Akane Miyazaki

Morphology Control of Platinum Nanoparticles and their Catalytic Properties

Platinum nanoparticles with different morphology were prepared by reduction of K2PtCl4 solution in the presence of different capping polymers. It was found that the shapes and the sizes of the Pt nanocrystals resulted were related to the kind of capping polymer used. When poly(vinylpyrrolidon) (PVP), poly(N-isopropylacrylamide) (NIPA) and sodium poly(acrylate) (SPA) were used as capping agents, the dominant shapes of the Pt nanocrystals observed by transmission electron microscopy were hexagonal (≈62%), square (≈67%) and triangular (≈41%), respectively. The average sizes of Pt nanocrystals were 6.9, 13.6 and 14.6 nm for capping polymers of PVP, NIPA and SPA, respectively. The colloidal Pt nanoparticles with different morphologies were supported on γ-Al2O3 (1 wt.% Pt) and then their catalytic activity for NO reduction by CH4 was tested in the 350–600°C temperature range. Additionally, the catalytic activities of these alumina-supported Pt nanocrystals were compared with a conventional catalyst having the average size of Pt particles of ≈2.4 nm. Over the alumina-supported Pt nanocrystals as compared with the conventional Pt/Al2O3, it was observed that the NO/CH4 reaction yields to NH3 and CO decreased significantly and on the other hand, the yield to N2O increased. The experimental results are suggesting that the catalytic behavior can be tuned in a convenient way through the morphological control of the metal nanoparticles.

NO reduction by CH4 over well-structured Pt nanocrystals supported on γ-Al2O3

Abstract Platinum nanocrystals, with an average diameter of 12 nm, were prepared by the reduction of K 2 PtCl 4 with H 2 in the presence of the polymer of N-isopropylacrylamide. The Pt nanocrystals, having mainly cubic shape (≈64%), were supported on γ-Al 2 O 3 and then tested for NO/CH 4 reaction. In contrast to the conventional Pt/γ-Al 2 O 3 catalyst, the formation of NH 3 and CO as side products was not evidenced below 600°C for Pt nanocrystals supported on alumina [Pt(100)/Al 2 O 3 ]. On the other hand, higher yield to N 2 O was observed for Pt(100)/Al 2 O 3 as compared with the conventional catalyst. Both, the size and dominant crystallographic orientation of the supported Pt particles have been found to be important factors for the catalyst activity for NO/CH 4 reaction.

Acute toxicity of chlorophenols to earthworms using a simple paper contact method and comparison with toxicities to fresh water organisms.

An acute toxicity test of chlorophenols on earthworms (Eisenia fetida) was performed using a simple paper contact method proposed by OECD testing guideline no. 207, that were applied as an earthworm toxicity test. The median lethal concentration, EC50, had significant correlation with logP(ow) (1-octanol/water partition coefficient) of the chemicals. The toxicity of chlorophenols on E. fetida was compared with toxicities for other species: an algae (Selenostrum capricornutum), a crustacean (Daphnia magna), and a fish (Oryzias latipes). It was found that the toxicity of chlorophenols was almost same for E. fetida and for fresh water organisms. These results suggest the possibility of drawing correlations between the effects of pollutants on living things in different environments, fresh water and soil.

Effect of platinum morphology on lean reduction of NO with C3H6

The relationship between the morphology (size and shape) of alumina supported Pt nanoparticles and catalytic behaviour for lean reduction of NO with C3H6 is investigated. It is revealed that the conversion of the low index facets of the mainly cubic Pt nanocrystals of around 12 nm to higher index planes, taking place under reaction conditions, is associated with substantial changes in the catalytic activity and selectivity to reaction products.

Solid-liquid interfacial reaction of Zn2+ ions on the surface of amorphous aluminosilicates with various Al/Si ratios

