Gon Seo

Postsynthetic Modification Switches an Achiral Framework to Catalytically Active Homochiral Metal−Organic Porous Materials

The postsynthetic modification strategy is adopted to demonstrate for the first time the syntheses of catalytically active chiral MOPMs from a preassambled achiral framework, MIL-101, by attaching L-proline-derived chiral catalytic units to the open metal coordination sites of the host framework. Various characterization techniques (including PXRD, TGA, IR, and N(2) absorption measurements) indicated that the chiral units are successfully incorporated into MIL-101, keeping the parent framework intact. The new chiral MOPMs show remarkable catalytic activities in asymmetric aldol reactions (yield up to 90% and ee up to 80%). It is interesting to note that these heterogeneous catalysts show much higher enantioselectivity than the corresponding chiral catalytic units as homogeneous catalysts. This study demonstrates a simple and efficient route for the generation of catalytically active chiral MOPMs. A variety of chiral catalytic units can be, in principle, incorporated into chemically robust achiral MOPMs with large pores by postmodification and the resulting chiral MOPMs may find useful applications in catalytic asymmetric transformations.

Highly Selective Carbon Dioxide Sorption in an Organic Molecular Porous Material

The organic molecular porous material 1 obtained by recrystallization of cucurbit[6]uril (CB[6]) from HCl shows a high CO(2) sorption capacity at 298 K, 1 bar. Most interestingly, 1 showed the highest selectivity of CO(2) over CO among the known porous materials so far. The remarkable selectivity of CO(2) may be attributed to the exceptionally high enthalpy of adsorption (33.0 kJ/mol). X-ray crystal structure analysis of CO(2) adsorbed 1 revealed three independent CO(2) sorption sites: two in the 1D channels (A and B) and one in the molecular cavities (C). The CO(2) molecules adsorbed at sorption site A near the wall of the 1D channels interact with 1 through hydrogen bonding and at the same time interact with those at site B mainly through quadrupole-quadrupole interaction in a T-shaped arrangement. Interestingly, two CO(2) molecules are included in the CB[6] cavity (site C), interacting not only with the carbonyl groups of CB[6] but also with each other in a slipped-parallel geometry. The exceptionally selective CO(2) sorption properties of 1 may find useful applications in the pressure swing adsorption (PSA) process for CO(2) separation not only in the steel industry but also in other industries such as natural gas mining.

Improvement in capacitive deionization function of activated carbon cloth by titania modification

Activated carbon cloth (ACC) was modified by the reaction between polar groups on its surface and metal alkoxides of titanium, silicon, aluminum and zirconium to enhance its capacitive deionization (CDI) performance. Incorporated state of metals and surface property of modified ACC were deduced from surface analysis results obtained using FE-SEM, XRD, XPS and zeta-potential meter. Titania was highly dispersed on the ACC surface with tetrahedral coordination, and the incorporated titania was effective to decrease physical adsorption of NaCl and to increase electric field adsorption, resulting in a significant enhancement of CDI performance. The negligible contribution of silica, alumina and zirconia modifications suggested that the small oxidation-reduction potential of titania was responsible for the enhancement of the electric field adsorption. Reversibility of adsorption and desorption operation on titania-modified ACC were also discussed relating to its CDI function.

Role of titania incorporated on activated carbon cloth for capacitive deionization of NaCl solution.

Adsorption isotherms of NaCl on activated carbon cloth (ACC) and titania-incorporated activated carbon cloth (Ti-ACC) under an electric field were investigated to deduce the role of titania in capacitive deionization (CDI) of NaCl. Electrosorption of NaCl on the ACC was significantly increased by titania incorporation, whereas its physical adsorption was considerably decreased, resulting in an improved performance of the Ti-ACC as a CDI electrode. Langmuir isotherms based on a localized and fixed amount of adsorption were suitable for the simulation of electrosorption and physical adsorption of ions on the ACC electrodes. The variances of q(m) and b of Langmuir isotherms with electric potential indicate increases in the number of ions per adsorption site and in electrosorption strength of ions by titania incorporation. A cyclic voltammetric study for ion adsorption on ACC electrodes confirms the reversibility between electrosorption and desorption of ions, regardless of titania incorporation.

