• Journal of Industrial and Engineering Chemistry
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• 제68권
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• pp.380-386
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• 2018

A sustainable method was developed for the upgrade of biomass derived vanillin (a typical model compound of lignin) into the potential liquid biofuels over a layered double hydroxide supported Pd catalyst (abbreviated as CoAl-LDH/Pd). The CoAl-LDH/Pd catalyst showed high catalytic activity towards the hydrodeoxygenation of vanillin into 2-methoxy-4-methylphenol (MMP) under mild conditions in aqueous media. High MMP yield up to 86% was produced at $120^{\circ}C$ after 4 h. Kinetic studies revealed that the rate-determining step for the hydrodeoxygenation of vanillin was the hydrogenolysis of vanillyl alcohol. More importantly, the CoAl-LDH/Pd catalyst was highly stable without the loss of activity.

• Bulletin of the Korean Chemical Society
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• 제8권4호
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• pp.233-235
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• 1987

The kinetics of the 1,3-dipolar cycloaddition of p-substituted 3-phenylsydnones 1a-d with DMAD have been investigated. The reaction rates over a temperature range $100-140^{\circ}C$ were measured by UV spectrometry. The reactions found to be second-order overall, insensitive to the dielectric constants of the solvents, and characterized by a large entropy of activation. These findings are consistent with the rate-determining step involving the formation of cyclic transition state 1 and the reaction proposed to be concerted.

• Bulletin of the Korean Chemical Society
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• 제10권2호
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• pp.155-158
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• 1989

The rates of complexation of the 18-C-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) with $K^+,\;Ca^{2+},\;Sr^{2+},\;and\;Ba^{2+}$ in methanol solution have been determined at 25$^{\circ}C$ by a pressure-jump technique. The Eigen Winkler mechanism has been applied to interprete the kinetic data. The results suggest that the rate determining step of the complexation in methanol is the rearrangement of the ligand in the outer sphere ion-dipole pair to form a stable encapsulated complex of the metal ion by the crown ether.

• 공업화학
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• 제7권5호
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• pp.861-868
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• 1996

n-butene의 i-butene으로의 골격 이성질화 반응은 발열반응으로서 열역학적으로 저온($100^{\circ}C{\sim}150^{\circ}C$)에서 최고수율을 나타내며 반응 mechanism은 carbonium ion의 형성과 methyl기의 골격치환에 따른 2step으로 규정된다. 산처리되어 강산점을 가지는 zeolite, alumina와 비교하여, $Pt/MoO_3/SiO_2$ 촉매 사용시 $110^{\circ}C$ 등온 환원반응 실험으로 설명되는 Proton의 증가된 표면 이동 속도는 골격 이성질화 반응시 carbonium ion의 형성을 빠르게 촉진시킬 수 있으며, 이에 따라 $110^{\circ}C$에서 1-butene의 수율은 최대치로 나타나며 부산물은 생성되지 않는다. $110^{\circ}C$에서의 등온 환원반응에서 $Pt/MoO_3/SiO_2$가 $Pt/MoO_3/Al_2O_3$보다 높은 proton spillover 속도를 보이지만 약 90분 경과한 $MoO_3$ 표면의 proton 포화상태에서는 i-butene의 반응수율이 같고, $MoO_3$가 없는 zeolite, $Pt/SiO_2$보다 높은 전환율을 보이므로 proton spillover에 의한 carbonium ion의 생성이 반응속도를 조절하는 것으로 나타난다. $Pt/MoO_3/SiO_2$에서 산점의 증가, Pt 및 $MoO_3$ 함량의 증감은 i-butene 수율에 영향을 미치지 않으며, 이는 proton spillover에 의한 Pt 표면위의 carbonium ion의 형성이 속도 결정 단계이기 때문인 것으로 사료된다.

• Journal of Power Electronics
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• 제11권2호
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• pp.194-201
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• 2011

The air flow supplied to a fuel cell system is one of the most significant factors in determining fuel efficiency. The conventional method of controlling the air flow is to fix the oxygen supply at an estimated constant rate for optimal efficiency. However, the actual optimal point can deviated from the pre-set value due to temperature, load conditions and so on. In this paper, the maximum efficiency point tracking (MEPT) algorithm is proposed for finding the optimal air supply rate in real time to maximize the net-power generation of fuel cell systems. The fixed step MEPT algorithm has slow dynamics, thus it affects the overall efficiency. As a result, the variable step MEPT algorithm is proposed to compensate for this problem instead of a fixed one. The complete small signal model of a PEM Fuel cell system is developed to perform a stability analysis and to present a design guideline. For a design example, a 1kW PEM fuel cell system with a DSP 56F807 (Motorola Inc) was built and tested using the proposed MEPT algorithm. This control algorithm is very effective for a soft current change load like a grid connected system or a hybrid electric vehicle system with a secondary energy source.

