Pd Phase Research Articles

Study on the correlation between the surface active species of Pd/cordierite monolithic catalyst and its catalytic activity

Two Pd-loading routes and three Pd-precursor matters were adopted to prepare Pd/(Ce,Y)O2/γ-Al2O3/cordierite monolithic catalyst. The surface active species on the catalyst were characterized by XPS, and its catalytic activity for methane combustion was tested, and the dynamics of the catalytic combustion reaction was also discussed. Pd-loading route and Pd-precursor mass have a significant influence on the catalytic activity and surface active species. The sol dipping method is more advanced than the aqueous solution impregnating method. PN-sol catalyst, by sol dipping combined with Pd(NO3)2-precursor, has the best catalytic activity. The physical reason is the unique active Pd phase coexisting with active PdO phase on the surface, and thus the Pd3d5/2 binding energy of surface species and apparent activation energy of combustion reaction are considerably decreased. The catalytic activity index, Pd3d5/2 binding energy and apparent activation energy are highly tied each other with exponential relations.

Acetylene hydrogenation over structured Au-Pd catalysts.

AuPd nanoparticles were prepared following a methodology designed to produce core-shell structures (an Au core and a Pd shell). Characterisation suggested that slow addition of the shell metal favoured deposition onto the pre-formed core, whereas more rapid addition favoured the formation of a monometallic Pd phase in addition to some nanoparticles with the core-shell morphology. When used for the selective hydrogenation of acetylene, samples that possessed monometallic Pd particles favoured over-hydrogenation to form ethane. A sample prepared by the slow addition of a small amount of Pd resulted in the formation of a core-shell structure but with an incomplete Pd shell layer. This material exhibited a completely different product selectivity with ethylene and oligomers forming as the major products as opposed to ethane. The improved performance was thought to be as a result of the absence of Pd particles, which are capable of forming a Pd-hydride phase, with enhanced oligomer selectivity associated with reaction on uncovered Au atoms.

Effects of PdO decoration on the sensing behavior of SnO2 toward carbon monoxide

We deposited PdO nanoparticles on SnO2 thin films and studied the CO gas sensing behavior of the PdO-decorated sensors at temperatures below 250°C. The PdO nanoparticles and the SnO2 thin film were both prepared by reactive sputter deposition. The PdO decoration increases the resistivity of the SnO2 thin film as a result of the formation of the P–N junction. The sensing behavior of the sensor at 100°C and below can be understood simply by the oxygen ionosorption model. At temperatures at 150°C and above, the sensor demonstrates a fast response followed by a progressive conductance decay during the CO exposure. The observation is likely related with adsorption kinetics of CO and O2 on Pd nanoislands formed as a result of PdO reduction. PdO reduction and reoxidation occur in the temperature range between 100 and 150°C under the CO sensing condition, and thereby greatly influencing the sensing behavior of the sensor. The sensor signal of the PdO-decorated sensor is about three times that of the bare SnO2 sensor at 150°C and above. The PdO decoration also significantly reduces the recovery time of the SnO2 sensor. The faster recovery is ascribed to the presence of the residual metal Pd phase, which promotes the spill-over effect.

A DFT Study of CO Oxidation at the Pd–CeO2(110) Interface

Ceria-supported Pd is one of the main components in modern three-way catalysts in automotive applications to facilite CO oxidation. The exact form in which Pd displays its high activity remains not well understood. We present a DFT+U study of CO oxidation for single Pd atoms located on or in the ceria surface as well as a Pdn nanorod model on the CeO2(110) surface. The oxidation of Pd to the 2+ state by ceria weakens the Pd–CO bond for the single Pd models and, in this way, facilitates CO2 formation. After CO oxidation by O of the ceria surface, Pd relocates to a position below the surface for the Pd-doped model; in this state, CO adsorption is not possible anymore. With Pd on the surface, O2 will adsorb and dissociate leading to PdO, which can be easily reduced to Pd. The reactivity of the Pd nanorod is low because of the strong bonds of the metallic Pd phase with CO and the O atom derived from O2 dissociation. These findings show that highly dispersed Pd is the most likely candidate for CO oxidation in ...

