Efficient Catalytic Production of Hydrogen Peroxide Using Tin-containing Zeolite Fixed Palladium Nanoparticles with Oxidation Resistance

The metal surfaces tend to be oxidized in air through dissociation of the O−O bond of oxygen to reduce the performances in various fields. Although several ligand modification routes have alleviated the oxidation of bulky metal surfaces, it is still a challenge for the oxidation resistance of small-size metal nanoparticles. Herein, we fixed the small-size Pd nanoparticles in tin-contained MFI zeolite crystals, where the tin acts as an electron donor to efficiently hinder the oxidation of Pd by weakening the adsorption of molecular oxygen and suppressing the O−O cleavage. This oxidation-resistant Pd catalyst exhibited superior performance in directly synthesizing hydrogen peroxide from hydrogen and oxygen, with the productivity of hydrogen peroxide at ≈10,170 mmol g_Pd⁻¹ h⁻¹, steadily outperforming the catalysts tested previously. This work leads to the hypothesis that tin is an electron donor to realize oxidation-resistant Pd within zeolite crystals for efficient catalysis to overcome the limitation of generally supported Pd catalysts and further motivates the use of oxidation-resistant metal nanoparticles in various fields.     

Supported Pd–Cu Bimetallic Nanoparticles That Have High Activity for the Electrochemical Oxidation of Methanol

Monodisperse bimetallic Pd–Cu nanoparticles with controllable size and composition were synthesized by a one‐step multiphase ethylene glycol (EG) method. Adjusting the stoichiometric ratio of the Pd and Cu precursors afforded nanoparticles with different compositions, such as Pd₈₅–Cu₁₅, Pd₅₆–Cu₄₄, and Pd₃₉–Cu₆₁. The nanoparticles were separated from the solution mixture by extraction with non‐polar solvents, such as n‐hexane. Monodisperse bimetallic Pd–Cu nanoparticles with narrow size‐distribution were obtained without the need for a size‐selection process. Capping ligands that were bound to the surface of the particles were removed through heat treatment when the as‐prepared nanoparticles were loaded onto a Vulcan XC‐72 carbon support. Supported bimetallic Pd–Cu nanoparticles showed enhanced electrocatalytic activity towards methanol oxidation compared with supported Pd nanoparticles that were fabricated according to the same EG method. For a bimetallic Pd–Cu catalyst that contained 15 % Cu, the activity was even comparable to the state‐of‐the‐art commercially available Pt/C catalysts. A STEM‐HAADF study indicated that the formation of random solid‐solution alloy structures in the bimetallic Pd₈₅–Cu₁₅/C catalysts played a key role in improving the electrochemical activity.     

Single-Atom or Dual-Atom in TiO2 Nanosheet: Which is the Better Choice for Electrocatalytic Urea Synthesis?

As rising star materials, single-atom and dual-atom catalysts have been widely reported in the electro-catalysis area. To answer the key question: single-atom and dual-atom catalysts, which is better for electrocatalytic urea synthesis? we design two types of catalysts via a vacancy-anchorage strategy: single-atom Pd₁−TiO₂ and dual-atom Pd₁Cu₁−TiO₂ nanosheets. An ultrahigh urea activity of 166.67 mol_urea mol_Pd⁻¹ h¹ with the corresponding 22.54 % Faradaic efficiency at −0.5 V vs. reversible hydrogen electrode (RHE) is achieved over Pd₁Cu₁−TiO₂, which is much higher than that of Pd₁−TiO₂. Various characterization including an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and theoretical calculations demonstrate that dual-atom Pd₁Cu₁ site in Pd₁Cu₁−TiO₂ is more favorable for producing urea, which experiences a C−N coupling pathway with a lower energy barrier compared with Pd₁ in Pd₁−TiO₂.     

刺状Pd纳米粒子的室温合成及其对乙醇氧化的电催化性能

室温下以氯化胆碱为稳定剂,用化学还原法合成了刺状Pd纳米粒子(Pdtnh0o0r0n).透射电子显微镜和电化学循环伏安研究结果表明Pdtnh0o0r0n具有较高密度的台阶位,与商业Pd黑催化剂相比较,Pdtnh0o0r0n对乙醇氧化的电催化活性显著提高,氧化电流密度是商业Pd黑催化剂的1.2倍(-0.40--0.30V)-1.5倍(-0.65--0.40V),起始氧化电位和峰电位均负移50mV.相同电流密度下,Pdtnh0o0r0n催化剂对乙醇的氧化电位均更低.     

