Sung-Won Ham

Effect of promoters including WO3 and BaO on the activity and durability of V2O5/sulfated TiO2 catalyst for NO reduction by NH3

Abstract The effect of tungsten and barium oxides on the activity and durability of V2O5/TiO2 catalyst for NO reduction by NH3 was examined. Tungsten enhanced the NO removal activity of V2O5 catalyst supported on sulfur-free TiO2, while no effect of tungsten was observed for the V2O5 catalyst supported on sulfated TiO2. The tungsten oxide promotes the formation of polymeric vanadate that is a strong active reaction site for NO reduction by NH3. When both tungsten and sulfur simultaneously exist on the surface of V2O5/TiO2, the sulfur species seems to play a more important role for NO removal activity than tungsten. The tungsten oxide on the V2O5/TiO2 catalyst also enhances the activity for SO2 oxidation by promoting the adsorption of SO2, regardless of the presence of sulfur species on the catalyst surface. The NO removal activity of V2O5 catalyst supported on sulfur-free TiO2 has been significantly reduced by barium oxide, mainly due to the formation of inactive VOBa compound through the strong interaction of vanadia with barium oxide. No change of NO removal activity over V2O5-BaO/sulfated TiO2, however, was examined by the addition of barium oxide, since the structure of vanadium oxide was not altered on the surface of the sulfated TiO2. The SO2 oxidation reaction over V2O5-BaO/TiO2 catalysts was significantly suppressed by the addition of barium oxide to the catalyst. The barium oxide seems to reduce the redox ability of vanadium oxide on the catalyst surface as well as the adsorption capacity of SO2. Based on the temperature programmed reduction (TPR), Raman and XPS observations, the surface structure of vanadium and its interaction with tungsten and barium oxides has been illustrated when sulfur exists on the surface of TiO2.

Characteristics of V2O5 supported on sulfated TiO2 for selective catalytic reduction of NO by NH3

V2O5 supported on sulfated TiO2 catalyst was investigated by using Raman and infrared spectroscopies to examine the surface structure of vanadia and the hydroxyl groups of titania along with the sulfate species on the catalyst surface. The surface structure of vanadia plays a critical role, particularly for the reduction of NO by NH3. The polymeric vanadate species on the catalyst surface is the active reaction site for this reaction system. The surface sulfate species enhanced the formation of the polymeric vanadate by reducing the available surface area of the catalyst. The formation of the polymeric vanadate species on the catalyst surface also depends on the number of hydroxyl groups on the support. Both the sulfate and the vanadate species strongly interacted with the hydroxyl groups on titania. The fewer the number of the hydroxyl sites on the catalyst surface became by increasing the calcination temperatures, the more the polymeric vanadate species formed. A model was proposed to elucidate the progressive alteration of the surface structure of vanadia by the amounts of V2O5 loadings and the sulfate species on the catalyst surface.

Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for no reduction by NH3

Deactivation of copper-ion-exchanged hydrogen-mordenite-type zeolite catalyst by SO2 for NO reduction by NH3 was examined in a fixed-bed flow reactor. The deactivation of the catalyst was strongly dependent on reaction temperature. At high reaction temperatures over 300°C, the catalyst did not lose its initial activity up to 50 h of operation, regardless of SO2 feed concentration from 500 to 20,000 ppm. However, at low reaction temperatures near 250°C, apparent deactivation did occur. Changes in the physicochemical properties such as surface area and sulfur content of deactivated catalyst well correlated with catalyst activity, depending upon reaction temperatures. The deactivation was due to pore blocking and/or filling by deactivating agents, which plugged and/or filled the pores of catalyst. The deactivating agents deposited on the catalyst surface were presumed to be (NH4)2SO4 and/or (NH4)HSO4 from the results of TGA and ion-chromatography measurement.

Effect of oxygen on selective catalytic reduction of NO by NH3 over copper ion exchanged mordenite-type zeolite catalyst

The effect of oxygen on the selective catalytic reduction of NO by NH3 was examined over a copper exchanged mordenite type zeolite catalyst. The catalytic activity for NO reduction by NH3 in the presence of oxygen was at least one order of magnitude higher than that in the absence of oxygen and it was fully reversible with respect to the presence of oxygen in the feed gas stream. Based upon ESR, TPD, TPO and TPSR studies, the redox behavior of copper ions was closely related to the enhancement of NO removal activity by the introduction of oxygen to the feed gases.

Low temperature oxidation of CO over supported PdCl2-CuCl2 catalysts

PdCl2-CuCl2 catalyst supported on activated carbon was examined for the low temperature oxidation of CO. The catalyst developed in the present study was active and stable at ambient conditions if water were existing in the feed gas stream. The addition of Cu(NO3)2 into the PdCl2-CuCl2 catalyst significantly enhanced the CO oxidation activity. X-ray diffraction study revealed that the role of Cu(NO3)2 was to stabilize active Cu(II) species, Cu2Cl(OH)3, on the catalyst surface which maintains the redox property of palladium. When HC1 and SO2 were also existing in the feed, they easily inactivated the catalyst. It was found that HC1 and SO2 inhibited the formation of active Cu(II) species on the catalyst surface.