Low temperature homogenization in nanocrystalline PdCu thin film system

Diffusion and solid state reactions were investigated in Pd–Cu nanocrystalline films by means of secondary neutral mass spectrometry depth profiling technique. The heat treatments were made at low temperatures (where the volume diffusion was frozen in) for long enough annealing times to reach saturation. In the early stage there is a grain boundary interdiffusion. At longer times first a Pd plateau developed inside the Cu layer. Later on the Cu penetration was also more and more extended in the Pd, even the average composition of Cu in Pd became higher than the average Pd composition in Cu. Depending on the ratio of the initial thicknesses, the system (for thickness ratios corresponding to 50/50 Cu/Pd or to 75/25 Cu/Pd) arrived either at the mixture of pure Pd and β-CuPd phase or to the mixture of α′-Cu3Pd and β-CuPd phases, respectively, as dictated by the phase diagram. The process is interpreted as grain boundary diffusion induced solid state reaction.

Structure and Mössbauer Analysis of Melt-Spun Fe-Pd Ribbons Containing Ni and Co

Fe68.45Pd28.21Co1.66Ni1.66 alloy in ribbon geometry was produced by melt spinning. The microstructure of the samples was examined using scanning electron microscopy. The structural identification of the as-spun ribbon sample and the annealed ones was performed by means of X-ray diffraction. All the Bragg peaks were indexed based on an fcc type structure of (γ-Fe, Pd) phase with a lattice parameter a = 3.742 (3) Å. This result was proved by Mössbauer technique. The annealed ribbon at 600 °C shows an L10 ordered fct structure. An endothermic reaction at T = 358 °C followed by an exothermic one at 390 °C were observed on heating. These reactions were attributed to the Curie temperature of nickel and to the annihilation of an excess of quenched-in vacancies, respectively.

Effect of Pre-Reduction on the Properties and the Catalytic Activity of Pd/Carbon Catalysts: A Comparison with Pd/Al2O3

The effect of pre-reduction in solution with chemical reagents on the catalytic performance and catalyst properties of Pd/carbon catalysts was systematically investigated with a multitechnique approach. The results are critically discussed in comparison to those recently obtained on analogous Pd/alumina catalysts. It was proved that the Pd phase on the carbon surface is characterized by a high mobility, opposite to what occurs on alumina. As a result, the Pd particles on carbon aggregate together during pre-reduction, with a consequent decrease in available metal surface. Pd particles remain aggregated also in reaction conditions; the decreased Pd dispersion negatively affects the catalyst activity in the debenzylation of 4-benzyloxyphenol.

Influence of Ethanol Catalyzed Oxidation on the Activity of Pd/C with Different Ratio of Pd and Carbon

To investigate the influence of ethanol catalyzed oxidation on activity of Pd/C with different ratio of Pd and C. Pd/C catalyst samples with Pd loads of 20, 30, 40 and 50 wt% were obtained by chemical reduction reaction of PdCl2 and NaBH4. The samples morphology and structure were characterized by XRD and SEM. The electrocatalytic oxidation activities of ethanol were examined by cyclic voltammetry in alkaline media. The results show that a face centered cubic (FCC) Pd phase can be identified in the sample powders. The average particle size of the Pd/C powder is about 10 nm. The performance of ethanol oxidation on 40 % Pd/C electro-catalyst is better than that of the other Pd/C samples.

Modeling of Nanostructured Palladium Anode in Solid Oxide Fuel Cells

In this paper, a mode of nanostructured Pd anode of SOFCs is presented to calculate the effects of nanoparticles on the SOFCs' electrodes performance. Nanostructured electrodes of the SOFCs prepared by wet impregnation have attracted increasing attention as the most effective way to make highly active and advanced structures in the electrodes. The effects of infiltrated Pd-nanoparticles on the performance of Nickel/ Gadolinium doped Ceria (Ni/GDC) anode of SOFC are investigated. It is observed that a small amount of Pd catalyst has a significant decreasing effect on overpotential of anodes. One-dimensional analysis is carried out using a simplified geometry to calculate the effective polarization resistance by assuming the ionic conductor phase (GDC) as columns and the Pd phase mounted on these columns. The results of modeling are presented and compared with the experimental data as a function of temperature.

