In Situ Dispersion of Palladium on TiO2 During Reverse Water–Gas Shift Reaction: Formation of Atomically Dispersed Palladium

The application of single-atom catalysts (SACs) to high-temperature hydrogenation requires materials that thermodynamically favor metal atom isolation over cluster formation. We demonstrate that Pd can be predominantly dispersed as isolated atoms onto TiO₂ during the reverse water–gas shift (rWGS) reaction at 400 °C. Achieving atomic dispersion requires an artificial increase of the absolute TiO₂ surface area by an order of magnitude and can be accomplished by physically mixing a precatalyst (Pd/TiO₂) with neat TiO₂ prior to the rWGS reaction. The in situ dispersion of Pd was reflected through a continuous increase of rWGS activity over 92 h and supported by kinetic analysis, infrared and X-ray absorption spectroscopies and scanning transmission electron microscopy. The thermodynamic stability of Pd under high-temperature rWGS conditions is associated with Pd-Ti coordination, which manifests upon O-vacancy formation, and the artificial increase in TiO₂ surface area.     

Catalytic Hydrodechlorination of 1,2,4,5‐Tetrachlorobenzene over Various Supports Loaded Palladium Catalysts

Water pollution by polychlorinated aromatic hydrocarbons has always been a global issue. In this work, we reported a synthesis of supported palladium catalysts Pd/C, Pd/CeO₂, Pd/SBA‐15, Pd/ZrO₂,Pd/SiO₂, and Pd/Al₂O₃ as well as their catalytic activities on hydrodechlorination (HDC) of 1,2,4,5‐tetrachlorobenzene (TeCB). These Pd catalysts were characterized by Brunauer‐Emmett‐Teller (BET) specific surface area, Transmission electron microscopy (TEM), X‐ray diffraction (XRD), energy Dispersive X‐ray Fluorescence (EDXRF), CO‐chemisorption, and H2‐temperature programmed reduction (H2‐TPR) analysis. Pd/C, Pd/CeO₂ and Pd/SBA‐15 catalysts showed relatively high catalytic activities. The catalytic activities were associated with dispersion of Pd, metal surface area, and reaction temperature, etc.     

Selective Hydrogenation of Citral over a Carbon‐titania Composite Supported Palladium Catalyst

A novel carbon‐titania composite material, C/TiO₂, has been prepared by growing carbon nanofibers (CNFs) on TiO₂ surface via methane decomposition using Ni‐Cu as a catalyst. The C/TiO₂ was used for preparing supported palladium catalyst, Pd/C/TiO₂. The support and Pd/C/TiO₂ catalyst were characterized by BET, SEM, XRD and TG‐DTG. Its catalytic performance was evaluated in selective hydrogenation of citral to citronellal, and compared with that of activated carbon supported Pd catalyst. It was found that the Pd/C/TiO₂ catalyst contains 97% of mesopores. And it exhibited 88% of selectivity to citronellal at citral conversion of 90% in citral hydrogenation, which was much higher than that of activated carbon supported Pd catalyst. This result may be attributed to elimination of internal diffusion limitations, which were significant in activated carbon supported Pd catalyst, due to its microporous structure.     

High Electrocatalytic Activity of Pt–Pd Binary Spherocrystals Chemically Assembled in Vertically Aligned TiO2 Nanotubes

To obtain noble metal catalysts with high efficiency, long‐term stability, and poison resistance, Pt and Pd are assembled in highly ordered and vertically aligned TiO₂ nanotubes (NTs) by means of the pulsed‐current deposition (PCD) method with assistance of ultrasonication (UC). Here, Pd serves as a dispersant which prevents agglomeration of Pt. Thus Pt–Pd binary catalysts are embed into TiO₂ NTs array under UC in sunken patterns of composite spherocrystals (Sps). Owing to this synthesis method and restriction by the NTs, the these catalysts show improved dispersion, more catalytically active sites, and higher surface area. This nanotubular metallic support material with good physical and chemical stability prevents catalyst loss and poisoning. Compared with monometallic Pt and Pd, the sunken‐structured Pt–Pd spherocrystal catalyst exhibits better catalytic activity and poison resistance in electrocatalytic methanol oxidation because of its excellent dispersion. The catalytic current density is enhanced by about 15 and 310 times relative to monometallic Pt and Pd, respectively. The poison resistance of the Pt–Pd catalyst was 1.5 times higher than that of Pt and Pd, and they show high electrochemical stability with a stable current enduring for more than 2100 s. Thus, the TiO₂ NTs on a Ti substrate serve as an excellent support material for the loading and dispersion of noble metal catalysts.     

