Showing papers on "Palladium published in 2020"
TL;DR: This work contributes a superior catalyst for ketone/aldehydes hydrogenation, but also deepens the knowledge on their hydrogenation mechanism and guides people to engineer the catalytic behaviors as needed.
Abstract: Selective reduction of ketone/aldehydes to alcohols is of great importance in green chemistry and chemical engineering. Highly efficient catalysts are still demanded to work under mild conditions, especially at room temperature. Here we present a synergistic function of single-atom palladium (Pd1) and nanoparticles (PdNPs) on TiO2 for highly efficient ketone/aldehydes hydrogenation to alcohols at room temperature. Compared to simple but inferior Pd1/TiO2 and PdNPs/TiO2 catalysts, more than twice activity enhancement is achieved with the Pd1+NPs/TiO2 catalyst that integrates both Pd1 and Pd NPs on mesoporous TiO2 supports, obtained by a simple but large-scaled spray pyrolysis route. The synergistic function of Pd1 and PdNPs is assigned so that the partial Pd1 dispersion contributes enough sites for the activation of C=O group while PdNPs site boosts the dissociation of H2 molecules to H atoms. This work not only contributes a superior catalyst for ketone/aldehydes hydrogenation, but also deepens the knowledge on their hydrogenation mechanism and guides people to engineer the catalytic behaviors as needed.
194 citations
21 Feb 2020
TL;DR: Palladium has been the key element for several C-C bond-forming reactions, especially the Nobel-acclaimed Suzuki, Heck, and Sonogashira cross-coupling reactions, among others.
Abstract: Palladium (Pd) has been the key element for several C–C bond-forming reactions, especially the Nobel-acclaimed Suzuki, Heck, and Sonogashira cross-coupling reactions, among others. This review arti...
176 citations
TL;DR: N nanoporous palladium hydride is reported as electrocatalyst for electrochemical N 2 reduction under ambient conditions, achieving a high ammonia yield rate and the reduction of energy barrier for the rate-limiting *N 2 H formation step.
Abstract: The electrocatalytic nitrogen reduction reaction (NRR) is an alternative eco-friendly strategy for sustainable N2 fixation with renewable energy. However, NRR suffers from sluggish kinetics owing to difficult N2 adsorption and N≡N cleavage. Now, nanoporous palladium hydride is reported as electrocatalyst for electrochemical N2 reduction under ambient conditions, achieving a high ammonia yield rate of 20.4 μg h-1 mg-1 with a Faradaic efficiency of 43.6 % at low overpotential of 150 mV. Isotopic hydrogen labeling studies suggest the involvement of lattice hydrogen atoms in the hydride as active hydrogen source. In situ Raman analysis and density functional theory (DFT) calculations further reveal the reduction of energy barrier for the rate-limiting *N2 H formation step. The unique protonation mode of palladium hydride would provide a new insight on designing efficient and robust electrocatalysts for nitrogen fixation.
157 citations
TL;DR: An alternative strategy is described that exploits simple visible-light excitation of palladium to drive both oxidative addition and reductive elimination with low barriers, and palladium-catalyzed carbonylations can thereby proceed under ambient conditions, with challenging aryl or alkyl halides and difficult nucleophiles, and generate valuable carbonyl derivatives in a now-versatile fashion.
Abstract: Transition metal-catalyzed coupling reactions have become one of the most important tools in modern synthesis. However, an inherent limitation to these reactions is the need to balance operations, because the factors that favor bond cleavage via oxidative addition ultimately inhibit bond formation via reductive elimination. Here, we describe an alternative strategy that exploits simple visible-light excitation of palladium to drive both oxidative addition and reductive elimination with low barriers. Palladium-catalyzed carbonylations can thereby proceed under ambient conditions, with challenging aryl or alkyl halides and difficult nucleophiles, and generate valuable carbonyl derivatives such as acid chlorides, esters, amides, or ketones in a now-versatile fashion. Mechanistic studies suggest that concurrent excitation of palladium(0) and palladium(II) intermediates is responsible for this activity.
146 citations
145 citations
01 May 2020
TL;DR: The studies open up a new method to the design of an ultra-small metal nanoparticle for the catalytic dehydrogenation of HCOOH.
