Layered double hydroxide supported nanopalladium catalyst for Heck-, Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes

Clay based heterogeneous catalysts for carbon-nitrogen bond formation: a review

Clay and modified clay-based catalysts are widely used in organic transformation. Owing to the interlayer ions and good ion exchange capacity of clay, replacement with another ion and incorporation of different nanomaterials can be done. Due to these significant properties of clay, it can be utilized in the synthesis of various organic compounds. Carbon-nitrogen bonded compounds possess diverse applications in different fields. These compounds are prepared using different solid acid heterogeneous catalysts. This review presents a detailed discussion on clay used for the carbon-nitrogen bond formation reaction, such as the Biginelli reaction and A3 and KA2 coupling reactions. Additionally, other C-N bond formation reactions using various clay-based catalysts such as bentonite, montmorillonite, hydrotalcite and halloysite clay with various metals, metal oxides, Kegging type heteropoly acid and various nanomaterial incorporated clay heterogeneous catalysts are discussed.

Reduced Tiara-like Palladium Complex for Suzuki Cross-Coupling Reactions

The design of highly active and structurally well-defined catalysts has become a crucial issue for heterogeneous catalysed reactions while reducing the amount of catalyst employed. Beside conventional synthetic routes, the employment of polynuclear transition metal complexes as catalysts or catalyst precursors has progressively intercepted a growing interest. These well-defined species promise to deliver catalytic systems where a strict control on the nuclearity allows to improve the catalytic performance while reducing the active phase loading. This study describes the development of a highly active and reusable palladium-based catalyst on alumina (Pd8 /Al2 O3 ) for Suzuki cross-coupling reactions. An octanuclear tiara-like palladium complex was selected as active phase precursor to give isolated Pd-clusters of ca. 1 nm in size on Al2 O3 . The catalyst was thoroughly characterised by several complementary techniques to assess its structural and chemical nature. The high specific activity of the catalyst has allowed to carry out the cross-coupling reaction in 30 min using only 0.12 mol % of Pd loading under very mild and green reaction conditions. Screening of various substrates and selectivity tests, combined with recycling and benchmarking experiments, have been used to highlight the great potentialities of this new Pd8 /Al2 O3 catalyst.

High-Performance Novel Polyoxometalate-LDH Nanocomposite-Modified Thin-Film Nanocomposite Forward Osmosis Membranes: A Study of Desalination and Antifouling Performance

Numerous investigations have focused on creating effective membranes for desalination in order to alleviate the water scarcity crisis. In this study, first, LDH nanoplates were synthesized and utilized to alter the surface of thin-film composite (TFC) membranes in the course of this investigation. Following that, a simple technique was used to produce a novel nanocomposite incorporating LDH layers and Na14(P2W18Co4O70)·28H2O polyoxometalate nanoparticles, resulting in the creation of a fresh variety of thin-film nanocomposite (TFN). The performance of all of the membranes acquired was examined in the process of forward osmosis (FO). The impact of the compounds that were prepared was assessed on the hydrophilicity, topology, chemical structure, and morphology of the active layer of polyamide (PA) through analysis methods such as atomic force microscopy (AFM), energy-dispersive X-ray (EDX), FTIR spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and water contact angle (WCA) goniometry. After evaluating the outcomes of both modified membrane types, it was observed that the membrane equipped with the nanocomposite modifier at a concentration of 0.01 wt % exhibited the highest water flux, measuring 46.6 LMH and selectivity of 0.23 g/L. This membrane was thus considered the best option. Furthermore, the membrane's ability to prevent fouling was examined, and the findings revealed an enhancement in its resistance to fouling in comparison to the filler-free membrane.