Cerium impregnated H-mordenite as a catalyst for shape-selective isopropylation of naphthalene. Selective deactivation of acid sites on the external surface

Abstract The impregnation of cerium is the effective method for the deactivation of external acid sites of H-mordenite. The selectivity of 2,6-DIPN in the isopropylation of naphthalene was enhanced by the impregnation with such a large amount as 30–50 wt.-% of cerium without significant decrease of catalytic activity. The highest selectivity of 2,6-DIPN was achieved up to 70% over a highly dealuminated H-mordenite, (HM(128); SiO 2 /Al 2 O 3 = 128, with 30 wt.-% of cerium. The enhancement of the selectivity is ascribed to the deactivation of external acid sites judging from the activity of the cracking reaction of 1,3,5-triisopropylbenzene. The effective pore radius was not reduced by the modification. The ceria is highly dispersed only on the external surface of H-mordenite without any formation of new kinds of acid sites. The 129 Xe NMR observation suggfests that cerium is not in the pores, but on the external surfaces. The deactivation of the external acid sites is a characteristic property for cerium. Lanthanum and neodymium inhibited catalytic activity of the isopropylation because the pores were narrowed by their impregnation. A possible reason of the deactivation is ascribed to the amphoteric property of ceria.

Hydrogenation of furfural over copper-containing catalysts

Abstract Furfuryl alcohol is the main product of the vapor-phase hydrogenation of furfural over copper-containing catalysts such as copper-chromium oxide and palladium-loaded CuY. The amount of furan adsorbed on CuY increases with increasing degree of Cu(II) ion exchange. The evidence of interaction between Cu(II) ion and the furan ring is demonstrated in the ir and EPR spectra. High selectivity to furfuryl alcohol and the absence of tetrahydrofurfuryl alcohol formation over copper-containing catalysts is interpreted in terms of the interaction between Cu(II) ion and the furan ring of furfural preventing the furan ring from being hydrogenated. This interaction also explains the enhancement of conversion to furfuryl alcohol on PdCuY. Here the active site for the selective formation of furfuryl alcohol is the Cu(II) ion interacting with the furan ring while Pd activating the hydrogen.

Post-synthetic preparations of titanium-containing mesopore molecular sieves

Abstract Titanium-substituted mesoporous molecular sieves were prepared post-synthetically by applying Ti-butoxide in ethanol solutions of different concentrations to MCM-41, MCM-48, and KIT-1. The catalysts obtained were characterized by XRD, FT-IR, UV–Vis spectroscopies, XAS, and N 2 physisorption. Incorporation of Ti seems to promote further crosslinking of the mesoporous walls of the samples, and resulted in wall thickness increases. The post-synthetically prepared Ti-mesoporous derivatives using titanium butoxide grafting were catalytically active for the selective oxidation of 2,6-di- tert -butylphenol with H 2 O 2 . Their activities depended on the Ti concentration of the catalysts. Comparison works with hydrothermally prepared Ti-MCM-41, Ti-HMS or post-synthetically prepared Ti-mesopore catalysts, either using titanocene grafting or by TiCl 4 atom planting method, are also reported.

High activity of acid-treated quail eggshell catalysts in the transesterification of palm oil with methanol.

The transesterification of palm oil with methanol was investigated over calcium oxide catalysts prepared by calcining eggshells of quail and chicken. Compared to chicken eggshell, the palisade layer of quail eggshell had more closely dispersed micron-sized pores. Following treatment with 0.005M HCl solution for 2h to remove its dense cuticle layer and subsequent calcination above 800 degrees C, the quail eggshell had a large amount of strong basic sites and showed high catalytic activity comparable to that of potassium methoxide in the transesterification. The acid-treated, quail eggshell catalyst steadily maintained high conversions of over 98% during repeated fivefold usage at 65 degrees C with a reactant composed of methanol/oil (as mol)=12/1 and oil/catalyst (as g)=2/0.03.

Skeletal isomerization of 1-butene over ferrierite and ZSM-5 zeolites : influence of zeolite acidity

Three ferrierite (FER) and five ZSM-5 (MFI) zeolites with SiO2Al2O3 ratio ranging from 27 to 2000 are tested as catalysts for the skeletal isomerization of 1-butene at 350–450°C and atmospheric total pressure in order to study the influence of acidity and pore structure of zeolite on conversion and selectivity. The catalytic and NH3 temperature-programmed desorption results from FER and MFI catalysts with the same SiO2/Al2O3 ratio reveal that the pore structure of FER zeolite rather than its acidity may play an important role in achieving high selectivity for the skeletal isomerization of 1-butene to isobutene.

31P, 27Al, and 129Xe NMR study of phosphorus-impregnated HZSM-5 zeolite catalysts

Abstract Phosphorus-impregnated HZSM-5 zeolite has been characterized by 31 P and 27 Al magic angle spinning NMR and 129 Xe NMR spectroscopy. All the NMR data clearly indicate that the phosphorus compound reacts initially with the framework aluminum, modifying the chemical environment of the internal zeolite surface. Excessive impregnation of phosphorus did not change the physicochemical environment of the channel any further, as the chemical shift in 129 Xe NMR indicated. This reaction of the phosphorus compound with the framework aluminum is responsible for changes in the adsorption and catalysis of the zeolite.