Loading Palladium Research Articles

Porous and Homogeneous Nanoheterojunction-Accumulating PdO@ZnO Structure for Exhaled Breath Ammonia Sensing.

The functional gas sensor device plays a pivotal role in intelligent medical treatment, among which metal oxide semiconductors are widely studied because of their inexpensiveness and ease of fabrication. However, the metal oxide sensors present a significant challenge in detecting NH3 at ppm levels within complex exhaled gases. Herein, the ZnO/PdO-x series were prepared by in situ loading palladium particles and calcining using nano-ZIF-8 as a precursor, which not only provided more transport path for ammonia adsorption but also achieved homogeneous nanoheterojunction accumulation structure. The tailor-made ZnO/PdO-2 sensor exhibits the optimum gas sensitivity, with a response value of 5.56 for 100 ppm of NH3 at 160 °C and a lower detection limit of 0.75 ppm. Particularly, it has a clear quantitative response to the actual exhaled gas of liver and kidney patients. By elucidating the intrinsic link between the in situ loading of MOF templates and the sensing mechanism, it is expected to broaden the rational design of metal-oxide sensors and thus provide an effective method for clinical detection.

3D-Printing Functional Ceramic for One-Step Fabrication of Pd/C Catalytic Reactor

Catalysts are widely used in the chemical industry because of their environmental friendliness and low energy consumption. However, integrated fabrication of catalytic reactors (CRs) remains challenging. In this study, we propose the integrated manufacturing of a palladium-carbon (Pd/C) CR for the first time. The outer shell ink comprises Al2O3 powder and aluminum dihydrogen phosphate (AP), whereas the inner core ink consists of activated carbon powder, AP, and polymethylmethacrylate (PMMA). By integrating with the coaxial 3D printing strategy, the Pd/C CR can be freeform-designed with different core thicknesses, lengths, and shapes (W-type, L-type, and U-type). Based on this, a CR with excellent catalytic properties was further developed by loading palladium (Pd) particles. Typically, the resultant Pd/C CR with a length of 2.5 cm exhibits a catalytic efficiency of up to 97.6% after 60 min. This method of preparing Pd/C CR using coaxial 3D printing combines multimaterial 3D printing, integrated molding, and complex biomimetic structure fabrication. This offers a feasible and cost-effective solution that uses a simple fabrication process.

Construction of Marigold-like Poly(vinyl alcohol) Microspheres for Catalytic Microreactors.

It has long been pursued to develop polymer microspheres with various special morphologies and structures for better results in applications such as catalysis, drug delivery, and bioscaffolds. However, it remains a challenge to develop a facile method to produce poly(vinyl alcohol) (PVA) microspheres with special morphologies. Herein, a micron-sized marigold-like poly(vinyl alcohol) (CE-PVATPA) microsphere was engineered and fabricated by a feasible strategy, that is, emulsification-cross-linking, freeze-drying, and secondary acetal reaction steps. The morphological evolution of microspheres was systematically investigated under different conditions, and the procedure of constructing PVA microspheres with stabilizing marigold-like structures was proposed. More importantly, a specially structured PVA microsphere microreactor synergistically loading palladium metal nanoparticles (CE-PVATPA@Pd) for the heterogeneous catalyst 4-nitrophenol (4-NP) could be further demonstrated, which indicated high catalytic activity and excellent recyclability. The resultant stabilized fabricating method is promising to provide valuable guidance for the design and fabrication of a high-performance PVA microsphere microreactor.

