DFT studies of the characteristics of Pd−Pt core-shell clusters

It is reported that Pd?Pt core-shell type nanoclusters in which the inner atoms of the Pd cluster are substituted by Pt significantly enhance the catalytic activity for cycloocatdiene hydrogenation. In order to discuss the electronic states of core-shell clusters, DFT calculations were carried out for Pd₁₃, Pt₁₃, Pt/Pd₁₂, Pd/Pt₁₂ Pd₃₈ and Pd₆/Pt₃₂ clusters. From these calculations, it was found that the charge transfer between the core atoms and the shell atoms played an important role for the modification of the electronic state of the surface atoms in them.     

Esterification of acetic acid with n-Butanol using vanadium oxides supported on γ-alumina

Esterification of acetic acid with n-Butanol has been studied in a heterogeneous reaction system using two γ-alumina-supported vanadium oxide catalysts with different V loadings, which were prepared by the impregnation of a precipitated alumina. The alumina support and the supported catalysts were characterized using X-ray diffraction, N₂ adsorption, EDX analysis and NH₃-TPD techniques. The effects of the reaction time, of the molar ratio of the reactants, of the speed of agitation and of the mass fraction of the catalyst on the catalytic properties were studied. In the presence of the supported catalyst containing 10 wt % V₂O₅ (10V-Al₂O₃ sample) the conversion reached 87.7% after 210 min of reaction at 100 °C with an n-Butanol-to-acetic acid mole ratio equal to one. The conversion as well as the total acidity measured by TPD of NH₃ increased in the following order: Al₂O₃ < 5V-Al₂O₃ (5 wt % V₂O₅/Al₂O₃) < 10V-Al₂O₃. In all cases the reaction was completely selective to n-butyl acetate. Nevertheless, a loss in catalytic activity after three reaction cycles with 10 V₂O₅–Al₂O₃ catalyst was observed.     

The dispersity of γ-alumina supported rhenium from hydrogen pulse chemisorption

The applicability of hydrogen chemisorption in a pulse chromatographic system for determining the dispersity of -alumina supported rhenium catalysts (10.4 wt.% and 1.04 wt.%) preheated in hydrogen at 550–800 °C is shown.

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, - (10,4 .% 1,04 .%), 550–800°C.

     

Electrocatalytic oxidation of formic acid on functional MWCNTs supported nanostructured Pd–Au catalyst

In this work, PdAu nanocatalysts with different weight ratio of Pd and Au supported on functional multi-walled carbon nanotubes (f-MWCNTs) were prepared, and their electrocatalytic activity for the oxidation of formic acid was also studied. The electrocatalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical results showed that the 4Pd1Au/f-MWCNTs (by weight) catalyst, exhibited distinctly higher activity and better stability in formic acid electrooxidation than the Pd/f-MWCNTs catalyst. The Nano-Au improves potentially the performance of Pd-based electrocatalysts for the direct formic acid fuel cells (DFAFCs).     

EQCM studies on Pd–Ni alloy oxidation in basic solution

Processes of electrochemical oxidation of Pd-rich Pd–Ni alloys in basic solutions were studied with the aim of electrochemical quartz crystal microbalance. Potentials of current peaks of Ni(II)/Ni(III) redox couple are independent of alloy composition. On the other hand, Ni(II)/Ni(III) redox couples formed on Pd–Ni alloys and Ni differ in respect to the structure of involved compounds and the processes of transport of the species accompanying oxidation/reduction reaction. The process of oxidation of Pd exhibits some differences between pure Pd and Pd–Ni alloys. This concerns mainly on participation of adsorbed water/OH⁻ in Pd oxidation process. In the initial stages of Pd oxidation, the source of oxygen is water/OH⁻ from the bulk of the solution. At this stage of the process, the product of Pd oxidation could be described as Pd(OH)₂ or PdOH₂O. With further progress in oxidation process, adsorbed species, water/OH⁻, start to play a decisive role. Hydrous species, i.e. Pd(OH)₂ or PdOH₂O, are also reduced in the final stages of Pd(II) reduction process. This study is dedicated to the 70th birthday of Professor Oleg Petrii.     

Preparation of carbon supported Pd–Pb hollow nanospheres and their electrocatalytic activities for formic acid oxidation

Pd–Pb hollow nanospheres dispersed on carbon black were developed by a galvanic replacement reaction between sacrificial cobalt nanoparticles and Pd²⁺, Pb²⁺ ions. The as-prepared catalysts were characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The electrochemical measurements show that the as-prepared catalysts have excellent catalytic activity for formic acid electrooxidation, which is attributed to the large surface area caused by the hollow structure and the lead doping effect which might modify the electronic structure of the catalysts.     