Abstract: Ultra-small nano-sized palladium particles were successfully stabilized within the pores of diamine groups grafted open metal site metal-organic frameworks of Cr-MIL-101; coordinated diamine groups of ethylene diamine (ED) and propyl diamine (PD) on the active site of chromium units of Cr-MIL-101. The physiochemical properties of the Pd@Cr-MOFs were investigated using FTIR, XRD, SEM/EDX mapping, TEM, BET, and AAS. The Cr-MIL-101 stabilized ultra-small Pd nanoparticles, Pd@(ethylene diamine)/Cr-MIL-101, and Pd@(propyl diamine)/Cr-MIL-101, displayed catalytic activity for clean dehydrogenation of formic acid and generation of hydrogen at room temperature. The resultant Pd@ED/Cr-MIL-101 catalyst indicates high catalytic activity with turnover frequency (TOF) of 583 h−1 at 328 K, which is superior to most of the reported catalysts, including Pd@PD/Cr-MIL-101 with TOF 532 h−1. Our studies open up a new method to the design of an ultra-small metal nanoparticle for the catalytic dehydrogenation of HCOOH.
134 citations
TL;DR: It is demonstrated that alloying is an effective strategy to alleviate palladium operation stability due to CO poisoning on surface by co-reduction of palladium and silver precursors in aqueous solution using dioctadecyldimethylammonium chloride as the structure-directing agent.
Abstract: Palladium is a promising material for electrochemical CO2 reduction to formate with high Faradaic efficiency near the equilibrium potential. It unfortunately suffers from problematic operation stability due to CO poisoning on surface. Here, it is demonstrated that alloying is an effective strategy to alleviate this problem. Mesoporous PdAg nanospheres with uniform size and composition are prepared from the co-reduction of palladium and silver precursors in aqueous solution using dioctadecyldimethylammonium chloride as the structure-directing agent. The best candidate can initiate CO2 reduction at zero overpotential and achieve high formate selectivity close to 100% and great stability even at <-0.2 V versus reversible hydrogen electrode. The high selectivity and stability are believed to result from the electronic coupling between Pd and Ag, which lowers the d-band center of Pd and thereby significantly enhances its CO tolerance, as evidenced by both electrochemical analysis and theoretical simulations.
132 citations
TL;DR: This review describes the controlled synthesis of Pd-based nanoparticles in polyol medium, focusing on the progress in terms of tailoring size, morphology, structure, and surface state, and the use of palladium nanoparticles, in a polyol solvent, applied in two of the most relevant PD-catalyzed processes, i.e., couplings and hydrogenation reactions, including multistep processes.
Abstract: Alcohols, in particular polyols, are well-known for the synthesis of metal nanoparticles, often acting as reducing agents, solvents, and stabilizers. Given not only their structural flexibility depending on the number of OH functions and their inherent H bonding interactions, but also the wide range of polyol molecular weights readily available, different physicochemical properties (boiling point, polarity, viscosity) could be exploited toward the synthesis of well-defined nanomaterials. In particular, the relevance of the supramolecular structure of polyols has a fundamental impact on the formation of metal nanoparticles, thereby favoring the dispersion of the nanoclusters. In the field of the metal-based nanocatalysis, palladium occupies a privileged position mainly due to its remarkable versatility in terms of reactivity representing a foremost tool in synthesis. In this review, we describe the controlled synthesis of Pd-based nanoparticles in polyol medium, focusing on the progress in terms of tailoring size, morphology, structure, and surface state. Moreover, we discuss the use of palladium nanoparticles, in a polyol solvent, applied in two of the most relevant Pd-catalyzed processes, i.e., couplings and hydrogenation reactions, including multistep processes.
130 citations
TL;DR: This work provides guidance for synthesizing high-activity catalysts by confining hetero-atoms into the crystal lattice of bimetallene and also a very novel mechanism for the growth of bicentallene made of highly immiscible components.
