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This article is an account of the work carried out in the authors' laboratory illustrating the usefulness of dendrimer design for nanoparticle palladium catalysis. The "click" synthesis of dendrimers constructed generation by generation by 1-->3 C connectivity, introduces 1,2,3-triazolyl ligands insides the dendrimers at each generation. Complexation of the ligands by Pd(II) followed by reduction to Pd(0) forms dendrimer-stabilized Pd nanoparticles (PdNPs) that are extremely reactive in the catalysis of olefin hydrogenation and C-C bond coupling reactions. The stabilization can be outer-dendritic for the small zeroth-generation dendrimer or intra-dendritic for the larger first- and second-generation dendrimers. The example of the Miyaura-Suzuki reaction that can be catalyzed by down to 1 ppm of PdNPs with a "homeopathic" mechanism (the less, the better) is illustrated here, including catalysis in aqueous solvents.

Over the past decades, significant attempts have been devoted to the preparation of click dendrimers for using novel catalysts in chemical processes. The click dendrimers were synthesized using copper-catalyzed 1,3-dipolar cycloaddition reaction of an azide with a terminal alkyne to afford a 1,2,3-triazole. These materials have aroused great interest in several fields. Numerous click dendrimers were synthesized in almost good yields via the CuAAC "click" reaction and their catalytic applications have been investigated. This mini-review aims to present the fundamental advances in the click chemistry area applied to dendrimers synthesis as well as their catalytic applications in different chemical processes. [ABSTRACT FROM AUTHOR]

Click chemistry involving copper-catalyzed azide–alkyne cycloaddition (CuAAC) is one of the most useful and powerful methods to construct metallodendrimers. The design of such strategies includes the choice of the copper(I) catalyst source which is critical in the case of the click synthesis of dendrimers. The 1,2,3-triazolyl-containing dendrimers that are produced provide useful intradendritic ligands that are active in supramolecular recognition and catalysis. This account dedicated to K. Peter C. Vollhardt summarizes work conducted mainly in the authors' Bordeaux laboratory. 1 Introduction 2 Click Copper Catalyzed Azide–Alkyne Cycloaddition Metallodendrimer Constructions 3 The Copper-Catalyzed Azide–Alkyne Cycloaddition Reactions in Dendrimers: Mind the Copper(I) Catalyst 4 Redox Recognition with Triazolylferrocenyl- and Triazolylbiferrocenyl- Terminated Dendrimers 5 Click Catalysis with Extremely Efficient Intradendritic Triazolyl– Copper(I) Complexes 6 Click Dendrimers as Stabilizers for Very Efficient Nanoparticle Catalysis of Cross-Coupling Carbon–Carbon Bond Formation and Redox Reactions 7 Click Dendrons and Dendrimers for Efficient Catalysis Using Magnetically Recoverable Catalysts 8 Conclusion and Prospects [ABSTRACT FROM AUTHOR]

Abstract: Dendronized polymer (DP)-encapsulated gold nanoparticles (AuNPs) are well prepared and characterized, and their catalytic performance is also evaluated. First, the nanoreactors self-assembled from water-soluble 1,2,3-triazolyl DP 1 are employed as templates to generate DP-encapsulated AuNPs. The resulting AuNPs are characterized through UV-visible spectroscopy and high-resolution transmission electron microscopy. The catalytic activity of DP-encapsulated AuNPs was estimated by the conversion of 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) in water and an extremely catalytic activity is found for the reduction reaction with remarkable TONs up to 2000 and TOFs up to 7350 h− 1. This catalytic performance is comparable to these micellar AuNPs encapsulated by the known analogues including the trz-containing triethylene glycol (TEG) and polyethylene glycol (PEG) dendrimers, which may be because that DPs 1 has the similar behavior in solution as the dendrimer analogues.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Modern methods that involve intradendritic catalysis are introduced in this feature article. Supramolecular principles, therefore, derive from the concept of the unimolecular dendritic micelle introduced by Newkome. When the micellar effect is combined with intradendritic ligand acceleration, copper(I) catalysts or palladium nanoparticles (PdNPs) are required at the ppm level for efficient reactions. Applications range from organic catalysis to catalysis by metal complexes of intradendritic ligands and dendrimer-stabilized nanoparticles (NPs) that are located at the dendrimer core or between the dendrimer tethers. Bimetallic nanoparticle-cored dendrimers including superparamagnetic iron oxide nanoparticles (SPIONs) are especially promising due to very facile magnetic separation. [ABSTRACT FROM AUTHOR]

Abstract: Transition metal nanoparticles (TMNPs) are very efficient catalysts even without ligands for a large number of reactions. On the other hand, comparison between catalytic efficiencies of TMNPs is key to mechanistic understanding. Here late TMNPs stabilized by a click dendrimer containing an arene core and 27 triethylene glycol (TEG) termini have been synthesized for Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au by NaBH4 reduction in water of TM cations that are coordinated to the dendritic triazole groups. All these late TMNPs have been characterized by transmission electron microcopy with core sizes being between 1.4 and 5.2 nm and by UV-vis spectroscopy. The catalytic activities of these freshly synthesized TMNPs under N2 have been compared for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4, a standard reference reaction. Kinetic studies and induction times for this reaction have been recorded. They show that the catalytic activity is all the better as the metal atoms are more electron rich and that the click dendrimer frame sterically inhibits the rate-limiting approach of the substrates to the TMNP surface. These stereoelectronic trends are in agreement with Ballauffs’ mechanism involving NP restructuration as rate limiting.Graphical Abstract: Catalysis of 4-nitrophenol reduction by NaBH4 by eleven “click” dendrimer-stabilized late yransition-metal nanoparticles is compared. A remarkable increase of catalytic activity has been disclosed in the periodic table upon increasing the TM atomic number both from the first row down to the third-raw TMs and within the same row of transition metals. [ABSTRACT FROM AUTHOR]