Evaluation of a photoelectrochemical platform based on strontium titanate, sulfur doped carbon nitride and palladium nanoparticles for detection of SARS-CoV-2 spike glycoprotein S1

This work aims to develop a photoelectrochemical (PEC) platform for detection of SARS-CoV-2 spike glyprotein S1. The PEC platform is based on the modification of a fluorine-doped tin oxide (FTO) coated glass slide with strontium titanate (SrTiO₃ or ST), sulfur-doped carbon nitride (g-C₃N₄-S or CNS) and palladium nanoparticles entrapped in aluminum hydroxide matrix (PdAlO(OH) or PdNPs). The PEC platform was denoted as PdNPs/CNS/ST/FTO and it was characterized by SEM, TEM, FTIR, DRX, and EIS. The PEC response of the PdNPs/CNS/ST/FTO platform was optimized by evaluating the effects of the concentration of the donor molecule, the nature of the buffer, pH, antibody concentration, potential applied to the working electrode, and incubation time. The optimized PdNPs/CNS/ST/FTO PEC platform was modified with 5 μg mL^-1 of antibody for determination of SARS-CoV-2 spike glycoprotein S1. A decrease in the photocurrent was observed with an increase in the concentration of SARS-CoV-2 from 1 fg mL^-1 to 1000 pg mL^-1 showing that the platform is a promising alternative for the detection of S1 protein from SARS-CoV-2. The designed PEC platform exhibited recovery percentages of 96.20% and 109.65% in artificial saliva samples.

Robust C-PdNi-CNF Sandwich-Structured Catalyst for Suzuki Reactions and Experimental Study on the Mechanism

The stability of metal nanoparticles is one of the key issues for their catalytic applications. In this study, we fabricated a sandwich structure to protect the metal nanoparticles. A carbon layer was used to wrap the PdNi nanoparticles on the carbon fiber, and the whole preparation process was simple and green. Electron transfer occurs between the carbon layer and the metal nanoparticles, making the two more closely combined. As a catalyst for the Suzuki reaction, it exhibits highly efficient catalysis and excellent stability. The calculated TOF reaches 18 662 h^-1. After nine cycles, there was almost no decrease in performance. Additionally, we found that the addition of iodobenzene into the chlorobenzene reaction system could significantly improve the chlorobenzene conversion, and we proved that the catalyst has fine activity and stability with a bright future in commercial applications. The possible catalytic mechanism of Suzuki reaction was proposed based on experimental results. This study provides a simple and green method to prepare encapsulated metal nanoparticle catalysts and gives a deep insight into Suzuki reaction.

Reusable Pd-PolyHIPE for Suzuki-Miyaura Coupling

Palladium was immobilized on a highly porous copolymer of 4-vinylpyridine and divinylbenzene (polyHIPE-poly(high internal phase emulsion)) using palladium(II) acetate to obtain PolyPy-Pd with 6.1 wt % or 0.57 mmol Pd/g. The immobilized catalyst was able to catalyze the coupling of iodobenzene and phenylboronic acid in ethylene glycol monomethyl ether/water (3:1) within 4 h at rt and complete conversion was observed when 2.5 mol % of Pd per PhI was used. The reaction tolerated a wide range of substituents on the aromatic ring. Iodobenzene derivatives with electron-withdrawing substituents showed higher reactivity, while the opposite was true for the phenylboronic acid series. The polyHIPE-supported Pd catalyst was also used for the direct conversion of phenylboronic acid to biphenyl through an iodination/coupling reaction sequence. The recyclability of the heterogeneous catalyst was also optimized, and by finding a suitable combination of solvents for the loading of Pd, the reaction, and the isolation of the product, the solid-supported catalyst was completely regenerated and used in the next reaction with the same activity.

