PdCu Alloy Research Articles

The Promotion Effect of Cu on the Pd/C Catalyst in the Chemoselective Hydrogenation of Unsaturated Carbonyl Compounds

Highly efficient and selective hydrogenation of a,b-unsaturated carbonyl compounds to unsaturated alcohol using bimetallic palladium-copper supported on carbon (denoted as Pd-Cu(3.0)/C; 3.0 is Pd/Cu molar ratio) catalyst is demonstrated. Pd-Cu(3.0)/C catalyst was prepared via a simple hydrothermal route under air atmosphere at 150 °C for 24 h followed by reduction with hydrogen at 400°C for 1.5 h. The chemoselective hydrogenation of typical a,b-unsaturated carbonyl ketone (2-cyclohexene-1-one) and aldehyde (trans-2-hexenaldehyde), and chemoselective hydrogenation of FFald and (E)-non-3-en-2-one mixture demonstrated high productivity, leading to high selectivity of unsaturated alcohols. The presence of bimetallic Pd-Cu alloy phase with relatively high H2 uptakes was observed, enabling to preferentially hydrogenate C=O rather than to C=C bonds under mild reaction conditions. Pd-Cu(3.0)/C catalyst was found to stable and reusable for at least four reaction runs and the activity and selectivity of the catalyst can be restored to the original after rejuvenation with H2 at 400 °C for 1.5 h. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Influence of Pd deposition pH value on the performance of Pd-CuO/SiO2 catalyst for semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY)

The selective hydrogenation of CC to C=C bonds is an important step, yet remains to be a great challenge in chemical industry. In this study, we have revealed the influence of Pd deposition pH value on the catalytic performance of Pd-CuO/SiO2 catalyst for the semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY). Trace amount of Pd (about 500 ppm) was loaded via deposition-reduction method on CuO/SiO2 support by using H2PdCl4 solution as precursor and NaBH4 as reductant, respectively. The pH value at which Pd was deposited was adjusted to about 5 and 7 by adding NaOH solution. The obtained catalysts were characterized by several techniques including XRD, TEM, H2-TPR, etc. In the case of pH value of 5, the CuO was partially dissolved during the deposition and then co-reduced with Pd2+ by NaBH4, forming PdCu alloy structure in sub-nanometer. In contrast, no PdCu alloy structure was observed when pH value was 7. The kinetics of MBY semi-hydrogenation over both catalysts were compared. The former PdCu alloy catalyst showed very high selectivity towards the semi-hydrogenation of MBY due to its low activity in hydrogenation of C=C bond in 2-methyl-3-buten-2-ol (MBE). The results herein demonstrated that the pH value where Pd was deposited played a crucial role in determining the catalytic performance of PdCu catalyst.

Surface segregation of PdM (M=Cu, Ag, Au) alloys and its implication to acetylene hydrogenation, DFT-based Monte Carlo simulations

The surface composition and atomic arrangement of heterogeneous catalysts determine the surface chemistry and are necessary information for understanding surface catalytic reactions. Compared with monometallic catalysts, alloy catalysts are more complicated because of possible surface segregation or adsorption-induced segregation which may change under different reaction atmosphere. Construction of reasonable slab models to study reactions on alloy surfaces is of importance. Here we proposed a density functional theory based Monte Carlo method (DFT-MC) and used it to investigate the surface composition and atomic arrangement of the (111) surfaces of 1:1 PdAg, PdAu and PdCu alloys in vacuum and under the acetylene partial hydrogenation conditions modeled by co-adsorption of H and acetylene and of H and ethylene. Our DFT-MC simulations indicate that Au and Ag segregate on the PdAu(111) and PdAg(111) surfaces while Pd is enriched on the PdCu(111) surface under vacuum conditions. The surface Pd contents of PdAg and PdAu tend to increase under partial hydrogenation conditions. Analyses reveal that the co-adsorption energies on the ideal (bulk-cut) surfaces correlate linearly with the values on the segregated surfaces and there is also a linear relationship for the d-band centers between the ideal and segregated surfaces. The present study provides a way to construct more realistic models for studying reactions on alloy surfaces.

