An EQCN assessment of electrocatalytic oxidation of methanol at nanostructured Au–Pt alloy nanoparticles

Alloy nanocrystals encapsulated with alkyl dithiolates (“core-shell” nanoparticles) serve as an intriguing class of nanostructured catalysts. This paper reports the preliminary results of an electrochemical quartz-crystal nanobalance (EQCN) investigation of mass transport associated with the catalytic activation and methanol oxidation at nanostructured Au–Pt nanocrystals. It is demonstrated that the catalytic activation and oxidation of methanol are accompanied by mass fluxes across the nanostructured film. The mass transport involves oxidation–reduction of surface oxygenated species, methanol adsorption and oxidation, solvent breath and product release. The implication of the EQCN results to the understanding of the core-shell nanostructured catalytic mechanism is discussed.     

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.     

Highly active electrocatalysis of hydrogen evolution reaction in alkaline medium by Ni–P alloy: A capacitance-activity relationship

Different weights of amorphous Ni–P alloy with same P contents were electrodeposited on nickel plate with same area used as cathode for hydrogen evolution reaction(HER). The amorphous Ni–P alloy coatings were characterized for their surface morphology and composition through Scanning electron microscopy(SEM) and Energy dispersive X-ray spectroscopy(EDS) techniques, X-ray photoelectron spectroscopy(XPS) and X-ray diffraction(XRD) analysis. The electrocatalytic activity for HER in alkaline medium is determined by linear scan voltammetry(LSV) and a relationship between HER activity and capacitance is established. The capacitance varies with the loading of the Ni–P on Ni plate but the activity for HER is directly proportional to the capacitance in alkaline and vice versa. 3#Ni–P/Ni containing 3.85 mg Ni–P alloy with highest capacitance performs the best catalytic activity. This work provides direct evidence to explore the capacitance influence on the electrocatalystic activity for the HER.     

Reduction of carbon dioxide by hydrogen on metal–carbon catalysts under supercritical conditions

The reduction of carbon dioxide with hydrogen on metal–carbon (Ru, Rh, Ir) catalysts is investigated under supercritical conditions for the first time. High selectivity (close to 100%) toward methanation with good stability of catalytic activity is observed for Ru- and Rh-containing catalyst, while the preferred reduction to CO is observed for Ir/C catalyst.     

The Boudouard–Bell reaction analysis under high pressure conditions

A new method for the measurement of solid fuel reactivity towards carbon dioxide has been developed. This new method takes into account high-pressure and temperature effects. Three devolatilized carbonaceous materials have been used in experiments: chars derived from lignite, bituminous coal and blast furnace coke. Processes were carried out at temperatures of 800, 850 and 900?°C and pressures of 1.52, 2.5 and 3.4?MPa. Analysis of the product gas composition was carried out with the maximum degree of conversion of CO₂ (??_m) proposed as a representative reactivity parameter. Arrhenius and Eyring relationships have been analyzed, and values of the activation energy and activation volume have been calculated.     

Highly efficient oxidation of alcohols using Oxone~ as oxidant catalyzed by ruthenium complex under mild reaction conditions

Aromatic and alkyl alcohols were oxidized to the corresponding aldehydes or ketones at room temperature with high conversion and selectivity using Oxone(?)(2KHSO_5·KHSO_4·K_2SO_4)as oxidant catalyzed by ruthenium complex Quin-Ru-Quin(where Quin = 8-hydroxyquinoline).The reaction time is very short and the preparation of complex is simple.     

Base metal-catalyzed alcohol C–C couplings under hydrogen transfer conditions

Comparing to classical Grignard-type carbonyl additions, transfer hydrogenative C–C bond-forming reactions using alcohols as carbonyl precursors have shown remarkable advantages from the perspective of atom economy, step economy and redox economy. The significant drawbacks of conventional method, such as the use of multi-step reactions, the premetalated reagents, and stoichiometric oxidants and reductants, can be avoided by using hydrogen transfer processes. Moreover, the development of reactions employing earth-abundant and eco-friendly base metal as catalysts is an important objective in modern sustainable chemistry. In this review, we summarized recent advances in base metal-catalyzed C–C coupling of alcohols under hydrogen transfer conditions.     

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...     

β-Oxo-sulfoxide rearrangements under sila-Pummerer reaction conditions

Under sila-Pummerer reaction conditions, the β-oxo-sulfoxide 1 gave rise to a new pentacyclic compound 5. The structure of 5 was deduced from spectral data and by X-ray analysis of the sulfoxide 6 which was formed by subsequent oxidation.     