Layered Double Hydroxide Catalysts Preparation, Characterization and Applications for Process Development: An Environmentally Green Approach

The adage of new generation of fine chemicals process is the best process applied in the absence of conventional methods. However, many methods use different reaction parameters, such as basic and acidic catalysts, for example oxidation, reduction, bromination, water splitting, cyanohydrin, ethoxylation, syngas, aldol condensation, Michael addition, asymmetric ring opening of epoxides, epoxidation, Wittig and Heck reaction, asymmetric ester epoxidation of fatty acids, combustion of methane, NOx reduction, biodiesel synthesis, propylene oxide polymerization. Layered Double Hydroxides (LDHs) have received considerable attention due their potential applications in flame retardant and has excellent medicinal property for reducing acidity. These catalysts are characterized using analytical techniques, such as: X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), Raman spectroscopy, Thermogravimetric-Differential Thermal Analyzer (TG-DTA), Scanning electron microscope (SEM), Transmission electron microscopes (TEM), Brunauer-Emmett-Teller (BET) surface area, N2 Adsorption-desorption, Temperature programmed reduction (TPR), X-ray photoelectrons spectroscopy (XPS), which gives its overall picture of its structure, porosity, morphology, thermal stability, reusability, and activity of catalysts. LDHs catalysts have proven to be economic and environmentally friendly. The above discussed applications make these catalysts unique from Green Chemistry point of view since they are reusable, and eco-friendly catalysts. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Pd-Nanoparticles@Layered Double Hydroxide/ Reduced Graphene Oxide (Pd NPs@LDH/rGO) Nanocomposite Catalyst for Highly Efficient Green Reduction of Aromatic Nitro Compounds

A facile chemical method is developed to fabricate well-dispersed and an approx. 5 nm sized Pd-nanoparticles (Pd-NPs) deposited ZnAl-LDH/rGO nanocomposite (Pd NPs@LDH/rGO) as a highly efficient and stable catalyst for...

Progresses in chitin, chitosan, starch, cellulose, pectin, alginate, gelatin and gum based (nano)catalysts for the Heck coupling reactions: A review

Heck cross-coupling reaction (HCR) is one of the few transition metal catalyzed CC bond-forming reactions, which has been considered as the most effective, direct, and atom economical synthetic method using various catalytic systems. Heck reaction is widely employed in numerous syntheses including preparation of pharmaceutical and biologically active compounds, agrochemicals, natural products, fine chemicals, etc. Commonly, Pd-based catalysts have been used in HCR. In recent decades, the application of biopolymers as natural and effective supports has received attention due to their being cost effective, abundance, and non-toxicity. In fact, recent studies demonstrated that biopolymer-based catalysts had high sorption capacities, chelating activities, versatility, and stability, which make them potentially applicable as green materials (supports) in HCR. These catalytic systems present high stability and recyclability after several cycles of reaction. This review aims at providing an overview of the current progresses made towards the application of various polysaccharide and gelatin-supported metal catalysts in HCR in recent years. Natural polymers such as starch, gum, pectin, chitin, chitosan, cellulose, alginate and gelatin have been used as natural supports for metal-based catalysts in HCR. Diverse aspects of the reactions, different methods of preparation and application of polysaccharide and gelatin-based catalysts and their reusability have been reviewed.

Influence of adsorption of ionic liquid constituents on the stability of layered double hydroxide colloids

The influence of ionic liquid (IL) anions and cations on the charging and aggregation properties of layered double hydroxide (LDH) nanoparticles was systematically studied. Surface charge characteristics were explored using zeta potential measurements, while aggregation processes were followed in dynamic light scattering experiments in aqueous IL solutions. The results revealed that the aggregation rates of LDHs were sensitive to the composition of ILs leading to IL-dependent critical coagulation concentration (CCC) values being obtained. The origin of the interparticle forces was found to be electrostatic, in line with the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, as the experimental aggregation kinetics were in good agreement with the predicted data. The ion specific adsorption of IL anions led to different surface charge densities for LDHs, which decreased in the order Cl^- > Br^- > DCA^- > SCN^- > NO₃^- for counterions and BMIM⁺ > BMPYR⁺ > BMPY⁺ > BMPIP⁺ in the case of coions resulting in weaker electrical double layer repulsion in these sequences. Since van der Waals forces are always present and their strength does not depend significantly on the ionic strength, the CCC values decreased in the above order. The present results shed light on the importance of the interfacial arrangement of the IL constituent ions on the colloidal stability of particle dispersions and provide important information on the design of stable or unstable particle-ionic liquid systems.

