Microtextural and surface chemical heterogeneities of activated carbons (AC) have been studied to see their distinctive role for the adsorption of CO2, CO and N2 at 25 °C and up to 850 Torr. Not only the microtextural properties influence the adsorption of the gases, particularly CO2, but the chemical surface heterogeneity also plays a significant role for CO2 adsorption. The volume of ultramicropores < 7 Å is of predominantly importance in high CO2 adsorption at pressures above 30 Torr. However, the average size of micropores and their size distribution, and the chemical surface heterogeneity are much more critical at the Henry’s law region (< 30 Torr). The latter could be well characterized by the amount and Henry constant of CO2 adsorption at the low pressures, the Toth model parameters, the change in CO2/ CO and CO2/ N2 selectivities with respect to pressure, the amount of CO from the thermal decomposition, and the direct probing of very strong basicity sites using a technique that is the temperature-programmed desorption of CO2 adsorbed. All of them are consistent with the difference in the energetic nonuniformity between ACs studied, except for the last measure whose results could be reasonably explained when combining with the microtextural heterogeneity.

Combustion of ethanol (EtOH) at low temperatures has been studied using titania- and silica-supported platinum nanocrystallites with different sizes in a wide range of 1~25 nm, to see if EtOH can be used as a clean, alternative fuel, i.e., one that does not emit sulfur oxides, fine particulates and nitrogen oxides, and if the combustion flue gas can be used for directly heating the interior of greenhouses. The results of H2-N2O titration on the supported Pt catalysts with no calcination indicate a metal dispersion of 0.97±0.1, corresponding to ca. 1.2 nm, while the calcination of 0.65% Pt/SiO2 at 600 and 900℃ gives the respective sizes of 13.7 and 24.6 nm when using X-ray diffraction technique, as expected. A comparison of EtOH combustion using Pt/TiO2 and Pt/SiO2 catalysts with the same metal content, dispersion and nanoparticle size discloses that the former is better at all temperatures up to 200℃, suggesting that some acid sites can play a role for the combustion. There is a noticeable difference in the combustion characteristics of EtOH at 80~200℃ between samples of 0.65% Pt/SiO2 consisting of different metal particle sizes; the catalyst with larger platinum nanoparticles shows higher intrinsic activity. Besides the formation of CO2, low-temperature combustion of EtOH can lead to many other pathways that generate undesired byproducts, such as formaldehyde, acetaldehyde, acetic acid, diethyl ether, and ethylene, depending strongly on the catalyst and reaction conditions. A 0.65% Pt/SiO2 catalyst with a Pt crystallite size of 24.6 nm shows stable performances in EtOH combustion at 120℃ even for 12 h, regardless of the space velocity allowed.

The present work has been devoted to the catalytic reduction of N2O by H2 with Pt/SiO2 catalysts at very low temperatures, such as 110oC, and their nanoparticle sizes have been determined by using H2-N2O titration, X-ray diffraction(XRD) and high-resolution transmission electron microscopy(HRTEM) measurements. A sample of 1.72% Pt/SiO2, which had been prepared by an ion exchange method, consisted of almost atomic levels of Pt nanoparticles with 1.16 nm that are very consistent with the HRTEM measurements, while a Pt/SiO2 catalyst possessing the same Pt amount via an incipient wetness technique did 13.5 nm particles as determined by the XRD measurements. These two catalysts showed a noticeable difference in the on-stream deN2O activity maintenance profiles at 110℃. This discrepancy was associated with the nanoparticle sizes, i.e., the Pt/SiO2 catalyst with the smaller particle size was much more active for the N2O reduction. When repeated measurements of the N2O reduction with the 1.16 nm Pt catalyst at 110oC were allowed, the catalyst deactivation occurred, depending somewhat on regeneration excursions.

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.

Nitrous oxide (N2O) 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 CO2. Although such N2O emissions from both natural and anthropogenic sources occur, the latter can be controlled using suitable abatement technologies, depending on them, to reduce N2O below acceptable or feasible levels. This paper has extensively reviewed the anthropogenic N2O 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 N2O emission sources, such as adipic acid production plants. Challengeable approaches to this source are discussed to promote establishment of advanced N2O emission control technologies.

