Pd Catalysts Research Articles

Template-OrientedPolyaniline-Supported Palladium Nanoclusters for Reductive Homocoupling of Furfural Derivatives.

Developing well-defined structures and desired properties for porous organic polymer (POP) supported catalysts by controlling their composition, size, and morphology is of great significance. Herein, we report a preparation of polyaniline (PANI) supported Pd nanoparticles (NPs) with controllable of the structure and morphology. The protocol involves the introduction of MnO2 with different crystal structures (α, β, γ, δ, ε) serving as both reaction templates and oxidants. MnO2 selectively oxidizes the aniline to polyaniline with diverse regular distribution of benzene and quinone, thus leading to the Pd/PANI catalyst growth mode which prominently impacts the charge transfer between Pd and PANI, as well as the dispersion of metal NPs. In particular, Pd/ε-PANI greatly improves the turnover frequency (TOF), up to 88.3 h-1,in the reductive coupling of the furfural derivatives to potential bio-based plasticizers. Systematic characterizations reveal the unique oxidation state of the support in the Pd/ε-PANI catalyst and coordination mode of Pd that drives the formation of highly dispersed Pd nanoclusters. Density functional theory (DFT) calculations show the more electron rich Pd/PANI catalyst has the lower energy barrier in the oxidative addition step, which favors the C-C coupling reaction.

Template‐Oriented Polyaniline‐Supported Palladium Nanoclusters for Reductive Homocoupling of Furfural Derivatives

AbstractDeveloping well‐defined structures and desired properties for porous organic polymer (POP) supported catalysts by controlling their composition, size, and morphology is of great significance. Herein, we report a preparation of polyaniline (PANI) supported Pd nanoparticles (NPs) with controllable structure and morphology. The protocol involves the introduction of MnO2 with different crystal structures (α, β, γ, δ, ϵ) serving as both the reaction template and the oxidant. The different forms of MnO2 each convert aniline to a PANI that contains a unique regular distribution of benzene and quinone. This leads to the Pd/PANI catalysts with different charge transfer properties between Pd and PANI, as well as different dispersions of the metal NPs. In this case, the Pd/ϵ‐PANI catalyst greatly improves the turnover frequency (TOF; to 88.3 h−1), in the reductive coupling of furfural derivatives to potential bio‐based plasticizers. Systematic characterizations reveal the unique oxidation state of the support in the Pd/ϵ‐PANI catalyst and coordination mode of Pd that drives the formation of highly dispersed Pd nanoclusters. Density functional theory (DFT) calculations show the more electron rich Pd/PANI catalyst has the lower energy barrier in the oxidative addition step, which favors the C−C coupling reaction.

Mutual Reinforcement of Evaporation and Catalysis for Efficient Freshwater–Salt–Chemical Production

AbstractThe development of mutually reinforcing solar‐driven interfacial evaporation (SDIE) and integrated functional materials/systems to achieve efficient production of freshwater and energy/matters simultaneously under extremely high solar utilization is in high demand. Herein, an integrated SDIE reaction system (reduced graphene oxide (rGO)‐palladium (Pd) catalytic evaporator, rGO‐Pd) is first reported, where SDIE and the integrated catalytic reaction are mutually reinforced. The apparent utilization of solar to thermal energy by the integrated SDIE reaction system is a combination of evaporative utilization and catalytic utilization. The reaction heat released by the rGO‐Pd catalytic evaporator enhances its anti‐salt water production performance to a record of 12.7 L m−2 h−1, surpassing the reported performance of other integrated SDIE reaction systems. In the rGO‐Pd catalytic evaporator, the synergetic effect of photothermal and rapid mass transfer significantly increases the catalytic activity (turnover frequency) of Pd catalysts up to a record 125.07 min−1, which is about 3.75 times of the condition without light. This integrated SDIE reaction system can effectively and simultaneously produce freshwater, salt, and catalyzed chemicals after evaporating water to dryness. This study paves the way for SDIE's high‐performance applications in future integrated water, energy, and environmental systems.

