Palladium-copper Catalysts Research Articles

Tandem Electrocatalytic Alkyne Semihydrogenation over Bicomponent Catalysts through Hydrogen Spillover.

Electrocatalytic alkyne semihydrogenation under mild conditions is a more attractive approach for alkene production than industrial routes but suffers from either low production efficiency or high energy consumption. Here, we describe a tandem catalytic concept that overcomes these challenges. Component (i), which can trap hydrogen effectively, is partnered with component (ii), which can readily release hydrogen for hydrogenation, to enable efficient generation of active hydrogen on component (i) at low overpotentials and timely (i)-to-(ii) hydrogen spillover and facile desorptive hydrogenation on component (ii). We examine this concept over bicomponent palladium-copper catalysts for the production of representative 2-methyl-3-butene-2-ol (MBE) from 2-methyl-3-butyne-2-ol (MBY) and achieve a record high MBE production rate of 1.44 mmol h-1 cm-2 and a Faraday efficiency of ~88.8 % at a low energy consumption of 1.26 kWh kgMBE -1. With these catalysts, we further achieve 60 h continuous production of MBE with record high profit space.

Novel Cu and Pd-Cu Catalysts Supported on Multi-Walled Carbon Nanotubes for Steam Reforming and Decomposition of Methanol

In this study, multi-walled carbon nanotubes (MWCNTs) were prepared by chemical vapour deposition (CVD) using acetylene as a carbon source over an iron catalyst. As-prepared MWCNTs were used to support modern mono-copper, palladium, and bimetallic palladium-copper catalysts, and their feasibility for hydrogen production was tested during steam reforming of methanol (SRM) and methanol decomposition (DM). The structural characteristics of the MWCNTs were evaluated using the SEM and XRD methods. The physicochemical properties of the monometallic and bimetallic catalysts were analysed using the TPR and XRD methods. The promotion effect of palladium on methanol conversion rate and H2 productivity in the case of the copper catalysts was demonstrated. The enhanced activity of the Cu/MWCNTs after palladium promotion was due to the formation of Pd-Cu alloy compound.

One-Pot Synthesis of (Z)-β-Halovinyl Ketones via the Cascade of Sonogashira Coupling and Hydrohalogenation

Herein, we report an efficient method for the synthesis of (Z)-β-halovinyl ketones through a one-pot Sonogashira coupling and hydrohalogenation reaction promoted by palladium-copper catalyst and Brønsted acid. The ynone intermediates are generated in situ from readily available acid chlorides and terminal alkynes at room temperature, which are directly converted to (Z)-β-halovinyl ketones by treating with triflic acid. This method avoids the use of an external halogen source and features broad substrate scope, high yield, and good to excellent stereoselectivity.

Mechanistic Studies of Methanol Synthesis Reaction over Cu and Pd–Cu Catalysts

Monometallic copper and bimetallic palladium–copper catalysts supported on ZnO–Al2O3, CeO2–Al2O3 and ZrO2–Al2O3 were prepared by conventional impregnation method and tested in the methanol synthesis reaction in a gradient less reactor under elevated pressure (3.5 MPa) at 220°C. The physicochemical properties of prepared catalytic systems were studied using BET, TPR-H2, TPD-NH3, XRD, SEM-EDS and FT-IR techniques. The results of XRD and SEM-EDS measurements showed the formation of Pd–Cu alloy during the activation of bimetallic catalysts. It was found that the formed alloy was responsible for the improved activity and selectivity of catalysts in the studied reaction. Among investigated catalysts, the highest formation rate of methanol was observed with 2%Pd–20%Cu/ZnO–Al2O3 system. Based on the results of FT-IR measurements it can be concluded that hydrogen molecules adsorb dissociatively on the metallic copper surface to form hydrogen atoms, increasing the hydrogen spillover effect on the metal-support interface. In contrast, CO2 adsorb on the oxygen vacancies of the support to form carbonates, which can further undergo hydrogenation to methanol.

