Search

Dehydration reactions are important in the petroleum and petrochemical industries, especially for the feedstock production. In this work, the catalytic activity of zeolites with different acidities for the dehydration of ethanol to ethylene and diethylether is investigated by density functional calculations on cluster models of three isomorphous B, Al, and Ga substituted H-ZSM-5 zeolites. Both unimolecular and bimolecular mechanisms are investigated. Detailed reaction profiles for the dehydration reaction, assuming either a stepwise or a concerted mechanism, were calculated by using the ONIOM(MP2:M06-2X) + SCREEP method. The adsorption energies of ethanol are −21.6, −28.1, and −27.7 kcal mol−1 on H-[B]-ZSM-5, H-[Al]-ZSM-5, and H-[Ga]-ZSM-5 zeolites, respectively. The activation energies for the rate-determining step of the unimolecular concerted mechanism for the ethylene formation are 48.5, 42.6, and 43.6 kcal mol−1 on H-[B]-ZSM-5, H-[Al]-ZSM-5, and H-[Ga]-ZSM-5 zeolites, respectively. The activation energies for the ethoxy formation as the rate-determining step for the bimolecular formation of diethylether are 42.3, 40.0, and 41.1 kcal mol−1 on H-[B]-ZSM-5, H-[Al]-ZSM-5, and H-[Ga]-ZSM-5 zeolites, respectively. The results indicate that the catalytic activities for the dehydration of ethanol decrease in the order H-[Al]-ZSM-5 ~ H-[Ga]-ZSM-5 > H-[B]-ZSM-5. Besides the acid strength, the zeolite framework affects the reaction by stabilizing the reaction intermediates, leading to more stable adsorption complexes and lower activation barriers. [ABSTRACT FROM AUTHOR]

Coumarin, which is an important material class of substrate in agricultural and pharmaceutical industries, can be obtained by the Pechmann condensation reaction. In this work, coumarin was synthesized from ethyl acetoacetate and resorcinol with sulfuric acid as the catalyst with 86% yield under a mild condition. The product was confirmed by IR, H NMR, and C NMR spectroscopy. Reaction rates at difference temperatures between 273 and 313 K were used to determine the apparent activation energy of the reaction to be 34.7 kJ/mol. Molecular-level understanding about the mechanism of Pechmann condensation reaction was revealed by the complimentary M06-2X density functional theory. The reaction proceeded via a three-step mechanism; transesterification, intramolecular hydroxylalkylation, and dehydration. The intrinsic activation energies of these three steps were calculated to be 136.7, 76.5, and 134.0 kJ/mol, respectively. The calculated apparent activation energy of 40.0 kJ/mol was in agreement with the experimental data. The transesterification was considered as the rate-determining step of the reaction. Graphical abstract: [ABSTRACT FROM AUTHOR]

The mechanism of ethylene oxidation to ethylene glycol on the permanganate material has been investigated by density functional theory with the M06-L functionals. Effect of the BF coordination to the MnO on the mechanism has been examined in details. The initial step is the activation of ethylene C=C bond via the [3+2] electrocyclic addition. The calculated reaction barrier of this step on MnO material (53.67 kJ mol) is decreased significantly with the presence of BF (32.37 kJ mol). In the next step of cyclic intermediate hydration to ethylene glycol, the activation energies for the first and second hydrations are 136.14 and 93.03 kJ mol on BF-MnO , and 147.08 and 134.87 kJ mol on MnO . These results demonstrate that the BF coordinated to the MnO material can enhance the overall conversion of ethylene to ethylene glycol. Molecular orbital analysis provides more understanding regarding the role of BF in this reaction. Graphical abstract: [ABSTRACT FROM AUTHOR]