Ultra-fast catalytic hydrodechlorination of chloroacetic acids over Pd catalyst supported on CeO2 with exposed (1 1 0) plane

Chloroacetic acids were frequently detected in the chlorination drinking water. Herein, Pd/CeO2 catalysts with varied CeO2 exposed planes were prepared, and the catalysts were applied for the liquid phase hydrodechlorination (HDC) of monochloroacetic acid (MCAA) at ambient temperature and pressure. The CeO2 nanorod (r-CeO2) with (1 1 0) plane supported Pd catalysts showed higher Pd dispersion and CO adsorption amount than that of CeO2 nanocube (c-CeO2) with (1 0 0) face and octahedron counterparts (o-CeO2) with (1 1 1) plane. The HDC rate of MCAA reached 99.5% after reaction for 5 min at a catalyst dosage of 0.1 g l−1 under pH 5.6 over the dp-Pd1/r-CeO2 catalyst prepared via the deposition precipitation (dp) method. The MCAA removal efficiencies were only 19.8% and 11.5% over dp-Pd1/c-CeO2 and dp-Pd1/o-CeO2, respectively. DFT simulation results showed that the adsorption energy between Pd and r-CeO2 was higher than that of CeO2 nanocube and octahedron, suggesting that compared with (1 0 0) and (1 1 1) planes, the r-CeO2 with exposed (1 1 0) plane favored the anchor of Pd nanoparticles. Higher Pd dispersion and appropriate Pdn+/Pd0 ratio (0.86) accounted for the ultra-fast catalytic HDC reaction. Additionally, the pre-adsorption of reactant over the catalyst surface favored the HDC reaction. The HDC of polychlorinated acetic acids over c-CeO2 and o-CeO2 supported Pd catalysts were significantly accelerated compared with that of MCAA, while the dechlorination of trichloroacetic acid (TCAA) was remarkably depressed over dp-Pd1/r-CeO2 due to the weak affinity of the catalyst surface for TCAA.

Carbonylative Self-Coupling of Aryl Boronic Acids Using a Confined Pd Catalyst within Melamine Dendron and Fibrous Nano-Silica: A CO Surrogate Approach.

Development of heterogeneous catalysts with tunable activity and selectivity has posed a persistent challenge. This study addresses this challenge by fabricating a hybrid environment through the combination of mesoporous silica and N-rich melamine dendron via covalent grafting, allowing for controllable growth and encapsulation of Pd NPs. This catalyst presented an excellent catalytic activity for the oxidative carbonylative self-coupling of aryl boronic acids to afford symmetric biaryl ketones using N-formyl saccharin as a sustainable solid CO source and Cu as a co-catalyst.

Pd Nanoparticle-Decorated Novel Ternary Bi2O2CO3-Bi2MoO6-CuO Heterojunction for Enhanced Photo-electrocatalytic Ethanol Oxidation.

Recently, photo-electrooxidation of fuel using a noble metal-semiconductor junction has been one of the most promising approaches in fuel cell systems. Herein, we report the development of a Pd-supported Bi2MoO6-Bi2O2CO3-CuO novel ternary heterojunction for ethanol oxidation in alkali in the presence and absence of visible light. Various spectroscopic and microscopic characterization techniques confirm strong coupling between palladium nanoparticles and Bi2MoO6-Bi2O2CO3-CuO ternary heterojunction supports. The photo-electrocatalytic efficacy of the synthesized catalysts was inspected by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The CV study reveals that the forward peak current density (in mA mg-1 of Pd) of the synthesized quaternary heterojunction was about 1482.5, which is 2.4, 4, and 4.6 times higher than that of Pd/CuO (608.3), Pd/Bi2MoO6-Bi2O2CO3 (368.3), and similarly synthesized Pd catalyst (321.5) under visible light radiation. The best heterojunction catalyst shows 2.21-fold higher peak current density in visible light compared to that in dark. CA study reveals that after operation for 6000 s, the current density of the quaternary electrode is 1.5 and 3.4 times greater than that of Pd/CuO and Pd/C catalysts, respectively. The greater photocurrent response, lower photoluminescence (PL) emission intensity, and smaller semicircle arc in the Nyquist plot of the quaternary catalyst demonstrate the efficient segregation and higher charge transfer conductance of photogenerated charges to facilitate the photo-electrooxidation process of ethanol. The stability test shows that the quaternary catalyst loses only 9.8 and 7.7% of its maximum current density after 500 cycles of CV operation in the dark and light, respectively, indicating that light energy is more beneficial in establishing high stability. The dramatic enhancement of the photo-electrocatalytic activity of the quaternary electrode is owing to the lower band gap, high ECSA, enhanced charge separation of photogenerated carriers (e--h+), and all cocatalytic support of Bi2MoO6, Bi2O2CO3, and CuO in Pd/ Bi2MoO6-Bi2O2CO3-CuO under visible light radiation. The morphology and structure of the used quaternary catalyst are tested using FESEM and PXRD. Finally, ex situ FTIR spectroscopy and HPLC techniques help understand the ethanol electrooxidation reaction mechanism.

