Pd-Cu Catalysts Research Articles

Synergistic effects of second metals on performance of (Co, Ag, Cu)-doped Pd/Al2O3 catalysts for 2-ethyl-anthraquinone hydrogenation

Hydrogenation of 2-ethyl-anthraquinone (EAQ) has been studied over Al2O3-supported monometallic Pd and bimetallic Pd-Co, Pd-Ag, and Pd-Cu catalysts prepared by incipient wetness co-impregnation method. The catalytic performance of the bimetallic catalysts could be greatly affected by the reduction temperature and mass ratio of the second metal (M=Co, Ag, Cu) to Pd (M/Pd). The highest catalytic activity, along with the high selectivity is achieved over Pd-Co catalysts having M/Pd=0.25 reduced at a low temperature of 80°C, with an increase in an order of magnitude in the reaction rate compared to the monometallic Pd catalyst. This could be ascribed to the synergistic effects of the Pd-Mα+ structure formed at low reduction temperature, which is confirmed by the results of H2-TPR, FTIR of CO adsorbed, STEM-EDX and XPS characterizations. The experimental data were satisfactorily fitted to a Langmuir-Hinshelwood (L-H) model involving a surface reaction controlling mechanism for EAQ hydrogenation. The results revealed that the surface reaction rate constant remarkably increased over bimetallic Pd-Co and Pd-Ag catalysts, implying that their superior activity is due to the more facile activation of carbonyl bond of EAQ on Pd-Mα+ sites than on Pd sites.

A novel process for nitrate reduction in water using bimetallic Pd-Cu catalysts supported on ion exchange resin

In this work, a Pd-Cu catalyst supported on a macroporous anion exchange resin was used in two novel processes to treat water contaminated with nitrates. The catalytic performance was evaluated in a continuous fixed bed reactor. The process (Reaction+Ion Exchange) – Regeneration, named RIE-R, has two steps: 1- reaction and ion exchange (RIE); 2- Regeneration (R). It was found that a hydrogen flow rate increase does not affect the nitrate removal efficiency during the RIE step, while the selectivity to nitrogen decreased. The presence of competing ions (sulphate, bicarbonate, chlorides) led to a decrease in the nitrate removal efficiency. In any case, the water obtained in the process meets the limits established by the World Health Organization. During the regeneration step, carried out by bubbling hydrogen to the catalytic bed, 100% of nitrates present in the resin at the end of the RIE cycle were eliminated.The other process, named IE-R, has a first step in which only ion exchange of nitrates occurs, and a second one during which the catalyst is regenerated. This process has worse performance compared to the RIE-R. Only 36.7% of the nitrates present in the resin at the beginning of the regeneration were eliminated.The catalyst was characterized by CO chemisorption, SEM, EPMA, TEM, and XRD. Pd migration towards the external surface occurs during the reaction, and also a decreased in dispersion takes place, leading to a small decrease in activity detected in consecutive reaction-regeneration cycles.A regeneration mechanism is presented.

Electroreduction of Carbon Dioxide to Hydrocarbons Using Bimetallic Cu-Pd Catalysts with Different Mixing Patterns.

Electrochemical conversion of CO2 holds promise for utilization of CO2 as a carbon feedstock and for storage of intermittent renewable energy. Presently Cu is the only metallic electrocatalyst known to reduce CO2 to appreciable amounts of hydrocarbons, but often a wide range of products such as CO, HCOO-, and H2 are formed as well. Better catalysts that exhibit high activity and especially high selectivity for specific products are needed. Here a range of bimetallic Cu-Pd catalysts with ordered, disordered, and phase-separated atomic arrangements (Cuat:Pdat = 1:1), as well as two additional disordered arrangements (Cu3Pd and CuPd3 with Cuat:Pdat = 3:1 and 1:3), are studied to determine key factors needed to achieve high selectivity for C1 or C2 chemicals in CO2 reduction. When compared with the disordered and phase-separated CuPd catalysts, the ordered CuPd catalyst exhibits the highest selectivity for C1 products (>80%). The phase-separated CuPd and Cu3Pd achieve higher selectivity (>60%) for C2 chemicals than CuPd3 and ordered CuPd, which suggests that the probability of dimerization of C1 intermediates is higher on surfaces with neighboring Cu atoms. Based on surface valence band spectra, geometric effects rather than electronic effects seem to be key in determining the selectivity of bimetallic Cu-Pd catalysts. These results imply that selectivities to different products can be tuned by geometric arrangements. This insight may benefit the design of catalytic surfaces that further improve activity and selectivity for CO2 reduction.

