Pd Ni Catalysts Research Articles

Effect of Pt and Pd promoter on Ni supported catalysts—A TPR/TPO/TPD and microcalorimetry study

The promoting effect of Pt and Pd in bimetallic Ni–Pt and Ni–Pd catalysts supported on alumina nano-fibre (Alnf) were tested for the liquid phase reforming of sorbitol to produce hydrogen. The mono- and bimetallic catalysts were studied by different characterisation techniques such as: temperature programmed reduction, oxidation, CO desorption, microcalorimetry, TEM and STEM/EDX. Although bimetallic catalysts have long been the subject of great interest because of their exceptional properties compared to the monometallic catalysts, the reason behind their improved activity is still a question of debate. Experimental evidence showed that the addition of both Pt and Pd—even in a very small fraction—to the Ni catalyst increases its reducibility significantly. The TEM and STEM/EDX analysis confirmed that Pt and Ni are present as alloys in nano-sized rod shaped particles. At the same time it was found that the CO differential heat of adsorption is appreciably lowered in the bimetallic catalysts. This is substantial because reducing the CO binding strength can avoid the poisoning of the active metal sites. As a result, we demonstrate that the rate of H 2 formation from sorbitol reforming was 3 to 5 times higher for bimetallic catalysts when compared to the monometallic catalysts.

Activity and selectivity for hydroisomerisation of n-decane over Ni impregnated Pd/H-mordenite catalysts

Nickel impregnated Pd/H-mordenite catalysts with different Ni contents were synthesised and tested for hydroisomerisation of n-decane with flow H2 gas. The XRD analysis of the catalysts showed the decrease of intensity with increase in Ni addition. The average metal particle size, measured by TEM, is also increased by increasing the Ni loading up to 0.2 wt.%. The acidity of the catalysts measured by TPD of ammonia revealed the ion-exchange of the some acid sites by Ni2+. The oxidation states of Pd and Ni were identified by XPS. The reducibility of H-mordenite supported Pd, Ni and Ni-Pd catalysts was studied by TPR. The catalytic activities of Ni containing and Ni free Pd/H-mordenite catalysts were studied and found that addition of Ni up to 0.2 wt.% over 0.1 wt.% Pd/H-mordenite, increased the n-decane conversion and isomerisation selectivity. As the Ni content exceeded 0.2 wt.%, the conversion and cracked products are found to decrease and increase. Further Ni containing Pd/H-mordenite showed increased sustainability and favoured the protonated cyclopropane (PCP) intermediate mechanism in n-decane isomerisation. It has been concluded that Ni impregnated Pd/H-mordenite showed good activity towards n-decane isomerisation where isomerized products mixture showed better octane number.

Maximising carbon nanofiber and hydrogen production in the catalytic decomposition of ethylene over an unsupported Ni-Cu alloy

Abstract A Ni-Cu (4:1 wt/wt) metal alloy catalyst has been studied for the catalytic decomposition of ethylene to produce hydrogen and carbon nanofibers. To maximise ethylene conversion in a horizontal tube reactor with high residence times, hydrogen yields and selectivities, the temperature, sample mass and ethylene flow rate were varied. Both high ethylene conversions (>80%) and high hydrogen selectivities (75%) were obtained at 873 and 923 K. The highest coke yield obtained after just 3 h was around 480 gC/gNi+Cu at 873 K (86% ethylene conversion) and was significantly higher than the value of 250 gC/gNi+Cu which was previously reported as the maximum coke yield for the decomposition of ethylene over Ni-Cu catalysts at this temperature. At 923 K, the optimum conditions were achieved with 50 mg of Ni-Cu, which gave ethylene conversions of 74%, a hydrogen selectivity of 71%, hydrogen yields in excess of 4000 mo l H 2 / mo l Ni + Cu and even higher coke yields of 1112 gC/gNi+Cu after 15 h with the catalyst still possessing high catalytic activity. The Ni-Cu (4:1 wt/wt) catalyst behaved similarly to a Ni-Pd (4:1 wt/wt) catalyst, which suggests that unsupported Ni-Cu alloys can replace the more expensive Ni-Pd alloys for the catalytic decomposition of hydrocarbons. In addition, there were no obvious structural differences between the carbon nanofibers obtained with the Ni-Cu and Ni-Pd alloys, which were twisted, branched and straight nanofibers composed of crystalline and amorphous carbon with diameters ranging from 30 to 300 nm.