TiO2- and SiO2-supported Co3O4, Pt and Co3O4-Pt catalysts have been studied for CO and C3H8 oxidations at temperatures less than 250℃ which is a lower limit of light-off temperatures to oxidize them during emission test cycles of gasoline-fueled automotives with TWCs (three-way catalytic converters) consisting mainly of Pt, Pd and Rh. All the catalysts after appropriate activation such as calcination at 350℃ and reduction at 400℃ exhibited significant dependence on both their preparation techniques and supports upon CO oxidation at chosen temperatures. A Pt/TiO2 catalyst prepared by using an ion-exchange method (IE) has much better activity for such CO oxidation because of smaller Pt nanoparticles, compared to a supported Pt obtained via an incipient wetness (IW). Supported Co3O4-only catalysts are very active for CO oxidation even at 100℃, but the use of TiO2 as a support and the IW technique give the best performances. These effects on supports and preparation methods were indicated for Co3O4-Pt catalysts. Based on activity profiles of CO oxidation at 100℃ over a physical mixture of supported Pt and Co3O4 after activation under different conditions, and typical light-off temperatures of CO and unburned hydrocarbons in common TWCs as tested for C3H8 oxidation at 250℃ with a Pt-exchanged SiO2 catalyst, this study may offer an useful approach to substitute Co3O4 for a part of platinum group metals, particularly Pt, thereby lowering the usage of the precious metals.

The formation of ConTiOn+₂ compounds, i.e., CoTiO₃ and Co2TiO₄, in a 5 wt% CoOx/TiO2 catalyst after calcination at different temperatures has been characterized via scanning electron microscopy (SEM), Raman and X-ray photoelectron spectroscopy (XPS) measurements to verify our earlier model associated with Co3O4 nanoparticles present in the catalyst, and laboratory-synthesized ConTiOn+₂ chemicals have been employed to directly measure their activity profiles for CO oxidation at 100˚C. SEM measurements with the synthetic CoTiO₃ and Co2TiO₄ gave the respective tetragonal and rhombohedral morphology structures, in good agreement with the earlier XRD results. Weak Raman peaks at 239, 267 and 336 cm-1 appeared on 5 wt% CoOx/TiO₂ after calcination at 570oC but not on the catalyst calcined at 450˚C, and these peaks were observed for the ConTiOn+₂ compounds, particularly CoTiO3. All samples of the two cobalt titanate possessed O 1s XPS spectra comprised of strong peaks at 530.0±0.1 eV with a shoulder at a 532.2-eV binding energy. The O 1s structure at binding energies near 530.0 eV was shown for a sample of 5 wt% CoOx/TiO₂, irrespective to calcination temperature. The noticeable difference between the catalyst calcined at 450 and 570˚C is the 532.2 eV shoulder which was indicative of the formation of the ConTiOn+₂ compounds in the catalyst. No long-life activity maintenance of the synthetic ConTiOn+₂ compounds for CO oxidation at 100˚C was a good vehicle to strongly support the reason why the supported CoOx catalyst after calcination at 570˚C had been practically inactive for the oxidation reaction in our previous study; consequently, the earlier proposed model for the Co₃O₄ nanoparticles existing with the catalyst following calcination at different temperatures is very consistent with the characterization results and activity measurements with the cobalt titanates.

