Moon Hyeon Kim

Surface chemical structures of CoO x /TiO2 catalysts for continuous wet trichloroethylene oxidation

An earlier sample of 5% CoOx/TiO2 used for the wet oxidation of TCE at 310 K forca. 6 h has been characterized with a fresh catalystvia XRD and XPS measurements. The binding energy for Co 2p3/2 of the fresh sample appeared at 781.3 eV, which was very similar to the chemical states of CoTiOx such as Co2TiO4 and CoTiO3, whereas the spent catalyst indicated a 780.3-eV main peak for Co 2p3/2 with a satellite structure at a higher energy region. This binding energy was almost equal to that of Co3O4 among reference Co compounds used. The phase structure of Co3O4 was revealed upon XRD measurements for all the catalyst samples. Based on these XPS and XRD results, a surface chemical structure of CoOx species existing with the fresh catalyst can be proposed to be predominantly Co3O4 encapsulated completely by very thin filmlike CoTiOx consisting of Co2TiO4 and/or CoTiO3, with a tiny amount of Co3O4 particles covered partially by such cobalt titanates which may be responsible to the initial catalytic activity. Those CoTiOx overlayers on Co3O4 particles may be readily removed into the wet media within 1 h at 310 K based on our earlier study, thereby giving rapid increase in the catalytic activity for that period.

Emission Control Technologies for N2O from Adipic Acid Production Plants

Abstract Nitrous oxide (N 2 O) is one of six greenhouse gases listed up in the Kyoto Protocol, and it effects a strong global warming because of its much greater global warming potential (GWP), by 310 times over a 100-year time horizon, than CO 2 . Although such N 2 O emissions from both natural and anthropogenic sources occur, the latter can be controlled using suitable abatement technologies, depending on them, to reduce N 2 O below acceptable or feasible levels. This paper has extensively reviewed the anthropogenic N 2 O emission sources and their related compositions, and the state-of-the-art non-catalytic and catalytic technologies of the emissions controls available currently to representative, large N 2 O emission sources, such as adipic acid production plants. Challengeable approaches to this source are discussed to promote establishment of advanced N 2 O emission control technologies. Key Words : Nitrous oxide (N 2 O), Global warming, Anthropogenic sources, Adipic acid, Catalytic emission controls

Parametric Study on the Deactivation of Supported Co3O4 Catalysts for Low Temperature CO Oxidation

Abstract This study focused on the influences of a variety of reaction parameters and guest molecules such as H 2 O and C 3 H 8 on the deactivation of supported Co 3 O 4 catalysts for CO oxidation. Additionally, the physical features of and carbon deposition on some samples after the reaction under the chosen conditions were determined by BET and X-ray diffraction as well as by carbon analyses to deduce the precursors associated with catalyst deactivation. Activity maintenance profiles of the catalysts for CO oxidation at 100°C significantly depended on the support for Co 3 O 4 nanoparticle dispersion, the loading, the preparation technique and the calcination temperature. The best on-stream performance was achieved using a 5% Co 3 O 4 /TiO 2 catalyst prepared by the incipient wetness method followed by calcination at 350°C. All the reaction parameters chosen here such as the reaction temperature, the feed gas composition of CO, O 2 , H 2 O and C 3 H 8 , and the gas space velocity strongly influenced the extent of catalyst deactivation during CO oxidation and also the rate of catalyst deactivation. However, the deactivation behavior is very complicated. No appreciable changes in the surface area, the porosity, and the phase of the Co 3 O 4 nanoparticles and their size occurred even for the samples that were severely deactivated. Significant deposition of carbon on the catalysts after the reaction was visible and it depended on the reaction parameters chosen here. Consequently, this extensive parametric study on the deactivation of catalysts during oxidation and with the chosen reaction parameters and guest gases can lead to an understanding of the deactivation precursors that are associated with carbonaceous species including carbonates and surface free carbon.