PHASE RESPONSE CURVES PROVIDE INSIGHT INTO THE PATHOPHYSIOLOGY OF TREMOR DISORDERS AND NOVEL POTENTIAL TREATMENT STRATEGIES

Treatment options for tremor remain limited despite it being the most common movement disorder encountered by neurologists. A significant limitation to the development of new treatment strategies has been a...

Recovery of high-purity metallic Pd from Pd(II)-sorbed biosorbents by incineration

This work reports a direct way to recover metallic palladium with high purity from Pd(II)-sorbed polyethylenimine-modified Corynebacterium glutamicum biosorbent using a combined method of biosorption and incineration. This study is focused on the incineration part which affects the purity of recovered Pd. The incineration temperature and the amount of Pd loaded on the biosorbent were considered as major factors in the incineration process, and their effects were examined. The results showed that both factors significantly affected the enhancement of the recovery efficiency and purity of the recovered Pd. SEM-EDX and XRD analyses were used to confirm that Pd phase existed in the ash. As a result, the recovered Pd was changed from PdO to zero-valent Pd as the incineration temperature was increased from 600 to 900°C. Almost 100% pure metallic Pd was recovered with recovery efficiency above 99.0% under the conditions of 900°C and 136.9 mg/g.

A key role for iodobenzene in the direct C–H bond functionalisation of benzoxazoles using PhI(OAc)2 mediated by a Pd(OAc)2/1,10-phenanthroline catalyst system: in situ formation of well-defined Pd nanoparticles

PhI(OAc)2 has previously been reported as a reagent for the direct arylation of C–H bonds in benzoxazole in a PdII/IV-mediated process. However, evidence reported here suggests this reagent degrades to iodobenzene under the literature reported reaction conditions. Further, we present evidence for the rapid formation of Pd0 nanoparticles in this reaction, leading us to question what is the active catalytic Pd phase in coupling chemistry?

Pd2Cd11− (0.21≤δ≤0.51)–a partly disordered γ-brass type phase and Pd0.238Cd0.762-a γ-brass related incommensurate phase in the palladium–cadmium system

The Cd rich part of the Cd–Pd phase diagram was reassessed by means of synthesis and single crystal and powder X-ray diffraction. The region contains two phases that have been reported to have substantial compositional widths, Cd11Pd2 and Cd4Pd. The phase Cd11Pd2 that has previously been reported to be a disordered γ-brass crystallizing is space group P4̄3m is here shown to crystallize in I4̄3m and the mechanism for compositional variation is explained. The phase Pd4Cd has previously been shown to constitute a phase field or a phase bundle of modulated structures and here we determine the structure of a compound Pd0.238Cd0.762 which crystallizes in the orthorhombic superspace group Fmmm(α00)0s0 (F=[(½, ½, 0, 0); (½, 0, ½, 0 ); (0, ½, ½, 0 )] with the fundamental cell dimensions a=4.687(2) Å, b=10.000(1) Å, c=14.140(2) Å, q=0.6432(6)a⁎.

Again regarding the Al−Pd phase diagram

The Al−Pd phase diagram was experimentally reinvestigated in the region around the equiatomic composition. The high-temperature β-phase (CsCl-type structure) forming around AlPd transforms by cooling to a rhombohedral β′-phase, which only being metastable, strongly resists transformation to the stable low-temperature μ-phase (FeSi-type structure). The composition of the β-phase ranges between Al57.5Pd42.5 (at 949°C) and Al45Pd55 (at 1315°C). The highest existence temperature of the μ-phase is 745°C at ∼Al52Pd48. The reaction β↔μ+δ occurs at 735°C and Al53Pd47 composition; the reaction β↔μ+ν occurs (provisionally) at somewhat below 630°C and ∼Al48Pd52 composition. No eutectoid decomposition of the ν-phase was observed down to 400°C. A compositional continuity of the high-temperature complex ε6 and ε28 phases is argued.

Decoration of Pd nanoparticles on ZnO-branched nanowires and their application to chemical sensors

We have coated zinc-oxide (ZnO)-branched tin oxide (SnO2) nanowires with a Pd shell layer via a sputtering method and subsequently investigated the effects of thermal annealing. By the thermal annealing, the Pd shell layers were agglomerated to form the nanoparticles, being comprised of the cubic Pd phase. Sensing measurement in terms of NO2 gas revealed that the morphology of the Pd nanoparticles affected the sensing capability, in that the abundant and dense Pd nanoparticles obtained at certain temperatures enhanced the sensitivity to NO2 gas. We suggest that the spillover effect of Pd nanoparticles played a significant role in enhancing the response.

