Low Palladium Research Articles

Utilizing Anionic-Pillared Metal-Organic frameworks for low carbon and efficient palladium recovery via constructing a waste-free cycle

The palladium recycling from palladium-containing effluent is crucial with and challenging for the sustainable development of resource recovery, and it has not been investigated by using anion-pillared metal–organic frameworks (APMOFs). Herein, based on the similarity of the anionic pillars (TiF62-/GeF62-/SiF62-) to PdCl42- in size, charge and shape, we demonstrate the porous frameworks Ti-APMOF, Ge-APMOF, and Si-APMOF enriched with exchangeable anionic pillars as the materials for the palladium capture. Ti-APMOF demonstrated the optimal performance, showcasing a palladium recovery capacity of 568.18 mg/g, as well as treating 4180 bed volumes palladium-containing solutions in the fixed-bed experiment after granulation. Moreover, the regeneration solution could be reused to synthesize Ti-APMOF with hardly decrease in performance, realizing the reuse of TiF62- and the Waste-free cycle. Various experiments and characterization results uncovered that the adsorption mechanism was ion-exchange between TiF62- and PdCl42-. The excellent performance of Ti-APMOF is attributed to having more empty orbitals to overlap with the electron-bearing orbitals of PdCl42- and the shape memory effect of the anion pillar was employed to offer selectivity. Additionally, carbon emission and costing analysis suggest that the Ti-APMOF preparation of low carbon emission brings less impact on the environment, and the economic viability of this APMOF-based with an input–output ratio of 170 %. Overall, this work advances a green and viable strategy to recover palladium from spent sources.

Sustainable catalytic hydrogenation of high concentration nitrate to ammonia over Ruthenium-based catalysts

Elevated nitrate levels in natural water bodies significantly disrupt the global nitrogen cycle and pose a substantial environmental and human health risk. This study investigates the selective conversion of nitrate to ammonia via catalytic hydrogenation. This highly efficient and selective process offers a sustainable alternative to traditional ammonia production methods while simultaneously addressing nitrate pollution. Ruthenium (Ru) catalysts supported on ceria (CeO2), titania (TiO2), and tin dioxide (SnO2) were synthesized using a simple impregnation method, incorporating oxygen vacancies and low Palladium (Pd) loadings (0.25–0.5 wt%) to enhance catalytic performance. Ru-Pd/CeO2 exhibited superior activity and selectivity, maintaining near 100 % ammonia selectivity across various nitrate concentrations. At 75 °C, complete conversion of 2000 ppm nitrate to ammonia was achieved within 80 min using Ru-Pd/CeO2, and the yield of ammonia can reach up to 16440 mg•h−1•gRu-1. Subsequent ammonia enrichment through evaporation yielded pure ammonia solutions up to 3.6 wt%. Characterization and theoretical calculations suggest that abundant oxygen vacancies on the CeO2 surface and efficient hydrogen spillover from Pd nanoparticles synergistically contribute to the Ru-Pd/CeO2 catalyst’s superior performance. The catalyst exhibited excellent stability and reusability, maintaining high activity and selectivity over four cycles. This research presents a promising strategy for addressing nitrate pollution in water bodies while offering a sustainable and environmentally friendly route for ammonia synthesis. The findings of this study lay the foundation for further advancing and potentially implementing catalytic hydrogenation technology for nitrate pollution remediation and ammonia synthesis.

Elucidating the Synergistic Promotional Mechanism of Water and Oxygen in the Aerobic C-C Homocoupling Reaction Catalyzed by Visible-Light-Derived Core-Shell Pd@A-CQDs Nanostructures.

