Yong-Ki Park

Deterioration Mode of Barium-Containing NOx Storage Catalyst

Barium-containing NOx storage catalyst showed serious deactivation under thermal exposure at high temperatures. To elucidate the thermal deterioration of the NOx storage catalyst, four types of model catalyst, Pt/Al2O3, Ba/Al2O3, Pt–Ba/Al2O3, and a physical mixture of Pt/Al2O3 + Ba/Al2O3 were prepared and their physicochemical properties such as BET, NO TPD, TGA/DSC, XRD, and XPS were evaluated while the thermal aging temperature was increased from 550 to 1050°C. The fresh Pt–Ba/Al2O3 showed a sorption capacity of 3.35 wt%/g-cat. but the aged one revealed a reduced capacity of 2.28 wt%/g-cat. corresponding to 68% of the fresh one. It was found that this reduced sorption capacity was directly related to the deterioration of the NOx storage catalyst by thermal aging. The Ba on Ba/Al2O3 and Pt–Ba/Al2O3 catalysts began to interact with alumina to form Ba–Al solid alloy above 600°C and then transformed into stable BaAl2O4 having a spinel structure. However, no phase transition was observed in the Pt/Al2O3 catalyst having no barium component, even after aging at 1050°C.

MECHANISTIC STUDY OF THE SCR OF NO WITH PROPYLENE OVER CO/ZSM-5 USING IN-SITU FT-IR

The selective catalytic reduction (SCR) of NO with propylene over Co-exchanged ZSM-5 (Co/ZSM-5) was studied using in-situ FTIR. Propylene was activated easily by NO in the absence of oxygen above 200°C, leading to the formation of three different types of surface NCO species; Cobonded (2235 and 2195 cm−1), Si-bonded (2300 cm−1) and Al-bonded (2272 cm−1). These surface NCO species were stable in NO or oxygen atmosphere up to 400°C but in NO+oxygen they were easily converted to the final products of N2 and CO2. It is supposed that the SCR of NO over Co/ZSM-5 occurs through the Co- and Al-bonded NCO intermediates and its conversion is the rate-limiting step.

Plasma-Enhanced Methane Direct Conversion over Particle-Size Adjusted MOx/Al2O3 (M = Ti and Mg) Catalysts

AbstractnNon-oxidative methane activation over particle-size adjusted alumina catalysts loaded with metal oxide (Al2O3, MgO/Al2O3, and TiO2/Al2O3) was investigated with a dielectric barrier discharge reactor using 10xa0% CH4 in Ar at plasma induced temperature. Plasma-assisted catalytic activity for direct conversion of methane over the catalysts was compared with that using plasma only. Catalyst hybrid reaction in a non-thermal discharge showed that MgO/Al2O3 had the highest activity for methane conversion. C2, C3, and C4 hydrocarbons were formed as products; ethane, ethylene, and acetylene were predominant over all catalysts. The effect of varying particle size of the MgO/Al2O3 catalyst was also examined. The conversion of methane over MgO/Al2O3 dramatically increased with decreasing catalyst particle size from 1.70 to 0.25xa0mm. It is interesting to note that distribution of C2 hydrocarbons was tuned by changing the particle size of the catalyst. It was also observed that the gas flow rate, frequency, and power supplied affected direct conversion of methane and selectivity of products significantly.

Comparison of selective catalytic reduction of NO with C3H6 and C3H8 over Cu(II)-ZSM-5 and Co(II)-ZSM-5

Selective n catalytic reduction (SCR) of NO with propene (C3H6-SCR) and propane (C3H8-SCR) over different levels n of Cu(II) or Co(II) ion exchanged into ZSM-5 zeolite has been evaluated under flowing conditions with n 1500 ppm of NO + 4500 ppm of C3H6 or C3H8 n+ 3 vol.% of oxygen in helium at a gas hourly space velocity n of 20000 h−1s. increasing temperature. Cu-ZSM-5 (Si/Al = 15, Cu/Al = 0.46) shows its highest NO conversion n at 440–500°C for C3H6-SCR and at 340–600°C for C3H8-SCR. However, Co-ZSM-5 (Si/Al = 14, Co/Al = 0.43) shows its n highest NO conversion at 460°C for C3H6-SCR and at 550°C for C3H8-SCR. The conversion efficiency n at the optimum reaction temperatures was 98% for C3H6-SCR over Cu-ZSM-5 (Si/Al = 15, Cu/Al = 0.46), 96% n for C3H8-SCR over Cu-ZSM-5 (Si/Al = 15, Cu/Al = 0.46), 75% for C3H8-SCR over Co-ZSM-5 (Si/Al = 14, Co/Al = 0.43) n and 31% for C3H6-SCR over Co-ZSM-5 (Si/Al = 14, Co/Al = 0.43). All NOx species adsorbed on the copper ion in ZSM-5 n are desorbed below 430°C and are not observed in the temperature range for the highest NO conversion n for C3H6-SCR. However, in Co-ZSM-5, Co-(NO)2 species are observed up to 450°C by IR absorption. A reaction n pathway at 450°C for C3H6-SCR over Cu-ZSM-5 is proposed based on Cu-allyl, Cu-allyl oxime, Cu-ethenyl isocyanate, Cu-primary amine and Cu-ethenyl reaction intermediates identified by IR absorption. A different pathway n is proposed for C3H8-SCR over Cu-ZSM-5 at 250–340°C and for C3H8-SCR over Co-ZSM-5 at 230–550°C based on n CH3NO2, HNCO, CO2, Al-NCO, Si-NCO and Co-NCO reaction intermediates identified by IR absorption.

