Pd Catalysts Research Articles

Catalytic performance of a single atom Pd1Ag10/Al2O3 catalyst for the selective hydrogenation of acetylene: The role of CO-induced segregation

The single-atom Pd catalysts based on silver-rich bimetallic compositions are known for their extremely high ethylene selectivity in the acetylene hydrogenation reaction; however, their activity is noticeably lower than that of traditional monometallic Pd catalysts. The aim of the work was to apply a method of CO-induced segregation to increase the concentration of single atom Pd1 sites on the surface of Pd1Ag10/Al2O3 catalyst without noticeable formation of multiatomic Pdn (n ≥ 2) ensembles. It has been experimentally established by DRIFTS-CO and XPS methods that the effect of 30 vol% CO exposure temperature on the increase of surface Pd1 sites concentration in the range of 50 to 350 °C has a volcano-like dependence with a maximum at ∼ 200–250 °C. The catalytic tests show a considerable enhancement in activity for samples treated in CO at 200–250 °C (the temperature of 100 % acetylene conversion is reduced by ∼ 30 °C), while the C2H4 selectivity was similar for both freshly reduced and CO-treated catalysts. These results demonstrate the use of CO-induced segregation as a promising method for the controlled increase in the concentration of isolated Pd1 sites to improve the activity of silver-rich palladium catalyst without compromising its selectivity.

Mg Electrodes Coiled with Cu Wires Promoted Formation of Diphenylacetylene from Tetrachloroethylene and Bromobenzene: One-step Electrochemical Synthesis without Pd Catalyst

Mg Electrodes Coiled with Cu Wires Promoted Formation of Diphenylacetylene from Tetrachloroethylene and Bromobenzene: One-step Electrochemical Synthesis without Pd Catalyst

On the Design of the Metal-Support Interface in Methanol Electrocatalytic Oxidation.

In this work, we present a theoretical investigation of the SrTiO3 perovskite-supported Pd catalyst in the methanol electro-oxidation reaction. In order to determine the metal-support interactions, we designed a system consisting of a Pd (100) double layer supported on one of the two possible terminations of the (100) perovskite surface. These terminations are characterized by different reducibilities of the layers directly interacting with the Pd bilayer and result in the difference in the stability of the surface-bound intermediates. Despite the fact that the Pd surface is identical in terms of geometry, we observed significant differences in the overpotential required for the reaction; in the case of TiO2 termination, the overpotential has been determined to be 0.68 V, while in the case of SrO termination, it amounts to as much as 1.35 V. We further investigate the charge transfers within the components of the system and the geometries of the intermediates to unravel the role of the electron structure on the overall efficiency of the process.

Helical Star-Shaped Bottlebrush Polymers: From Controlled Synthesis to Tunable Photoluminescence and Circularly Polarized Luminescence.

The controlled synthesis of star-shaped bottlebrush polymers with tunable topologies is a challenge. However, such materials may exhibit distinct photoluminescence properties. Bottlebrush polymers have polymerization-induced emission (PIE) properties due to their aggregated side chains, and aggregation-induced emission (AIE) is also a unique luminescent property. In this work, we prepared a variety of highly active alkyne Pd catalysts and polymerized poly(L/D-lactic acid) macromonomers containing polymerizable phenylisocyanide groups as end groups to obtain a variety of topologically structured bottlebrush polymers with controllable molecular weights and narrow molecular weight distributions. Bottlebrush polymers with tetraphenyl ethylene (TPE) units as the core exhibit tunable photoluminescence and circularly polarized luminescence properties. We propose that such properties are due to the unique AIE characteristics of the TPE unit combined with the PIE characteristics of the bottlebrush polymer.

A strong metal-support interaction strategy for enhanced proton-coupled electron transfer and promoted photocatalytic H2O2 production in pure water

Proton-coupled electron transfer (PCET) is a key factor in determining the H2O2 production efficiency from oxygen reduction reaction (ORR) or direct H2/O2 reaction, which usually requires the aid of proton donors including alcohols. Here, we report a strong metal-support interaction (SMSI) strategy to facilitate the PCET process of a typical Pd/TiO2 photocatalyst for photocatalytic ORR into H2O2 production in pure water. Compared to conventional Pd/TiO2 photocatalysts, the Pd/TiO2 photocatalyst with SMSI between Pd and TiO2 (Pd/TiO2-850H) promotes photocatalytic H2O2 production in pure water by 4.21-fold, which can be ascribed to that the SMSI simultaneously promotes the H2O dissociation and the photogenerated charge transfer from TiO2 to Pd catalyst, enabling highly efficient proton transfer to be participated into converting •O2- to H2O2. Moreover, the formation of TiO2-x overlayer caused by SMSI suppresses the H2O2 decomposition and stabilizes Pd NPs, finally achieving an H2O2 production rate of 4.10 mmol g−1 h−1, which surpasses most metal/TiO2 photocatalytic system.

