Palladium Catalysis for Aerobic Oxidation Systems Using Robust Metal–Organic Framework

Described here is a new and viable approach to achieve Pd catalysis for aerobic oxidation systems (AOSs) by circumventing problems associated with both the oxidation and the catalysis through an all‐in‐one strategy, employing a robust metal–organic framework (MOF). The rational assembly of a Pd^II catalyst, phenanthroline ligand, and Cu^II species (electron‐transfer mediator) into a MOF facilitates the fast regeneration of the Pd^II active species, through an enhanced electron transfer from in situ generated Pd⁰ to Cu^II, and then Cu^I to O₂, trapped in the framework, thus leading to a 10 times higher turnover number than that of the homogeneous counterpart for Pd‐catalyzed desulfitative oxidative coupling reactions. Moreover, the MOF catalyst can be reused five times without losing activity. This work provides the first exploration of using a MOF as a promising platform for the development of Pd catalysis for AOSs with high efficiency, low catalyst loading, and reusability.     

Immobilized Pd on a NHC functionalized metal–organic framework MIL-101(Cr): an efficient heterogeneous catalyst in Suzuki−Miyaura coupling reaction in water

A novel Pd−NHC functionalized metal–organic framework (MOF) based on MIL-101(Cr) was synthesized and used as an efficient heterogeneous catalyst in the C-C bond formation reactions. Using this heterogeneous Pd catalyst system, the Suzuki−Miyaura coupling reaction was accomplished well in water, and coupling products were obtained in good to excellent yields in short reaction time. The Pd−NHC−MIL-101(Cr) was characterized using some different techniques, including Fourier transform-infrared, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, inductively coupled plasma and elemental analysis. The microscopic techniques showed the discrete octahedron structure of MIL-101(Cr), which is also stable after chemical modification process to prepare the catalyst system. The TEM images of the catalyst showed the existence of palladium nanoparticles immobilized in the structure of the catalyst, while no reducing agent was used. It seems that the NHC groups and imidazolium moieties in the structure of the MOF can reduce Pd (II) to Pd (0) species. This modified MOF substrate can also prevent aggregation of Pd nanoparticles, resulting in high stability of them in organic transformation. The Pd−NHC−MIL-101(Cr) catalyst system could be simply extracted from the reaction mixture, providing an efficient synthetic method for the synthesis of biaryls derivatives using the aforementioned coupling reaction. The Pd−NHC−MIL-101(Cr) catalyst could be recycled in this organic reaction with almost consistent catalytic efficiency.     

Amino-Induced 2D Cu-Based Metal–Organic Framework as an Efficient Heterogeneous Catalyst for Aerobic Oxidation of Olefins

With the assistance of hydrogen bonds of the o-amino group, we have successfully tuned a coordination structure from a metal–organic polyhedron (MOP) to a two-dimensional (2D) metal–organic framework (MOF). The amino group forms hydrogen bonds with the two vicinal carboxylic groups, and induces the ligand to coordinate with copper ions to form the 2D structure. The obtained 2D Cu-based MOF (Cu-AIA) has been applied as an efficient heterogeneous catalyst in the aerobic epoxidation of olefins by using air as oxygen source. Without the aggregation problem of active sites in MOPs, Cu-AIA possesses much higher reactivity than MOP-1. Furthermore, the amino group of the framework has been used as a modifiable site through post-synthetic metalation (PSMet) to prepare a 2D MOF-supported Pd single-site heterogeneous catalyst, which shows excellent catalytic performance for the Suzuki reaction. It indicates that Cu-AIA can also work as a good 2D MOF carrier for the derivation of other heterogeneous catalysts.     

An eco-friendly and energy-efficient protocol for the Heck reaction under solar radiation catalyzed by rice husk silica‐anchored cinchonine.Pd nanocomposite