Abstract: The design of catalysts with high activity and robust stability for alkaline hydrogen evolution reaction (HER) remains a great challenge. Here, we report an efficient catalyst of two-dimensional bimetallene hydrides, in which H atoms stabilize the rhodium palladium bimetallene. The system exists because of the introduction of H that is in situ chemically released from the formaldehyde solution during the synthesis. This provides a highly stable catalyst based on an unstable combination of metal elements. Density functional theory calculations show the H is confined by electronic interactions and the Miedema rule of reverse stability of the RhPd alloy. The obtained catalyst exhibits outstanding alkaline HER catalytic performance with a low overpotential of 40 mV at 10 mA cm-2 and remarkable stability for over 10 h at 100 mA cm-2. The experimental results show that the confined H improve the activity, while the ultrathin sheet-like morphology yields stability. Our work provides guidance for synthesizing high-activity catalysts by confining heteroatoms into the crystal lattice of bimetallene and also a very novel mechanism for the growth of bimetallene made of highly immiscible components.
116 citations
TL;DR: In this article, a palladium-supported o-phenylenediamine-functionalized Fe3O4 magnetic nanoparticles are presented for the Suzuki-Miyaura coupling of various aryl halides with phenylboronic acids.
104 citations
TL;DR: In this paper, a strategy to tune the ligand electronic and steric effects in a concerted fashion is reported, which can lead to simultaneous enhancement of several parameters (activity, stability, polymer molecular weight, melting point, branching density) for both the nickel and palladium catalysts.
Abstract: For transition metal-based olefin polymerization catalysts, ligand steric and electronic effects can strongly influence important catalytic properties. However, the simultaneous tuning of both steric and electronic effects has not been explored in most of the previous studies. In this contribution, a strategy to tune the ligand electronic and steric effects in a concerted fashion is reported. In such a system, both dibenzhydryl groups and multiple methoxy/fluoro groups were installed in α-diimine ligands. In addition to strongly influencing ligand electronics, the methoxy/fluoro groups can interact with the dibenzhydryl groups and efficiently increase ligand sterics. In ethylene polymerization, this concurrent tuning of electronic and steric effects can lead to simultaneous enhancement of several parameters (activity, stability, polymer molecular weight, melting point, branching density) for both the nickel and palladium catalysts. The effectiveness of this strategy is highly attractive for future studies in other catalytic systems.
TL;DR: Developments in iron- and cobalt-catalyzed C(sp3)-H bond functionalization reactions are described, with an emphasis on their applications in organic synthesis, i.e., the synthesis of natural products and pharmaceuticals and/or their modification.
Abstract: Direct C-H bond functionalization catalyzed by non-precious transition metals is an attractive strategy in synthetic chemistry Compared with the precious metals rhodium, palladium, ruthenium, and iridium commonly used in this field, catalysis based on non-precious metals, especially the earth-abundant ones, is appealing due to the increasing demand for environmentally benign and sustainable chemical processes Herein, developments in iron- and cobalt-catalyzed C(sp3)-H bond functionalization reactions are described, with an emphasis on their applications in organic synthesis, ie, the synthesis of natural products and pharmaceuticals and/or their modification
TL;DR: In this article, the separation of Pt, Pd and rhodium by ion exchange resins from various solutions while considering the presence of other metals such as other PGMs, Au, Ag and base metals.
TL;DR: Tuning the compositions and structures of Pd-based nanomaterials and their supports has shown great potentials in facilitating the sluggish ethanol oxidation reaction (EOR) in alkaline direct ethan...
Abstract: Tuning the compositions and structures of Pd-based nanomaterials and their supports has shown great potentials in facilitating the sluggish ethanol oxidation reaction (EOR) in alkaline direct ethan...
TL;DR: The intrinsic driving force of palladium single atom with high site density under reducing atmosphere, and its unique catalytic performance for hydrogenation reactions, are elucidated.
Abstract: Single-atom catalysts (SACs) have shown superior activity and/or selectivity for many energy- and environment-related reactions, but their stability at high site density and under reducing atmosphere remains unresolved. Herein, we elucidate the intrinsic driving force of a Pd single atom with high site density (up to 5 wt %) under reducing atmosphere, and its unique catalytic performance for hydrogenation reactions. In situ experiments and calculations reveal that Pd atoms tend to migrate into the surface vacancy-enriched MoC surface during the carburization process by transferring oxide crystals to carbide crystals, leading to the surface enrichment of atomic Pd instead of formation of particles. The Pd1 /α-MoC catalyst exhibits high activity and excellent selectivity for liquid-phase hydrogenation of substituted nitroaromatics (>99 %) and gas-phase hydrogenation of CO2 to CO (>98 %). The Pd1 /α-MoC catalyst could endure up to 400 °C without any observable aggregation of single atoms.
