbon Nanofibers Promoting the Polysulfides Conversion for High-Sulfur-Loading Lithium-Sulfur Batteries

High sulfur loading is essential for achieving high energy density lithium-sulfur (Li-S) batteries. However, serious issues such as low sulfur utilization, poor cycling stability, and sluggish rate performance have been exposed when increasing the sulfur loading for freestanding cathodes. To solve these problems, the adsorption/catalytic ability of high-sulfur-loading cathode toward polysulfides must be improved. Herein, based on excellent properties of cationic MOFs, we proposed that Cu-Mo bimetallic nanoparticles embedded in multifunctional freestanding nitrogen-doped porous carbon nanofibers (Cu-Mo@NPCN) with efficient catalytic sites could be prepared by facile MoO₄^2- anion exchange of cationic MOFs. And, the sulfur embedded in Cu-Mo@NPCN was directly used as self-supporting electrodes, enabling a high areal capacity, good rate performance, and decent cycling stability even under high sulfur loading. The freestanding Cu-Mo@NPCN/10.3S cathode achieves a high volumetric capacity of 1163 mA h cm^-3 and a decent areal capacity of 9.3 mA h cm^-2 at 0.2 C with a sulfur loading of 10.3 mg cm^-2. This work provides an innovative approach for engineering a freestanding sulfur cathode and would forward the development of cationic MOF-derived bimetallic catalysts in various energy storage systems.

Recent progress of Ga-based liquid metals in catalysis

Within the last decade, the application of gallium-based liquid metals in catalysis has received great attention from around the world. This article provides an overview concerning Ga-based liquid metals (LMs) in energy and environmental applications, such as the catalytic synthesis of ethylene by non-petroleum routes via Pd-Ga liquid catalysts, alkane dehydrogenation via Pd-Ga or Pt-Ga catalysts, CO2 hydrogenation to methanol via Ni Ga or Pd/Ga2O3 catalysts, and catalytic degradation of CO2 via EGaIn liquid metal catalysts below 500 °C, where Ga-based liquid metal catalysts exhibit high selectivity and low energy consumption. The formation of isolated metal sites in a liquid metal matrix allows the integration of several characteristics of multiphase catalysis (particularly the operational friendliness of product separation procedures) with those of homogeneous catalysis. In the end, this article sheds light on future prospects, opportunities, and challenges of liquid metal catalysis.

Confinement of Ultrasmall Bimetallic Nanoparticles in Conductive Metal-Organic Frameworks via Site-Specific Nucleation

Conductive metal-organic frameworks (cMOFs) are emerging materials for various applications due to their high surface area, high porosity, and electrical conductivity. However, it is still challenging to develop cMOFs having high surface reactivity and durability. Here, highly active and stable cMOF are presented via the confinement of bimetallic nanoparticles (BNPs) in the pores of a 2D cMOF, where the confinement is guided by dipolar-interaction-induced site-specific nucleation. Heterogeneous metal precursors are bound to the pores of 2D cMOFs by dipolar interactions, and the subsequent reduction produces ultrasmall (≈1.54 nm) and well-dispersed PtRu NPs confined in the pores of the cMOF. PtRu-NP-decorated cMOFs exhibit significantly enhanced chemiresistive NO₂ sensing performances, owing to the bimetallic synergies of PtRu NPs and the high surface area and porosity of cMOF. The approach paves the way for the synthesis of highly active and conductive porous materials via bimetallic and/or multimetallic NP loading.

Synthesis of carbon-supported sub-2 nanometer bimetallic catalysts by strong metal-sulfur interaction

Small-sized bimetallic nanoparticles that integrate the advantages of efficient exposure of the active metal surface and optimal geometric/electronic effects are of immense interest in the field of catalysis, yet there are few universal strategies for synthesizing such unique structures. Here, we report a novel method to synthesize sub-2 nm bimetallic nanoparticles (Pt-Co, Rh-Co, and Ir-Co) on mesoporous sulfur-doped carbon (S-C) supports. The approach is based on the strong chemical interaction between metals and sulfur atoms that are doped in the carbon matrix, which suppresses the metal aggregation at high temperature and thus ensures the formation of small-sized and well alloyed bimetallic nanoparticles. We also demonstrate the enhanced catalytic performance of the small-sized bimetallic Pt-Co nanoparticle catalysts for the selective hydrogenation of nitroarenes.