Catalytic Transfer Hydrogenation of Furfural to 2-Methylfuran and 2-Methyltetrahydrofuran over Bimetallic Copper-Palladium Catalysts.

The catalytic transfer hydrogenation of furfural to the fuel additives 2-methylfuran (2-MF) and 2-methyltetrahydrofuran (2-MTHF) was investigated over various bimetallic catalysts in the presence of the hydrogen donor 2-propanol. Of all the as-prepared catalysts, bimetallic Cu-Pd catalysts showed the highest catalytic activities towards the formation of 2-MF and 2-MTHF with a total yield of up to 83.9 % yield at 220 °C in 4 h. By modifying the Pd ratios in the Cu-Pd catalyst, 2-MF or 2-MTHF could be obtained selectively as the prevailing product. The other reaction conditions also had a great influence on the product distribution. Mechanistic studies by reaction monitoring and intermediate conversion revealed that the reaction proceeded mainly through the hydrogenation of furfural to furfuryl alcohol, which was followed by deoxygenation to 2-MF in parallel to deoxygenation/ring hydrogenation to 2-MTHF. Finally, the catalyst showed a high reactivity and stability in five catalyst recycling runs, which represents a significant step forward toward the catalytic transfer hydrogenation of furfural.

Innovative ZrO2-supported CuPd catalysts for the selective production of hydrogen from methanol steam reforming

Low temperature methanol steam reforming (MSR) is an attractive source of nearly CO-free H2 for fuel cells application. However, there is still a lack of efficient catalysts able to operate at low temperatures (≤220°C), where MSR is equilibrium-limited. Pd-based catalysts are regarded as an alternative to conventional Cu-based catalysts for MSR, but their low MSR selectivity limit their application. This work studies the effect of Cu as MSR promoter of Pd/ZrO2 catalysts, with special emphasis on the improvement of MSR selectivity. The influence of ZrO2 structure support, monoclinic and cubic, on the MSR behavior is also studied. CuPd/ZrO2-m catalysts with enhanced activity and MSR selectivity are developed. This superior performance was attributed to a strong interaction between Pd and Cu and an enhanced dispersion of the metal phase when ZrO2 with monoclinic structure was used as support.

Electrochemical Oxidation of Polyalcohols in Alkaline Media on Palladium Catalysts Promoted by the Addition of Copper

Pd-Cu catalysts (Pd63Cu37/C, Pd46Cu54/C, Pd28Cu72/C, Pd11Cu89/C) and Pd/C were synthesized, characterized, and used to electrochemically oxidize ethylene glycol (EG), propylene glycol (PG), and glycerol (G). The oxidation rate at −0.4V vs SCE after 3hours on each PdCu/C catalyst was compared Pd/C. The oxidation rate for every polyalcohol on every PdCu/C catalyst was at least 3 times greater than on the Pd/C catalyst. The greatest promotion for the oxidation of EG was observed on Pd28Cu72/C (7 times faster), for PG was on Pd11Cu89/C (12 times), and for G was on Pd63Cu37/C (14 times). We observe a decrease in density of states near the Fermi level with increasing amount of Cu and a shift of the d-band center away from the Fermi energy. This surface electronic perturbation could be one of the factors affecting the oxidation of the polyalcohols. A second factor could be the bi-functional effect as we also observe an increase in hydroxyl adsorption at lower potentials on all PdCu/C compared to Pd/C. Therefore, we suggest that the combination of both of these effects, electronic and bifunctional, contributes to the promotion of the oxidation of these polyalcohols. Furthermore, the ratio of Cu to Pd appears to play an important role in the oxidation rate.

Preparation of PdCu Alloy Nanocatalysts for Nitrate Hydrogenation and Carbon Monoxide Oxidation

Alloying Pd with Cu is important for catalytic reactions such as denitrification reaction and CO oxidation reaction, but understanding of the catalyst preparation and its correlation with the catalyst’s activity and selectivity remains elusive. Herein, we report the results of investigations of the preparation of PdCu alloy nanocatalysts using different methods and the catalytic properties of the catalysts in catalytic denitrification reaction and CO oxidation reaction. PdCu alloy nanocatalysts were prepared by conventional dry impregnation method and ligand-capping based wet chemical synthesis method, and subsequent thermochemical activation as well. The alloying characteristics depend on the bimetallic composition. PdCu/Al2O3 with a Pd/Cu ratio of 50:50 was shown to exhibit an optimized hydrogenation activity for the catalytic denitrification reaction. The catalytic activity of the PdCu catalysts was shown to be highly dependent on the support, as evidenced by the observation of an enhanced catalytic activity for CO oxidation reaction using TiO2 and CeO2 supports with high oxygen storage capacity. Implications of the results to the refinement of the preparation of the alloy nanocatalysts are also discussed.