TL;DR: In this article, the catalytic behavior of Pd-based catalysts with tunable nanostructures and coordination bonds was investigated, and the evolution of the Pd entities were precisely regulated by controlled thermal treatment.
Abstract: Alternative palladium (Pd)-based catalysts to toxic mercuric chloride catalysts in vinyl chloride manufacture via acetylene hydrochlorination is currently limited by the lack of efficient and durable active sites. Here, the catalytic behavior of Pd-based catalysts with tunable nanostructures and coordination bonds were investigated. The evolution of Pd entities were precisely regulated by controlled thermal treatment. Pyridinic nitrogen is shown to regulate the nanostructures and coordination bonds of Pd sites, improve the thermal stability of Pd atoms, promote the adsorption of acetylene and enrich hydrogen chloride. These results indicate that Pd single-atom is more active than Pd nanoparticle or Pd cluster. The catalytic performance of Pd single-atom catalyst can be further improved by substituting Pd-Cl bond with Pd-N bond, with PdN2 identified as the efficient and durable active sites. Furthermore, the enrichment of hydrogen chloride enables the Pd single-atom catalysts to produce vinyl chloride via a non-hydrogen chloride excess method, which is a breakthrough in the existing industrial system. Our strategy for controlling the catalytic behavior of Pd sites is of a broad application prospect for the precise control and design of metal active sites.
TL;DR: In this article, the selective hydrogenation of acetylene has been studied over AgPd and CuPd catalysts. Controlled surface reactions were used to synthesize these bimetallic nanoparticles on both TiO2 and SiO2 sup...
Abstract: The selective hydrogenation of acetylene has been studied over AgPd and CuPd catalysts. Controlled surface reactions were used to synthesize these bimetallic nanoparticles on both TiO2 and SiO2 sup...
TL;DR: A catalytic asymmetric conjugate hydrophosphination of α,β-unsaturated amides is accomplished by virtue of the strong nucleophilicity of copper(I)-PPh2 species, which provides an array of chiral phosphines bearing an amide moiety in high to excellent yields with excellent enantioselectivity.
Abstract: A catalytic asymmetric conjugate hydrophosphination of α,β-unsaturated amides is accomplished by virtue of the strong nucleophilicity of copper(I)-PPh2 species, which provides an array of chiral phosphines bearing an amide moiety in high to excellent yields with excellent enantioselectivity. Furthermore, the dynamic kinetic resolution of unsymmetrical diarylphosphines (HPAr1Ar2) is successfully carried out through the copper(I)-catalyzed conjugate addition to α,β-unsaturated amides, which affords P-chiral phosphines with good-to-high diastereoselectivity and high enantioselectivity. 1H NMR studies show that the precoordination of HPPh2 to copper(I)-bisphosphine complex is critical for the efficient deprotonation by Barton's Base. Moreover, the relative stability of the copper(I)-(R,RP)-TANIAPHOS complex in the presence of excessive HPPh2, confirmed by 31P NMR studies, is pivotal for the high asymmetric induction, as the ligand exchange between bisphosphine and HPPh2 would significantly reduce the enantioselectivity. At last, a double catalytic asymmetric conjugate hydrophosphination furnishes the corresponding product in high yield with high diastereoselectivity and excellent enantioselectivity, which is transformed to a chiral pincer palladium complex in moderate yield. This chiral palladium complex is demonstrated as an excellent catalyst in the asymmetric conjugate hydrophosphination of chalcone.
TL;DR: A carbon atomization process that allows one not only to redisperse metal nanoparticles, but also to recover deactivated catalysts is reported, which opens up a window to preparation of sintering-resistant single atoms catalysts and regeneration of deactivated industrial catalysts.
