Supported Alloy Catalysts Research Articles

Supported Alloy Catalysts for Diversification of Biomass Resources

Supported Alloy Catalysts for Diversification of Biomass Resources

Improved performance of electrochemical reduction of CO2 to HCOOH by Cu incorporation into the supported Au monolayer on tungsten carbide: A DFT study

Electrochemical reduction of CO2 into useful chemicals and fuels is a promising strategy to achieve carbon neutrality and storage of renewable electricity. But the realization of industrial application of this technology is hindered by the high energy consumption and low product selectivity. Using the first-principles methods, we explored the mechanism of electrochemical reduction of CO2 on Cu1Au8/WC(0001), in comparison with that on AuML/WC(0001) and CuML/WC(0001). The calculated results showed that incorporating of Cu into Au monolayer significantly enhanced the electrochemical adsorption of CO2, promoting the generation of HCOOH on the alloy surface. Electronic properties such as charge density differences (CDD), Bader charges and density of states (DOS) were investigated to reveal the intrinsic physical origin of the enhanced interaction between OCHO and the catalyst, which results in the improvement in the selectivity and reactivity of CO2 reduction to formic acid (HCOOH) on Cu1Au8/WC(0001). Cu1Au8/WC(0001) was confirmed to be a promising bifunctional catalyst for the efficient conversion of toxic CO to CO2 and selectively reduction of CO2 to useful value-added chemical HCOOH. This work provides a clue to design supported alloy catalysts with high product selectivity and catalytic activity for CO2RR.

Design and synthesis of Ni3ZnC0.7 catalyst derived from a bimetallic Ni/Zn metal-organic frameworks for efficient synthesis of 2-arylbenzimidazole

Developing efficient bimetallic Ni/Zn metal organic frameworks (MOFs) derived Ni3ZnC0.7 alloy catalyst for cyclization reactions is highly anticipated. Bimetallic Ni/Zn-PTA MOFs with flower-like microspheres morphology was synthesized by using a facile hydrothermal method and used as a precursor for preparation of the catalyst. Then, a ZnO supported Ni-Ni3ZnC0.7 incorporated carbon catalyst (Ni-Ni3ZnC0.7/ZnO-C) was obtained by deriving from the Ni/Zn-PTA MOFs through one-step pyrolysis. The developed Ni-Ni3ZnC0.7/ZnO-C catalyst was used as a recoverable heterogeneous catalyst for synthesis of 2-arylbenzimidazoles by cyclization reaction of phenylmethanamines and 2-nitroanilines in good yields. Various characterizations (e.g. SEM/EDX, XRD, TEM, FT-IR, XPS and Raman) revealed that the catalyst exhibited good performance for cyclization reaction, which are ascribed to particular hierarchical structure, as well as synergistic effect between Ni and Ni3ZnC0.7. As a result, the Ni-Ni3ZnC0.7/ZnO-C catalyst showed excellent stability and activity for the condensation cyclization reaction. This bimetallic MOFs-derived Ni-Ni3ZnC0.7 catalyst opens up a potential way for fabricating other Carbon supported alloy catalysts in heterogeneous catalysis reactions.

Facile Synthesis of Highly Dispersed and Well-Alloyed Bimetallic Nanoparticles on Oxide Support.

Supported alloy catalysts play a pivotal role in many heterogeneous catalytic processes of socioeconomic and environmental importance. But the controlled synthesis of supported alloy nanoparticles with consistent composition and tight size distribution remains a challenging issue. Herein, a simple yet effective method for preparation of highly dispersed, homogeneously alloyed bimetallic nanoparticles on oxide supports is reported. This method is based on solid solution of metal cations in parent oxide and strong electrostatic adsorption of a secondary metal species onto the oxide surface. In the reductive annealing process, hydrogen spillover occurs from the surface metal with a higher reduction potential to the solute metal in solid solution, leading to metal exsolution and homogenous alloying of the metals on the oxide surface. The ceria-supported Ni-Pt alloy is chosen as a model catalyst and hydrazine monohydrate decomposition is chosen as a probe reaction to demonstrate this method, and particularly its advantages over the conventional impregnation and galvanic replacement methods. A systematic application of this method using different oxides and base-noble metal pairs further elucidates its applicability and generality.

