Catalytic Properties Of Pd Research Articles

Kinetics of methane combustion on model supported Pd/LaxMnO3 natural gas vehicle catalysts: Sensitivity of La-stoichiometry on the catalytic properties of Pd

The kinetics of the catalytic CH4/O2 reaction has been studied on 1 wt% Pd/LaxMnO3 with x = 0.7, 1.0 and 1.3. Steady-state kinetic measurements have been performed in lean conditions at 400 °C on pre-reduced and on aged catalysts after exposure to wet atmosphere at 750 °C. A single site reaction mechanism occurs preferentially on Pd/La1.3MnO3 exhibiting a La-rich surface. In contrast a dual-site reaction mechanism, combining Pd and surface reactive oxygen species from the support, is preferentially involved on Pd-La0.7MnO3 characterized by a Mn-rich surface. Pd/LaMnO3 exhibits a mixed regime but subsequent deterioration of the Pd-LaxMnO3 interface during thermal aging leads to increasing contribution of the single site reaction mechanism. High surface Pd/Mn ratio and high concentration of Pdn+ with n > 2 can be considered as good descriptors to probe the efficacy of Pd/LaxMnO3 catalysts. Remarkably, the high thermal stability of the Pd-La0.7MnO3 interface, preserving the Pd dispersion on Pd/La0.7MnO3, leads to lower sensitivity to deactivation.

Black phosphorous/palladium functionalized carbon aerogel nanocomposite for highly efficient ethanol electrooxidation.

Direct ethanol fuel cells have great potential for practical power applications due to their easy operation, high energy density, and low toxicity. However, the slow and incomplete ethanol electrooxidation (EEO) reaction is a major drawback that hinders the development of this type of fuel cell. Here, we report a facile approach for the preparation of highly active, low cost and stable electrocatalysts based on palladium (Pd) nanoparticles and black phosphorus/palladium (BP/Pd) nanohybrids supported on a carbon aerogel (CA). The nanocomposites show remarkable catalytic performance and stability as anode electrocatalysts for EEO in an alkaline medium. A mass peak current density of 8376 mA mgPd -1 is attained for EEO on the BP/Pd/CA catalyst, which is 11.4 times higher than that of the commercial Pd/C catalyst. To gain deep insight into the structure-property relationship associated with superior electroactivity, the catalysts are well characterized in terms of morphology, surface chemistry, and catalytic activity. It is found that the BP-doped CA support provides high catalyst dispersibility, protection against leaching, and modification of the electronic and catalytic properties of Pd, while the catalyst modifies CA into a more open and conductive structure. This synergistic interaction between the support and the catalyst improves the transport of active species and electrons at the electrode/electrolyte interface, leading to rapid EEO reaction kinetics.

Morphological, Structural, and Catalytic Properties of Pd–CeO2/Al2O3 Compositions and Thereof Coatings in the Oxidation of Methane

The morphological and structural properties of Pd–CeO2/Al2O3 catalytic compositions annealed at 100, 500, and 1000°С are studied, along with thereof coatings deposited on metallic foil via cold gas dynamic spraying. The influence of the preparation technique of the initial catalytic composition and introducing active component into a coating on their phase states, particle sizes, and activitites is elucidated. It is shown that introducing active components via impregnation into preliminarily sprayed alumina layer ensures the uniform distribution of Pd and Ce in the support profile, the formation of nanosized PdO particles, and the phase of interaction between the components of the catalyst and support. The impregnated catalyst shows the highest activity in the reaction of methane oxidation. The technique for preparing coatings has no limitations when scaled up and can find application in manufacturing full-size catalysts on metallic foil for different types of power engineering devices.

Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes

Summary Surface and interfacial engineering of heterogeneous metal catalysts is effective and critical for optimizing selective hydrogenation for fine chemicals. By using thiol-treated ultrathin Pd nanosheets as a model catalyst, we demonstrate the development of stable, efficient, and selective Pd catalysts for semihydrogenation of internal alkynes. In the hydrogenation of 1-phenyl-1-propyne, the thiol-treated Pd nanosheets exhibited excellent catalytic selectivity (>97%) toward the semihydrogenation product (1-phenyl-1-propene). The catalyst was highly stable and showed no obvious decay in either activity or selectivity for over ten cycles. Systematic studies demonstrated that a unique Pd-sulfide/thiolate interface created by the thiol treatment was crucial to the semihydrogenation. The high catalytic selectivity and activity benefited from the combined steric and electronic effects that inhibited the deeper hydrogenation of C=C bonds. More importantly, this thiol treatment strategy is applicable to creating highly active and selective practical catalysts from commercial Pd/C catalysts for semihydrogenation of internal alkynes.