Platinum nanoparticles supported on zirconia–carbon black nanocomposites for methanol oxidation reaction

Platinum (Pt) nanoparticles supported on zirconia–carbon black nanocomposites (Zr–C), which annealed at different temperatures, used as Pt/Zr–C electrocatalysts for methanol oxidation reaction (MOR) are prepared and characterized in this study. Transmission electron microscope images and X-ray diffraction analysis showed that the diameters of Pt nanoparticles are around 3–4 nm. Electrocatalytic MOR performances of these Pt/Zr–C electrocatalysts are investigated by cyclic voltammetry, CO-stripping voltammetry, and chronoamperometry. All the Pt/Zr–C electrocatalysts synthesized in this study exhibited higher MOR efficiency than that of the commercial E-TEK Pt/C electrocatalyst, and the electrocatalyst using Zr–C support annealed at 300 °C, achieving the highest MOR efficiency among all the electrocatalysts.     

Efficient chemiluminescence by aptamer – reactant platform combination with activated Ag–Au alloy nanoparticles for cobalt detection

This article deals with the detection of Co(II) in real water sample using aptamer – reactant platform combination with activated Ag–Au alloy nanoparticles (NPs) by chemiluminescence (CL) method. CL is attributed to a catalytically enhanced decomposition of H₂O₂ by aptamer conjugated Ag–Au alloy NPs to produce reactive oxygen species. The Ag–Au alloy NPs were prepared by chemical method using double reducing agent (i.e. trisodium citrate and polyethylenimine) and used for detection of Co(II) from water by CL method. CL experiments were carried out with the variation of different parameters such as pH, concentration of luminol, concentration of H₂O₂ and Ag–Au alloy NPs. We found that Ag–Au alloy NPs have very good efficiency towards Co(II) detection. Analytical parameters and kinetics were studied in detail to know the nature and mechanism of CL in presence of aptamer conjugated Ag–Au alloy NPs. The linear range of the CL sensor of Co(II) is covered concentration from 0.01 to 10 µg/L with detection limit of 0.001 µg/L. The relative standard deviation for determination of Co(II) was 6.65 in 10 replicated measurements. CL method is first time applied to detect the Co(II) in real water samples at very low level using aptamer conjugated Ag–Au NPs as a catalyst.     

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...     

Photocatalytic oxidation of acetaldehyde by hybrid Pt/WO3–MOR photocatalysts under visible or sunlight irradiation

A hybrid photocatalyst was prepared from visible light-responsive Pt/WO₃ and siliceous mordenite (MOR) zeolite by simple impregnation with an aqueous solution of (NH₄)₁₀W₁₂O₄₁·5H₂O. Unmodified Pt/WO₃ had low photocatalytic activity in gas phase oxidation of acetaldehyde because of its low surface area (3–5 m²/g). In contrast, the Pt/WO₃–MOR had higher photocatalytic activity under focused sunlight and Xe lamp irradiation. Pt/WO₃–MOR with low WO₃ content (<20 wt%) adsorbed sufficient acetaldehyde, but absorption of light in the visible region was low. The optimum zeolite content enhancing the photocatalytic activity of Pt/WO₃ was estimated to be 30–50 % (w/w). Adsorption of the gaseous reactants and the efficiency of absorption of incident light are both important aspects of high photocatalytic activity.     

Selected electrochemical properties of Pd–Au alloys: hydrogen absorption and surface oxidation

Hydrogen absorption into and surface oxidation of Pd–Au alloys in acidic solutions were studied by cyclic voltammetry (CV) and chronoamperometry (CA) coupled with the electrochemical quartz crystal microbalance (EQCM). The influence of alloy bulk and surface composition on the process of oxidation of absorbed hydrogen was examined. The stresses induced by hydrogen insertion in Pd–Au alloys were compared with the case of pure Pd. The potential corresponding to the formation of a monolayer of surface oxide was determined for Pd–Au alloys of different surface states. Electrochemical dissolution of Pd–Au alloys was investigated.     

Base-free aerobic oxidation of glycerol on TiO_2-supported bimetallic Au–Pt catalysts

