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Yu, Jong-Sung,Larry Kevan 순천대학교 기초과학연구소 1991 基礎科學硏究誌 Vol.2 No.-
The catalytic oxidation of propylene over copper(Ⅱ)-exchanged X and Y zeolites in the presence of the different major cocations, Mg^2+, Ca^2+, Li^+, Na^+, K^+, and H^+, was studied as a function of the oxygen/propylene mole ratio in a flow system at 350℃. The yield of acrolein was optimized for a ratio of unity. The catalytic activities and the changes in cupric ion species were studied by gas chromatography and electron spin resonance. The catalytic activity for this reaction is shown to be due to copper species and is greatly dependent on the type of major cocation in the zeolites. Y zeolites are slightly more effective for the selective oxidation of propylene to acrolein than the corresponding X zeolites. The dependence of the product yields and the Cu(Ⅱ) concentration on the oxygen/propylene mole ratio indicates two parallel pathways for partial oxidation to acrolein and complete oxidation to carbon dioxide and water. It is suggested that partial oxidation is catalyzed by Cu(Ⅰ), perhaps in a Cu_2O/CuO phase, and that complete oxidation is catalyzed by Cu(Ⅱ). An induction period for acrolein formation is observed. Catalyst deactivation is also observed and associated with coke formation which can be monitored by a singlet electron spin resonance signal.
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Formation of New Copper(Ⅱ) Species during Propylene Oxidation on Copper(Ⅱ)-Exchanged X Zeolite
Yu, Jong-Sung,Kevan, Larry 순천대학교 기초과학연구소 1991 基礎科學硏究誌 Vol.2 No.-
The migration of copper(Ⅱ) species and their coordination complexes in the zeolite framework was investigated during propylene oxidation on CuK-X zeolite in a flow system under conditions of excess oxygen and correlated with the reactivity over the temperature range of 100-400℃. Electron spin resonance (ESR) and electron spin echo modulation (ESEM) are used to monitor the different Cu(Ⅱ) species generated, their stereochemistry, their site locations, their migration, and the coordination during the reaction in K-X zeolite. The development of three new Cu(Ⅱ) species has been observed by ESR during the reaction depending upon the reaction temperature. One new cupric ion species developed at relatively low reaction temperature is assigned to a copper(Ⅱ)-CO_2 complex in site SII′in the β-cage. At higher reaction temperature, the development of another new cupric ion species with g_?? > g_1 is assigned to a trigonal bipyramidal cupric ion in site SII between the α- and β-cages. This cupric ion coordinates to two hydroxyl groups and three zeolite framework oxygens to give a Cu(O_2)_3(OH)_2 complex. This species is best developed in the reaction temperature range corresponding to 20-40% propylene conversion. A third Cu(Ⅱ) species developed at still higher reaction temperature is suggested to be a copper(Ⅱ)-CO_3 complex in site SII^* in the α-cage on the basis of CO_2 adsorption experiments and ESEM analysis.
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Yu, Jong-Sung,Kevan, Larry 순천대학교 기초과학연구소 1991 基礎科學硏究誌 Vol.2 No.-
Electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies have been used to characterize the aqueous coordination and location of catalytically active Cu(Ⅱ) cation-exchanged into K-Y zeolite. The higher Si/Al ratio in CuK-Y compared to CuK-X gives rather different ESR parameters for Cu(Ⅱ). Under complete hydration, ESR indicates freely rotating Cu(Ⅱ) ions in the α cage, and the corresponding ESEM indicates six directly bound water molecules. Under partial dehydration, ESR shows that Cu(Ⅱ) becomes immobilized near the six-ring window of the zeolite, and the corresponding ESEM indicates coordination to three water molecules. Upon dehydration at high temperature, ESR shows that the cupric ions mainly move into the β cage and hexagonal prism. The Cu(Ⅱ)-catalyzed oxidation of propylene over dehydrated CuK-Y zeolite with low Cu(Ⅱ) exchange was studied over the temperature range of 160 to 400℃ under conditions of excess oxygen in a flow system in order to investigate the temperature dependence of the catalytic activity, the migration of Cu(Ⅱ) species, the Cu(Ⅱ) coordination complexes formed in the zeolite framework, and the comparison with previous results on CuK-X zeolite. The catalytic activity of CuK-Y was comparable to that of CuK-X under the same conditions. The propylene conversion increased in the same fashion with the reaction temperature and the extent of exchanged Cu(Ⅱ) for both X and Y type zeolite. ESR studies also show that Cu(Ⅱ) migrates during reaction from the initial SI, SI′ sites to SII^* and/or SII sites near a six-ring window at which site coordination with propylene occurs prior to reaction. The development of two new Cu(Ⅱ) species has been observed by ESR during the reaction depending on the reaction temperature. The first new species is developed at relatively low reaction temperature and is suggested to be a Cu(O_2)_3CO_3 complex in site SII^*. At higher reaction temperature, another new cupric ion species with reversed g values(g_?? > g_1) is observed and is assigned to a trigonal-bipyramidal cupric ion in site SII coordinating to two hydroxyl groups and three zeolite framework oxygens to give a Cu(O_2)_3(OH)_2 complex. This species is best developed in the reaction temperature range corresponding to 15-50% propylene conversion. At still higher reaction temperature the two new species decompose and disappear, and the cupric ions are redistributed into the same sites as in the dehydrated state. These results are compared with those in X zeolite during cupric ion catalyzed propylene oxidation.