Metal nanoparticles have been widely used for catalysis because of its excellent catalytic activity and selectivity. Green and sustainable supports play a quite important role in the enhancement of the efficiency and recyclability of metal nanoparticles. Here, a cellulose/β-cyclodextrin hydrogel is applied to support tannic acid-encapsulated metal (such as Ag, Au, Pd and Cu) nanoparticles to generate nanocomposite hydrogels for catalysis. TEM analysis indicates that these metal nanoparticles have the average diameters of 6.5 nm for Au nanoparticles, 7.0 nm for Ag nanoparticles, 5.0 nm for Pd nanoparticles and 4.0 nm for Cu nanoparticles, respectively. The catalytic activities of the as-prepared metal nanocomposite hydrogels are estimated in a series of chemical reactions in the aqueous system. The recyclability, applicability and generality of these nanocomposite hydrogels are also well investigated. The nanocomposite hydrogels can be reused for at least 10 times in the 4-nitrophenol reduction, 8 times for Suzuki–Miyaura coupling reaction and 6 times for click reaction, respectively. Furthermore, good yields are obtained in the catalytic process. This study gives a green and sustainable strategy to support metal nanoparticles with good catalytic activity and recyclability. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) have been synthesized directly inside liposomes using honey as a reducing agent. The obtained aggregates, named Cassyopea® Gold due to the method used for their preparation, show remarkable properties as reactors and carriers of the investigated AuNPs. A mean size of about 150 nm and negative surface charge of -46 mV were measured for Cassyopea® Gold through dynamic light scattering and zeta potential measurements, respectively. The formation of the investigated gold nanoparticles into Cassyopea® liposomes was spectroscopically confirmed by the presence of their typical absorption band at 516 nm. The catalytic activity of the combined liposome–AuNP nanocomposites was tested via the thermal cis–trans isomerization of resonance-activated 4-methoxyazobenzene (MeO-AB). The kinetic rate constants (kobs) determined at 25 °C in the AuNP aqueous solution and in the Cassyopea® Gold samples were one thousand times higher than the values obtained when performing MeO-AB cis–trans conversion in the presence of pure Cassyopea®. The results reported herein are unprecedented and point to the high versatility of Cassyopea® as a reactor and carrier of metal nanoparticles in chemical, biological, and technological applications. [ABSTRACT FROM AUTHOR]

In this study, we have reported an eco-friendly, very simple, in-situ method for the synthesis of silver-reduced graphene oxide nanocomposite (Ag-rGO) by using ascorbic acid and chitosan as stabilizing and reducing agents. Chitosan is a naturally occurring polysaccharide polymer with excellent adhesion properties which allows the binding of silver ions to the chitosan matrix, thereby reducing it. The addition of chitosan-stabilized silver nanoparticles to rGO increases its mechanical properties, yielding a nanocomposite. The catalytic activity of the synthesized silver-rGO nanocomposite for the reduction of p-nitrophenol is examined. The Ag-rGO exhibits good catalytic activity for the reduction of p-nitrophenol within a very short duration of time. [ABSTRACT FROM AUTHOR]

Dentromers (from dentro, δεντρο: tree in Greek), and meros (μεροσ, in greek: part) are introduced as a family of dendrimers constructed according to successive divergent 1 → 3 branching. The smaller dentromers have 27 terminal branches. With alcohol termini they were originally named arborols by Newkome, who pioneered 1 → 3 constructions of dendrimers and dendrons. Giant dentromers have been constructed and decorated in particular with ferrocene and other redox active groups. The synthesis, specific properties, and applications are examined in this mini review article dedicated to Don Tomalia, with an emphasis on dense peripheral packing favoring the functions of encapsulation, redox sensing, and micellar template for catalysis in water and aqueous solvents. [ABSTRACT FROM AUTHOR]

High-performance catalysts for the oxygen reduction and hydrogen evolution reactions (ORR and HER, respectively) are highly sought-after, particularly with the commitment of numerous agencies to the removal of conventional gas vehicles in the next few decades. Surprisingly little focus has been placed on the development of magnetic models to describe these systems. The current work will review the current understanding of surface heterogeneous catalysis across select magnetic surfaces, with attention focused on studies involving extended surfaces, which inherently are more accessible to fundamental analysis than the more applied nanoparticle systems. However, even the most up-to-date magnetic variants of this theory have focused on the tight binding limit of the d-band model. In this limit, the reactivity of the surface is governed by the position of the center of the d-band, and the model does not account for the higher moments of the d-band, such as the width, asymmetry, and modality. A summary of the theory supporting this analysis will be presented, along with a summary of the current literature on this level of analysis. The review will then conclude with a discussion of suggested directions for future investigations. [ABSTRACT FROM AUTHOR]

The increasing use of nanomaterials in consumer products is expected to lead to environmental contamination sometime soon. As water pollution is a pressing issue that threatens human survival and impedes the promotion of human health, the search for adsorbents for removing newly identified contaminants from water has become a topic of intensive research. The challenges in the recyclability of contaminated water continue to campaign the development of highly reusable catalysts. Although exfoliated 2D MXene sheets have demonstrated the capability towards water purification, a significant challenge for removing some toxic organic molecules remains a challenge due to a need for metal-based catalytic properties owing to their rapid response. In the present study, we demonstrate the formation of hybrid structure AuNPs@MXene (Mo2CT x ) during the sensitive detection of Au nanoparticle through MXene sheets without any surface modification, and subsequently its applications as an efficient catalyst for the degradation of 4-nitrophenol (4-NP), methyl orange (MO), and methylene blue (MB). The hybrid structure (AuNPs@MXene) reveals remarkable reusability for up to eight consecutive cycles, with minimal reduction in catalytic efficiency and comparable apparent reaction rate constant (K app) values for 4-NP, MB, and MO, compared to other catalysts reported in the literature. [ABSTRACT FROM AUTHOR]

Fine-tuned interaction between reacting molecules and metal surface is of great importance in heterogeneous catalysis for the design of highly selective processes. Conventional strategies based on adjusting the intrinsic catalyst properties such as particle size, metal-support interaction and morphology suffer from complicated and time-consuming synthetic procedures. Recently, the modification of metal nanoparticles with non-metallic promoters has been demonstrated as an effective tool to regulate the interfacial environment of metallic catalysis. Herein, we will give an overview of recent progress in this area. A general analysis will be proposed about the electronic, steric effects and new functionalities imposed by non-metallic promoters of metal catalysts. The potential for the selectivity enhancement of the promoted metal catalysts in various industrially important reactions is discussed. [ABSTRACT FROM AUTHOR]

Metal nanoframes have gained tremendous attention in the domain of modern research and development due to their distinctive 3D spatial structure, efficient physiochemical properties, and comparatively good activity. Different strategies have been implicated by the researchers to design nanoframes of varying chemical natures and shapes. Most of the synthetic protocols being adopted to design nanoframes consist of two main steps: nucleation and the growth of solid particles and, secondly, excavation of the interiors. In this context, many synthetic methods are overviewed. To show their unprecedented performance or activity, a few applications in catalysis, biomedicine, theranostics, SERS, the sensing of different materials, the reduction of CO2, etc., are also discussed. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal Nanomaterials titled "Catalysis by Metal-Oxide Nanostructures." The issue features several research papers that highlight the diverse applications of metal-oxide nanostructures in catalytic processes. The papers cover topics such as selective hydrogenation, electrocatalysis, magnetic core-shell catalysts, functionalized magnetic nanoparticles, photocatalysis, biomass conversion, heterojunction synthesis, nucleic acid interactions, wastewater treatment, partial hydrogenation, CO2 conversion, metal-organic-framework-supported nanocatalysts, Fenton catalysts, hydrogen evolution reactions, gold catalysts, metal-support interactions, and catalytic methane decomposition. The papers provide insights into the potential of metal-oxide nanostructures for sustainable and efficient catalysis. [Extracted from the article]