An eco-friendly and energy-efficient protocol for the Heck reaction under solar radiation catalyzed by rice husk silica‐anchored cinchonine.Pd nanocomposite

An environmentally friendly and energy-efficient method for the carbon–carbon bond formation via cross-coupling Heck reaction using rice husk silica-anchored cinchonine.Pd nanocomposite as a heterogeneous catalyst under concentrated solar radiation is being reported. In this investigation, first, silica nanoparticles were synthesized using rice husks as available agricultural bioresources. Then, the surface of nano silica was modified by grafting (3-mercaptopropyl) trimethoxysilane, and after that, thiol-ene free radical reaction of its SH groups with alkene function of cinchonine by azobisisobutylonitrile initiator. Finally, the target nanocomposite, nano SiO2-S-Cin.Pd, was created via loading palladium nanoparticles into the mesoporous nanocomposite by its reaction by palladium acetate, followed by ethanol reduction. The structure and morphology of the nano SiO2-S-Cin.Pd nanocomposite was characterized using Fourier transform infrared spectra, X-ray diffraction patterns, energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The catalytic ability of this nanocomposite was investigated in the arylation of olefins in both concentrated solar radiation and conventional thermal conditions. A comparison of the conventional and CSR methods for C–C bond formation in PEG, showed that the CSR approach is a better alternative route with a high energy-saving strategy. The nanocatalyst is easily removed from the mixture and has been tested on several runs without a loss of catalytic activity. The heterogeneity of the nano SiO2-S-Cin.Pd catalyst was confirmed by hot filtration test. This method has the advantages of simple methodology, easy work-up, high yields, short reaction times, and greener conditions. In addition to convenience, this technology improves product purity and offers economic and environmental benefits.

Catalytic activity of a palladium(ii) complex modified on multi-wall carbon nanotubes: an efficient catalyst for the Suzuki cross-coupling reaction

We prepared a novel palladium (Pd) catalyst by loading palladium chloride onto novel functionalized multi-wall carbon nanotubes (MWCNTs). The Pd(ii)/MWCNT complex efficiently and selectively catalyzed large-scale synthesis of target molecules with high yield and large turnover numbers.

A novel magnetic cluster modified palladium-cellulose nanocrystal hybrids as recyclable catalyst for 4-nitrophenol reduction

The development of noble metal catalysts with high catalytic performance and low metal loading has attracted a lot of interest. However, the separation of the used nanoscale catalyst from the process is challenging. Most of the separation system, such as resin or membrane leads to a sacrifice of high surface area as well as catalytic efficiency. Herein, two series of recyclable catalysts were synthesized by loading palladium (Pd) particles onto melamine formaldehyde (MF) modified cellulose nanocrystals (CNC) and dopamine (DA) coated CNC. In situ co-precipitation of magnetic nanoparticle (MNP) clusters were used to impart magnetic characteristic to the catalysts. This magnetic cluster successfully achieved high magnetization without aggregation. The amount of palladium precursor added to the catalytic systems was optimized, where 10-Pd-PDC yielded 10.83 ± 2.43 nm discrete Pd loaded hybrids. The catalytic performance was assessed by the reduction of 4-nitrophenol (4-NP) in the presence of sodium borohydrides (NaBH 4 ). The 4-NP reduction mechanisms were analyzed using the Langmuir-Hinshelwood model and the apparent rate constant k (s -1 ), turnover frequency (TOF, h -1 ) and activity factors (s -1 g -1 ) were determined to be 2.142 × 10 -3 , 305.82 and 535.5 using MNP2-Pd-MC respectively. An induction time was observed for MNP4 or 5-Pd-PDC, where was attributed to the unignitable diffusion time for reagents to cross the thick PDA and MNP layer. The separation efficiency of the magnetic catalysts was evaluated by monitoring the absorbance at 400 nm as a function of separation time, and the MNP2-Pd-MC could be recycled 7 times without severe loss. Pd-MF-CNC displayed excellent catalytic performance for the reduction of 4-NP, while Pd-PDA-CNC possessed an inferior catalytic reactivity due to the reduced catalytic surface area. The developed templated MNP could be extended to other systems allowing for the recycling and reuse of the catalysts.

Phosphonated Polyethylenimine Maghemite Nanoparticles: A Convenient Support of Palladium for Cross-Coupling Reactions

Phosphonated polyethylenimine grafted on iron oxide nanoparticles was used as a magnetic support for loading palladium. This cheap and accessible heterogeneous catalyst demonstrated good efficiency in Suzuki-Miyaura, Mizoroki-Heck, and Tsuji-Trost couplings. The nanocomposite is resistant to harsh conditions and can therefore be recycled up to 10 cycles with high catalyst efficiency.