Synergistic Homogeneous Asymmetric Cu Catalysis with Pd Nanoparticle Catalysis in Stereoselective Coupling of Alkynes with Aldimine Esters.

Understanding the nature of a transition-metal-catalyzed process, including catalyst evolution and the real active species, is rather challenging yet of great importance for the rational design and development of novel catalysts, and this is even more difficult for a bimetallic catalytic system. Pd(0)/carboxylic acid combined system-catalyzed allylic alkylation reaction of alkynes has been used as an atom-economical protocol for the synthesis of allylic products. However, the asymmetric version of this reaction is still rather limited, and the in-depth understanding of the nature of active Pd species is still elusive. Herein we report an enantioselective coupling between readily available aldimine esters and alkynes using a synergistic Cu/Pd catalyst system, affording a diverse set of α-quaternary allyl amino ester derivatives in good yields with excellent enantioselectivities. Mechanistic studies indicated that it is most likely a synergistic asymmetric molecular Cu catalysis with Pd nanoparticle catalysis. The Pd catalyst precursor is transformed to soluble Pd nanoparticles in situ, which are responsible for activating the alkyne to an electrophilic allylic Pd intermediate, while the chiral Cu complex of the aldimine ester enolate provides chiral induction and works in synergy with the Pd nanoparticles.

Boosting γ-valerolactone production from ethyl levulinate hydrogenation over Pd catalyst via alloying with Co and synergistic catalysis with HZSM-5

Boosting γ-valerolactone production from ethyl levulinate hydrogenation over Pd catalyst via alloying with Co and synergistic catalysis with HZSM-5

Bornylimidazo[1,5‑a]pyridin-3-ylidene allylic Pd catalyst with optimal electronic and steric properties for synthesis of 3,3’-disubstituted oxindoles

Bornylimidazo[1,5‑a]pyridin-3-ylidene allylic Pd catalyst with optimal electronic and steric properties for synthesis of 3,3’-disubstituted oxindoles

In situ synthesis and deposition of palladium nanoparticles on gas diffusion layers via gamma radiolysis for cathode electrodes in proton exchange membrane fuel cells

This study investigates gamma radiolysis technique for synthesising and depositing palladium (Pd) nanoparticles on gas diffusion layers (GDLs). The Pd-coated GDLs were then used to fabricate MEAs, which were evaluated for their single-cell performance. The fabricated PEMFCs with Pd-loaded GDLs successfully generated potential and produced electricity, with the PEMFC with a Pd-loaded GDL prepared using a 0.05 M Pd precursor solution and 50 KGy dose achieved performances comparable to the PEMFC with commercial gas diffusion electrodes (GDEs). This study represents the first demonstration of a functional PEMFC using a novel gamma radiolysis-synthesised Pd catalyst GDL as the cathode electrode.

Optimal design of PdAu/In2O3 catalysts for CO2 hydrogenation

Efficient catalyst design has garnered significant interest in recent decades due to its potential to address both the challenges of the greenhouse effect and energy shortages by facilitating the conversion of CO2 into valuable chemicals through catalytic reactions. To investigate maximizing the synergistic effects of supported PdAu catalysts, we conducted first-principles calculations on the activation and decomposition of CO2 and H2 on the PdAu/In2O3(110) system. The results demonstrate that the incorporation of a secondary metal (Au) into the supported Pd catalyst, in conjunction with precise control over Au concentration, exerts influence on both reactant binding energy and activation. The adsorption and activation of CO2 at the interface sites of Au4/In2O3(110) and PdAu3/In2O3(110) are not observed. The transition state for the dissociation of CO2 into *CO and *O is determined based on adsorbed CO2, providing insights into the properties of activated CO2. The Bronsted–Evans–Polanyi relation, which correlates activation barriers (Ea) with reaction energies (Er), was established for the CO2 dissociation mechanism on PdAu/In2O3(110) catalysts using equation E = 0.4Ea + 0.63. It was carried out to investigate the H2-dissociated adsorption processes and mobility energy on various PdAu/In2O3(110) catalysts. Finally, a highly efficient Pd2Au2/In2O3 catalyst for the hydrogenation of CO2 into methanol has been proposed. This research provides valuable insights into the hydrogenation of CO2 to methanol using bimetal-oxide catalysts and contributes to the optimization of the design of PdAu/In2O3 catalysts for CO2 reactions.