Much experimental work has been contributed to all-metal σ, π and δ-aromaticity among transition metals, semimetallics and other metals in the past two decades. Before our focused investigations on the properties of triangular and sandwich-shaped all-metal aromatics, A. I. Boldyrev presented general discussions on the concepts of all-metal σ-aromaticity and σ-antiaromaticity for metallo-clusters. Schleyer illustrated that Nucleus-Independent Chemical Shifts (NICS) were among the most authoritative criteria for aromaticity. Ugalde discussed the earlier developments of all-metal aromatic compounds with all possible shapes. Besides the theoretical predictions, many stable all-metal aromatic trinuclear clusters have been isolated as the metallic analogues of either the σ-aromatic molecule's [H3]+ ion or the π-aromatic molecule's [C3H3]+ ion. Different from Hoffman's opinion on all-metal aromaticity, triangular all-metal aromatics were found to hold great potential in applications in coordination chemistry, catalysis, and material science. Triangular all-metal aromatics, which were theoretically proved to conform to the Hückel (4n + 2) rule and possess the smallest aromatic ring, could also play roles as stable ligands during the formation of all-metal sandwiches. The triangular and sandwich-shaped all-metal aromatics have not yet been specifically summarized despite their diversity of existence, puissant developments and various interesting applications. These findings are different from the public opinion that all-metal aromatics would be limited to further applications due to their overstated difficulties in synthesis and uncertain stabilities. Our review will specifically focus on the summarization of theoretical predictions, feasible syntheses and isolations, and multiple applications of triangular and sandwich shaped all-metal aromatics. The appropriateness and necessities of this review will emphasize and disseminate their importance and applications forcefully and in a timely manner. [ABSTRACT FROM AUTHOR]

This article discusses recent developments in the photocatalytic reduction of nitro compounds to valuable intermediates, such as amines and azo compounds. Nitro compounds are widely used in various industries but pose environmental and health hazards due to their toxicity and nondegradability. Traditional reduction methods often use harsh conditions and toxic chemicals, making the utilization of photocatalytic organic transformations an attractive option for sustainable and green chemical processes. The article provides an overview of different photocatalytic systems, including metal-organic frameworks, semiconductors, and nanocomposites, and explores their synthesis, performance, stability, recyclability, and selectivity. The use of hole scavengers and sacrificial reagents to enhance the reduction process is also mentioned. The studies demonstrate the potential of these photocatalytic systems for efficient and environmentally friendly nitro compound reduction. [Extracted from the article]

Developing green fibrous materials with uniformly distributed metal nanoparticles for highly efficient and recyclable catalysis remains a major challenge. Herein, we developed a simple, effective, and green method to immobilize gold nanoparticles (AuNPs) on polydopamine (PDA)-functionalized silk fibers (SFs) for efficient catalytic reduction of 4-nitrophenol (4-NP). The density and size of AuNPs on the PDA-coated SFs can be tuned by adjusting precursor concentration and synthesis duration, respectively. The AuNPs-PDA-SFs catalysts prepared under optimized conditions could catalyze the reduction of 4-NP, 4-nitroaniline (4-NA), and 4-amino-3-nitrophenol (4-A-3-NP) at the apparent rate constants of 0.087, 0.091, and 0.063 min−1, respectively. After six rounds of flow-through reduction of 4-NP, the AuNPs-PDA-SFs could maintain a 4-NP conversion rate greater than 92%, indicating their superior reusability and consistent catalytic activity. Due to the protein properties of SFs, the AuNPs-PDA-SFs can be degraded by enzymes and alkali solutions. This work may provide new insights for designing advanced fiber-supported recyclable catalysts with high catalytic performance and reusability in wastewater treatment. [ABSTRACT FROM AUTHOR]

Electric fields have been highlighted as a smart reagent in nature's enzymatic machinery, as they can directly trigger or accelerate chemical processes with stereo- and regio-specificity. In enzymatic catalysis, controlled mass transport of chemical species is also key in facilitating the availability of reactants in the active reaction site. However, recent progress in developing a clean catalysis that profits from oriented electric fields is limited to theoretical and experimental studies at the single molecule level, where both the control over mass transport and scalability cannot be tested. Here, we quantify the electrostatic catalysis of a prototypical Huisgen cycloaddition in a large-area electrode surface and directly compare its performance to the conventional Cu(I) catalysis. Our custom-built microfluidic cell enhances reagent transport towards the electrified reactive interface. This continuous-flow microfluidic electrostatic reactor is an example of an electric-field driven platform where clean large-scale electrostatic catalytic processes can be efficiently implemented and regulated. Can we utilize electric fields (EF) as a smart reagent to catalyze chemical processes? Here the authors develop a continuous-flow electrostatic reactor as a microfluidic platform that allows for the effective catalysis of click reaction over a large electrode surface exploiting voltage-controlled EF as the sole catalyst. [ABSTRACT FROM AUTHOR]

The leaching phenomenon of gold (Au) nanomaterials by Pb2+ ions in the presence of 2-mercaptoethanol (2-ME) and thiosulfate (S2O32− ion) has been systematically applied to a Pb2+ ion sensor. To further investigate the role of Pb2+ ions in sensors containing Au nanomaterials, we revisited the leaching conditions for Au nanorods and compared them with the results for Au nanotriangles. By monitoring the etching rate, it was revealed that Pb2+ ions were important for the acceleration of the etching rate mainly driven by 2-ME and S2O32− pairs, and nanomolar detection of Pb2+ ions were shown to be promoted through this catalytic effect. Using the etchant, the overall size of the Au nanorods decreased but showed an unusual red-shift in UV-Vis spectrum indicating increase of aspect ratio. Indeed, the length of Au nanorods decreased by 9.4% with the width decreasing by 17.4% over a 30-min reaction time. On the other hand, the Au nanotriangles with both flat sides surrounded mostly by dense Au{111} planes showed ordinary blue-shift in UV-Vis spectrum as the length of one side was reduced by 21.3%. By observing the changes in the two types of Au nanomaterials, we inferred that there was facet-dependent alloy formation with lead, and this difference resulted in Au nanotriangles showing good sensitivity, but lower detection limits compared to the Au nanorods. [ABSTRACT FROM AUTHOR]