High ethanol sensitivity of Palladium/TiO2 nanobelt surface heterostructures dominated by enlarged surface area and nano-Schottky junctions

TiO₂ nanobelts were prepared by the hydrothermal growth method. The surface of the nanobelts was coarsened by selective acid corrosion and functionalized with Pd catalyst particles. Three nanobelt samples (TiO₂ nanobelts, surface-coarsened TiO₂ nanobelts and Pd nanoparticle/TiO₂ nanobelt surface heterostructures) were configured as gas sensors and their sensing ability was measured. Both the surface-coarsened nanobelts and the Pd nanoparticle-decorated TiO₂ nanobelts exhibited dramatically improved sensitivity to ethanol vapor. Pd nanoparticle-decorated TiO₂ nanobelts with surface heterostructures exhibited the best sensitivity, selectivity, working temperature, response/recovery time, and reproducibility. The excellent ethanol sensing performance is attributed to the large surface area and enhancement by Schottky barrier-type junctions between the Pd nanoparticles and TiO₂ nanobelts.     

Palladium nanoparticles‐decorated triethanolammonium chloride ionic liquid‐modified TiO2 nanoparticles (TiO2/IL‐Pd): A highly active and recoverable catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous medium

In this work, an easily obtained procedure was successfully implemented to prepare novel palladium nanoparticles decorated on triethanolammonium chloride ionic liquid‐functionalized TiO₂ nanoparticles [TiO₂/IL‐Pd]. Different methods were carried out for characterizations of the synthesized nanocatalyst (HR‐TEM, XPS, XRD, FE‐SEM, EDX, FT‐IR and ICP). TiO₂/IL‐Pd indicated good catalytic activity for the Suzuki–Miyaura cross‐coupling reaction of arylboronic acid with different aryl halides in aqueous media at ambient temperature. The recycled catalyst was investigated with ICP to amount of Pd leaching after 6 times that had diminished slightly, Thus, was confirmed that the nanocatalyst has a good sustainability for C–C Suzuki–Miyaura coupling reaction. The catalyst can be conveniently separated by filtration of the reaction mixture and reused for 6 times without significant loss of its activity. It supplies an environmentally benign alternative path to the existing protocols for the Suzuki–Miyaura reaction.     

Synthesis and Performance of Polyvinylpyrrolidone‐Protected Pd Nanoparticles Supported on TiO2MWCNTs under Protection of PVP for in Alcohols Oxidation in Alkaline Media

This paper describes the synthesis and performance of Pd/p‐TiO₂‐MWCNTs for alcohol electrooxidation. Regulation of the steric repulsive forces of polyvinylpyrrolidone was used to achieve even dispersion of Pd nanoparticles over the TiO₂ surfaces. The order of the electroactivities of the Pd/p‐TiO₂? MWCNTs in alcohol oxidation was ethanol>ethylene glycol>methanol. The order of the stabilities of alcohol oxidation by Pd/p‐TiO₂? MWCNTs was ethylene glycol>ethanol>methanol. Electroimpedance spectroscopy showed that at a potential of ?0.1 V, the Pd/p‐TiO₂? MWCNTs had good tolerance of adsorbed CO in ethylene glycol oxidation, and at ?0.2 V, the Pd/p‐TiO₂? MWCNTs had good adsorbed CO tolerance in methanol oxidation.     

A Novel Way to Prepare TiO2 and γ‐Al2O3 Supported Catalysts with Large Surface Areas

Several TiO₂ and γ‐Al₂O₃ supported catalyst systems were prepared by a novel way and characterized by X‐ray diffraction, Raman spectroscopy and BET surface area measurement. The results show: (1) all the samples, including MoO₃/TiO₂, WO₃/TiO₂, V₂O₅/TiO₂, FeSO₄/γ‐Al₂O₃, Al₂ (SO₄)₃/γ‐Al₂O₃, K₂CO₃/‐Al₂O₃ and so on, prepared by impregnating TiO₂·H₂O or pseudo‐boehmite AlO(OH) with the active components then calcining at a high temperature exhibit much larger surface areas than that of pure TiO₂ or γ‐Al₂O₃ calcined at the same temperature; (2) the surface area of the sample increases with the increase in the coverage of active component on the surface of the support; (3) when the content of active component reaches its utmost monolayer dispersion capacity, the surface area of the sample is the largest, and then decreases when the content of active component exceeds its dispersion threshold.     