Metal-Oxo Electronic Tuning via In Situ CO Decoration for Promoting Methane Conversion to Oxygenates over Single-Atom Catalysts

Direct methane conversion (DMC) to oxygenates at low temperature is of great value but remains challenging due to the high energy barrier for C−H bond activation. Here, we report that in situ decoration of Pd₁-ZSM-5 single atom catalyst (SAC) by CO molecules significantly promoted the DMC reaction, giving the highest turnover frequency of 207 h⁻¹ ever reported at room temperature and ~100 % oxygenates selectivity with H₂O₂ as oxidant. Combined characterizations and DFT calculations illustrate that the C-atom of CO prefers to coordinate with Pd₁, which donates electrons to the Pd₁−O active center (L−Pd₁−O, L=CO) generated by H₂O₂ oxidation. The correspondingly improved electron density over Pd−O pair renders a favorable heterolytic dissociation of C−H bond with low energy barrier of 0.48 eV. Applying CO decoration strategy to M₁-ZSM-5 (M=Pd, Rh, Ru, Fe) enables improvement of oxygenates productivity by 3.2–11.3 times, highlighting the generalizability of this method in tuning metal-oxo electronic structure of SACs for efficient DMC process.     

Facile Synthesis of Pd‐Ni Nanoparticles on Reduced Graphene Oxide under Microwave Irradiation for Formic Acid Oxidation

Pd and Pd_x Ni nanoparticles have been supported on reduced graphene oxide (Pd/rGO and Pd_x Ni/rGO ) by using the microwave‐assisted heating method in glycol. The morphology, composition and electrochemical performance have been characterized by TEM , XRD , XPS and electrochemical methods. The XRD and XPS results show that there are no PdNi alloy particles formed in Pd_x Ni/rGO and the composites exist mostly in the form of Pd⁰ and NiOOH species. The electrochemical results reveal that Pd_x Ni/rGO synthesized from the feeding source of Pd and Ni with an atomic ratio of 4∶1 exhibits higher activity, better stability and smaller electron transfer resistance toward formic acid electro‐oxidation compared with commercial Pd/C, Pd/rGO and other Pd_x Ni/rGO samples. The excellent electrocatalytic performance indicates that the addition of appropriate amount of Ni can greatly enhance the activity and stability of Pd catalysts for formic acid oxidation.     

An enhanced Nonenzymatic Electrochemical Glucose Sensor Based on Copper‐Palladium Nanoparticles Modified Glassy Carbon Electrodes

Novel copper‐palladium nanoparticles modified glassy carbon electrodes (Cu−Pd/GC) with enhanced nonenzymatic sensing for glucose were facilely prepared by one‐step electrodeposition. The structure and composition of the prepared nanoparticles were characterized by XRD, SEM, TEM and EDS, respectively. The electrode modified process was characterized by electrochemical impedance spectroscopy. Cyclic voltammetry and chronoamperometric experiments were used to evaluate the electrocatalytic activities of the electrodes toward glucose. The surface morphology and the electrocatalytic activities of Cu−Pd/GC was compared to Pd and Cu nanoparticles modified glassy carbon electrodes (Pd/GC and Cu/GC), respectively. Thanks to homogeneous distribution of Cu−Pd nanoparticles and the synergistic effect of Cu and Pd atoms, Cu−Pd/GC exhibited the highest sensitivity (298 μA mM⁻¹ cm⁻²) and the widest linear amperometric response (0.01 mM to 9.6 mM, R²=0.996) toward glucose compared to Pd/GC and Cu/GC. The detection limit of Cu−Pd/GC was 0.32 μM (S/N=3). In addition, the as‐prepared Cu−Pd/GC glucose sensor also exhibited exceptional capabilities of anti‐interference, reproducibility and long‐term stability. The as‐prepared sensor was also evaluated for determination of glucose concentration in human blood serum samples, which exhibited high reliability and accuracy, having great potential in clinical application.     