The integration of dual asymmetric catalysis is highly beneficial for the synthesis of organic molecules with multiple stereocenters. However, two major issues that need to be addressed are the intrinsic deactivation of dual-species and the extrinsic conflict of reaction conditions. To overcome these concerns, we have utilized the compartmental and thermoresponsive properties of poly(N-isopropylacrylamide) (PNIPAM) to develop a cross-linked PNIPAM-hydrogel-supported bifunctional catalyst. This catalyst is designed with Rh(diene) species situated on the outer surface and Ru(diamine) species positioned within the interior of the hydrogel. The compartmental function of PNIPAM in the middle overcomes intrinsic mutual deactivations between the dual-species. The thermoresponsive nature of PNIPAM allows for precise control of catalytic pathways in resolving external conflicts by controlling the reaction switching between an Rh-catalyzed enantioselective 1,4-addition at 50°C and a Ru-catalyzed asymmetric transfer hydrogenation (ATH) at 25°C. As we envisioned, this sequential 1,4-addition/reduction dual enantioselective cascade reaction achieves a transformation from incompatibility to compatibility, resulting in direct access to γ-substituted cyclic alcohols with dual stereocenters in high yields and enantio/diastereoselectivities. Mechanistic investigation reveals a reversible temperature transition between 50°C and 25°C, ensuring a cascade process comprising a 1,4-addition followed by the ATH process. Dual asymmetric catalysis is powerful for the synthesis of multi-stereocenter molecules, however, the integration of dual catalysts remains challenging due to the intrinsic deactivation of dual-species and extrinsic conflict of reaction conditions. Here, the authors develop a compartmental and thermoresponsive poly(N-isopropylacrylamide)-hydrogel-supported bifunctional catalyst to overcome these challenges. [ABSTRACT FROM AUTHOR]

The present review is devoted to the application of transition metal complexes with such ligands as amino acids, peptides and carbohydrates in catalysis. The literature published over the past 20 years is surveyed. Among the distinctive features of these ligands are their versatility, optical activity, stability and availability. Furthermore, depending on the specific synthetic task to be solved, these ligands open up almost infinite opportunity for modification. Largely thanks to their multifaceted reactivity, transition metal complexes with amino acids, peptides and carbohydrates can catalyze most of the known chemical reactions affording optically pure compounds. In this review, the emphasis is placed upon C(sp3)–H activation, cross-coupling and hydrogenation (including traditional hydrogenation in the presence of hydrogen gas and hydrogenation with hydrogen transfer) reactions. The choice is not accidental, since these reactions on the one hand display the catalytic versatility of the above complexes, and on the other hand, they are widely employed in industry. [ABSTRACT FROM AUTHOR]

This work focuses on the synthesis of a new series of amphiphilic derivatives of calix[4]arenes for the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The aggregation properties of synthesized calix[4]arenes were studied using various techniques (fluorescence spectroscopy, nanoparticle tracking analysis, and dynamic light scattering). Increasing the length of the alkyl substituent led to stronger hydrophobic interactions, which increased polydispersity in solution. The zwitterionic nature of the synthesized calix[4]arenes was established using different types of dyes (Eosin Y for anionic structures and Rhodamine 6G for cationic structures). The synthesized calix[4]arenes were used as organic stabilizers for CuI. The catalytic efficiency of CuI-calix[4]arene was compared with that of the phase transfer catalyst tetrabutylammonium bromide (TBAB) and the surfactant sodium dodecyl sulfate (SDS). For all calixarenes, the selectivity in the CuAAC reaction was higher than that observed when TBAB and SDS were estimated. [ABSTRACT FROM AUTHOR]

A single-step method for aniline formation was examined. Using a vanadate catalyst with an iron oxide co-catalyst and hydroxylamine hydrochloride as the amine source, an up to 90% yield of aniline was obtained with high selectivity. Further study showed that the overall reaction was pseudo-second order in terms of hydroxylamine concentration. Regioselective H-D exchange experiments suggest that the C-N bond formation step occurs via an irreversible electrophilic pathway. Based on all of the key observations, a mechanism is proposed. [ABSTRACT FROM AUTHOR]

We here report the synthesis, characterization, and catalytic performance of new supported Pd(0) catalysts. The catalysts were characterized by SEM, TEM, XRD, FT-IR, VSM, XPS, TG and AAS. The results showed that the catalyst exhibited good catalytic activity in the reaction of degradation of 4-NP and organic dyes MO and MB in water with NaBH4 and amino borane (AB) as the hydrogen sources. At the same time, the catalyst has good recoverability and is easily recovered and recycled from the reaction mixture by applying an external magnet and reusing it in five cycles without significant loss in activity. In the present work, our deliberately designed experiments demonstrate that Ni@Pd immobilized on the surface of hollow Fe3O4@PPy-Gly (HFPG) under mild condition. It exhibits high activity for the reduction of 4-NP and organic dyes by NaBH4 and AB. [ABSTRACT FROM AUTHOR]

The design and fabrication of nanomaterials with controllable morphology and size is of critical importance to achieve excellent catalytic performance in heterogeneous catalysis. In this work, cobalt oxide (Co3O4) nanostructures with different morphologies (nanoplates, microflowers, nanorods and nanocubes) were successfully constructed in order to establish the morphology–property–performance relationship of the catalysts. The morphology and structure of the nanostructured Co3O4 were characterized by various techniques, and the catalytic performance of the as-prepared nanostructures was studied by monitoring the reduction of p-nitrophenol to p-aminophenol in the presence of excess NaBH4. The catalytic performance was found to be strongly dependent on their morphologies. The experimental results show that the pseudo-first-order reaction rate constants for Co3O4 nanostructures with various shapes are, respectively, 1.49 min−1 (nanoplates), 1.40 min−1 (microflowers), 0.78 min−1 (nanorods) and 0.23 min−1 (nanocubes). The Co3O4 nanoplates exhibited the highest catalytic activity among the four nanostructures, due to their largest specific surface area, relatively high total pore volume, best redox properties and abundance of defect sites. The established correlation between morphology, property and catalytic performance in this work will offer valuable insight into the design and application of nanostructured Co3O4 as a potential non-noble metal catalyst for p-nitrophenol reduction. [ABSTRACT FROM AUTHOR]