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Yu, Jong-Sung,Kevan, Larry 순천대학교 기초과학연구소 1991 基礎科學硏究誌 Vol.2 No.-
The copper(Ⅱ)-catalyzed oxidation of propylene on CuK-X zeolite was studied under conditions of excess oxygen over the temperature range of 100 to 400℃ ini a flow system to investigate the temperature dependence of the catalytic activity and the migration of copper(Ⅱ) species and Cu(Ⅱ) coordination complexes in the zeolite framework. It is shown that the percent of propylene conversion depends upon the reaction temperature and upon the extent of Cu(Ⅱ) exchanged into the zeolite. Temperature causes the cupric ions to migrate near the six-ring window between the α and β cages of the zeolite structure where they complex with propylene and induce the oxidation reaction. Arrhenius activation energies decrease with increasing copper(Ⅱ) content. The decreasing activation energy with decreasing Cu(Ⅱ) content is associated with different site occupancies of Cu(Ⅱ) within the zeolite structure. Electron spin resonance studies show that cupric ions are initially distributed in SI hexagonal prism sites and SI′sites in the β cage adjacent to the hexagonal prisms in dehydrated CuK-X zeolite. During reaction, Cu(Ⅱ) migrates from these sites to sites SII′ and SII near the six-ring window between the α and β cages at which site coordination with propylene, constrained to the α cage, occurs prior to reaction. Cu(Ⅱ) is reduced to Cu(Ⅰ) by propylene to form a Cu(Ⅰ) complex, which is subsequently oxidized by oxygen to regenerate Cu(Ⅱ) and to yield CO_2 and water as reaction products. A new cupric ion species with g_Ⅱ = 2.267 and A_Ⅱ = 183×10^-4㎝^-1 developed during the reaction. This is proposed to be a cupric ion in site SII′in the β cage coordinating to CO_2 located in the α cage of the zeolite structure based on CO_2 adsorption experiments and on electron spin-echo modulation analysis.
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Stanciu, Luminita A,Roberts, Kevan,Papadopoulos, Nikolaos G,Cho, Sang-Heon,Holgate, Stephen T,Coyle, Anthony J,Johnston, Sebastian L BioMed Central 2005 Respiratory research Vol.6 No.-
<P><B>Background</B></P><P>Virus infections are the major cause of asthma exacerbations. CD8<SUP>+ </SUP>T cells have an important role in antiviral immune responses and animal studies suggest a role for CD8<SUP>+ </SUP>T cells in the pathogenesis of virus-induced asthma exacerbations. We have previously shown that the presence of IL-4 during stimulation increases the frequency of IL-5-positive cells and CD30 surface staining in CD8<SUP>+ </SUP>T cells from healthy, normal subjects. In this study, we investigated whether excess IL-4 during repeated TCR/CD3 stimulation of CD8<SUP>+ </SUP>T cells from atopic asthmatic subjects alters the balance of type 1/type 2 cytokine production in favour of the latter.</P><P><B>Methods</B></P><P>Peripheral blood CD8<SUP>+ </SUP>T cells from mild atopic asthmatic subjects were stimulated <I>in vitro </I>with anti-CD3 and IL-2 ± excess IL-4 and the expression of activation and adhesion molecules and type 1 and type 2 cytokine production were assessed.</P><P><B>Results</B></P><P>Surface expression of very late antigen-4 [VLA-4] and LFA-1 was decreased and the production of the type 2 cytokines IL-5 and IL-13 was augmented by the presence of IL-4 during stimulation of CD8<SUP>+ </SUP>T cells from mild atopic asthmatics.</P><P><B>Conclusion</B></P><P>These data suggest that during a respiratory virus infection activated CD8<SUP>+ </SUP>T cells from asthmatic subjects may produce excess type 2 cytokines and may contribute to asthma exacerbation by augmenting allergic inflammation.</P>
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Yu, Jong-sung,Larry Kevan 순천대학교 기초과학연구소 1992 基礎科學硏究誌 Vol.3 No.-
The effects of reoxidation and water vapor on the selective partial oxidation of propylene to acrolein over Cu(II)-exchanged X and Y zeolites were examined as a function of the oxygen-to-propylene mole ratio in a flow system at 350℃. The catalytic activity and the reduction of cupric ion species during reaction were studied by gas chromatography and electron spin resonance spectroscopy. The effects of both reoxidation and water vapor introduction resulted in a selective increase of acrolein formation during reaction. The cupric ion intensity in the zeolite decreases during propylene oxidation at low oxygen-to-propylene mole ratios. Reoxidation after propylene oxidation is suggested to increase the formation of copper oxides, CuO and Cu_2O, in the zeolite framework. Cuprous oxide formed during the reaction is suggested to be an active species for the partial oxidation of propylene to acrolein. The introduction of water vapor decreases Cu(II) reduction and decreases coke formation in the zeolite, this decreases catalyst deactivation during reaction. After introduction of water vapor, cuprous ion in an exchange site and cuprous oxide are suggested to be active for acrolein formation.
