Electrooxidation of ethanol on carbon nanotubes–nickel nanoparticles composites in alkaline media

In this report, the preparation of carbon nanotubes–Ni nanoparticles composites (CNT–Ni) is presented. The morphology and elemental composition of CNT–Ni composites were examined by transmission electron microscopy and X-ray diffraction. The electrochemical behaviour of carbon nanotubes–Ni nanoparticles composites in an aqueous solutions of alkali and alkaline solutions of ethanol has been studied by linear sweep voltammetry. The peak on the potentiodynamic curve for CNT–Ni composite electrode in alkaline solutions of ethanol is observed which is ascribed to the ethanol oxidation in alkaline medium. The results obtained are discussed from the point of view of employment of the CNT–Ni composites for the catalytic electrodes of fuel cells.     

Pt–Ni alloy nanoparticles supported on multiwalled carbon nanotubes for methanol oxidation in alkaline media

The Pt–Ni alloy nanoparticles with different Pt/Ni atomic ratios supported on functionalized multiwalled carbon nanotubes surface were synthesized via an impregnation-reduction method. The nanocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. XRD demonstrated that Pt was alloyed with Ni. TEM showed that the Pt–Ni alloy nanoparticles were uniformly dispersed on the multiwalled carbon nanotubes (MWCNTs) surface, indicating appropriate amount of Ni in Pt–Ni alloy which facilitates the dispersion of nanoparticles on the MWCNT surface. XPS revealed that the Pt 4f peak in Pt–Ni/MWCNT (4:1) catalyst shifted to a lower binding energy compared with Pt/MWCNT catalyst, and nickel oxides/hydroxides such as NiO, Ni(OH)₂, and NiOOH were on the surface of Pt–Ni nanoparticles. Electrochemical data based on cyclic voltammetry and chronoamperometric curves indicated that Pt–Ni (4:1) alloy nanoparticles exhibited distinctly higher activity and better stability than those of Pt/MWCNTs toward methanol oxidation in alkaline media.     

Non-aqueous sol–gel preparation of carbon-supported nickel nanoparticles

This work addresses the novel non-aqueous sol–gel process preparation of carbon-supported nickel nanoparticles. In the sol–gel process, ethanol, nickel nitrate or nickel (П) acetylacetonate, and citric acid were used as solvent, source of metallic element, and chelating agent, respectively. Hexadecylamine (HDA), oleic acid and oleylamine were used as surfactants. The calcination process was performed under protecting Ar or N₂ flowing. Carbon supported nickel nanoparticles can be prepared by this sol–gel process. Moreover, no grain growth occurs in a temperature range of 200 K, meaning that the grain size of the nickel nanoparticles can be controlled in this sol–gel process. The nickel nanoparticles can display typical superparamagnetic behavior at room temperature when HDA has been used. This novel method is expected to have wide applications in the field of metallic nanoparticles.     

Radiation formation of Al–Ni bimetallic nanoparticles in aqueous system

This work concerns the study of Al–Ni bimetallic nanoparticles synthesized by gamma-radiolysis of aqueous solution containing aluminium chloride hexahydrate, nickel chloride hexahydrate, polyvinyl alcohol for capping colloidal nanoparticles, and isopropanol as radical scavenger. While the Al/Ni molar ratio is kept constant, size of the nanoparticles can be well controlled by varying the radiation dose. The products were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction analysis (XRD). Observations of UV–vis absorption spectra and TEM images showed that as the radiation dose increases from 50 to 100 kGy the particle size decreases and the number particles distribution increases. It may be explained due to the competition between nucleation and aggregation processes in the formation of metallic nanoparticles under irradiation. The EDX and XRD analysis confirmed directly the formation of Al–Ni bimetallic nanoparticles in form of alloy nanoparticles.     

High activity of Pt–Rh supported on C–ITO for ethanol oxidation in alkaline medium

Research on Chemical Intermediates - PtRh/C–ITO electrocatalysts were prepared in a single-step method using H2PtCl6·6H2O and RhCl3·xH2O as metal sources, sodium borohydride as the...     

