Baik-Hyon Ha

Catalytic Decomposition of Nitric-Oxide on Copper Zeolites

Abstract The catalytic activity for NO decomposition, H 2 -TPR, CO-TPR and O 2 -TPD of various Cu/ zeolites —especially mordenites— and Cu/non-zeolites with different silica/alumina ratios and frameworks were examined. The copper was loaded by impregnation of cupric nitrate solution, which was followed by redox treatment with H 2 /O 2 at 500°C. As a result, Cu 2+ ions and copper oxide crystals were found on the external surface of the zeolite crystals. The catalytic activities for the Cu/ zeolites increased with the Cu 2+ content as well as with the silica/alumina ratio. For Cu/non-zeolite catalysts, however, low activity was observed in spite of the presence of Cu 2+ . The reducibility of Cu 2+ ions and the desorptibility of extra-lattice oxygen from copper oxide located on the zeolites, which increased with the silica/alumina ratio, may be related to the catalytic activity. We observed through our study that active species for NO decomposition are not only copper ions such as Cu 2+ and Cu 2+ but also CuO. We propose that all of them are involved in the decomposition activity which is also strongly affected by the zeolite structure.

Metal dispersed activated carbon fibers and their application for removal of SOx

Uniformly metal dispersed ACFs were prepared by mixing organometallic compounds with THF and pitch. The solvent was removed from this mixture and then pitch was spun, stabilized, carbonized and activated. The specific surface areas and pore size distributions of prepared ACFs and DeSOx catalytic reactivities were determined. The mesopores of ACF were developed by the addition of Co, Ni, Mn. The DeSOx catalytic reactivity of Ni, Pd, Co, V and Cr dispersed ACFs demonstrated much higher continuous reaction conversion than reference pitch-ACF.

Pore structures and acidities of al-pillared montmorillonite

Korean montmorillonite was intercalated with Al-hydroxypolycation solution aged for 1, 4 and 7 days and then calcined at 400 ‡C, 600 ‡C and 760 ‡C, respectively. Basal spacings by XRD, pore structure (micro- and mesopore distributions and surface areas) by nitrogen (or argon) adsorption at liquid nitrogen (or argon) temperature and acidity (distribution and acid-amount) by NH3-TPD were investigated for the samples. The basal spacing formed by intercalation appeared at about 17 å and decreased with the heating temperature for the sample intercalated with the Alhydroxypolycation solution aged for 1 day. However, for the one aged for 7 days, the spacing remained constant. The total surface area and pore-volume also increased with aging time of the Al-solution, in which micro-pore area increased more rapidly. Argon adsorption indicated that three modal distributions of 3.3, 3.7 and 4.3 å in micropore radius appeared, in which 3.3 å readily was reduced by heating. NH3-TPD showed that two ammonia-desorption peaks appeared at 230 ‡C and 430 ‡C, respectively. The maximum acid-amount for the intercalated sample appeared as 86 meq./100 g-solid, and the values decreased with the heating temperature, especially for the peak at 430 ‡C.

Reduction Behavior of Copper Oxide in Copper/Mordenites

Reduction behavior of CuO particles in copper/mordenites which were prepared by impregnation and redox-treatment with H2/O2 was studied by H2-and CO-TPR. NH3-TPD, CO oxidation, and NO decomposition. Most of copper in hydrogen-form mordenite (HM) and in aluminum-deficient mordenites (DM) forms CuO after redox-treatment including negligible amount of Cu(II) ions. CuO in mordenite redox-treated at 500°C shows a reduction peak by H2-TPR and two reduction peaks by CO-TPR. The reducibility of CuO and catalytic activity of CO oxidation and NO decomposition in DM were better than that in HM. NH3-TPD shows different desorption temperature of copper ammonia complex with various silica/alumina ratio. It gives an information on the effect of silica/alumina ratio on the property of Cu(II) ion in the structure. The reducibility of CuO in copper/mordenites redox-treated at 750°C decreases due to deterioration of mordenite crystal.

Characterization of transition metal-impregnated LaAl complex oxides for catalytic combustion

Abstract The effects of transition metals on LaAl complex oxide support were investigated in order to develop a high-temperature combustion catalyst. The properties of the catalysts were examined by X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), temperature-programmed reduction (TPR), and BET. The activities of the catalysts were investigated by methane combustion. Increasing the calcination temperature from 1000 to 1600°C resulted in the crystallization of each LaAl complex oxide from an amorphous form to the La-β-Al2O3 phase of a layered structure. During calcination, the addition of chromium retarded the crystallization of the support. However, the addition of copper to the LaAl complex oxide accelerated the crystallization of the support. The Cr-impregnated LaAl complex oxide retained a large surface area of 10 m2/g even after calcination at 1400°C. However, the surface area of the Cu-impregnated LaAl complex oxide decreased abruptly to 1 m2/g after calcination at 1400°C. The surface composition of chromium did not change significantly with increasing calcination temperature. However, the surface composition of copper decreased gradually with increasing calcination temperature, implying the formation of a solid solution with the LaAl complex oxide. Whereas the catalytic acitivity of the Cu-impregnated LaAl complex oxide decreased abruptly with increasing calcination temperature, most of the catalytic activity of Cr-impregnated LaAl complex oxide was maintained after calcination at 1400°C.

