Pd Catalysts Research Articles

Flexible α‐Diimine Ni(II) and Pd(II) Catalysts Featuring Backbone and Axial Cycloalkyl Substituents in Ethylene (Co)polymerization

ABSTRACTRecently, axial flexible substituents have found widespread application in ethylene (co)polymerization catalyzed by late transition metals, yielding impressive results. In this research, we designed and synthesized a novel class of flexible α‐diimine Ni(II) and Pd(II) catalysts, distinguished by their flexible backbones and axial substituents that both incorporate cycloalkyl moieties. During nickel‐catalyzed ethylene polymerization, these flexible nickel catalysts demonstrated high activity (well above 106 g/(mol Ni·h)) and thermal stability, producing polyethylenes with very high molecular weights (up to 1022 kg/mol) and branching densities (up to 103/1000C). Interestingly, the catalyst reported in this study exhibits higher activity compared to nickel catalysts with classic and rigid backbones. The resultant polyethylene materials exhibited outstanding mechanical properties and elastic recovery (with a strain recovery (SR) of up to 79%), qualifying them as high‐performance thermoplastic elastomers. In contrast, during palladium‐catalyzed ethylene polymerization, these flexible palladium catalysts showed moderate activity (level of 105 g/(mol Pd·h)) and generated polyethylenes with high branching densities (up to 99/1000C) and molecular weights (up to 203 kg/mol). In the case of palladium‐catalyzed copolymerization of ethylene with methyl acrylate (MA), the copolymerization activity was notably reduced compared to homopolymerization, resulting in E‐MA copolymers with lower molecular weights and higher branching densities. However, under the experimental copolymerization conditions, we successfully obtained copolymers with significant incorporation (1.53–4.54 mol%) of MA. It is worth noting that the cyclohexyl group displayed superior chain transfer inhibition in both nickel and palladium systems compared to the cyclopentyl group. Nevertheless, a notable difference was observed in their influence on branching density regulation: in the nickel system, the cyclohexyl group facilitated the formation of polyethylenes with higher branching, while in the palladium system, it had the opposite effect when compared to the cyclopentyl group.

Pd catalysts supported on γ-Al2O3 immobilized with ionic liquids: an efficient and recyclable system for C‒C bond formation

Pd catalysts supported on γ-Al2O3 immobilized with ionic liquids: an efficient and recyclable system for C‒C bond formation

Recent Advance in the Reductive Heck Cyclization for the Formation of Five to Nine Member Rings

Palladium-catalyzed reactions are widely used for creating carbon-carbon and carbon- heteroatom bonds, with the Heck reaction being particularly valuable for forming rings of various sizes, including medium-sized rings. Recent reports have shown the synthetic potential of intramolecular Heck reactions for assembling rings of seven or more members. While the regioselectivity of this cyclization is often unpredictable in the absence of directing groups, the reductive Heck cyclization strategy can help minimize this issue. Nickel catalysts are also valuable due to their abundance and environmentally friendly nature, playing a pivotal role in producing biologically significant carbocycles and heterocycles. The use of both Pd(0) and Ni(0) catalysts, with or without chiral ligands, has been successful in forming five to ninemember ring heterocycles and carbocycles in a simple, cost-effective manner. This review provides a comprehensive survey of the literature from the past decade on the use of reductive Heck cyclization methodology, including mechanistic details as needed.

Improving electrocatalytic formic acid oxidation performance via catalyst layer design utilizing porous boron nitride-supported Pd catalysts

Improving electrocatalytic formic acid oxidation performance via catalyst layer design utilizing porous boron nitride-supported Pd catalysts

Development of magnetically retrievable nanostructure Pd catalyst system supported on keratin-Schiff base and its application in catalytic and antioxidant activities

Development of magnetically retrievable nanostructure Pd catalyst system supported on keratin-Schiff base and its application in catalytic and antioxidant activities

Mechanistic Insights into the Aerobic Oxidation of 2,5-Bis(hydroxymethyl)furfural to 2,5-Furandicarboxylic Acid on Pd Catalysts.