Organoselenium ligands for heterogeneous and nanocatalytic systems: development and applications

Organoselenium ligands have attracted great attention among researchers during the past two decades. Various homogeneous, heterogeneous and nanocatalytic systems have been designed using such ligands. Although reports on selenium ligated homogeneous catalysts are quite high in number, significant work has also been done on the development of heterogeneous and nanocatalytic systems using organoselenium ligands. A review article, focusing on the utility of organoselenium compounds in the development of catalytic systems, was published in 2012 (A. Kumar, G. K. Rao, F. Saleem and A. K. Singh, Dalton Trans., 2012, 41, 11949). Moreover, it mainly covered the homogeneous catalysts. There are no review articles in the literature on heterogeneous and nanocatalytic systems designed using organoselenium compounds and their applications. Hence, this perspective aims to cover the developments pertaining to the synthetic aspects of such catalytic systems (using organoselenium compounds) and their applications in catalysis of a variety of chemical transformations. Salient features and advantages of organoselenium compounds have also been highlighted to justify the rationale behind their use in catalyst development. Their performance in various chemical transformations [viz. Suzuki-Miyaura coupling, Heck coupling, Sonogashira coupling, O-arylation of phenol, transfer hydrogenation of aldehydes and ketones, aldehyde-alkyne-amine (A3) coupling, hydration of nitriles, conversion of aldehydes to amides, cross-dehydrogenative coupling (CDC), photodegradation of substrates (formic acid, methylene blue), reduction of nitrophenols, electrolysis (hydrogen evolution reaction and oxygen reduction reactions), organocatalysis and dye sensitized solar cells] and relevant aspects of catalytic processes (such as recyclability, substrate scope and green aspects) have been critically analyzed. Future perspectives have also been discussed.

Prospects and Applications of Palladium Nanoparticles in the Cross-coupling of (hetero)aryl Halides and Related Analogues

Discovering efficient methods for the formation of carbon-carbon bonds is a central ongoing theme in organic synthesis. Cross-coupling reactions catalysed by metal nanoparticles are attractive alternatives to the traditional use of metal counterparts due to the catalytic tunability, selectivity, recyclability and reusability of the nanoparticles. The ongoing search for sustainable processes demands that reusable and environmentally benign catalysts are used. While the advantages of nanoparticles catalysts over bulk catalysts cannot be overemphasised, the problem of sintering, agglomeration and leaching are drawbacks to their full industrial applications. Hence, efforts are being made towards advancing the efficiency of the catalytic nanoparticle systems over the years. This review presents the progress, the challenges and the prospects of palladium nanoparticle with focus on Heck, Suzuki, Hiyama and Sonogashira cross-coupling reactions involving (hetero) aryl halides and the analogues.

First-principles molecular dynamics study on the surface chemistry and nanotribological properties of MgAl layered double hydroxides

Layered double hydroxides (LDHs) are promising materials for lubrication. However, the underlying mechanism that leads to the low friction of the material is not well-understood. In this study, density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations have been used to study the reduced friction mechanism of MgAl-LDH. Our results indicate that the introduction of trivalent cations has a significant impact on the friction reduction of the LDH. Besides, the lateral force shows a strong correlation with the coverage of the hydroxyl group on the surface. By using AIMD simulation, we show that the water/hydroxide molecules interact with the surface through strong hydrogen bonds that confine the movement and the orientation of the intercalated molecules on the surface. Furthermore, the friction is reduced when the water thickness is increased. The reaction pathways of water with the LDH surface has been investigated using well-tempered metadynamics simulation. We found that the LDH can promote proton transfer, leading to the formation of hydroxide intermediates (OH), which then chemically adsorb on the surface. The chemical adsorption of the hydroxide intermediates can cleave the O-H bonds on the LDH surface.