An Effective Non-Enzymatic Glucose Biosensor Based on Nanostructured CuxO/Cu Electrodes Synthesized in Situ by Copper Anodization

Potentiostatic anodization was developed to synthesize copper oxide/copper (Cu_xO/Cu, x=1,2) electrode with nano structure for sensitive non-enzymatic glucose detection. At a catalytic potential of 0.55 V, the CuO/Cu electrode presented a high sensitivity of 2954.38 μA mM⁻¹ cm⁻² to glucose and a linear range of 0.1 mM to 1.3 mM. The response time is less than 3 s with addition of 0.1 mM glucose. The CuO/Cu electrode above was anodized in 1M KOH solution at −100 mV and the morphology was compact nanoparticles and sparsely dispersed nanosheets, which enlarged the surface area and provided abundant electrocatalytic active sites. Compared the sensing property of electrodes with different morphologies, it indicated that nanostructure was significant to the efficient glucose catalytic oxidation process and it could be regulated by changing the potential and electrolyte concentration during anodization.     

Highly Selective Pd–Cu/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for Liquid-Phase Hydrogenation: The Influence of the Pd: Cu Ratio on the Structure and Catalytic Characteristics

The structure and catalytic characteristics of a series of Pd–Cu/α-Al₂O₃ catalysts with Pd: Cu ratio varied from Pd₁–Cu_0.5 to Pd₁–Cu₄ were studied. The use of α-Al₂O₃ with a small surface area (S_sp = 8 m²/g) as a support made it possible to minimize the effect of diffusion on the catalytic characteristics and to study the structure of Pd–Cu nanoparticles by X-ray diffraction (XRD) analysis. The XRD analysis and transmission electron microscopy (TEM) data indicated the formation of uniform bimetallic Pd–Cu nanoparticles (d = 20–60 nm), whose composition corresponded to a ratio between the metals in the catalyst, and also the absence of monometallic Pd⁰ and Cu⁰ nanoparticles. The study of catalytic properties in the liquid-phase hydrogenation of diphenylacetylene (DPA) showed that the activity of the catalysts rapidly decreased with the Cu content increase; however, in this case, the yield of a desired alkene compound significantly increased. The selectivity of alkene formation on the catalysts with the ratios Pd: Cu = 1: 3 and 1: 4 was superior to the commercial Lindlar catalyst.     

Tuning the Composition of PdCuNi Hollow Nanospheres for Low Cost and Efficient Catalyst Towards Glycol Electrooxidation

In this research, we reported an effective approach to prepare low cost and efficient electrocatalyst for the glycol electrooxidation. The synthetic process involves the replacement reactions between CuCl₂/H₂PdCl₄ and Ni nanospheres template. Through controlling the precursor ratio, the Pd/Cu/Ni ratio of the final trimetallic products can be tuned. The prepared electrocatalysts present a monodispersed nanospheres structure with a hollow cavity. The prepared Pd₄₁Cu₂₇Ni₉ shows the best catalytic activity (0.021 A cm⁻² at 0.9 V vs. RHE) for glycol electrooxidation, which is much higher than that of the commercial Pd/C (0.0014 A cm⁻² at 0.9 V vs. RHE).     

Pd nanoparticles supported on CeO2 as efficient catalyst for hydrogen generation from formaldehyde solution at room temperature

A facile and efficient method for facilitating hydrogen generation from formaldehyde aqueous solution was developed using Pd nanoparticles supported on CeO₂ (Pd/CeO₂) as the catalyst. The prepared Pd/CeO₂ catalyst exhibited 100% H₂ selectivity and excellent catalytic activity for formaldehyde dehydrogenation with the initial rate of 2089 ml min⁻¹ g_Pd⁻¹ at room temperature and atmospheric pressure without any extra additive. The prepared catalyst was stable and reusable, and its catalytic activity kept almost unchanged after it was reused for the fifth run. Therefore, it is considered that this Pd/CeO₂ based hydrogen generation system may serve as an alternative hydrogen supply candidate for practical application.     

Pd(II) inhibition during hexacyanoferrate(III) oxidation of sugars: A kinetic study

An inhibition effect of PdCl₂ on the rate of oxidation of sugars by alkaline hexacyanoferrate(III) has been observed. The order of reactions in hexacyanoferrate(III) and OH⁻ is zero and unity, respectively, while that in sugars decreases from unity at higher sugar concentration. The kinetic data and spectrophotometric evidence support the formation of {Pd^II − (sugar)} and {Pd^II − sugar)₂} complexes and their resistance to react with Fe(CN)₆³⁻ © 1996 John Wiley & Sons, Inc.     

