PdO Nanoparticles Research Articles

Size‐Dependent Catalytic Activity Over MOF‐Derived Cobalt Oxide Supported PdO Nanoparticles in Suzuki Reaction

ABSTRACTPalladium nanoparticles immobilized on ZIF 67‐derived porous CoOx were prepared by wet‐impregnation method, followed by calcination at different temperatures. The calcination temperature has been employed to effectively manipulate the size of metal nanoparticles, where higher calcination temperatures resulted in larger sizes. The experimental results revealed that by manipulating the calcination temperature, the synthesis of palladium nanoparticles with varying sizes could be effectively controlled. Increasing the calcination temperature resulted in larger particle sizes. At a calcination temperature of 350°C, the synthesis process produced the smallest palladium nanoparticles, averaging 1.35 nm in size, facilitating the reaction between aryl halides and arylboronic acids with yields ranging from 83% to 99%. Furthermore, these nanoparticles demonstrated superior catalytic activity and recyclability.

Oxidation cocatalyst/S-scheme junction cooperatively assists photocatalytic H2 production in ternary hybrid: The case of PdO@TiO2-Cu2O

Solar-driven photocatalytic hydrogen production from water splitting holds significant potential in addressing the energy crisis and environmental pollution. However, rapid recombination of photogenerated carriers and insufficient surface catalytic reaction kinetics hinder the photocatalytic process. Constructing the catalytic systems with multi-channel charge-separation can effectively alleviate those issues. In this work, ternary PdO@TiO2-Cu2O composites have been synthesized through precursor calcination and low-temperature reduction, where PdO and Cu2O nanoparticles couple with the TiO2 nanorods. Comparing to single TiO2, binary PdO@TiO2 and TiO2-Cu2O, the PdO@TiO2-Cu2O hybrid exhibits enhanced photocatalytic hydrogen production performance (5831μmol g-1h−1), with a hydrogen production rate more than three times that of single TiO2. Based on the band structures of TiO2 and Cu2O, along with the photochemical/electrochemical, in-situ EPR, Photoluminescence (PL) tests, and work function calculations, the formation of an S-scheme heterojunction at the TiO2-Cu2O interface under light illumination facilitates the recombination of electrons in the conduction band (CB) of TiO2 with holes in the valence band (VB) of Cu2O. In this regard, the established built-in electric field significantly accelerates the transfer of photogenerated charges while preserving their respective strong oxidation and reduction capabilities. Meanwhile, the introduction of PdO enriches the holes and further enhances the rate of charge separation. This S-scheme heterojunction with directional charge transfer and oxidation cocatalyst collectively form multi-channels of charge separation, optimizing charge migration and enabling efficient hydrogen production, thus improving the photocatalytic capability of pristine TiO2. This study provides a rational approach to construct efficient S-scheme heterojunction/oxidation cocatalyst multi-component catalytic systems for water splitting into hydrogen.

Macroporous Poly(hydromethylsiloxane) Networks as Precursors to Hybrid Ceramics (Ceramers) for Deposition of Palladium Catalysts.

Poly(hydromethylsiloxane) (PHMS) was cross-linked with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (D4Vi) in water-in-oil High Internal Phase Emulsions to form macroporous materials known as polyHIPEs. It was shown that in the process of pyrolysis under Ar atmosphere at 520 °C, the obtained polyHIPEs were converted to ceramers with high yields (82.8-88.0 wt.%). Structurally, the obtained ceramers were hybrid ceramics, i.e., they consisted of Si-O framework and preserved organic moieties. Macropores present in the polyHIPE precursors remained in ceramers. Ceramers contained also micro- and mesopores which resulted from the precursor's mass loss during pyrolysis. Total pore volume and BET specific surface area related to the existence of micro- and mesopores in ceramers depended on the PHMS: D4Vi ratio applied in polyHIPE synthesis. The highest total pore volume (0.143 cm3/g) and specific surface area (344 m2/g) were reached after pyrolysis of the precursor prepared with the lowest amount of D4Vi as compared to PHMS. The composite materials obtained after deposition of PdO nanoparticles onto ceramers followed by reduction of PdO by H2 were active and selective catalysts for phenylacetylene hydrogenation to styrene.