Oxygen reduction on bimodal nanoporous palladium–copper catalyst synthesized using sacrificial nanoporous copper

Abstract

Direct Synthesis of Hydrogen Peroxide Using Cs-Containing Heteropolyacid-Supported Palladium–Copper Catalysts

The direct synthesis of hydrogen peroxide (H2O2) from molecular hydrogen and oxygen could represent a green and economically attractive alternative to the current indirect anthraquinone process used for the industrial production of hydrogen peroxide. This reaction has been investigated using palladium supported on the Cs-containing heteropolyacid Cs2.5H0.5PW12O40. In addition, the effect of adding copper as a potential activity promoter was investigated. These catalysts were also evaluated for the subsequent degradation of hydrogen peroxide. The catalytic activity of the 0.5 wt%Pd/Cs2.5H0.5PW12O40 catalyst towards hydrogen peroxide synthesis was greater than that of both the mono-metallic Cu or bi-metallic Pd–Cu analogues with the incorporation of Cu to Pd resulting in a significant decrease in catalytic selectivity for the formation of hydrogen peroxide. Moreover, 0.5 wt%Pd/Cs2.5H0.5PW12O40 also showed low activity towards the degradation of hydrogen peroxide. Hence the use of the Cs-containing heteropolyacid as a support for Pd gives higher rates of hydrogen peroxide formation when compared with different supported Pd catalysts prepared using supports used in previous studies.

Bimetallic Pd–Cu/ZnO–Al2O3 and Pd–Cu/ZrO2–Al2O3 catalysts for methanol synthesis

Monometallic copper and bimetallic palladium-copper catalysts supported on ZnO–Al2O3 and ZrO2–Al2O3 were prepared by conventional impregnation method and tested in methanol synthesis reaction under elevated pressure (3.5 MPa) in gradientless reactor at 220°C. The physicochemical properties of prepared catalytic systems were studied using BET, X-ray, TPR-H2, TPD-NH3 techniques. The promotion effect of palladium on catalytic activity and selectivity of copper supported catalyst in methanol synthesis reaction was proven. The highest activity of this system is explained by the Pd–Cu alloy formation.

Bimetallic Pd-Cu/ZnO-Al2O3 and Pd-Cu/ZrO2-Al2O3 Catalysts for Methanol Synthesis

Monometallic copper and bimetallic palladium-copper catalysts supported on ZnO-Al 2 O 3 and ZrO 2 -Al 2 O 3 were prepared by conventional impregnation method and tested in methanol synthesis reaction under elevated pressure (3.5 MPa) in gradientless reactor at 220 °C. The physicochemical properties of prepared catalytic systems were studied using BET, X-Ray, TPR-H 2 , TPD-NH 3 techniques. The promotion effect of palladium on catalytic activity and selectivity of copper supported catalyst in methanol synthesis reaction was proven. The highest activity of this system is explained by the Pd-Cu alloy formation.

Elimination of nitrate in secondary effluent of wastewater treatment plants by Fe0 and Pd-Cu/diatomite

Abstract Because total nitrogen (TN), in which nitrate (NO3–) is dominant in the effluent of most wastewater treatment plants, cannot meet the requirement of Chinese wastewater discharge standard (<15 mg/L), NO3– elimination has attracted considerable attention. In this research, the novel diatomite-supported palladium-copper catalyst (Pd-Cu/diatomite) with zero-valent iron (Fe0) was tried to use for catalytic reduction of nitrate in wastewater. Firstly, specific operational conditions (such as mass ratio of Pd:Cu, catalyst amounts, reaction time and pH of solution) were optimized for nitrate reduction in artificial solution. Secondly, the selected optimal conditions were further employed for nitrate elimination of real effluent of a wastewater treatment plant in Beijing, China. Results showed that 67% of nitrate removal and 62% of N2 selectivity could be obtained under the following conditions: 5 g/L Fe0, 3:1 mass ratio (Pd:Cu), 4 g/L catalyst, 2 h reaction time and pH 4.3. Finally, the mechanism of catalytic nitrate reduction was also proposed.

Synergistic Effects in Bimetallic Palladium-Copper Catalysts Improve Selectivity in Oxygenate Coupling Reactions.

Condensation reactions such as Guerbet and aldol are important since they allow for C-C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts. A combination of XRD, EXAFS, TEM, and CO chemisorption and TPD revealed the formation of CuPd bimetallic nanoparticles with a Cu-enriched surface. Finally, density functional theory studies suggest that the surface segregation of Cu atoms in the bimetallic alloy catalyst produces Cu sites with increased reactivity, while the Pd sites responsible for unselective decarbonylation pathways are selectively poisoned by CO.