Unraveling the adsorption-limited hydrogen oxidation reaction at palladium surface via in situ electron microscopy

Palladium (Pd) catalysts have been extensively studied for the direct synthesis of H2O through the hydrogen oxidation reaction at ambient conditions. This heterogeneous catalytic reaction not only holds considerable practical significance but also serves as a classical model for investigating fundamental mechanisms, including adsorption and reactions between adsorbates. Nonetheless, the governing mechanisms and kinetics of its intermediate reaction stages under varying gas conditions remain elusive. This is attributed to the intricate interplay between adsorption, atomic diffusion, and concurrent phase transformation of catalyst. Herein, the Pd-catalyzed, water-forming hydrogen oxidation is studied in situ, to investigate intermediate reaction stages via gas cell transmission electron microscopy. The dynamic behaviors of water generation, associated with reversible palladium hydride formation, are captured in real time with a nanoscale spatial resolution. Our findings suggest that the hydrogen oxidation rate catalyzed by Pd is significantly affected by the sequence in which gases are introduced. Through direct evidence of electron diffraction and density functional theory calculation, we demonstrate that the hydrogen oxidation rate is limited by precursors' adsorption. These nanoscale insights help identify the optimal reaction conditions for Pd-catalyzed hydrogen oxidation, which has substantial implications for water production technologies. The developed understanding also advocates a broader exploration of analogous mechanisms in other metal-catalyzed reactions.

Stable and Versatile Pd Precursors for the Preparation of Robust Pd Catalysts Under Continuous-Flow.

To achieve global sustainability, the chemical and engineering communities require the development of versatile precursors that can be used to synthesize robust catalysts. To meet this demand, we developed a new Pd precursor for highly efficiently incorporating fine Pd-metal into supports. An atmospherically stable Pd precursor (Pd-80) was prepared by thermally promoting the aerobic oxidation of tetrakis(triphenylphosphine)palladium. The physical properties of Pd-80 were investigated by NMR spectroscopy, SEM, XPS, solvent-relaxation NMR spectroscopy, and dynamic light scattering (DLS) experiments. We also prepared a cordierite-supported Pd catalyst (Pd/cordierite) by stirring Pd-80 and cordierite powder in chloroform at room temperature. Pd/cordierite selectively catalyzed the hydrogenation of various reducible functional groups, including alkynes, azides, nitro groups, olefins, CO2Bn, N-Cbz, O-Bn, aromatic ketones, and styrene oxide, in continuous-flow hydrogenation reactions. The Pd/cordierite-catalyzed continuous-flow hydrogenation of nitrobenzene derivatives afforded the corresponding anilines, with catalytic activities maintained for over 250 h of continuous operation with a turnover number (TON) of 61,090.

Layered silicate PLS-3 with PREFER structure supported Pd nanoparticles: A recyclable catalyst for the synthesis of furfuryl ethyl ether

Supported Pd catalysts has found wide applications in reductive etherification of aldehydes. However, the synthesis of furfural-derived ethers on Pd catalysts has encountered great challenges because several side reactions such as over-hydrogenation of furan ring and decarbonylation always occur simultaneously under the reaction conditions. We herein reported the catalytic performance of Pd nanoparticles (∼4 nm) supported on the external surface of layered structured PLS-3 zeolite with narrow pore size (<0.4 nm) and large external surface area (80–100 m2/g). The PLS-3 with Si/Al of 92 having total acid sites of 93 μmol/g showed satisfied ether selectivity. Pd nanoparticles located on the external surface showed better etherification selectivity than those confined in the framework, due to the less diffusion limitation of furfural acetal as an intermediate.

Investigation of n-Butane Conversion on Pd, Rh, Ru Catalysts Supported by Al2O3 and SiO2

This study explored the dehydrogenation of n-butane using Pd, Rh, and Ru catalysts on aluminum and silicon oxide supports. Aluminum oxide (Al2O3) showed superior conversion of n-butane, especially with 1% Pd/γAl2O3, yielding 31% target alkenes. This catalyst offers potential for scaling up n-butane dehydrogenation technology.