A novel core@double shell magnetic nitrogen-doped carbon nanotubes as a support for palladium nanoparticles: A highly efficient magnetic catalyst in the direct reductive coupling of nitroarenes and alcohols

Palladium nanoparticles anchored to the core-double shell magnetic nitrogen-doped carbon (Fe3O4@N-C) nanotubes have been successfully synthesized and characterized. It is possible to load palladium nanoparticles inside and outside of the nanotube. The catalytic performance of the as-prepared nanohybrids was evaluated by the one-pot synthesis of the imine and secondary amine directly from the readily available and stable nitrobenzene and benzyl alcohol precursors under exogenous base and solvent-free conditions. It showed excellent performance in this cascade reaction, as measured by high nitrobenzene conversion (99%) and turnover frequency (3.96 h−1).

Novel Pd-loaded self-standing hierarchical pore structure silicalite for low temperature toluene catalytic combustion

A novel Pd-loaded self-standing hierarchical pore structure silicalite were obtained by a handy polymer form board assisted hydrothermal method. The selected foam-shaped form board of a polyurethane (PU) foam monolith was regarded as the precursor of the self-standing hierarchical pore structure silicalite. The fruiting silicalite can steadily hold unique macroporous network structure and shape of the anterior original PU foam board . By means of the BET and BJH pore size distribution tests, the as-synthesis silicalite demonstrated hierarchical pore structure. The method of in-situ reduction was wielded to load palladium on the silicalite, and the catalytic performance of the catalyst to decompose toluene was tested at multiple burning temperatures. The experimental results revealed that the Pd-loaded catalyst can effectively decompose toluene at nearly 230°C, realizing low-temperature catalytic combustion of toluene.

Understanding the Effect of Blending Ethanol with Formic Acid on Pd Activity Towards Acidic Oxidation of Concentrated Formic Acid

Direct liquid fuel cells are among the most promising energy conversion devices for sustainable energy applications, especially as portable energy sources. The two most effective fuels are methanol and formic acid (FA), and even though methanol has higher energy content, it is toxic, non-renewable, and has high fuel crossover. However, FA can be produced easily from biomass and it is non-toxic and has a higher open circuit potential among other factors1. Usually, FA can be oxidized through two pathways, a direct pathway that is most desirable and directly produces CO2 2. While the indirect pathway produces CO as an intermedia that can adsorb to the catalyst surface deactivating it (poisoning effect)3. Palladium is known to be the most active catalyst for FA oxidation in acidic media4 but it is also easily poisoned by CO accumulation on its surface. The increase in FA concentration to get higher energy density would make the indirect oxidation pathway more favorable lowering the efficiency of the fuel cell. To overcome this problem low molecular weight organic additives were suggested to be used in combination with FA to suppress this poisoning effect by competing with CO molecules for the adsorption sites on the catalyst surface.In this work, the effect of using ethanol and FA blend fuels on the behavior of Pd/C towards FA oxidation was investigated. The preliminary cyclic voltammetry study showed promising results about ethanol's ability to inhabit the indirect FA oxidation pathway. However, the results obtained by the chronopotentiometry and by studying the first derivatives of the cyclic voltammetry data give more insightful results on the effect of ethanol in the fuel blend. It was found that ethanol will inhabit the indirect oxidation of FA up to specific concentration but it will also affect the direct oxidation after a giving time and that the applied potential will have an effect on the adsorption orientation of Ethanol molecules on the catalyst surface. References 1) Sun, J.; Luo, X.; Cai, W.; Li, J.; Liu, Z.; Xiong, J.; Yang, Z. Ionic-Exchange Immobilization of Ultra-Low Loading Palladium on a RGO Electro-Catalyst for High Activity Formic Acid Oxidation. RSC Adv. 2018, 8 (33), 18619–18625.2) Jiang, K.; Zhang, H.-X.; Zou, S.; Cai, W.-B. Electrocatalysis of Formic Acid on Palladium and Platinum Surfaces: From Fundamental Mechanisms to Fuel Cell Applications. Phys Chem Chem Phys 2014, 16 (38), 20360–20376.3) Gunji, T.; Matsumoto, F. Electrocatalytic Activities towards the Electrochemical Oxidation of Formic Acid and Oxygen Reduction Reactions over Bimetallic, Trimetallic and Core–Shell-Structured Pd-Based Materials. Inorganics 2019, 7 (3), 36.4) Gharib, A.; Arab, A. Improved Formic Acid Oxidation Using Electrodeposited Pd–Cd Electrocatalysts in Sulfuric Acid Solution. Int. J. Hydrog. Energy 2021, 46 (5), 3865–3875.

