Pd-Cu Catalysts Research Articles

Elimination of NO3- from water using Pd and PdCu catalysis supported on ZrO2–CeO2 materials: Effect of the support preparation

The catalytic reduction of NO3− in synthetic and real water samples was studied using Pd and PdCu catalysts supported on pure CeO2 and CeO2 modified with 5 wt%. ZrO2. The supports were prepared by both calcination and sol-gel methods to study the effect of the preparation on the catalytic performance. The prepared catalysts were characterized by different techniques, including N2 physisorption, SEM-EDS, XRD, XPS, and TPR. Monometallic Pd catalysts were active in NO3− elimination, and the addition of Cu generated new active sites. The catalysts synthesized by calcination presented lower NO3− removal capacity compared to those prepared by sol-gel, due to their lower surface area and porosity. Oxygen vacancies (Ce+4/Ce+3 couple) were verified in the supports prepared by sol-gel by XPS. These vacancies were more evident in the materials modified with ZrO2. All the catalysts evaluated presented good selectivity (above 90%) to N2, the innocuous and desired product. The PdCu/ZCBSG catalyst showed the highest activity, due to the better dispersion of ZrO2 on CeO2 on the support, corroborated by XRD and EDS analysis. Besides, this catalyst was evaluated in the NO3− reduction in real water samples, extracted from the Puelche Aquifer, in Buenos Aires, Argentina.

A performance improvement of enzyme-based electrochemical lactate sensor fabricated by electroplating novel PdCu mediator on a laser induced graphene electrode

A lactate sensor for lactate sensing using porous laser-induced graphene (LIG) electrodes with an electrodeposited PdCu catalyst was developed in this study. CO2 laser was used to convert the polyimide film surface to multilayered LIG. The morphology and composition of LIG were analyzed through field-emission scanning electron microscopy and Raman spectroscopy, respectively, to confirm that the fabricated LIG electrode was composed of porous and stacked graphene layers. PdCu was electrodeposited on the LIG electrode and lactate oxidase (LOx) was immobilized on the LIG surface to create a LOx/PdCu/LIG structure. According to the Randles–Ševčík equation, the calculated active surface area of the fabricated PdCu/LIG electrode was ∼12.8 mm2, which was larger than the apparent area of PdCu/LIG (1.766 mm2) by a factor of 7.25. The measured sensitivities of the fabricated lactate sensors with the LOx/PdCu/LIG electrode were −51.91 μA/mM·cm2 (0.1–5 mM) and −17.18 μA/mM·cm2 (5–30 mM). The calculated limit of detection was 0.28 μM. The selectivity of the fabricated lactate sensor is excellent toward various potentially interfering materials such as ascorbic acid, uric acid, lactose, sucrose, K+ and Na+.

Tailoring Amorphous PdCu Nanostructures for Efficient C-C Cleavage in Ethanol Electrooxidation.

The large-scale application of direct ethanol fuel cells has long been obstructed by the sluggish ethanol oxidation reaction at the anode. Current wisdom for designing and fabricating EOR electrocatalysts has been focused on crystalline materials, which result in only limited improvement in catalytic efficiency. Here, we report the amorphous PdCu (a-PdCu) nanomaterials as superior EOR electrocatalysts. The amorphization of PdCu catalysts can significantly facilitate the C-C bond cleavage, which thereby affords a C1 path faradic efficiency as high as 69.6%. Further tailoring the size and shape of a-PdCu nanocatalysts through the delicate kinetic control can result in a maximized mass activity up to 15.25 A/mgPd, outperforming most reported catalysts. Notably, accelerated durability tests indicate that both the isotropic structure and one-dimensional shape can dramatically enhance the catalytic durability of the catalysts. This work provides valuable guidance for the rational design and fabrication of amorphous noble metal-based electrocatalysts for fuel cells.

Electrochemical Hydrogenation of Furfural in Aqueous Acetic Acid Media with Enhanced 2-Methylfuran Selectivity Using CuPd Bimetallic Catalysts.