The work considers the preparation in an undivided cell of Pd–Cu and Pd–Au bimetallic nanoparticles (NPs) by methylviologen (MV2+)-mediated electrochemical reduction of equimolar amounts of Cu(II), Pd(II), and Au(I) in the presence of poly(N-vinylpyrrolidone) (PVP) and nanocellulose (NC) under controlled potential of the generating MV•+ cation radical in aqueous medium at room temperature. Electrosyntheses are performed by sequential or joint reduction of metal ions by passing a theoretical charge. When Pd(II) ions are added to CuNPs, as well as when Au(I) ions are added to PdNPs, a galvanic replacement process is observed, namely oxidation of Cu0 by Pd(II) and Pd0 Au(I) ions. The results of the complete reduction are nanocomposites of mainly spherical MNPs, dispersed in the solution bulk and stabilized by PVP on the surface of the NC. In the sequential synthesis of CuNPs and then PdNPs, the nanocomposite is represented as Cu2O nanoroses coated with fine PdNPs. Pd nanocomposites with Cu2O or Au are represented mainly by spherical particles with size of 4–50 nm depending on the production method. X-ray powder diffraction (XRPD) data of the nanocomposites confirm the formation of a mixture of PdNPs (0.8–10 nm) with large gold crystallites (up to 24 nm), as well as the oxidation of CuNPs to cuprite (Cu2O). The size of the metal crystallites and copper oxide varies in the range from 0.8 to 24 nm. In the test reaction of p‑nitrophenol reduction with sodium borohydride in aqueous medium, all of the tested nanocomposites show time-increasing catalytic activity. When Cu is added to Pd, the catalytic reduction reaction is maintained, while the addition of Au to Pd decreases the catalytic activity of PdNPs by an order of magnitude. [ABSTRACT FROM AUTHOR]

Polysaccharide/silica hybrid microcapsules were prepared using ionic gelation followed by spray-drying. Chitosan and alginate were used as biopolymer matrices, and in situ prepared silica was used as a structuring additive. The prepared microparticles were used in two very different applications: the encapsulation of hydrophilic molecules, and as a support for palladium nanoparticles used as catalysts for a model organic reaction, namely the reduction of p-nitrophenol by sodium borhydride. In the first application, erioglaucine disodium salt, taken as a model hydrophilic substance, was encapsulated in situ during the preparation of the microparticles. The results indicate that the presence of silica nanostructures, integrated within the polymer matrix, affect the morphology and the stability of the particles, retarding the release of the encapsulated substance. In the second application, chloropalladate was complexed on the surface of chitosan microparticles, and palladium(II) was subsequently reduced to palladium(0) to obtain heterogeneous catalysts with an excellent performance. [ABSTRACT FROM AUTHOR]

Methods for carrying out coupling reactions in the chemistry of alkynes to form C–C bonds (oxidative dehydrocondensation reactions, Cadiot–Chodkiewicz reaction, and Sonogashira reaction) are analyzed and generalized. Protocols of synthesis of products of these reactions are also presented, including homogeneous and heterogeneous catalytic systems. In all cases, emphasis is placed on the kinetics and mechanisms of reactions with the discussion of the results of kinetic and spectrometric studies of the mechanisms of coupling reactions involving Cu(I, II, III), Au(I, III), Pd(0, I, II), and Fe (0, I, II, III) complexes. Particular attention is paid to the heterogeneous catalysis of oxidation reactions of alkynes with the participation of nanoparticles and nanoclusters of Pd, Au, Ag, and other metals. The nature of the intermediates containing these metals and the relationships between various oxidative and nonoxidative transformations of alkynes are discussed. [ABSTRACT FROM AUTHOR]

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Assessing competitive environmental catalytic reduction processes via NaBH4 is essential, as BH4− is both an energy carrier (as H2) and a reducing agent. A comprehensive catalytic study of the competition between the borohydride hydrolysis reaction (BHR, releasing H2) and 4-nitrophenol reduction via BH4− on M0- and M/M′ (alloy)-nanoparticle catalysts is reported. The results reveal an inverse correlation between the catalytic efficiency for BH4− hydrolysis and 4-nitrophenol reduction, indicating that catalysts performing well in one process exhibit lower activity in the other. Plausible catalytic mechanisms are discussed, focusing on the impact of reaction products such as 4-aminophenol and borate on the rate and yield of BH4− hydrolysis. The investigated catalysts were Ag0, Au0, Pt0, and Ag/Pt-alloy nanoparticles synthesized without any added stabilizer. Notably, the observed rate constants for the 4-nitrophenol reduction on Ag0, Ag-Pt (9:1), and Au0 are significantly higher than the corresponding rate constants for BH4− hydrolysis, suggesting that most reductions do not proceed through surface-adsorbed hydrogen atoms, as observed for Pt0 nanoparticles. This research emphasizes the conflicting nature of BH4− hydrolysis and reduction processes, provides insights for designing improved catalysts for competitive reactions, and sheds light on the catalyst properties required for each specific process. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) lamellar Zn metal–organic framework (Zn-MOF, 1) with a fluorescent 1,6-di(pyridin-3-yl)pyrene (3-DPPy) and 1,4-benzenedicarboxylate (BDC2−) bridging linkers was prepared and structurally characterized. The chemical formula of 1 is [Zn(μ-3-DPPy)(μ-BDC)]n. The mononuclear Zn(II) ion, acting as a node, is tetrahedrally coordinated with two 3-DPPy and two BDC linkers. The coordination environment of Zn(II) is a distorted tetrahedral geometry. The Zn-MOF is the sql network structure based on topology analysis. The undulated 2D sheets of 1 tightly pack together to form a lamellar structure. The pyrene moieties are parallelly oriented to each other. The Zn-MOF is not porous, possibly because the mononuclear Zn(II) node did not form cluster-based secondary building units due to the less symmetric 3-DPPy. The steady-state fluorescence measurements indicate that the fluorescence signal of the 1 is slightly blue-shifted compared to the free 3-DPPy in the solid state. The excimer emission band at 463 nm for crystalline 3-DPPy is shifted to 447 nm for 1. The value of 447 nm is also a blue-shift value compared to nonsubstituted pyrene crystals (470 nm). Despite its nonporosity, the surface Lewis acidic sites of 1 could catalyze the transesterification of esters. Surface defect sites are responsible for this catalytic activity. [ABSTRACT FROM AUTHOR]

Bifunctional catalysts consisting of metal-containing nanoparticles (NPs) and zeolite supports have received considerable attention due to their excellent catalytic properties in numerous reactions, including direct (biomass is a substrate) and indirect (platform chemical is a substrate) biomass processing. In this short review, we discuss major approaches to the preparation of NPs in zeolites, concentrating on methods that allow for the best interplay (synergy) between metal and acid sites, which is normally achieved for small NPs well-distributed through zeolite. We focus on the modification of zeolites to provide structural integrity and controlled acidity, which can be accomplished by the incorporation of certain metal ions or elements. The other modification avenue is the adjustment of zeolite morphology, including the creation of numerous defects for the NP entrapment and designed hierarchical porosity for improved mass transfer. In this review, we also provide examples of synergy between metal and acid sites and emphasize that without density functional theory calculations, many assumptions about the interactions between active sites remain unvalidated. Finally, we describe the most interesting examples of direct and indirect biomass (waste) processing for the last five years. [ABSTRACT FROM AUTHOR]