Rational design and precise synthesis of biogenic noble-metal-based catalysts possessing distinctive structure and composition play a crucial role in the chemical industry, enabling sustainable construction of an inclusive range of chemical resources. In this study, we have effectively fabricated Pd@A-CQDs through a straightforward one-pot aqueous protocol assisted by visible light employing renewable biomass-derived amine-rich carbon quantum dots (A-CQDs). The remarkable visible light harnessing capability (bandgap, ca. 2.81 eV), high density (35.7 × 1018 cm-3), and long lifetime (25 ps) of photocharge carriers and amine-rich surface in A-CQDs make them ideal candidates as both reducing and stabilizing agents, thereby facilitating the in situ construction of metallic Pd(0) nanoparticles. Comprehensive physicochemical characterizations have provided compelling evidence for the spherical morphology of Pd@A-CQDs core-shell nanostructures, with ultrathin A-CQDs shells of ca. 1.9 nm and an average diameter of 14 ± 1 nm. The effectiveness of the synthesized Pd@A-CQDs catalysts was assessed in the ligand- and base-free homocoupling reaction of arylboronic acids in water at ambient temperature. The catalytic tests demonstrated the selective production of the homocoupled compound over protodeboronation products with excellent yield and high catalyst recyclability under ambient conditions. The protocol employed exhibited a high TOF (1.05 × 10-2 mol g-1 min-1) and a low E-factor, with a remarkably low palladium loading. XPS analysis confirmed the retention of the metallic nature of the palladium core within the catalysts during the reaction. The catalytic function of the palladium core in conjunction with the A-CQDs shell, along with the promotional effects provided by water and oxygen for the formation of nucleophilic tetravalent boron, was conclusively recognized by 11B NMR and O2-TPD measurements. The obtained experimental results deliver valuable insights into the probable reaction pathway for the homocoupling reaction catalyzed by the Pd@A-CQDs catalysts. Through a comprehensive and sustainable evaluation, the current methodology exhibits superior performance compared to previously documented techniques in relation to estimated circularity and adherence to good manufacturing practices (GMP).

Palladium-Catalyzed Trifluoroacetylation of Arylboronic Acids Using a Trifluoroacetylation Reagent.

A new trifluoroacetylation reagent was developed by using inexpensive and readily available trifluoroacetic anhydride and N-phenyl-4-methylbenzenesulfonamide for the first time. The reaction of (het)aryl boronic acids with the new trifluoroacetylation reagent, N-phenyl-N-tosyltrifluoroacetamide, proceeded smoothly in the presence of a palladium catalyst to provide trifluoromethyl ketones in satisfactory to excellent yields. Various groups, including the synthetically useful functional groups Cl, TMS, and PhCO, were tolerated well under the current reaction conditions. This new trifluoroacetylation reagent can be used in the large-scale synthesis of trifluoromethyl ketones, even at a low palladium catalyst loading.

Low palladium content CeO2/ZnO composite for acetone sensor with sub-second response prepared by ultrasonic method

Low palladium content CeO2/ZnO composite for acetone sensor with sub-second response prepared by ultrasonic method

Palladium-Catalyzed Cyanations of Aryl Imidazolylsulfonates with K4[Fe(CN)6]: A Pragmatic Approach to Benzonitriles from Phenols

AbstractA general Pd-catalyzed approach for the conversion of phenols into benzonitriles via aryl imidazolylsulfonates with a non-toxic cyanide source, potassium ferrocyanide, has been developed. Salient features of this method include low palladium precatalyst loadings (as low as 1.0 mol% total Pd), mild reaction conditions, and environmentally benign by-products compared to other (pseudo)halide aryl electrophiles. The initial scope of the reaction on a range of phenolic precursors is demonstrated including a one-pot, two-step approach to convert phenols directly into benzonitriles.

The Influence of Ligands on the Pd-Catalyzed Diarylation of Vinyl Esters.

The impact of ligands on the palladium-catalyzed 1,2-diarylation reaction course is presented. The application of Pd-dmpzc as a catalyst provides an efficient, chemoselective and sustainable protocol for the synthesis of valuable 1,2-diphenylethyl acetates. The reaction is conducted in water under mild conditions. Reaction products can be easily separated from the reaction mixture and catalyst by simple extraction. What is more, the rational choice of catalyst significantly reduces the leaching of the metal into the product and its contamination (0.1 ppm). Efficient phase separation and ultralow Pd leaching enable the reuse of the water medium containing the Pd-dmpzc catalyst several times without a significant loss of activity and with even higher selectivity (from 95% to 100% in the third cycle). The recyclability of both the catalyst and the reaction medium together with high chemoselectivity and low palladium leaching reduces the amount of waste and the cost of the process, exhibiting an example of a sustainable and green methodology.