Activity and Durability of Iron-exchanged Mordenite-type Zeolite Catalyst for the Reduction of NO by NH3

NO removal activity and the durability of iron-exchanged mordenite type zeolite catalyst (FeHM) have been examined in a continuous fixed bed flow reactor. The catalytic activity for NO reduction by NH3 in the presence of oxygen was much higher than that in the absence of oxygen, and it was fully reversible with respect to the presence of oxygen in the feed gas stream. The oxidation ability of SCR catalysts including FeHM was critical for both reactions of NH3 and SO2 oxidation, thus for the NO removal activity and its sulfur tolerance. The maximum conversion of NO for FeHM catalyst with respect to the reaction temperature shifted to the higher temperature due to its mild oxidation ability. The deactivation behaviors such as the changes of the physicochemical properties of the catalyst and the loss of NO removal activity induced by SO2 could not be distinguished, regardless of the metals exchanged in zeolite. However, the amount of deactivating agents deposited on the catalyst surface depended on the species of metals exchanged on the mordenite type zeolite, which was mainly attributed to the oxidation ability of metals for SO2 conversion to SO3.

Effect of calcination temperature on the characteristics of SOsk4/2-/TiO2 catalysts for the reduction of NO by NH3

The catalytic activity of sulfated titania (ST) calcined at a variety of temperatures has been investigated for selective catalytic reduction (SCR) of NO by NH3. The NO removal activity of ST catalyst mainly depends on its sulfur content, indicating critical role of sulfur species on the surface of TiO2. The role of sulfur is mainly the formation of acid sites on the catalyst surface. The presence of both BrØnsted and Lewis acid sites on the surface of sulfated titania has been identified by IR study with the adsorption of NH3 and pyridine on ST. The reduction of the intensity of IR bands representing BrØsted acid sites is more pronounced than that revealing Lewis acid sites as the calcination temperature increases. It has been further clarified by IR study of ST500 catalyst evacuated at a variety of temperatures. The NO removal activity also decreases with the increase of the catalyst calcination temperature. It simply reveals that BrØnsted acid sites induced by sulfate on the catalyst surface are primarily responsible for the enhancement of catalytic activity of ST catalyst containing sulfur for NO reduction by NH3.

Selective catalytic reduction of NOx, by propene over copper-exchanged pillared clays

Copper-exchanged pillared clays were examined as an SCR catalyst for NOx, removal by propene. Both micropores and mesopores were simultaneously developed by pillaring a bentonite with TiO2. Therefore, TiO2-pillared clay has about 8 to 9 times higher surface area and 3 times higher pore volume than the parent unpillared bentonite. The presence of water in the feed gas stream caused a small and reversible inhibition effect on NO removal activity of Cu/Ti-PILC. The water tolerance of Cu/Ti-PILC was higher than copper-exchanged zeolites such as CuHM and Cu/ZSM-5 due to its high hydrophobicity as confirmed by H2O-TPD experiment. Copper-exchanged PILC was confirmed to be an active catalyst for NOx, removal by propene. The addition of copper to TiO2-pillared clay greatly enhanced the catalytic activity for NO removal. Cupric ions on Ti-PILC were active reaction sites for the present reaction system. The state of copper species on the surface of Ti-PILC varied with the content of copper and TiO2. The catalyst having more easily reducible cupric ions showed maximum NO conversion at relatively lower reaction temperatures. It indicates that the redox behavior of cupric ions is directly related to NO removal mechanism. The redox property of cupric ions depended on the copper content and dehydration temperature of PILC.

Sulfur Tolerance of Mordenite Type Zeolite Containing Cupric Ions for No Reduction by Nh3

Summary The effect of SO 2 on the rate of the selective catalytic reduction(SCR) of NO by NH 3 over a mordenite type zeolite catalyst has been examined in a flow reactor system. The deactivation of the catalyst is strongly dependent on the reaction temperature and independent of the SO 2 feed concentration. The sulfur content of the catalyst and its surface area appear to be dominant deactivation parameters. The catalytic activity is inversely related to the sulfur content of the catalyst.

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

- and -supported , Pt and -Pt catalysts have been studied for CO and oxidations at temperatures less than 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 and reduction at exhibited significant dependence on both their preparation techniques and supports upon CO oxidation at chosen temperatures. A Pt/ 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 -only catalysts are very active for CO oxidation even at , but the use of as a support and the IW technique give the best performances. These effects on supports and preparation methods were indicated for -Pt catalysts. Based on activity profiles of CO oxidation at over a physical mixture of supported Pt and after activation under different conditions, and typical light-off temperatures of CO and unburned hydrocarbons in common TWCs as tested for oxidation at with a Pt-exchanged catalyst, this study may offer an useful approach to substitute for a part of platinum group metals, particularly Pt, thereby lowering the usage of the precious metals.