Characteristics and combustion/decomposition activities of CuO/mordenite

Abstract Various amounts of copper oxide were loaded by impregnation of copper salt solution on dealuminated mordenites and redox-treated at 500°C and 750°C. The catalysts were characterized by XRD, ESR, H 2 -TPR and O 2 -TPD, and tested for the combustion of methane, acetone, benzene and 1-hexene, and NO decomposition. The redox-treatment induced most of the copper to exist as a CuO crystallite on the mordenite and its reducibility decreased as the temperature increased. Redox-treatment at 750°C reduced the crystallinity of the mordenite and increased the size of the CuO crystallite, especially for the samples with a higher CuO content. The optimum amount of copper for the combustion was 3–5 wt.%. However, the activity of the NO decomposition increased with the amount of CuO present. Maximum activities were observed for both the combustion and the NO decomposition when the ratio of silica/alumina was 20∼30. These results suggest that forming CuO crystallites, including clusters and ion exchanged Cu 2+ ions, on dealuminated mordenite by the impregnation of copper salt is desirable for the preparation of the catalysts for combustion/NO decomposition.

Characteristics of CuO—Cr2O3/mordenite and its catalytic activity for combustion and NO decomposition

Abstract Copper and chrome oxide were co-impregnated on mordenites and characterized by XRD, ESR, and H 2 -TPR. The catalysts, subjected to aH 2 O 2 cycle at 500°C and 750°C, were examined for combustion of methane and acetone, and for NO decomposition. An easily reducible Cr Cu oxide complex was formed by the addition of chrome oxide to copper oxide on the mordenites after the redox treatment (H 2 O 2 ) at 500°C. However, the redox treatment at 750°C transformed the oxide complex to copper chromate. No difference was found in the activity of NO decomposition between CuO/mordenite and CuO Cr 2 O 3 /mordenite redox-treated at 500°C. For both methane oxidation and NO decomposition, maximum activity appeared at CuO(7) Cr 2 O 3 (7)/mordenite redox-treated at 750°C, resulting in the formation of copper chromate. Dealumination also increased the activities, and the maximum activity appeared at a silica/alumina ratio of 20–30.

The influence of mordenite characteristics in mordenite mixed with alumina on cracking of vacuum gas oil

Catalytic cracking of vacuum gas oil has been investigated at 500 ‡C over mixed catalysts in a micro-activity tester. The catalyst consists of mordenite treated by either HCl/steam or HF and alumina prepared at pH of 9.5 or 7.8. The catalysts retaining mordenite in which SiO2/Al2O3 weight ratio ranged from 15 to 20 show the max-imum activity and selectivity for gasoline. Both the activity and selectivity for gasoline seem to depend strongly on both acid strength of mixed catalysts and mesopore volume of the mordenite. It is found, however, that the selectivity of kerosene+diesel in liquid product as well as the yield of aromatics in gasoline are influenced more by mesopore volume of mordenite than by acid properties of mordenite in the catalyst of mordenite/alumina.

TPR study on differently prepared copper mordenites

Three kinds of copper mordenite such as copper ion-exchanged, impregnated and physically mixed hydrogen mordenites were prepared and TPR study was carried out. For the fresh ion-exchanged mordenite, two distinct reduction processes were observed; one for the reduction of Cu(II) ion to Cu(I) ion at 225°C and the other for the reduction of Cu(I) to copper metal at 480°C, respectively. Successive TPR/oxygen-treatment lowered the first reduction temperature to 200°C and raised the hydrogen consumption. However, the second peak at 480°C for Cu(I) to copper metal was diminished. The reduction peak at 200°C may be an indicative of the newly formed ionic compounds such as cluster of copper ions. Impregnation of cupric salts leads to the formation of similar cluster of copper ions as those appeared in ion-exchanged mordenite. The treatments of CuO-mixed mordenite also decreased the reduction temperature due to the well dispersed CuO particles on the crystal surface and also formed the same cluster copper ions as appeared in the ion-exchanged one. The cluster of copper ions on the crystal surface created the higher activity for CO oxidation.

Comparison of adsorption and catalysis on Na, K and Ca faujasite type zeolites

Abstract The adsorption of cyclohexane and the cracking of isooctane have been studied on several Y zeolites containing various amounts of Ca, K or Na ions. The content and nature of cations produce opposite effects on isooctane cracking rates and cyclohexane adsorption equilibrium. Hence, it is suggested that there is a competitive adsorption of saturated molecules on acidic and cationic sites. Due to the equilibrium of this adsorption on the two centers, the high (or low) catalytic activities are correlated, respectively, to the low (or high) adsorptive properties. The hypothesis also explains the important rise in catalytic activity at low cation content and the inverse range of catalytic activities and adsorptive properties for the series CaHY, NaHY, KHY.