Single-Crystalline Mesoporous Palladium and Palladium-Copper Nanocubes for Highly Efficient Electrochemical CO 2 Reduction

Single-Crystalline Mesoporous Palladium and Palladium-Copper Nanocubes for Highly Efficient Electrochemical CO ₂ Reduction

Study of carbon supported CuPd alloy nanoparticles with Pd-rich surface for the electrochemical formate oxidation and CO2 reduction

Carbon supported copper-palladium alloy nanoparticles (CuPd/C) with Pd-rich surface synthesized via the adsorbate induced surface segregation method were tested toward both the electrochemical oxidation of formate into electricity and CO2, and the reduction of CO2 to produce formate. An upshift of the d-band center and opposite binding energy shifts of Cu and Pd core levels were experimentally observed using X-ray photoelectron spectroscopy (XPS). This perturbation of the surface electronic structure of the CuPd/C nanoparticles leads to the lowering of the bonding strength of key adsorbate species for both the formate oxidation and electrochemical CO2 reduction, which increased the catalytic activity toward both reactions. Amongst the different compositions of CuxPd1-x/C, the 20:80 molar% of Cu:Pd concentration shows an important improvement toward formate oxidation (FO) compared to the other CuxPd1-y compositions and the monometallic Pd. On the other hand, CuxPd1-x/C catalyst with the 60:40 molar% of Cu:Pd concentration shows the highest faradaic efficiency for the electrochemical CO2 reduction toward the formate production. Therefore, by selecting a bimetallic CuxPd1-x/C alloy that (1) optimizes the formate oxidation current density and (2) the faradaic efficiency of the electrochemical reduction of CO2 into formate, a novel sustainable and regenerative power source (i.e., combining a direct formate fuel cell and a CO2 reduction unit into a single regenerative energy system) could be developed.

Fabrication of Z-scheme CuPd/SrTiO3–CuPd–Bi2O3 photocatalyst for converting organic dye containing N and S elements into (NH4)2SO4

Several novel Z-scheme CuPd/SrTiO 3 –CuPd–Bi 2 O 3 photocatalysts are prepared via chemical reduction and calcination methods to degrade organic dyes containing N and S and convert NO 2 - , NO 3 - and SO 3 2- into (NH 4 ) 2 SO 4 . Sodium borohydride (NaBH 4 ), ascorbic acid (C 6 H 8 O 6 ) and hydrazine hydrate (N 2 H 4 ·H 2 O) are selected as reductants to deposit CuPd alloy nanoparticles on corresponding photocatalyst. The influence of solar light irradiation time on photocatalytic degradation of organic dye and conversion of the generated inorganic ions is studied. The reusability and stability of the prepared photocatalysts are assessed. The results indicate that the Z-scheme CuPd/SrTiO 3 –CuPd–Bi 2 O 3 photocatalyst prepared by using NaBH 4 has best photocatalytic activity, reusability and stability. The capture experiment of active species proves that holes play crucial roles in photocatalytic degradation of organic dyes and conversion of SO 3 2- and electrons are momentous for the conversions of NO 2 - and NO 3 - . A possible mechanism on photocatalytic degradation of organic dyes containing N and S and conversions of NO 2 - , NO 3 - and SO 3 2- into (NH 4 ) 2 SO 4 caused by Z-scheme CuPd/SrTiO 3 –CuPd–Bi 2 O 3 photocatalyst is proposed. • Several novel photocatalysts are prepared via chemical reduction and calcination. • CuPd alloy cocatalyst is introduced to Z-scheme SrTiO 3 /Bi 2 O 3 photocatalytic system. • Effect of CuPd alloy gained via three reductants on catalyst activity is clarified. • Formation of alloy can boost synergistic effect of Cu and Pd in reduction reaction. • The catalyst can selectively convert organic dye containing N and S into (NH 4 ) 2 SO 4 .