Influence of Thermal Treatments on the Reducibility and Catalytic Properties of Pd Supported Over Ce0.6Zr0.4Ox/SiO2 and Ce0.73Tb0.27Ox/SiO2 for Methane Oxidation

Influence of Thermal Treatments on the Reducibility and Catalytic Properties of Pd Supported Over Ce_0.6Zr_0.4O_<i>x</i>/SiO₂ and Ce_0.73Tb_0.27O_<i>x</i>/SiO₂ for Methane Oxidation

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.

The effect of calcination temperature on physicochemical properties of alumina as a support for acetylene selective hydrogenation catalyst

The influence of the presence of transition alumina phases on the catalytic properties of Pd–Ag/Al2O3 was investigated for selective hydrogenation of acetylene in operating conditions near a commercial plant. Transition alumina samples were prepared by calcination in the temperature range of 1080–1150 °C. It was observed that by increasing the α-phase content of alumina sample, acidity and surface area were decreased while average pore diameter was increased. From the viewpoint of catalytic performance, increasing the calcination temperature caused acetylene conversion to be decreased and ethylene selectivity to be increased. The higher the α-phase content in alumina support, the better its selectivity.

Effect of co-deposition of LaFeO3 on the catalytic properties of Pd on Al2O3 support for CO–O2 and NO–CO reactions

Pd/LaFeO3/Al2O3 catalysts were prepared by co-deposition of Pd and LaFeO3 perovskite oxides in the intrapores of Al2O3 by the incipient wetness method. Pd and LaFeO3 perovskite oxides were highly dispersed on Al2O3 in the inside pore. H2-TPR studies revealed that the oxidation state, dispersion and redox properties of Pd were affected by the presence of LaFeO3 with close proximity. The Pd and LaFeO3 co-deposited Al2O3 catalysts exhibited much higher activity for CO oxidation and NO–CO reaction than Pd/Al2O3 catalysts.

Tunability of catalytic properties of Pd-based catalysts by rational control of strong metal and support interaction (SMSI) for selective hydrogenolyic C–C and C–O bond cleavage of ethylene glycol units in biomass molecules

The catalytic properties of Pd can be fine-tuned through the formation of bimetallic nanoparticles with the support.

Enhanced catalytic performance of Pd catalyst for formic acid electrooxidation in ionic liquid aqueous solution

A protic ionic liquid (IL), n-butylammonium nitrate (N4NO3), is prepared and employed as the electrolyte for formic acid electrooxidation reaction (FAOR) on Pd catalysts. The oxidation peak potential of FAOR in the IL solution shows about a 200 mV negative shift as compared with those in traditional H2SO4/HClO4 electrolytes, suggesting that FAOR can be more easily carried out on Pd catalysts in IL media. The catalytic properties of Pd toward FAOR are not only dependent on the concentration of IL, as a consequence of the varied electronic conductivity of the IL solution, but also on the high potential limit of the cyclic voltammograms. When the Pd catalyst is cycled up to 1.0 V (vs. SCE), which induces a significant oxidation of Pd, it shows ca. 4.0 times higher activity than that not subjected to the Pd oxidation (up to 0.6 V). The Pd oxides, which are more easily formed in IL solution than in traditional H2SO4/HClO4 electrolytes, may play a crucial role in increasing the catalytic activities of Pd toward FAOR. Our work would shed new light on the mechanism of FAOR and highlight the potential applications of IL as green and environment-friendly electrolytes in fuel cells and other technologies.

Facile fabrication of Pd nanoparticle/Pichia pastoris catalysts through adsorption–reduction method: A study into effect of chemical pretreatment

Based on rapid adsorption and incomplete reduction in Pd (II) ions by yeast, Pichia pastoris (P. pastoris) GS115, the effects of pretreatment on adsorption and reduction of Pd (II) ions and the catalytic properties of Pd NP/P. pastoris catalysts were studied. Interestingly, the results showed that the adsorption ability of the cells for Pd (II) ions was greatly enhanced after they were pretreated with aqueous HCl, aqueous NaOH and methylation of amino group. For the reduction in the adsorbed Pd (II) ions, more slow reduction rates by pretreated P. pastoris cells were displayed compared with the cells without pretreatment. Using the reduction of 4-nitrophenol as a model reaction, the Pd NP/P. pastoris catalysts based on the cells after pretreatment with aqueous HCl, aqueous NaOH and methylation of amino group exhibited higher stability than the unpretreated cells. The enhanced stability of the Pd catalysts can be attributed to smaller Pd NPs, better dispersion of the Pd NPs, and stronger binding forces of the pretreated P. pastoris for preparing the Pd NPs. This work exemplifies enhancing the stability of Pd catalysts through pretreatments.