Sonochemical synthesis of graphene oxide supported Pt–Pd alloy nanocrystals as efficient electrocatalysts for methanol oxidation

Pt–Pd bimetallic nanoparticles supported on graphene oxide (GO) nanosheets were prepared by a sonochemical reduction method in the presence of polyethylene glycol as a stabilizing agent. The synthetic method allowed for a fine tuning of the particle composition without significant changes in their size and degree of aggregation. Detailed characterization of GO-supported Pt–Pd catalysts was carried out by transmission electron microscopy (TEM), AFM, XPS, and electrochemical techniques. Uniform deposition of Pt–Pd nanoparticles with an average diameter of 3 nm was achieved on graphene nanosheets using a novel dual-frequency sonication approach. GO-supported bimetallic catalyst showed significant electrocatalytic activity for methanol oxidation. The influence of different molar compositions of Pt and Pd (1:1, 2:1, and 3:1) on the methanol oxidation efficiency was also evaluated. Among the different Pt/Pd ratios, the 1:1 ratio material showed the lowest onset potential and generated the highest peak current density. The effect of catalyst loading on carbon paper (working electrode) was also studied. Increasing the catalyst loading beyond a certain amount lowered the catalytic activity due to the aggregation of metal particle-loaded GO nanosheets.     

Pd supported on N-doped-ordered mesoporous carbons’ catalysts for selective hydrodechlorination of 4-chlorophenol

Pd catalysts supported on N-doped-ordered mesoporous carbons (NOMC) have been prepared and tested for selective hydrogenation of 4-chlorophenol (4-CP) with H₂. The difference from the previous methods is that the NOMC was synthesized using urea as nitrogen source via one-pot route. The rate constant of Pd/NOMC for hydrodechlorination of 4-CP was about 135.9 h^?1 which were higher than Pd/OMC (65.6 h^?1) and Pd/AC (20.8 h^?1). It could be attributed to the synergetic effects of mesoporous structure, N-doped supports, and the stabilized small PdNPs. The conversion changed from 100 to 90.2% after the sixth reaction using Pd/NOMC which could be caused by the palladium leaching.     

Comparison of two preparation methods of supported Li?Ni catalyst on alumina for selective oxidation of methane

Lithium-added nickel catalysts on alumina were prepared for CO₂ reforming of methane by two methods, precipitation and impregnation. Performances of the catalysts were investigated by TG, CO-adsorption and SEM analysis. The catalyst with ratio of Li/Ni=1.0 prepared by precipitation method has high nickel dispersion, catalytic activity and stability for CO₂ reforming of methane.     

Effect of γ-irradiation on the catalytic activity and selectivity of γ-alumina II. Conversion of isopropanol

The catalytic conversion of isopropanol was conducted over a poorly crystalline -alumina irradiated with different doses of -rays (25–150 Mrad). The catalytic reaction was carried out at 180–400°C in a flow technique under atmospheric pressure. The results showed that the dose of 25 Mrad resulted in a decrease of about 50% of the dehydration activity which suffered a further slight decrease upon irradiation at a dose of 50 Mrad. Increasing the dose in the range of 50–150 Mrad effected an increase in the dehydration activity reaching a maximum limit at 100 Mrad, then decreased abruptly by a dose of 150 Mrad. -irradiation led also to creation of some active sites contributing in dehydrogenation of isopropanol to producing acetone. These results were discussed in terms of removal of Brönsted acidity (25–50 Mrad), responsible for the dehydration reaction and to transformation of Lewis to Brönsted acidity (100 Mrad) by the action of liberated water from the dehydration reaction. The drop in dehydration activity due to irradiation at 150 Mrad might result from an efficient removal of the Brönsted acid sites created. The induced dehydrogenation activity of irradiated aluminas was attributed to creation of some electron-donor centers.     

In situ Raman and in situ XRD analysis of PdO reduction and Pd° oxidation supported on γ-Al2O3 catalyst under different atmospheres

Reduction of Pd° and decomposition of palladium oxide supported on γ-alumina were studied at atmospheric pressure under different atmospheres (H(2), CH(4), He) over a 4 wt% Pd/Al(2)O(3) catalyst (mean palladium particle size: 5 nm with 50% of small particles of size below 5 nm). During temperature programmed tests (reduction, decomposition and oxidation) the crystal domain behaviour of the PdO/Pd° phase was evaluated by in situ Raman spectroscopy and in situ XRD analysis. Under H(2)/N(2), the reduction of small PdO particles (<5 nm) occurs at room temperature, whereas reduction of larger particles (>5 nm) starts at 100 °C and is achieved at 150 °C. Subsequent oxidation in O(2)/N(2) leads to reoxidation of small crystal domain at ambient temperature while oxidation of large particles starts at 300 °C. Under CH(4)/N(2), the small particle reduction occurs between 240 and 250 °C while large particle reduction is fast and occurs between 280 and 290 °C. Subsequent reoxidation of the catalyst reduced in CH(4)/N(2) shows that small and large particle oxidation of Pd° starts also at 300 °C. Under He, no small particle decomposition is observed probably due to strong interactions between particles and support whereas large particle reduction occurs between 700 and 750 °C. After thermal decomposition under He, the oxidation starts at 300 °C. Thus, the reduction phenomenon (small and large crystal domain) depends on the nature of the reducing agent (H(2), CH(4), He). However, whatever the reduction or decomposition treatment or the crystal domain, Pd° oxidation starts at 300 °C and is completed only at temperatures higher than 550 °C. Under lean conditions, with or without water, the palladium consists of reduced sites of palladium (Pd°, Pd(δ+) with δ < 2 or PdO(x) with x < 1) randomly distributed on palladium particles.     