Enhancing fuel cell catalyst layer stability using a dual-function sulfonated silica-based ionomer

Sulfonated-silica ceramic carbon electrodes (SS-CCE) were prepared by an in-situ sol-gel reaction where tetraethylorthosilicate and 3-trihydroxysilyl-1-propanesulfonic acid (TPS) are polymerized in the presence of a commercial Pt/C catalyst. The resultant catalyst layer is a promising candidate for application in proton exchange membrane fuel cells (PEMFCs), however their durability is unproven to date. To that end, we have examined the durability of these SS-CCE’s in fuel cells. The SS-CCE was subjected to an accelerated stress testing (AST) and its fuel cell performance was assessed before and after the AST. Remarkably, the SS-CCE was substantially more durable than a conventional Nafion-based electrode employing the identical Pt/C catalyst. Detailed electrochemical tests and post-mortem analysis of each electrode revealed in addition to its primary function of conducting ions/retaining water, the sulfonated silica ionomer takes on the dual role of stabilizing the Pt/C catalysts through an electronic effect that mitigates Pt nanoparticles Ostwald ripening/agglomeration. The method for producing SS-CCE is highly versatile and could potentially be employed with any fuel cell catalyst. It is therefore proposed that this dual-function ionomer could be paired with almost any Pt/C (or supported alloy catalyst) and extend the operational lifetime of fuel cells without comprising beginning of life performance.

NiCu single atom alloys catalyze the C[sbnd]H bond activation in the selective non- oxidative ethanol dehydrogenation reaction

NiCu single atom alloy (SAA) nanoparticles supported on silica are reported to catalyze the non-oxidative dehydrogenation of ethanol, selectively to acetaldehyde and hydrogen products by facilitating the CH bond cleavage. The activity and selectivity of the NiCu SAA catalysts were compared to monometallic copper and to PtCu and PdCu single atom alloys, in a flow reactor at moderate temperatures. In-situ DRIFTS showed that the silica support facilitates the OH bond cleavage of ethanol to form ethoxy intermediates over all the supported alloy catalysts. However, these remain unreactive up to 250 °C for the Cu/SiO2 monometallic nanoparticles, while in the NiCu SAA, acetaldehyde is formed at much lower temperatures, below 150 °C. In situ DRIFTS was also used to identify the CH activation step as the rate determining step of this reaction on all the copper catalysts we examined. The presence of atomically dispersed Ni in Cu significantly lowers the CH bond activation barrier, whereas Pt and Pd atoms were found less effective. This work provides direct evidence that the CH bond cleavage is the rate determining step in ethanol dehydrogenation over this type catalyst.

Carbon nanotubes as catalyst supports for ethanol oxidation

Multiwalled carbon nanotubes were obtained by chemical vapor deposition of xylene–ferrocene and employed as supports for PtSn alloy nanoparticles synthesized by the polyol method. The same metal alloy catalyst was also supported on Vulcan XC-72R to compare the influence of the substrate on the catalyst behavior for ethanol oxidation. The physical characterization of the carbon samples and supported alloy catalysts was performed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Ethanol oxidation was chosen as a reaction model to study the electrocatalytic behavior of the supported PtSn nanoparticles. Cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy were used for the electrochemical characterization. The PtSn/MWNT electrodes show a better catalytic behavior for ethanol oxidation than PtSn/Vulcan XC-72R electrodes.

The hydrogenation of triglycerides using supported alloy catalysts. II. Silica-supported Pd-Cu catalysts

Silica-supported Ni-Ag catalysts with a loading of 2·1·0.6% (w/w) total metal have been prepared using the precursors nickel dimethylglyoxime and silver nitrate by means of a simple impregnation method. The resulting catalysts were activated by calcination at 260°C in air, followed by hydrogen reduction at 450°C. They were then employed for soyabean oil hydrogenation at 1 bar H2 pressure and 160°C in a stirred batch reactor. Characterisation of the catalysts using temperature-programmed reduction and electron microscopy indicated that alloying of nickel and silver had occurred, but metal particle composition, for a given overall composition, varied with metal particle size and smaller metal particles were nickel rich. The hydrogenation activity and selectivity measurements revealed that the catalysts were more active and selective than a commercial nickel catalyst. Furthermore, the specific activities of the alloy catalysts were a maximum for alloys in the range 70–90 at. % Ni. However, the supported alloy catalysts also gave rise to greater trans isomerisation than the commercial catalyst. This is attributed to hydrogen deficiency caused by large triglyceride molecules blocking hydrogen chemisorption on small nickel particles (10–50 A in diameter), leading to enhanced cis-trans isomerisation.