Influence of the Ce–Zr promoter on Pd behaviour under dynamic CO/NO cycling conditions: a structural and chemical approach

The behaviour of the Pd phase in three way catalysts (TWCs) having a Ce-Zr oxide as a promoter component has been examined under CO/NO cycling conditions. In order to extract information on the role of the noble metal and the metal-promoter interface, two catalysts in, respectively, the presence or the absence of the promoter and having a similar Pd particle size were analyzed by a synchronous multitechnique approach using X-ray absorption (XAS) or high energy X-ray diffraction (HXRD) in combination with diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and mass spectrometry (MS). From a structural point of view it is shown that the promoter oxide strongly influences Pd behaviour, limiting morphological (size/shape) and structural (formation of carbide/oxide phases) modifications occurring under dynamic conditions in the absence of the promoter. Activity measurements show that these phenomena have important chemical consequences in terms of CO/NO pollutant metal coverage(s), the occurrence of NO and/or CO dissociation steps as well as the subsequent transformation of the pollutants into CO2 and N2.

Recovery of metallic palladium from hydrochloric acid solutions by a combined method of adsorption and incineration

This study evaluated the recovery of palladium (Pd) by ion exchange resins from hydrochloric acid solutions using a combined method of adsorption and incineration. Lewatit MonoPlus TP 214 was selected as a representative commercial ion exchange resin and its adsorption performance was evaluated. Kinetic and isotherm experiments revealed that Pd(II) adsorption equilibrium was reached within 21h, and the maximum uptake estimated by the Langmuir model was 241.1±11.6mg/g. To recover Pd as a solid form, the Pd ions-loaded resin was incinerated. The effects of incineration temperature and Pd amount were examined to enhance the recovery efficiency and purity of the recovered Pd. SEM–EDX and XRD analyses were used to confirm existence of Pd phase in ash incinerated in air at 600°C and 900°C. Both the incineration temperature and Pd amount significantly affected the recovery efficiency and purity. The form of Pd was changed from PdO to Pd0 as the incineration temperature was increased from 600°C to 900°C. At 900°C and 258.5mg/g of Pd(II) uptake, metallic Pd was successfully recovered with 99.0% of recovery efficiency and 96.1% of purity. Consequently, it can be claimed that the sorption–incineration process is likely an effective way enabling simple and fast recovery of precious metals as a metallic form from waste solutions.

Pt promotional effects on Pd–Pt alloy catalysts for hydrogen peroxide synthesis directly from hydrogen and oxygen

H2O2 synthesis directly from H2 and O2 over supported Pd–Pt alloy catalysts was carried out using a semibatch reactor under ambient conditions. As compared to pure Pd, the performance of Pd–Pt catalysts was enhanced significantly. The promotional role of Pt was studied systematically by using in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (DRIFTS), quantitative powder X-ray diffraction (XRD), X-rays photoelectron spectroscopy (XPS), and temperature-programmed desorption of H2/O2 (H2/O2-TPD). The spectra of DRIFT, XPS, and XRD demonstrate the formation of Pd–Pt alloy particles, which surfaces are enriched by Pt accompanying with possible electron transfer from Pd to Pt. The addition of Pt into Pd phase was proposed to impact on reactants adsorption, stabilization of intermediates such as OOH and OH radicals, and the formation and decomposition of H2O2.

ChemInform Abstract: Supported Transition Metal Catalysts for Hydrodechlorination Reactions

AbstractReview: overview of existing methods, benefits of catalytic hydrodechlorination (HDC) over separation/oxidation methods, detailed considerations of liquid phase HDC of chlorophenols over Al supported Pd and gas phase conversion of halogenated aromatics over silica supported Ni; 321 refs.

Rabeprazole extended-release 50 mg compared with esomeprazole 40 mg and rabeprazole delayed release 20 mg

Rabeprazole extended-release 50 mg compared with esomeprazole 40 mg and rabeprazole delayed release 20 mg