• 대한화학회지
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• 제26권1호
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• pp.1-6
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• 1982

Thiophenol이 ${\alpha}$-methylstyrene에 부과되는 반응에 대하여 CNDO/2 방법을 써서 분자궤도론적으로 고찰하였다. 전체 부가반응은 두 단계, 즉 (1)티오페놀이 분해하여 Phenylthiyl 라디칼이 되는 단계와 (2)이 라디칼이 ${\alpha}$-methylstyrene에 부가되어 새로운 단위체 라디칼이 되는 단계로 되어 있으나 부가반응속도를 결정하는데 지배적인 과정은 첫째 (1)과정임을 계산결과로 알 수 있었다. 이것이 바로 thiyl라디칼의 치환기에 대한 Hammertt관게에서 陰의 ${\rho}$값이 실험적으로 얻어진 이유이다. ${\rho}$-chlorophenylthiyl 및 m-trifluoromethyl phenylthiyl 라디칼이 ${\rho}$-methoxy-${\alpha}$-methylstyrene에 부가될 때 Hammett 직선관계로 부터 벗어나는 이유는 전체 반응속도에 미치는 부가반응단계 (2)의 기여가 증가하였기 때문이라고 설명 할 수가 있었다.

• Bulletin of the Korean Chemical Society
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• 제34권6호
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• pp.1722-1726
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• 2013

A kinetic study on nucleophilic substitution reactions of phenyl Y-substituted-phenyl carbonates (5a-5j) with ethylamine in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$ is reported. The plots of $k_{obsd}$ vs. [amine] are linear for the reactions of substrates possessing a strong electron-withdrawing group (EWG) but curve upward for those of substrates bearing a weak EWG, indicating that the electronic nature of the substituent Y in the leaving group governs the reaction mechanism. The reactions have been concluded to proceed through a stepwise mechanism with one or two intermediates (a zwitterionic tetrahedral intermediate $T^{\pm}$ and its deprotonated form $T^-$) depending on the nature of the substituent Y. Analysis of Bronsted-type plots and dissection of $k_{obsd}$ into microscopic rate constants have revealed that the reactions of substrates possessing a strong EWG (e.g., 5a-5f) proceed through $T^{\pm}$ with its formation being the rate-determining step, while those of substrates bearing a weak EWG (e.g., 5g-5j) proceed through $T^{\pm}$ and $T^-$.

• 대한화학회지
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• 제41권6호
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• pp.299-303
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• 1997

4-치환 Phenyl ethyl benzylphosphonate의 알칼리 가수분해 반응에 대한 속도 상수($k_{OH}$)를 UV-Vis 분광 광도계로서 결정하였다. 활성화 엔트로피(${\Delta}S^{\neq}$)값은 큰 음의 값을 가졌으며 이 결과는 활성화 엔트로피가 양의 값이나 작은 음의 값으로 기대되는 해리 반응(EA)과 일치하지 않았고 좋은 Hammett 상관 관계식으로부터 속도결정단계에서 이탈기에 의해 음의 전하가 거의 발생하지 않는 회합성(AE) 메커니즘이 일어남을 강력히 암시하고 있다. 반응속도론적 연구 결과에 의하면 4-치환 Phenyl ethyl benzylphosphonate의 가수분해 반응은 해리 메커니즘으로 진행되지 않음을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2263-2270
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• 2014

Solvolysis rate constants of 2-phenylethyl-(2-$PhCH_2CH_2OCOCl$, 1) and 2,2-diphenylethyl chloroformate (2,2-$Ph_2CHCH_2OCOCl$, 2), together with the previously studied solvolyses of ${\alpha}$- and ${\beta}$-substituted chloroformate ester derivatives, are reported in pure and binary solvents at $40.0^{\circ}C$. The linear free energy relationship (LFER) and sensitivities (l and m) to changes in solvent nucleophilicity ($N_T$) and solvent ionizing power ($Y_{Cl}$) of the solvolytic reactions are analyzed using the Grunwald-Winstein equation. The kinetic solvent isotope effects (KSIEs) in methanol and activation parameter values in various solvents are investigated for 1 and 2. These results support well the bimolecular pathway with same aspects. Furthermore, the small negative values of the entropies of activation of solvolysis of 1 and 2 in the highly ionizing aqueous fluoroalcohols are consistent with the ionization character of the rate-determining step, and the KSIE values of 1.78 and 2.10 in methanol-d indicate that one molecule of solvent acts as a nucleophile and the other acts as a general-base catalyst. It is found that the ${\beta}$-substituents in alkyl chloroformate are not the important factor to decide the solvolysis reaction pathway.

• 공업화학
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• 제5권4호
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• pp.637-645
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• 1994

254nm 이상의 파장을 갖는 자외선 램프가 설치된 광조사장치를 이용하여 상용성 저밀도 폴리에틸렌을 100시간 동안 광분해시켰다. 20여 단계가 넘는 복잡한 광분해 반응단계 중에서 필름의 물성을 크게 저하시키는 중요 3단계로 정하고 간단하게 변수를 정의하여 반응 모델식을 설정하였으며, IR스펙트럼을 이용하여 광분해 과정중에 생성되는 과산화물과 카르보닐기의 흡광도를 시간의 함수로 해석하여 각 단계에서의 속도상수와 활성화 에너지를 구하였다. 이들 자료로부터 논란이 되고 있는 반응 메카니즘을 정리할 수 있었으며 속도 결정 단계를 정하였다.