Nanostructured Pd/Ag/Ni electrocatalysts for the Hydrogen Evolution Reaction

As palladium is the one of the most effective electrocatalyst for the hydrogen evolution reaction, it is crucial the development of new catalysts that require small amounts of palladium to perform, but that are highly active. In this work, the electrochemical characterization of a novel electrode with low palladium content is reported, where Pd nanoparticles are supported on macroporous nickel electrodes that contain silver nanoparticles previously electrodeposited on the surface, which after heat-treatment become rich in corners and edges. The values of η100 (overpotential needed to produce a fixed amount of hydrogen) and jm (indicative of catalytic activity per unit mass of metal nanoparticles) improved (for example, at 80 °C, a η100 of 109.9 mV and a jm of 12587 A·g−1) those of other authors who applied bimetallic AgPd nanoparticles for the HER, showing that the incorporation of nanostructures (Pd over Ag) significantly reduced the energy investment required to produce hydrogen due to synergistic effects between the deposited Pd particles and the electrodeposited silver, enhancing the catalytic activity.

Rapid separation of the low concentration Pd from Pd-Pt coexisting systems: Cyano-group’s monomer-specific affinity

Rapid separation of low concentration palladium (Pd) from Pd-Platinum (Pt) coexisting systems remains a formidable challenge, primarily due to the undifferentiated substitution of ligands in Pd/Pt complexes by adsorption sites. The development of an adsorbent featuring monomer-specific affinity adsorption sites for Pd/Pt could mitigate this drawback. Herein, Manganese hexacyanoferrate (MnHCF) possessing the sensitivity and specificity to Pd ions (Pd(II)) was synthesized via the facile co-precipitation method. MnHCF could rapidly and selectively capture 90.30 % of Pd(II) from a 10 ppm Pd-Pt coexisting system within just 5 min. Spectroscopic analyses and density functional theory (DFT) calculations indicated that cyano-group (CN) in MnHCF exhibited the monomer-specific affinity for targeted capturing Pd via the direct and strong coordination interaction (Fe-CN-PdCl2), which was co-determined by the electron-losing of C (0.06 e) and N (0.07 e) atom. At the same time, CN could neither react directly with the fully coordinated [PtCl6]2− species nor substitute the Cl− ligand, both of which contributed to the non-adsorption of Pt, thus triggering the Pd-Pt separation. This study provides a promising candidate adsorbent for practical applications in platinum group metals recovery by the design of adsorption sites with monomer-specific affinity.

Palladium-Catalyzed Regioselective B(3,5)-Dialkenylation and B(4)-Alkenylation of o-Carboranes.

Picolyl group directed B(3,5)-dialkenylation and B(4)-monoalkenylation of o-carboranes has been developed with a very low palladium catalyst loading. The degree of substitution is determined by the cage C(2)-substituents due to steric reasons. On the basis of experimental results, a plausible mechanism is proposed including electrophilic palladation and alkyne insertion followed by protonation.

Enantioselective C-H Arylation for Axially Chiral Heterobiaryls.

An enantioselective palladium-catalyzed C-H arylation of functionalized pyrazoles/triazoles/imidazoles is developed, affording a variety of axially chiral ortho-nitro/formyl-substituted heterobiaryls with excellent enantioselectivities and good yields. The method features a deuterated P-chiral phosphorus ligand CD3-AntPhos, a broad substrate scope of functionalized heterobiaryls, mild reaction conditions, and low palladium loadings.

Photocatalytic Semi-Hydrogenation of Alkynes: A Game of Kinetics, Selectivity and Critical Timing.