에틸렌글리콜 양 조절에 의해 제조된 팔라듐구리 촉매를 이용한 개미산연료전지 성능평가

에틸렌글리콜 양 조절에 의해 제조된 팔라듐구리 촉매를 이용한 개미산연료전지 성능평가

Highly-active Pd–Cu electrocatalysts for oxidation of ubiquitous oxygenated fuels

Nanostructured palladium-copper electrocatalysts with Pd:Cu ratios of 1:3, 1:1, and 3:1 were synthesized using a Sacrificial Support Method (SSM) in combination with the thermal reduction of metal precursors. The materials were comprehensively characterized by X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning and Transmission Electron Microscopy (SEM and TEM), surface area measurements (Brunauer-Emmett-Teller, BET) and Differential Electrochemical Mass Spectroscopy (DEMS). The SSM method enables the preparation of nano-sized unsupported Pd-Cu catalysts with uniformly-distributed particles and high surface area, in the range of 40m2gcatalyst−1. Their catalytic activity for the electrooxidation of several alcohols (methanol, ethanol, ethylene glycol and glycerol) was investigated in alkaline media. In situ Infrared Reflection Adsorption Spectroscopy (IRRAS) and Density Functional Theory (DFT) calculations were used in order to understand the mechanism of the various alcohols electrooxidation reactions.

Highly selective catalysts for liquid-phase hydrogenation of substituted alkynes based on Pd—Cu bimetallic nanoparticles

Catalytic properties of Pd—Cu bimetallic catalysts supported on SiO2 and Al2O3 were studied in a model reaction of selective hydrogenation of diphenylacetylene. Application of PdCu2(AcO)6 heterobimetallic acetate complex as a precursor made it possible to obtain homogeneous Pd—Cu bimetallic nanoparticles. This result was supported by the data of IR spectroscopy of adsorbed CO. The Pd-Cu catalysts showed considerably higher selectivity than monometallic samples. Moreover, the introduction of copper decreases the hydrogenation rate of diphenylethylene (DPE) to diphenylethane. As a result, the maximum yield of the target product, DPE, increased from 78 to 93% in the presence of Pd—Cu catalysts.

Synergistic integration of catalysis and ion-exchange for highly selective reduction of nitrate into N2

An integrated process synergistically combining the advantages of catalysis and ion-exchange is demonstrated for the selective and complete degradation of NO3− from contaminated water. To realize this process, PdCu catalysts were supported on an ion-exchange resin. The functional resin captures NO3− in an ion-exchange mode, whereas the concentrated NO3− in the resin is fully reduced by the supported PdCu in a catalytic regeneration mode. The complete conversion of the captured NO3− indicates that the solid-state diffusion of NO3− within the resin is possible through consecutive ion-hopping. Catalytic resin regeneration under H2/CO2 (1/1, v/v) was found to reduce NO3− to N2 selectively without the formation of the toxic byproduct NH4+. The complete suppression of the NH4+ formation (∼100% N2 selectivity) has never been reported previously. It is well known that the accumulation of OH− ions generated during the NO3− reduction significantly enhances the formation of NH4+. We propose that OH− ions generated on the catalyst surface are rapidly captured by the ion-exchange sites of the resin, thus minimizing the detrimental interaction between OH− and the catalyst surface. The ion-exchange/catalytic regeneration cycle could be repeated up to five times without a loss of the NO3− ion-exchange capacity or catalytic regenerability.

PdCu Nanoalloy Electrocatalysts in Oxygen Reduction Reaction: Role of Composition and Phase State in Catalytic Synergy.