Effect of de-alloying of Pt–Ni bimetallic nanoparticles on the oxygen reduction reaction

Carbon-supported Pt–Ni alloy nanoparticles with various compositions were prepared by a borohydride reduction method in anhydrous ethanol solvent. Here, we surveyed effect of thermally induced de-alloying on activity of the oxygen reduction reaction (ORR). Especially, changes in surface and bulk structures were investigated through electrochemical and spectroscopic measurements. The activity of as-prepared Pt–Ni alloy nanoparticles showed a monotonous dependence on Pt content. However, heat-treatment induced the phase separation between Pt and NiO and the resultant enhancement in ORR activity without significant increase in surface Pt concentration.     

Oxygen reduction reaction on carbon supported Palladium–Nickel alloys in alkaline media

Carbon supported Palladium–Nickel alloys with various compositions (Pd–Ni/C) were synthesized by chemical reduction of the co-precipitated Pd and Ni hydroxides on carbon. The structure of these alloys was characterized using X-ray diffraction (XRD) analysis. The catalytic activity of Pd–Ni/C for oxygen reduction reaction (ORR) in alkaline media was studied using a glassy carbon rotating disk electrode (RDE). Pd/C showed ORR activity close to that of Pt/C. The activities of Pd–Ni (3:1)/C and Pd–Ni (1:1)/C were found unchanged compared with that of Pd/C. Ni/C showed about 175 mV lower onset potential than Pt/C, and the activity of Pd–Ni (1:3)/C was observed to be between that of Pd/C and Ni/C.     

Highly selective catalysts for liquid-phase hydrogenation of substituted alkynes based on Pd—Cu bimetallic nanoparticles

Catalytic properties of Pd—Cu bimetallic catalysts supported on SiO₂ and Al₂O₃ were studied in a model reaction of selective hydrogenation of diphenylacetylene. Application of PdCu₂(AcO)₆ heterobimetallic acetate complex as a precursor made it possible to obtain homogeneous Pd—Cu bimetallic nanoparticles. This result was supported by the data of IR spectroscopy of adsorbed CO. The Pd-Cu catalysts showed considerably higher selectivity than monometallic samples. Moreover, the introduction of copper decreases the hydrogenation rate of diphenylethylene (DPE) to diphenylethane. As a result, the maximum yield of the target product, DPE, increased from 78 to 93% in the presence of Pd—Cu catalysts.     

Density functional study of small bimetallic Ag–Pd clusters

The geometric and electronic properties of small Ag_mPd_n clusters with m + n = 2–5 are studied within the framework of density functional theory in conjunction with two hybrid and one GGA exchange–correlation functional. For every composition, the global minimum is identified by using geometry optimization for a collection of initial structures. Results indicate that, for bimetallic tetramers and pentamers, the clusters shift from two-dimensional to three-dimensional structures with the addition of a second Pd atom. Ag₂Pd₂ is identified as the most stable tetramer by the calculation of the excess energy and second energy difference of bimetallic clusters. Concerning the fragmentation channels it is seen that the most favourable route in the majority of cases is via the evaporation of a single atom. Density of states calculations reveal that the increase of Pd content depletes the isolated s states close to the Fermi level, while at the same time shifts the d states to higher energies.     

Pd–Co bimetallic nanoparticles supported on graphene as a highly active catalyst for Suzuki–Miyaura and Sonogashira cross-coupling reactions

Graphene (G) supported Pd–Co bimetallic nanoparticles (NPs) as a highly active catalyst was prepared by a chemical reduction method and used for coupling reactions. With the characterization of X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectrum, the composition of resulting Pd–Co material was identified to be alloy structural. The Pd–Co (1:1)/G exhibited the highest catalytic activity for the Sonogashira-type coupling reactions and also exerted satisfied catalytic activity and recycle stability for Suzuki–Miyaura cross-coupling reactions. This Pd–Co/G material also possessed other advantages such as low-cost, easy recycled from reaction system by a magnet for their magnetic property, and easy experimental handling.     

Effects of various chemical synthetic routes on structural and magnetic features of Mn–Pt bimetallic nanoparticles

Mn–Pt nanoparticles were synthesized by ‘wet-chemical’ methods, in various organic solvents and with several combinations between organometallic precursors and capping ligands. The results show that the size of the obtained nanoparticles can be tuned between 2 and 9 nm, through adjustment of the synthetic conditions, including the nature and concentration of the starting reagents and the choice of reaction temperatures. Some of the as-prepared samples present exchange bias features probably due to the simultaneous occurrence of antiferromagnetic MnO and ferrimagnetic Mn₃O₄ oxides. Magnetic characterization of annealed alloy nanoparticles indicates the co-existence of both superparamagnetic and interacting nanoparticles as well as the presence of two different hard and soft magnetic phases, displaying high coercivity values at 10 K.     