This review presents the state of the art of interactions between two different families of nanoobjects: nanoparticles—mainly metal nanoparticles, and dendrimers—mainly phosphorhydrazone dendrimers (or dendrons). The review firstly presents the encapsulation/protection of existing nanoparticles (organic or metallic) by phosphorus-based dendrimers and dendrons. In the second part, several methods for the synthesis of metal nanoparticles, thanks to the dendrimer that acts as a template, are presented. The properties of the associations between dendrimers and nanoparticles are emphasized throughout the review. These properties mainly concern the elaboration of diverse types of hybrid materials, some of them being used as sensitive chemosensors or biosensors. Several examples concerning catalysis are also given, displaying in particular the efficient recovery and reuse of the catalytic entities. [ABSTRACT FROM AUTHOR]

Nanoscopic materials have demonstrated a versatile role in almost every emerging field of research. Nanomaterials have come to be one of the most important fields of advanced research today due to its controllable particle size in the nanoscale range, capacity to adopt diverse forms and morphologies, high surface area, and involvement of transition and non-transition metals. With the introduction of porosity, nanomaterials have become a more promising candidate than their bulk counterparts in catalysis, biomedicine, drug delivery, and other areas. This review intends to compile a self-contained set of papers related to new synthesis methods and versatile applications of porous nanomaterials that can give a realistic picture of current state-of-the-art research, especially for catalysis and sensor area. Especially, we cover various surface functionalization strategies by improving accessibility and mass transfer limitation of catalytic applications for wide variety of materials, including organic and inorganic materials (metals/metal oxides) with covalent porous organic (COFs) and inorganic (silica/carbon) frameworks, constituting solid backgrounds on porous materials. [ABSTRACT FROM AUTHOR]

Dynamic metal nanoclusters have garnered widespread attention due to their unique properties and potential applications in various fields. Researchers have been dedicated to developing new synthesis methods and strategies to control the morphologies, compositions, and structures of metal nanoclusters. Through optimized synthesis methods, it is possible to prepare clusters with precise sizes and shapes, providing a solid foundation for subsequent research. Accurate determination of their crystal structures is crucial for understanding their behavior and designing custom functional materials. Dynamic metal nanoclusters also demonstrate potential applications in catalysis and optoelectronics. By manipulating the sizes, compositions, and surface structures of the clusters, efficient catalysts and optoelectronic materials can be designed and synthesized for various chemical reactions and energy conversion processes. This review summarizes the research progress in the synthesis methods, crystal structure characterization, and potential applications of dynamic metal nanoclusters. Various nanoclusters composed of different metal elements are introduced, and their potential applications in catalysis, optics, electronics, and energy storage are discussed. Additionally, the important role of dynamic metal nanoclusters in materials science and nanotechnology is explored, along with an overview of the future directions and challenges in this field. [ABSTRACT FROM AUTHOR]

The need for an alternative energy source that is both clean and abundant has led to research into a hydrogen economy. Hydrogen gas can be produced slowly via the hydrolysis of sodium borohydride (NaBH4). A catalyst can be used to speed up the rate at which hydrogen is produced, however many catalysts involve relatively expensive materials like precious metals. This study explores a novel copper nanoparticle supported on a graphene-like material composite as a catalyst for the hydrolysis of NaBH4. The material was characterized via powdered X-ray diffraction (P-XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and Energy Dispersive spectroscopy (EDS). The P-XRD confirmed the crystallinity structures of graphene-like material (GLM) and copper nanoparticles supported over graphene-like material (CuGLM). The P-XRD spectra indicated the (110), (111), and (200) lattice planes of copper nanoparticles. In FTIR analysis, the shifted and sharpening functional group peaks were observed when copper nanoparticles were supported by the GLM template. The TEM result indicated that the copper nanoparticle had a size of approximately 10 nm. The catalyst (CuGLM) was tested under different doses of NaBH4, solution pH, and reaction temperatures. Temperature data were used to determine the activation energy of the reaction to be 46.8 kJ mol−1, which is competitive when compared to similar catalysts. The catalyzed reaction generated the highest volume of hydrogen at pH 8 (51 mL), 303 K (32 mL), and 1225 μmol of NaBH4 (37 mL). The catalyst was found to be able to be used multiple times in succession without any significant loss in hydrogen generated. This catalyst is an exciting option for the sustainable generation of hydrogen gas as a fuel source. [ABSTRACT FROM AUTHOR]

The dwindling supply of fossil fuels has prompted the search for an alternative energy source that could effectively replace them. Potential renewable energy sources such as solar, wind, tidal, and geothermal are all promising but each has its own drawbacks. Hydrogen gas on the other hand can be combusted to produce energy with only water as a byproduct and can be steadily generated via the aqueous media hydrolysis reaction of Sodium Borohydride (NaBH4). This study successfully synthesized fused carbon spheres derived from sugar and decorated them with platinum nanoparticles to form a novel composite material (PtFCS) for catalyzing this reaction. The platinum nanoparticles were produced by reducing chloroplatinic acid in a solution with sodium borohydride and using sodium citrate as a capping agent for the nanoparticles. Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were used to characterize and determine the size and shape of the Pt nanoparticles (PtNPs) and fused carbon spheres. TEM was able to determine the average size of the fused carbon spheres to be 200 nm and the average size for the PtNPs to be 2–3 nm. The PtFCS composite was tested for its ability to catalyze the hydrolysis of NaBH4 under various reaction conditions including various solution pH, various temperatures, and various dosages of sodium borohydride. The catalyst was found to perform the best under acidic solution conditions (pH 6), producing hydrogen at a rate of 0.0438 mL/mgcat·min. The catalyst was determined to have an activation energy of 53.0 kJ/mol and could be used multiple times in succession with no loss in the volume of hydrogen produced. This sugar-derived composite catalyst shows promise and could be implemented as a sustainable catalyst for the generation of hydrogen fuel. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have emerged as a promising class of porous materials for various applications such as catalysis, gas storage, and separation. This review provides an overview of MOFs' synthesis, properties, and applications in these areas. The basic concepts of MOFs, and their significance in catalysis, gas storage, and separation are introduced. The general synthetic approaches for MOFs, the factors influencing MOF synthesis, and the recent advancements in MOF synthesis are discussed. The structural properties, porosity, surface area, chemical and thermal stability, and tunability of MOFs are described. The review also covers MOFs' applications in catalysis, including homogeneous and heterogeneous catalysis and biocatalysis, as well as gas storage, including hydrogen, methane, and carbon dioxide storage. Additionally, it highlights MOFs application in gas separation, such as separating hydrogen, carbon dioxide, and nitrogen from other gases. Finally, the challenges in MOF synthesis and characterization, future research directions, and potential for commercialization and industrial applications are discussed. This review demonstrates the versatility and potential of MOFs as next-generation materials for catalysis, gas storage, and separation. [ABSTRACT FROM AUTHOR]