Highly Selective Semihydrogenation via a Wettability-Regulated Mass Transfer Process

Desired catalytic performance can be achieved by regulating the wettability of heterogeneous catalysts. Herein, by loading palladium nanoparticles within heterostructural gel supports, we achieved the wettability-controlled selective hydrogenation of phenylacetylene (PT) into styrene (ST) or ethylbenzene (ET) in aqueous media. During catalysis, the selectivity toward ST improved significantly as the catalyst hydrophilicity increased. Additionally, catalyst’s wettability had a negligible influence on its efficiency in the hydrogenation of PT. Mechanistic studies revealed that the catalyst’s wettability has less effect on its affinity for PT but markedly influences its affinity for ST. Hydrophobic catalysts favorably adsorbed semi-hydrogenated products (ST) and fully hydrogenated them to the corresponding ET. Contrastingly, hydrogenation of PT over hydrophilic catalysts remained in a semi-hydrogenated state owing to the quick desorption of ST from the catalyst surface, resulting from weak ST-catalyst interactions. We believe that the proposed strategy will be applicable in a wide range of heterogeneous catalysis reactions.

A bio-inspired dynamic filter with unidirectional channels based on cross-linked cellulose loading palladium nanoparticles for catalytic reduction of 4-nitrophenol

To remove the pollutants nitrophenol in wastewater, a bio-inspired dynamic filter (CE-Pd-EPI) with in-situ synthesized palladium nanoparticles (PdNPs) was prepared via chemical cross-linking and freeze casting. This bio-inspired filter has a hierarchical dual-porous structure with micron-scale unidirectional channels and nanoscale pores. This hierarchical porous structure facilitates rapid mass transfer of the liquid. Therefore, this filter can completely reduce 4-nitrophenol (4-NP, 2 mM) in 3 min. The rate constant (k) and turnover frequency (TOF) are 2.42 min−1 and 13.17 min−1, respectively, which are better than most reports so far. Moreover, this filter can also instantaneously catalyze the reduction of methylene blue (MB) to colorless. After five cycles, the conversion of 4-NP and MB by the filter still reaches 99.9%, demonstrating its excellent catalytic stability and reusability. In addition, in a continuous fluid catalytic system this filter has a low pressure (only 0.84 kPa) due to its bio-inspired unidirectional channel structure, which is extremely important for continuous industrial application. This bio-inspired dynamic filter has a guiding significance for the removal of organic pollutants in wastewater in industrial applications. Therefore, the bio-inspired dynamic filter described in this study has a great potential in the field of water treatment and environmental protection.

Pd/Fe2O3 with Electronic Coupling Single-Site Pd-Fe Pair Sites for Low-Temperature Semihydrogenation of Alkynes.

