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Abstract: Quantum chemical calculations were employed to develop a better understanding of the adsorption properties of BaNaY interacting with molecules relevant to deNO x catalysis. First, various basis sets and levels of theory were tested for barium-containing species and gas-phase reactions, and it was shown that the choice of the basis set for barium is critical. Density functional theory (DFT) with the B3LYP functional and SDD as the basis set was selected based on its combination of relative accuracy and speed. This level of theory was then used to calculate energies, geometries, and frequencies for acetaldehyde, acetic acid, nitromethane, and water adsorbed and in the gas phase. The predicted properties were compared to experiment where available and reasonable agreement was found. To study the effect of the zeolite framework on the adsorption properties, the size of the zeolite cluster was increased from 6T to 36T to 96T using the embedded ONIOM method. Inclusion of van der Waals interactions with increasing cluster size only changed the adsorption enthalpy by a small amount for all of the adsorbates studied. It was found that the interaction between the empty 6s orbital of Ba and the lone pair orbital of the oxygen atom in the adsorbed state, revealed by natural bond orbital analysis, correlates with the adsorption enthalpy and the gas-phase charge of the oxygen atom that interacts with Ba. [Copyright &y& Elsevier]

Knudsen dynamics simulations were performed in cylindrical pores with multiple sections of different diameters. The number and location of hits between particles and the pore walls can be related to the known distributions in the uniform diameter cases. Both sweep-gas and pass-through modes of operation were examined. The contact of the particles traveling inside the pores with the pore walls can be regulated by adjusting the aspect ratio (section length/section diameter) of the pore sections and the ratio of their cross-sectional areas. The results were found to be independent of the transition angle between sections except for very smooth transitions. Analytical expressions were developed to relate the transmission probability in pores of multiple sections to the transmission probabilities of the constituent sections. [Copyright &y& Elsevier]

Modeling and simulation at different scales were used to study mass transport and residence times of particles in nanostructured membranes with uniform cylindrical pores of 10-150 nm diameter and up to 5 µm long. Analytical equations of the possible mass-transport mechanisms inside the pores were used to determine that diffusion dominates over convection under the conditions of interest for selective oxidation: 700 K and pressure near atmospheric. Molecular dynamics simulations showed that surface diffusion is present only at temperatures < 700 K. Knudsen diffusion was identified as the dominant mechanism. Simulations based on its principles were performed using an ensemble of particles in a boundary-driven simulation cell, providing the average number of hits between a particle and the pore wall and the dependency of the residence time on the pore dimensions. The differences between operating a nanostructured membrane reactor in sweep-gas and pass-through modes were also investigated. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory (DFT) and hybrid quantum mechanics/molecular mechanics (QM/MM) calculations were used to study stable intermediates for alkene epoxidation using Mn-porphyrin catalysts. For the reaction intermediate involving complexation of the alkene with the oxidized Mn-porphyrin, four intermediates have been proposed in the literature. A concerted mechanism with no intermediate has also been proposed, and these five mechanisms could all involve the formation of a product complex. Our calculations show that the product complex has the lowest energy, followed by the radical intermediate. The metallaoxetane intermediate is much higher in energy, and the calculations do not support carbocation or pi-radical cation intermediates. A polarizable continuum model was used to account for solvent effects, and the calculated energies of solvation are comparable for all minima along the reaction path. [Copyright &y& Elsevier]

The article presents a study on noncontact catalysis on initiation of selective ethylbenzene oxidation by Au cluster-facilitated cyclooctene epoxidation. Topics discussed include noncontact catalytic system (NCCS), an intermediate produced by one catalytic reaction serves as an intermediary; enable an independent reaction to proceed. An example is the selective oxidation of ethylbenzene; and selective epoxidation of cyclooctene generated cyclooctenyl peroxy.

Abstract: Experimental results in the literature show that two metal-organic frameworks (MOFs) containing copper and cobalt nodes are active for hydroperoxide decomposition, which is an important reaction in auto-oxidation processes. Density functional theory (DFT) calculations reported here for these systems suggest that the metal sites in the interior of these MOFs are not the active sites for this type of reaction due to the steric effects of the adjacent linkers. This implies that the experimental catalysis observed may occur on the exterior surface of the MOF crystals. Additional calculations with a copper paddlewheel node show that, despite being able to form complexes with hydroperoxides, the metal sites in copper paddlewheels do not catalyze hydroperoxide decomposition. Preliminary calculations involving undercoordinated metal atoms as a model for metal sites on the MOF exterior crystal surface suggest that these sites could be catalytically active. [Copyright &y& Elsevier]

[Display omitted] • Addresses gaps in review literature by proposing a comprehensive mechanistic view for heterogenous nickel-acid catalysts. • Highlights relevant conditions to steer product distributions of ethylene oligomerization towards desirable products. • Focuses on environmentally-friendly and flexlble catalysts to produce a range of products for ever-changing market demands. Light alkene oligomerization on heterogeneous acidic catalysts is widely and successfully used in current commercial processes. However, ethylene oligomerization remains inefficient due to ethylene's inability to form reaction intermediates to a sufficient extent on acid sites. Adding Ni(II) on solid acids can more efficiently catalyze ethylene oligomerization and selectively produce butenes to fuel range products. The review proposes a complete and detailed mechanism of heterogenous Ni-catalyzed oligomerization, whose structures are supported by combining various studies throughout recent literature, and focuses on the bifunctional effects of the nickel and acid sites on ethylene oligomerization. Using experiments, first-principles calculations, and kinetic modeling, Ni2+ has been shown to selectively oligomerize ethylene to light, linear alkenes via the Cossee-Arlman mechanism, while Brønsted H+ sites catalyze further alkylation, cracking, and isomerization reactions. The effects of reaction conditions and catalyst properties on selectivity and activity for oligomerization are systematically discussed. Tuning the relative nickel-to-acid site ratio and the framework support can allow for an optimal catalyst design directed towards desirable products. [ABSTRACT FROM AUTHOR]