Boronate Covalent and Hybrid Organic Frameworks Featuring PIII and P=O Lewis Base Sites

Two covalent organic frameworks comprising Lewis basic P^III centers and Lewis acidic boron atoms were prepared by poly-condensation reactions of newly obtained tris(4-diisopropoxyborylphenyl)phosphine with 2,3,6,7,10,11-hexahydroxytriphenylene and 2,3,6,7-tetrahydroxy-9,10-dimethylanthracene. Obtained materials exhibit significant sorption of dihydrogen (100 cm³ g⁻¹ at 1 bar at 77 K), methane (20 cm³ g⁻¹ at 1 bar at 273 K) and carbon dioxide (50 cm³ g⁻¹ at 1 bar at 273 K). They were exploited as solid-state ligands for coordination of Pd⁰ centers. Alternatively, in a bottom-up approach, boronated phosphine was treated with Pd₂dba₃ and poly-condensated, yielding hybrid materials where the polymer networks are formed by means of covalent boronate linkages and coordination P−Pd bonds. In addition, the analogous materials based on phosphine oxide were synthesized. The DFT calculations on framework–guest interactions revealed that the behavior of adjacent boron and phosphorus/phosphine oxide centers is reminiscent of that found in Frustrated Lewis Pairs and may improve sorption of selected molecules.     

An Electrochemical ATP Biosensor with Enzymes Entrapped within a PEDOT Film

This paper reports on the electrochemical behavior of an ATP biosensor that utilizes glucose oxidase (GOx) and hexokinase (Hex) immobilized within the electroactive polymer, polyethylenedioxythiophene (PEDOT). This biosensor design detects ATP indirectly at 0.85 V vs. Ag/AgCl based on the oxidation current for enzymatically generated H₂O₂, and at −0.20 V; a potential at which improved analyte selectivity is achieved. The detection figures of merit at both detection potentials are a response time of 15±1 s, an experimental detection limit of 10.0±0.2 μmol L⁻¹ (S/N=3), and a sensitivity in the range of 100–500 mA M⁻¹cm⁻².     

Structural and Oxidation State Alternatives in Platinum and Palladium Complexes of a Redox-Active Amidinato Ligand

Reaction of [Pt(DMSO)₂Cl₂] or [Pd(MeCN)₂Cl₂] with the electron-rich LH=N,N’-bis(4-dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL₂] ( 1 ) but dinuclear [Pd₂L₄] ( 2 ), a paddle-wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV-vis-NIR spectroscopy, magnetic resonance) and TD-DFT calculations as metal(II) species with noninnocent ligands L⁻. The reversibly accessible cations [PtL₂]⁺ and [Pd₂L₄]⁺ were also studied, the latter as [Pd₂L₄][B{3,5-(CF₃)₂C₆H₃}₄] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [Pt^II(L⁻)₂] or [Pt^.(L )₂], [Pt^II(L^0.5−)₂]⁺ or [Pt^III(L⁻)₂]⁺, [(Pd^II)₂(μ-L⁻)₄] or [(Pd^1.5)₂(μ-L^0.75−)₄], and [(Pd^2.5)₂(μ-L⁻)₄]⁺ or [(Pd^II)₂(μ-L^0.75−)₄]⁺. In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL₂] with an N-Pt-N bite angle of 62.8(2)° in contrast to [Pd₂L₄], and the dimetal (Pd₂⁴⁺→Pd₂⁵⁺) instead of ligand (L⁻→L ) oxidation of the dinuclear palladium compound.     

Self-Assembly of a Redox Active,Metallosupramolecular [Pd3L6]6+ Complex Using a Rotationally Flexible Ferrocene Ligand

A new ferrocene-containing [Pd₃( L_4EFc )₆]⁶⁺(X⁻)₆ ( C ⋅ BF₄ and C ⋅ SbF₆ where X=BF₄⁻ or SbF₆⁻) self-assembled double-walled triangle has been synthesized from the known, rotationally flexible, 1,1′-bis(4-pyridylethynyl)ferrocene ligand ( L_4EFc ), and characterized by ¹H, ¹³C and diffusion ordered (DOSY) NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HR−ESI−MS), X-ray crystallography and cyclic voltammetry (CV). The molecular structures confirmed that double-walled triangle cage systems ( C ⋅ BF₄ and C ⋅ SbF₆ ) were generated. C ⋅ BF₄ was shown to interact with the anionic guest, p-toluenesulfonate. CV experiments revealed that the triangles were redox active, however addition of the guest did not influence the redox potentials.     

