Bimetallic Pd-Ni Catalysts Research Articles

Bimetallic catalysts for the hydrogenation of aromatic nitro compounds

The catalytic activity of bimetallic Pd-Ni, Pd-Cu, and Pd-Ag catalysts in the reaction of nitrobenzene hydrogenation was studied. It was found that the rate of hydrogenation on the bimetallic catalysts was higher than that on palladium metal (palladium black), and it depended on catalyst preparation pro cedures. The catalytic activity of the bimetallic systems increased in the order Pd-Cu< Pd-Ag ≪ Pd-Ni.

Characterization and reactivity of Al2O3 supported Pd-Ni bimetallic catalysts for hydrodechlorination of chlorobenzene

A series of Al2O3 supported bimetallic Pd-Ni catalysts were prepared by deposition–precipitation method. The physico-chemical properties of the catalysts were evaluated by different characterization techniques such as temperature programmed reduction (TPR), temperature programmed desorption of H2 (TPD), X-ray photoelectron spectroscopy (XPS), Braunner–Emmet–Teller (BET) surface area and pulse CO chemisorption. The activities of bimetallic Pd-Ni/Al2O3 catalysts were evaluated for continuous fixed bed gas phase hydrodechlorination of chlorobenzene operating at 140°C under atmospheric pressure. The activity profiles demonstrate that an exceptional activity and stability of Pd-Ni/Al2O3 catalysts is accomplished by judicial variation of Ni composition with respect to Pd, which had arrived at Pd and Ni in 0.5:0.5 (wt%) ratio, while high Ni loaded Pd-Ni catalysts exhibit poorer stability. The high activity and stability of optimal catalyst is invoked due to formation of very active Pd-Ni interfaces embedded with Pdδ+ species, whereas lower stability resulted in high Ni loaded catalysts is due to aggregation of Ni component on topical Pd surface. The activity of mono and bimetallic catalysts are well correlate with the characterization results.

Nanoporous PdNi Bimetallic Catalyst with Enhanced Electrocatalytic Performances for Electro-oxidation and Oxygen Reduction Reactions

A nanoporous PdNi (np-PdNi) bimetallic catalyst fabricated by electrochemically dealloying a Pd20Ni80 alloy in an acid solution is reported. Residual Ni in the nanoporous alloy can be controlled by tuning dealloying potentials and the electrocatalysis of the np-PdNi shows evident dependence on Ni concentrations. With ∼9 at.% Ni, the np-PdNi bimetallic catalyst presents superior electrocatalytic performances in methanol and formic acid electro-oxidation as well as oxygen reduction in comparison with commercial Pd/C and nanoporous Pd (np-Pd). The excellent electrocatalytic properties of the dealloyed np-PdNi bimetallic catalyst appear to arise from the combined effect of unique bicontinuous nanoporosity and bimetallic synergistic action.

Biogas reforming over bimetallic PdNi catalysts supported on phosphorus-modified alumina

A series of bimetallic PdNi catalysts supported on alumina modified with different amounts of phosphorus (0.5–5 wt%) were prepared. The effect of phosphorus content on the structure, surface properties and catalytic behavior of supported PdNi catalysts in biogas reforming was studied. The physicochemical properties of the samples were characterized by using different techniques: N 2 adsorption–desorption isotherms, X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (TPD), thermogravimetric and differential thermal analysis (TG/DTA) and scanning transmission electron microscopy (STEM). The catalytic properties of the catalysts were evaluated in the reaction of reforming of methane with CO 2. It was shown that increasing the P content (≥1 wt%) leads to agglomeration of the metal Ni particles, as well as to increase of the total acidity of the catalysts. Within bimetallic system, the PdNi catalyst with 0.5 wt% phosphorus showed the best performance and stability caused by the presence of highly dispersed nickel particles on the catalyst surface due to the strong interaction between supported species and alumina.