Herein, we report a series of CuPd catalysts for electrochemical hydrogenation (ECH) of furfural to 2-methylfuran (MF or FurCH3 where Fur=furyl) in aqueous 0.1 M acetic acid (pH 2.9). The highest faradaic efficiency (FE) for MF reached 75 % at -0.58 V vs. reversible hydrogen electrode with an average partial current density of 4.5 mA cm-2 . In situ surface-enhanced Raman spectroscopic and kinetic isotopic experiments suggested that electrogenerated adsorbed hydrogen (Hads ) was involved in the reaction and incorporation of Pd enhanced the surface coverage of Hads and optimized the adsorption pattern of furfural, leading to a higher FE for MF. Density functional theory calculations revealed that Pd incorporation reduced the energy barrier for the hydrogenation of FurCH2 * to FurCH3 *. Our study demonstrates that catalyst surface structure/composition plays a crucial role in determining the selectivity in ECH and provides a new strategy for designing advanced catalysts for ECH of bio-derived oxygenates.

Electrochemical Hydrogenation of Furfural in Aqueous Acetic Acid Media with Enhanced 2‐Methylfuran Selectivity Using CuPd Bimetallic Catalysts

AbstractHerein, we report a series of CuPd catalysts for electrochemical hydrogenation (ECH) of furfural to 2‐methylfuran (MF or FurCH3 where Fur=furyl) in aqueous 0.1 M acetic acid (pH 2.9). The highest faradaic efficiency (FE) for MF reached 75 % at −0.58 V vs. reversible hydrogen electrode with an average partial current density of 4.5 mA cm−2. In situ surface‐enhanced Raman spectroscopic and kinetic isotopic experiments suggested that electrogenerated adsorbed hydrogen (Hads) was involved in the reaction and incorporation of Pd enhanced the surface coverage of Hads and optimized the adsorption pattern of furfural, leading to a higher FE for MF. Density functional theory calculations revealed that Pd incorporation reduced the energy barrier for the hydrogenation of FurCH2* to FurCH3*. Our study demonstrates that catalyst surface structure/composition plays a crucial role in determining the selectivity in ECH and provides a new strategy for designing advanced catalysts for ECH of bio‐derived oxygenates.

Electroreduction of carbon dioxide to multi-electron reduction products using poly(ionic liquid)-based Cu-Pd catalyst

Electrocatalytic reduction of CO2 (CO2RR) to multi-electron (> 2e–) products provides a green and sustainable route for producing fuels and chemicals. Introducing the second metal element is a feasible strategy for "managing" the key intermediate on Cu-based materials to further improve the CO2RR catalytic performance. In this work, palladium, which promises the generation of CO, was introduced into the poly(ionic liquid)-based copper hybrid (Cu@PIL) to construct a novel Cu-Pd bimetallic electrocatalyst (Cu@PIL@Pd). Remarkably, with a small dosage of palladium (2.0 mol% compared with Cu), a high faradaic efficiency (FE) for C2+ products (68.7%) was achieved at –1.01 V (with respect to the reversible hydrogen electrode (RHE), the same below) with a high partial current density of 178.3 mA cm–2. Meanwhile, high selectivity towards CH4 (FE = 42.5%) and corresponding partial current density of 172.8 mA cm–2 were obtained on the same catalyst at –1.24 V, signifying a significant potential-dependent selectivity. Mechanistic studies reveal that both copper and palladium oxides are reduced to metallic states during the CO2RR. The presence of the adjoint copper phase and the highly dispersed electrostatic layer promote the generation of CO on the palladium components (both the PdO2 phase and the Pd(II) site). Besides, the local CO* was enriched by the significant diffusion resistance of CO in the PIL layer. The spillover of CO* from Pd sites to the adjoint Cu sites, accompanied by the increased local concentration of CO* around Cu sites, accounted for the observed good CO2RR catalytic performance, especially the high C2+ product selectivity.