Reduction of Nitrate in Secondary Effluent of Wastewater Treatment Plants by Fe0 Reductant and Pd–Cu/Graphene Catalyst

Nitrate reduction has attracted considerable attention from wastewater in wastewater management because total nitrogen (TN), in which nitrate (NO3 −) is dominant in the effluent of most wastewater treatment plants, cannot meet the requirement of Chinese wastewater discharge standard (<15 mg/L). In this study, the novel graphene–supported palladium–copper catalyst (Pd–Cu/graphene) with Fe0 reductant was investigated in the advanced treatment of nitrate. Series of specific operational conditions (such as mass ratio of Pd:Cu, catalyst amounts, reaction time, and pH of solution) were optimized for nitrate reduction in the artificial solution, and then, the selected optimal conditions were further applied for investigating the nitrate elimination of real effluent of a wastewater treatment plant in Beijing, China. Results indicated that 82 % of nitrate removal and 66 % of N2 selectivity could be obtained under the optimum condition: 5 g/L Fe0, 3:1 mass ratio (Pd:Cu), 4 g/L catalyst, 2 h reaction time, and pH 5.1. Finally, the nitrate catalytic reduction mechanism was also analyzed and interpreted.

Low temperature selective oxidation of methane to methanol using titania supported gold palladium copper catalysts

Selective oxidation of methane using AuPdCu/TiO2 catalysts.

Supported palladium–copper catalysts: Preparation and catalytic behavior in hydrogen-related reactions

Two series of highly dispersed supported Pd–Cu catalysts were prepared using different supports: highly acidic aluminum fluoride HS-AlF3, characterized by high surface area, and active carbon, both prepared by different preparation methods (fluorolytic sol–gel method and co-impregnation). A variety of techniques: chemisorption of hydrogen, XRD, TEM, and catalytic performance in two hydrogen-related probe reactions (in n-pentane hydroisomerization and CCl4 hydrodechlorination) were employed to probe metal dispersion and the extent of interaction between two metal components. A reasonable degree of bimetal intermixing in Pd–Cu/HS-AlF3 catalysts synthesized by fluorolytic co-gelation was recognized by the catalytic behavior in bifunctional hydroisomerization of n-pentane. A significantly decreased, compared to pure palladium, hydrogenation–dehydrogenation potential of Pd–Cu alloys led to a weaker performance of bimetallic catalysts. Similarly, it was found that incipient wetness co-impregnation of active carbon resulted in the formation of catalysts characterized by good metal dispersion and significant extent of Pd–Cu alloying. Although the monometallic 2wt% Cu/carbon catalyst is nearly inactive in CCl4 hydrodechlorination, copper addition to palladium in the co-impregnated catalysts had very pronounced effect, vastly increasing the selectivity toward longer than methane hydrocarbons.

Applicability of a catalytic reduction method using a palladium–copper catalyst and hydrazine for the denitration of a highly concentrated nitrate salt solution

Denitration of a highly concentrated sodium nitrate (NaNO3) aqueous solution via a catalytic reduction method using a palladium–copper catalyst supported on carbon powder (Pd–Cu/C) and hydrazine (N2H4) was investigated. It was demonstrated that nitrate ion (NO3 −) in a 5 mol L−1 NaNO3 solution was completely reduced through an intermediate nitrite ion (NO2 −) to nitrogen compounds such as nitrogen, nitrous oxide, and ammonia. By comparing the reaction rates of NO3 − and NO2 − obtained using catalysts with various Pd–Cu compositions and different reductants (hydrogen (H2) or N2H4), it was determined that the catalyst with a molar ratio of Pd:Cu = 1:0.66 provides the maximum reaction rates for NO3 − and NO2 − using N2H4, and that not only the reactions of NO3 − and NO2 − but also that of N2H4 were affected by the Pd–Cu composition.

Kinetics of Nitrate Hydrogenation in Water on Alumina and Niobia Supported Palladium-Copper Catalysts

Abstract The kinetics of nitrate hydrogenation in water over niobia- and alumina-supported Pd-Cu catalysts were examined. A Langmuir-Hinshelwood kinetic model fitted concentration data, providing consistent kinetic and thermodynamic parameters. The kinetic model assumed a bimolecular surface reaction as the rate-determining step, with two types of sites. Pd-Cu/gamma-Al2O3 was active and selective under the reaction conditions. However, Pd-Cu/Nb2O5 deactivated during time on stream, and a deactivation function was added to the kinetic model to best fit the experimental data.