Abstract: The sintering of supported metal nanoparticles is a major route to the deactivation of industrial heterogeneous catalysts, which largely increase the cost and decrease the productivity. Here, we discover that supported palladium/gold/platinum nanoparticles distributed at the interface of oxide supports and nitrogen-doped carbon shells would undergo an unexpected nitrogen-doped carbon atomization process against the sintering at high temperatures, during which the nanoparticles can be transformed into more active atomic species. The in situ transmission electron microscopy images reveal the abundant nitrogen defects in carbon shells provide atomic diffusion sites for the mobile atomistic palladium species detached from the palladium nanoparticles. More important, the catalytic activity of sintered and deactivated palladium catalyst can be recovered by this unique N-doped carbon atomization process. Our findings open up a window to preparation of sintering-resistant single atoms catalysts and regeneration of deactivated industrial catalysts.
TL;DR: In this article, a review of the palladium and copper catalyzed Sonogashira cross coupling achieved in recent years concerning substrates, different catalyst systems and reaction conditions is presented.
Abstract: Sonogashira coupling involves coupling of vinyl/aryl halides with terminal acetylenes catalyzed by transition metals, especially palladium and copper. This is a well known reaction in organic synthesis and plays a role in sp2-sp C-C bond formations. This cross coupling was used in synthesis of natural products, biologically active molecules, heterocycles, dendrimers, conjugated polymers and organic complexes. This review paper focuses on developments in the palladium and copper catalyzed Sonogashira cross coupling achieved in recent years concerning substrates, different catalyst systems and reaction conditions.
TL;DR: This study represents the first example of CO2 hydrogenation by bimetallic hydride clusters and underscores the importance of accounting for higher energy isomers for cluster catalytic activity.
Abstract: Mass spectrometric analysis of the anionic products of interaction between bimetallic palladium-copper tetrahydride anions, PdCuH4-, and carbon dioxide, CO2, in a reaction cell shows an efficient generation of the PdCuCO2H4- intermediate and formate/formic acid complexes. Multiple structures of PdCuH4- and PdCuCO2H4- are identified by a synergy between anion photoelectron spectroscopy and quantum chemical calculations. The higher energy PdCuH4- isomer is shown to drive the catalytic hydrogenation of CO2, emphasizing the importance of accounting for higher energy isomers for cluster catalytic activity. This study represents the first example of CO2 hydrogenation by bimetallic hydride clusters.
TL;DR: In this article, a meta-C-H allylation of arenes has been achieved with the aid of a palladium catalyst, pyrimidine-based auxiliary, and allyl phosphate.
Abstract: Controlling remote selectivity and delivering novel functionalities at distal positions in arenes are an important endeavor in contemporary organic synthesis. In this vein, template engineering and mechanistic understanding of new functionalization strategies are essential for enhancing the scope of such methods. Herein, meta-C-H allylation of arenes has been achieved with the aid of a palladium catalyst, pyrimidine-based auxiliary, and allyl phosphate. 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) was found as a critical solvent in this transformation. The role of HFIP throughout the catalytic cycle has been systematically studied. A broad substrate scope with phenethyl ether, phenol, benzylsulfonyl ester, phenethylsulfonyl ester, phenylacetic acid, hydrocinnamic acid, and 2-phenylbenzoic acid derivatives has been demonstrated. Interestingly, conformationally flexible arenes have also been selectively allylated at the meta-position using allyl phosphate. A combination of 1H NMR, 31P NMR, ESI-MS, kinetic experiments, and density functional theory (DFT) computations suggested that reaction proceeds through a ligand-assisted meta-C-H activation, allyl addition forming a Pd-π-allyl complex which is then followed by a turnover determining the C-C bond formation step leading to the meta-allylated product.
TL;DR: In this paper, a bidentate phosphino-modified magnetic nanoparticles-anchored palladium complex (PdCl2-Fe3O4@SiO2-2P) was developed as a clean and efficient heterogeneous catalyst for the carbon-carbon coupling polycondensations.