Heteroatoms‐Stabilized Single Palladium Atoms on Amorphous Zeolites: Breaking the Tradeoff between Catalytic Activity and Selectivity for Alkyne Semihydrogenation

AbstractAs a fundamental industrial catalytic process, the semihydrogenation of alkynes presents a challenge in striking a balance between activity and selectivity due to the issue of over‐hydrogenation. Herein, we develop an efficient catalytic system based on single‐atom Pd catalysts supported on boron‐containing amorphous zeolites (Pd/AZ−B), achieving the tradeoff breaking between the activity and selectivity for the selective hydrogenation of alkynes. Advanced characterizations and theoretical density functional theory calculations confirm that the incorporated B atoms in the Pd/AZ−B can not only alter the geometric and electronic properties of Pd atoms by controlling the electron migration from Pd but also mitigate the interaction between alkene and the catalyst supports. This boosts the exceptional catalytic efficacy in the semihydrogenation of phenylacetylene to styrene under mild conditions (298 K, 2 bar H2), achieving a recorded turnover frequency (TOF) value of 24198 h−1 and demonstrating 95 % selectivity to styrene at full conversion of phenylacetylene. By comparison, the heteroatom‐free amorphous zeolite‐anchored Pd nanoparticles and the commercial Lindlar catalyst have styrene selectivities of 73 % and 15 %, respectively, under identical reaction conditions. This work establishes a solid foundation for developing highly active and selective hydrogenation catalysts by controllably optimizing their electronic and steric properties.

Heteroatoms-Stabilized Single Palladium Atoms on Amorphous Zeolites: Breaking the Tradeoff between Catalytic Activity and Selectivity for Alkyne Semihydrogenation.

As a fundamental industrial catalytic process, the semihydrogenation of alkynes presents a challenge in striking a balance between activity and selectivity due to the issue of over-hydrogenation. Herein, we develop an efficient catalytic system based on single-atom Pd catalysts supported on boron-containing amorphous zeolites (Pd/AZ-B), achieving the tradeoff breaking between the activity and selectivity for the selective hydrogenation of alkynes. Advanced characterizations and theoretical density functional theory calculations confirm that the incorporated B atoms in the Pd/AZ-B can not only alter the geometric and electronic properties of Pd atoms by controlling the electron migration from Pd but also mitigate the interaction between alkene and the catalyst supports. This boosts the exceptional catalytic efficacy in the semihydrogenation of phenylacetylene to styrene under mild conditions (298 K, 2 bar H2), achieving a recorded turnover frequency (TOF) value of 24198 h-1 and demonstrating 95 % selectivity to styrene at full conversion of phenylacetylene. By comparison, the heteroatom-free amorphous zeolite-anchored Pd nanoparticles and the commercial Lindlar catalyst have styrene selectivities of 73 % and 15 %, respectively, under identical reaction conditions. This work establishes a solid foundation for developing highly active and selective hydrogenation catalysts by controllably optimizing their electronic and steric properties.

Atomically Dispersed Palladium Catalyst for Chemoselective Hydrogenation of Quinolines.

Chemoselective hydrogenation of quinoline and its derivatives is a significant strategy to achieve the corresponding 1,2,3,4-tetrahydroquinolines (py-THQ) for various potential applications. Here, we precisely constructed a titanium carbide supported atomically dispersed Pd catalyst (PdSA+NC/TiC) for quinoline hydrogenation, delivering above 99% py-THQ selectivity at complete conversion with an outstanding turnover frequency (TOF) of 463 h-1. AC-HAADF-STEM and XAFS demonstrate that the atomic dispersion of Pd includes Pd-Ti2C2 single atoms and Pd clusters with atomic-layer thickness. Theoretical calculation and experimental results revealed that H2 dissociation and subsequent hydrogenation rates were greatly promoted over Pd clusters. Although the adsorption of quinolines and intermediates are easier on Pd clusters than on Pd single atoms, the desorption of py-THQ is more favored over Pd single atoms than over Pd clusters. The desorption step may be the main reason for 5,6,7,8-tetrahydroquinoline (bz-THQ) and decahydroquinoline (DHQ) formation. Thus, a low reaction activity and py-THQ selectivity were received over PdSA/TiC and PdNP/TiC, respectively.