Catalytic combustion of light hydrocarbons over Pd − Pt/Al2O3: The hidden Pt1 active sites

Rationalizing the roles of different active phases in Pd − Pt/Al2O3 for light hydrocarbon (methane, ethane, propane, ethylene, and propylene) catalytic combustion is of central importance in producing practical air pollution abatement and power generation systems. So far, considerable efforts have been paid to understanding the microstructural evolution of Pd − Pt catalysts during high-temperature ageing, while much less is known about the key features in these catalysts at industry-related mild temperatures (e.g., ≤ 550 °C). In this article, by starting from platinum and palladium nitrates impregnated on commercially available γ-Al2O3, the microstructural evolution of Pd − Pt/Al2O3 induced by calcinations at below 550 °C in air was distinguished and further disentangled by comparison with the cases of Pt/Al2O3. Supported by electron microscopy, in situ DRIFTS, and other characterizations, we showed that the PdO nanoparticles on Pd − Pt/Al2O3 catalysts worked not only as a reactive phase for alkane combustion, but also as a “trapper” that reduced the amount of single-site Pt1 species by anchoring and aggregating them on the PdO (101) surface during calcinations. Since these Pt single atoms were highly reactive for the combustion of alkenes, Pd − Pt/Al2O3 exhibited enhanced methane/ethane/propane oxidation activity with increasing Pd contents, but were weaker ethylene and propylene oxidizers than Pt/Al2O3. Water and sulfur tolerance tests were also performed to evaluate the true practicability of the catalysts, which demonstrated the overall higher robustness of the Pd-free recipes for light hydrocarbon combustion.

Construction of mesoporous PdO/YVO4 p-n heterojunction wrinkled-nanosheets fostering electron transfer for boosted photocatalytic atrazine degradation under visible light

Heterogeneous photocatalysis is an environmentally friendly and sustainable process for water purification. Unluckily, the significant propensity for photo-induced charge carriers to recombine rapidly, as well as poor responsiveness to visible light, are substantial shortcomings in conventional semiconductor photocatalysis. In this study, a facile surfactant-mediated solvothermal process, along with an impregnation approach was applied to fabricate a series of PdO/YVO4 p-n heterostructures with diverse PdO contents for atrazine (AT) oxidation under visible light. Diverse characterization tools confirmed the homogeneous dispersion of PdO nanoparticles (NPs) on mesoporous YVO4 nanosheets, thereby forming p-n junctions and facilitating charge carriers' separation. Moreover, the fabricated p-n heterojunction materials exhibited enhanced photoabsorbance abilities. It was demonstrated that the inclusion of PdO NPs considerably enhanced the photocatalytic capability and performance of the YVO4 candidate under visible light. The complete atrazine decomposition was accomplished on 2.0 g/L of 0.6 wt% PdO/YVO4 with a remarkable rate constant of 52.51 × 10−3 min−1 which was ca. 25.6-folds more than that achieved on bare YVO4 (2.05 × 10−3 min−1), while maintaining a 98.0 % recycling rate. The p-n heterojunction photocatalyst constructed between PdO and YVO4 exhibited a key role in improving the photoharvesting capability and accelerating the separation of photo-produced carriers, generating highly reactive oxygen species to degrade AT effectively. All in all, this achievement proposes a new YVO4-based heterostructures that can effectively eliminate organic contaminants in wastewater and also presents novel ideas for designing other heterojunctions.