Fabrication and catalytic properties of Pd and Ce decorated carbon nanotube-TiO2 composite catalysts for low-temperature CO oxidation

In this paper, a series of Pd-Ce/acid-treated carbon nanotube (TCNT)-TiO2 composite catalysts were designed and fabricated carefully for low temperature CO oxidation. After covering of TiO2 on the surface of CNT, the catalytic activity enhanced obviously because of the synergetic effect of CNT and TiO2. The composite material CNT-TiO2 was more suitable for the catalytic support than only TCNT or TiO2. The experimental conditions, such as the ratio of CNT/TiO2, the prepared method of Pd nanoparticles, the effect of the Ce element, etc., were investigated in detail. The final result showed that Pd-Ce/TCNT-TiO2 catalyst prepared by NH3 coordination impregnation method when TCNT:TiO2=12:88–24:76 had superior activity on low temperature CO oxidation. The high dispersion of Pd nanoparticles and enriched surface Pd species on the Pd-Ce/CNT-TiO2 catalyst prepared by NH3 coordination impregnation method was the two main reasons of obtaining higher catalytic performance. By adjusting the research conditions, the CO molecules could be complete oxidized at about 35°C, which was lower than many catalysts reported in the existed literature.

Reversible hydrogen storage in vapour deposited Mg-5 at.% Pd powder composites

Mg-5 at.% Pd powder composites derived from multilayered films of Mg and Pd deposited in Pd/Mg/Pd/Mg/Pd layer configuration by thermal evaporation reversibly store about 3.5 wt.% hydrogen up to 15 cycles under mild conditions of pressure and temperature. Hydrogenation takes place at 0.15 MPa hydrogen pressure while dehydrogenation occurs in a dynamic rotary vacuum. Each process is completed in about three hours. The temperature of a dehydrogenation or hydrogenation step is about 5–10 K higher than the preceding hydrogenation or dehydrogenation step. The hydrogenation temperature of the first cycle is 343 K whereas the dehydrogenation temperature of the 15th cycle is 423 K. The hydrogen storage capacity of composite is the manifestation of fine-grained microstructure of Mg and the catalytic properties of Pd. It declines beyond 423 K due to the exhaustion of metallic Pd as a result of the formation of Mg–Pd intermetallic compounds. This approach presents a simple and rapid method of preparing Mg–Pd composites for hydrogen storage applications.

Catalytic properties of Pd supported on hexaaluminate coated alumina in low temperature combustion of coal mine ventilation air methane

Palladium supported on γ-Al2O3 has been demonstrated as most active catalyst for catalytic combustion of methane. However, the sintering of support and PdO seriously affects its activity. We prepared a composite Pd/hexaaluminate/Al2O3 catalyst and compared its catalytic activity as well as sintering behavior with Pd/Al2O3. This composite catalyst exhibits higher activity and better resistance to sintering. The effect of water vapor presented in feed has also been investigated.

CO2-selective methanol steam reforming on In-doped Pd studied by in situ X-ray photoelectron spectroscopy

In situ X-ray photoelectron spectroscopy (in situ XPS) was used to study the structural and catalytic properties of Pd–In near-surface intermetallic phases in correlation with previously studied PdZn and PdGa.Room temperature deposition of ∼4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453K in vacuum yields a ∼1:1 Pd/In near-surface multilayer intermetallic phase. This Pd1In1 phase exhibits a similar “Cu-like” electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd1Zn1 counterpart.Catalytic characterization of the multilayer Pd1In1 phase in MSR yielded a CO2-selectivity of almost 100% between 493 and 550K. In contrast to previously studied In2O3-supported PdIn nanoparticles and pure In2O3, intermediate formaldehyde is only partially converted to CO2 using this Pd1In1 phase. Strongly correlated with PdZn, on an In-diluted PdIn intermetallic phase with “Pd-like” electronic structure, prepared by thermal annealing at 623K, methanol steam reforming is suppressed and enhanced CO formation via full methanol dehydrogenation is observed.To achieve CO2-TOF values on the isolated Pd1In1 intermetallic phase as high as on supported PdIn/In2O3, at least 593K reaction temperature is required. A bimetal-oxide synergism, with both bimetallic and oxide synergistically contributing to the observed catalytic activity and selectivity, manifests itself by accelerated formaldehyde-to-CO2 conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd1In1 inhibited inverse water–gas-shift reaction on In2O3 and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO2-selectivity of the supported catalyst.