Palladium Nanoparticles Supported on Titanium‐Doped Graphitic Carbon Nitride for Formic Acid Dehydrogenation

Pd nanoparticles (NPs) supported on Ti‐doped graphitic carbon nitride (g‐C₃N₄) were synthesized by a deposition–precipitation route and a subsequent reduction with NaBH₄. The features of the NPs were studied by XRD, TEM, FTIR, XPS, EXAFS and N₂‐physisorption measurements. It was found that the NPs had an average size of 2.9 nm and presented a high dispersion on the surface of Ti‐doped g‐C₃N₄. Compared to Pd loaded on pristine g‐C₃N₄, the Pd NPs supported on Ti‐doped g‐C₃N₄ exhibited a high catalytic activity in formic acid dehydrogenation in water at room temperature. The enhanced activity could be attributed to the small Pd NPs size, as well as the strong interaction between Pd NPs and Ti‐doped g‐C₃N₄.     

Palladium Single Atoms on TiO2 as a Photocatalytic Sensing Platform for Analyzing the Organophosphorus Pesticide Chlorpyrifos

Traditional methods for analyzing organophosphorus pesticide chlorpyrifos, usually require the tedious sample pretreatment and sophisticated bio‐interfaces, leading to the difficulty for real‐time analysis. Herein, we use palladium single‐atom (PdSA)/TiO₂ as a photocatalytic sensing platform to directly detect chlorpyrifos with high sensitivity and selectivity. PdSA/TiO₂, prepared by an in situ photocatalytic reduction of PdCl₄^2? on the TiO₂, shows much higher photocatalytic activity (10 mol g^?1 h^?1) for hydrogen evolution reaction than Pd nanoparticles (1.95 mol g^?1 h^?1), and excellent stability. In the presence of chlorpyrifos, the photocatalytic activity of PdSA/TiO₂ decreases. Through this inhibition effect the platform can realize a detection limit for chlorpyrifos of 0.01 ng mL^?1, much lower than the maximum residue limit (10 ppb) permitted by the U.S. Environmental Protection Agency.     

Oxygen‐Promoted CH Bond Activation at Palladium

[Pd(P(Ar)(tBu)₂)₂] ( 1 , Ar=naphthyl) reacts with molecular oxygen to form Pd^II hydroxide dimers in which the naphthyl ring is cyclometalated and one equivalent of phosphine per palladium atom is released. This reaction involves the cleavage of both C? H and O? O bonds, two transformations central to catalytic aerobic oxidizations of hydrocarbons. Observations at low temperature suggest the initial formation of a superoxo complex, which then generates a peroxo complex prior to the C? H activation step. A transition state for energetically viable C? H activation across a Pd? peroxo bond was located computationally.     

Controlled Aqueous Solution Synthesis of Platinum–Palladium Alloy Nanodendrites with Various Compositions Using Amphiphilic Triblock Copolymers

In a recent study, we demonstrated that Pluronic F127 triblock copolymer plays a critical role in the formation of dendritic Pt nanostructures (L. Wang, Y. Yamauchi, J. Am. Chem. Soc. 2009 , 131, 9152–9153). Herein, we expand this concept to produce novel dendritic Pt–Pd alloy nanoparticles. In this paper, a very simple, one‐step and efficient route is proposed to directly produce dendritic Pt–Pd alloy nanoparticles with high surface area in high yield, which is carried out simply by stirring an aqueous solution that contains K₂PtCl₄ and Na₂PdCl₄ binary precursors in the presence of Pluronic F127 block copolymer and ascorbic acid at room temperature within 30 min without the need for any template, seed‐mediated growth, or additive. By simply changing the compositional ratios of the Pt and Pd sources in the precursor solutions, Pt–Pd nanodendrites with various compositions can be easily produced. Because of its unique simplicity, the proposed approach can be considered as a powerful strategy for producing Pt–Pd alloy nanoparticles with unique nanoarchitectures for commercial devices.     