3D nitrogen-doped carbon nanofoam arrays embedded with PdCu alloy nanoparticles: Assembling on flexible microelectrode for electrochemical detection in cancer cells

In this work, we developed a novel and facile strategy for the synthesis of a highly active and stable electrocatalyst based on PdCu alloy nanoparticles (PdCu-ANPs) embedded in 3D nitrogen-doped carbon (NC) nanofoam arrays (NFAs), which were assembled on flexible carbon fiber (CF) microelectrode for in situ sensitive electrochemical detection of biomarker H2O2 in cancer cells. Our results showed that NC-NFAs support possessed a unique hierarchically porous architecture by integrating the macrospores in arrays scaffold within mesopores in individual NC nanofoam, which offered exceptionally large surface area for embedding high-density PdCu-ANPs in it as well as facilitated the mass transfer and molecular diffusion during the electrochemical reaction. Taking the advantages of the unique structural merit of NC-NFAs support and excellent electrocatalyitc properties of PdCu-ANPs that embedded in it, the resultant PdCu-ANPs/NC-NFAs modified CF microelectrode exhibited good electrochemical sensing performances towards H2O2 including a wide linear range from 2.0 μM to 3.44 mM, a low detection limit of 500 nM, as well as good reproducibility, stability and anti-interference ability. When used in real-time in situ tracking H2O2 secreted from different types of human colorectal cancer cells, i.e., HCT116, HT29, SW48 and LoVo, it can distinguish the types of cancer cells by measuring the number of extracellular H2O2 molecules released per cell, which demonstrates its great promise in cancer diagnose and management.

Monodisperse CuPd alloy nanoparticles as efficient and reusable catalyst for the C (sp2)–H bond activation

Metal‐catalyzed selective activation of C–H bonds is very important for the construction of a variety of biologically active molecules. Supported alloy nanoparticles are of great interest in various catalytic applications due to the synergistic effects between different metals. Here, well‐dispersed CuPd alloy nanoparticles supported on reduced graphene oxide (rGO) were synthesized and found to be highly efficient and recyclable catalyst for the chelation‐assisted C (sp2)–H bond activation. Aromatic ketones or esters were synthesized via the cross‐dehydrogenative coupling (CDC) reaction between 2‐arylpyridines and alcohols or acids. Moreover, the catalyst was recovered and used for five times without significantly losing activity.

Improved charge carrier separation of Schottky junction containing a bimetallic Cu-Pd alloy and N-Bi2WO6 square-shaped discs for photocatalytic H2 performance

Bimetallic alloy nanospheres hybridized with semiconductor square-shaped discs are promising catalysts for photocatalytic water splitting, because they exhibit multicomponent interactions, high catalytic activity, and stability. Herein, Cu-Pd/N-Bi2WO6 heterostructures consisting of bimetallic Cu-Pd alloy nanospheres uniformly dispersed on N-Bi2WO6 square-shaped discs are reported. The as-prepared 1 wt% Cu-Pd/N-Bi2WO6 catalyst exhibits a higher H2 production rate (4213 µmol/g) under simulated solar light illumination than N-Bi2WO6 (291 µmol/g). The considerably high H2 production rate is ascribed to the exposed catalytically active sites of the Cu-Pd alloy nanospheres, which facilitate the formation of rapid charge transfer channels between Cu-Pd and N-Bi2WO6. Moreover, the photocatalyst stability is improved by aggregation of the highly dispersed Cu-Pd alloy nanospheres on the N-Bi2WO6 surface. Accordingly, a reaction mechanism based on the work functions of the bimetallic Cu-Pd alloy nanospheres and N-Bi2WO6 square-shaped discs is proposed to elucidate the photocatalytic reaction pathway. The holes (which accumulate in the N-Bi2WO6 square-shaped discs) and Pd (which acts as an electron channel) can effectively inhibit the recombination of charge carriers, and Cu (which acts as the cocatalyst) can synergistically increase the H+ reduction rate. This study provides a new effective route for the design of high-performance heterostructures for efficient photocatalytic H2 production.

Ultrathin PdCu alloy nanosheet-assembled 3D nanoflowers with high peroxidase-like activity toward colorimetric glucose detection.

