RESUMO
We report a computational study of the mechanism and determination of the rate constants of the Fe + CO2â FeO + CO reaction, in the 1000-3000 K temperature range, at the CCSD(T)/CBS//B3LYP/def2-TZVP level of theory. The overall rate constant was obtained by a Kinetic Monte Carlo simulation. The calculated rate constant, at 2000 K, is 9.72 × 10-13 cm3 molecule-1 s-1, in agreement with experimental measurements: 2.97 × 10-13 cm3 molecule-1 s-1 [A. Giesen et al., Phys. Chem. Chem. Phys., 2002, 4, 3665] and 1.13 × 10-13 cm3 molecule-1 s-1 [V. N. Smirnov, Kinet. Catal., 2008, 49, 607]. Our study shows that this reaction follows a complex mechanism, with multiple reaction paths contributing to the overall rate, and that CCSD(T) accurately describes this transition metal reaction.
RESUMO
A complete state-averaged active space self-consistent field (SA-CASSCF) calculation by means of the SA-CASSCF(18,14)-in-BP86 Miller-Manby embedding approach was performed to explore the ground and excited electronic states of the trans-[RuCl(NO)(NH3)4]2+ complex. Insights into the NO photodissociation mechanism and Ru-NO bonding properties are provided. In addition, spin-orbit (SO) interactions were taken into account to describe and characterize the spin-forbidden transitions observed at the low-energy regions of the trans-[RuCl(NO)(NH3)4]2+ UV-Vis spectrum. The SA-CASSCF(18,14)-in-BP86 electronic spectrum is in great agreement with the experimental data of Schreiner [Schreiner et al., Inorg. Chem., 1972, 11, 880].
RESUMO
The aldol reaction catalyzed by an amine-substituted mesoporous silica nanoparticle (amine-MSN) surface was investigated using a large molecular cluster model (Si392O958C6NH361) combined with the surface integrated molecular orbital/molecular mechanics (SIMOMM) and fragment molecular orbital (FMO) methods. Three distinct pathways for the carbinolamine formation, the first step of the amine-catalyzed aldol reaction, are proposed and investigated in order to elucidate the role of the silanol environment on the catalytic capability of the amine-MSN material. The computational study reveals that the most likely mechanism involves the silanol groups actively participating in the reaction, forming and breaking covalent bonds in the carbinolamine step. Therefore, the active participation of MSN silanol groups in the reaction mechanism leads to a significant reduction in the overall energy barrier for the carbinolamine formation. In addition, a comparison between the findings using a minimal cluster model and the Si392O958C6NH361 cluster suggests that the use of larger models is important when heterogeneous catalysis problems are the target.