2,5-Furandicarboxylic acid (FDCA) is one of the top selected value-added chemicals, which can be obtained by the aerobic oxidation of 2,5-bis(hydroxymethyl)furfural (BHMF) over a Pd-based catalyst. However, the elucidation of the reaction mechanism was hindered by its rapid kinetics. Herein, employing the density functional theory (DFT) calculations, we delve into the detailed reaction pathways of the BHMF oxidation into FDCA over Pd(111) and PdHx(111) identifying the rate-determining steps. The results demonstrated that 2,5-diformylfuran (DFF) and 5-formyl-2-furancarboxylic acid (FFCA) are the important intermediates, while the oxidation of FFCA is the rate-limiting step with the energy barrier of 0.68 and 0.51 eV on Pd(111) and PdH1/4(111), respectively. By comparison of the d-band center of Pd(111) and PdHx(111) surfaces and the overall energy barrier of this reaction over these two surfaces, it makes clear that the occupation of H atoms in the Pd bulk changes the surface electronic structures and enhances the binding energy of BHMF with the PdHx surface, which consequently speeds up the conversion of BHMF into FDCA. Water plays a crucial role in facilitating the activation of O2 via the H-transfer by constructing a hydrogen-bonding chain with the O2 and OH*. The activation of molecular oxygen experiences enhancement through the synergy of OH* and H2O, resulting in the production of actomic oxygen (O*). Both O* and OH* actively participate in the BHMF oxidation, where O* improved the activation toward initial critical reaction pathways on Pd(111) while OH* exhibited its pronounced impact on the latter two key processes on both Pd(111) and PdH1/4(111). This study will contribute to well understanding the oxidation mechanism of BHMF into FDCA over Pd-based catalysts and establish a theoretical framework for the potential development of an effective catalyst.

Tailoring Metal–Oxide Interfaces via Selectively CeO2-Decorated Pd Nanocatalysts with Enhanced Catalytic Performance

Metal–oxide interfaces play a prominent role in heterogeneous catalysis. Tailoring the metal–oxide interfaces effectively enhance the catalytic activities and thermal stability of noble metal catalysts. In this work, polyvinyl alcohol-protected reduction and L-arginine induction methods are adopted to prepare Pd catalysts (Pd/Al2O3-xCeO2) that are selectively decorated by CeO2, which form core–shell-like structures and generate more Pd-CeO2 interfacial sites, so that the three-way catalytic activity of Pd/Al2O3-xCeO2 catalysts is obviously significantly enhanced due to more adsorption oxygen at the interface of Pd-CeO2 and good low-temperature reducibility. At the moment, the Pd/Al2O3-xCeO2 catalysts exhibit excellent thermal stability after being calcined at 900 °C for 5 h, owing to the Pd species being highly redispersed on CeO2 and part of the Pd species being incorporated into the lattice of CeO2. This is a major reason for the Pd/Al2O3-xCeO2 catalysts to maintain high catalytic activity after aging at high temperatures. It is concluded that the metal–oxide interfaces and the interaction between Pd NPs and CeO2 are responsible for the excellent catalytic performance and stability of Pd/Al2O3-xCeO2 catalysts in three-way reactions.

Synthesis of Telechelic Isotactic Polypropylenes for Circular Polypropylene-like Materials via Chain Transfer Polymerization.

While synthesizing circular polymers with telechelic polyolefin building blocks recently emerged as a promising strategy for addressing conventional polyethylenes' sustainability challenges, the lack of telechelic iPP (tPP) with sufficient difunctional purity for polycondensation has been limiting the development of circular polypropylenes with iPP-like structures and properties. Here we described a combined approach of coordinative chain transfer polymerization and transition-metal-catalyzed quenching reaction with various acyl chlorides, affording tPPs with a high difunctional ratio (up to ∼99%) and broad end functional group scope. The steric effect of polymeryl-Zn species and the role of Pd catalyst were revealed by DFT. This method also solved the low difunctional ratio challenge for telechelic polyethylenes. Ester-linked iPPs with iPP-like structure and thermomechanical properties and PE/iPP multiblock copolymers were synthesized by the resulting tPPs.

Virucidal and Bactericidal Properties of Biocompatible Copper Textiles

AbstractThe COVID‐19 pandemic highlights the global threat posed by emerging viruses, emphasizing the critical need for effective strategies to combat pathogen transmission. Moreover, alongside emerging viruses, the increasing threat of antimicrobial resistance further reinforces the need to develop novel methods for infection control. Anti‐pathogenic coatings on textiles offer a promising solution; in this study, three electroless copper‐plated fabrics are evaluated for their antipathogenic properties following International Standards Organisation (ISO) standards. Prior to electroless plating, materials are activated either by immersion in a Pd catalyst solution (material A) or by ink‐jet printing Cu/Ag catalyst along the weft (material B) or warp thread (material C). This study demonstrates that activation method influences the materials antipathogenic performance, with all materials achieving complete bactericidal/fungicidal neutralization within 30 min of incubation. Material B exhibits up to 4‐log virucidal effects within 1 h against viruses such as coronavirus (OC43, 229E), Influenza A (H1N1), and Rotavirus A. Furthermore, biocompatibility testing indicates that material B exhibited low in vitro cytotoxicity. Textile B demonstrates strong antibacterial results even after one year of accelerated aging with no significant difference (P = 0.74) in efficiency against MRSA, highlighting promising applications for infection control in clinical settings reducing pathogen transmission, nosocomial infections and the associated economic burden.