（英）二氧化钛/石墨烯复合材料对水溶液中钯离子的吸附性能研究

本文合成了一种新型二氧化钛/石墨烯(TiO2-Gr)复合材料吸附剂,研究了其对水溶液中Pd(II)的吸附作用,并与TiO2的吸附性能进行了比较。制得的TiO2-Gr吸附剂分别进行了透射电子显微镜(TEM)表征及X射线衍射(XRD)分析,考察了吸附过程中时间、溶液p H、吸附剂用量、离子强度、Pd(II)浓度和温度等参数对吸附量的影响。研究了吸附过程中动力学、热力学及吸附等温线。结果表明吸附过程符合假二级动力学模型,吸附等温线符合Langmuir和Freundlich等温吸附方程。对热力学函数(吉布斯函数变、焓变、熵变)测定表明,本文合成的TiO2-Gr吸附剂对Pd(II)的吸附属于自发吸热反应。     

Molten‐Salt‐Mediated Synthesis of an Atomic Nickel Co‐catalyst on TiO2 for Improved Photocatalytic H2 Evolution

Atomic co‐catalysts offer high potential to improve the photocatalytic performance, of which the preparation with earth‐abundant elements is challenging. Here, a new molten salt method (MSM) is designed to prepare atomic Ni co‐catalyst on widely studied TiO₂ nanoparticles. The liquid environment and space confinement effect of the molten salt leads to atomic dispersion of Ni ions on TiO₂, while the strong polarizing force provided by the molten salt promotes formation of strong Ni?O bonds. Interestingly, Ni atoms are found to facilitate the formation of oxygen vacancies (OV) on TiO₂ during the MSM process, which benefits the charge transfer and hydrogen evolution reaction. The synergy of atomic Ni co‐catalyst and OV results in 4‐time increase in H₂ evolution rate compared to that of the Ni co‐catalyst on TiO₂ prepared by an impregnation method. This work provides a new strategy of controlling atomic co‐catalyst together with defects for efficient photocatalytic water splitting.     

Syntheses and Characterizations of Two Palladium(II) Complexes of 5‐Mercapto‐1‐methyltetrazole

Reaction of PdCl₂(CH₃CN)₂ with the sodium salt of 5‐mercapto‐1‐methyltetrazole (MetzSNa) in methanol solution affords an interesting dinuclear palladium complex [Pd₂(MetzS)₄ ] ( 1 ). However, treatment of PdCl₂(CH₃CN)₂ with neutral MetzSH ligand in methanol solution produces a mononuclear palladium complex [Pd(MetzSH)₄]Cl₂ ( 2 ). Both complexes were characterized by IR, ¹HNMR, UV‐Vis spectroscopy as well as X‐ray crystallography. Single‐crystal X‐ray diffraction analyses of two complexes lead to the elucidation of the structures and show that 1 possesses an asymmetric structure: one Pd atom is tetracoordinated by three sulfur atoms and one nitrogen atom to form PdS₃N coordination sphere, the other Pd atom is tetracoordinated by three nitrogen atoms and one sulfur atom to form PdSN₃ coordination sphere. The molecules of 1 are associated to 1‐D infinite linear chain by weak intermolecular Pd···S contacts in the crystal lattice. In 2 , the Pd atom lies on an inversion center and has a square‐planar coordination involving the S atoms from four MetzSH ligands. The two chloride ions are not involved in coordination, but are engaged in hydrogen bonding.     

Supramolecular photocatalyst of Palladium (II) Encapsulated within Dendrimer on TiO2 nanoparticles for Photo‐induced Suzuki‐Miyaura and Sonogashira Cross‐Coupling reactions

In this study, synthesis, characterization and catalytic performance of a novel supramolecular photocatalytic system including palladium (II) encapsulated within amine‐terminated poly (triazine‐triamine) dendrimer modified TiO₂ nanoparticles (Pd (II) [PTATAD] @ TiO₂) is presented. The obtained nanodendritic catalyst was characterized by FT‐IR, ICP‐AES, XPS, EDS, TEM, TGA and UV‐DRS. The as‐prepared nanodendritic catalyst was shown to be highly active, selective, and recyclable for the Suzuki–Miyaura and Sonogashira cross‐coupling of a wide range of aryl halides including electron‐rich and electron‐poor and even aryl chlorides, affording the corresponding biaryl compounds in good to excellent yields under visible light irradiation. This study shows that visible light irradiation can drive the cross‐coupling reactions on the Pd (II) [PTATAD] @ TiO₂ under mild reaction conditions (27–30 °C) and no additional additives such as cocatalysts or phosphine ligands. So, we propose that the improved photoactivity predominantly benefits from the synergistic effects of Pd (II) amine‐terminated poly (triazine‐triamine) dendrimer on TiO₂ nanoparticles that cause efficient separation and photogenerated electron–hole pairs and photoredox capability of nanocatalyst which all of these advantages due to the tuning of band gap of catalyst in the visible light region.     

