• Journal of the Korean Chemical Society
• /
• v.56 no.1
• /
• pp.164-168
• /
• 2012

• Journal of the Korean Chemical Society
• /
• v.56 no.6
• /
• pp.720-724
• /
• 2012

Under pseudo-first order conditions, the monomeric species of Cr(VI) was found to be kinetically active in the absence of phenanthroline (phen) whereas in the phen-promoted path, the Cr(VI)-phen complex undergoes a nucleophilic attack by etane-1,2-diol to form a ternary complex which subsequently experience a redox decomposition leading to hydroxy ethanal and Cr(III)-phen complex. The effect of the cationic surfactant (CPC), anionic surfactant (SDS) and neutral surfactant (TX-100) on the unpromoted and phen-promoted path have been studied. Micellar effects have been explained by considering the preferential partitioning of reactants between the micellar and aqueous phase. Combination of TX-100 and phenanthroline will be the ideal for chromic acid oxidation of ethane-1,2-diol in aqueous media.

• Journal of the Korean Chemical Society
• /
• v.57 no.6
• /
• pp.703-711
• /
• 2013

In the present investigation, kinetic studies of oxidation of formic acid with and without catalyst and promoter in aqueous acid media were studied under the pseudo-first order conditions [formic acid]T ${\gg}[Cr(VI)]_T$ at room temperature. In the 1,10-phenanthroline (phen) promoted path, the cationic Cr(VI) phen complex is the main active oxidant species undergoes a nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a redox decomposition through several steps leading to the products $CO_2$ and $H_2$ along with the Cr(III) phen complex. The anionic surfactant (i.e., sodium dodecyl sulfate, SDS) and neutral surfactant (i.e., Triton X-100, TX-100) act as catalyst and the reaction undergo simultaneously in both aqueous and micellar phase with an enhanced rate of oxidation in the micellar phase. Whereas the cationic surfactant (i.e., N-cetyl pyridinium chloride, CPC) acts as an inhibitor restricts the reaction to aqueous phase. The observed net enhancement of rate effects has been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. The neutral surfactant TX-100 has been observed as the suitable micellar catalyst for the phen promoted chromic acid oxidation of formic acid.

• Advances in nano research
• /
• v.12 no.3
• /
• pp.291-300
• /
• 2022

The behavior of hydrogen species on the surface of the catalyst during the Lewis acid transformation to form Brønsted acid sites over the spherical silica-supported WO_x catalyst was investigated. To understand the structure-activity relationship of Lewis acid transformation and hydrogen bonding interactions, we explore the potential of using the in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) with adsorbed ammonia and hydrogen exposure. From the results of in situ DRIFTS measurements, Lewis acid sites on surface catalysts were transformed into new Brønsted acid sites upon hydrogen exposure. The adsorbed NH₃ on Lewis acid sites migrated to Brønsted acid sites forming NH⁴⁺. The results show that the dissociated H atoms present on the catalyst surface formed new Si-OH hydroxyl species - the new Brønsted acid site. Besides, the isolated Si-O-W species is the key towards H-bond and Si-OH formation. Additionally, the H atoms adsorbed surrounding the Si-O-W species of mono-oxo O=WO₄ and di-oxo (O=)₂WO₂ species, where the Si-O-W species are the main species presented on the Inc-SSP catalysts than that of the IWI-SSP catalysts.

• Bulletin of the Korean Chemical Society
• /
• v.27 no.10
• /
• pp.1623-1632
• /
• 2006

NiO supported on zirconia modified with $MoO_3$ for acid catalysis was prepared by drying powdered $Ni(OH)_2-Zr(OH)_4$ with ammonium heptamolybdate aqueous solution, followed by calcining in air at high temperature. The characterization of prepared catalysts was performed using FTIR, Raman, XRD, and DSC. $MoO_3$ equal to or less than 15 wt% was dispersed on the surface of catalyst as two-dimensional polymolybdate or monomolybdate, while for $MoO_3$ above 15 wt%, crystalline orthorhombic phase of $MoO_3$ was formed, showing that the critical dispersion capacity of $MoO_3$ on the surface of catalyst is 0.18 g/g NiO-$ZrO_2$ on the basis of XRD analysis. Acidity and catalytic activities for acid catalysis increased with the amount of dispersed $MoO_3$. The high acid strength and acidity was responsible for the Mo=O bond nature of the complex formed by the interaction between $MoO_3$ and $ZrO_2$. The catalytic activity for acid catalysis was correlated with the acidity of the catalysts measured by the ammonia chemisorption method.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.197-197
• /
• 2011