The semi-hydrogenation reaction of alkynes is important in the fine chemicals and pharmaceutical industries, and it is thus important to find catalytic processes that will drive the reaction efficiently and at a low cost. The real challenge is to drive the alkyne-to-alkene reaction while avoiding over-hydrogenation to the saturated alkane moiety. The problem is more difficult when dealing with aromatic substitution at the alkyne center. Simple photocatalysts based on Palladium tend to proceed to the alkane, and stopping at the alkene with good selectivity requires very precise timing with basically no timing tolerance. We report here that the goal of high conversion with high selectivity could be achieved with TiO2-supported copper (Cu@TiO2), although with slower kinetics than for Pd@TiO2. A novel bimetallic catalyst, namely, CuPd@TiO2 (0.8% Cu and 0.05% Pd), with methanol as the hydrogen source could improve the kinetics by 50% with respect to Cu@TiO2, while achieving selectivities over 95% and with exceptional timing tolerance. Further, the low Palladium content minimizes its use, as Palladium is regarded as an element at risk of depletion.

Pyrazine Derivative as Supramolecular Host for Immobilization of Palladium Nanoparticles for Efficient Suzuki Coupling

AbstractPalladium nanoparticles (NPs) have been extensively explored as unique catalyst for carbon‐carbon coupling reactions. Nonetheless, because of extreme tendency of nanoparticles to undergo agglomeration, the immobilization of these metal NPs on organic frameworks is an important area of research. The present investigation demonstrates the synthesis of pyrazine derivative PYZ‐TA as a supramolecular host for holding co‐released Pd NPs derived from the original catalyst (Pd(II)) under standard Suzuki coupling. Unprecedent, physical bars are not required to capture Pd NPs within the pores of supramolecular host. The as obtained catalyst PYZ‐TA@Pd exhibits high potential to undergo self‐assembly in solid as well as in liquid state. The PYZ‐TA@Pd ensemble shows high catalytic activity and recyclability (up to seven cycles) in Suzuki‐Miyaura coupling reactions using low palladium loading and provides the corresponding products in excellent yields (up to 98 %). Therefore, this study provides an efficient strategy to develop an easy to synthesize palladium centered solid catalyst through coordination between organic host and Pd NPs.

Palladium nanoparticles supported on reduced graphene oxide (Pd@rGO): an efficient heterogeneous catalyst for Suzuki–Miyaura, Heck–Matsuda and Double Suzuki–Miyaura cross-coupling reactions

Synthesis of biaryls, terphenyls and cinnamates using a reduced graphene oxide-supported palladium nanoparticle (Pd@rGO)-based nanocatalyst with low palladium loadings.

Modular One‐Step Three‐Component Assembly of Isochromans via Palladium/Norbornene Cooperative Catalysis

AbstractWe herein report a modular one‐step three‐component protocol for the assembly of isochromans, which involved a Catellani/oxa‐Michael addition cascade. This approach features readily available starting materials, mild reaction conditions, low palladium catalyst loading, good scalability as well as high step‐ and atom‐economy.

Electromagnetic Mill Promoted Mechanochemical Solvent-Free Palladium-Catalyzed Borylation of Aryl Bromides.

The electromagnetic mill (EMM) promoted mechanochemical solvent-free palladium-catalyzed borylation of aryl bromides using low palladium catalyst loading (0.05-0.5 mol %) was realized. This protocol exhibits many advantages, such as broad substrate scope, good functional group tolerance, short reaction times, no additional heating, and practical gram-scale synthesis. This EMM system not only showed excellent prospects for industrial application but also unlocked broad areas of solvent-free solid-state metal-catalyzed syntheses.