Tripod Immobilization of Triphenylphosphane on a Silica‐Gel Surface to Enable Selective Mono‐Ligation to Palladium: Application to Suzuki–Miyaura Cross‐Coupling Reactions with Chloroarenes

A silica‐supported triphenylphosphane (Silica‐3p‐TPP) with a Ph₃P‐type core, immobilized on a silica surface, was synthesized and characterized by nitrogen‐absorption measurements and solid‐state NMR spectroscopy. The tripodal immobilization constrains the mobility of the phosphane molecule and causes the lone pair on the phosphorus atom to face in the direction perpendicular to the support, resulting in the selective formation of a 1:1 metal–phosphane species that is free from unfavorable steric repulsions caused by the silica surface. Heterogeneous Pd catalysts created in this manner enabled room‐temperature Suzuki–Miyaura cross‐coupling reactions with unactivated chloroarenes, despite the moderate electronic and steric nature of the Ph₃P‐based ligands. These catalysts also showed potential in reactions with more challenging substrates under mild conditions. Tripodally immobilized and well‐dispersed phosphanes on the silica surface were crucial for high catalytic activity.     

Atomically Dispersed Copper–Platinum Dual Sites Alloyed with Palladium Nanorings Catalyze the Hydrogen Evolution Reaction

Designing highly active catalysts at an atomic scale is required to drive the hydrogen evolution reaction (HER). Copper–platinum (Cu‐Pt) dual sites were alloyed with palladium nanorings (Pd NRs) containing 1.5 atom % Pt, using atomically dispersed Cu on ultrathin Pd NRs as seeds. The ultrafine structure of atomically dispersed Cu‐Pt dual sites was confirmed with X‐ray absorption fine structure (XAFS) measurements. The Pd/Cu‐Pt NRs exhibit excellent HER properties in acidic solution with an overpotential of only 22.8 mV at a current density of 10 mA cm⁻² and a high mass current density of 3002 A g⁻¹_(Pd+Pt) at a −0.05 V potential.     

Kinetic Evidence for the Influence of Subsurface Oxygen on Palladium Surfaces Towards CO Oxidation at High Temperatures

Transient state kinetics of the catalytic oxidation of CO with O₂ on Pd‐surfaces has been measured under isothermal conditions by using a molecular beam approach. Systematic studies were carried out as a function of reaction temperature and CO+O₂ composition. With sufficient kinetic evidence, we have demonstrated the positive influence of subsurface oxygen towards CO‐adsorption and oxidation to CO₂ at high temperatures (600–900 K) on Pd‐surfaces, and the likely electronic nature of the surface changes with oxygen in the subsurface. These studies also provide a direct proof for CO‐adsorption with a significantly reactive sticking coefficient at high temperatures on Pd‐surfaces exhibiting a significant subsurface O‐coverage.     

Effect of Calcination Temperature and Pretreatment with Reaction Gas on Properties of Co/γ‐Al2O3 Catalysts for Partial Oxidation of Methane

The effects of calcination temperature and feedstock pretreatment on the catalytic performance of Co/γ‐Al₂O₃ catalysts were studied for partial oxidation of methane (POM) to synthesis gas, with emphasis on the role of feedstock pretreatment. The physicochemical properties of the catalysts were characterized by N₂ adsorption, X‐ray diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature‐programmed reduction (H₂‐TPR), and Raman spectroscopy. The results showed that the pretreatment of the catalyst by reaction gas significantly improved the catalytic activity and stability for the POM reaction. On the other hand, the effect of calcination temperature was less significant. Although the initial activity was increased by an increased calcination temperature, the catalyst without the feedstock pretreatment suffered a rapid deactivation. The reaction‐atmosphere pretreatment was revealed as a process that mainly modified the surface structure of the catalyst. In that process, the formation of a CoAl₂O₄‐like compound led to high Co metal dispersion after reduction, and the transformation of the carrier into α‐Al₂O₃ occurred over the catalyst surface. Both the high dispersion of cobalt and the presence of α‐Al₂O₃ surface phase were assumed as the important factors resulting in an excellent catalytic performance in terms of high activity and high stability.