An environmentally friendly and energy-efficient method for the carbon–carbon bond formation via cross-coupling Heck reaction using rice husk silica-anchored cinchonine.Pd nanocomposite as a heterogeneous catalyst under concentrated solar radiation is being reported. In this investigation, first, silica nanoparticles were synthesized using rice husks as available agricultural bioresources. Then, the surface of nano silica was modified by grafting (3-mercaptopropyl) trimethoxysilane, and after that, thiol-ene free radical reaction of its SH groups with alkene function of cinchonine by azobisisobutylonitrile initiator. Finally, the target nanocomposite, nano SiO₂-S-Cin.Pd, was created via loading palladium nanoparticles into the mesoporous nanocomposite by its reaction by palladium acetate, followed by ethanol reduction. The structure and morphology of the nano SiO₂-S-Cin.Pd nanocomposite was characterized using Fourier transform infrared spectra, X-ray diffraction patterns, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The catalytic ability of this nanocomposite was investigated in the arylation of olefins in both concentrated solar radiation and conventional thermal conditions. A comparison of the conventional and CSR methods for C–C bond formation in PEG, showed that the CSR approach is a better alternative route with a high energy-saving strategy. The nanocatalyst is easily removed from the mixture and has been tested on several runs without a loss of catalytic activity. The heterogeneity of the nano SiO₂-S-Cin.Pd catalyst was confirmed by hot filtration test. This method has the advantages of simple methodology, easy work-up, high yields, short reaction times, and greener conditions. In addition to convenience, this technology improves product purity and offers economic and environmental benefits.     

Palladium nanoparticles encapsulated in a metal-organic framework as efficient heterogeneous catalysts for direct C2 arylation of indoles

Highly dispersed palladium nanoparticles (Pd NPs) encapsulated in the mesoporous cages of the metal-organic framework (MOF) MIL-101(Cr) have been prepared by using the wetness impregnation method. The Pd NPs were characterized by powder X-ray diffraction (PXRD), N(2) adsorption, transmission electron microscopy, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The particles size ((2.6±0.5) nm) of the obtained Pd NPs was in good agreement with the cage diameters (2.9 and 3.4 nm) of the MOF. The resulting Pd/MIL-101(Cr) catalyst exhibited extremely high catalytic activities in the direct C2 arylation of substituted indoles by using only 0.1 mol% of the Pd catalyst. Moreover, the catalyst is easily recoverable and can be reused several times without leaching into solution and loss of activity. The combination of the highly dispersible Pd NPs within the accessible mesoporous cages and the favorable adsorption of the aryl halides on MIL-101 are suspected to be the main reasons for the observed high activities of the Pd/MIL-101(Cr) catalyst in the direct C2 arylation of indoles.     

Polypyrrole-palladium nanocomposite coating of micrometer-sized polymer particles toward a recyclable catalyst

A range of near-monodisperse, multimicrometer-sized polymer particles has been coated with ultrathin overlayers of polypyrrole-palladium (PPy-Pd) nanocomposite by chemical oxidative polymerization of pyrrole using PdCl(2) as an oxidant in aqueous media. Good control over the targeted PPy-Pd nanocomposite loading is achieved for 5.2 μm diameter polystyrene (PS) particles, and PS particles of up to 84 μm diameter can also be efficiently coated with the PPy-Pd nanocomposite. The seed polymer particles and resulting composite particles were extensively characterized with respect to particle size and size distribution, morphology, surface/bulk chemical compositions, and conductivity. Laser diffraction studies of dilute aqueous suspensions indicate that the polymer particles disperse stably before and after nanocoating with the PPy-Pd nanocomposite. The Fourier transform infrared (FT-IR) spectrum of the PS particles coated with the PPy-Pd nanocomposite overlayer is dominated by the underlying particle, since this is the major component (>96% by mass). Thermogravimetric and elemental analysis indicated that PPy-Pd nanocomposite loadings were below 6 wt %. The conductivity of pressed pellets prepared with the nanocomposite-coated particles increased with a decrease of particle diameter because of higher PPy-Pd nanocomposite loading. "Flattened ball" morphologies were observed by scanning/transmission electron microscopy after extraction of the PS component from the composite particles, which confirmed a PS core and a PPy-Pd nanocomposite shell morphology. X-ray diffraction confirmed the production of elemental Pd and X-ray photoelectron spectroscopy studies indicated the existence of elemental Pd on the surface of the composite particles. Transmission electron microscopy confirmed that nanometer-sized Pd particles were distributed in the shell. Near-monodisperse poly(methyl methacrylate) particles with diameters ranging between 10 and 19 μm have been also successfully coated with PPy-Pd nanocomposite, and stable aqueous dispersions were obtained. The nanocomposite particles functioned as an efficient catalyst for the aerobic oxidative homocoupling reaction of 4-carboxyphenylboronic acid in aqueous media for the formation of carbon-carbon bonds. The composite particles sediment in a short time (相似文献   

