Piti Treesukol

Adsorption of ethylene, benzene, and ethylbenzene over faujasite zeolites investigated by the ONIOM method

The performance of the ONIOM (Our-own-N-layered Integrated molecular Orbital + molecular Mechanics) approach utilizing 10 combinations of two-layer ONIOM2 schemes has been tested for various sizes of faujasite clusters containing up to 84T tetrahedral atoms and the complexes they form with ethylene, benzene, and ethylbenzene molecules. Interaction energies of the adsorbates with a 3T bare quantum cluster are calculated to be −8.14, −7.48, and −7.76 kcal/mol at B3LYP/6-31G(d,p) level of theory, respectively. The long-range effects of the extended structure of zeolite were found to differentiate the stability of adsorption complexes that cannot be drawn from the typical 3T quantum cluster. The interaction energies of ethylene, benzene, and ethylbenzene molecules on the more realistic cluster, 84T, using ONIOM2(B3LYP/6-311++G(d,p):UFF) scheme are predicted to be −8.75, −15.17, and −21.08 kcal/mol, respectively, which compare well with the experimental estimates of −9.1, −15.3, and −19.6 kcal/mol, respectively. This finding clearly demonstrates that the interaction between adsorbate and acidic zeolites does not depend only on the Bronsted group center but also on the lattice framework surrounding the adsorption site. The results obtained in this study suggest that the ONIOM approach, when carefully calibrated, is a computationally efficient and accurate method for studying adsorption of aromatics on zeolites.

Structures and potential energy surface of faujasitic zeolite/water

Abstract The structures and the potential energy surface of the system faujasitic zeolite/water have been investigated by Hartree-Fock, second-order Moller-Plesset (MP2) and by the density functional theory (DFT) calculations, using five basis sets 6-31G(d), 6-31G(d,p), 6-311G(d), 6-311G(d,p) and 6-311 + G(d,p). The DFT calculations employ the Becke-3-Lee-Yang-Parr (B3LYP) and Becke-Lee-Yang-Parr (BLYP) density functional, and, for comparisons, the local density approximation with the Vosko-Wilk-Nusair (VWN) functional. The B3LYP approach is found to yield better agreement with the corresponding experimental results than the VWM and BLYP functionals. The B3LYP amd MP2 levels of theory yield basically the same results. Results of B3LYP with a 6-311 + G(3df,2p) basis set are also very close to those of the very accurate coupled pair functional (CPF) method. Also proton affinities (PA) computed by B3LYP reproduce the corresponding CPF and G1 results very well. The predicted PA of faujasitic catalyst is estimated to be 294 ± 3 kcal/mol, which is in the range of the experimentally determined value of 291–300 kcal/mol. The interaction of faujasite catalyst with water has revealed that the structures can be stabilized by the formation of two hydrogen bonds with water molecules adsorbed at the bridging hydroxyl groups which can act either as a proton acceptor or as a proton donor. Comparison of the faujasite complexes with silanol and hydrogen halides has demonstrated that the faujasitic zeolite is a strong acid. The potential energy surfaces of faujasite zeolite/water has been investigated and analytical interaction potentials have been derived.

A full quantum embedded cluster study of proton siting in chabazite

We propose a computational strategy within the full quantum embedded cluster methodology for modeling reactivity in extended systems. This method takes advantages of the embedded cluster methodology for treating interactions in the active region accurately while allowing interactions with the remaining crystal framework to be treated fully quantum mechanically by using the ab initio tight-binding theory. We have applied this method to study proton siting in chabazite. We found that our calculated relative stability of proton at four different oxygen sites agree well with those from previously periodic calculations, though the computational demand for the present approach is much less.