Steering the Absorption Configuration of Intermediates over Pd-Based Electrocatalysts toward Efficient and Stable CO2 Reduction.

Palladium (Pd) catalysts are promising for electrochemical reduction of CO2 to CO but often can be deactivated by poisoning owing to the strong affinity of *CO on Pd sites. Theoretical investigations reveal that different configurations of *CO endow specific adsorption energies, thereby dictating the final performances. Here, a regulatory strategy toward *CO absorption configurations is proposed to alleviate CO poisoning by simultaneously incorporating Cu and Zn atoms into ultrathin Pd nanosheets (NSs). As-prepared PdCuZn NSs can catalyze CO production at a wide potential window (-0.28 to -0.78 V vs RHE) and achieve a maximum FECO of 96% at -0.35 V. Impressively, it exhibits stable CO production of 100 h under ∼95% FECO with no decay. Combined results from X-ray analysis, in situ spectroscopy, and theoretical simulations suggest that the codoping strategy not only optimizes the electronic structure of Pd but also weakens the binding strengths of *CO and increases the proportion of weak-binding linear *CO absorption configuration on catalysts' surfaces. Such targeted adoption of weakly bound configurations abates the energy barrier of *CO desorption and facilitates CO production. This work confers a useful design tactic toward Pd-based electrocatalysts, codoping for steering adsorption configuration to achieve highly selective and stable CO2-to-CO conversion.

Tuning metal-support interactions in MOF-derived CoNi@NC supported Pd catalysts for efficient hydrogenation of bicarbonate using glycerol as a hydrogen donor.

The hydrogenation of bicarbonate, a byproduct of CO2 captured in alkaline solutions, into formic acid (FA) using glycerol (GLY) as a hydrogen source offers a promising carbon-negative strategy for reducing CO2 emissions. While Pd-based catalysts are effective in this reaction, they often require high temperatures, leading to low FA yield due to strong hydrogen adsorption on Pd surfaces. In this work, metal-organic framework derived N-doped carbon encapsulated CoNi alloy nanoparticles (CoNi@NC) were prepared, acid-leached, and employed as a support to modulate the electronic structure of Pd-based catalysts. The electron transfer driven by the Mott-Schottky effect increases the electron density of Pd, lowers its d-band center, and thereby weakens hydrogen adsorption on Pd. Consequently, Pd/CoNi@NC achieved a full conversion of GLY with 87.2% yield of lactic acid and 57.3% yield of FA, outperforming Pd/NC and Pd/C. Additionally, Pd/CoNi@NC demonstrated high catalytic stability and was magnetically separable for ease of use.

Lignin-Based Nanoparticles Stabilized Pickering Emulsion for Enhanced Catalytic Hydrogenation.

The development of green and easily regulated amphiphilic particles is crucial for advancing Pickering emulsion catalysis. In this study, lignin particles modified via sulfobutylation were employed as solid emulsifiers to support Pd nanoparticles (NPs), thereby enhancing the catalytic efficiency of biphasic reactions. Sulfobutylation of lignin effectively adjusted the hydrophilic-hydrophobic balance, resulting in controlled emulsion types and droplet sizes. Pd NPs were loaded onto lignin with a 50% sulfobutylation ratio through the in situ reduction of active functional groups, further stabilized by the cross-linked network structure of lignin. In the hydrogenation of nitrobenzene, the Lig-50S-0.6Pd catalyst exhibited superior activity compared to traditional Pd/C catalysts, which is attributed to the high retention of active sites and increased interfacial area. This work underscores the potential for designing lignin-based amphiphilic particles and developing Pickering emulsion-enhanced reactions.

Controlling Catalyst Speciation to Achieve Room Temperature Pd‐Catalyzed Aminations with Aryl and Heteroaryl Chlorides

The amination of aryl halides with palladium catalysts (Buchwald‐Hartwig amination) is a widely used transformation in synthetic and drug discovery chemistry. In this report, we demonstrate that a monometallic 2‐phosphinoimidazole Pd catalyst exhibits comparable or enhanced reactivity when compared to all ligands screened for room temperature amination of aryl chlorides with secondary amines. The di‐tert‐butylphosphine derivative showed extremely high reactivity while the di‐isopropyl variant led to almost complete loss of catalytic activity. Computational and experimental mechanistic and kinetic studies indicate that a monometallic Pd structure rather than a bimetallic Pd structure is key to fast catalysis. The di‐tert‐butylphosphine ligand has fast catalysis because it thermodynamically disfavors the formation of a much less active bimetallic Pd complex. A wide substrate scope is demonstrated for the arylation of secondary amines with aryl chlorides using our new catalyst system.