Cobalt titanates (CoTiOx), such as CoTiO3 and Co2TiO4, have been synthesized via a solid-state reaction and characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) measurement techniques, prior to being used for continuous wet trichloroethylene (TCE) oxidation at 36℃, to support our earlier chemical structure model for Co species in 5 wt% CoOx/TiO2 (fresh) and (spent) catalysts. Each XRD pattern for the synthesized CoTiO3 and Co2TiO4 was very close to those obtained from the respective standard XRD data files. The two CoTiOx samples gave Co 2p XPS spectra consisting of very strong main peaks for Co 2p3/2 and 2p1/2 with corresponding satellite structures at higher binding energies. The Co 2p3/2 main structure appeared at 781.3 eV for the CoTiO3, and it was indicated at 781.1 eV with the Co2TiO4. Not only could these binding energy values be very similar to that exhibited for the 5 wt% CoOx/TiO2 (fresh), but the spin-orbit splitting (ΔE) had also no noticeable difference between the cobalt titanates and a sample of the fresh catalyst. Neither of all the CoTiOx samples were active for the wet TCE oxidation, as expected, but a sample of pure Co3O4 had a good activity for this reaction. The earlier proposed model for the surface CoOx species existing with the fresh and spent catalysts is very consistent with the XPS characterization and activity measurements for the cobalt titanates.

Despite the wide distribution of air pollutants, the concentrations of indoor air pollutants may be the dominant risk factor in personal exposure due to the fact that most people spend an average of 80% of their time in enclosed buildings. Researches for improvement of indoor air quality have been developed such as installation of air cleaning device, ventilation system, titanium dioxide(TiO2) coating and so on. However, it is difficult to evaluate the magnitude of improvement of indoor air quality in field study because indoor air quality can be affected by source generation, outdoor air level, ventilation, decay by reaction, temperature, humidity, mixing condition and so on. In this study, evaluation of reduction of formaldehyde and nitrogen dioxide emission rate in indoor environments by TiO2 coating material was carried out using mass balance model in indoor environment. we proposed the evaluation method of magnitude of improvement in indoor air quality, considering outdoor level and ventilation. Since simple indoor concentration measurements could not properly evaluate the indoor air quality, outdoor level and ventilation should be considered when evaluate the indoor air quality.

Oxidative TCE decomposition over TiO2-supported single and complex metal oxide catalysts has been conducted using a continuous flow type fixed-bed reactor system. Different types of commercial TiO2 were used for obtaining the supported catalysts via an incipient wetness technique. Among a variety of titanias and metal oxides used, a DT51D TiO2 and CrOx would be the respective promising support and active ingredient for the oxidative TCE decomposition. The TiO2-based CrOx catalyst gave a significant dependence of the catalytic activity in TCE oxidation reaction on the metal loadings. The use of high CrOx contents for preparing CrOx/TiO2 catalysts might produce Cr2O3 crystallites on the surface of TiO2, thereby decreasing catalytic performance in the oxidative decomposition at low reaction temperatures. Supported CrOx-based bimetallic oxide systems offered a very useful approach to lower the CrOx amounts without any loss in their catalytic activity for the catalytic TCE oxidation and to minimize the formation of Cl-containing organic products in the course of the catalytic reaction.

Catalytic wet oxidation of trichloroethylene (TCE) in water has been conducted using TiO2-supported cobalt oxides at 36oC with a weight hourly space velocity of 7,500 h-1. 5% CoOx/TiO2, prepared by using an incipient wetness technique, might be the most promising catalyst for the wet oxidation although it exhibited a transient behavior in time on-stream activity. Not only could the bare support be inactive for the wet decomposition reaction, but no TCE removal also occurred by the process of adsorption on TiO2 surface. The catalytic activity was independent of all particle sizes used, thereby representing no mass transfer limitation in intraparticle diffusion. XPS spectra of both fresh and used Co surfaces gave different surface spectral features for each CoOx. Co 2p3/2 binding energy for Co species in the fresh catalyst appeared at 781.3 eV, which is very similar to the chemical states of CoTiOx such as Co2TiO4 and CoTiO3. The used catalyst exhibited a 780.3-eV main peak with a satellite structure at 795.8 eV. Based on XPS spectra of reference Co compound, the TCE-exposed Co surfaces could be assigned to be in the form of mainly Co3O4. XRD patterns for 5% CoOx/TiO2 catalyst indicated that the phase structure of Co species in the catalyst even before reaction is quite comparable to the diffraction lines of external Co3O4 standard. A model structure of CoOx present predominantly on titania surfaces would be Co3O4, encapsulated in thin-film CoTiOx species consisting of Co2TiO4 and CoTiO3, which may be active for the decomposition of TCE in a flow of water.