Influence of heat treatment on the size of sodium lignosulfonate particles in water—ethanol media

Russian Chemical Bulletin - Dynamic light scattering and size exclusion chromatography were used to investigate the size of sodium lignosulfonate particles in water—ethanol media and the...     

Controlled green synthesis of Au–Pt bimetallic nanoparticles using chlorogenic acid

Research on Chemical Intermediates - Well-dispersed Au–Pt alloyed bimetallic nanoparticles are synthesized using chlorogenic acid as the only reducing agent and stabilizer to reduce Au/Pt...     

Electrocatalytic oxidation of alcohols on gold in alkaline media: base or gold catalysis?

On the basis of a comparison of the oxidation activity of a series of similar alcohols with varying pK(a) on gold electrodes in alkaline solution, we find that the first deprotonation is base catalyzed, and the second deprotonation is fast but gold catalyzed. The base catalysis follows a Hammett-type correlation with pK(a), and dominates overall reactivity for a series of similar alcohols. The high oxidation activity on gold compared to platinum for some of the alcohols is related to the high resistance of gold toward the formation of poisoning surface oxides. These results indicate that base catalysis is the main driver behind the high oxidation activity of many organic fuels on fuel cell anodes in alkaline media, and not the catalyst interaction with hydroxide.     

The effect of framework functionality on the catalytic activation of supported Pd nanoparticles in the Mizoroki–Heck coupling reaction

Palladium nanoparticles (Pd-NPs) were supported on functional and nonfunctional Co-coordination polymers (Pd/CoBDCNH₂ and Pd/CoBDC). Advanced analytical techniques revealed that Pd-NPs are supported on the external surface of the polymer framework and the functionalized framework possesses effective influence to prevent Pd-NP aggregation. Supported Pd-NPs were effectively applied as heterogeneous recyclable catalysts in the Mizoroki–Heck C–C cross coupling reactions of iodobenzene and either aromatic or aliphatic terminal alkenes. Catalytic results exhibited that highly dispersed Pd-NPs with low loading (1%) on the functional polymer (Pd/CoBDCNH₂) are more effective than aggregated Pd-NPs with high loading (9%) on the nonfunctional polymer (Pd/CoBDC). Both catalysts can simultaneously provide high activity and selectivity to E-coupled products, high efficiency in low amounts, easy separation of heterogeneous catalyst and appropriate performance in the recycling reaction without addition of a reducing agent.     

Effect of oxygen addition on the hydrogen production from ethanol steam reforming in a Pd–Ag membrane reactor

In this communication, a porous stainless steel (PSS) tube was electrolessly plated into Pd–Ag membrane reactor which was used for separating hydrogen produced in an ethanol steam reforming reaction with the addition of oxygen, which has not been reported before. Palladium and silver were deposited on porous stainless steel tube via the sequential electroless plating procedure with an overall film thickness of 20 μm and Pd/Ag weight ratio of 78/22. Ethanol–water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2 or 0.7) were fed concurrently into the membrane reactor packed with MDC-3. The reaction temperatures were set at 593–723 K and the pressures 3–10 atm. The effect of oxygen addition plays a vital role on the ethanol steam reforming reaction, especially for the Pd–Ag membrane reactor in which a higher flux of hydrogen is required. If oxygen in the feed is not sufficient, it would be possible that steam reforming reaction prevails. Inversely, high O₂ addition will shift the reaction scenario to be partial oxidation dominating, and selectivity of CO₂ increases with increasing oxygen feed. At high pressure, autothermal reaction of ethanol would be easily reached.     

Electrochemical determination of the surface composition of Pd–Pt core–shell nanoparticles

Different amounts of Pt atoms were deposited onto the surface of Pd nanoparticles supported on carbon black by hydroquinone reduction method in anhydrous ethanol. Here, we surveyed electrochemical probing of surface compositions of Pd–Pt surface alloys. They were calculated from hydrogen desorption, carbon monoxide adlayer oxidation, and reduced carbon dioxide oxidation charges. The surface composition of Pt drastically increased up to Pt[0.3]/Pd/C (23.1 at.% of Pt) and then approached that of pure Pt with the moderate rate of increase.