Selective hydrogenation of succinic acid to gamma-butyrolactone with PVP-capped CuPd catalysts

A reusable catalyst with a low metal loading amount of PVP-capped Pd rich CuPd nanoparticles was explored for highly selective production of γ-butyrolactone via hydrogenation of succinic acid at mild hydrogen pressure.

Multiple remote C(sp3)-H functionalizations of aliphatic ketones via bimetallic Cu-Pd catalyzed successive dehydrogenation.

The dehydrogenation-triggered multiple C(sp3)-H functionalizations at remote positions γ, δ or ε, ζ to carbonyl groups of aliphatic ketones with aryl/alkenyl carboxylic acids as coupling partners have been achieved using a bimetallic Cu-Pd catalyst system. This reaction allows access to alkenylated isocoumarins and their derivatives in generally good yields with high functional group tolerance. The identification of bimetallic Cu-Pd synergistic catalysis for efficient successive dehydrogenation of aliphatic ketones, which overcomes the long-standing challenge posed by the successive dehydrogenation desaturation of terminally unsubstituted alkyl chains in aliphatic ketones, is essential to achieving this bimetallic Cu-Pd catalyzed dehydrogenation coupling reaction.

Enhancement of activity and selectivity to nitrogen in catalytic nitrate reduction by use of conductive carbon catalytic supports and control of hydrogen mass transfer regime

Carbon materials with different structural properties (activated carbon, carbon nanofibers, reduced graphene oxide, graphite, and carbon black) were used as supports of Pd-Cu (5 wt%) catalysts for the catalytic reduction of NO3- in batch reactors. In general, those catalyst with smaller metal nanoparticles and carbon supports with higher specific surface area were more active, although remarkable activity was also observed for catalysts with relatively large nanoparticles and conductive supports. Conductivity of carbon supports also contributed to a lower selectivity to NH4+, which can be ascribed to higher charge transfer between metal and support reducing activation of intermediate species. The decrease of H2 feed into the reaction system resulted in external (gas-liquid) mass transfer constrains, as evidenced by the parameters describing control regime, and led to diminished NH4+ selectivity, particularly in the case of catalysts with conductive supports. Approaches combining control of mass transfer regime and conductive carbon catalytic supports can be useful to enhance selectivity to N2, which is a major challenge in catalytic NO3- reduction.

Efficient purification of hydrogen cyanide by synergistic effects of electrochemical and liquid phase catalysis

In this study, Co, Cu, Pd, and Pd/Cu composite metal ions were used to synthesize metal nanoparticles with high efficiency in purifying hydrogen cyanide gas. The pure liquid phase catalytic purification of hydrogen cyanide gas was studied. According to the removal rate, the Pd/Cu composite metal ions had the best purification efficiency among the nanoparticles of different metal types. The removal rate order was Pd/Cu>Pd>Cu>Co. The gas after reaction were analyzed by gas chromatography, and it was found that HCN was converted into CO2, N2 and NH3 by nanoparticles. Then, Pd/Cu composite metal ions with the highest purification efficiency were used to study the electrochemical synergistic liquid-phase catalytic purification of HCN gas. The effects of electrochemical conditions and current on the electro-hydraulic synergistic purification were studied. The removal efficiency of HCN by electrochemical synergistic liquid phase catalysis was better than that by pure liquid phase catalysis. The different nanoparticles before and after HCN absorption were characterized and analyzed to explore the purification process of HCN. The purification mechanism of hydrogen cyanide by Pd-Cu catalyst under applied voltage was studied under certain conditions. During the catalytic reaction, the nano-catalyst was partially dissolved in liquid phase and partially HCN reacts with metal ions on the free or nanoparticles to form complex [Mc(CN)n]2−n. Homogeneous and quasi-homogeneous reactions in liquid phase interweave together to form a more complex reaction system.