Recoverable Palladium-Catalyzed Carbon-Carbon Bond Forming Reactions under Thermomorphic Mode: Stille and Suzuki-Miyaura Reactions

The reaction of [PdCl₂(CH₃CN)₂] and bis-4,4′-(R_fCH₂OCH₂)-2,2′-bpy (1a–d), where R_f = n-C₁₁F₂₃ (a), n-C₁₀F₂₁ (b), n-C₉F₁₉ (c) and n-C₈F₁₇ (d), respectively, in the presence of dichloromethane (CH₂Cl₂) resulted in the synthesis of Pd complex, [PdCl₂[4,4′-bis-(R_fCH₂OCH₂)-2,2′-bpy] (2a–d). The Pd-catalyzed Stille arylations of vinyl tributyltin with aryl halides were selected to demonstrate the feasibility of recycling usage with 2a as the catalyst using NMP (N-methyl-2-pyrrolidone) as the solvent at 120–150 °C. Additionally, recycling and electronic effect studies of 2a–c were also carried out for Suzuki-Miyaura reaction of phenylboronic acid derivatives, 4-X-C₆H₄-B(OH)₂, (X = H or Ph) with aryl halide, 4-Y-C₆H₄-Z, (Y = CN, H or OCH₃; Z = I or Br) in dimethylformamide (DMF) at 135–150 °C. At the end of each cycle, the product mixtures were cooled to lower temperature (e.g., −10 °C), and then catalysts were recovered by decantation with Pd leaching less than 1%. The products were quantified by gas chromatography/mass spectrometry (GC/MS) analysis or by the isolated yield. The complex 2a-catalyzed Stille reaction of aryl iodides with vinyl tributyltin have good recycling results for a total of 8 times, with a high yield within short period of time (1–3 h). Similarly, 2a–c-catalyzed Suzuki-Miyaura reactions also have good recycling results. The electronic effect studies from substituents in both Stille and Suzuki-Miyaura coupling reactions showed that electron withdrawing groups speed up the reaction rate. To our knowledge, this is the first example of recoverable fluorous long-chained Pd-catalyzed Stille reactions under the thermomorphic mode.

Water-Sculpting of a Heterogeneous Nanoparticle Precatalyst for Mizoroki-Heck Couplings under Aqueous Micellar Catalysis Conditions

Powdery, spherical nanoparticles (NPs) containing ppm levels of palladium ligated by t-Bu₃P, derived from FeCl₃, upon simple exposure to water undergo a remarkable alteration in their morphology leading to nanorods that catalyze Mizoroki-Heck (MH) couplings. Such NP alteration is general, shown to occur with three unrelated phosphine ligand-containing NPs. Each catalyst has been studied using X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and cryogenic transmission electron microscopy (cryo-TEM) analyses. Couplings that rely specifically on NPs containing t-Bu₃P-ligated Pd occur under aqueous micellar catalysis conditions between room temperature and 45 °C, and show broad substrate scope. Other key features associated with this new technology include low residual Pd in the product, recycling of the aqueous reaction medium, and an associated low E Factor. Synthesis of the precursor to galipinine, a member of the Hancock family of alkaloids, is suggestive of potential industrial applications.

Layered double hydroxides as heterogeneous catalyst systems in the cross-coupling reactions: an overview

Layered double hydroxides (LDHs) are recognized as two-dimensional (2D) clay materials, which comprise the interlayer anions and host layers with a positive charge (brucite-like M(OH)₆ octahedral). They have been used as effective and eco-friendly heterogeneous catalytic systems in cross-coupling reactions. In this review, we try to underscore the applications of (LDHs) as an efficient and green catalyst in some important name reactions, namely Suzuki, Heck, Sonogashira, and Ullmann cross-coupling reactions leading to carbon-carbon bond formations.

