Dispersed Palladium Research Articles

Silicate-induced high-temperature-resistant small-crystallite ceria support enhancing palladium-catalyzed low-concentration methane combustion

High-performance Pd/CeO2 catalysts for the purification of low-concentration methane in waste gases by catalytic combustion have long been pursued, given that methane is a potent greenhouse gas. The reduction in ceria oxygen supply and palladium dispersion, caused by ceria crystallite sintering, deactivates the catalyst. Here, we report an enhanced palladium catalyst supported on a silicate-induced small-crystallite ceria (7.2 nm) calcined at 800 °C, compared to the pristine ceria (50.7 nm). The catalyst was coated on a cordierite monolith for 0.1 vol% methane combustion, achieving 90 % methane conversion at 336 °C, which is 84 °C lower than the temperature required for Pd/CeO2 reference. The small-crystallite ceria exhibited a high oxygen supply capacity due to abundant oxygen vacancies, facilitating the conversion of carbon-containing intermediates from methane dissociation on palladium species, thereby enhancing the catalyst’s intrinsic activity. The catalyst, with increased palladium dispersion, demonstrated a methane reaction rate 6.7 times higher than that of the Pd/CeO2 at 280 °C. This study provides new insights into designing highly efficient Pd/CeO2-based catalysts for low-concentration methane combustion.

Amorphous hetero-structure iron/cobalt oxyhydroxide with atomic dispersed palladium for oxygen evolution reaction

The activity of iron oxyhydroxides (FeOOH) in oxygen evolution reaction (OER) is limited by their poor conductivity and the high energy barrier in the rate-determining step. Herein, we report the immobilization of atomic dispersed Pd species on Co doped FeOOH, realizing the preparation of amorphous hetero-structure FeCoaOOH-Pdb. In the case of Co/Fe of 0.68 and Pd/Fe of 0.026, the coexisting structure of nanorods and nanospheres with appropriate oxygen vacancies and unsaturated active centers increases the number of active sites and enhances the intrinsic activity of the electrocatalyst. The density functional theory results uncover that the FeCo0.68OOH-Pd0.026 optimizes the binding energies of *O and *OOH, and accelerates the OER kinetics. The rationally designed FeCo0.68OOH-Pd0.026 exhibits excellent OER activity and reliability, manifesting a Tafel slope of 37.5 mV dec−1, a low overpotential of 265.1 mV at 10 mA cm−2, which has the potential to realize the large-scale implementation of water splitting.

Enhanced electrocatalytic hydrodechlorination by modulating metal-support interaction and H generation of single-Pd-atom anchored NiFeP electrode

Electrocatalytic hydrodechlorination (EHDC) stands out as an economical and prospective technology for eliminating chlorinated organic pollutants. Single-atom catalyst engineering and metal-support interaction (MSI) offer the promising strategies for developing electrocatalysts with high atom utilization and reactivity. Herein, atomically dispersed palladium (Pd) anchored on the iron (Fe)-introduced nickel phosphide (NiFeP) support is reported. The prepared NiFeP-Pd electrode exhibits outstanding electrocatalytic activity in 4-CP removal efficiency (98.8 %) with an ultra-low dosage of Pd (0.0497 mg cm−2) and the highest reported MA value (446.01 min−1 g−1), surpassing Ni2P-Pd by 6.34 times. Experimental results combined with theoretical calculations suggest that the superior performance of NiFeP-Pd stems from the modulated support by Fe introduction, which not only enhances the generation of adsorbed atomic hydrogen species (H*), but also reduces the energy barrier of C-H formation on Pd sites by regulating the MSI. In addition, single-Pd-atom construction on NiFeP with good conductivity and large specific surface area makes the contributions as well.

Carbonized cellulose microspheres loaded with Pd NPs as catalyst in p-nitrophenol reduction and Suzuki-Miyaura coupling reaction