Construction of a MOF-Supported Palladium Catalyst via Metal Metathesis

A new MOF-supported heterogeneous palladium catalyst Pd/NBB-1 has been synthesized successfully through the effective metal metathesis between Pd(CF₃COO)₂ and NBB-1. NBB-1 is a two-dimensional zinc metal-organic framework constructed from 2-aminoterephthalate (NH₂−H₂BDC) and 2,2′-bipyridine-5-carboxylate (HBPC) by solvothermal method. The replacement efficiency of Pd(II) to Zn(II) is up to 72% after only 24 hours, which is beneficial to the catalytic application. Pd/NBB-1 with a low loading of 2 mol% works efficiently in the 1,4-addition reaction of arylboronic acids with α,β-unsaturated ketones in air, and its catalytic activity keeps unchanged after 3 reaction cycles. This work provides a new strategy to effectively prepare supported noble metal/MOF catalysts, which would further increase the practical applications of metal-organic frameworks.     

Controlled synthesis of magnetic Pd/Fe3O4 spheres via an ethylenediamine-assisted route

A simple route based on time-dependent growth was employed to synthesize solid and hollow spheres of Pd/Fe(3)O(4) nanocomposite. Transmission electron microscopic (TEM) imaging shows that the spheres are composed of nanocrystals with the solid spheres having a diameter of 533 nm whereas the hollow ones having a diameter of 520 nm and a shell thickness of 100 nm. An assembly-then-growth mechanism for the formation of the magnetic Pd/Fe(3)O(4) nanocomposite has also been elucidated on the basis of the experimental observations. It is demonstrated that the Pd/Fe(3)O(4) nanocomposite functions as a heterogeneous catalyst for the hydrogenation reaction of p-nitrophenol at room temperature under atmospheric pressure. Both the solid and hollow spheres possess unique magnetic properties so that they may be conveniently separated and recovered by a magnet after the catalytic reaction.     

Active and recyclable ordered mesoporous magnetic organometallic catalyst as high‐performance visible light photocatalyst for degradation of organic pollutants

A novel light‐active magnetic Pd complex as a photocatalyst was prepared through bonding organometallics to mesoporous silica channels formed on the surface of silica‐coated iron oxide nanoparticles. The nanocomposite (denoted as Fe₃O₄@SiO₂@m‐SiO₂@PDA‐Pd(0); PDA = 1,10‐phenanthroline‐2,9‐dicarbaldehyde) is more efficient and has higher photocatalytic capability in the degradation of 2,4‐dichlorophenol under visible light irradiation compared with virgin Pd complex (PDA‐Pd). This noteworthy photodegradation activity can be due to the high dispersion of Pd nanoparticles. High yield, low reaction time and non‐toxicity of the catalyst are the main merits of this protocol. Also magnetic separation is an environmentally friendly alternative method for the separation and recovery of the catalyst, since it minimizes the use of solvents and auxiliary materials, reduces operation time and minimizes catalyst loss by preventing mass loss and oxidation. The produced Pd catalyst was characterised using various techniques. Furthermore, transmission electron microscopy characterization was used for determining the structural properties of the Pd nanocatalyst.     

Pd/MOF‐199: As an efficient heterogeneous catalyst for the Suzukie Miyaura cross‐coupling reaction

Successful deposition of Pd nanoparticles is described using MOF‐199 as a support. Various characterization techniques including FTIR, XRD, SEM, BET‐BJH, TG‐DTA, and NH₃‐TPD were used to verify the efficiency of catalysts. Pd/MOF‐199 is utilized as a catalyst for Suzukie Miyaura reactions with reasonable to excellent reaction yields under reflux conditions in H₂O: ethanol solvent.     

Efficient Degradation of Cellulose in Its Homogeneously Aqueous Solution over 3D Metal-Organic Framework/Graphene Hydrogel Catalyst

Catalytic degradation of cellulose to chemicals is an attracting topic today for the conversion of biomass, and the development of novel catalysts is a key point. Since metal-organic frameworks (MOFs) possess uniform, continuous, and permeable channels, they are valuable candidate as catalysts. Here, a new 3D MOF/graphene catalyst was prepared by in situ growth of the zeolitic imidazolate frameworks (ZIF-8) nanoparticles inside the pore of an as-formed 3D reduced graphene oxide (rGO) hydrogel. The ZIF-8/rGO nanocomposite owns both micropores and mesopores with large specific surface area and plenty of acids sites, which is an idea catalyst for biomass degradation. Cellulose was dissolved in alkaline aqueous solution at first, and then it was degraded efficiently over the new catalyst under hydrothermal condition. The conversion reaches 100% while the main products are formic acid with a maximum yield of 93.66%. In addition, the catalyst can be reused with high activity.     