Intramolecular Palladium Catalyst Transfer on Benzoheterodiazoles as Acceptor Monomers and Discovery of Catalyst Transfer Inhibitors.

Intramolecular catalyst transfer on benzoheterodiazoles was investigated in Suzuki-Miyaura coupling reactions and polymerization reactions with tBu3PPd precatalyst. In the coupling reactions of dibromobenzotriazole, dibromobenzoxazole, and dibromobenzothiadiazole with pinacol phenylboronate, the product ratios of monosubstituted product to disubstituted product were 0/100, 27/73, and 89/11, respectively, indicating that the Pd catalyst undergoes intramolecular catalyst transfer on dibromobenzotriazole, whereas intermolecular transfer occurs in part in the case of dibromobenzoxazole and is predominant for dibromobenzothiadiazole. The polycondensation of 1.3 equivalents of dibromobenzotriazole with 1.0 equivalent of para- and meta-phenylenediboronates afforded high-molecular-weight polymer and cyclic polymer, respectively. In the case of dibromobenzoxazole, however, para- and meta-phenylenediboronates afforded moderate-molecular-weight polymer with bromine at both ends and cyclic polymer, respectively. In the case of dibromobenzothiadiazole, they afforded low-molecular-weight polymers with bromine at both ends. Addition of benzothiadiazole derivatives interfered with catalyst transfer in the coupling reactions.

Large-Area Printed Oxide Film Sensors Enabling Ultrasensitive and Dual Electrical/Colorimetric Detection of Hydrogen at Room Temperature.

Commercial hydrogen (H2) sensors operate at high temperatures, which increases power consumption and poses a safety risk owing to the flammable nature of H2. Here, a polymer-noble metal-metal oxide film is fabricated using the spin-coating and printing methods to realize a highly sensitive, low-voltage operation, wide-operating-concentration, and near-monoselective H2 sensor at room temperature. The H2 sensors with an optimized thickness of Pd nanoparticles and SnO2 showed an extremely high response of 16,623 with a response time of 6 s and a recovery time of 5 s at room temperature and 2% H2. At the same time, printed flexible sensors demonstrate excellent sensitivity, with a response of 2300 at 2% H2. The excellent sensing performance at room temperature is due to the optimal SnO2 thickness, corresponding to the Debye length and the oxygen and H2 spillover caused by the optimized coverage of the Pd catalyst. Furthermore, multistructures of WO3 and SnO2 films are used to fabricate a new type of dual-signal sensor, which demonstrated simultaneous conductance and transmittance, i.e., color change. This work provides an effective strategy to develop robust, flexible, transparent, and long-lasting H2 sensors through large-area printing processes based on polymer-metal-metal oxide nanostructures.

Off/on Switching of Electric Current as a Strategy for One‐Pot Synthesis of Bromoarylpyridines by Cross‐Coupling/ C−H Bromination

AbstractAn “OFF/ON” electric current switching protocol was developed as a new strategy for one‐pot organic synthesis. Suzuki‐Miyaura coupling of 2‐bromopyridines with arylboronic acids in an electrochemical cell was performed without applying an electric current, and subsequently, the Pd‐catalyzed electrochemical C−H bromination was conducted using the already‐present Pd catalyst to obtain 2‐(2‐bromoaryl)pyridines as products. The one‐pot synthesis of bromoarenes can also be achieved without adding an external Br source in the second step. Furthermore, an OFF/ON/OFF two‐times switching protocol also realized the formation of an N‐containing teraryl derivative.