Evaluation of Cobalt, Nickel, and Palladium Complexes as Catalysts for the Hydrogenation and Improvement of Oxidative Stability of Biodiesel

Developing effective catalysts that can selectively hydrogenate C=C bonds in biodiesel samples is vital as it tackles the major problem of oxidative stability, which greatly limits the utilization of biodiesel as an alternative fuel. In this work, Co, Ni, and Pd catalysts stabilized with the bidentate nitrogen ligands N-(3-(triethoxysilyl)propyl)pyridin-2-ylmethylimine and N-(3-(triethoxysilyl)propyl)picolinamide were synthesized, characterized, and used as pre-catalysts in the transfer hydrogenation of C=C bonds in fatty acid methyl esters. The active catalysts from the Co, Ni, and Pd complexes sequentially hydrogenate the C18:2 chains to C18:1, which is further converted to C18:0 in the FAMEs of both methyl linoleate and jatropha biodiesel. The hydrogenation process was kinetically controlled, and after 3 h it yielded a biodiesel sample that contained 25.83% C16:0, 12.52% C18:2, 41.54% C18:1, 14.47% C18:0 and 3.0% C18:2 isomers. The un-hydrogenated jatropha diesel, hydrogenated jatropha diesel, and a B20 blend of jatropha were tested for susceptibility to oxidation reactions using the Rancimat method and FTIR spectroscopy, and the partial hydrogenation had improved the induction period by 3 h.

Ethanol Oxidation Reaction on Electrodeposited Pd and Sb‒Pd Catalysts in Alkaline Solution Containing Na or Li Cations

Abstract This work reports the galvanostatical electrodeposition of Pd and Sb‒Pd catalysts on rotating glassy carbon (GC) electrode using surfactant-free electrolytes and the prepared catalysts were tested is the electro-oxidation reactions in alkaline solutions. Characterization of Pd and Sb‒Pd catalysts was performed with scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) technique. Cyclic voltammetry (CV) and chronoamperometry were applied in order to study the electrocatalytic behavior of Pd and Sb‒Pd catalysts in the ethanol oxidation reaction (EOR) in alkaline solution containing Na+ or Li+ cations from the point of the impact of the selected alkali metal cations on the electrocatalytic activity. The peak current of EOR at Pd and Sb‒Pd catalysts in the solution with Li+ cations is 2.5 times higher compared to the values obtained in the solution with Na+ cations. EOR starts at rather negative potentials in LiOH solution regarding NaOH for approximately 0.03 V indicating the active role of OHad and the impact of the nature of alkali metal cations which consequently arises from the formation of OHad ‒ cation clusters. The role of Sb in bimetallic catalyst was established by adjusting the extent and persistence of OHad surface coverage.

Pd catalysts in the mild reductive depolymerization of Soda lignin: Support and Cu addition effects

This study pioneers the exploration of the structure-performance relationship of 5 wt% Pd and PdCu catalysts on 3 supports (γ-Al2O3, SiO2, and activated carbon (AC)) in the mild reductive depolymerization (MRD) of Soda lignin. While all catalysts achieve similar final weight average molecular weight (Mw) reduction (≈ 85 %), Pd/AC and PdCu/AC show significant differentiation from solvolysis already after 2 h and 3 h, compared to 6 h and 20 h for Pd and PdCu on oxide supports. This study also highlights the importance of hydrogenation of C=C bonds in monomer side-chains for maximizing monomer yields. Particularly PdCu/SiO2 is characterized by the lowest monomer yields (7 wt%) due to its low hydrogenation activity, while catalysts like Pd(Cu)/Al2O3, Pd/SiO2, and Pd/AC, with more expressed hydrogenation, achieve a total monomer yield of up to 14 wt%. Additional findings confirm that on γ-Al2O3, the co-impregnation of Cu and Pd leads to the formation of a chemical bond between Pd2+ and Cu1+, resulting in a new mixed metal oxide Pd-Cu–O phase. On SiO2, Pd2+ and Cu1+ do not form a chemical bond, however, the presence of Cu1+ in close proximity to Pd2+ significantly alters the selectivity of the PdCu/SiO2 catalyst due to synergetic effects. PdCu/AC maintains similar selectivity to Pd/AC, except for reduced hydrogenation over time, due to the lack of interaction between Pd and Cu on the AC surface. This research also delves into the MRD mechanism of Soda lignin over Pd and PdCu catalysts, focusing on the β-O-4 linkage cleavage and the subtle differences in reaction pathways depending on the catalyst. These findings bridge gaps in understanding the MRD of actual lignin feedstocks, offering valuable insights for catalyst development and process optimization.