Abstract The adsorption behavior of Zn2+ ions onto the surface of amorphous aluminosilicates was studied using both potentiometric and spectroscopic methods (XANES: X-ray Absorption Near-Edge Structure). The aluminosilicates were prepared with different Al/Si ratios in order to compare the reactivities of surface aluminol and silanol groups toward Zn2+ ions. Potentiometric experiments were performed by maintaining the reacting suspensions at constant pH, ionic strength, and solid concentration, while Zn concentration was increased by stepwise addition. Our results showed that the surface aluminol and silanol groups possess significantly different reactivities toward Zn2+ ions. The reaction of Zn2+ ions with aluminol groups occurs through three processes: (i) surface complexation, (ii) dissolution, and (iii) re-sorption. A stoichiometric relationship was confirmed for the surface complexation between the aluminol groups and Zn2+ ions: two moles of H+ ions were released for one mole of Zn2+ ion adsorption. Following the surface complexation process, measurable amounts of zinc and aluminum ions were found to be mobilized from the surface of the solid to the liquid phase; subsequently, these ions precipitated on the solid surface, and possibly formed a co-precipitate with the hydrotalcite-type structure. On the other hand, a stoichiometric relationship was not obtained for the sorption of Zn2+ ions on silanol groups, and therefore, it was concluded that Zn2+ ions are retained on the surface of amorphous aluminosilicates by two different reactions. One reaction involves the surface complexation between Zn2+ ions and surface aluminol groups, which proceeds rapidly. The other reaction is the slow retention of Zn2+ ions onto silanol and/or aluminol groups, which could be the surface precipitation of Zn(OH)2 or the co-precipitation of Zn2+-Al3+ hydroxides. It can be suggested that the total sorption behavior of Zn2+ ions on amorphous aluminosilicates with different Al/Si ratios can be represented as the sum of the individual reactions of Zn2+ ions toward the aluminol and silanol groups. The potentiometric results were confirmed by XANES data. It was clearly evident that only the aluminol groups were responsible for surface complexation of Zn2+ ions. An equilibrium constant was calculated for this reaction.

Chemical and morphological evolution of supported Ru nanoparticles during oxidative conversion of methane

Alumina supported Ru nanoparticles, with an initial average size of 5.8 nm, show high activity and yield to CO and H2 at lower temperature than the conventionally prepared catalysts.

Investigation of the morphology–catalytic reactivity relationship for Pt nanoparticles supported on alumina by using the reduction of NO with CH4 as a model reaction

The morphological evolution of large Pt nanoparticles supported on alumina in reaction conditions has a significant impact on the catalytic behaviour for the NO/CH4 reaction.

Preparation, characterization and catalytic behavior of Pt-Cu nanoparticles in methane combustion

Abstract Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1:1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.

Sorption behavior of the Pt(II) complex anion on manganese dioxide (δ-MnO2): a model reaction to elucidate the mechanism by which Pt is concentrated into a marine ferromanganese crust

It is difficult to directly investigate the chemical state of Pt in marine ferromanganese crusts (a mixture of hydrous iron(III) oxide and manganese dioxide (δ-MnO2)) because it is present at extremely low concentration levels. This paper attempts to elucidate the mechanism by which Pt is concentrated into marine ferromanganese crust from the Earth’s continental crust through ocean water. In this investigation, the sorption behavior of the Pt(II) complex ions on the surface of the δ-MnO2 that is a host of Pt was examined as a model reaction. The δ-MnO2 sorbing Pt was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) to determine the chemical state of the Pt. Hydrolytic Pt(II) complex ions were specifically sorbed above pH 6 by the formation of a Mn-O-Pt bond. XPS spectra and XANES spectra for δ-MnO2 sorbing Pt showed that the sorbed Pt(II) was oxidized to Pt(IV) on δ-MnO2. The extended X-ray absorption fine structure (EXAFS) analysis showed that the coordination structure of Pt sorbed on δ-MnO2 is almost the same as that of the [Pt(OH)6]2− complex ion used as a standard. Therefore, the mechanism for the concentration of Pt in marine ferromanganese crust may be an oxidative substitution (penetration of Pt(IV) into structure of δ-MnO2) by a reduction-oxidation reaction between Pt(II) in [PtCl4-n(OH)n]2− and Mn(IV) in δ-MnO2 through a Mn-O-Pt bond.

Impact of particle size and metal–support interaction on denitration behavior of well-defined Pt–Cu nanoparticles

Well-dispersed Pt–Cu nanoparticles with two average sizes were synthesized: small (≈1.6 nm) and large (≈4.8 nm), respectively. The effects of size and support on the catalytic behavior of the nanoparticles for denitration reaction were analyzed. Both the unsupported and alumina-supported nanoparticles of smaller average size (1.6 nm) were very active, completely converting NO3− and NO2− (an intermediate reaction product) to N2 and NH4+. They were also more selective of N2 compared to the larger particles. The effects of particle size and alumina support on the denitration rate constants were analyzed in detail. The kinetic investigation indicates that the catalytic behavior is strongly related to the size of Pt–Cu nanoparticles as well as to the metal–support interaction. Generally, the larger nanoparticles proved to be less active, but on the other hand, they are less influenced by the support than the smaller ones. The metal–support interaction for bimetallic nanoparticles with smaller average size proved to be a key factor both for nitrate and nitrite reduction. Consideration of the reaction mechanism is made in light of the experimental results.