Synthesis and characterization of electrodeposited Ni–Pd alloy electrodes for methanol oxidation

A wide compositional range of Ni–Pd alloy catalysts were prepared by electrodeposition for use as anode materials for methanol oxidative fuel cells in alkaline conditions. Structural characterization of the electrocatalysts in their as-plated condition revealed that the Ni–Pd catalysts synthesized were nanocrystalline, single phase, face centered cubic materials, indicating the formation of complete solid solution in the alloy. Compositional analysis of the alloys indicated that the palladium composition of the alloy increased with decrease in current density. This change in the composition of the alloy resulted in a shift in the X-ray diffraction peaks. The percentage shift in the d-spacing calculated from X-ray diffraction is in good agreement with percentage of palladium in the alloy. The electrocatalysts prepared are active for methanol oxidation in alkaline medium.

Effect of Ni, Pd and Ni–Pd nano-islands on morphology and structure of multi-wall carbon nanotubes

In this research, the effect of Ni, Pd and Ni–Pd catalysts have studied on morphology and structure of synthesized multi-wall carbon nanotubes (MWCNTs). Initially, thin films of Ni (with two thicknesses of 10 and 20 nm), Pd/Ni (5/10 nm) and Pd (10 nm) were deposited as catalysts on SiO 2 (60 nm)/Si(1 0 0) substrates, using dc magnetron sputtering technique. The deposited films were annealed at 900 °C in ammonia environment for 45 min, in order to obtain nano-structured catalyst on the surface. Using scanning electron microscopy (SEM), the average size of Ni nano-islands (synthesized by the 10 and 20 nm Ni films), Pd and Ni–Pd nano-islands were measured about 55, 110, 45 and 50 nm, respectively. According to X-ray photoelectron spectroscopy analysis (XPS), the ratio of Ni/Pd on the surface was about 3 for the bilayer sample. The CNTs were synthesized on the nano-island catalysts at 940 °C in CH 4 ambient using a thermal chemical vapor deposition method. The results revealed that average diameter of the CNTs were about 70, 110, 120 nm for Ni, Ni–Pd and Pd catalysts, respectively. Raman spectra of the MWCNTs showed that intensity ratio of two main peaks located in the range of 1550–1600 and 1250–1450 cm −1 (as a quality factor for the CNTs) for Ni, Pd and Ni–Pd catalysts were 1.42, 0.91 and 0.85, respectively. Therefore, based on our data analysis, although addition of Pd to Ni catalyst caused a considerable reduction in the quality of the grown MWCNTs as compared to the pure Ni catalyst, but it resulted in an enhancement in the methane decomposition rate. For the pure Pd catalyst samples, both a slow methane decomposition rate as compared with Ni–Pd catalyst samples and a poor quality of CNTs were observed as compared with the Ni catalyst, under similar experimental conditions.

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.

Surface modification of Ni catalysts with trace Pd and Rh for oxidative steam reforming of methane

Abstract Bimetallic catalysts (Pd–Ni and Rh–Ni) were prepared by co-impregnation and sequential impregnation methods to investigate catalytic performance in oxidative steam reforming of methane. These bimetallic catalysts gave high methane conversion even at low W / F such as 0.07 g h/mol. The thermographical observation clearly demonstrated that the catalyst bed temperature was strongly dependent on the preparation method. The bimetallic catalyst prepared from the sequential impregnation method exhibited much higher resistance to hot-spot formation in oxidative reforming of methane. In particular, Pd–Ni catalysts prepared by the sequential impregnation method showed higher resistance to hot-spot formation than monometallic Pd and Ni catalysts, and this can be a synergetic effect of Pd and Ni. Temperature-programmed reduction (TPR) with H 2 revealed that the addition of Pd or Rh by a sequential impregnation method greatly promoted the reduction of Ni species. Extended X-ray absorption fine structure (EXAFS) analysis confirmed the formation of Pd–Ni alloy and the preferential location of Pd atoms on the surface of the bimetallic particles over the Pd/Ni catalysts. Surface modification of Ni with Pd by sequential impregnation is effective for promotion of the activity and suppression of hot-spot formation.

