Dahee Park

Influence of hot carriers on catalytic reaction; Pt nanoparticles on GaN substrates under light irradiation

We report the hot carrier-driven catalytic activity of two-dimensional arrays of Pt nanoparticles on GaN substrate under light irradiation. In order to elucidate the effect of a hot carrier in a catalytic chemical reaction, the CO oxidation reaction was carried out on Pt nanoparticles on p- and n-type GaN under light irradiation. Metal catalysts composed of Pt nanoparticles were prepared using two different preparation methods: the one-pot polyol reduction and are plasma deposition methods. Under light irradiation, the catalytic activity of the Pt nanoparticles supported on GaN exhibited a distinct change depending on the doping type. The catalytic activity of the Pt nanoparticles on the n-doped GaN wafer decreased by 8-28% under light irradiation, compared to no irradiation (i.e., in the dark), while the Pt nanoparticles on the p-doped GaN wafer increased by 11-33% under light irradiation, compared to no irradiation. The catalytic activity increased on the smaller Pt nanoparticles, compared to the larger nanoparticles, presumably due to the mean free path of hot carriers. Based on these results, we conclude that the flow of hot carriers generated at the Pt-GaN interface during light irradiation is responsible for the change in catalytic activity on the Pt nanoparticles.

The effect of loading on sintering and catalytic activity of Pt/SiO2 hybrid catalyst powders synthesized via spray pyrolysis

Platinum (Pt) is commonly used as a heterogeneous catalyst to effectively convert carbon monoxide (CO) from automobile exhaust gas into carbon dioxide (CO2). Platinum/silica (Pt/SiO2) hybrid catalyst powders with varying Pt content were synthesized via a spray pyrolysis process. The average particle size and specific surface area of the Pt nanoparticles on the Pt/SiO2 hybrid catalyst powders were characterized as-prepared and after heat treatment. As the Pt loading increased, the Pt nanoparticles grew on the surface of the SiO2 as a result of sintering, and the catalytic efficiency decreased. This work demonstrates that the Pt/SiO2 (4 wt% Pt) hybrid catalyst powder is suitable as a hightemperature automobile exhaust catalyst, compared with the Pt/SiO2 hybrid catalyst powder with high Pt loading (14 wt% Pt), indicating that metal nanoparticle loading is a key factor for determining catalytic activity.

Pt/oxide nanocatalysts synthesized via the ultrasonic spray pyrolysis process: engineering metal–oxide interfaces for enhanced catalytic activity

We show that Pt nanoparticles synthesized on oxide nanocatalysts exhibit catalytic activity enhancement depending on the type of the oxide support. To synthesize the Pt/oxide nanocatalysts, we employed a versatile synthesis method using Pt nanoparticles (NPs) supported on various metal oxides (i.e., SiO2, CeO2, Al2O3, and FeAl2O4) utilizing ultrasonic spray pyrolysis. Catalytic CO oxidation was carried out on these catalysts, and it was found that the catalytic activity of the Pt NPs varied depending on the supporting oxide. While Pt/CeO2 exhibited the highest metal dispersion and active surface area, Pt/FeAl2O4 exhibited the lowest active surface area. Among the Pt/oxide nanocatalysts, Pt NPs supported on CeO2 showed the highest catalytic activity. We ascribe the enhancement in turnover frequency of the Pt/CeO2 nanocatalysts to strong metal–support interactions due to charge transport between the metal catalysts and the oxide support. Such Pt/oxide nanocatalysts synthesized via spray pyrolysis offer potential possibilities for large-scale synthesis of tailored catalytic systems for technologically relevant applications.

Fabrication and Pore Characteristics of Cu Foam by Slurry Coating Process

Metallic porous materials have many interesting combinations of physical and geometrical properties with very low specific weight or high gas permeability. In this study, highly porous Cu foam is successfully fabricated by a slurry coating process. The Cu foam is fabricated specifically by changing the coating amount and the type of polyurethane foam used as a template. The processing parameters and pore characteristics are observed to identify the key parameters of the slurry coating process and the optimized morphological properties of the Cu foam. The pore characteristics of Cu foam are investigated by scanning electron micrographs and micro-CT analyzer, and air permeability of the Cu foam is measured by capillary flow porometer. We confirmed that the characteristics of Cu foam can be easily controlled in the slurry coating process by changing the microstructure, porosity, pore size, strut thickness, and the cell size. It can be considered that the fabricated Cu foams show tremendous promise for industrial application.

The Effect of Fe and Fe 2 O 3 Powder Mixing Ratios on the Pore Properties of Fe Foam Fabricated by a Slurry Coating Process

Abstract Metal foams have a cellular structure consisting of a solid metal containing a large volume fraction ofpores. In particular, open, penetrating pores are necessary for industrial applications such as in high temperature filtersand as a support for catalysts. In this study, Fe foam with above 90% porosity and 2 millimeter pore size was suc-cessfully fabricated by a slurry coating process and the pore properties were characterized. The Fe and Fe 2 O 3 powdermixing ratios were controlled to produce Fe foams with different pore size and porosity. First, the slurry was preparedby uniform mixing with powders, distilled water and polyvinyl alcohol(PVA). After slurry coating on the polyure-thane(PU) foam, the sample was dried at 80 o C. The PVA and PU foams were then removed by heating at 700C for 3hours. The debinded samples were subsequently sintered at 1250 o C with a holding time of 3 hours under hydrogenatmosphere. The three dimensional geometries of the obtained Fe foams with an open cell structure were investigatedusing X-ray micro CT(computed tomography) as well as the pore morphology, size and phase. The coated amount ofslurry on the PU foam were increased with Fe

A study on the oxidation behavior of nickel alloys at elevated temperatures

This study was conducted with the aim to investigate the high temperature oxidation behavior of Inconel 750 alloy, which has excellent high temperature corrosion resistance among Ni-based super alloys. In the study, the temperature was set at 700°C, 900°C and 1100°C in the atmospheric environment; the heat treatment holding time was increased to 1 hour, 6 hours and 12 hours at each temperature to investigate the weigh increase behavior at each condition; and the shape of the oxide layer formed on the surface and the distribution of the elements were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).

Fabrication of Fe-Cr-Al Porous Metal with Sintering Temperature and Times

Abstract The porous metals are known as relatively excellent characteristic such as large surface area, light, lowerheat capacity, high toughness and permeability. The Fe-Cr-Al alloys have high corrosion resistance, heat resistance andchemical stability for high temperature applications. And then many researches are developed the Fe-Cr-Al porous met-als for exhaust gas filter, hydrogen reformer catalyst support and chemical filter. In this study, the Fe-Cr-Al porous met-als are developed with Fe-22Cr-6Al(wt) powder using powder compaction method. The mean size of Fe-22Cr-6Al(wt)powders is about 42.69 µm. In order to control pore size and porosity, Fe-Cr-Al powders are sintered at 1200~1450 o Cand different sintering maintenance as 1~4 hours. The powders are pressed on disk shapes of 3 mm thickness usinguniaxial press machine and sintered in high vacuum condition. The pore properties are evaluated using capillary flowporometer. As sintering temperature increased, relative density is increased from 73% to 96% and porosity, pore size aredecreased from 27 to 3.3%, from 3.1 to 1.8 µm respectively. When the sintering time is increased, the relative densityis also increased from 76.5% to 84.7% and porosity, pore size are decreased from 23.5% to 15.3%, from 2.7 to 2.08 µmrespectively. Keywords: Porous metal, Fe-Cr-Al alloy, Sintering Temperature, Porosity, Pore size