Mesoporous Metal–Organic Frameworks for Catalytic RNA Deprotection and Activation

A metal–organic framework (MOF) with mespores (2 to 50 nm) allows the inclusion of large biomolecules, such as nucleic acids. However, chemical reaction on the nucleic acids, to further regulate their bioactivity, is yet to be demonstrated within MOF pores. Here, we report the deprotection of carbonate protected RNA molecules (21 to 102 nt) to restore their original activity using a MOF as a heterogeneous catalyst. Two MOFs, MOF-626 and MOF-636 are designed and synthesized, with mesopores of 2.2 and 2.8 nm, respectively, carrying isolated metal sites (Ni, Co, Cu, Pd, Rh and Ru). The pores favor the entrance of RNA, while the metal sites catalyze C−O bond cleavage at the carbonate group. Complete conversion of RNA is achieved by Pd-MOF-626, 90 times more efficiently than Pd(NO₃)₂. MOF crystals are also removable from the aqueous reaction media, leaving a negligible metal footprint, 3.9 ppb, only 1/55 of that using homogeneous Pd catalysts. These features make MOF potentially suited for bioorthogonal chemistry.     

Synthesis of gold and palladium nanoparticles supported on CuO/rGO using imidazolium ionic liquid for CO oxidation

A simple ionic liquid-assisted approach for the fabrication of graphene-based nanocomposite is reported. Pd–CuO/rGO and Au–CuO/rGO nanocomposites are successfully fabricated with the assistance of the ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate. The physicochemical features of nanocomposite are systematically characterized by XRD, FT-IR, Raman spectroscopy, XPS, TGA, FESEM, AFM, and HRTEM. Carbon monoxide has been used as a probe molecule to emphasize the performance of the fabricated materials. The results indicate that the incorporation of a little quantity of ionic liquid results in the creation of uniformly dispersed NPs simultaneously with the reduction of graphene oxide (GO) into rGO, which leads to a low-temperature CO oxidation process. Besides, the Au–CuO/rGO catalyst achieved excellent durability in CO oxidation for 14 h, without detectable deactivation. The low-temperature CO oxidation was mainly induced by the synergistic effects between the components of catalysts. The Au or Pd and CuO combination not only generates more interfaces, which is more favorable for the activation of oxygen but also enhances the catalyst reduction behavior. Consequently, a graphene composite catalyst can be considered a potential CO oxidation candidate.

     

Pd@tetrahedral hollow magnetic nanoparticles coated with N‐doped porous carbon as an efficient catalyst for hydrogenation of nitroarenes

Hollow magnetic nanoparticles (MNPs) with tetrahedral morphology were synthesized and then covered by a shell prepared by coating with melamine–formaldehyde followed by the introduction of glucose‐derived carbon. Subsequently, Pd nanoparticles were immobilized and the core–shell nanocomposite was carbonized. The obtained magnetic catalyst was successfully applied for the hydrogenation of nitroarenes in aqueous media. To investigate the effects of the morphology of MNPs, the nature of carbon shell, and the order of incorporation of Pd nanoparticles, several control catalysts, including the MNPs with different morphologies (disc‐like and cylinder); MNPs coated with different shells (sole glucose‐derived carbon or melamine–formaldehyde carbon shell); and a nanocomposite, in which Pd was immobilized after carbonization, were prepared and examined as catalyst for the model reaction. To justify the observed different catalytic activities of the catalysts, their Pd loadings, leaching, and specific surface areas were compared. The results confirmed that tetrahedral MNPs coated with porous N‐rich carbon shell exhibited the best catalytic activity. The high catalytic activity of this catalyst was attributed to its high surface area and the interaction of N‐rich shell with Pd nanoparticles that led to the higher Pd loading and suppressed Pd leaching.     