DRIFTS–XANES study of Pd-Ni/(Ce,Zr)O x/Al 2O 3 model automotive catalysts

Pd-Ni catalysts supported on Al 2O 3 and (Ce,Zr)O x /Al 2O 3, both in fresh and thermally aged states, were examined with the main aim of determining the effects of Ni and Ce-Zr mixed oxide on the catalytic activity for CO and C 3H 6 oxidation, and NO reduction reactions under stoichiometric conditions. For this purpose, catalytic activity results were analysed in conjunction with DRIFTS and XANES spectra recorded under reaction conditions to obtain information on the processes occurring in the catalysts during the course of the reactions. While a nickel-induced promotion of the formation of contacts between palladium and the Ce-Zr mixed oxides generally enhances the CO oxidation performance of the catalyst, it results detrimental to the NO reduction activity. This has been related to the higher difficulty in achieving the most active metallic palladium state for comparatively similar particle sizes in the presence of such contacts. Comparison of DRIFTS spectra under various reactant mixtures and between fresh and aged systems was shown to explain in a unique way the detrimental catalytic effects of hydrocarbon self-poisoning and sintering of the active components in the catalysts.

06/00140 Preparation and characterization of PtSn/C anodeelectrocatalysts for direct ethanol fuel cell: Jiang, L. et al. Catalysis Today, 2004, 93–95, (1), 665–670

Carbon-supported PdNi catalysts for the ethanol oxidation reaction in alkaline direct ethanol fuel cells are successfully synthesized by the simultaneous reduction method using NaBH4 as reductant. X-ray diffraction characterization confirms the formation of the face-centered cubic crystalline Pd and Ni(OH)2 on the carbon powder for the PdNi/C catalysts. Transmission electron microscopy images show that the metal particles are well-dispersed on the carbon powder, while energy-dispersive X-ray spectrometer results indicate the uniform distribution of Ni around Pd. X-ray photoelectron spectroscopy analyses reveal the chemical states of Ni, including metallic Ni, NiO, Ni(OH)2 and NiOOH. Cyclic voltammetry and chronopotentiometry tests demonstrate that the Pd2Ni3/C catalyst exhibits higher activity and stability for the ethanol oxidation reaction in an alkaline medium than does the Pd/C catalyst. Fuel cell performance tests show that the application of Pd2Ni3/C as the anode catalyst of an alkaline direct ethanol fuel cell with an anion-exchange membrane can yield a maximum power density of 90 mW cm−2 at 60 °C.

Catalytic Behavior of Pd–Ni/Composite Anode for Direct Oxidation of Methane in SOFCs

Electrocatalysis of a Pd–Ni/composite anode (small amounts of Pd–Ni catalyst on a lanthanum chromite-based porous composite anode) for direct oxidation of dry methane in solid oxide fuel cells (SOFCs) was studied at . Synergy of Pd and Ni catalysts was observed for the direct oxidation of dry methane. Maximum power densities with the Pd–Ni/composite anode were 150 and at 1073 and , respectively. Carbon deposition on the Pd–Ni/composite anode was quite low under both open- and closed-circuit conditions. Therefore, stable power generation was performed under the closed-circuit condition, and no physical damage was observed for the cell under the open-circuit condition with dry methane. XRD analysis suggested the formation of Pd–Ni alloy on the composite anode. A suitable reaction scheme for the direct oxidation of dry methane over the Pd–Ni/composite anode was proposed on the basis of the kinetic experiment, the gasification experiment of the deposited carbon by steam, and impedance spectra. The decomposition of to and C, and the gasification of C by to and CO, are key reactions for the effective direct oxidation of dry over the Pd–Ni/composite anode.

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.