Characterization and reactivity of γ-Al_2O_3 supported Pd–Ni bimetallic nanocatalysts for selective hydrogenation of cyclopentadiene

Several g-Al2O3 supported Pd–Ni bimetallic nanocatalysts(Pd–Ni(x:y)/Al2O3; where x and y represent the mass ratio of Pd and Ni, respectively) were prepared by the impregnation method and used for selective hydrogenation of cyclopentadiene to cyclopentene. The Pd–Ni/Al2O3 samples were confirmed to generate Pd–Ni bimetallic nanoparticles by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The catalytic activity was assessed in view of the effects of different mass ratios of Pd and Ni, temperature, pressure, etc. Among all the samples, the Pd–Ni(1:1)/Al2O3(PN-1:1) catalyst showed extremely high catalytic ability. The conversion of cyclopentadiene and selectivity for cyclopentene can be simultaneously more than 90%.     

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.     

Co@Pt–Ru core-shell nanoparticles supported on multiwalled carbon nanotube for methanol oxidation

A novel synthesis route concerning reduction of cobalt core onto the surface of multiwalled carbon nanotubes (MWCNTs) and then substitution of part of Co core with Pt–Ru precursor was developed to synthesize the core-shell Co@Pt–Ru/MWCNTs catalyst. In this synthesis route, sodium borohydride and hydrazine hydrate were employed to reduce cobalt step by step in order to control the size of cobalt and the growth speed of cobalt crystal. The novel core-shell Co@Pt–Ru/MWCNTs catalyst shows good electrocatalysis towards methanol oxidation.     

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...     

A tandem Baylis-Hillman-singlet oxygen oxidation reaction for facile synthesis of γ-substituted γ-hydroxybutenolides

A series of highly functionalised γ-hydroxyacryl γ-hydroxybutenolides, 2, were synthesised in 25-50% overall yields in two or three steps from 2-furfural using a tandem Baylis-Hillman-singlet oxygen oxidation reaction.     

Characterization and reactivity of γ-Al_2O_3 supported Pd–Cu bimetallic nanocatalysts for the selective oxygenization of cyclopentene

In this work, Pd–Cu/γ-Al_2O_3 is prepared by the impregnation method and investigated for selective oxygenization of cyclopentene to cyclopentanone. A series of bimetallic Pd–Cu/γ-Al_2O_3 nanocatalysts were prepared and the structures characterized by XRD, XPS and TEM. We determined that the obtained Pd–Cu/γ-Al_2O_3(molar ratio Pd:Cu = 5:1) was an efficient catalyst for the oxygenization of cyclopentene to cyclopentanone with 95% selectivity and 85% conversion(100 °C, 1 MPa initial O_2 pressure, 7 h).     

Preparation of carbon supported Pd–P catalyst with high content of element phosphorus and its electrocatalytic performance for formic acid oxidation

The carbon supported Pd–P (Pd–P/C) anodic catalyst in direct formic acid fuel cell (DFAFC) was prepared with a novel phosphorus reduction method. The Pd–P/C catalyst obtained possesses the high content of P⁰ in the alloying state. Because alloying P⁰ could decrease the 3d electron density of Pd and the adsorption affinity of CO and H on Pd, alloying P⁰ would promote the formic acid (FA) oxidation through the direct pathway. Therefore, the electrocatalytic performance of the Pd–P/C catalyst for the FA oxidation is much better than that of the Pd/C catalyst.     

Theoretical studies on the inactivation mechanism of γ-aminobutyric acid aminotransferase

The inactivation mechanism of γ-aminobutyric acid aminotransferase (GABA-AT) in the presence of γ-vinyl-aminobutyric acid, an anti-epilepsy drug, has been studied by means of theoretical calculations. Density functional theory methods have been applied to compare the three experimentally proposed inactivation mechanisms (Silverman et al., J. Biol. Chem., 2004, 279, 363). All the calculations were performed at the B3LYP/6-31+G(d,p) level of theory. Single point solvent calculations were carried out in water, by means of an integral equation formalism-polarizable continuum model (IEFPCM) at the B3LYP/6-31+G(d,p) level of theory. The present calculations provide an insight into the mechanistic preferences of the inactivation reaction of GABA-AT. The results also allow us to elucidate the key factors behind the mechanistic preferences. The computations also confirm the importance of explicit water molecules around the reacting center in the proton transfer steps.