Excited-state proton transfer (ESPT) processes of 2-(2'-hydroxyphenyl)benzimidazole (HBI) and its complexation with protic solvents (HO, CHOH, and NH) have been investigated by both static calculations and dynamics simulations using density functional theory (DFT) at B3LYP/TZVP theoretical level for ground state (S) and time-dependent (TD)-DFT at TD-B3LYP/TZVP for excited state (S). For static calculations, absorption and emission spectra, infrared (IR) vibrational spectra of O-H mode, frontier molecular orbitals (MOs), and potential energy curves (PECs) of proton transfer coordinate were analyzed. Simulated absorption and emission spectra show an agreement with available experimental data. The hydrogen bond strengthening in the S state has been proved by the changes of IR vibrational spectra and bond parameters of the hydrogen moiety with those of the S state. The MOs provide the visual electron density redistribution confirming the hydrogen bond strengthening mechanism. The PECs show that the proton transfer (PT) process is easier to occur in the S state than the S state. Moreover, on-the-fly dynamics simulations of all systems were carried out to provide the detailed information on time revolution. The results revealed that the excited-state intermolecular proton transfer for HBI is fast, whereas the excited-state intermolecular proton transfer for HBI with protic solvents are slower than that of HBI because the competition between intra- and intermolecular hydrogen-bonds between HBI and protic solvent. These intermolecular hydrogen-bonds hinder the formation of tautomer, hence explaining the low quantum yield found in the protic solvent experiment. Especially for HBI complexing with methanol, only ESIntraPT occurs with small probability compared to HBI with water and ammonia.
Fatty acid transformation to alkane in biomass conversion process goes through deoxygenation (DO) reaction with two possible pathways of hydrodeoxygenation (HDO) or decarbonylation (DCO) that yield different alkane products and water or CO as by-products. The favorability of aldehyde hydrogenation step can lead to HDO route rather than DCO route. The Co/γ-Al 2 O 3 catalyst was previously observed experimentally to promote HDO and DCO routes while mostly DCO route was promoted on Ni/γ-Al 2 O 3 catalyst. This work, we performed density functional theory (DFT) calculations to understand the role of metal species Co and Ni supported on γ-Al 2 O 3 on aldehyde hydrogenation which could lead to the occurrence of HDO. The structural and electronic properties of supported Co 13 and Ni 13 clusters on γ-Al 2 O 3 were examined. The perimeter site between the metal cluster and Al atom of γ-Al 2 O 3 support is found to be an active site on both catalysts. The calculations suggest that Co 13 /γ-Al 2 O 3 is more kinetically and thermodynamically favorable for acetaldehyde hydrogenation than Ni 13 / γ-Al 2 O 3 . The metal clusters also act as active sites for H 2 dissociation. The supported Co 13 cluster is oxidized at a higher degree results in higher negative charges of dissociated H 2 while those on supported Ni 13 shows heterolytic cleavage of H 2 yielding both positive and negative hydrogen charges. This behavior could facilitate lower energy barrier of hydrogenation observed on Co 13 /γ-Al 2 O 3 catalyst.
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