Catalytic reduction of p-nitrophenol is usually carried out using transition metal nanoparticles such as gold, palladium, silver, and copper, especially palladium nanoparticles (Pd NPs), which are characterized by fast reaction rate, high turnover frequency, good selectivity, and high yield. However, the aggregation and precipitation of the metals lead to the decomposition of the catalyst, which results in a significant reduction of the catalytic activity. Therefore, the preparation of homogeneous stabilized palladium nanoparticles catalysts has been widely studied. Stabilized palladium nanoparticles mainly use synthetic polymers. Cellulose microspheres, as a natural polymer material with low-cost and porous fiber network structure, are excellent carriers for stabilizing metal nanoparticles. Cellulose microspheres impregnated with palladium metal nanoparticles were carbonized to have a larger specific surface area and highly dispersed palladium nanoparticles, which exhibited excellent catalytic activity in the catalytic reduction of p-nitrophenol. In this work, the cellulose carbon-based microspheres palladium (Pd@CCM) catalysts were designed and characterized by SEM, TEM, EDS, XRD, FTIR, XPS, TGA, BET, and so on. Furthermore, the catalytic performance of Pd@CCM catalysts was investigated via p-nitrophenol reduction, which showed high catalytic activity. This catalyst also exhibited excellent catalytic performance in the Suzuki-Miyaura coupling reaction. Linking aromatic monomer and benzene through Suzuki-Miyaura coupling was presented as an effective route to obtaining biaryls, and the synthesis method is low-cost and simple. In addition, Pd@CCM showed desirable recyclability while maintaining its catalytic activity even after five recycles. This work is highly suggestive of the design and application of the heterogeneous catalyst.

Precise molecular sieving using metal‐doped ultramicroporous carbon membranes for H2 separation

AbstractBlue hydrogen produced from fossil fuels is recognized as a promising large‐scale technology for realizing the hydrogen economy. Membrane‐based separation is emerging as a viable alternative to traditional hydrogen purification technologies. Here, we present a facile strategy for fabricating carbon molecular sieve (CMS) hollow fiber membranes containing uniformly dispersed palladium (Pd) nanoparticles. The Pd nanoparticles, anchored in the carbon strands of CMS membranes, induced the carbon matrix toward a more ordered structure arrangement through a synergistic effect of entropy‐driven size exclusion and acceleration of graphitization. As a result, the doped Pd nanoparticles facilitated the formation of ultramicropores <3.3 Å in the CMS membranes, which enabled a precise molecular sieving ability between H2 and CO2 with H2/CO2 selectivity up to 247. Furthermore, the membrane presented good mixed gas separation performances and was stable for over 250 h under simulated harsh industrial conditions.

Mesoporous Ceria and Ceria‐Praseodymia as High Surface Area Supports for Pd‐based Catalysts with Enhanced Methane Oxidation Activity

AbstractIn recent years, Pd/CeO2 materials have proven to be effective catalysts for the total oxidation of methane. In this work, three different synthesis routes were used to prepare high specific surface area supports, consisting of pure CeO2 and 10 at% Pr‐doped ceria (Ce90Pr10). Nano‐structured spheres were obtained with a microwave‐assisted synthesis, dumbbell‐like particles were produced through a urea‐based hydrothermal method, and ordered mesoporous oxides were prepared by using SBA‐15 as hard‐template. The six materials were then impregnated with 2 wt% Pd, calcined at 500 °C, and comprehensively characterized. All the samples retained their high surface area after impregnation (75–110 m2 g−1), allowing a good dispersion of palladium. No significant structural or morphological differences were observed upon Pr doping, but a higher Pd oxidation state was induced by Pr‐doped supports. However, all Pd/CeO2 and Pd/Ce90Pr10 catalysts exhibited similar activity for dry methane oxidation below 500 °C, regardless of the synthesis technique and of the Pr presence: they all achieved almost complete CH4 oxidation at 400 °C, showing a really remarkable improvement with respect to analogous low surface area supports. A promoting role of Pr was instead noticed in wet conditions, thanks to its ability to counteract water‐induced deactivation phenomena.

Dynamic structural evolution of MgO-supported palladium catalysts: from metal to metal oxide nanoparticles to surface then subsurface atomically dispersed cations.

Supported noble metal catalysts, ubiquitous in chemical technology, often undergo dynamic transformations between reduced and oxidized states-which influence the metal nuclearities, oxidation states, and catalytic properties. In this investigation, we report the results of in situ X-ray absorption spectroscopy, scanning transmission electron microscopy, and other physical characterization techniques, bolstered by density functional theory, to elucidate the structural transformations of a set of MgO-supported palladium catalysts under oxidative treatment conditions. As the calcination temperature increased, the as-synthesized supported metallic palladium nanoparticles underwent oxidation to form palladium oxides (at approximately 400 °C), which, at approximately 500 °C, were oxidatively fragmented to form mixtures of atomically dispersed palladium cations. The data indicate two distinct types of atomically dispersed species: palladium cations located at MgO steps and those embedded in the first subsurface layer of MgO. The former exhibit significantly higher (>500 times) catalytic activity for ethylene hydrogenation than the latter. The results pave the way for designing highly active and stable supported palladium hydrogenation catalysts with optimized metal utilization.