Phosphine-Built-in Porous Organic Cage for Stabilization and Boosting the Catalytic Performance of Palladium Nanoparticles in Cross-Coupling of Aryl Halides

Herein, we report first a novel phosphine-containing porous organic cage (PPOC) from a [2 + 3] self-assembly of triphenyl phosphine-based trialdehyde and (S,S)-1,2-diaminocyclohexane via dynamic imine chemistry, which was employed as a porous material for the controlled growth of palladium nanoparticles (NPs) due to the strong affinity of Pd to the phosphine ligand based on the principle of hard and soft acids and bases. Comprehensive characterizations including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, NMR, and X-ray absorption spectroscopy reveal that ultrafine Pd NPs with narrow size distribution (1.7 ± 0.3 nm) and enhanced surface electronic density via a strong interaction between NPs and phosphine were homogeneously dispersed in the PPOC. The resultant catalyst Pd@PPOC exhibits remarkably superior catalytic activities for various cross-coupling reactions of aryl halides, for example, Sonogashira, Suzuki, Heck, and carbonylation. The catalytic activity of Pd@PPOC outperforms the state-of-the-art Pd complexes and other Pd NPs supported on N-containing porous cages under identical conditions, owing to the enhanced surface electronic density of Pd NPs and their high stability and dispersibility in solution. More importantly, Pd@PPOC is highly stable and easily recycled and reused without loss of their catalytic activity. This work provides a new functional POC with extended potentials in catalysis and material science.

Ultrafine PdCu Nanoclusters by Ultrasonic-Assisted Reduction on the LDHs/rGO Hybrid with Significantly Enhanced Heck Reactivity

A series of hierarchical nanosheet array-like Co-Al layered double hydroxides (LDHs)/reduced graphene oxide (rGO) hybrid supported ultrafine PdCu nanocluster (NC) catalysts m-PdCu_x/LDHs/rGO (x: Cu/Pd molar ratio of 1.5, 3.0, and 5.5; m: Pd loadings of ∼0.80, 0.40, 0.11, and 0.01 wt %) were assembled via an ultrasonic-assisted NaBH₄ reduction-sol immobilization strategy. The as-obtained catalysts display ultrafine PdCu alloy NCs with sizes of ∼0.9-1.8 nm finely tuned by both Cu/Pd ratios and Pd loadings and mainly distributed on the edge sites of LDH nanosheets and part of LDHs-rGO junctions upon the unique hierarchical nanosheet array-like structure. Three catalysts 0.85-PdCu_1.5/LDHs/rGO, 0.83-PdCu_3.0/LDHs/rGO, and 0.80-PdCu_5.5/LDHs/rGO exhibit excellent Heck reactivity for iodobenzene with styrene, of which the 0.83-PdCu_3.0/LDHs/rGO shows the highest activity, much higher than Pd/LDHs/rGO and single LDHs or GO supported PdCu_3.0 catalysts, attributed to the ultrafine PdCu_3.0 NCs, the largest electron density of the Pd⁰ center, and the strongest PdCu_3.0 NCs-LDHs-rGO three-phase synergistic effect. The lowest Pd-loading sample 0.01-PdCu_3.0/LDHs/rGO shows an unprecedented turnover frequency of 210 000 h^-1 (Pd dosage: 2 × 10^-5 mol %) with the highest value so far, excellent adaptability for substrates, and reusability. The present work provides a versatile method for designing hierarchically structured ultrafine Pd-M alloy NC catalysts for varied catalysis processes.

Hydrotalcite-Supported Ag/Pd Bimetallic Nanoclusters Catalyzed Oxidation and One-Pot Aldol Reaction in Water

A highly active hydrotalcite-supported Ag/Pd bimetallic nanocluster catalyst has been developed by a simple, easy and safe chemical reduction method. The catalyst was characterized by high-resolution transmission electron microscopy (HR-TEM), which revealed very small (3.2 ± 0.7 nm) nanoclusters with a narrow size distribution. The bimetallic Ag/Pd catalyst showed strong cooperation between Ag and Pd for the alcohol oxidation reaction. The developed catalyst provided an efficient and environmentally friendly method for alcohol oxidation and one-pot cross-aldol condensation in water. A broad scope of α,β-unsaturated ketones with good to excellent yields were obtained under very mild conditions. This catalytic system offers an easy preparation method with a simple recovery process, good activity and reusability of up to five cycles without significant loss in the catalytic activity.