Oxidative dehydrogenation of 4-vinylcyclohexene into styrene over ZrO2 catalyst promoted with Fe2O3 and CaO

The oxidative dehydrogenation of 4-vinylcyclohexene (VCH) into styrene was carried out in the presence of oxygen over a ZrO2 catalyst promoted with Fe2O3 and CaO. Intrinsically, ZrO2 showed high dehydrogenation activity, which resulted in 80% styrene selectivity with 45% conversion at 425 °C and LHSV 3 h−1. When the ZrO2 was further promoted with calcium and iron, CaO/Fe2O3/ZrO2, the highest styrene selectivity of 88.9% was obtained as well as the lowest deactivation. The deactivation of catalyst was prohibited properly through the introduction of oxygen in the reactant together with the modification of Fe2O3/ZrO2 with CaO. The CaO/Fe2O3/ZrO2 showed constant catalytic activity and selectivity for more than 50 h without deactivation. The selectivity of styrene was strongly influenced by the mole ratio of O2/VCH and 95% selectivity with 80% conversion was obtained at O2/VCH mole ratio of 6 over Fe2O3/ZrO2. It is thought that the oxidative dehydrogenation proceeds through the dehydrogenation (DH) of ring-hydrocarbon of VCH followed by selective combustion of hydrogen (SHC) and the high selectivity of styrene was achieved by the bi-functional role of ZrO2 for DH and SHC reactions.

Mechanistic study of SCR-NO with methane over Pd-loaded BEA zeolite

Abstract The SCR of NO with methane in excess oxygen was carried out over Pd-exchanged BEA zeolites prepared by two different methods; one is exchanged with Pd on H–BEA zeolites (Si/Al=12.5) having organic template in zeolite and the other on H–BEA without template. The Pd-exchange on BEA in the presence of organic compound is an efficient way to introduce PdO species selectively onto the external site of zeolite pore, which seemed to be responsible for the enhanced SCR activity at lower temperature. This synergistic effect could be explained by the bifunctional role of PdO clusters for an easier activation of methane and ion exchanged Pd 2+ or protonic site of zeolite for the reduction of NO with the activated methane.

Spectroscopic monitoring for the formation of mesoporous MCM-41 materials upon microwave irradiation

The mesoporous MCM-41 materials were prepared in very short crystallization time (∼40 min) upon microwave irradiation in comparison with conventional hydrothermal heating method. With both microwave irradiation and hydrothermal heating, the MCM-41 formation via supramolecular templating method has been monitored by fluorescence and electron spin resonance (ESR) spectroscopy. Pyrene as a fluorescence probe and 4-(N,N-dimethyl-N-hexadecyl)ammonium-2,2,6,6-tetramethyl piperidinyloxy iodide (CAT16) as a spin probe were respectively dissolved into the micelle solutions to form the MCM-41 precursor gels. These probes allow the monitoring of the supramolecular interaction between the anionic silicate species and the cationic surfactant molecules during the MCM-41 formation. Analyses of fluorescence and ESR spectra indicate that the fast increase of hydrophobicity and microviscosity at the solubilzation sites of the probes results from the accelerated condensation of silicates onto the micelle surface upon microwave irradiation. The fluorescence change from the silicate L-center in the MCM-41 precursor gel also probes the fast silicate condensation upon microwave irradiation. It seems that the fast formation of MCM-41 upon microwave irradiation is ascribed to the microwave-susceptible head groups of surfactant molecules in addition to fast dissolution of the precursor gel.