Dispersing single palladium atoms on a support is promising to minimize the usage of palladium and improve the selectivity for alkyne semihydrogenation, but its activity is often very low as a result of unfavorable H2 activation. Here, we load palladium onto α-Fe2O3(012) to construct highly active and stable single-site Pd-Fe pairs with luxuriant d-electron domination near the Fermi level driven by strong electronic coupling and prove that Pd-Fe pairs cooperatively adsorb H2 and dissociate an H─H bond, whereas solo Pd sites enable preferential desorption of C═C intermediate, thus achieving both high activity and high selectivity for alkyne hydrogenation. This catalyst exhibits state-of-the-art performance in purifying acetylene of ethylene stream, with 99.6% and 100% conversion and 96.7% and 94.7% selectivity at 353 and 393 K, respectively, and excellent stability with negligible activity decay after a 200 h test. This single-site pair inherits the advantage but overcomes the weakness of both Pd ensemble and single Pd atoms, enabling ultralow-Pd-loading catalysts for selective hydrogenation.

Solvent-free aerobic selective oxidation of benzyl alcohol catalyzed by palladium nanoparticles supported on nitrogen-containing ordered mesoporous carbon

A series of nitrogen-containing ordered mesoporous carbon (NOMC) materials have been prepared by a one-pot soft-templating method under an aqueous solution by adopting various nitrogen-containing precursors. The synthesized NOMC materials were utilized as catalyst supports to load palladium (Pd). The ordered mesostructures of NOMC have been reserved after the loading of Pd, and Pd nanoparticles were well dispersed on the surface of NOMC materials. The analytic results of XPS confirmed that the supported Pd species existed mainly in the form of metallic Pd (Pd0) and there was a probable interaction between Pd and nitrogen species of NOMC. In the solvent-free aerobic oxidation of benzyl alcohol, the Pd/NOMC materials demonstrated high catalytic activities, affording a maximum yield of benzaldehyde up to 95% at 95 °C of reaction temperature.

Controllable morphology of Pd-loaded potassium tantalates with high catalytic performance for ethylene glycol electrooxidation

In this work, potassium tantalates (KxTaxO3x, x = 1 or 2) with different crystal structures and morphologies are synthesized with a one-step hydrothermal method. The concentration of the KOH reactant played a crucial role in controlling the morphology of KxTaxO3x. When the concentration of KOH is low, an octahedral pyrochlore (K2Ta2O6) is obtained. In contrast, the cubic perovskite (KTaO3) is obtained at high KOH concentrations. Pd nanoparticles loaded onto K2Ta2O6 and KTaO3 (Pd/K2Ta2O6, Pd/KTaO3) electrocatalysts are then prepared with reflux reduction in ethanol. X-ray photoelectron spectroscopy results imply that the loading palladium is in the main Pd° form. The electrocatalytic activity of the Pd/K2Ta2O6 and Pd/KTaO3 electrocatalysts is investigated using cyclic voltammetry (CV) toward ethylene glycol (EG) oxidation in an alkaline medium. The CV results show that Pd/K2Ta2O6 and Pd/KTaO3 electrocatalysts modified glassy carbon electrodes have excellent catalytic activity for EG electrooxidation in an alkaline medium, superior to that of commercial Pd/C (10%). The enhancement of their electrocatalytic activity was owing to the synergistic reaction between Pd and KxTaxO3x. In addition, the electronic structure of the Pd/K2Ta2O6 and Pd/KTaO3 electrocatalysts was assessed using density functional theory. The calculation results indicated that electron transfer occurred in the complex region of Pd and KxTaxO3x.

Preparation of high electrochemical activity Pd/RGO composites on the microemulsion interface through radiation technique

Radiation techniques, with their advantages of being clean, economical, and efficient, have been widely studied for the synthesis of nanocomposites. In this study, reduced graphene loading palladium nanoparticles (Pd/RGO) were prepared in situ in a single step at the phase interface of an ionic liquid (IL)-based microemulsion of these nanoparticles exposed to a high-energy electron beam. The influence of the radiation dose and initial mass ratio of graphene oxide (GO) and PdCl2 were studied. In addition, the effect of the length of the alkyl chain of the IL on the shape and Pd nanoparticle content of Pd/RGO composites, as well as their electrochemical activity, were investigated in detail. The radiation dose did not affect the shape of the Pd nanoparticles but increased the Pd nanoparticle content of the Pd/RGO composites when the dose exceeded 80 kGy. The Pd nanoparticle content of the Pd/RGO composites decreased as the alkyl chain length of the ILs and the initial mass ratio of GO and PdCl2 increased. Both the Pd nanoparticle content and their distribution in the Pd/RGO composites have a great influence on their electrochemical performance. Finally, Pd/RGO composites with excellent electrochemical activity were produced efficiently by using the radiation technique. This study provides a basis for the synthesis of carbon-based noble metal nanocomposites using a simple clean and efficient method.