Abstract: Conjugated polymers are usually synthesized by homogeneous palladium complexes-catalyzed Heck, Suzuki, and Stille coupling reactions, which suffer from the non- recyclability of expensive palladium catalysts and palladium contamination of the desired polymer due to palladium leaching. In order to overcome these drawbacks, a bidentate phosphino-modified magnetic nanoparticles-anchored palladium complex (PdCl2-Fe3O4@SiO2-2P) as a clean and efficient heterogeneous catalyst for the carbon–carbon coupling polycondensations was developed in present work. The PdCl2-Fe3O4@SiO2-2P catalyst exhibited an enhanced catalytic activity for Heck, Suzuki, and Stille coupling polymerizations, as compared with the most commonly used homogeneous Pd(PPh3)4. Moreover, this heterogeneous palladium catalyst showed advantage of much less palladium impurity (below 13 ppm) in the isolated polymers. Importantly, PdCl2-Fe3O4@SiO2-2P can facilely be separated from the reaction products and recovered by using an external magnetic field, and recycled at least eight times with almost consistent catalytic activity.
TL;DR: In this paper, the singe-atom doping effect on CO2 red carbon dioxide has been investigated at the atomic level in gold nanoclusters, where the structure and electrocatalytic properties at atomic level are correlated.
Abstract: Atomically precise gold nanoclusters provide opportunities for correlating the structure and electrocatalytic properties at the atomic-level. Here, we report the singe-atom doping effect on CO2 red...
TL;DR: By means of ambient pressure X-ray photoelectron spectroscopy, this paper investigated the reactivity of coal-based catalysts for methane combustion on natural gas vehicles at low temperature.
Abstract: Palladium-based catalysts are attractive for methane combustion on natural gas vehicles at low temperature. By means of ambient pressure X-ray photoelectron spectroscopy, we investigated the reacti...
TL;DR: A streamlined method for asymmetric synthesis of β-aryl β-lactams from propanoic acid and aryl iodides via Pd-catalyzed sequential C(sp3)–H functionalization is reported.
Abstract: β-Lactams are important scaffolds in drug design and frequently used as reactive intermediates in organic synthesis. Catalytic reactions featuring intramolecular C–H amidation of alkyl carboxamide ...
TL;DR: In this article, a series of bulky yet flexible cycloalkyl substituted α-diimine ligands and the corresponding nickel and palladium catalysts were described and compared to the rigid phenyl substituted catalysts generated polyethylene with much lower branching density in ethylene polymerization.
TL;DR: Low catalytic platinum-palladium nanowires with a subtle lattice strain and Boerdijk-Coxeter helix type morphology are synthesized through a surfactant-free, thermal single phase solvent method and exhibit significantly improved electrocatalytic activity and stability for the oxygen reduction reaction.
Abstract: Electrocatalytic activity of alloy nanocatalytsts can be manipulated effectively by tuning their physical properties (ensemble, geometric, and ligand effects) to afford optimal surface structure and compositions for proton exchange membrane fuel cell (PEMFC) application. Herein, highly catalytic platinum-palladium nanowires (PtnPd100-n NWs) with a subtle lattice strain and Boerdijk-Coxeter helix type morphology are synthesized through a surfactant-free, thermal single phase solvent method. X-ray diffraction results show that PtnPd100-n NWs are exposed through the (111) facets and their shrinking or expanding lattice parameters can be modulated by the alloy compositions. Electrochemical results reveal that their high catalytic activity correlates with the lattice shrinking, facets, and bimetallic compositions, showing higher activity when the ratio of Pt and Pd is ∼78:22, which is further supported by DFT results. Compared to the nanoparticle type platinum-palladium alloyed catalysts with similar metal compositions (PtnPd100-n NPs), the PtnPd100-n NWs exhibit significantly improved electrocatalytic activity and stability for the oxygen reduction reaction. These findings open new strategies to design the highly active and stable alloy nanocatalysts with controllable compositions.
TL;DR: It is reported that merging palladium catalysis with hydrogen atom transfer (HAT) photocatalysis enabled direct arylations and alkenylations of aldehyde C–H bonds, facilitating visible light-catalysis.
Abstract: Herein, we report that merging palladium catalysis with hydrogen atom transfer (HAT) photocatalysis enabled direct arylations and alkenylations of aldehyde C–H bonds, facilitating visible light-cat...