Cross Couplings of Cinnamates to Benzo‐Fused Oxanorbornadienes

AbstractPotential exo‐specific [3+2] cascade cyclizations between o‐Br‐substituted cinnamates (CM−Br) and benzo‐fused 7‐oxa‐norbornadiene (Bz‐OND) by Pd‐mediated catalysis were explored both in racemic and asymmetric methods. A systematic study on Pd(II) catalysts, silane additives, carbonate bases, solvents, chiral diphosphines within a reaction temperature range of 60–80 °C were carried out. The best combination was between methyl o‐Br‐cinnamate and Bz‐OND catalyzed by Pd(OAc)2/dppf and /DM‐BINAP, respectively, in CH3CN at 80 °C. The desired racemic and optically active Bz‐OND‐fused indanes bearing 1‐carbonylmethylidene (CBM) unit were thus afforded in 95 % and 71 % yields and with enantioselectivities of up to 43 % ee. The optimal asymmetric recipe can be applied to alkyl, aryl cinnamates, 4‐substituted, and 5‐substituted o‐bromo‐cinnamates. Exclusive hydrogenations from the exo‐face of the CBM alkene units can be readily done by Pd(0)/charcoal in EtOAc, affording the product complementary to the direct Rh(I)‐catalyzed cyclization.

Palladium-copper bimetallic surfaces as electrocatalysts for the ethanol oxidation in an alkaline medium

Two types of Cu-modified Pd catalysts supported on high area carbon were prepared: Pd nanoparticles modified with a sub-monolayer of underpotentially deposited Cu (Cu@Pd/C) and Pd-Cu alloy nanoparticles (Pd-Cu/C), and examined for the ethanol oxidation reaction (EOR) in alkaline solution. The catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, as well as cyclic voltammetry. As reference catalysts, Pd/C and Pt/C were used. The electrochemically active surface area of all samples was determined from COads and Cuupd desorption and Pd oxide reduction, and used to assess their intrinsic activity for EOR. Intimate contact of Pd with Cu atoms enhanced its activity, regardless of the type of bimetal catalyst. The atomic Pd:Cu ratio between 2:1 and 4:1 appears to be optimal for high activity. The most active catalyst under the potentiodynamic conditions was Cu@Pd/C with θ(Cu) = 0.21,although Pd-Cu/C was superior during the potentiostatic test. All bimetallic catalysts surpassed Pd/C in mass activity. The EOR activity of Pt/C was higher compared to Pd-based catalysts at low potentials, both in terms of specific and mass activity, but with a significant decline over a 30-min potentiostatic stability test.

Catalytic hydrogenation of Cl-oxyanion pollutants in water

Pt and Pd catalysts supported on alumina have been tested and characterised for the catalytic hydrogenation of chlorates at room temperature and atmospheric pressure. Metallic nanoparticles are the catalytic active species, obtaining better results with the Pt than with the Pd catalysts. It is observed that the activity of the Pt catalysts depends on the metal precursor used for their preparation and the calcination temperature as these factors lead to different platinum dispersion on the alumina surface. The best results were obtained with the catalysts prepared from metal precursors containing Cl atoms and calcined at lower temperatures, as smaller metallic crystallites are formed. The chlorate reduction profiles displayed a pseudo-first order kinetic towards chlorate. The optimised catalyst was tested for the reduction of the different Cl-oxyanions, proving that the reaction rate depends on the chlorine valence of the ion following this order: ClO4- < ClO3- < ClO2-. This is due to the different molecular geometry of the anions that results in different stability of the ClOx-. The optimised catalyst was fully stable in successive uses, being active for the simultaneous reduction of chlorate, chlorite and bromate in water.