A graphene oxide-modified biosensor for non-invasive glucose monitoring in college athletes

The study aims to address the need for accurate and real-time monitoring of glucose levels in college athletes during physical activities. This work reports on the development of an electrochemical sensor that uses glucose oxidase (GOx) immobilized on PdO nanoparticles to reduce graphene oxide (rGO) nanocomposite printed on a cellulose substrate (GOx/PdO-rGO/C-PE). The successful reduction of GO to rGO, the production of the PdO-rGO nanocomposite, and the electropolymerization of GOx on the PdO-rGO nanocomposite were all validated by the material characterization. The biosensor's electrochemical response investigation showed that its detection limit was 0.046 μM and its sensitivity was 0.03239 μA/μM. Excellent stability, reproducibility, and glucose selectivity were shown by the GOx/PdO-rGO/C-PE, which makes it a viable option for consistent and dependable glucose sensing in real-world applications. The real sample analysis assessed how well the combination of GOx/PdO-rGO/C-PE could identify glucose in human serum. Furthermore, under a variety of real-world conditions, such as during various physical activities and at different times of the day, the sensor demonstrated outstanding performance in real-time glucose monitoring. These findings imply that the GOx/PdO-rGO/C-PE offers accurate and dependable readings in the field of non-invasive glucose monitoring, which will be especially helpful for college and professional athletes.

Biosynthesis Parameters Control the Physicochemical and Catalytic Properties of Microbially Supported Pd Nanoparticles.

The biosynthesis of Pd nanoparticles supported on microorganisms (bio-Pd) is achieved via the enzymatic reduction of Pd(II) to Pd(0) under ambient conditions using inexpensive buffers and electron donors, like organic acids or hydrogen. Sustainable bio-Pd catalysts are effective for C-C coupling and hydrogenation reactions, but their industrial application is limited by challenges in controlling nanoparticle properties. Here, using the metal-reducing bacterium Geobacter sulfurreducens, it is demonstrated that synthesizing bio-Pd under different Pd loadings and utilizing different electron donors (acetate, formate, hydrogen, no e- donor) influences key properties such as nanoparticle size, Pd(II):Pd(0) ratio, and cellular location. Controlling nanoparticle size and location controls the activity of bio-Pd for the reduction of 4-nitrophenol, whereas high Pd loading on cells synthesizes bio-Pd with high activity, comparable to commercial Pd/C, for Suzuki-Miyaura coupling reactions. Additionally, the study demonstrates the novel synthesis of microbially-supported ≈2nm PdO nanoparticles due to the hydrolysis of biosorbed Pd(II) in bicarbonate buffer. Bio-PdO nanoparticles show superior activity in 4-nitrophenol reduction compared to commercial Pd/C catalysts. Overall, controlling biosynthesis parameters, such as electron donor, metal loading, and solution chemistry, enables tailoring of bio-Pd physicochemical and catalytic properties.

In situ preparation of SnO2/Pd@TiO2 bilayer sensor for highly sensitive and fast detection of H2S based on electrohydrodynamic jet printing

A micron-scale bilayer H2S sensor fabricated by electrohydrodynamic (EHD) jet printing in situ was evaluated. The prepared sensor consisted of a Pd@TiO2 cover layer (porous catalytic sensing layer), a SnO2 bottom layer (electron transport layer) and a Sn-Ti transition layer between them. The addition of TiO2 nanoparticles to the cover layer led to a porous structure after one-step sintering. The increase in specific surface area and the formation of heterojunction effectively improved the sensor sensitivity. The PdO nanoparticles loaded on the surface of TiO2 nanoparticles further improved the performance due to its catalysis. Since the kinetic energy of droplets of the same size generated by EHD inkjet printing is about 48 times that of inkjet printing, the film density is much higher than that of inkjet printing. The relatively dense bottom layer, and the thick and stable transition layer improved the long-term stability of the sensor. The detection limit of the sensor is 6 ppb, with linear range of 0.02–10 ppm H2S. The response and recovery times are 7 s and 45 s (2 ppm H2S), respectively. After 9 months of intermittent measurement, the response of the sensor to 2 ppm H2S decreased by only 10.6%.

Enabling direct oxidation of ethane to acetaldehyde with oxygen using supported PdO nanoparticles.