Pd–Cu/AC and Pt–Cu/AC catalysts for nitrate reduction with hydrogen: Influence of calcination and reduction temperatures

The influence of calcination and reduction temperatures on the catalytic properties of Pd–Cu and Pt–Cu bimetallic catalysts supported on activated carbon for the reduction of nitrates was studied. The catalysts were prepared using different calcination and reduction temperatures, and the respective activities and selectivities for the reduction of nitrates in water with hydrogen were assessed. It was found that the different preparation conditions lead to different catalytic performances. For both catalysts, the activity decreases by increasing calcination and reduction temperatures, whereas the effect on the selectivity is not uniform. For the 1%Pd–0.3%Cu (wt.%) catalyst, the nitrate conversion after 5 h of reaction varies from 93% (sample calcined at 200 °C and not reduced) to 25% (sample calcined and reduced at 400 °C). The formation of alloys during the preparation of the catalysts is prejudicial for nitrate reduction. In all the preparation conditions tested the Pd–Cu pair is more selective for the transformation of nitrate into nitrogen. All the samples have been characterized by nitrogen adsorption at −196 °C, CO adsorption microcalorimetry, TPR, XRD, XPS and TEM.

Formation of palladium(0) nanoparticles at microbial surfaces

The increasing demand and limited natural resources for industrially important platinum-group metal (PGM) catalysts render the recovery from secondary sources such as industrial waste economically interesting. In the process of palladium (Pd) recovery, microorganisms have revealed a strong potential. Hitherto, bacteria with the property of dissimilatory metal reduction have been in focus, although the biochemical reactions linking enzymatic Pd(II) reduction and Pd(0) deposition have not yet been identified. In this study we investigated Pd(II) reduction with formate as the electron donor in the presence of Gram-negative bacteria with no documented capacity for reducing metals for energy production: Cupriavidus necator, Pseudomonas putida, and Paracoccus denitrificans. Only large and close-packed Pd(0) aggregates were formed in cell-free buffer solutions. Pd(II) reduction in the presence of bacteria resulted in smaller, well-suspended Pd(0) particles that were associated with the cells (called "bioPd(0)" in the following). Nanosize Pd(0) particles (3-30 nm) were only observed in the presence of bacteria, and particles in this size range were located in the periplasmic space. Pd(0) nanoparticles were still deposited on autoclaved cells of C. necator that had no hydrogenase activity, suggesting a hydrogenase-independent formation mechanism. The catalytic properties of Pd(0) and bioPd(0) were determined by the amount of hydrogen released in a reaction with hypophosphite. Generally, bioPd(0) demonstrated a lower level of activity than the Pd(0) control, possibly due to the inaccessibility of the Pd(0) fraction embedded in the cell envelope. Our results demonstrate the suitability of bacterial cells for the recovery of Pd(0), and formation and immobilization of Pd(0) nanoparticles inside the cell envelope. However, procedures to make periplasmic Pd(0) catalytically accessible need to be developed for future nanobiotechnological applications.

Pt and/or Pd Supported/Incorporated Catalyst on Perovskite-Type Oxide for Water Gas Shift Reaction

Catalytic properties of Pd and/or Pt supported/incorporated on/in perovskite-type oxides for water gas shift (WGS) reaction have been investigated. We found that the dominant reaction mechanism over these catalysts was redox mechanism by CO and steam, and their redox properties were controllable by the bulk structure of perovskite.

Catalytic oxidation of ethylene to acetic acid on Pd–HPA/SiO2 catalysts with different heteropoly acids

The effect of different heteropoly acids (HPA) on the catalytic properties of Pd–HPA/SiO2 in the selective oxidation of ethylene to acetic acid was investigated in this work. The results demonstrated that a good balance of Bronsted acid sites and Pd2+ ions stabilized by Bronsted acid sites was an indispensable factor in producing acetic acid.

Mechanism of Suppression of Carbon Deposition on the Pd−Ni/Ce(Sm)O2−La(Sr)CrO3 Anode in Dry CH4 Fuel

Catalytic properties of Pd−Ni catalysts were studied to clarify the mechanism of suppression of carbon deposition on a Pd−Ni catalyst supported on a composite of Ce(Sm)O2 and La(Sr)CrO3, which is a promising anode material for direct oxidation of dry CH4 in solid oxide fuel cells (SOFCs). The catalytic activity of Pd−Ni catalysts for the carbon formation in the decomposition of CH4 was found to be strongly dependent on the support materials. Carbon deposition was remarkably suppressed on Pd−Ni/Ce(Sm)O2 and Pd−Ni/La(Sr)CrO3 catalysts, whereas Pd−Ni/SiO2 and Pd−Ni/carbon catalysts were very active for the formation of carbon nanofibers. TEM analysis showed the morphology of the Pd−Ni particles and carbon deposit on the Pd−Ni/Ce(Sm)O2 catalyst was quite different from that on the Pd−Ni/C catalyst. XRD and TEM-EDS analysis indicate that Ce and Sm were doped into the Pd−Ni alloy from the Ce(Sm)O2 supports. High catalytic activity of the Pd−Ni/Ce(Sm)O2 catalyst for steam reforming indicates that the Pd−Ni catal...