Precisely identify the geometry of catalyst particles from S/TEM images via a boundary attention deep learning network

The size and shape of the nanoparticles have a great impact on their performances as catalysts. Traditional method of manually measuring particles from scanning/transmission electron microscopy (S/TEM) images has limited counting ability of only up to hundreds of particles, not enough to support an accurate statistic and besides, the one dimensional (1D) manual measurement by drawing a line across nanoparticles would induce large bias given the practical supported catalysts whose particles always present irregular geometry. To develop an automatic and precise recognition method based on TEM data has been a long-standing demand to facilitate a highly efficient catalytic dispersion evaluation. In this paper, we propose an end-to-end boundary attention deep learning network to recognize nanoparticles in S/TEM images. The proposed model is an extension of the U-Net embedding a residual boundary attention module to extract the edge information of catalyst particles and a fusion module to exploit the edge features, gradient features and the results out from decoder to enhance recognition performance. Results demonstrate that the proposed boundary attention structure is superior to well-accepted U-Net framework in dealing with the precise particle recognition. Using our new method, a particle size distribution of PdCu catalyst at statistic scale of 14,000 + is achieved, through which more reliable and accurate results of S/TEM characterization can be obtained to facilitate efficient and reliable evaluation of catalysts dispersion.

Crystal orientation effects on the electrochemical conversion of CO2 to syngas over Cu-M (M = Ag, Ni, Zn, Cd, and Pd) bimetal catalysts

CO2 electrochemical reduction to syngas (CO2RR-to-syngas) is an environment friendly and promising CO2 utilization technology. However, there are still few efficient catalysts for CO2RR-to-syngas electrolysis. The crystal orientation regulation is one of the important methods to enhance the activity of catalyst and there is still a lack of systematic research in this field. In this work, a comparative study of the Cu-M bimetal catalysts (BMCs) for CO2RR-to-syngas is carried out using density functional theory (DFT) calculations to examine the crystal orientation effects. The results indicate that the reaction barrier is significantly changed on different crystal orientations. Gibbs free energy change of the potential limiting step (ΔGPLS) on the Cu (110) surface is lower than those on the Cu (111) and Cu (100) surfaces. The Cu-Pd catalyst exhibits better catalytic activity for HER than Cu-Ag, Cu-Ni, Cu-Zn, and Cu-Cd catalysts. CO2RR activity of the Cu-Pd catalyst is better than that of most of the catalysts reported so far. The Cu-Ni catalyst exposing the Cu(100) surface is the only catalyst which is more favorite to CO2RR than HER. This work provides guidance for the design of highly efficient catalysts for CO2RR-to-syngas.

Electrochemical conversion of CO2 to syngas over Cu-M (M = Cd, Zn, Ni, Ag, and Pd) bimetal catalysts

The electrochemical reduction of CO2 to syngas (H2 + CO) offers a resultful solution for the ongoing carbon emission and energy crisis issues. However, there are still few efficient catalysts for CO2RR-to-syngas electrolysis. Herein, a density functional theory (DFT) study of the Cu-M (M = Cd, Zn, Ni, Ag, and Pd) bimetal catalysts (BMCs) for CO2RR and HER is reported. The results indicate that the reaction barrier is significantly changed in the electrochemical conversion of CO2 into CO and HER by changing the Cu/M ratio. d band center (εd) has a good linear relationship with ΔGH*, ΔGCOOH* and ΔGCO*, so εd is a good descriptor for hydrogen reduction reaction (HER) and carbon dioxide reduction reaction (CO2RR) activity. The Cu-Pd catalyst displays outstanding catalytic activity for HER and CO2RR. HER activity of the Cu-Pd catalyst is even comparable to that of the current most effective Pt catalysts. Compared with other catalysts with different Cu/M ratios (Cu/M = 0.5 and Cu/M = 2), the Cu-Cd catalyst at low Cu/Cd ratio (0.5) is the only catalyst which is more favorite to CO2RR than HER. This theoretical study may provide guidance to design the effective electrocatalysts for the CO2RR and HER, and shed light on the application of Cu-based bimetal materials in syngas production.