Microwave-Assisted Decarbonylation of Biomass-Derived Aldehydes using Pd-Doped Hydrotalcites

Catalytic decarbonylation is an underexplored strategy for deoxygenation of biomass-derived aldehydes owing to a lack of low-cost and robust heterogeneous catalysts that can operate in benign solvents. A family of Pd-functionalized hydrotalcites (Pd-HTs) were synthesized, characterized, and applied to the decarbonylation of furfural, 5-hydroxymethylfurfural (HMF), and aromatic and aliphatic aldehydes under microwave conditions. This catalytic system delivered enhanced decarbonylation yields and turnover frequencies, even at a low Pd loading (0.5 mol %). Furfural decarbonylation was optimized in a benign solvent (ethanol) compatible with biomass processing; HMF selectively afforded an excellent yield (93 %) of furfuryl alcohol without humin formation; however, a longer reaction favored the formation of furan through tandem alcohol dehydrogenation and decarbonylation. Yields of the substituted benzaldehydes (37-99 %) were proportional to the calculated Mulliken charge of the carbonyl carbon. Activity and selectivity reflected loading-dependent Pd speciation. Continuous-flow testing of the best Pd-HT catalyst delivered good stability over 16 h on stream, with near-quantitative conversion of HMF.

Monolith catalyst design via 3D printing: a reusable support for modern palladium-catalyzed cross-coupling reactions

The use of an additive manufacturing procedure for the modification of catalytic structures is currently gaining popularity in the field of catalysis.

Catalysis with magnetically retrievable and recyclable nanoparticles layered with Pd(0) for C–C/C–O coupling in water

Nanoparticles layered with palladium(0) were prepared from nano-sized magnetic Fe₃O₄ by coating it with silica and then reacting sequentially with phenylselenyl chloride under an N₂ atmosphere and palladium(ii) chloride in water. The resulting Fe₃O₄@SiO₂@SePh@Pd(0) NPs are magnetically retrievable and the first example of NPs in which the outermost layer of Pd(0) is mainly held by selenium. The weight percentage of Pd in the NPs was found to be 1.96 by ICP-AES. The NPs were authenticated via TEM, SEM-EDX, XPS, and powder XRD and found to be efficient as catalysts for the C–O and C–C (Suzuki–Miyaura) coupling reactions of ArBr/Cl in water. The oxidation state of Pd in the NPs having size distribution from ∼12 to 18 nm was inferred as zero by XPS. They can be recycled more than seven times. The main features of the proposed protocols are their mild reaction conditions, simplicity, and efficiency as the catalyst can be separated easily from the reaction mixture by an external magnet and reused for a new reaction cycle. The optimum loading (in mol% of Pd) was found to be 0.1–1.0 and 0.01–1.0 for O-arylation and Suzuki–Miyaura coupling, respectively. For ArCl, the required amount of NPs was more as compared to that needed for ArBr. The nature of catalysis is largely heterogeneous.

Fe₃O₄@SiO₂@SePh@Pd(0) (Pd, 1.96%) as the first example of NPs having a Pd(0) layer held by selenium can execute C–C/C–O coupling in 2–6 h (80 °C).

Enhanced Heck reaction on flower-like Co(Mg or Ni)Al layered double hydroxide supported ultrafine PdCo alloy nanocluster catalysts: the promotional effect of Co

