Surface Composition Control of the Binary Au–Ag Catalyst for Enhanced Oxidant-Free Dehydrogenation

Covalent Organic Framework Impregnated with Silver and Copper Nanoparticles: An Advanced Approach for Catalytic Degradation of Organic Pollutants in Wastewater

In this study, we introduce an economically viable and scalable process for developing a novel covalent organic framework (COF), which is a cross-linked polymer. The resulting material, TzTFB-COF, is successfully functionalized with silver and copper nanoparticles, which show high adequacy in the degradation of nitroaromatic compounds (NACs). For the synthesis of TzTFB-COF, s-tetrazine diamine (Tz) and 1,3,5-triformylbenzene (TFB) are chosen as building blocks, which exhibit a high density of nitrogen-containing sites. TzTFB-COF shows good chemical and thermal stability (>300 °C). For functionalization of TzTFB-COF with silver and copper nanoparticles, a solution infiltration technique is used. The composite materials, i.e., Ag@TzTFB-COF and Cu@TzTFB-COF, have been characterized using various spectroscopic and analytical techniques, which show high activity, high selectivity, and excellent chemical and thermal stability up to 350 °C. The silver and copper contents of Ag@TzTFB-COF and Cu@TzTFB-COF are determined to be 9.6 and 12.4 wt % by inductively coupled plasma optical emission spectrometer (ICP-OES). The catalytic efficiency of the synthesized Ag@TzTFB-COF and Cu@TzTFB-COF materials is assessed in the context of catalyzing the hydrogenation of NACs. Experimental results reveal a remarkable catalytic performance when conducted in an aqueous medium, and notably, the materials demonstrate substantial potential for reusability across multiple catalytic cycles. The determined parameters for the catalytic hydrogenation reaction, i.e., the rate constants and Gibbs free energies, are found to be 0.0185 s-1 and 9.878 kJ/mol for Ag@TzTFB-COF and 0.0219 s-1 and 9.615 kJ/mol for Cu@TzTFB-COF. Thus, the catalytic reaction exhibits characteristics of endothermic, endergonic, and nonspontaneous nature.

Creation of a Highly Active Small Cu-Based Catalyst Derived from Copper Aluminium Layered Double Hydroxide Supported on α-Al2 O3 for Acceptorless Alcohol Dehydrogenation

A highly dispersed carbonate-intercalated Cu2+ -Al3+ layered double hydroxide (CuAl LDH) was created on an unreactive α-Al2 O3 surface (CuAl LDH@α-Al2 O3 ) via a simple coprecipitation method of Cu2+ and Al3+ under alkaline conditions in the presence of α-Al2 O3 . A highly reducible CuO nanoparticles was generated, accompanied by the formation of CuAl2 O4 on the surface of α-Al2 O3 (CuAlO@α-Al2 O3 ) after calcination at 1073 K in air, as confirmed by powder X-ray diffraction (XRD) and Cu K-edge X-ray absorption near edge structure (XANES). The structural changes during the progressive heating process were monitored by using in-situ temperature-programmed synchrotron XRD (tp-SXRD). The layered structure of CuAl LDH@α-Al2 O3 completely disappeared at 473 K, and CuO or CuAl2 O4 phases began to appear at 823 K or 1023 K, respectively. Our synthesised CuAlO@α-Al2 O3 catalyst was highly active for the acceptorless dehydrogenation of benzylic, aliphatic, or cyclic aliphatic alcohols; the TON based on the amount of Cu increased to 163 from 3.3 of unsupported CuAlO catalyst in 1-phenylethanol dehydrogenation. The results suggested that Cu0 was obtained from the reduction of CuO in the catalyst matrix during the reaction without separate reduction procedure and acted as a catalytically active species.

Catalysis of Alloys: Classification, Principles, and Design for a Variety of Materials and Reactions

Alloying has long been used as a promising methodology to improve the catalytic performance of metallic materials. In recent years, the field of alloy catalysis has made remarkable progress with the emergence of a variety of novel alloy materials and their functions. Therefore, a comprehensive disciplinary framework for catalytic chemistry of alloys that provides a cross-sectional understanding of the broad research field is in high demand. In this review, we provide a comprehensive classification of various alloy materials based on metallurgy, thermodynamics, and inorganic chemistry and summarize the roles of alloying in catalysis and its principles with a brief introduction of the historical background of this research field. Furthermore, we explain how each type of alloy can be used as a catalyst material and how to design a functional catalyst for the target reaction by introducing representative case studies. This review includes two approaches, namely, from materials and reactions, to provide a better understanding of the catalytic chemistry of alloys. Our review offers a perspective on this research field and can be used encyclopedically according to the readers' individual interests.

