Activity Of Noble Metal Catalysts Research Articles

Coalescence of Au-Pd Nanoropes and their Application as Enhanced Electrocatalysts for the Oxygen Reduction Reaction.

Lattice distortions and defects can lead to a strain effect that greatly affects the electronic structure of the noble metal surface and the chemical adsorption of ligands on the surfaces. Introducing defects is an efficient strategy to improve the activity of noble metal catalysts. Herein, a fusion approach is developed to fine-tune the defects and lattice strain in Au-Pd nanowires. Specifically, braided strands in Au-Pd nanoropes gradually coalesce to form solid nanowires upon H2 O2 treatment and heating, leading to a series of Au-Pd nanowires with various amounts of defects. Owing to the 1D morphology, as well as the optimized lattice strain and surface electronic structure, the intermediate Au-Pd nanowire obtained after 60min heating (denoted as Au-Pd NW60 ) exhibits excellent catalytic activity and stability toward the oxygen reduction reaction, with the half-wave potential at 0.918V, 45mV higher than that of the commercial Pt/C; and specific activity reaches up to 1.7mA cm-2 , 7.3 times higher than that of the Pt/C.

Synergistic Effects of Crystal Phase and Strain for N2 Dissociation on Ru(0001) Surfaces with Multilayered Hexagonal Close-Packed Structures.

The synergistic effects of strain and crystal phase on the reaction activity of nitrogen molecule dissociation have been studied using density functional theory calculations on Ru(0001) surfaces with multilayered hexagonal close-packed structures. The phase transformation from hexagonal close-packed phase (2H) to face-centered cubic (3C) phase or unconventional phases (4H, DHCP, 6H1, and 6H2) would occur under the uniaxial tensile strain loaded along the c axis. The close-packed surfaces of unconventional crystal phases show an enhanced chemical reactivity for N adsorption due to the upshifted d-band center of Ru. However, the N2 adsorption energy is almost independent of the applied strain and crystal phase. The optimized catalytic activity of Ru(0001) surfaces with the unconventional phases is found for the N2 dissociation through breaking the scaling relationships between the reaction barrier and reaction energy. Our results indicate that the strain-induced phase transformation is an effective method to improve the catalytic activity of noble metal catalysts toward the N2 dissociation reaction.

Ternary NiCoP urchin like 3D nanostructure supported on nickel foam as a catalyst for hydrogen generation of alkaline NaBH4

Hydrogen storage materials processing had bestowed vitality in the hydrogen production which leads to the development of diverse catalytic technologies satisfying efficiency improvement and economic versatility. Herein, we developed a ternary 3D urchin like nickel and cobalt transition metal phosphide catalyst deposited on nickel foam (NiCoP/NF) for hydrolysis of NaBH4 via an easy synthesis route of hydrothermal in-situ deposition followed by phosphidation. Its distinctive urchin like morphological architecture and crystal configuration enable the supported catalyst to exhibit a remarkable catalytic activity. Synergistic effect of binary metal composite was investigated through preparation of various heterogeneous NiCoP/NF catalysts with different elemental metal ratio. Among the different NiCoP/NF prepared, Ni0.8Co1.2P/NF demonstrated the highest hydrogen yield of 3986 (mL min−1 g−1) with an activation energy of 38.3 (kJ mol−1) relatively comparable to the activity of noble metal catalysts. The overall performance of the catalyst is due to the following factors: the innate characteristics of phosphidized transition metal, the existence of bimetallic synergetic feature and morphological construction.

Hydrothermal synthesis of sandwich interspersed LaCO3OH/Co3O4/graphene oxide composite and the enhanced catalytic performance for methane combustion

Novel structured LaCO3OH/Co3O4/graphene oxide composite was synthesized through a hydrothermal process using a certain ratio of urea (N), LaCoO3 (LC) and graphene oxide (GO) as starting materials. Morphology characterizations showed that as-prepared composite had sandwich structure interspersed on graphene oxide sheets. The LaCO3OH nano-sheets were self-organized into stratiform nano-structures, where spherical Co3O4 nano-particles with a diameter of 17–31 nm were homogeneously distributed between two adjacent LaCO3OH nano-sheets, forming sandwich structure. At the same time, the sandwich structure inlaid on the surface of two-dimensional GO, forming sandwich structure interspersed morphology. The results indicated that the amount of urea additive (m(N)) played a key role in the formation of the neoteric morphology. The LaCO3OH/Co3O4/graphene oxide composite showed optimized catalytic performance for methane combustion as 50% methane conversion at 315 °C and 90% at 420 °C when m(N)/m(LC) = 5, which can match the activity of noble metal catalysts. The enhanced catalytic performance was attributed to its unique loaded structure with high surface area and more exposed active sites, which showed enhanced application in methane combustion as a new type of Pt-group metals free catalyst. In addition, stability performance was systematically studied, indicating that the synthesized catalyst has great potential for industrial applications.