Enzyme-mimetic properties of nanomaterials can be efficiently tuned by controlling their size, composition, and structure. Here, ultrathin PdCu alloy nanosheet-assembled three-dimensional (3D) nanoflowers (Pd1Cux NAFs) with tunable surface composition are obtained via a generalized strategy. In presence of H2O2, the as-synthesized Pd1Cux NAFs can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to the oxidized form of TMB (oxTMB) with a characteristic absorption peak at 652 nm. Interestingly, Pd1Cux NAFs show obviously composition-dependent peroxidase-like catalytic activities because of the synergistic interaction of nanoalloy. Additionally, different from 2D Pd nanosheets, the distinctive 3D superstructures are featured with rich approachable sites and proper layer spacing, which are in favor of fast mass transport and electron transfers during the catalytic process. Among the studied Pd1Cux NAFs, the Pd1Cu1.7 NAFs show the highest enzyme-like activities and can be successfully applied for the colorimetric detection of glucose with a low detection limit of 2.93 ± 0.53μM. This work provides an efficient avenue to fabricate PdCu NAF nanozymes in biosensing toward glucose detection. Two-dimensional (2D) PdCu ultrathin nanosheet-assembled 3D nanoflowers (Pd1Cux NAFs) with tunable surface composition exhibit substantially enhanced intrinsic peroxidase-like catalytic activities. The Pd1Cu1.7 NAFs are successfully used as peroxidase mimic catalyst for the colorimetric detection of glucose with low detection limit of 2.93μM.

Temperature Dependence of Hydrogen Solubility and Diffusivity in Hydrogen Permeable Membrane of Pd-Cu Alloy with B2-Type Crystal Structure

The temperature dependence of hydrogen solubility and diffusivity of Pd–53mol%Cu alloy membrane with the B2–type crystal structure has been investigated. The hydrogen permeation tests are performed using ultra–pure hydrogen (more than 9N) purified by a Pd–Ag alloy membrane to avoid any influences of impurities. It is found that the hydrogen permeability decreases significantly at low temperatures, especially near room temperature. The time dependence of hydrogen flux is monitored and found that the hydrogen flux decreases gradually during about 4 ~ 5 days after rapid cooling down to room temperature from 623 K.The results of the temperature dependence of the hydrogen permeability are analyzed in view of the consistent description of hydrogen permeation based on hydrogen chemical potential, where the hydrogen flux is proportional to the product of the mobility for hydrogen diffusion, B, and the PCT factor, fPCT. In this study, the pressure–composition–isotherms (PCT curves) for Pd–53Cu alloy with B2 structure are measured for the first time by the in–situ XRD–PCT method, and they are applied to estimate the PCT factors. Then, the temperature dependence of the PCT factor and the mobility for hydrogen diffusion is evaluated. It is revealed that the decrement in hydrogen permeability at low temperatures is mainly attributable to the decrement of the mobility for hydrogen diffusion.According to the positron annihilation experiments, the defects density is considered to be small in Pd–53Cu alloy with the B2 structure even at room temperature, suggesting that the excess Cu atoms in Pd–53Cu alloy occupy the positions of Pd sublattice, at which the Cu atoms form a local BCC–Cu unit. The diffusion of Cu atoms corresponds to the diffusion of BCC–Cu units in the B2 structure. Therefore the diffusion of Cu atoms and the configuration of BCC–Cu units in B2 structure could be a key to understand the gradual transition of hydrogen diffusivity at low temperatures.

Monodisperse CuPd alloy nanoparticles supported on reduced graphene oxide as efficient catalyst for directed C−H activation

The palladium-catalyzed selective activation of CH bonds is of great importance for the construction of diverse bioactive molecules. Herein, monodisperse CuPd alloy nanoparticles supported on reduced graphene oxide have been used as high efficient and recyclable catalyst for C(sp3)−H acyloxylation of 8-methylquinolines in good yields under mild conditions. The developed catalytic system proceeds with low palladium loading, good catalyst recyclability, high step and atom efficiency, excellent chemo and regioselectivity, good substrate and functional group compatibility, and applicable for large scale up synthesis. Preliminary studies were carried out to gain insights into the heterogeneous catalysis mechanism.