Industrial-scale production of acetaldehyde relies heavily on homogeneous catalysts. Here, we used ethane as the feedstock and developed ZSM-5-supported PdO nanoparticles for the direct oxidation of ethane to acetaldehyde by utilizing O2 and CO. PdO nanoparticles clearly demonstrate effective activity and prevent the further deep oxidation of acetaldehyde.

Superior catalytic combustion of methane over Pd supported on oxygen vacancy-rich NiAl2O4

The high concentration of oxygen vacancies and the presence of stable PdO nanoparticles collectively enhance the exceptional activity and durability of the Pd/NiAl2O4 catalyst in the methane combustion process.

Trace PdO and Co-MOF derivative modified SnO2 nanofibers for rapid triethylamine detection with little humidity disturbance

Triethylamine (TEA) is a significant compound, but it is toxic and flammable. Since the humidity in the environment is constantly changing, it is meaningful to develop a sensor that can detect TEA efficiently and is less disturbed by humidity. Here, Pd nanoparticles with a small particle size (about 4 nm) were prepared by reduction method and dispersed on Co-MOF (ZIF-67). Pd@ZIF-67-derived trace PdO and Co3O4 nanoparticles were evenly decorated on SnO2 nanofibers by electrospinning and calcination. The ratios of PdO to SnO2 in PdO-Co3O4-SnO2 were 0.012 wt% and 0.048 wt%, respectively. The response of the sensor based on 0.012 wt% PdO-Co3O4-SnO2 to 20 ppm TEA was 14 at 240 °C. The response time was 3 s and the lowest concentration actually detected was 1 ppm. The synergistic effects of oxygen vacancy, p-n junction, electron sensitization of PdO and morphology of composite improved sensing performance. In addition, due to the inhibition of hydroxyl poisoning by PdO and the oxidation assisting effect of Co3O4, the composite had excellent humidity resistance.

Effects of dealumination on the methane-combustion activity of Pd/SSZ-13 catalysts

This study investigated the effects of dealumination on Pd/SSZ-13 catalysts for methane combustion. Pd(1)/SSZ-13 (HTA), prepared by treating the catalyst hydrothermally at 750 °C, displayed extremely low catalytic activity. In contrast, Pd(1)/SSZ-13 (DeAl), prepared by treating the SSZ-13 support hydrothermally followed by Pd impregnation, exhibited superior catalytic activity for methane oxidation. Catalytic properties, including zeolite hydrophobicity and Pd location and states, were investigated by using various characterization techniques to clarify the differences between the catalysts. Most Pd species in the Pd/SSZ-13 (HTA) catalyst existed as Pd ions, which were not very active for the reaction. On the contrary, most Pd species in the Pd(1)/SSZ-13 (DeAl) catalyst existed as PdO nanoparticles at the external surface, which were highly active for methane oxidation. The study results suggested that the amount of external PdO nanoparticles should be maximized in order to make Pd/SSZ-13 catalyst highly active for methane combustion, which was achieved by dealuminating the SSZ-13 support before Pd impregnation.

Ultra-high sensitive and selective NO2 gas sensing performance of Au/Pd co-functionalized ZnO nanowires by a one-pot hydrothermal method

The gas sensing properties of semiconducting metal oxides will be further improved by the co-functionalization of bimetallic noble elements. However, most methods for the preparation of co-functionalized metal oxides of two noble metals are complex and costly. In this study, the Au/Pd co-functionalized ZnO nanowires were prepared by a facile one-pot hydrothermal method. The crystal structure, nano-size, chemical composition and morphology of the samples were tested by XRD, TEM, XPS and SEM, respectively. The Au and Pd elements were distributed on the ZnO nanowire surface in the form of Au, Pd and PdO nanoparticles, and some of them were doped into the lattice of ZnO. The gas sensing results showed that the response of 1 mol% Au/Pd–ZnO was 732.4 to 5 ppm NO2 gas at optimal operating temperature of 100 °C, which was 32 times higher than that of pristine ZnO, and the response/recovery times were significantly reduced to only 36/6 s. This sample also exhibits a good reproducibility. Moreover, the Au/Pd co-functionalization can significantly enhance the selectivity of the ZnO nanowires to NO2 gas. Our work showed that the activation energy can be further reduced to 0.172 eV by Au/Pd co-functionalization.