Thermally stable ultra-small Pd nanoparticles encapsulated by silica: elucidating the factors determining the inherent activity of noble metal catalysts

1.1 nm Pd nanoparticles embedded in silica nanospheres were prepared by an improved one-step reverse micelle method, which show superior activity and thermal stability. Pd active surface area is the determining factors for the activity.

4,6-Dimethyl-dibenzothiophene conversion over Al 2O 3–TiO 2-supported noble metal catalysts

Al 2O 3 and Al 2O 3–TiO 2 (molar ratio Al/Ti = 2, AT2) mixed oxides were synthesized using a low-temperature sol–gel method and were further pore-filling impregnated to obtain Pd and Pt catalysts with ∼1 wt% nominal metal loading. Simultaneous impregnation was used to prepare bimetallic materials at Pd:Pt = 80:20. Solids characterization was carried out by N 2-physisorption, high-resolution transmission electron microscopy (HR-TEM and E-FTEM), X-ray diffraction, temperature-programmed reduction and CO-chemisorption. Reduced (350 °C, H 2 flow) catalysts were tested in the 4,6-dimethyl-dibenzothiophene hydrodesulfurization (HDS) (in n-dodecane, at 300 °C and 5.5 MPa, batch reactor). In Pd-containing materials, TiO 2 incorporation into the alumina support was favorable to the catalytic activity of noble metal catalysts, where bimetallic Pd–Pt with AT2 carrier had the highest organo-S compound conversion. Enhanced intrinsic activity (per exposed metallic site) was obtained in Pt-containing catalysts supported on the AT2 mixed oxide (as compared to alumina-supported ones). Yield to different products over various catalysts seemed to be strongly influenced by metallic particles dispersion.

Fundamental Calculations on the Surface Area Determination of Supported Gold Nanoparticles by Alkanethiol Adsorption

Surface area determination is a crucial step for the characterization of the activity of noble metal catalysts. Not only the development of useful determination methods but foremost the understanding of surface properties and their conversion into mathematical expressions are essential to obtain reliable results. A selective method to gain access to the specific surface area of gold on oxidic supports is the chemisorption of alkanethiol from suspensions. Therefore, the concentration of a 1-dodecanthiol solution before and after immersion of supported gold catalysts was determined by gas chromatography. To convert the concentration information into a specific surface area, the surface coverage, the surface atom concentration, the interatomic Au-Au distance, and the particle morphology were considered. Further calculations afforded the determination of a mean particle diameter. A good agreement was found between gold particle sizes obtained from transmission electron microscopy and thiol adsorption. The given mathematical expressions are highly valuable for a broad range of chemisorption methods and noble metal catalysts.

Synthetic Studies of Cobalt Carbonyl by Noble Metal Catalysts. I. The Effects of the Form of Cobalt Feed and Noble Metal Catalysts

Abstract A novel method of synthesizing cobalt carbonyl was investigated by using noble metal catalysts. It has been observed that the materials containing palladium, i. e., palladium black, palladium chloride, palladium acetylacetonate, bistriphenylphosphine dichloropalladium, and palladium-on-carriers, have a catalytic effect on the cobalt carbonylation reaction, and that palladium-on-carbon (Pd-C) is the most active catalyst. The reactivity of cobalt compounds in the cobalt carbonylation reaction catalyzed by noble metals increases in this order: CoSO4<<CoO\lesssimCo(OAc)2\lesssimCo-oleate<Co(OH)2. When the Pd-C catalyst is used, cobalt hydroxide reacts with synthesis gas of 150 kg/cm2 to give cobalt carbonyl almost quantitatively, even at from 50 to 55°C. The catalytic activities of noble metals were shown to be, in the order of decreasing activity: Pd>Au>Pt>>Ag. The effect of the catalyst concentration and the activity of noble-metal catalysts were also compared with those in the case of dicobalt octacarbonyl, as an autocatalyst.