Oxidation and Reduction of the Metal Surface in Supported Pt Using Dissociative N2O Adsorption Coupled with H2 and CO Titration

Not only was the surface site density in a 0.78% Pt/SiO2 catalyst determined by using selective chemisorption techniques, but the surface chemistry related to decompositive N2O adsorption on the Pt surface was also described byin situ DRIFTS techniques. The“O”, coverage established by N2O decomposition at 363 K on a clean Pt surface was equal to thatvia hydrogen adsorption at 300 K; however, both the coverage of chemisorbed oxygenvia O2 chemisorption at 300 K and the COirr coverage were somewhat lower than the“O” monolayer coverage. Surface titration of the“O”-covered Pt crystallites after N2O decomposition at 363 K gave a consistent Pts density with the hydrogen chemisorption.In situ DRIFTS spectra of CO adsorbed at 300 K on both clean and H-covered Pt surfaces exhibited a strong peak at 2,076 cm−1 for linearly adsorbed CO with a small extent of multi-coordinated CO near 1,803 cm−1. The adsorption of CO at 300 K on an“O”,-covered Pt surfacevia dissociative N2O adsorption at 363 K appeared subsequently a band at 2,186 cm−1 due to a tiny amount of PtsO crystallites, which could be completely reduced to H-covered ones, when titrated with H2 at 300 K. The adequate description for these CO adsorption behaviors on different surfaces is PtsO+2CO(g)→PtsCO+CO2(g), although to very small extent, the addition onto PtsO occurs. Spectra of CO adsorbed on the oxidized Ptsvia N2O decomposition gave consistent surface chemistry within situ gravimetric measurements. The surface reactions acquired by DRIFTS spectra potentially offer an approach to remove N2O from emission sources by combining its catalytic dissociation with titration of the chemisorbed“O” atoms using either H2 or CO, particularly H2 because of complete recovery to a clean Pts.

Catalytic Technologies for Nitric Acid Plants N2O Emissions Control: In-Duct-Dependent Technological Options

A unit emission reduction of nitrous oxide (N2O) from anthropogenic sources is equivalent to a 310-unit CO2 emission reduction because the N2O has the global warming potential (GWP) of 310. This greatly promoted very active development and commercialization of catalysts to control N2O emissions from large-scale stationary sources, representatively nitric acid production plants, and numerous catalytic systems have been proposed for the N2O reduction to date and here designated to Options A to C with respect to in-duct-application scenarios. Whether or not these Options are suitable for N2O emissions control in nitric acid industries is primarily determined by positions of them being operated in nitric acid plants, which is mainly due to the difference in gas temperatures, compositions and pressures. The Option A being installed in the NH3 oxidation reactor requires catalysts that have very strong thermal stability and high selectivity, while the Option B technologies are operated between the NO2 absorption column and the gas expander and catalysts with medium thermal stability, good water tolerance and strong hydrothermal stability are applicable for this option. Catalysts for the Option C, that is positioned after the gas expander thereby having the lowest gas temperatures and pressure, should possess high deN2O performance and excellent water tolerance under such conditions. Consequently, each deN2O technology has different opportunities in nitric acid production plants and the best solution needs to be chosen considering the process requirements.

Wet oxidation of trichloroethylene over well-characterized CoOx/TiO2 catalysts

The 5% CoOx/TiO2 catalyst, well-characterized earlier, consisting of complete CoTiOx overlayers on Co3O4 nano-particles (“Type A”) after calcination at 843 K but of clean Co3O4 particles (“Type B”) after a continuous wet oxidation of trichloroethylene (TCE) at 310 K forca. 6 h, has been used to investigate the influence of operating variables on the activity and the stability of the Type B Co3O4 particles during wet catalysis. At 310 K, the catalyst exhibited a 48% steady-state conversion with a transient behavior in activity up toca. 1 h on stream. As the reaction temperature increased, higher performances were achieved and the transient period disappeared, which might be due to easier decapsulation of the Type A Co3O4 particles at higher temperatures to form the Type B Co3O4 particles very active for this wet oxidation reaction. All wet activities were equal to those based on the concentration of Cl− ions produced, implying the complete oxidation of TCE to HCl and CO2, and significant decrease in pH occurred because of the HCl formation. The supported CoOx was very stable for the wet oxidation at 310 K, even forca. 36 h, and XPS measurements of samples of the catalyst following the wet oxidation for desired hours were in good agreement with our earlier proposed model for CoOx species.

Low-temperature Reduction of N 2 O by H 2 over Pt/SiO 2 Catalysts

【The present work has been devoted to the catalytic reduction of

CO and C 3 H 8 Oxidations over Supported Co 3 O 4 , Pt and Co 3 O 4 -Pt Catalysts: Effect on Their Preparation Methods and Supports, and Catalyst Deactivation

N_2O

Preparation and characterization of supported Pt nanoparticles for N 2 O-H 2 reaction

by

Oxidation of gaseous elemental mercury by hydrochloric acid over CuCl2/TiO2-based catalysts in SCR process

H_2