Rapid and Sustainable Electrochemical Pd Catalyst Generation from Bulk Metal.

Palladium catalysts form a cornerstone of modern chemistry with upmost scientific and industrial impact. Bulk palladium metal itself is chemically inert, and a sequence of chemical transformations has to be utilized to convert the metal into Pd pre-catalyst covered by ligands. However, the "cocktail" of catalysis concept discovered recently has shown that Pd systems can efficiently operate in catalysis without the necessity of a complicated and expensive pre-installed ligand environment. Here, we point out on a green and sustainable process for Pd active species generation without the need of waste-abundant pre-catalyst-related chemistry. In this work, an electric current was used to generate an active Pd catalyst from a bulk metal in an ionic liquid medium for the efficient cross-coupling of aryl iodides/bromides and boronic acids. Synthetically important Suzuki cross-coupling was utilized as a representative test reaction to confirm the idea. It should be emphasized that electric current is used only at the Pd dissolution stage. Afterwards, the electrodes are removed from the reaction mixture and a standard reaction procedure can be followed. The reported catalyst preparation process via electrochemical dissolution is potentially compatible with a number of already existing catalytic methods.

Enhanced Electrochemical CO2 Reduction Using Nonthermal Plasma: Insights into Pd Catalyst Reactivation and Precise Control of H2O2 for Improved CO2 Reduction Reaction Activity

This study investigates the electrochemical reduction of CO2 on Pd/C with in situ‐generated H2O2 through low‐temperature nonthermal plasma. Catalyst deactivation, a common challenge in CO2 conversion, is addressed by leveraging the oxidizing environment created by H2O2. Experimental studies using linear sweep voltammetry and cyclic voltammetry demonstrate significantly improved CO2 reduction activity during plasma discharge, correlated with an enlarged hydrogen desorption peak. Multicomponent physics‐based computational simulation highlights the role of H2O2, a long‐lived species, in enhancing CO2 reduction. Formic acid is identified as a major liquid product, validated by nuclear magnetic resonance. The presence of H2O2 prevents CO poisoning on Pd surfaces, and H2O2 electroreduction alters hydrogen sorption, potentially creating an active PdHx phase for effective CO2 reduction. The study demonstrates the precise control of H2O2 concentration through nonthermal plasma, offering insights into Pd catalyst reactivation and improved CO2 reduction activity. These findings contribute to the understanding of electrochemical CO2 reduction mechanisms and provide a basis for optimizing catalytic processes in the presence of H2O2.

Interrupting Associative π-σ-π Isomerization Enables Z-Retentive Asymmetric Tsuji-Trost Reaction.

The asymmetric Tsuji-Trost reaction has been extensively studied due to its importance in establishing stereogenic centers, often adjacent to an E-olefin moiety in organic molecules. The generally preferential formation of chiral E-olefin products is believed to result from the thermodynamically more stable syn-π-allylpalladium intermediate. The rapid associative π-σ-π isomerization makes it challenging to synthesize chiral Z-olefin products via the transient anti-π-allylpalladium intermediate. Herein, we report a strategy for regulating associative π-σ-π isomerization by tuning the steric bulkiness of the ligands, allylic leaving groups, and counteranions. The utilization of a Pd catalyst derived from chiral phosphoramidite ligands interrupts the associative π-σ-π isomerization, enabling a highly efficient Z-retentive asymmetric Tsuji-Trost reaction toward an array of α-amino acid derivatives bearing a Z-olefin motif in high yields (up to 95%) and excellent stereoselectivity (up to 99% ee and >19:1 Z/E) with low catalyst loading (0.1 mol %). The mechanistic insights and the design strategy reported in this work pave the way for rational developments of Z-retentive asymmetric Tsuji-Trost-type reactions.