CO Oxidation at Near-Ambient Temperatures over TiO2-Supported Pd-Cu Catalysts: Promoting Effect of Pd-Cu Nanointerface and TiO2 Morphology.

Significant improvement of the catalytic activity of palladium-based catalysts toward carbon monoxide (CO) oxidation reaction has been achieved through alloying and using different support materials. This work demonstrates the promoting effects of the nanointerface and the morphological features of the support on the CO oxidation reaction using a Pd-Cu/TiO2 catalyst. Pd-Cu catalysts supported on TiO2 were synthesized with wet chemical approaches and their catalytic activities for CO oxidation reaction were evaluated. The physicochemical properties of the prepared catalysts were studied using standard characterization tools including SEM, EDX, XRD, XPS, and Raman. The effects of the nanointerface between Pd and Cu and the morphology of the TiO2 support were investigated using three different-shaped TiO2 nanoparticles, namely spheres, nanotubes, and nanowires. The Pd catalysts that are modified through nanointerfacing with Cu and supported on TiO2 nanowires demonstrated the highest CO oxidation rates, reaching 100% CO conversion at temperature regime down to near-ambient temperatures of ~45 °C, compared to 70 °C and 150 °C in the case of pure Pd and pure Cu counterpart catalysts on the same support, respectively. The optimized Pd-Cu/TiO2 nanowires nanostructured system could serve as efficient and durable catalyst for CO oxidation at near-ambient temperature.

Influence of H2 availability in the catalytic reduction of nitrates in fixed bed reactors

The effect of H2 availability in the catalytic reduction of NO3− was studied through experimental tests and theoretical estimations of mass transfer regime for H2, CO2 and NO3−. The experiments were carried out in a fixed bed reactor packed with bimetallic 0.75% (w) Pd-Cu catalysts supported on granular activated carbon at 25 °C. External mass transfer limitations were only significant in the case of H2 and resulted in lower selectivity to NH4+, particularly in the low gas surface velocity range (0.09–0.019 cm/s). Low availability of H2, becoming the limiting reagent for the reaction, contributed to lower selectivity to NH4+ due to lower H:N ratio at the catalyst surface. Decreasing space–time also led to lower selectivity to NH4+, probably due to the neutralization of OH− by the available H+ at catalytic sites, thus controlling local pH and favoring N2 production. Reduction of selectivity to NH4+ was achieved with lower loss of activity and NO3− conversion when gas flow was decreased than when liquid flow was decreased. The results indicate that the design and operation of reactors for the catalytic reduction of NO3− should consider conditions leading to H2 transfer control in order to reduce selectivity to NH4+, even though this could be at the expense of reaction rate and NO3− conversion.

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.

Tuning the intermediate reaction barriers by a CuPd catalyst to improve the selectivity of CO2 electroreduction to C2 products

Electrochemical CO2 reduction is a promising strategy for the utilization of CO2 and intermittent excess electricity. Cu is the only single metal catalyst that can electrochemically convert CO2 into multicarbon products. However, Cu exhibits an unfavorable activity and selectivity for the generation of C2 products because of the insufficient amount of CO* provided for the C-C coupling. Based on the strong CO2 adsorption and ultrafast reaction kinetics of CO* formation on Pd, an intimate CuPd(100) interface was designed to lower the intermediate reaction barriers and improve the efficiency of C2 product formation. Density functional theory (DFT) calculations showed that the CuPd(100) interface enhanced the CO2 adsorption and decreased the CO2* hydrogenation energy barrier, which was beneficial for the C-C coupling. The potential-determining step (PDS) barrier of CO2 to C2 products on the CuPd(100) interface was 0.61 eV, which was lower than that on Cu(100) (0.72 eV). Encouraged by the DFT calculation results, the CuPd(100) interface catalyst was prepared by a facile chemical solution method and characterized by transmission electron microscopy. CO2 temperature-programmed desorption and gas sensor experiments further confirmed the enhancement of the CO2 adsorption and CO2* hydrogenation ability of the CuPd(100) interface catalyst. Specifically, the obtained CuPd(100) interface catalyst exhibited a C2 Faradaic efficiency of 50.3% ± 1.2% at −1.4 VRHE in 0.1 M KHCO3, which was 2.1 times higher than that of the Cu catalyst (23.6% ± 1.5%). This study provides the basis for the rational design of Cu-based electrocatalysts for the generation of multicarbon products by fine-tuning the intermediate reaction barriers.