Recoverable low fluorine content palladium complex-catalyzed Suzuki-Miyaura and Sonogashira coupling reactions under thermomorphic mode

The reaction of [PdCl2(CH3CN)2] and bis-5,5'-(RfCH2OCH2)-2,2′-bpy (1), where Rf = n-C4F8H, in the presence of dichloromethane (CH2Cl2) resulted in the synthesis of low fluorine content Pd complex, [PdCl2 [5,5′-bis-(RfCH2OCH2)-2,2′-bpy] (2). The Pd-catalyzed Suzuki-Miyaura and Sonogashira coupling reactions of several aryl halides with their respective reagents were selected to demonstrate the feasibility of catalytic activity and recycling usage with 2 as the catalyst by using dibutyl ether (DBE) as the solvent at 140–145 °C under the thermomorphic mode. The Pd complex 2-catalyzed Suzuki-Miyaura reactions of different aryl iodides with phenylboronic acid derivatives have showed good recycling results though its activity was observed to decrease after the fifth cycle. Similarly, 2-catalyzed Sonogashira reactions of several aryl iodides with phenyl acetylene have also displayed good recycling results for a total of up to 8 cycles, with a high yield and TON. The electronic effect studies from substituents in both Suzuki-Miyaura and Sonogashira coupling reactions showed that electron withdrawing groups on the aryl iodide speed up the reaction rate. Furthermore, the catalytic activity of the Pd complex (2) showed a better result with the more reactive aryl iodide compared to the less reactive aryl bromide and chloride. To our knowledge, this is the first example of recoverable low fluorine content Pd-catalyzed Suzuki-Miyaura and Sonogashira reactions under the thermomorphic mode.

Recovery of palladium from a low grade palladium solution by anionic-ion exchange: kinetics, equilibrium, and metal competition.

Petroleum spent catalysts may contain a significant amount of palladium (Pd) together with other major [aluminum (Al), nickel (Ni), and molybdenum (Mo)] and minor [iron (Fe), lead (Pb), and vanadium (V)] elements. Due to the high intrinsic value of Pd and its scarcity in natural ores, its recovery is highly desired. For this purpose, the ability of a strong basic anionic- resin, Purogold™ A194 resin, to remove Pd from the solution was assessed. Data from kinetic and equilibrium studies, performed under batch mode in 1 mol/L of NaCl and 1 mol/L of HNO3 at (21 ± 1) °C, revealed that the removal of Pd fits well a pseudo-second-order kinetic model [constant rate value, k2, of (0.062 ± 0.010) g/(mmol.min)] and a Langmuir isotherm [maximum sorption capacity of (0.80 ± 0.02) mmol/g with an affinity of resin binding sites towards Pd, KL, of (0.18 ± 0.02) L/mmol], respectively. The sorption of other metals (Al, Fe, Pb, Mo, Ni, and V) that may be present in spent catalyst leachates was tested under similar experimental conditions [CM = 2.5 mmol/L, 1 mol/L of NaCl and 1 mol/L of HNO3 at (21 ± 1) °C)] and the resin showed little affinity towards each one of these metals. Also, simultaneous multi-element batch experiments with Pd and the major components (M = Al, Ni, and Mo ions) ([M]/[Pd] molar ratios between 3.4 and 52 were used) pointed out that the resin is highly selective towards Pd suggesting that the resin can be used in the selective recovery of Pd from petroleum spent catalyst leachates.

Supported palladium-catalyzed carbonylative cyclization of 2-bromonitrobenzenes and alkynes to access quinolin-4(1H)-ones

A palladium supported on graphitic carbon nitride (Pd/g-C3N4) catalyzed carbonylative cyclization of 2-bromonitrobenzenes and alkynes has been developed for the expedite construction of quinolin-4(1H)-one scaffolds. By using a low loading heterogeneous palladium catalyst, Mo(CO)6 as both the CO surrogate and the reductant, and nitroarenes as the nitrogen source, the reaction proceeded well to give a variety of quinolin-4(1H)-ones in good to excellent yields.

Recoverable Low Fluorine Content Palladium Complex-Catalyzed Suzuki-Miyaura and Sonogashira Coupling Reactions Under Thermomorphic Mode

Recoverable Low Fluorine Content Palladium Complex-Catalyzed Suzuki-Miyaura and Sonogashira Coupling Reactions Under Thermomorphic Mode