An Experimental and Theoretical Study on the Aldol Condensation on Zirconium-Based Metal-Organic Framework

The aldol condensation of acetone in zirconium-based metal-organic framework functionalized by a sulfonic acid group (UiO-66-SO3H) has been theoretically investigated using the density functional theory. Acetone adsorbed on the UiO-66-SO3H with the adsorption energy of -17.4 kcal/mol. The catalyzed reaction has been proposed to be a two-step mechanism: the tautomerization of keto form to produce enol form of acetone, and the aldol condensation to produce diacetone alcohol. The activation energies were calculated to be 27.2 and 6.4 kcal/mol, respectively. For the experimental part, UiO-66-SO3H catalyst was synthesized and characterized by X-ray diffraction and IR spectroscopy. The catalytic reaction was carried out in a stirred batch reactor at different temperatures to optimize the reaction conditions. The obtained products were analyzed by 1H-NMR spectroscopy and chromatography techniques. This study demonstrated that UiO-66-SO3H can be used as a solid catalyst for the aldol condensation reaction.

Adsorption of Ammonia on Zirconium-Based Metal-Organic Framework: A Combined Experimental and Theoretical Study

Zirconium-based Metal-organic framework ((Zr6O4(OH)4(1,4-benzenedicarboxylate)6), UiO-66) is one of the most outstanding MOFs for heterogeneous catalysis owning to its high thermal and chemical stabilities. 1,4-benzenedicarboxylate, which is an organic linker of UiO-66, can be functionalized by a sulfonic acid group (UiO-66-SO3H) for several acid-catalyzed reactions. In this work, the structures and acidity of the synthesized UiO-66 and UiO-66-SO3H were characterized using X-ray diffraction, IR-spectroscopy and adsorption experiments. The adsorption of ammonia on UiO-66 type frameworks was studied on the C162H122O67SZr12 cluster model by different DFT functionals including B3LYP, CAM-B3LYP, M06-L, PBE, TPSS and ωB97X-D. The adsorption energies were calculated to be -16.4, -19.2, -18.0, -19.7, -17.4 and -19.3 kcal/mol, respectively, which agreed well with the value from MP2 calculation (-17.9 kcal/mol). This study provides a guideline on the suitable calculation models and yield more insights on the adsorption in acid-functionalized UiO-66 MOF framework.

Combined Computational and Experimental Studies of Trans- and Cis-Isomers of Potassium Diaquabis(Oxalato)Chromate (III)

The trans- and cis-isomers of potassium diaquabis(oxalato)chromate (III) were studied computationally and experimentally. The structures of trans- and cis-configurations of [Cr(H2O)2(C2O4)2]- were optimized by DFT methodology with various functionals namely: B3LYP, CAM-B3LYP, TPSS, PBE, M06-L and ωB97X-D along with the more sophisticated MP2 method. The calculations show that the most stable forms for both isomers are in quartet states. The results from all DFT methods reveal that the cis-isomer is literally more stable than the trans-isomer with the lower average relative energy of 2.1 kcal/mol. These are consistent with the results from MP2 calculation and experimental observation. The absorption wavelengths for the excited states of trans- and cis-structures were calculated by the time-dependent density functional theory (TDDFT) method. For the experiments, the trans- and cis-isomers of potassium diaquabis(oxalato)chromate (III) were synthesized and characterized by UV-Vis spectrophotometry. Both isomers have two maximum absorption wavelengths at 415 and 560 nm.

Methane dissociative reaction on Rh-decorated carbon and boron-nitride nanotubes

The methane decomposition reactions catalyzed by Rh decorated carbon nanotube and by Rh decorated boron-nitride nanotube have been investigated by means of the density functional theory with the M06-L hybrid functional. In both cases, the single-step dissociative adsorption of methane are proposed. According to the activation energy, Methane decomposition on the Rh boron-nitride is preferable than that on the Rh carbon nanotube. An anionic Rh atom on boron-nitride is responsible for the lowering of activation energy of methane decomposition. Moreover, changes in electron configuration of Rh atom upon the metal support interaction can alter the mechanism significantly therefore it is worth to be further investigated in details.