Highly active Pd[sbnd]Cu catalysts for electrooxidation of 2-propanol

A sacrificial support method (SSM) in combination with chemical reduction of metal precursors was used for the preparation of palladium–copper catalysts. Three materials with Pd:Cu ratios of 1:3, 1:1 and 3:1 were synthesized and characterized by XRD, SEM, TEM and BET methods. The catalytic activity for the electrooxidation of 2-propanol was investigated. The SSM method allowed for the preparation of nano-sized unsupported PdCu catalysts with uniformly distributed particles. The surface area of all materials was in the range of 50m2g−1. The mass activity of Pd3Cu catalyst 790mAg−1Pd is significantly higher than other reports in the literature making this material state-of-the-art in the reaction of 2-propanol electrooxidation.

Hydrogen sulfide tolerance of palladium–copper catalysts for PEM fuel cell anode applications

The H 2S-tolerance of Palladium–Copper nanoparticle catalysts supported on carbon black employed on PEMFC anodes operating on H 2S-contaminated anode feeding streams is described. The anode feeding consists of 80% H 2, ∼20% N 2 (in vol.), and 8 ppm H 2S. Catalyst performances were evaluated by estimating the cell potential reduction due to H 2S contamination through lifetime tests. It is found that the H 2S-tolerance of PdCu catalysts depends on the concentration of copper, as confirmed by a catalyst pre-leaching procedure. This methodology is employed in order to remove copper atoms from the catalyst surface, which is confirmed by energy dispersive X-ray spectroscopy and X-ray diffraction techniques. This method generates catalysts with lower copper content and higher susceptibility to H 2S. Moreover, it is proposed a new and effective catalytic activity recovering technique to restore the performance of PdCu catalysts after H 2S exposure.

Hydrogen-assisted dechlorination of 1,2-dichloroethane on active carbon supported palladium–copper catalysts

A series of active carbon supported palladium–copper catalysts with varying amounts of both metal components and overall metal loading 2 wt.%, prepared by incipient wetness impregnation were characterized by temperature programmed reduction (TPR), hydrogen chemisorption, temperature programmed (palladium) hydride decomposition (TPHD), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). TPHD and XRD studies indicated that the bimetallic Pd–Cu/C catalysts exhibited a considerable degree of alloying. Pd/C, Cu/C and Pd–Cu/C catalysts were investigated in the hydrodechlorination (HdCl) of 1,2-dichloroethane in the gas phase at a relatively low reaction temperature (210–230 °C). All catalysts showed fair stability with time on stream (up to ∼15 h). The Pd/C and Pd-rich Pd–Cu catalysts essentially retained their initial activity while the bimetallic samples with higher Cu content exhibited some deactivation at the initial stage of reaction. Cu-rich bimetallic samples exhibited the highest selectivities toward ethene (desired reaction product), >90%. For all bimetallic Pd–Cu/C samples, this selectivity gradually increased with time on stream. XPS studies of freshly reduced and post-reaction catalysts did not support the hypothesis that during hydrodechlorination the surface of Pd–Cu is being gradually enriched in copper, as could be expected of a higher affinity of copper to chlorine. Post-reaction deposits investigated by the temperature programmed hydrogenation (TPH) showed substantial amounts of chlorine on the copper catalyst, whereas all palladium-containing Pd–Cu/C samples exhibited only carbon-containing deposit, with C 2-hydrocarbons desorbing at a relatively low temperature (300 °C). Suggested interpretation of catalytic data includes both the role of C 2H x species building up on catalyst's surface during hydrodechlorination as well as the role of Pd–Cu mixed sites in the mechanism of hydrogen-assisted dechlorination of 1,2-dichloroethane.

ChemInform Abstract: Novel Synthesis of Functionalized Benzo(b)furans (III) and Homologues by Use of a Palladium-Copper Catalyst System.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Nitrate catalytic reduction in water using niobia supported palladium–copper catalysts

Niobia and alumina supported palladium catalyst promoted by copper were investigated in the reaction of nitrate catalytic reduction in water and characterized by temperature programmed reduction, physisorption, H2 chemisorption and X-ray diffraction. Niobia supported Pd–Cu catalysts were as active and selective as an alumina supported catalyst. All catalysts had similar turnover frequencies independent of the support. The control of pH and the interaction between Pd and Cu were critical to improving the selectivity and activity of Pd–Cu/Nb2O5 catalysts.