Direct oxidation of methanol to formaldehyde by N2O on [Fe]1+ and [FeO]1+ sites in Fe–ZSM-5 zeolite: A density functional theory study

Change in the Nature of ZSM-5 Zeolite Depending on the Type of Metal Adsorbent-The Analysis of DOS and Orbitals for Iron Species

Transition-metal-modified zeolites have recently gained the greatest interest among scientists. Ab initio calculations within the density functional theory were used. The exchange and correlation functional was approximated with the Perdew-Burke-Ernzerhof (PBE) functional. Cluster models of ZSM-5 (Al₂Si₁₈O₅₃H₂₆) zeolites were used with Fe particles adsorbed above aluminum. The adsorption of three iron adsorbates inside the pores of the ZSM-5 zeolite-Fe, FeO and FeOH-was carried out with different arrangements of aluminum atoms in the zeolite structure. The DOS diagram and the HOMO, SOMO and LUMO molecular orbitals for these systems were analyzed. It has been shown that depending on the adsorbate and the position of aluminum atoms in the pore structure of the zeolite, the systems can be described as insulators or conductors, which significantly affects their activity. The main aim of the research was to understand the behavior of these types of systems in order to select the most efficient one for a catalytic reaction.

Dehydrogenation of ethanol to acetaldehyde with nitrous oxide over the metal-organic framework NU-1000: a density functional theory study

The conversion of ethanol to more valuable hydrocarbon compounds receives great attention in chemical industries because it could diminish the dependency on petroleum as raw material. We investigate the catalytic performance of Fe-supported MOF NU-1000 for the dehydrogenation of ethanol to acetaldehyde with nitrous oxide (N2O) by deriving the relevant reaction profiles with density functional theory calculations. In the proposed mechanism, the activation barrier of the rate-determining step is almost four times lower in the presence of N2O than without it. The supported NU-1000 framework plays also important role since it facilitates electron transfers and stabilizes all species along the reaction coordinate. When considering the catalytic activity of tetravalent metal centers (Zr, Hf and Ti) substituted into NU-1000 it is found that their activity decreases in the order Hf ≥ Zr > Ti, based on activation energies and turnover frequencies (TOF). Concerning MOF linkers, we show that the catalytic activity is not further improved by functionalizing NU-1000 with either electron-donating or electron-withdrawing organic groups.

DFT Study on the Catalytic Activity of ALD-Grown Diiron Oxide Nanoclusters for Partial Oxidation of Methane to Methanol

Using density functional theory (DFT), we studied the catalytic activity of iron oxide nanoclusters that mimic the structure of the active site in the soluble form of methane monooxygenase (sMMO) for the partial oxidation of methane to methanol. Using N₂O as the oxidant, we consider a radical-rebound mechanism and a concerted mechanism for the oxidation of methane on either a bridging oxygen (O_b) or a terminal oxygen (O_t) active site. We find that the radical-rebound pathway is preferred over the concerted pathway by 40-50 kJ/mol, but the desorption of methanol and the regeneration of the oxygen site are found to be the highest barriers for the direct conversion of methane to methanol with these catalysts. As demonstrated by a population analysis, the O_x (x = b or t) site behaves as an oxygen radical during the H abstraction, and the [Fe⁺-O_x^-] site behaves as a Lewis acid-base pair during the concerted C-H cleavage. Molecular orbital decomposition analysis further demonstrates electron transfer during the oxidation and reduction steps of the reaction. High-level multireference calculations were also carried out to further assess the DFT results. Understanding how these systems behave during the proposed reaction pathways provides new insights into how they can be tuned for methane partial oxidation.

DFT investigations for the catalytic reaction mechanism of methane combustion occurring on Pd(ii)/Al-MCM-41

In this work, a theoretical analysis was carried out on the mechanism of methane combustion occurring on single site palladium oxide species [Pd]2+ supported on Al-MCM-41 silica. Single site Pd-oxo and PdO2-superoxo structures were used to represent the active centers. Activation energies for all the elementary steps involved in the oxidation of methane into formaldehyde are presented. The competition of methane/methanol substrates on active sites was examined. It was found that the formation of methanol via the reaction of methane with the superoxo species, formed via the adsorption of O2 on reduced Pd(ii) centers, facilitates the production of the very active Pd-oxo catalytic sites.

A mechanistic study of ethanol transformation into ethene and acetaldehyde on an oxygenated Au-exchanged ZSM-5 zeolite

Ethanol transformation to ethene and acetaldehyde over low- and high-spin state oxygenated Au-exchanged ZSM-5 zeolite have been investigated by means of density functional calculations with the M06-L functional.

Reaction mechanism of methanol to formaldehyde over Fe- and FeO-modified graphene

We employed periodic DFT calculations (PBE-D2) to investigate the catalytic conversion of methanol over graphene embedded with Fe and FeO. Two possible pathways of dehydrogenation to formaldehyde and dehydration to dimethyl ether (DME) over these catalysts were examined. Both processes are initiated with the activation of methanol over the catalytic center through O-H cleavage. As a result, a methoxo-containing intermediate is formed. Subsequently, H-transfer from the methoxy to the adjacent ligand leads to the formation of formaldehyde. Conversely, the activation of the second methanol over the intermediate gives DME and H2O. Over Fe/graphene, the dehydration process is kinetically and thermodynamically preferable. Unlike Fe/graphene, FeO/graphene is predicted to be an efficient catalyst for the dehydrogenation process. Oxidative dehydrogenation over FeO/graphene takes place through two steps with free energy barriers of 5.7 and 10.2 kcal mol(-1).

Direct oxidation of methane to methanol on Fe–O modified graphene

The reaction mechanisms of the partial oxidation of methane to methanol over FeO/graphene are unraveled using an advanced DFT approach.

A DFT study on the [VO]1+-ZSM-5 cluster: direct methanol oxidation to formaldehyde by N2O

The mechanism of direct oxidation of methanol to formaldehyde by N2O has been theoretically investigated by means of density functional theory over an extra framework species in ZSM-5 zeolite represented by a [(SiH3)4AlO4](1-)[V-O](1+) cluster model. The catalytic reactivity of these species is compared with that of mononuclear (Fe-O)(1+) sites in ZSM-5 investigated in our earlier work at the same level of theory (J. Catal. 2011, 282, 191). The [V-O](1+) site in ZSM-5 zeolite shows an enhanced catalytic activity for the reaction. The calculated vibrational frequencies for grafted species on vanadium sites on the surface are in good agreement with the experimental values. According to the theoretical results obtained in this study the [V-O](1+) site in the ZSM-5 catalyst has an important role in the direct catalytic oxidation of methanol to formaldehyde by N2O.