The effect of Ni in Pd–Ni/(Ce,Zr)O x/Al 2O 3 catalysts used for stoichiometric CO and NO elimination. Part 2: Catalytic activity and in situ spectroscopic studies

Pd–Ni catalysts supported on Al 2O 3, (Ce,Zr)O x /Al 2O 3, and (Ce,Zr)O x were examined with the principle objective of determining the effects of Ni on catalytic activity for CO oxidation and NO reduction reactions under stoichiometric conditions. Catalytic activity findings for the CO + O 2 and CO + O 2 + NO reactions were analyzed in conjunction with in situ DRIFTS and XANES results to obtain information on the processes occurring in the catalysts during the course of the reactions. The results reveal a significant dependence on the nature of the support in terms of the catalytic changes produced by nickel. In the absence of significant nickel-induced electronic perturbations of palladium, these are related to indirect effects on palladium distribution over the catalysts or to a certain impediment of the interactions between active palladium and Ce–Zr mixed-oxide components. Significant promotion of CO oxidation was observed for the (Ce,Zr)O x /Al 2O 3-supported catalyst, which reveals a relevant role for the particle size of the nanostructured Ce–Zr mixed oxide in this reaction.

The effect of Ni in Pd–Ni/(Ce,Zr)O x/Al 2O 3 catalysts used for stoichiometric CO and NO elimination. Part 1: Nanoscopic characterization of the catalysts

Pd–Ni catalysts supported on Al 2O 3, (Ce,Zr)O x /Al 2O 3, and (Ce,Zr)O x are characterized at a nanoscopic level using mainly electron microscopy-related techniques (HREM images, XEDS, and Z-contrast images/EELS spectra done with TEM and STEM instruments). The presence of rather homogeneous Ce–Zr mixed oxide nanostructures is revealed from analysis of HREM pictures. Analysis of the Pd–Ni/(Ce,Zr)O x /Al 2O 3 system shows the existence of preferential interactions of Pd and Ni with the (Ce,Zr)O x and Al 2O 3 components, respectively, as evidenced mainly by XEDS and confirmed by FMR. Dispersion states of the metals and particle size distributions of palladium are inferred from analysis of Z-contrast images and EELS spectra. The results are complemented by XPS and XAFS results used to analyse the chemical state of the metallic components in the catalysts and their dispersion over the different supports.

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.

Hydrogen production on Ni–Pd–Ce/γ-Al 2O 3 catalyst by partial oxidation and steam reforming of hydrocarbons for potential application in fuel cells

A series of catalysts of nickel–palladium–cerium supported upon alumina have been investigated in order to obtain a suitable catalyst that could be used in the process of producing hydrogen for the potential application in fuel cell by partial oxidation and steam reforming (POSR) of mixtures of hydrocarbons. Investigated results showed that little addition of cerium into Ni–Pd catalyst could definitely improve its stability of hydrogen production from mixtures of hydrocarbons by POSR method. The experimental results also showed that the optimum compositions of Ni–Pd–Ce catalyst were the molar ratio of Ni to Pd as 1:0.09 and containing of Ce 0.5 wt%, shortened as Ni–Pd–Ce-0.5 catalyst. XRD results for the typical catalysts showed that it mainly displayed the γ-Al 2O 3 and Ni peaks. SEM and TG results for the fresh and used Ni–Pd–Ce-0.5 catalysts, lasted for 540 h, did not show much difference on their surface patterns and TG curves, respectively. This indicated this catalyst would be a practical catalyst to produce hydrogen from liquid fuel by POSR method for potential application in fuel cells.

Synergy of Pd and Ni Catalysts for Direct Oxidation of Methane Over Lanthanum Chromite Based Anodes

Continuous operation of solid oxide fuel cells (SOFC) with dry methane fuel was performed with a low loading of Pd-Ni catalyst on a lanthanum chromite based porous composite anode at 1073-1173 K. Synergy of Pd and Ni catalysts was observed for the direct oxidation of methane. The maximum power densities with the Pd-Ni/composite anode were 150 mW cm -2 at 1073 K and 360 mW cm -2 at 1173 K. No physical damage was observed for the SOFC during the exposure experiment of the Pd-Ni/composite anode to methane under open circuit conditions. A suitable reaction scheme is proposed for the Pd-Ni synergy catalysts for the direct oxidation of dry methane.