Fabrication of highly dispersed Pd-Mn3O4 catalyst for efficient catalytic propane total oxidation

Adjusting the interaction between dual active components for enhancing volatile organic compounds (VOCs) degradation is an effective but still challenging means of air pollution control. Herein, a limited pyrolysis oxidation strategy was adopted to prepare Pd-Mn3O4 spinel catalysts with uniform morphology and active component dispersion. Among these, 1.08Pd-Mn3O4 presented the highest catalytic efficiency with a T90 value of 240 °C, which was 94 °C lower than that of Mn3O4. Characterization and density functional theory (DFT) calculation results revealed that the strong metal-support interaction (SMSI) effect between Pd and Mn3O4 promoted the redistribution of surface charges, thus strengthening the oxidation-reduction ability of the active sites. Moreover, the SMSI effect led to a better migration of surface oxygen species, and boosted the generation of active surface oxygen species. Simultaneously, the Pd catalyst further reduced the energy barrier in the initial stage of the dehydrogenation of propane. Overall, this study provided a novel design strategy for dual active components catalysts with SMSI effect and extended the application of these catalysts in the important field of VOCs elimination.

Highly safe aqueous rechargeable batteries via electrolyte regeneration using Pd–MnO2 catalytic cycle

Long-term operation of aqueous Zn-ion batteries causes Zn metal corrosion at the anode due to the thermodynamic instability of Zn in aqueous electrolytes, leading to significant hydrogen (H2) accumulation, which seriously endangers battery safety. Herein, we propose a self-regulating battery based on internal electrolyte-regeneration mechanisms that control H2 production/annihilation reactions automatically and effectively suppress the pressure increase and electrolyte depletion within the cell. This is accomplished by activating a water-regenerating chemical reaction between MnO2 on the cathode and H2 via a Pd catalyst, which significantly relieves the reaction's endothermicity. By electrochemically charging the cell, the resultant Mn2+ and Zn2+ ions in the electrolyte can be easily reversed to their original chemical states, i.e., MnO2 and Zn metal on the cathode and anode, respectively. This new strategy overcomes the safety challenge posed by H2 accumulation, which is one of the key hurdles to the commercialization of aqueous rechargeable batteries.

Continuous Ligand-Free Catalysis Using a Hybrid Polymer Network Support.

Although the pharmaceutical and fine chemical industries primarily utilize batch homogeneous reactions to carry out chemical transformations, emerging platforms seek to improve existing shortcomings by designing effective heterogeneous catalysis systems in continuous flow reactors. In this work, we present a versatile network-supported palladium (Pd) catalyst using a hybrid polymer of poly(methylvinylether-alt-maleic anhydride) and branched polyethyleneimine for intensified continuous flow synthesis of complex organic compounds via heterogeneous Suzuki-Miyaura cross-coupling and nitroarene hydrogenation reactions. The hydrophilicity of the hybrid polymer network facilitates the reagent mass transfer throughout the bulk of the catalyst particles. Through rapid automated exploration of the continuous and discrete parameters, as well as substrate scope screening, we identified optimal hybrid network-supported Pd catalyst composition and process parameters for Suzuki-Miyaura cross-coupling reactions of aryl bromides with steady-state yields up to 92% with a nominal residence time of 20 min. The developed heterogeneous catalytic system exhibits high activity and mechanical stability with no detectable Pd leaching at reaction temperatures up to 95 °C. Additionally, the versatility of the hybrid network-supported Pd catalyst is demonstrated by successfully performing continuous nitroarene hydrogenation with short residence times (<5 min) at room temperature. Room temperature hydrogenation yields of >99% were achieved in under 2 min nominal residence times with no leaching and catalyst deactivation for more than 20 h continuous time on stream. This catalytic system shows its industrial utility with significantly improved reaction yields of challenging substrates and its utility of environmentally-friendly solvent mixtures, high reusability, scalable and cost-effective synthesis, and multi-reaction successes.