Nanoporous Pd-Cu thin films as highly active and durable catalysts for oxygen reduction in alkaline media

A facile electrochemical etching approach was developed and implemented to enhance the electrocatalytic performance of Pd-Cu films for oxygen reduction reaction (ORR) in alkaline media. The nanoporous (np) Pd-Cu was synthesized through electrochemical de-alloying of pre-deposited Pd-Cu films. Scanning electron microscopy (SEM) with energy dispersive spectroscopy was employed to confirm the residual amount of Cu in the np structure. The accordingly prepared np catalysts showed excellent ORR activity up to 1.11 A/mgPd at a potential of 0.9 V vs. RHE which is around 22-times and 6.2-times higher than that of a plain Pd film and commercial Pd/C catalyst, respectively. The ORR activity enhancement is attributed to the unique porous structure, large Pd surface area, and modified electronic structure of Pd with residual Cu as confirmed by the SEM, hydrogen underpotential deposition, and CO stripping characterizations. The np Pd-Cu catalyst also showed excellent durability which is manifested by a negligible decrease in the half-wave potential (4 mV negative shift) after 10,000 potential cycles in alkaline media. These findings provide insights into the rational design of an electrocatalyst's structure utilizing an electrochemical de-alloying method to achieve high atomic utilization and improved catalytic performance.

Crystallographic Orientation Dependence of Surface Segregation and Alloying on PdCu Catalysts for CO2 Hydrogenation.

The influence of the crystallographic orientation on surface segregation and alloy formation in model PdCu methanol synthesis catalysts was investigated in situ using near-ambient pressure X-ray photoelectron spectroscopy under CO2 hydrogenation conditions. Combined with scanning tunneling microscopy and density functional theory calculations, the study showed that submonolayers of Pd undergo spontaneous alloy formation on Cu(110) and Cu(100) surfaces in vacuum, whereas they do not form an alloy on Cu(111). Upon heating in H2, inward diffusion of Pd into the Cu lattice is favored, facilitating alloying on all Cu surfaces. Under CO2 hydrogenation reaction conditions, the alloying trend becomes stronger, promoted by the reaction intermediate HCOO*, especially on Pd/Cu(110). This work demonstrates that surface alloying may be a key factor in the enhancement of the catalytic activity of PdCu catalysts as compared to their monometallic counterparts. Furthermore, it sheds light on the hydrogen activation mechanism during catalytic hydrogenation on copper-based catalysts.

Influence of metal ratio on alumina-supported CuPd catalysts for the production of tetrahydrofuran from succinic acid

The present research studies the influence of metal ratio on the construction of γ-Al2O3 supported CuxPdy (x + y = 10 wt%) bimetallic catalysts for the hydrogenation of succinic acid (SA) to tetrahydrofuran (THF). Synergistic effects between Cu and Pd due to alloying formation are responsible for the enhanced activity of the bimetallic catalysts compared to the monometallic ones. The Cu-rich CuPd catalysts, particularly Cu8Pd2/γ-Al2O3 and Cu6Pd4/γ-Al2O3, have emerged as the best catalysts for the production of THF with yields of 85–90%. The key factor that distinguishes them from the rest is the presence of isolated Cu components which holds the potential for further reduction of the intermediate γ-butyrolactone while restraining the hydrogenolysis of SA to butyric acid over the Pd sites.