A series of PdCo alloy nanocluster (NC) catalysts x-PdCo_r/Co(Mg or Ni)Al-LDH (x: Pd loading, r: Co/Pd molar ratio) were synthesized by immobilizing ultrafine PdCo_r-PVP NCs on flower-like layered double hydroxide (LDH) supports. The sizes of PdCo alloy NCs of the catalysts can be elaborately tuned in ∼1.6-3.2 nm by both Co/Pd ratios and Pd loadings, and the PdCo NCs are mainly dispersed on the edge sites of LDH nanosheets upon a flower-like morphology. The PdCo bimetallic catalysts 0.81-PdCo_0.10/MgAl-LDH (2.6 ± 0.6 nm), 0.86-PdCo_0.28/MgAl-LDH (2.3 ± 0.7 nm) and 0.79-PdCo_0.54/MgAl-LDH (3.2 ± 0.9 nm) exhibit enhanced activity compared with the monometallic Pd catalyst for Heck coupling of iodobenzene with styrene. Particularly, 0.86-PdCo_0.28/MgAl-LDH shows the highest activity, which can be attributed to its smallest PdCo_0.28 alloy NCs, and the maximum electron density of the Pd⁰ center resulted from the electron transfer from Co and the strongest PdCo_0.28 NCs - LDH synergistic effect. 0.67-PdCo_0.28/CoAl-LDH shows much better activity than those of 0.64-PdCo_0.28/NiAl-LDH and 0.86-PdCo_0.28/MgAl-LDH. The lowest Pd loading sample 0.01-PdCo_0.28/CoAl-LDH (1.6 ± 0.4 nm) shows an ultrahigh turnover frequency of 163 000 h^-1 (Pd: 1.9 × 10^-5 mol%), which is the highest value obtained so far. Meanwhile, the catalyst shows excellent adaptability for the substrates and can be reused for 12 runs without significant loss of activity. The present work may provide a new idea for the simple and green synthesis of ultrafine Pd-based non-noble bimetallic catalysts for varied catalytic processes.

Microwave-Assisted Palladium-Catalyzed Cross-Coupling Reactions: Generation of Carbon–Carbon Bond

Cross-coupling reactions furnishing carbon–carbon (C–C) bond is one of the most challenging tasks in organic syntheses. The early developed reaction protocols by Negishi, Heck, Kumada, Sonogashira, Stille, Suzuki, and Hiyama, utilizing palladium or its salts as catalysis have, for decades, attracted and inspired researchers affiliated with academia and industry. Tremendous efforts have been paid to develop and achieve more sustainable reaction conditions, such as the reduction in energy consumption by applying the microwave irradiation technique. Chemical reactions under controlled microwave conditions dramatically reduce the reaction time and therefore resulting in increase in the yield of the desired product by minimizing the formation of side products. In this review, we mainly focus on the recent advances and applications of palladium catalyzed cross-coupling carbon–carbon bond formation under microwave technology.

Advances in mineral processing technologies related to iron, magnesium, and lithium

Exploitation and utilization of mineral resources have played a vital role in China’s rapid economic developments. Although the history of mineral processing is quite long, technologies in this field have varied with the changes of market demands. This is particularly the case for minerals whose high-grade deposits are depleting. The aim of this review is to present our recent efforts on developing new routes for the utilization of low-grade minerals, such as iron ores and brine-containing lithium. The emphasis on the two minerals lies in the fact that iron plays a vital role in modern-day civilization and lithium is a key component in electric vehicles for transportation. Furthermore, the utilization of magnesium chloride reserves, one of the largest wastes in western China, as raw materials for fabrication of functional materials is also included in this review.

Cyclodextrin polymer networks decorated with subnanometer metal nanoparticles for high-performance low-temperature catalysis

The synthesis of support materials with suitable coordination sites and confined structures for the controlled growth of ultrasmall metal nanoparticles is of great importance in heterogeneous catalysis. Here, by rational design of a cross-linked β-cyclodextrin polymer network (CPN), various metal nanoparticles (palladium, silver, platinum, gold, and rhodium) of subnanometer size (<1 nm) and narrow size distribution are formed via a mild and facile procedure. The presence of the metal coordination sites and the network structure are key to the successful synthesis and stabilization of the ultrasmall metal nanoparticles. The as-prepared CPN, loaded with palladium nanoparticles, is used as a heterogeneous catalyst and shows outstanding catalytic performance in the hydrogenation of nitro compounds and Suzuki-Miyaura coupling reaction under mild conditions. The CPN support works synergistically with the metal nanoparticles, achieving high catalytic activity and selectivity. In addition, the catalytic activity of the formed catalyst is controllable.