The hydrogenation of triglycerides using supported alloy catalysts. I. Silica-supported Ni-Ag catalysts

The hydrogenation of triglycerides using supported alloy catalysts. I. Silica-supported Ni-Ag catalysts

Ethanol Oxidation on Carbon Supported Pt-Sn Electrocatalysts Prepared by Reduction with Formic Acid

Carbon supported alloy catalysts were prepared by reduction of Pt and Sn precursors with formic acid and characterized by X-ray diffraction, high-resolution transmission electron microscopy, and X-ray absorption spectroscopy techniques. Their electrocatalytic activity for ethanol oxidation was compared with commercial and electrocatalysts and the differences discussed in terms of intrinsic properties of the materials. The activity for ethanol oxidation in linear sweep voltammetry experiments at room temperature is greatly enhanced, mainly at low potentials, on (3:1) and (2:1) catalysts prepared by the formic acid method, while only a slight improvement is observed on (9:1) prepared with formic acid and on from E-TEK. The commercial catalyst showed a higher current performance as anode material in a direct ethanol fuel cell operating at 90 and . At the low temperatures of the electrochemical experiments, the rate determining step (rds) of ethanol oxidation is the removal of -species, which is enhanced by the presence of Sn oxides. At the higher temperatures of the fuel cell, instead, the rds is the dissociative adsorption of ethanol and/or the oxidation of acetaldehyde to acetic acid: both these reactions are favored by an increase of the Sn content in the alloyed state.

Ultra-thin porous silica coated silver–platinum alloy nano-particle as a new catalyst precursor

Templated sol–gel encapsulation of surfactant-stabilised micelles containing metal precursor(s) with ultra-thin porous silica coating allows solvent extraction of organic based stabiliser from the composites in colloidal state hence a new method of preparing supported alloy catalysts using the inorganic silica-stabilised nano-sized, homogenously mixed, silver–platinum (Ag–Pt) colloidal particles is reported.

Compositional and structural characterization of isolated Pb-Bi microcrystals co-vapor deposited onto amorphous carbon

Recent interest in heterogeneous nucleation of binary alloys requires a knowledge of the structure and composition of deposits. Analytical electron microscopy and x-ray microanalysis is well suited to obtaining such information and has already been applied to the overall characterization of a collection of isolated microcrystals. The methods for performing this characterization are well documented; however, the application of the technique to the determination of composition of individual microcrystals as a function of crystal size is less well documented. In addition to the fundamental interest such information provides, it is of practical importance in such disciplines as supported alloy catalysts where a size-dependent composition and/or structural behavior may change both the selectivity and reactivity of a catalyst.The specimens in this investigation were prepared by co-vapor deposition of Pb and Bi onto hot amorphous carbon substrates between 150°C and 250°C. The Pb and Bi were co-evaporated from separate filaments of Mo and Ta, respectively, or an alloy of PbBi was evaporated from a single filament of tantalum with no significant difference occurring in the deposits prepared by either method.

Morphology and composition of PtPd alloy crystallites on SiO 2 in reactive atmospheres

Scanning transmission electron microscopy and energy dispersive X-ray microanalysis are used to examine the structure, sintering rates and chemical composition of 20 to 200-Å-diameter PtPd alloy crystallites on planar amorphous SiO 2. Oxygen causes PtPd alloy crystallites to separate into distinct crystallites of metal and tetragonal PdO, both of which are in contact with the SiO 2 support. Oxide is first observed at 300 to 400 °C depending on composition, and the oxide begins to decompose at 650 °C and completely disappears between 740 and 850 °C. For high Pt alloys the oxide nucleates and grows at one side of the metal particles but for high Pd alloys small (20 to 40 Å) Pt particles form around the edges of the PdO crystal. The oxide can be reduced by H 2 even at room temperature and this produces distinct and separated Pt and Pd-rich particles as shown by single particle microanalysis. These morphologies are presumably caused by stronger interfacial interactions between PdO and SiO 2 compared to that between metal and the oxides. A stability diagram for formation of oxide shows that oxide is formed only for alloys containing at least 15% Pd. Evaporation of Pt as PtO 2 is inhibited by the presence of Pd and growth of crystallites is slower for alloys than for pure Pt metal. Implications of these results on the structures of supported alloy catalysts will be discussed.