The Design and Science of Polyelemental Nanoparticles

Polyelemental nanoparticles (PE NPs) containing four or more elements in a single NP have intriguing intrinsic properties compared to their single-element counterparts. The fusion of diverse elements induces synergistic effects including new physical and chemical phenomena. However, conventional methods have not offered effective strategies for the uniform creation of PE NPs with high reproducibility. Recently, with advances in nanoscience, several new methods have been developed using both thermodynamic and kinetic approaches and, often, the interplay between them. In this Perspective, we highlight recent key advances in the design of PE NPs and their underlying formation mechanisms. We discuss the potential applications of PE NPs and the outlook and future directions for this field.

Bimetallic Catalysts for Volatile Organic Compound Oxidation

In recent years, the impending necessity to improve the quality of outdoor and indoor air has produced a constant increase of investigations in the methodologies to remove and/or to decrease the emission of volatile organic compounds (VOCs). Among the various strategies for VOC elimination, catalytic oxidation and recently photocatalytic oxidation are regarded as some of the most promising technologies for VOC total oxidation from urban and industrial waste streams. This work is focused on bimetallic supported catalysts, investigating systematically the progress and developments in the design of these materials. In particular, we highlight their advantages compared to those of their monometallic counterparts in terms of catalytic performance and physicochemical properties (catalytic stability and reusability). The formation of a synergistic effect between the two metals is the key feature of these particular catalysts. This review examines the state-of-the-art of a peculiar sector (the bimetallic systems) belonging to a wide area (i.e., the several catalysts used for VOC removal) with the aim to contribute to further increase the knowledge of the catalytic materials for VOC removal, stressing the promising potential applications of the bimetallic catalysts in the air purification.

Regioselective generation and reactivity control of subnanometric platinum clusters in zeolites for high-temperature catalysis

Subnanometric metal species (single atoms and clusters) have been demonstrated to be unique compared with their nanoparticulate counterparts. However, the poor stabilization of subnanometric metal species towards sintering at high temperature (>500 °C) under oxidative or reductive reaction conditions limits their catalytic application. Zeolites can serve as an ideal support to stabilize subnanometric metal catalysts, but it is challenging to localize subnanometric metal species on specific sites and modulate their reactivity. We have achieved a very high preference for localization of highly stable subnanometric Pt and PtSn clusters in the sinusoidal channels of purely siliceous MFI zeolite, as revealed by atomically resolved electron microscopy combining high-angle annular dark-field and integrated differential phase contrast imaging techniques. These catalysts show very high stability, selectivity and activity for the industrially important dehydrogenation of propane to form propylene. This stabilization strategy could be extended to other crystalline porous materials.

A general synthesis approach for supported bimetallic nanoparticles via surface inorganometallic chemistry

The synthesis of ultrasmall supported bimetallic nanoparticles (between 1 and 3 nanometers in diameter) with well-defined stoichiometry and intimacy between constituent metals remains a substantial challenge. We synthesized 10 different supported bimetallic nanoparticles via surface inorganometallic chemistry by decomposing and reducing surface-adsorbed heterometallic double complex salts, which are readily obtained upon sequential adsorption of target cations and anions on a silica substrate. For example, adsorption of tetraamminepalladium(II) [Pd(NH3)42+] followed by adsorption of tetrachloroplatinate [PtCl42−] was used to form palladium-platinum (Pd-Pt) nanoparticles. These supported bimetallic nanoparticles show enhanced catalytic performance in acetylene selective hydrogenation, which clearly demonstrates a synergistic effect between constituent metals.