Bimetallic nano alloy architecture on a special polymer: Ni or Cu merged with Pd for the promotion of the Mizoroki–Heck reaction and the Suzuki–Miyaura coupling

Novel Ni-Pd and Cu-Pd bimetallic nano alloys was designed and heterogenized on the highly robust ABPBI [poly(2,5-benzimidazole)] polymer in high yields using NaBH4 as reducing agent. These were versatile ligand free catalysts for the Mizoroki–Heck reaction and Suzuki–Miyaura coupling. The bimetallic Ni-Pd-ABPBI catalyst for the Mizoroki–Heck reaction of 4-iodo anisole could be recycled 5 times with high yields. Aryl bromides could also be activated for the Mizoroki–Heck reaction using Cu-Pd-ABPBI NP catalysts, with moderate yields. Synopsis Novel bimetallic Ni-Pd and Cu-Pd nano alloys, heterogenized on the robust ABPBI [poly(2,5-benzimidazole)] polymer using NaBH4 as reducing agent, is described. These were versatile ligand free, noble metal conservative catalysts, for the Mizoroki–Heck reaction and the Suzuki–Miyaura coupling. Aryl bromides were activated for the Mizoroki–Heck reaction using the Cu-Pd-ABPBI catalyst.

Quaternary Hydrides Pd1-y-zAgyCuzHx Embedded Atom Method Potentials for Hydrogen Energy Applications

The Pd-H system has attracted extensive attention. Pd can absorb considerable amount of H at room temperature, this ability is reversible, so it is suitable for multiple energy applications. Pd-Ag alloys possess higher H permeability, solubility and narrower miscibility gap with better mechanical properties than pure Pd, but sulfur poisoning remains an issue. Pd-Cu alloys have excellent resistance to sulfur and carbon monoxide poisoning and hydrogen embrittlement, good mechanical properties, and broader temperature working environments over pure Pd, but relatively lower hydrogen permeability and solubility than pure Pd and Pd-Ag alloys. This suggests that alloying Pd with Ag and Cu to create Pd-Ag-Cu ternary alloys can optimize the overall performance and substantially lowers the cost. Thus, in this paper, we provide the first embedded atom method potentials for the quaternary hydrides Pd1-y-zAgyCuzHx. The fully analytical potentials are fitted utilizing the central atom method without performing time-consuming molecular dynamics simulations.

Investigation of charge transfer interaction in heterometallic precursors to control their surface reactivity for MOCVD of Pd-Cu alloy films

The work aims to study main factors determining surface reactions mechanism of the heterometallic MOCVD precursors for multicomponent inorganic films. A set of theoretical and experimental techniques is proposed to investigate the electronic structure of the copper-palladium precursor to control its surface reactivity in MOCVD of Pd-Cu alloy films. The surface and bulk charge distribution in the heterometallic precursors CuPdL4 (1) and Cu(hfa)2PdLF2 (2) and parent monometallic complexes was carried out using both experimental X-ray photoelectron (XPS) and X-ray emission (XES) spectroscopies and theoretical techniques (DFT calculations and NBO analysis). Comparison of calculated and experimental atomic charges for monometallic and heterometallic complexes revealed the electronic density redistribution on oxygen and metal atoms due to electronic charge transfer interaction between monometallic fragments in the heterocomplex, which was confirmed by NBO analysis. The charge transfer intensity appeared to be stronger for the fluorinated precursor 2, indicating its greater resistance to thermal dissociation into monometallic fragments compared to 1, which was confirmed by the data on the bimetallic films composition. Thus, the evidenced charge transfer interaction can be altered by changing the composition of the precursors to control their surface reactivity and films composition.

Effects of van der Waals interactions on the structure and stability of Cu8-xPdx (x = 0, 4, 8) cluster isomers