Preparation of Pd-Ni Bimetallic Catalyst Supported on Polyphenol-Grafted Collagen Fiber and Its Catalytic Behavior in Nitrobenzene Hydrogenation

Preparation of Pd-Ni Bimetallic Catalyst Supported on Polyphenol-Grafted Collagen Fiber and Its Catalytic Behavior in Nitrobenzene Hydrogenation

High performance of a carbon supported ternary PdIrNi catalyst for ethanol electro-oxidation in anion-exchange membrane direct ethanol fuel cells

In this paper, we report the synthesis of a carbon supported ternary PdIrNi catalyst for the ethanol oxidation reaction in anion-exchange membrane direct ethanol fuel cells (AEM DEFCs). We demonstrate that the use of the ternary PdIrNi catalyst at the anode of an AEM DEFC can increase the peak power density by more than 122% as compared with the use of the monometallic Pd catalyst, 69% as compared with the use of the bimetallic PdIr catalyst, and 44% as compared with the use of the bimetallic PdNi catalyst. Cyclic voltammetry and chronopotentiometry analyses prove that the ternary PdIrNi catalyst is catalytically much more active and more stable than the monometallic Pd catalyst and the bimetallic PdIr and PdNi catalysts.

Influence of ni addition to a low-loaded palladium catalyst on the selective hydrogenation of 1-heptyne

Semi-hydrogenation of alkynes has industrial and academic relevance on a large scale. To increase the activity, selectivity and lifetime of monometallic catalysts, the development of bimetallic catalysts has been investigated. 1-Heptyne hydrogenation over low-loaded Pd and Ni monometallic and PdNi bimetallic catalysts was studied in liquid phase at mild conditions. XPS results suggest that nickel addition to Pd modifies the electronic state of palladium as nickel loading is increased. Low-loaded Pd catalysts showed the highest selectivities (> 95%). The most active prepared catalyst, PdNi(1%), was more selective than the Lindlar catalyst.

MCM-41 supported PdNi catalysts for dry reforming of methane

A series of bimetallic PdNi catalysts supported on mesoporous MCM-41 with different Ni content (Ni/Si ratio of 0.2–0.4) was synthesized. The effect of Pd addition to Ni-containing catalysts as well as the effect of the Ni content on the surface and catalytic properties of the catalysts was studied. The samples were characterized using various techniques, such as energy-dispersive X-ray spectroscopy, N2 adsorption–desorption isotherms, X-ray diffraction, thermogravimetric and differential analyses, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and temperature-programmed reduction. Reforming of methane with carbon dioxide was used as a test reaction. The results indicated that the addition of a small amount of Pd (0.5%) to Ni-containing catalysts leads to formation of small nano-sized, easy reducible NiO particles. Agglomeration of NiO as well as of metallic nickel phase over PdNi samples increased with increasing the Ni content. Formation of filamentous carbon over surface of spent monometallic Ni and bimetallic PdNi catalyst was observed. In spite of filamentous carbon deposition, the catalytic activity and stability of bimetallic PdNi catalysts are higher than those of monometallic Ni one. Within bimetallic system, the PdNi catalyst with Ni/Si ratio of 0.3 revealed the best performance and stability caused by presence of small nickel particles well dispersed on the catalyst surface.

Catalytic performance and QXAFS analysis of Ni catalysts modified with Pd for oxidative steam reforming of methane

Pd–Ni bimetallic catalysts prepared by co-impregnation and sequential impregnation methods were compared in the catalytic performance in oxidative steam reforming of methane. The sequential impregnation was more effective to the suppression of hot spot formation. According to the structural analysis by in situ quick-scanning X-ray absorption fine structure (QXAFS) during the temperature programmed reduction, the sequential impregnation method gave the bimetallic particles with higher Pd surface composition because of the low possibility of the Pd–Ni bond formation. Higher surface composition of Pd with higher reducibility than Ni is connected to the enhancement of the catalyst reducibility and the suppression of the hot spot formation.