Eggshell recycling for fabrication of Pd@CaO, characterization and high-performance solar photocatalytic activity.

Recycling of waste materials into useful products is a promising strategy for environmental protection. Eggshell is one of the globally produced huge wastes. In this work, calcium oxide (CaO) nanoparticles were recycled via calcination of chicken eggshells at 1100 °C for 2 h. A novel nanocomposite, made of loading palladium nanoparticles on calcium oxide surface (Pd@CaO), is successfully fabricated through solid-solid interaction. The materials were characterized using different physicochemical techniques: Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis), photoluminescence (PL) analysis, ultra-high resolution field emission scanning electron microscope (FE-SEM), transmittance electron microscope (TEM), and X-ray diffraction (XRD). The study sheds light on the ability of the materials to be used for detoxification of crystal violet dye as pollutant model under solar irradiation. The effects of operational conditions, such as catalyst mass, initial dye concentration, pH, and illumination time, have been tested. The optimum conditions for crystal violet photocatalytic degradation in the presence of Pd@CaO were mild conditions. Control experiments studied the effect of sunlight in the absence of the catalyst, and the effect of the catalyst in the absence of sunlight does not provide the significant removal exhibited in the presence of catalyst under solar irradiation.

Palladium Nanoparticles Anchored on Sustainable Chitin for Phenol Hydrogenation to Cyclohexanone

A kind of natural, sustainable, and abundant biomass, chitin, is used as support to load palladium nanoparticles catalyst (Pd–chitin) for the transfer hydrogenation of phenolic compounds to ketones...

Fabrication of CS/GA/RGO/Pd composite hydrogels for highly efficient catalytic reduction of organic pollutants.

In this study, natural polymer material chitosan (CS) and graphene oxide (GO) with large specific surface area were used to prepare a new CS/RGO-based composite hydrogel by using glutaraldehyde (GA) as cross-linking agent. In addition, a CS/GA/RGO/Pd composite hydrogel was prepared by loading palladium nanoparticles (Pd NPs). The morphologies and microstructures of the prepared hydrogels were characterized by SEM, TEM, XRD, TG, and BET. The catalytic performance of the CS/GA/RGO/Pd composite hydrogel was analyzed, and the experimental results showed that the CS/GA/RGO/Pd composite hydrogel had good catalytic performance for degradation of p-nitrophenol (4-NP) and o-nitroaniline (2-NA). Therefore, this study has potential application prospect in wastewater treatment and provides new information for composite hydrogel design.

Atmospheric Selective Oxidation of Benzyl Alcohol Catalyzed by Pd Nanoparticles Supported on CeO2 with Various Morphologies

AbstractA series of ceria materials with various morphologies including rod, polyhedron, cube, and mesostructures, have been synthesized and employed as catalyst supports to load palladium. The physicochemical properties of the synthesized materials have been characterized by XRD, N2 adsorption–desorption, TEM, XPS, and O2‐TPD techniques. The results show Pd can be well dispersed on the ceria supports, whereas Pd/CeO2 materials possess different proportion of oxidic Pd (Pd2+) and Ce3+ species. In the liquid‐phase selective oxidation of benzyl alcohol using O2 as an oxidant, Pd/CeO2‐poly demonstrates the highest catalytic activity, affording a maximum yield of benzaldehyde up to 87% under 90 °C. According characterization analysis, the combination of more Ce3+ species and higher proportion of Pd2+ as well as O2‐activating ability are responsible for the high catalytic activity of Pd/CeO2‐poly.