Catalysis for the hydrogenation of nitroaromatics by highly dispersed palladium nanoparticles anchored on a resorcin[4]arene-based metal–organic dimer containing amino groups

A new family of resorcin[4]arene-based metal–organic dimers (1–9) were self-assembled, and the catalyst Pd@2 displayed efficient catalytic performance for nitroarene hydrogenation.

Supported Atomically Dispersed Pd Catalyzed Direct Alkoxylation and Allylic Alkylation†

Comprehensive SummaryA new approach to allylic alkylation is realized using an atomically dispersed palladium catalyst (Pd1/TiO2‐EG). Unlike conventional methods that require derivation of substrates and utilization of additives, this method allows for direct allylic alkylation from allylic alcohols, producing H2O as the sole by‐product. The catalyst's high efficiency is attributed to the local hydrogen bonding at the organic‐inorganic interface (Pd‐EG interface), facilitating hydroxyl group activation for η3 π‐allyl complex formation. The system demonstrates successful direct C—O and C—C coupling reactions with high selectivity, requiring no additives. This study highlights the potential of supported atomically dispersed catalysts for greener and more efficient catalysis, meanwhile, offers unique insights into the distinct behavior of atomically dispersed catalysts in comparison to homogeneous or nanoparticle‐based catalysts.

Effect of the Nature of Supports and the Degree of Palladium Dispersion on the Catalyst Activity and Selectivity in the Sunflower Oil Hydrogenation Reaction

Effect of the Nature of Supports and the Degree of Palladium Dispersion on the Catalyst Activity and Selectivity in the Sunflower Oil Hydrogenation Reaction

Novel synergistically effects of palladium-iron bimetal and manganese carbonate carrier for catalytic oxidation of formaldehyde at room temperature

The elimination of formaldehyde at room temperature holds immense potential for various applications, and the incorporation of a catalyst rich in surface hydroxyl groups and oxygen significantly enhances its catalytic activity towards formaldehyde oxidation. By employing a coprecipitation method, we successfully achieved a palladium domain confined within the manganese carbonate lattice and doped with iron. This synergistic effect between highly dispersed palladium and iron greatly amplifies the concentration of surface hydroxyl groups and oxygen on the catalyst, thereby enabling complete oxidation of formaldehyde at ambient conditions. The proposed method facilitates the formation of domain-limited palladium within the MnCO3 lattice, thereby enhancing the dispersion of palladium and facilitating its partial incorporation into the MnCO3 lattice. Consequently, this approach promotes increased exposure of active sites and enhances the catalyst's capacity for oxygen activation. The co-doping of iron effectively splits the doping sites of palladium to further enhance its dispersion, while simultaneously modifying the electronic modification of the catalyst to alter formaldehyde's adsorption strength on it. Manganese carbonate exhibits superior adsorption capability for activated surface hydroxyl groups due to the presence of carbonate. In situ infrared testing revealed that dioxymethylene and formate are primary products resulting from catalytic oxidation of formaldehyde, with catalyst surface oxygen and hydroxyl groups playing a crucial role in intermediate product decomposition and oxidation. This study provides novel insights for designing palladium-based catalysts.

Catalytic upcycling of waste bisphenols via tandem amination-ammonolysis to high value diamines

Hydrogenated methylene dianiline (H12MDA) is a valuable precursor for thermoplastic polyurethane. Traditionally, H12MDA is obtained by hydrogenation of methylene dianiline (MDA). However, the route from aniline to MDA produces large acidic waste streams linked to the nitration of benzene and the HCl-catalyzed reaction with formaldehyde, as well as a poor selectivity for the 4,4′-isomer in the condensation reaction with formaldehyde. Herein, we report a green and efficient amination process for synthesis of H12MDA starting from (waste) bisphenols. Palladium on moderately acidic catalyst supports (carbon, Al2O3, ZrO2) provided excellent yields of H12MDA (>97%) in short reaction times (3 h) at 200 °C, with limited addition of H2 and NH3. It was found that the reaction partially proceeds via a secondary amine intermediate. A high dispersion of palladium is essential to achieve high yields of the desired H12MDA. Finally, the use of polycarbonate as an alternative feedstock for H12MDA was demonstrated via a tandem ammonolysis-amination process.