Palladium Catalysis for Aerobic Oxidation Systems Using Robust Metal–Organic Framework

Described here is a new and viable approach to achieve Pd catalysis for aerobic oxidation systems (AOSs) by circumventing problems associated with both the oxidation and the catalysis through an all‐in‐one strategy, employing a robust metal–organic framework (MOF). The rational assembly of a Pd^II catalyst, phenanthroline ligand, and Cu^II species (electron‐transfer mediator) into a MOF facilitates the fast regeneration of the Pd^II active species, through an enhanced electron transfer from in situ generated Pd⁰ to Cu^II, and then Cu^I to O₂, trapped in the framework, thus leading to a 10 times higher turnover number than that of the homogeneous counterpart for Pd‐catalyzed desulfitative oxidative coupling reactions. Moreover, the MOF catalyst can be reused five times without losing activity. This work provides the first exploration of using a MOF as a promising platform for the development of Pd catalysis for AOSs with high efficiency, low catalyst loading, and reusability.     

Directed C−H Activation and Tandem Cross-Coupling Reactions Using Palladium Nanocatalysts with Controlled Oxidation

Controlled oxidation of palladium nanoparticles provided high-valent Pd^IV oxo-clusters which efficiently promote directed C−H halogenation reactions. In addition, palladium nanoparticles can undergo changes in oxidation states to provide both high-valent Pd^IV and low-valent Pd⁰ species within one system, and thus a tandem reaction of C−H halogenation and cross-coupling (C−N, C−C, and C−S bond formation) was successfully established.     

Cobalt Carbonate as an Electrocatalyst for Water Oxidation

Co^II salts in the presence of HCO₃⁻/CO₃²⁻ in aqueous solutions act as electrocatalysts for water oxidation. It comprises of several key steps: (i) A relatively small wave at E_pa≈0.71 V (vs. Ag/AgCl) owing to the Co^III/II redox couple. (ii) A second wave is observed at E_pa≈1.10 V with a considerably larger current. In which the Co^III undergoes oxidation to form a Co^IV species. The large current is attributed to catalytic oxidation of HCO₃⁻/CO₃²⁻ to HCO₄⁻. (iii) A process with very large currents at >1.2 V owing to the formation of Co^V(CO₃)₃⁻, which oxidizes both water and HCO₃⁻/CO₃²⁻. These processes depend on [Co^II], [NaHCO₃], and pH. Chronoamperometry at 1.3 V gives a green deposit. It acts as a heterogeneous catalyst for water oxidation. DFT calculations point out that Coⁿ(CO₃)₃ⁿ⁻⁶, n=4, 5 are attainable at potentials similar to those experimentally observed.     

Self‐Assembly Film of Zeolite Y Nanocrystals Loading Palladium on an Au Electrode for Electrochemical Applications

Nano‐scale zeolite Y crystals were synthesized, and palladium nanoparticles were prepared in the supercage of the zeolite by “ship‐in‐a‐bottle” approach. A novel method to fabricate zeolite‐modified electrode (ZME) loading Pd nanoparticles was developed, in which the zeolite Y loading Pd²⁺ ions was self‐assembled on (3‐mercaptopropyl) trimethoxysilane‐attached Au surface to form the stable and density packed multilayers (SAM‐ZME). The structures of zeolite Y and the SAM‐ZME were investigated by using TEM, XRD and SEM techniques. Pd²⁺ ions in the SAM‐ZME were converted into Pd nanoparticles (Pd_n⁰) by two steps consisting of the electrochemical reduction as well as the succeeding admission and release of CO. The redox couple [Fe(CN)₆]^3?/4? was used to probe the electron‐transfer barrier properties during self‐assembling process. Moreover, the special properties of the SAM‐ZME loading Pd_n⁰ were studied by using cyclic voltammetry and CO‐probe in situ FTIR spectroscopy. The results illustrated that Pd_n⁰ in the SAM‐ZME exhibits higher electrocatalytic activity for oxidation of adsorbed CO than that of ZME prepared in our previous study by zeolite coating method. The present study is of importance in design and preparation of SAM‐ZME, which poccesseses excellent properties for the immobilization of electrocatalysts or biomolecules.