Preparation,structural characterization of a novel egg-shell palladium sulfide catalyst and its application in selective reductive alkylation reaction

A novel egg-shell Pd-S catalyst with palladium metal as the core and a membrane of palladium sulfide as the surface has been prepared by sulphidizing Pd/C with H₂S.This catalyst is effective for the reductive alkylation of p-amino diphenylamine（PADPA） and methylisobutyl ketone（MIBK） to afford N-（1,3-dimethylbutyl）-N′-phenyl-p-phenylenedianine（DBPPD） with conversion up to 99.42%and selectivity to 97.46%.Comparing with the other common palladium sulfide catalysts,the membrane of palladium sulfide on the surface and the core of palladium metal cause the Pd on the surface of the new catalyst in a lower sulfur coordination, which improves its activity.Our result indicates that this new egg-shell Pd-S/C is an efficient hydrogenation catalyst.     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.     

Visible light induced the high-efficiency spirocyclization reaction of propynamide and thiophenols via recyclable catalyst Pd/ZrO2

A new method for the synthesis of 3-thioazaspiro[4,5]trienones was developed using Pd nanoparticle catalysts,which are highly efficient,environmentally friendly and recyclable.Alkynes and thiophene phenols are effectively cyclized by Pd/ZrO2 catalyst under visible light irradiation.The present protocol simply utilizes visible light as the safe and ecofriendly energy source,and the Pd/ZrO2 nanocomposite as photocatalyst provides a simple and practical approach to various 3-thioazaspiro[4,5]trienones in moderate conditions to high yields.     

氮掺杂石墨烯量子点/钯纳米复合材料的研究

铂基催化剂因具有高催化活性、高稳定性而成为极其重要的能源转化催化剂。本文采用水热法合成氮掺杂石墨烯量子点支撑的钯纳米复合材料(Pd@N-GQDs),并将其用于碱性介质中甲醇的电催化氧化反应。实验结果表明,相比同类型材料钯负载于石墨烯纳米片(Pd@GS)、钯负载于石墨烯量子点(Pd@GQDs)和商业钯黑催化剂(Pd@C),Pd@N-GQDs纳米材料具有很高的催化活性和稳定性,并可减少催化剂材料中贵金属的使用量。     

Ruthenium Complexation in an Aluminium Metal–Organic Framework and Its Application in Alcohol Oxidation Catalysis

A ruthenium trichloride complex has been loaded into an aluminium metal–organic framework (MOF), MOF‐253, by post‐synthetic modification to give MOF‐253‐Ru. MOF‐253 contains open bipyridine sites that are available to bind with the ruthenium complex. MOF‐253‐Ru was characterised by elemental analysis, N₂ sorption and X‐ray powder diffraction. This is the first time that a Ru complex has been coordinated to a MOF through post‐synthetic modification and used as a heterogeneous catalyst. MOF‐253‐Ru catalysed the oxidation of primary and secondary alcohols, including allylic alcohols, with PhI(OAc)₂ as the oxidant under very mild reaction conditions (ambient temperature to 40 °C). High conversions (up to >99 %) were achieved in short reaction times (1–3 h) by using low catalyst loadings (0.5 mol % Ru). In addition, high selectivities (>90 %) for aldehydes were obtained at room temperature. MOF‐253‐Ru can be recycled up to six times with only a moderate decrease in substrate conversion.     

Urea metal-organic frameworks as effective and size-selective hydrogen-bond catalysts

A new urea-containing metal-organic framework (MOF) was synthesized to act as a heterogeneous catalyst. Ureas are well-known for self-recognition and aggregation behavior, resulting in loss of catalytic competency. The catalyst spatial isolation achievable in a porous MOF environment suggests a potentially general solution. The combination of a symmetrical urea tetracarboxylate strut, 4,4'-bipyridine, and Zn(NO(3))(2)·6H(2)O under solvothermal conditions afforded a new microporous MOF (NU-601). This material is indeed an effective hydrogen-bond-donor catalyst for Friedel-Crafts reactions between pyrroles and nitroalkenes, whereas a homogeneous urea is much less competent. The higher rates of reaction of small substrates relative to larger ones with NU-601 strongly suggest that catalysis primarily occurs within the pores of this new material rather than on its exterior. To the best of our knowledge, this approach is the first example of specific engineering of successful hydrogen-bonding catalysis into a MOF material.