Highly active SiO2-supported palladium nanoparticles prepared by a modified ammonia evaporation method for lean methane oxidation

By optimizing the ammonia evaporation (AE) method, highly active palladium nanoparticles were successfully deposited on fumed silica (f-SiO2) and exhibited excellent catalytic activity for the catalytic combustion of methane (CCM). It was manifested that the timing of ammonia introduction was of great importance in determining the particle sizes and electronic states of palladium nanoparticles, the desilication degree of SiO2 support material, and the redox properties and methane affinity of the Pd/f-SiO2-AE catalysts. The optimal Pd/f-SiO2-AE-2 catalyst, which converted 90% of lean methane at 333 °C at GHSV of 30,000 h − 1, performed better than its AE-1- and IM-prepared counterparts. In combination with complementary characterizations, DFT calculations and designed experiments, it was revealed that the uniformly dispersed palladium nanoparticles endowed the Pd/f-SiO2-AE-2 catalyst with more accessible sites. Moreover, the presence of Pd4+ species effectively promoted the methane adsorption capacity of the main active PdO phase, which was another critical reason for the outstanding performance. In addition, the necessity of the ammonia evaporation step was also elucidated by designed experiments. More importantly, taking the universality of this optimized AE method into consideration, our work thus put forward an effective and simple procedure to fabricate highly-active palladium nanoparticles for catalyst designers.

Synergy effect of highly dispersed palladium and Ni-SiW polyoxometalate-based metal-organic framework (POMOF) for highly efficient and selective nitroaromatics hydrogenation

The Pd/Ni-SiW catalysts with different Pd loadings (weight percent-0.77%, 1.41%, and 2.52%) are prepared by room-temperature precipitation method, which are with the Pd nanoclusters highly dispersed in Ni-SiW POMOF. These as-prepared catalysts show high catalytic activity for the hydrogenation of nitroaromatics under mild condition (hydrogen pressure-3.0 MPa and reaction temperature-40 ℃). Among them, the 1.41%Pd/Ni-SiW catalyst has 99% conversion, 100% selectivity and 255.5 h−1 TOF for p-nitroacetophenone hydrogenation to p-aminoacetophenone. The Pd nanoclusters are highly dispersed in the pores of Ni-SiW POMOF, resulting in appropriate size of the Pd nanoclusters making H2 much better dissociation, and the substrate is easily adsorbed at the Ni-SiW POMOF by the interaction of Ni-SiW POMOF-NO2 group. There is a synergistic effect between the Pd and Ni-SiW, which the existence of a two-dimensional framework composed of 4,4′-bipyridine and nickel nodes increases the adsorption capacity of nitro groups, thus preferentially adsorbing nitro groups.

Modulating adsorption of active hydrogen atoms on palladium nanoparticles: Doping ruthenium into metal–organic frameworks for efficient electrocatalytic hydrodechlorination

To simultaneously optimize the dispersion and electrocatalytic activity of palladium (Pd) nanoparticles, we report a novel Pd-NiRu-MOF/NF composite electrode with low noble metal dosage for electrocatalytic hydrodechlorination. The as-prepared electrode exhibits outstanding activity, particularly the complete dechlorination of 2-chlorophenol within 75 min at −0.85 V, outperforming reported state-of-the-art electrode materials. Moreover, the catalytic activity could be well-maintained after continuous five catalytic cycles and even 30-day exposure to air as well as deliver excellent catalytic performance for other priority chlorophenols. CO-stripping experiments demonstrate that the dispersion of Pd nanoparticles increases the electrochemically active surface area of Pd. X-ray photoelectron spectroscopy and density functional theory analysis disclose that the electronic structure of Pd is modulated via introducing Ru atoms into Pd-Ni-MOF/NF, thereby enhancing the adsorption of H*ads on Pd-NiRu-MOF/NF and boosting the electroreductive remediation of chlorophenols. Notably, the electrochemical dechlorination of chlorophenols remains effective in natural water or soil, indicating that Pd-NiRu-MOF/NF composite electrode has a good application potential in removing organic halides in wastewater or soil.

Size of cerium dioxide support nanocrystals dictates reactivity of highly dispersed palladium catalysts

The catalytic performance of heterogeneous catalysts can be tuned by modulation of the size and structure of supported transition metals, which are typically regarded as the active sites. In single-atom metal catalysts, the support itself can strongly affect the catalytic properties. Here, we demonstrate that the size of cerium dioxide (CeO 2 ) support governs the reactivity of atomically dispersed palladium (Pd) in carbon monoxide (CO) oxidation. Catalysts with small CeO 2 nanocrystals (~4 nanometers) exhibit unusually high activity in a CO-rich reaction feed, whereas catalysts with medium-size CeO 2 (~8 nanometers) are preferred for lean conditions. Detailed spectroscopic investigations reveal support size–dependent redox properties of the Pd-CeO 2 interface.

Palladium-Percolated Networks Enabled by Low Loadings of Branched Nanorods for Enhanced H2 Separations.