Detailed knowledge of the minimum energy and low-lying structures of metal clusters is crucial to understand their physicochemical properties. In this work, the effect of van der Waals (vdW) interactions on the structure and stability of Cu-Pd clusters is investigated. With this aim, a global search algorithm that combines the basin-hopping method and density functional theory is used to explore the potential energy surface of Cu8-xPdx (x = 0, 4, 8) clusters. We present the structural motifs adopted by the low-energy isomers obtained with the PBE gereralized gradient exchange-correlation functional, and with PBE supplemented by dispersion energy corrections as given by Grimme’s D3 method. The isomeric structures obtained by PBE and PBE-D3 methods are in general quite similar, except for minor changes in some particular isomers. Global structural explorations were also performed with the meta-GGA TPSS and the hybrid PBE0 functionals, showing a reasonable agreement with the results obtained with the PBE and corrected PBE-D3 functionals. The energetics of the clusters is investigated by analyzing the binding energy per atom. Binding ;1;energies become larger when vdW forces are included, and this contribution increases from Cu8 to Pd8 and then to Cu4Pd4. Mixing between Cu and Pd atoms to form nanoalloys is favorable, a feature consistent with the well-known formation of intermetallic compounds in the bulk Cu-Pd alloys. The HOMO-LUMO gap indicates that some isomers in Cu8 and Cu4Pd4 are more reactive than the lowest energy isomer, a feature that gives a hint into the importance that low-lying isomers may have in catalytic reactions. Binding energies and HOMO-LUMO gaps present a stronger dependence on the exchange-correlation functional than the cluster structures.

Selective hydrogenation of acetylene on Cu-Pd intermetallic compounds and Pd atoms substituted Cu(111) surfaces.

The selective hydrogenation of acetylene was studied on the ordered Cu-Pd intermetallic compounds (L10-type CuPd, L12-type Cu3Pd, and L12-type CuPd3) and Pd-modified Cu(111) surfaces through first-principles calculations. The catalytic selectivity and activity of Cu-Pd alloy catalysts are closely related to the crystal structure and composition of Cu-Pd intermetallic compounds and the size of Pd ensembles of Cu-based dilute alloy surface for the selective hydrogenation of acetylene to ethylene. Significantly, we found that the ordered Cu-Pd alloy surface containing isolated Pd atoms (i.e., L12-type Cu3Pd(111) surface) is highly efficient for the selective hydrogenation reaction of C2H2 + H2→ C2H4. The contiguous Pd atom ensembles (Pd dimer and trimer) are catalytically active towards C2H2 + H → C2H3 and C2H3 + H → C2H4 reactions than the single Pd atom on a Pd-decorated Cu(111) surface. However, the small Pd ensembles on Cu(111) present a low chemical activity for H2 dissociation compared with the ordered Cu-Pd intermetallic compounds. Our theoretical results provide a strategy of crystal phase and composition control for enhancing the selectivity and activity of Cu-Pd catalysts towards acetylene selective hydrogenation.

The robust peroxidase mimics within metal–organic frameworks for the sensitivity detection of H2O2 and glucose in serum

Ultrafine and uniform CuPd alloy nanoparticles encapsuled in MOF to detect H2O2 and glucose with a low detection limit.

A recyclable self-supported nanoporous PdCu heterogeneous catalyst for aqueous Suzuki-Miyaura cross-coupling.

Nanoporous PdCu (NP-PdCu) was prepared by the dealloying strategy from a PdCuAl ternary alloy precursor and characterized systematically using SEM, TEM, XRD, and XPS. NP-PdCu was demonstrated to be a competent self-supported heterogenous catalyst for Suzuki-Miyaura cross-coupling, affording a series of synthetically valuable biaryl compounds in good to excellent yields. This catalyst could be easily separated from the product via centrifugation and reused several times without obvious loss of catalytic performance.

Structure and properties of Cu-based alloys diluted by Pd and Ag

The microstructure, mechanical and electrical properties of Cu-Pd alloys (with Pd content not more than 8 at.%) and triple Cu-Pd-Ag alloys with 5 at.%Ag were studied. It was established that the strength and the recrystallization temperature of the Cu-Pd alloys increased with palladium content. A comparison of the electrical properties of these alloys when Pd content was increased from 0 to 8 at.%Pd was done. An anomaly was revealed in the Cu-5.9Pd and Cu-8Pd alloys: the plastic deformation does not lead to an increase in the electrical resistivity. It is due to the destruction of short range atomic order in the quenched Cu-Pd alloys under deformation. The alloying with silver leads to a further increase in strength with a constant electrical conductivity. It was found that annealing of the deformed Cu-Pd-Ag alloys at 200-300°C led to an increase in strength. It was shown that the effect was not related to the Pd-content and was due to silver only.