Design of yolk-shell structured PdSn@Pd@HCS nanocatalysts for efficient direct synthesis of H2O2

The direct synthesis of hydrogen peroxide (DSHP) from hydrogen and oxygen is a green synthesis method with a high atomic economy. However, H2O2 selectivity and productivity remain a key challenge, the OO bonds are easily broken with supported Pd catalysts to produce water. Herein, we report the synthesis of bimetallic catalyst PdSn@Pd@HCS by adapting reversed-phase micellar and galvanic replacement reaction. The novel bimetallic yolk-shell structure catalysts exhibit excellent catalytic performance, the selectivity and productivity of H2O2 reaching 98% and 4899 mmol/gPd·h − 1, respectively. Theoretical calculations reveal that the presence of Sn inside the bimetallic alloy can enhance the ligand effect and optimize the electronic structure of the surface Pd atoms, weakening the adsorption ability of O2 molecules and inhibiting the dissociation of OO bonded species, resulting in the enhancement of H2O2 selectivity and productivity. This work provides the groundwork for bimetallic yolk-shell structure catalysts to achieve the efficient synthesis of H2O2.

Effect of a phosphorus modifier on the behavior of palladium catalysts in direct synthesis of hydrogen peroxide

The behavior of palladium-phosphorus catalysts deposited on a Na-ZSM-5 zeolite support, in the direct synthesis of hydrogen peroxide under mild conditions has been studied. It was found that elemental phosphorus exerts a promoting effect on the activity and selectivity of Pd catalysts for synthesizing H2O2. A direct relationship between the P:Pd ratio (in the range P:Pd = 0: 1.0) and the activity of the catalysts is shown. The influence of phosphorus on the properties of palladium catalysts in side reactions: decomposition and hydrogenation of H2O2 is considered. The chemical and phase composition of Pd-P particles was studied by ICP, HRTEM, electron diffraction, and XRD methods. The modifying effect of phosphorus on the properties of Pd catalysts in the direct synthesis of H2O2 is associated with the formation of solid solutions between palladium and phosphorus, an increase in the dispersion, and the surface roughness of Pd-P particles.

Overcrowded Triply Fused Carbo[7]helicene.

This paper presents the synthesis and comprehensive analysis of a highly contorted and doubly negatively curved multihelicene compound, composed of three carbo[7]helicene units fused within a central six-membered ring. The synthesis of this compound involved a [2 + 2 + 2] cycloaddition reaction of 13,14-picyne, employing a Ni(0) catalyst, which exhibited superior performance compared to conventional Pd(0) catalysts. The evaluation of aromaticity in this triple carbo[7]helicene, utilizing magnetic and electronic criteria, led to noteworthy insights challenging the limitations of Clar's model of aromaticity.

Supported Noble Metal Catalysts and Adsorbents with Soft Lewis Acid Functions.

Heterogeneous noble metal catalysts exhibit various functions. Although their redox functions have been extensively studied, we focused on their soft Lewis acid functions. Supported Au, Pt, and Pd catalysts electrophilically attack the π-electrons of soft bases such as alkynes, alkenes, and aromatic compounds to perform addition and substitution reactions. Hydroamination, intramolecular cyclization of alkynyl carboxylic acids, isomerization of allylic esters, vinyl exchange reactions, Wacker oxidation, and oxidative homocoupling of aromatics are introduced based on a discussion of the active species and reaction mechanisms. Furthermore, the adsorption of sulfur compounds, which are soft bases, onto the supported AuNPs is discussed. The adsorption and removal of 1,3-dimethyltrisulfane (DMTS), which is the compound responsible for the stale odor of "hine-ka" in alcoholic beverages, particularly Japanese sake, is described.

Machine Learning-Guided Development of Trialkylphosphine Ni(I) Dimers and Applications in Site-Selective Catalysis.

Owing to the unknown correlation of a metal's ligand and its resulting preferred speciation in terms of oxidation state, geometry, and nuclearity, a rational design of multinuclear catalysts remains challenging. With the goal to accelerate the identification of suitable ligands that form trialkylphosphine-derived dihalogen-bridged Ni(I) dimers, we herein employed an assumption-based machine learning approach. The workflow offers guidance in ligand space for a desired speciation without (or only minimal) prior experimental data points. We experimentally verified the predictions and synthesized numerous novel Ni(I) dimers as well as explored their potential in catalysis. We demonstrate C-I selective arylations of polyhalogenated arenes bearing competing C-Br and C-Cl sites in under 5 min at room temperature using 0.2 mol % of the newly developed dimer, [Ni(I)(μ-Br)PAd2(n-Bu)]2, which is so far unmet with alternative dinuclear or mononuclear Ni or Pd catalysts.