Vibrational spectroscopy of the double complex salt Pd(NH3)4(ReO4)2, a bimetallic catalyst precursor

Tetraamminepalladium(II) perrhenate, a double complex salt, has significant utility in PdRe catalyst preparation; however, the vibrational spectra of this readily prepared compound have not been described in the literature. Herein, we present the infrared (IR) and Raman spectra of tetraamminepalladium(II) perrhenate and several related compounds. The experimental spectra are complemented by an analysis of normal vibrational modes that compares the experimentally obtained spectra with spectra calculated using DFT (DMol³). The spectra are dominated by features due to the ammine groups and the ReO stretch in T_d ReO₄^-; lattice vibrations due to the D_4h Pd(NH₃)₄²⁺ are also observed in the Raman spectrum. Generally, we observe good agreement between ab initio calculations and experimental spectra. The calculated IR spectrum closely matches experimental results for peak positions and their relative intensities. The methods for calculating resonance Raman intensities are implemented using the time correlator formalism using two methods to obtain the excited state displacements and electron-vibration coupling constants, which are the needed inputs in addition to the normal mode wave numbers. Calculated excited state energy surfaces of Raman-active modes correctly predict relative intensities of the peaks and Franck-Condon activity; however, the position of Raman bands are predicted at lower frequencies than observed. Factor group splitting of Raman peaks observed in spectra of pure compounds is not predicted by DFT.

Pt–FeOx/SiO2catalysts prepared by galvanic displacement show high selectivity for cinnamyl alcohol production in the chemoselective hydrogenation of cinnamaldehyde

Intimately interacting Pt–FeO_xentities preparedviagalvanic displacement are highly selective for the chemoselective hydrogenation of the CO bond in cinnamaldehyde.

Platinum carbonyl clusters stabilized by Sn(ii)-based fragments: syntheses and structures of [Pt6(CO)6(SnCl2)2(SnCl3)4]4−, [Pt9(CO)8(SnCl2)3(SnCl3)2(Cl2SnOCOSnCl2)]4−and [Pt10(CO)14{Cl2Sn(OH)SnCl2}2]2−

Low valent Pt carbonyl clusters decorated by Sn(ii) fragments have been obtained from [Pt₁₅(CO)₃₀]²⁻and SnCl₂.

Synthesis of heterocycles and fused heterocycles catalyzed by nanomaterials

The application of nanomaterials as heterogeneous catalyst for the synthesis of different heterocyclic systems is reviewed.

Segregation in bimetallic nanoparticles

Theoretical models and experimental results for segregation in bimetallic nanoparticles are discussed and compared in this perspective.

Dispersion and distribution of bimetallic oxides in SBA-15, and their enhanced activity for reverse water gas shift reaction

Bimetallic oxides could be well distributed on the SBA-15 surface, and exhibited high catalytic perforation for RWGS reaction.

Nanostructured materials for applications in heterogeneous catalysis

In this review, a brief survey is offered on the main nanotechnology synthetic approaches available to heterogeneous catalysis, and a few examples are provided of their usefulness for such applications. We start by discussing the use of colloidal, reverse micelle, and dendrimer chemistry in the production of active metal and metal oxide nanoparticles with well-defined sizes, shapes, and compositions, as a way to control the surface atomic ensembles available for selective catalysis. Next we introduce the use of sol-gel and atomic layer deposition chemistry for the production and modification of high-surface-area supports and active phases. Reference is then made to the more complex active sites that can be created or carved on such supports by using organic structure-directing agents. We follow with an examination of the ability to achieve multiple functionality in catalysis via the design of dumbbells, core@shell, and other complex nanostructures. Finally, we consider the mixed molecular-nanostructure approach that can be used to develop more demanding catalytic sites, by derivatizing the surface of solids or tethering or immobilizing homogeneous catalysts or other chemical functionalities. We conclude with a personal and critical perspective on the importance of fully exploiting the synergies between nanotechnology and surface science to optimize the search for new catalysts and catalytic processes.