The catalytic synergy of nanoalloy catalysts depends on the nanoscale size, composition, phase state, and surface properties. This report describes findings of an investigation of their roles in the enhancement of electrocatalytic activity of PdCu alloy nanoparticle catalysts for oxygen reduction reaction (ORR). Pd(n)Cu(100-n) nanoalloys with controlled composition and subtle differences in size and phase state were synthesized by two different wet chemical methods. Detailed electrochemical characterization was performed to determine the surface properties and the catalytic activities. The atomic-scale structures of these catalysts were also characterized by high-energy synchrotron X-ray diffraction coupled with atomic pair distribution function analysis. The electrocatalytic activity and stability were shown to depend on the size, composition, and phase structure. With Pd(n)Cu(100-n) catalysts from both methods, a maximum ORR activity was revealed at Pd/Cu ratio close to 50:50. Structurally, Pd50Cu50 nanoalloys feature a mixed phase consisting of chemically ordered (body-centered cubic type) and disordered (face-centered cubic type) domains. The phase-segregated structure is shown to change to a single phase upon electrochemical potential cycling in ORR condition. While the surface Cu dissolution occurred in PdCu catalysts from the two different synthesis methods, the PdCu with a single-phase character is found to exhibit a tendency of a much greater dissolution than that with the phase segregation. Analysis of the results, along theoretical modeling based on density functional theory calculation, has provided new insights for the correlation between the electrocatalytic activity and the catalyst structures.

Selective hydrogenolysis of sorbitol to ethylene glycol and propylene glycol on ZrO2-supported bimetallic Pd-Cu catalysts

Sorbitol is one of the key building blocks in catalytic conversion of biomass, and its selective hydrogenolysis to ethylene glycol and propylene glycol provides a viable and sustainable route towards the synthesis of the two glycols. Herein, the hydrogenolysis of biomass-derived sorbitol was studied on Pd-modified Cu/monoclinic zirconia (Pd-Cu/ZrO2) catalysts with a wide range of Cu/Pd atomic ratios in the presence of La(OH)3. The bimetallic Pd-Cu/ZrO2 catalysts showed superior activities and selectivities to the two target glycols, compared with the monometallic Cu/ZrO2 and Pd/ZrO2 catalysts under identical conditions. At nearly 100% sorbitol conversion, a combined selectivity of 61.7% to ethylene glycol, propylene glycol, and glycerol was obtained on Pd-Cu/ZrO2 (Cu/Pd=5) at 493 K under 5.0 MPa H2. Pd-Cu/ZrO2 was also stable and recyclable, in contrast to Cu/ZrO2, which suffered severe deactivation because of agglomeration of Cu particles during sorbitol hydrogenolysis. Clearly, the presence of Pd improved not only the activity and selectivity of the Cu catalyst, but also the hydrothermal stability. Characterization of these catalysts by X-ray diffraction, diffuse-reflectance infrared Fourier transform spectroscopy of CO adsorption, and H2 temperature-programmed reduction suggests that the Cu particles deposited on the Pd surfaces with close contact and strong interaction between the two metals, most likely involving electron transfer from Pd to Cu. Such structural and electronic effects are proposed as the critical contributors to the significant promoting effect of Pd on the activity and stability of Pd-Cu catalysts in sorbitol hydrogenolysis. These findings provide useful information for design of new Cu-based catalysts with higher efficiency and stability for selective hydrogenolysis of polyols and other biomass-derived reactants under hydrothermal conditions.

Optimisation of preparation method for Pd doped Cu/Al2O3 catalysts for selective acetylene hydrogenation

3 preparation methods were explored for preparing CuPd catalysts for selective acetylene hydrogenation leading to materials which were selective and active at lower temperatures than normally observed for Cu catalysts.

One-Pot Regioselective Synthesis of 5-Amino-3-Benzyl-7H-[1,3]Thiazolo[3,2-A]Pyrimidin-7-Ones via Sonogashira Coupling Reaction

GRAPHICAL ABSTRACT

Cu/Al2O3 catalysts modified with Pd for selective acetylene hydrogenation

A Cu/alumina catalyst has been modified by addition of various quantities of Pd. Characterisation suggests formation of a bimetallic with the surface dominated by Cu. Optimisation of the Cu:Pd ratio (50:1) resulted in a catalyst which combined the properties of Cu and Pd (high ethylene selectivity and activity at low temperature). Using a 3:1 H2:acetylene feed, >99% acetylene conversion and >70% ethylene selectivity was attained at 373K, representing a considerable reduction in the temperature necessary to achieve equivalent activity/selectivity over monometallic Cu. Increasing the H2:acetylene ratio to 10 resulted in >99% acetylene conversion at 363K as well as enhanced ethylene selectivity (>80%). Enhanced activity of Cu at low temperature is attributed to H2 dissociation on Pd with spillover onto Cu sites where the reaction takes place. These bimetallic CuPd catalysts offer sufficient activity at low temperature and could represent a replacement to the current industrial PdAg catalysts.