In situ confinement of PdO within zeolite as robust adsorbent/catalyst for toluene elimination

Herein, 1 wt% PdO nanoparticles were in situ confinement within HZSM-5 by one-pot hydrothermal method. Characterizations confirmed that Pd(en)22+ were first loaded on small pieces HZSM-5, after small HZSM-5 self-assembly aggregated into larger pieces, Pd active sites were sandwiched in the HZSM-5 crystal with small particle size and high dispersion. The sample was thermal-stable after calcination or utilization at 800 °C, which guaranteed Pd@Z5 a robust bi-functional adsorbent/catalyst for VOCs elimination. The adsorption capacity reached 58.5 mg/g in 100 ppm toluene/humid air, and the adsorption efficiency was not affected by 100 ∼ 500 ppm toluene. Pd@Z5 was stable for toluene oxidation in switching temperatures, PdO size was almost unchanged under 800 °C. Conversely, PdO impregnated directly on ZSM-5 suffered significant sintering after calcination at 800 °C, leading PdO nanoparticles decomposed and aggregated into larger nanoparticles. The adsorption capacity of Pd/Z5-800 declined by 40% and its T90 increased by 26 °C compared to Pd/Z5. Furthermore, Pd@Z5 showed better resistance to SO2 than Pd/Z5, demonstrating the sample had great potential for practical application.

Surface graft for effective PdO nanoparticles anchoring on Beta zeolite with outstanding lean methane combustion performance

A post-synthetic modification strategy for anchoring PdO nanoparticles on the Beta zeolite surface and obtaining stable and highly dispersed PdO sites with abundant active Pdn+ (0 < n < 2) species was reported. The modified Beta supported Pd catalyst with a 0.94 wt% Pd loading amount shows (>) 99% methane conversion at 375 °C with a space velocity of 30,000 mL h−1 g−1 and a satisfied long-term (>30 h) CH4 oxidation stability at 340 °C. Such a post-synthetic strategy provides a new way to disperse and stabilize noble metal particles on zeolite support for harsh catalytic process.

Mesoporous zirconia- supported PdO nanoparticles with promoted their photocatalytic ability for desulfurization of thiophene

Mesoporous zirconia- supported PdO nanoparticles with promoted their photocatalytic ability for desulfurization of thiophene

Pd-Ceria/CNMs Composites as Catalysts for CO and CH4 Oxidation.

The application of composite materials as catalysts for the oxidation of CO and other toxic compounds is a promising approach for air purification. In this work, the composites comprising palladium and ceria components supported on multiwall carbon nanotubes, carbon nanofibers and Sibunit were studied in the reactions of CO and CH4 oxidation. The instrumental methods showed that the defective sites of carbon nanomaterials (CNMs) successfully stabilize the deposited components in a highly-dispersed state: PdO and CeO2 nanoparticles, subnanosized PdOx and PdxCe1-xO2-δ clusters with an amorphous structure, as well as single Pd and Ce atoms, are formed. It was shown that the reactant activation process occurs on palladium species with the participation of oxygen from the ceria lattice. The presence of interblock contacts between PdO and CeO2 nanoparticles has an important effect on oxygen transfer, which consequently affects the catalytic activity. The morphological features of the CNMs, as well as the defect structure, have a strong influence on the particle size and mutual stabilization of the deposited PdO and CeO2 components. The optimal combination of highly dispersed PdOx and PdxCe1-xO2-δ species, as well as PdO nanoparticles in the CNTs-based catalyst, makes it highly effective in both studied oxidation reactions.

Effect of interaction between Pd and Fe in modified red mud on catalytic decomposition of toluene.