Nanoparticles (NPs) at high loadings are often used in mixed matrix membranes (MMMs) to improve gas separation properties, but they can lead to defects and poor processability that impede membrane fabrication. Herein, it is demonstrated that branched nanorods (NRs) with controlled aspect ratios can significantly reduce the required loading to achieve superior gas separation properties while maintaining excellent processability, as demonstrated by the dispersion of palladium (Pd) NRs in polybenzimidazole for H2 /CO2 separation. Increasing the aspect ratio from 1 for NPs to 40 for NRs decreases the percolation threshold volume fraction by a factor of 30, from 0.35 to 0.011. An MMM with percolated networks formed by Pd NRs at a volume fraction of 0.039 exhibits H2 permeability of 110Barrer and H2 /CO2 selectivity of 31 when challenged with simulated syngas at 200°C, surpassing Robeson's upper bound. This work highlights the advantage of NRs over NPs and nanowires and shows that right-sizing nanofillers in MMMs is critical to construct highly sieving pathways at minimal loadings. This work paves the way for this general feature to be applied across materials systems for a variety of chemical separations.

Bimetallic Atom Dual-Doped MoS2-Based Heterostructures as a High-Efficiency Catalyst To Boost Solar-Assisted Alkaline Seawater Electrolysis

For a large-scale production of green hydrogen via water splitting, seawater, because of its low-cost and abundant nature, is an attractive alternative to freshwater. An effective coordination purposely modulated electrocatalyst with high catalytic activity and selectivity is required to overcome the undesirable chlorine ion oxidation reaction that critically hampers electrolysis performance at the anode side. Herein, we reveal that dual-atomically dispersed palladium (Pd) and ruthenium (Ru) over two-dimensional MoS2 shelled CoNi alloy nanowires can obtain tailored properties to impressively improve hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities. The catalyst exhibits overpotentials for the HER and OER as low as 89 and 230 mV at 10 mA·cm–2 in alkaline freshwater, respectively, along with favorable stability. Theoretical studies indicate that dual-atomically dispersed Pd and Ru in MoS2 modifies S sites to be advantageous centers for optimum hydrogen adsorption, thus improving the catalytic activities. The electrolyzer of CoNi@MoS2–PdSARuSA(+,−) delivers a current response of 10 mA·cm–2 at small cell voltages of 1.45, 1.54, and 1.54 V along with high solar-to-hydrogen conversion efficiencies of 17.66, 17.71, and 18.14% in alkaline freshwater, simulated seawater, and natural seawater, respectively, beyond Pt/C(−)//RuO2(+) behaviors as well as previous reports.

Designing of Pd1/TiO2-x Nanosheets for the Electrocatalyzed Reduction of CO2

The electrochemical reduction of carbon dioxide into valuable products has attracted increasing attention to meet the demand for sustainable fuel, as well as achieving the carbon neutralization strategy. Pd is art of the state CO2RR catalyst but prone to be poisoned by the primary product CO. For the modulating the electronic state of Pd sites and therefore affinity for CO, we herein synthesized TiO2-x nanosheets to support Pd atoms. The oxygen vacancies were introduced into the titanium oxide by calcination to increase the electric conductivity of the titanium oxide, and more importantly, as a means of modifying the energy diagram of Pd. The morphology of the as-synthesized Pd1/TiO2-x was observed on high-resolution transmission electron microscope and Cs-corrected high-angle annular dark-field (HAADF)-scanning transmission electron microscope. The structure of the atomically dispersed palladium was also characterized by FTIR spectra of chemisorbed CO. The impedance of the Pd1/TiO2-x was determined to prove the improvement of its electric conductivity. The Faradaic efficiency for liquid products, mainly HCOOH/CH3OH of the electrochemical reduction of CO2 using this catalyst is 14.74%.

The effect of the support nature and palladium dispersion on activity and selectivity of the palladium catalyst in hydrogenation of sunflower oil

Samples of the powdered catalysts Pd/C and Pd/Ox, which were synthesized by depositing 0.5 and 1.0 wt.% Pd on carbon materials (Sibunit 159k, thermal black Т-900, Vulcan XC-72R) and oxide supports (Ox: γ-Al2O3, Cr2O3, Ga2O3, TiO2, Ta2O5 and V2O5, and kieselguhr FW-70), were studied. Their catalytic properties were investigated in the partial hydrogenation of sunflower oil. Comparative testing of the catalysts was performed in the kinetic mode using a static Parr reactor to estimate their activity and trans-isomerization selectivity. The effect of the average size of supported palladium particles (dCO) on the indicated characteristics in a wide range of dCO values was discussed.