Synthesis of Co-Deposited Electroless Pd-Cu Catalyst for Nitrate Reduction

Electrochemical and thermodynamic data obtained from the determination of the corrosion potentials of Cu and Pd in various reducing agents (formaldehyde, hypophosphite and ammonia borane) and their mixtures was used to formulate a stable electroless bath for co-deposition of Cu and Pd on Al2O3 substrate. The electrolessly deposited Pd-Cu catalyst was characterized using SEM, EDAX and BET measurements. The Pd-Cu catalyst on alumina was found to be active for nitrate reduction in aqueous solution. The activity and composition of the catalyst increased with electroless plating time up to 30 minutes whereupon the variation of metal composition was minimal. The BET measurement showed that the electroless plating decreases the BET surface area of the catalyst thereby suggesting a macroporous mechanism for nitrate reduction on electroless Pd-Cu catalyst. The supported electroless Pd-Cu catalyst converted most of the nitrate in solution into preferred nitrogen gas product rather than ammonia.

Synthesis of Co-Deposited Electroless Pd-Cu Catalyst for Nitrate Reduction

Electrochemical and thermodynamic data obtained from the determination of the corrosion (or open circuit potential or oxidation/reduction) potentials of Cu and Pd in various reducing agents (formaldehyde, hypophosphite and ammonia borane) and their mixtures was used to formulate a stable electroless bath for co-deposition of Cu and Pd on Al2O3 substrate. The electrolessly deposited Pd-Cu catalyst was characterized using SEM, EDAX and BET measurements. The Pd-Cu catalyst on alumina was found to be active for nitrate reduction in aqueous solution. The activity and composition of the catalyst increased with electroless plating time up to 30 minutes whereupon the variation of metal composition was minimal. The BET measurement showed that the electroless plating decreases the BET surface area of the catalyst thereby suggesting a macroporous mechanism for nitrate reduction on electroless Pd-Cu catalyst. A comparison of the performance of supported electroless Pd-Cu catalyst versus unsupported, precipitated Pd-Cu-containing particles showed that the unsupported Pd-Cu particles reduced nitrate at a faster rate than the Al2O3 supported electroless Pd-Cu catalyst but produced more ammonia. The supported electroless Pd-Cu catalyst converted most of the nitrate in solution into preferred nitrogen gas product rather than ammonia.

나노 크기의 타이타니아 담체를 활용한 Pd-Cu 촉매의 수중 질산성 질소 저감 반응에의 적용

In this study, we synthesized TiO2 supports with nanosized crystalline structure by solvothermal method and prepared TiO2 supported Pd-Cu catalysts. It was shown that the crystalline size of TiO2 support in the catalyst influenced on the catalytic activity of nitrate reduction in water. The catalyst with the smaller crystalline size of TiO2 support presented faster nitrate reduction rate, but had low nitrogen selectivity due to high pH environment of reaction medium during the reaction. Through injection of carbon dioxide as a pH buffer, the nitrogen selectivity increased by about 60%. Furthermore, we investigated that the relationships between the catalytic performance and the physicochemical properties of the prepared catalysts characterized by N2 adsoprtion-desorption, X-ray diffraction (XRD), H2-temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS).

ZrO2-modified Al2O3-supported PdCu catalysts for the water denitrification reaction

Monometallic Pd and bimetallic Pd–Cu catalysts supported on alumina, zirconia and ZrO2–Al2O3 mixed oxides of different composition were prepared and evaluated in the catalytic denitrification of water. The supports were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray (SEM/EDX), NH3-adsorption thermogravimetry and specific surface areas measured by the BET method. XRD studies showed that the predominant phase in the ZrO2-modified Al2O3 supports is the metastable tetragonal phase (57%) of zirconia. SEM/EDX results indicated that ZrO2 crystals are distributed homogeneously on the supports. Temperature-programmed reduction (TPR) experiments carried out on bimetallic PdCu catalysts showed that Pd is well dispersed on the modified supports and that there is a strong interaction between both metals. The modification of Al2O3 by the addition of ZrO2 not only improved the activity but also the selectivity to N2 of the PdCu catalysts.