MIL-53(Al)-derived bimetallic Pd–Co catalysts for the selective hydrogenation of 1,3-butadiene at low temperature

Selective hydrogenation of 1,3-butadiene is a crucial industrial process for the removing of 1,3-butadiene, a byproduct of butene production. Developing catalysts with high catalytic performance for the hydrogenation of 1,3-butadiene at low temperatures has become a research hotspot. In this study, bimetallic Pd–Co catalysts supported on Al2O3 derived from MIL-53(Al) at various calcination temperatures were synthesised via the co-impregnation method. These catalysts were structurally characterised using powder X-ray diffraction, thermogravimetric analysis, N2 adsorption–desorption, X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and inductively coupled plasma optical emission spectroscopy techniques. The characterisations revealed that Pd–Co nanoparticles, averaging 8.5–12.4 nm, were highly dispersed on Al2O3 derived from MIL-53(Al). The effects of reaction temperature, Pd and Co contents, space velocity, and calcination temperature on the catalytic performance for the hydrogenation of 1,3-butadiene were thoroughly investigated. The PdCo/MIL-53(Al)-A700 catalyst exhibited the highest catalytic activity for the hydrogenation of 1,3-butadiene at 40 °C and a space velocity of 900 L/(h·gcat). This catalyst demonstrated a strong synergistic interaction between Pd and Co nanoparticles, resulting in considerably better catalytic performance than the monometallic Pd catalyst under the same conditions. The PdCo/MIL-53(Al)-A700 catalyst achieved superior 1,3-butadiene conversion and total butene selectivity compared to the Pd/MIL-53(Al)-A700 catalyst. In addition, the PdCo/MIL-53(Al)-A700 catalyst maintained its catalytic activity and total butene selectivity after three regenerations in a flow of N2 at 200 °C. This work proposed a new pathway to design efficient and sustainable catalysts for 1,3-butadiene hydrogenation.

Heterogeneously catalyzed lignin depolymerisation in continuous flow: Assessing feedstock pretreatment and catalyst deactivation

Due to the large-scale production of lignin, continuous flow reactors are preferred for its further valorization through depolymerization. However, there is limited literature on their use in lignin depolymerization, especially concerning feedstock pretreatments and catalyst deactivation. Therefore, in this study, the impact of a batch solvolysis pretreatment on the mild reductive catalytic depolymerization of Soda lignin, with and without a Pd catalyst, is evaluated and catalyst deactivation is systematically assessed. The Pd catalyst substantially enhances Mw reductions, e.g., without feedstock pretreatment, it increases the Mw reduction from approximately 70 % to 90 % at low time-on-streams (T.O.S.). It also yields products with more functionalities from the untreated feedstock, i.e., at low T.O.S., the phenolic and aliphatic OH content increases from 4.21 to 4.89 mmol/g and 2.30 to 3.72 mmol/g, respectively. The differences are less pronounced with the pretreated feedstock due to condensation of the lignin structure. Furthermore, the high space–time that can be achieved at a short residence time negates the need for a pretreatment. Regarding deactivation, no significant Pd leaching or poisoning by S or Na was observed. The Pd nanoparticles grew from about 8 nm to 20 nm (pretreated feed) and 17 nm (untreated feed), which is likely due to the phase change from PdO to metallic Pd rather than deactivation through sintering. The support material changed from γ-Al2O3 to boehmite, leading to the loss of acid sites and morphological changes. While some indications for small amounts of coke deposits were observed, they could not be differentiated from interstitial water within the boehmite structure. Thus, the main cause for deactivation of the Pd catalyst was identified to be the hydrothermal instability of the alumina support.

Pd catalysts doped with B/C atoms in the subsurface: the positive effect of interstitial atoms in regulating the selectivity of acetylene catalytic hydrogenation.

At present, the modification of palladium (Pd) catalysts is an important topic due to its potential to enhance catalytic performance and reduce catalyst costs. In this work, boron (B) and carbon (C) are interstitially doped into the subsurface of Pd to construct Pd4LB2L and Pd4LC2L catalysts. The adsorption properties of acetylene and ethylene, the mechanism of acetylene hydrogenation, and ethylene selectivity are studied based on density functional theory (DFT) calculations. The results show that the ethylene selectivity of the Pd4LB2L catalyst is significantly enhanced compared with that of Pd(111). The adsorption of CH2CH2 is weakened substantially after B element doping, and the ethylene selectivity descriptor (Esel) value of the Pd4LB2L catalyst reaches 19.7 kJ mol-1. It is revealed that non-metallic atoms doped into the subsurface layer of metal catalysts change the adsorption of reactant/intermediate molecules and the selectivity of ethylene by affecting the electronic structure and properties of Pd atoms in the surface layer. This work provides insights into the selectivity of modified Pd-based catalysts for selective hydrogenation of acetylene and realization of cost-effective catalysts.

Anti-poisoning of CO and carbonyl species over Pd catalysts during the electrooxidation of ethylene glycol to glycolic acid at elevated current density

Incorporating Ni and Mo significantly boosts Pd-based catalysts' activity and durability in ethylene glycol electrochemical oxidation to glycolic acid, especially by enhancing CO poisoning resistance.