Understanding the interface between soluble metal complexes and supported metal particles is important in order to reveal reaction mechanisms in a new generation of highly active homogeneous transition metal catalysts. In this study, we show that, in the case of palladium forming on a carbon (Pd/C) catalyst from a soluble Pd(0) complex Pd2dba3, the nature of deposited particles on a carbon surface turns out to be much richer than previously assumed, even if a very simple experimental procedure is utilized without the use of additional reagents and procedures. In the process of obtaining a heterogeneous Pd/C catalyst, highly active "hidden" metal centers are formed on the carbon surface, which are leached out by the solvent and demonstrate diverse reactivity in the solution phase. The results indicate that heterogeneous catalysts may naturally contain trace amounts of molecular monometallic centers of a different nature by easily transforming them to the homogeneous catalytic system. In line with a modern concept, a heterogenized homogeneous catalyst precursor was found to leach first, leaving metal nanoparticles mostly intact on the surface. In this study, we point out that the previously neglected soft leaching process contributes to high catalyst activity. The results we obtained demand for leaching to be reconsidered as a flexible tool for catalyst construction and for the rational design of highly active and selective homogeneous catalytic systems, starting from easily available heterogeneous catalyst precursors. [ABSTRACT FROM AUTHOR]

1,2,3-Triazoles bearing additional functional groups have found applications as the ligands in catalysis of a broad scope of reactions, synthesis of transition metals complexes for various practicable purposes, and design of metal-based drugs. Triazolyl ligands accelerating CuAAC reactions, such as TBTA and TTTA, are nowadays commonly used in organic synthesis, and the search for novel ligands with a less complicated structure represents an important task. In the present work a series of hydroxyalkyltriazoles, containing a cyclooctane core, were synthesized via cycloaddition of readily available individual diastereomers of azidoalcohols or diazidodiols with phenylacetylene. The obtained hydroxyalkyltriazoles were probed as ligands for CuAAC reactions of benzyl azide with acetylenes, and 1-[(4-phenyl-1H-1,2,3-triazol-1-yl)methyl]cyclooctanol was demonstrated to act as an effective ligand for these processes. The complex salt of the abovementioned triazole and CuCl2 was readily obtained. According to X-ray diffraction analysis data, the complex contained two molecules of triazole, in which only N1-atoms of the triazole ring acted as coordination centers. Such a molecular structure correlates well with the efficiency of 1-[(4-phenyl-1H-1,2,3-triazol-1-yl)methyl]cyclooctanol as a ligand in CuAAC reactions: it is able to coordinate copper ions and, at the same time, it forms a sufficiently labile complex to not withdraw copper ions from the catalytic cycle. [ABSTRACT FROM AUTHOR]

Metal nanoparticles have gained considerable attention as versatile nanomaterials due to their size- and shape- dependent electrical, electronic, optical, and catalytic properties. Various physical and chemical approaches have been investigated for synthesizing metal nanoparticles, specifically gold nanoparticles due to their biocompatibility, antioxidant potentials, catalytic activity, and other promising characteristics. As the chemical based approaches have led to questions on toxicity, plant-based sources and microorganisms like bacteria, fungi and algae have been evaluated for synthesizing metal nanoparticles. Gold nanoparticles derived from biological sources are expected to have different properties than those derived from chemical sources, allowing for a wider range of applications. This review provides an overview of the myriad of sources explored for the synthesis of gold nanoparticles which have found useful applications in several fields. The general approach for synthesizing gold nanoparticles is provided followed by the major applications in specific fields namely medicine, biology, electrochemistry and catalysis. Additionally, the possible challenges and future prospects of biosynthesis of nanoparticles have been highlighted. This work could provide an update on the recent advances in the applications of biogenic nanoparticles for future developments. [ABSTRACT FROM AUTHOR]

Transition-metal-catalyzed asymmetric hydrogenation (AH) is a growing field and a fundamental tool for the construction of chiral compounds. The use of earth-abundant transition metals in AH reactions remains generally limited but has received increased attention in recent years due to cost, sustainability, and environmental concerns. Here, we will summarize progress in first row transition metal catalyzed AH of minimally functionalized alkenes, including scope, mechanism, and challenges in this field. 1 Introduction 2 Ti-Catalyzed AH of Minimally Functionalized Alkenes 3 Zr-Catalyzed AH of Minimally Functionalized Alkenes 4 Co-Catalyzed AH of Minimally Functionalized Alkenes 5 Fe-Catalyzed AH of Minimally Functionalized Alkenes 6 Summary and Outlook [ABSTRACT FROM AUTHOR]

Single-atom catalysts (SACs) have been synthesized using a variety of methods in recent years, and they have shown excellent catalytic activities. However, metal atoms show a high tendency to agglomerate in liquid media, making the single atom synthesis more difficult in liquid media. The synthesis of such metal single-atom catalysts that do not have strong ligand coordination is rarely reported in the literature. Herein, we report the facile synthesis of monodispersed Au atoms (Au1) through the reduction in HAuCl4 in 15-crown-5. The complete reduction in HAuCl4 was confirmed through UV-Vis spectroscopy. In addition, the Au was found in a zero valence state after reduction, which was confirmed through XPS and XANES results. Moreover, the dispersion of Au was confirmed as a single atom (Au1) through transmission electron microscopy and spherical aberration electron microscopy. The possible structure of this catalyst was proposed by matching the EXAFS results with the structure of Au1@15-crown-5 as -(OC2H4O)-AuCl2H2. The Au1@15-crown-5 showed high activity (TOF as high as 22,075) in the reduction in nitrophenol and nitroaniline to aminophenol and phenylenediamine by sodium borohydride. Because of the monodispersion of Au atoms, its performance is much better than noble nanoparticles and non-precious metal catalysts. [ABSTRACT FROM AUTHOR]

Oxanorbornene cored 0.5, 1.5 and 2.5 generation ester terminated PAMAM dendronized monomers with 2 and 6 carbon-containing alkyl spacer in the middle of oxanorbornene core and dendronized branching were synthesized. Monomers were polymerized through the ring-opening metathesis polymerization (ROMP) technique by using 2nd and 3rd generation Grubbs catalysts to get dendronized ROMP polymers. It was found that Grubbs 3rd generation catalyst works well for 0.5 generation dendronized ROMP polymer whereas Grubbs 2nd generation catalyst works for the higher generation. We also found the linker effect during polymerization as six-carbon linker monomers polymerize with high yield along with higher generation. Finally, dendronized ROMP-based PAMAM encapsulated zero valent Cu nanoparticle was synthesized by using a reducing agent, NaBH4. The catalytic activity of this nanoparticle was further investigated from the reduction of 4-nitrophenol to 4-aminophenol. [ABSTRACT FROM AUTHOR]