Catalytic Cracking for Propylene Production over Au Catalyst Supported by External Surface-Modified ZSM-5 Zeolite

To improve the yield of propylene in fluidized catalytic cracking, a series of different Au/ZSM-5-TOS catalysts were prepared by modifying ZSM-5, using an external surface modification method and Au nanoparticles. The modified catalyst maintained the MFI structure of ZSM-5, whereas the pore-opening size of the zeolite relatively decreased, without affecting its internal structure. The acidity of ZSM-5, especially the Brønsted acidity, reduced. Among the studied catalysts, the 0.2 wt% Au/ZSM-5-1%TOS catalyst exhibited the best feedstock conversion and propylene selectivity, along with a significant increase in propylene selectivity and a slight decrease in the conversion of light diesel oil, even after water vapor treatment at 800 °C for 4 h. Its catalytic activity at 360 °C exceeded that of ZSM-5 at 460 °C, showing great application potential in petrochemical processes.

Fundamental understanding of the synthesis of well-defined supported non-noble metal intermetallic compound nanoparticles

Fundamental insights into the synthesis of model-like, supported, non-noble metal intermetallic compound nanoparticle catalysts with phase pure bulk and bulk-like 1st-atomic-layer particle surface composition.

Green fabrication of hydrogel-immobilized Au@Ag nanoparticles using tannic acid and their application in catalysis

A catalytic hydrogel was obtained by immobilizing tannic acid reduced and stabilized Au@AgNPs on a PVA/TA hydrogel, used as the good solid catalyst for the degradation of environmental pollutants such as Congo red, 4-nitrophenol, -etc.

Facile Incorporation of Au Nanoparticles into an Unusual Twofold Entangled Zn(II)-MOF with Nanocages for Highly Efficient CO2 Fixation under Mild Conditions

Herein, a new porous Zn(II)-based metal-organic framework (MOF 1) has been prepared, the structure of which featured a twofold entangled motif based on two typical secondary building units (SBUs). The gas sorption studies indicated that MOF 1 may be explored as a useful platform to encapsulate metallic nanoparticles. Then the Au@1 composite has been prepared via a facile incorporation method without extra reducing agents. The Au@1 composite has been fully characterized by HRTEM, SEM-EDX, PXRD, gas sorption, XPS, ICP, etc. Catalytic experiments showed that the Au@1 composite had a perfect catalytic performance in CO₂ fixation for epoxides with different substituents under mild conditions.

Ag-Based nanocomposites: synthesis and applications in catalysis

Ag-Based nanocomposites, including supported Ag nanocomposites and bimetallic Ag nanocomposites, have been intensively investigated as highly efficient catalysts because of their high activity and stability, easy preparation, low cost, and low toxicity. Herein, we systematically summarize and comprehensively evaluate versatile synthetic strategies for the preparation of Ag-based nanocomposites, and outline their recent advances in catalytic oxidation, catalytic reduction, photocatalysis and electrocatalysis. In addition, the challenges and prospects related to Ag-based nanocomposites for various catalytic applications are also discussed. In light of the most recent advances in Ag-based nanocomposites for catalysis applications, this review provides a comprehensive assessment on the material selection, synthesis and catalytic characteristics of these catalysts, which offers a strategic guide to build a close connection between Ag nanocomposites and catalysis applications.

The preparation of new covalent organic framework embedded with silver nanoparticles and its applications in degradation of organic pollutants from waste water

Ag@TPHH-COF can be used as efficient catalyst for the reduction of the various nitroaromatic compounds and organic dyes in industrial wastewater.

Preparation of carbon-based AuAg alloy nanoparticles by using the heterometallic [Au4Ag4] cluster for efficient oxidative coupling of anilines

We herein report the preparation of unique heteroatom-doped and carbon-based AuAg alloy nanoparticles (NPs) via the pyrolysis of a structurally defined octanuclear heterometallic Au(i)-Ag(i) cluster [Au4Ag4(Dppy)4(Tab)4(MeCN)4](PF6)8 (2, Dppy = diphenylphosphine-2-pyridine and Tab = 4-(trimethylammonio)benzenethiolate). This cluster-precursor approach exerts a fine control over the spatial arrangement, size and uniformity of the AuAg alloy NPs as well as the doped heteroatoms (P, N, F and S). The optimized material prepared at 450 °C efficiently catalyzes the oxidative coupling of anilines to yield azobenzenes under mild conditions.