Hydrodechlorination of 1,2-dichloroethane on active carbon supported palladium–nickel catalysts

Two series of 2 wt.% Pd–Ni/active carbon catalysts prepared from chloride and nitrate salts were characterized by hydrogen chemisorption, temperature programmed palladium hydride decomposition and X-ray diffraction, and investigated in the hydrodechlorination of 1,2-dichloroethane in the gas phase at a relatively low reaction temperature (210–230 °C). All catalysts showed very high stability with time on stream. Ni-rich bimetallic samples exhibited the highest selectivities towards ethene (desired reaction product). Addition of palladium, the metal which is known for its high hydrogenation activity, resulted in a massive production of ethane, at the expense of ethene. The correlation between the turnover frequency towards ethene and Pd–Ni phase composition resembles very much an expected relationship between surface and bulk composition of Pd–Ni alloys. This suggests that surface nickel atoms are the active sites for hydrogen-assisted dechlorination of 1,2-dichloroethane. The overall results indicate that, in agreement with the literature, palladium segregates to the surface of Pd–Ni (even during hydrodechlorination), shaping the overall catalytic behavior of bimetallic Pd–Ni catalysts. The monometallic, 2 wt.% Ni/C prepared from the chloride precursor, was the only catalyst which showed a noticeable selectivity for vinyl chloride which gradually increased with time on stream. The temperature programmed hydrogenation of deposits left after the reaction showed the presence of surface carbon and rather negligible amounts of chlorine.

Model bimetallic Pd-Ni automotive exhaust catalysts: Influence of thermal aging and hydrocarbon self-poisoning

Bimetallic Pd-Ni catalysts supported on Al2O3 and (Ce,Zr)Ox/Al2O3 were examined with respect to their catalytic performance for the elimination of CO, NO and C3H6 under stoichiometric conditions. The effects of a thermal aging treatment at 1273K, reactant competition in the presence of the hydrocarbon and the influence of the presence of nickel in the catalyst have been analysed by XRD, HREM, catalytic activity measurements and in situ DRIFTS spectroscopy. Self-poisoning effects, induced by the presence of the hydrocarbon in the reactant mixture, were identified as the main factor affecting the light-off activity. While a Ni-induced preferential interaction between Pd and the Ce-Zr mixed oxide component appears, in general terms, to be beneficial for the catalytic performance of the fresh (Ce,Zr)Ox/Al2O3-supported bimetallic catalyst, it is shown to be detrimental for the aged system as a consequence of a facilitated degradation of the (Ce,Zr)Ox component and encapsulation of the active palladium particles.

Direct Oxidation of Methane by Pd–Ni Bimetallic Catalyst over Lanthanum Chromite Based Anode for SOFC

Abstract Steady generation of electricity with dry CH4 fuel, 150 mW·cm−2 at 1073 K and 360 mW·cm−2 at 1173 K, was successfully performed by a low loading of Pd–Ni bimetallic catalyst on a lanthanum chromite based porous-composite anode for solid oxide fuel cells (SOFC). The amounts of carbon deposition were quite small under the open and closed circuit conditions. The electrocatalytic activity of the Pd–Ni catalyst was significantly higher than that of Pd or Ni catalysts.

Catalytic hydrodechlorination of hexachlorobenzene on carbon supported Pd-Ni bimetallic catalysts

The study of the catalytic activity of carbon supported Pd-Ni catalysts for the hydrodechlorination of hexachlorobenzene was carried out in the liquid phase. The degree of dechlorination was found proportional to the surface Pd concentration, which is enhanced by the segregation of this element at the surface of the bimetallic particles.It is also shown that isolated Pd atoms located at the surface of Ni rich bimetallic particles are more active than those lying in larger ensembles.Finally bimetallic Pd-Ni catalysts containing only between 20 and 50 Pd atom%, although less active than pure Pd, lead to 75% of useful compounds, i.e. benzene, mono and dichlorobenzene.

Properties of Supported Pd-Ni Catalysts Prepared by Coexchange and by Organometallic Chemistry: I. Preparation and Characterization by X-Ray-Diffraction, Analytical Microscopy, and EXAFS

Silica-supported Pd-Ni bimetallic catalysts were prepared either by coexchange or via surface organometallic chemistry. In this later case, Ni(C5H5)2 was allowed to react with a reduced Pd/SiO2. The temperature of formation of the alloy was determined by in situ X-ray diffraction performed under flowing H2 and the atomic order was determined by EXAFS. It is shown that the alloy is already formed at 620 K with organometallic precursors, whereas 840 K is necessary with coexchanged solids. A comparison between the X-ray methods and a careful analysis of the particle composition by EDX-STEM shows that the organometallic route leads to nearly homogeneous alloys. Alloy formation also occurs with coexchanged precursors; however, nickel in strong interaction with the support and unalloyed palladium are also observed.