MoS2 nanoflowers (NFs) obtained through a hydrothermal approach were used as the substrate for the deposition of tiny spherical bimetallic AuAg or monometallic Au nanoparticles (NPs), leading to novel photothermal-assisted catalysts with different hybrid nanostructures and showing improved catalytic performance under NIR laser irradiation. The catalytic reduction of pollutant 4-nitrophenol (4-NF) to the valuable product 4-aminophenol (4-AF) was evaluated. The hydrothermal synthesis of MoS2 NFs provides a material with a broad absorption in the Vis-NIR region of the electromagnetic spectrum. The in situ grafting of alloyed AuAg and Au NPs of very small size (2.0–2.5 nm) was possible through the decomposition of organometallic complexes [Au2Ag2(C6F5)4(OEt2)2]n and [Au(C6F5)(tht)] (tht = tetrahydrothiophene) using triisopropilsilane as reducing agent, leading to nanohybrids 1–4. The new nanohybrid materials display photothermal properties arising from NIR light absorption of the MoS2 NFs component. The AuAg-MoS2 nanohybrid 2 showed excellent photothermal-assisted catalytic activity for the reduction of 4-NF, which is better than that of the monometallic Au-MoS2 nanohybrid 4. The obtained nanohybrids were characterised by transmission electron microscopy (TEM), High Angle Annular Dark Field—Scanning Transmission Electron Microscopy—Energy Dispersive X-ray Spectroscopy (HAADF-STEM-EDS), X-ray photoelectron spectroscopy and UV-Vis-NIR spectroscopy. [ABSTRACT FROM AUTHOR]

The second factor is the trapping of Rh atoms detached from large Rh crystallites by oxygen vacancies in the support surface. The interconnected rapid development of nanomaterials science and advanced analysis and imaging techniques at the nano-level scale (some "operando") fostered the parallel growth of heterogeneous catalysis and its evolution into "nano-catalysis" [[1], [3], [5]]. Their model accounts for the synergistic action of two factors that investigated the effects of the support OSC and Rh particle size on the performance of the Sabatier reaction under both integral and differential conditions to elucidate the combined role of these crucial catalyst design parameters on CO SB 2 sb methanation efficiency. The Rh/TiO SB 2 sb catalyst performance were insensitive to abrupt changes of the steam/C ratio between 2 and 7 and exhibited excellent time-on-stream stability at 500 and 650 °C. [Extracted from the article]

Ionic liquids are a family of liquids that are composed entirely of ions and usually have melting points lower than 100 °C. Extensive research, along with the ever-growing interest of the scientific community, allowed for the development of a multitude of ionic liquids with low melting points. Such compounds are considered neoteric materials as well as ideal, custom-made solvents for a variety of different chemical transformations. In this regard, the importance of phase transfer catalysis is evident in a diversity of substrates and reactions. The use of phase transfer catalysts allows the reaction to proceed, facilitating the transfer of otherwise insoluble reactants to the desired phase. Recent scientific advances led to the emergence of ionic liquids, which are excellent candidates as phase transfer catalysts. The inherent fine-tuning capability of these molecules, along with the potential of phase transfer catalytic reactions, epitomize the sustainable aspect of this field of research. Herein, a cohesive report of such applications will be presented, including the period from the last decade of the 20th century up to date. [ABSTRACT FROM AUTHOR]

Gold nanospecies produced by a historically inspired two-liquid phase system were immobilized on plate-like mesoporous silica, SBA-15, functionalized with mercaptopropyl groups by a post-synthesis method, and the resulting materials were tested in the oxidation of cyclohexene with molecular oxygen at atmospheric pressure. The main purpose of this approach was to compare the physicochemical properties and catalytic performance of these materials with those of previously reported related materials functionalized by in situ methods during synthesis. In addition, catalytic tests under ambient lighting and darkness and also in the presence and absence of the initiator tert-butyl hydroperoxide (TBHP) were carried out. The samples were characterized by chemical analysis, N2 adsorption/desorption, TGA, SEM, HRTEM, UV-vis spectroscopy and XPS. Gold nanoclusters and isolated gold atoms but no AuNPs were found in the catalysts (0.31–2.69 wt.% of gold). The XPS shows that nearly 60% of the -SH groups (1.33 wt.% of S) were oxidized to sulphonic groups upon gold immobilization. The AuNCs and isolated gold atoms evolved in the the reaction medium to form AuNPs. The activity of the samples was lower than that of the catalysts supported on related S-bearing SBA-15 functionalized in situ, which was attributed to their different Au/S ratios, which in turn regulated the evolutionary process of the gold species during the reaction. The catalysts turned out to be inactive in darkness, which evidences that the cyclohexene oxidation carried out at ambient illumination is actually photocatalyzed by the AuNPs formed in situ during the reaction. The TBHP initiator is required to obtain the activity in order to counteract the inhibitors of cyclohexene auto-oxidation present in the commercial reagent. On the other hand, no major differences in the selectivity among the different catalysts and reactions were observed, with 2-cyclohexen-1-one and 2-cyclohexen-1-ol resulting from the allylic oxidation as main products (selectivity of (one + ol) ~80% at a conversion ≥ 35%; one/ol~2). [ABSTRACT FROM AUTHOR]

The synthesis of surfactant-free and organic ligand-free metallic nanoparticles in solution remains challenging due to the nanoparticles' tendency to aggregate. Surfactant- and ligand-free nanoparticles are particularly desirable in catalytic applications as surfactants, and ligands can block access to the nanoparticles' surfaces. In this contribution, platinum nanoparticles are synthesized in aqueous solution without surfactants or bound organic ligands. Pt is reduced by sodium borohydride, and the borohydride has a dual role of reducing agent and weakly interacting stabilizer. The 5.3 nm Pt nanoparticles are characterized using UV-visible spectroscopy and transmission electron microscopy. The Pt nanoparticles are then applied as catalysts in two different reactions: the redox reaction of hexacyanoferrate(III) and thiosulfate ions, and H2O2 decomposition. Catalytic activity is observed for both reactions, and the Pt nanoparticles show up to an order of magnitude greater activity over the most active catalysts reported in the literature for hexacyanoferrate(III)/thiosulfate redox reactions. It is hypothesized that this enhanced catalytic activity is due to the increased electron density that the surrounding borohydride ions give to the Pt nanoparticle surface, as well as the absence of surfactants or organic ligands blocking surface sites. [ABSTRACT FROM AUTHOR]