As an industrial solid waste produced by alumina industry, red mud was modified as support of Pd catalysts for toluene catalytic oxidation in this paper. The xPd/MRM catalysts had high activity for toluene catalytic oxidation, and the 0.3Pd/MRM catalyst showed the best catalytic performance (T50 = 175 °C and T100 = 200 °C). The results indicated that the prepared 0.3Pd/MRM catalyst had more ratio of surface-adsorbed oxygen and Fe3+, rather than MRM and RM, which benefitted to the toluene oxidation. The excessive Pd species and the growth of the PdO nanoparticles negatively affected the catalytic efficiency of toluene. 0.4Pd/MRM activity decreased because of PdO aggregation in the catalyst, which could be confirmed by TEM analysis. The results of XPS, H2-TPR, FT-IR, O2-TPD, and Raman examination revealed that the formation of Pd-O-Fe under the interaction between Fe in MRM and Pd (Pd2+ + Fe 2+ → Pd0 + Fe3+) increased the electron transfer and raised the mobility of surface-adsorbed oxygen. Furthermore, in situ DRIFTS and GC-MS were used to detect intermediate products of catalytic reactions, and the reaction mechanism of catalysts was also studied. The catalytic oxidation of toluene on 0.3Pd/MRM catalyst might have two reaction paths simultaneously. The first reaction path would be toluene → species benzyl → benzaldehyde → benzoic acid → long-chain aldehydes or carboxylic acids → CO2 and H2O. The second reaction path would be toluene → benzene → phenol → long-chain aldehydes or carboxylic acids → CO2 and H2O.

Synthesis of novel graphene-based targeted hydrogen getter nanocomposites and their properties

The getter setting is critical for maintaining a high vacuum environment in the annular space of multilayer insulation in the cryogenic vessel. To maximize the sorption of residual gases, particularly hydrogen, an efficient targeted hydrogen getter must be designed. In this study, PdO nanoparticles and Alkyne-PVA were loaded onto graphene oxide to create an efficient and cost-effective targeted hydrogen getter. Raman, XRD, XPS, SEM, TEM, and other characterization methods were used to investigate the microstructure and morphology of the intermediate and Alkyne-PVA-(GO-PdO) nanocomposites. The “Getter Sorption Properties Test System” was used to evaluate the hydrogen sorption properties of the nanocomposites. The results show that the super high specific surface area and efficient network structure of GO can be used as a good substrate material for the loading of PdO nanoparticles and Alkyne-PVA, and that the nanocomposites prepared with reasonable ratios of PdO nanoparticles and Alkyne-PVA have excellent hydrogen sorption performance, and have promising application prospects. The simultaneous use of unsaturated hydrocarbon branched chain and Pd element to the construction of a low-temperature vacuum annular space hydrogen getter in this work is critical to the commercial popularization of hydrogen getters.

Revealing the Chemical State of Palladium in Operating In2 O3 Gas Sensors: Metallic Pd Enhances Sensing Response and Intermetallic Inx Pdy Compound Blocks It.

The sensing response of metal oxides activated with noble metal nanoparticles is significantly influenced by changes to the chemical state of corresponding elements under operating conditions. Here, a PdO/rh-In2 O3 consisting of PdO nanoparticles loaded onto rhombohedral In2 O3 was studied as a gas sensor for H2 gas (100-40000 ppm in an oxygen-free atmosphere) in the temperature range of 25-450 °C. The phase composition and chemical state of elements were examined by resistance measurements combined with synchrotron-based in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy. As found, PdO/rh-In2 O3 undergoes a series of structural and chemical transformations during operation: from PdO to Pd/PdHx and finally to the intermetallic Inx Pdy phase. The maximal sensing response (RN2 /RH2 ) of ∼5 ⋅ 107 towards 40000 ppm (4 vol %) H2 at 70 °C is correlated with the formation of PdH0.706 /Pd. The Inx Pdy intermetallic compounds formed around 250 °C significantly decrease the sensing response.