The aerobic oxidation of glycerol provides an economically viable route to glyceraldehyde, dihydroxyacetone and glyceric acid with versatile applications, for which monometallic Pt, Au and Pd and bimetallic Au–Pt, Au–Pd and Pt–Pd catalysts on Ti O2 were examined under base-free conditions. Pt exhibited a superior activity relative to Pd, and Au–Pd and Pt–Pd while Au was essentially inactive. The presence of Au on the Au–Pt/Ti O2 catalysts led to their higher activities(normalized per Pt atom) in a wide range of Au/Pt atomic ratios(i.e.1/3–7/1), and the one with the Au/Pt ratio of 3/1 exhibited the highest activity. Such promoting effect is ascribed to the increased electron density on Pt via the electron transfer from Au to Pt, as characterized by the temperature-programmed desorption of CO and infra-red spectroscopy for CO adsorption. Meanwhile,the presence of Au on Au–Pt/Ti O2, most like due to the observed electron transfer, changed the product selectivity, and facilitated the oxidation of the secondary hydroxyl groups in glycerol, leading to the favorable formation of dihydroxyacetone over glyceraldehyde and glyceric acid that were derived from the oxidation of the primary hydroxyl groups. The synergetic effect between Au and Pt demonstrates the feasibility in the efficient oxidation of glycerol to the targeted products, for example, by rational tuning of the electronic properties of metal catalysts.     

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.     

Catalytic oxidation of NO over Mn–Co–Ce–Ox catalysts: effect of reaction conditions

Manganese–cobalt–cerium oxide (Mn–Co–Ce–Ox) catalysts were synthesized by the co-precipitation method and tested for activity in low-temperature catalytic oxidation of NO in the presence of excess O₂. With the best Mn–Co–Ce mixed-oxide catalyst, approximately 80 % NO conversion was achieved at 150 °C and a space velocity of 35,000 h^?1. The effect of reaction conditions (reaction temperature, volume fractions of NO and O₂, gas hourly space velocity (GHSV), and catalyst stability) was investigated. The optimum reaction temperature was 150 °C. Increasing the O₂ content above 3 % results in almost no improvement of NO oxidation. This catalyst enables highly effective removal of NO within a wide range of GHSV. Furthermore, the stability of the Me–Co–Ce–Ox catalyst was excellent; no noticeable decrease of NO conversion was observed in 40 h.     

TG–FTIR analysis of oxidation kinetics of some solid fuels under oxy-fuel conditions

A possible technology that can contribute reduction of carbon dioxide emission is oxy-fuel combustion of fossil fuels enabling to increase CO₂ concentration in the exhaust gas by carrying out the combustion process with oxygen and replacing air nitrogen with recycling combustion products to obtain a capture-ready CO₂ stream. The laboratory studies and pilot-scale experiments discussed during the last years have indicated that oxy-fuel combustion is a favorable option in retrofitting conventional coal firing. Estonian oil shale (OS) with its specific properties has never been studied as a fuel in oxy-fuel combustion, so, the aim of the present research was to compare thermo-oxidation of OS and some coal samples under air and oxy-fuel combustion conditions by means of thermal analysis methods. Experiments were carried out in Ar/O₂ and CO₂/O₂ atmospheres with two oil shale and two coal samples under dynamic heating conditions. FTIR analysis was applied to characterize evolved gases and emission dynamics. Kinetic parameters of oxidation were calculated using a model-free kinetic analysis approach based on differential iso-conversional methods. Comparison of the oxidation characteristics of the samples was given in both atmospheres and it was shown that the oxidation process proceeds under oxy-fuel conditions by all studied fuels with lower activation energies, however, it can last longer as the same temperatures are compared.     

Pt–Ni carbon-supported catalysts for methanol oxidation prepared by Ni electroless deposition and its galvanic replacement by Pt

Pt–Ni particles supported on Vulcan XC72R carbon powder have been prepared by a combination of crystalline Ni electroless deposition and its subsequent partial galvanic replacement by Pt upon treatment of the Ni/C precursor by a solution of chloroplatinate ions. The Pt-to-Ni atomic ratio of the prepared catalyst has been confirmed by EDS analysis to be ca. 1.5:1. No shift of Pt XPS peaks has been observed, indicating no significant modification of its electronic properties, whereas the small shift of the corresponding X-ray diffraction (XRD) peaks indicates the formation of a Pt-rich alloy. No Ni XRD peaks have been observed in the XRD pattern, suggesting the existence of very small pockets of Ni in the core of the particles. The surface electrochemistry of electrodes prepared from the catalyst material suggests the existence of a Pt shell. A moderate increase in intrinsic catalytic activity towards methanol oxidation in acid has been observed with respect to a commercial Pt catalyst, but significant mass specific activity has been recorded as a result of Pt preferential confinement to the outer layers of the catalyst nanoparticles.     

Unexpected formation of β, meso-directly linked diporphyrins under Adler–Longo reaction conditions

Unexpected formation of β, meso-directly linked diporphyrin products has been described in the reactions of β-formyl porphyrins with pyrrole under Adler–Longo reaction conditions. Preliminary mechanistic studies indicates that β-dipyrromethane substituted porphyrin structure is the crucial intermediate for the formation of diporphyrin product.