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Yu,Jong-Sung,Larry Kevan,Vadim Kurshev,Back,Gern-Ho 國立昌原大學校 基礎科學硏究所 1994 基礎科學硏究所論文集 Vol.6 No.-
EPR and electron spin-echo modulation (ESEM) spectroscopies have been used to monitor the location of Pd' and its interaction with water, methanol, ethanol, ethene, benzene, carbon monoxide and ammonia in silicoaluminophosphate type 34(SAPO-34) molecular sieve containing Pd'' by ion exchange. After activation at 600℃, three different Pb' species are observed: A₁(g1=2,177), A₂(g1=2.136) and A₃(g1=2,070) with a common gⅡ=2.92. These correspond to three different site locations in the framework. A₁is assigned to the least accessible site Ⅲ in the centre of a hexagonal prism. A₃ to site I displaced from a six-ring into the ellipsoidal cage and A₂ to the most accessible site Ⅳ near an eight-ring window based on adsorption of oxygen and hydrogen and 31P modulations from the SAPO framework observed by ESEM. Oxygen and water oxidize Pd' ions in an activated sample to Pd'' ions complexed to O₂-, indicating water decomposition. Adsorption of methanol and ethanol causes a change in the EPR spectrum which indicates some relocation of Pd'to allow better coordination with one molecule of the alcohol. Exposure to ethene also changes the EPR spectrum, indicating interaction of Pd' with it. ESEM shows that the Pd' species coordinates to one ethene molecule. The adsorption of carbon monoxide results in a Pd' complex with three molecules of carbon monoxide based on resolved 13C superhyperfine splittings. Upon adsorption of ammonia, one molecule of ammonia coordinates to Pd' based on resolved nitrogen hyperfine coupling.
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Lee, Chul Wee,Yu, Jong-Sung,Larry Kevan 순천대학교 기초과학연구소 1992 基礎科學硏究誌 Vol.3 No.-
Dehydration, oxidation-reduction, and adsorbate (D_2O, CD_3OH, CO) interactions of PdSAPO_11 prepared by adding Pd(NH_3)_4Cl_2 during the synthesis of SAPO-11 have been studied and compared with (S)PdH-SAPO-11 and (i) PdH-SAPO-11 where (S) and (i) refer to solid-state ion exchange and impregnation, respectively. Diffuse reflectance spectra, electron spin resonance (ESR), and electon spin echo modulation (ESEM) spectroscopies are almost the same for the three differently prepared Pd-containing samples. ESR spectra of dehydrated samples at 600℃ show g_1=2.9 and 2.6 and g_1=2.1, which are assigned to two Pd(I) species. Adsorption of water on dehydrated samples induces decomposition of water and the formation of a Pd-oxygen radical complex. ESEM shows that, after adsorption of CD_3OH, the g_1=2.9 component of Pd(I) disappears and the g_1=2.6 Pd(I) coordinates to one methanol with a Pd-D distance of 0.39-0.40 nm. Pd(II) in SAPO-11 is reduced to Pd(I) by CO and forms at least two different Pd(I)-carbonyl complexes. Within the range of 0.5-1.0 mol % Pd in PdSAPO-11, it is most probable that the Pd ions are not in framework positions.
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