Cu supported on thin carbon layer-coated porous SiO2 for efficient ethanol dehydrogenation

The designed Cu/C/SiO₂ catalyst combines the favourable properties of carbon and silica, thus showing improved selectivity associated with good stability.

Bimetallic Rh–Fe catalysts for N2O decomposition: effects of surface structures on catalytic activity

Well-homogenized RhFe alloy nanoparticles and core–shell structured Fe@Rh nanoparticles were highly dispersed on SBA-15 and then applied to N₂O catalytic conversion.

Silica-Supported Au-Ag Catalysts for the Selective Hydrogenation of Butadiene

Gold and silver are miscible over the entire composition range, and form an attractive combination for fundamental studies on bimetallic catalysts. Au-Ag catalysts have shown synergistic effects for different oxidation and liquid-phase hydrogenation reactions, but have rarely been studied for gas-phase hydrogenation. In this study 3 nm particles of Au, Ag and Au-Ag supported on silica (SBA-15) were investigated as catalysts for selective hydrogenation of butadiene in an excess of propene. The Au catalyst was over an order of magnitude more active than the Ag catalyst at 120 °C. The initial activity of the Au-Ag catalysts scaled linearly with the Au-content, suggesting a direct correlation between the surface and overall compositions of the nanoparticles and the absence of synergistic effects. All Au-containing catalysts were highly selective to butenes (>99.9 %). The Au catalysts were stable, whereas the Au-Ag catalysts lost about half of their activity during 20 h run time at 200 °C, but the initial activity was restored by a consecutive oxidation-reduction treatment. Near ambient pressure x-ray photoelectron spectroscopy showed that exposure to H2 at elevated temperatures led to a gradual enrichment of the surface of the Au-Ag nanoparticles by Ag. These observations highlight the importance of considering progressive atomic rearrangements in bimetallic nanocatalysts under reaction conditions.

Effect of nanoscale flows on the surface structure of nanoporous catalysts

The surface structure and composition of a multi-component catalyst are critical factors in determining its catalytic performance. The surface composition can depend on the local pressure of the reacting species, leading to the possibility that the flow through a nanoporous catalyst can affect its structure and reactivity. Here, we explore this possibility for oxidation reactions on nanoporous gold, an AgAu bimetallic catalyst. We use microscopy and digital reconstruction to obtain the morphology of a two-dimensional slice of a nanoporous gold sample. Using lattice Boltzmann fluid dynamics simulations along with thermodynamic models based on first-principles total-energy calculations, we show that some sections of this sample have low local O2 partial pressures when exposed to reaction conditions, which leads to a pure Au surface in these regions, instead of the active bimetallic AgAu phase. We also explore the effect of temperature on the surface structure and find that moderate temperatures (≈300-450 K) should result in the highest intrinsic catalytic performance, in apparent agreement with experimental results.

Single target sputter deposition of alloy nanoparticles with adjustable composition via a gas aggregation cluster source

Alloy nanoparticles with variable compositions add a new dimension to nanoscience and have many applications. Here we suggest a novel approach for the fabrication of variable composition alloy nanoparticles that is based on a Haberland type gas aggregation cluster source with a custom-made multicomponent target for magnetron sputtering. The approach, which was demonstrated here for gold-rich AgAu nanoparticles, combines a narrow nanoparticle size distribution with in operando variation of composition via the gas pressure as well as highly efficient usage of target material. The latter is particularly attractive for precious metals. Varying argon pressure during deposition, we achieved in operando changes of AgAu alloy nanoparticle composition of more than 13 at%. The alloy nanoparticles were characterized by x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. The characteristic plasmon resonances of multilayer nanoparticle composites were analyzed by UV-vis spectroscopy. Tuning of the number of particles per unit area (particle densities) within individual layers showed an additional degree of freedom to tailor the optical properties of multilayer nanocomposites. By extension of this technique to more complex systems, the presented results are expected to encourage and simplify further research based on plasmonic multi-element nanoparticles. The present method is by no means restricted to plasmonics or nanoparticle based applications, but is also highly relevant for conventional magnetron sputtering of alloys and can be extended to in operando control of alloy concentration by magnetic field.

Ag-NPs embedded in two novel Zn3/Zn5-cluster-based metal–organic frameworks for catalytic reduction of 2/3/4-nitrophenol

Two novel microporous Zn-MOFs consist of different SBUs have been used to embed Ag NPs, resulting in two composite catalysts, which show outstanding catalytic activities toward the reduction of nitrophenol.