Methane decomposition into hydrogen and carbon nanofibers over supported Pd–Ni catalysts

The effect of the addition of different metals (Cu, Rh, Pd, Ir, and Pt) into supported Ni catalysts on the catalytic performance of methane decomposition into pure hydrogen and carbon was examined. The addition of Pd brought about considerable increases in the catalytic life and in the accumulated yields of hydrogen and carbon at the complete deactivation of the catalyst, while modification with the other metals decreased the yields compared to those for Ni/SiO 2. For the Ni catalysts modified with Pd, the appropriate preparation conditions of the catalysts, the effect of catalytic supports, and the optimum reaction temperature on the methane decomposition were examined. The hydrogen yield attained a high value, 16,000 mol H 2 /mol Pd+Ni, when Pd and Ni were of a mole ratio Pd/(Pd+Ni)=0.5 and a total loading Pd+Ni=37 wt% on carbon nanofiber support. This yield is the highest among those reported so far. Methane decomposition over Ni catalysts modified with Pd produced carbon nanofibers with unique structures, i.e., branched carbon nanofibers. XRD studies on the Ni catalysts modified with Pd indicated the formation of Pd–Ni alloys. The alloys are responsible for the increase in the catalytic life and the formation of carbon nanofibers with unique structures.

Hydrogen Production from Partial Oxidation and Steam Reforming of N‐octane Over Alumina‐supported Ni and Ni‐Pd Catalysts

AbstractHydrogen production by partial oxidation and steam reforming (POSR) of n‐octane was investigated over alumina‐supported Ni and Ni‐Pd catalysts. It showed that Ni‐Pd/Al2O3 had higher activity and hydrogen selectivity than the nickel catalyst under the experimental conditions, which indicated Ni‐Pd/Al2O3 could be an effective catalyst for the production of hydrogen from hydrocarbons.

Investigation of alumina-supported Ni and Ni-Pd catalysts by partial oxidation and steam reforming of n-octane

Aseries of nickel and nickel-palladium supported upon alumina catalysts were prepared in order to obtain a suitable catalyst that could be used in the process of producing hydrogen by partial oxidation and steam reforming of n-octane. Hydrogen production by partial oxidation and steam reforming (POSR) of n-octane was investigated over alumina-supported Ni and Ni-Pd catalysts. The process occurred by a combination of exothermic partial oxidation and endothermic steam reforming of n-octane. It was found that Ni/Al2O3 catalyst activity was high at high temperatures and increased with the Ni loadings. Its activity, however, was not obviously increased when Ni loadings were over 5.0 wt%. Compared with nickel catalyst, the bimetallic catalyst of Ni-Pd/A12O3 showed markedly increased activity and hydrogen selectivity at experimental conditions. The catalytic performance also became more stable when the palladium was added, which indicated that palladium plays an essential role in the catalytic action. The used catalysts of Ni-Pd/A12O3 were regenerated three times by using air at space velocity of 2,000 h−1 to obtain a long duration catalyst. Also, the typical catalyst was characterized by using SEM, BET, TG and ICP methods in detail.

Characterization of alumina-supported Ni and Ni-Pd catalysts for partial oxidation and steam reforming of hydrocarbons

Hydrogen production by partial oxidation and steam reforming (POSR) of n-octane has been investigated over alumina-supported Ni and Ni-Pd catalysts. The process was found to occur by a combination of exothermic partial oxidation and endothermic steam reforming. Ni/γ-Al2O3 catalysts had good activity at high temperatures; the activity increased with increasing Ni loadings up to 5.0wt.%. However, the Ni/γ-Al2O3 catalysts rapidly lost activity during the POSR process. XRD results showed that an increase in the particle size was the main reason for the poor stability of the Ni/γ-Al2O3 catalysts. A further important reason was the deposition of carbon produced during the POSR process on the Ni/γ-Al2O3 catalyst surface. The activity and hydrogen selectivity of Ni-Pd/γ-Al2O3 catalyst were significantly higher than the values of the nickel catalyst under the same experimental conditions. Catalytic stability was also enhanced by the presence of palladium. Such improvement indicates that palladium plays an important role in the catalytic action. SEM and TG results did not show any great difference between the fresh and spent Ni-Pd/γ-Al2O3 catalysts. Overall, the bimetallic Ni-Pd/γ-Al2O3 catalyst could be an effective catalyst for the production of hydrogen from hydrocarbons.