In this study, in contrast with cases in which Scanning Tunneling Microscopy (STM) tip-induced reactions were instigated by the tunneling electrons, the local electric field, or the mechanical force between a tip and a surface, we found that the tungsten oxide (WO3) covered tungsten (W) tip of a STM acted as a chemical catalyst for the S-H dissociative adsorption of phenylthiol and 1-octanethiol onto a Ge(100) surface. By varying the distance between the tip and the surface, the degree of the tip-catalyzed adsorption could be controlled. We have found that the thiol head-group is the critical functional group for this catalysis and the catalytic material is the WO3 layer of the tip. After removing the WO3 layer by field emission treatment, the catalytic activity of the tip has been lost. 3-mercapto isobutyric acid is a chiral bi-functional molecule which has two functional groups, carboxylic acid group and thiol group, at each end. 3-Mercapto Isobutyric Acid adsorbs at Ge(100) surface only through carboxylic acid group at room temperature and this adsorption was enhanced by the tunneling electrons between a STM tip and the surface. Using this enhancement, it is possible to make thiol group-terminated surface where we desire. On the other hand, surprisingly, the WO3 covered W tip of STM was found to act as a chemical catalyst to catalyze the adsorption of 3-mercapto isobutyric acid through thiol group at Ge(100) surface. Using this catalysis, it is possible to make carboxylic acid group-terminated surface where we want. This functional group-selective adsorption of bi-functional molecule using the catalysis may be used in positive lithographic methods to produce semiconductor substrate which is terminated by desired functional groups.

• Journal of Integrative Natural Science
• /
• v.8 no.2
• /
• pp.107-110
• /
• 2015

Amino acid-catalyzed directed asymmetric aldol reactions showed enhanced enantioselectivity when conducted in ionic liquids. Optically active products were afforded in better yields (up to 23% higher) and enantiomeric excess (up to 21% higher) in ionic liquids than in conventional organic solvents.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.200-200
• /
• 2011

Hierarchical mesoporous ZSM-5 with enhanced mesoporosity was synthesized by microwave through the rapid assembly via ionic interaction between sulfonic acid functionalized ZSM-5 nano particles and cationic surfactant. The catalytic performance of enhanced accessibility due to mesoporosity and acidity were investigated in the alkylation of mesitylene with benzyl alcohol as alkylating agent. The effect of mole ratio of aromatic with benzyl alcohol, reaction time and alkylation agent were also studied. The enhanced mesoporosity and acidity of sulfonic acid functionalized mesoporous ZSM-5 induced activity enhancement compared with non-functionalized mesoporous ZSM-5, sulfonic functionalized mesoporous ZSM-5 synthesized by hydrothermal method and conventional microporous ZSM-5. The sulfonic acid functionalized mesoporous ZSM-5 showed much higher chemoselectivity of benzylated mesitylene than others, whereas the others mainly show dibenzyl ether as product. This significant difference in catalytic selectivity was resulted from the existence of mesopores, which definitely allowed the benzylation in mesopores.

• Biotechnology and Bioprocess Engineering:BBE
• /
• v.9 no.4
• /
• pp.318-322
• /
• 2004

Lactic acid is an environmentally benign organic acid that could be used as a raw material for biodegradable plastics if it can be inexpensively produced by fermentation. Two genes (ldhL and ldhD) encoding the L-(+) and D-(-) lactate dehydrogenases (L-LDH and D-LDH) were cloned from Lactobacillus sp., RKY2, which is a lactic acid hyper-producing bacterium isolated from Kimchi. Open reading frames of ldhL for and ldhD for the L and D-LDH genes were 962 and 998 bp, respectively. Both the L(+)- and D(-)-LDH proteins showed the highest degree of homology with the L- and D-lactate dehydrogenase genes of Lactobacillus plantarum. The conserved residues in the catalytic activity and substrate binding of both LDHs were identified in both enzymes.

• Journal of Photoscience
• /
• v.10 no.1
• /
• pp.1-7
• /
• 2003

The results of recent work on the dye-sensitized photooxygenation of sulfides is discussed. In the case of dialkyl sulfides, the weakly bonded adduct initially formed with singlet oxygen (the persulfoxide) decays unproductively unless protonation by an acid (an alcohol or a carboxylic acid) facilitates its conversion to the sulfoxide. The effect is proportional to the strength of the acid (eg., less than 0.1 % chloroacetic acid in benzene is sufficient for maximal efficiency) and corresponds to general acid catalysis, suggesting that protonation of the persulfoxide occurs. On the other hand, with sulfides possessing an activated hydrogen in ${\alpha}$ position (eg., benzyl and allyl sulfides), hydrogen transfer becomes an efficient process in aprotic media and yields a S-hydroperoxysulfoniumm ylide, possibly arising from a conformation of the persulfoxide that is different from the one protonated in the presence of acids. Calculations on some substituted sulfides support this hypothesis. This process, which leads to C-S bond fragmentation with formation of an aldehyde, may be viewed as a general method for the preparation of aryl and heteroaryl aldehydes. In this effort, mechanistic studies offered new hints on the structure of the intermediate persulfoxide.