Effect of van der Waals interactions on the chemisorption and physisorption of phenol and phenoxy on metal surfaces

Thiazole modified covalent triazine framework as carcinogenic metabolites adsorbent: A DFT insight

The potential of a novel thiazole-modified covalent triazine framework (S-CTF) as surface for the adsorption and sensing of the carcinogenic metabolites acrylamide (AM), 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline (MEIQX), 2-amino-1-methyl-6-phenylimidazole[4,5-f]pyridine (PhlP) and 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) is explored. The selectivity, sensitivity, and adsorption properties of the S-CTF surface are investigated through noncovalent interaction (NCI), quantum theory of atoms in molecules (QTAIM) and symmetry adapted perturbation theory (SAPT0) analyses. All the analytes were found to be physiosorbed on the surface of the sensor with the following strength of interaction: MEIQX@S-CTF = PhlP@S-CTF > Trp-P-1@S-CTF > AM@S-CTF. Evaluation of the electronic properties was done by natural bond orbital (NBO), electron density difference (EDD), frontier molecular orbital (FMO) and density of states (DOS) analyses. Through SAPT0 analysis, MEIQX@S-CTF has shown to have the highest ESAPT0 energy data (-24.58 kcal/mol) whereas FMO analysis reveals that the S-CTF surface shows the highest sensing power for Trp-P-1 among all analytes.

A theoretical study of the oxidation of benzene by manganese oxide clusters: formation of quinone intermediates

Manganese oxides (MnxOy) have been widely applied in various chemical industrial processes owing to their long lifetime, low cost and high abundance. They have been used as co-reactants for the elimination of volatile organic compounds (VOCs); however, their oxidation mechanism is not clearly established. In this theoretical study, interaction capacities between benzene (C6H6) and MnxOy clusters, which were modeled with MnO2 and Mn2O3 molecules, were investigated by quantum chemical computations using density functional theory (DFT) with the PBE-D3 functional. The interaction capacity between C6H6 and MnxOy was evaluated, and the probing of the initial stage of the C6H6 oxidation at a molecular level offers an in-depth oxidation reaction path. Interaction energies computed in several spin states, along with the analysis of the electron distribution using the quantum theory of atoms in molecules, natural bond orbital and Wiberg bond index techniques as well as local softness values and MO energies of fragments, point out that the interaction between C6H6 and Mn2O3 is stronger than that with MnO2, amounting to -43 and -35 kcal mol-1, respectively, and the metal atom is identified as the primary active site. During the oxide cluster-assisted oxidation, benzene firstly undergoes an oxidation reaction by active oxygen to generate intermediates such as hydroquinone and benzoquinone. The pathway involving p-benzoquinone as the product (noted as PR1) is the most energetically favored one through a transition structure lying at 19 kcal mol-1, below the energy reference of the reactants, leading to an energy barrier significantly lower than that of 36 kcal mol-1 found for the gas phase oxidation reaction with molecular oxygen without the assistance of the oxide clusters. Potential energy profiles illustrating the reaction paths and molecular mechanisms were described in detail.

Linear Scaling Relationships for Furan Hydrodeoxygenation over Transition Metal and Bimetallic Surfaces

Brønsted-Evans-Polanyi (BEP) and transition-state-scaling (TSS) relationships have become valuable tools for the rational design of catalysts for complex reactions like hydrodeoxygenation (HDO) of bio-oil (containing heterocyclic and homocyclic molecules). In this work, BEP and TSS relationships are developed for all the elementary steps of furan activation (C and O hydrogenation and CHx -OHy scission, for both ring and open-ring intermediates) to oxygenates, ring-saturated compounds and deoxygenated products on the most stable facets of Ni, Co, Rh, Ru, Pt, Pd, Fe and Ir surfaces using Density Functional Theory (DFT) calculations. Furan ring opening barriers were found to be facile and strongly dependent on carbon and oxygen binding strength on the investigated surfaces. Our calculations suggest linear chain oxygenates form on Ir, Pt, Pd and Rh surfaces due to their low hydrogenation and high CHx -OHy scission barriers, while deoxygenated linear products are favoured on Fe and Ni surfaces due to their low CHx -OHy scission and moderate hydrogenation barriers. Bimetallic alloy catalysts were also screened for their potential HDO activity and PtFe catalysts were found to significantly lower the ring opening and deoxygenation barriers relative to the corresponding pure metals. The developed BEPs for monometallic surfaces can be extended to estimate the barriers on bimetallic surfaces for ring opening and ring hydrogenation reactions but fails to predict the barriers for open-ring activation reactions due to the change in transition state binding sites on the bimetallic surface. The obtained BEP and TSS relationships can be used to develop microkinetic models for facilitating accelerated catalyst discovery for HDO.

Reaction-driven selective CO2 hydrogenation to formic acid on Pd(111)

Conversion of CO₂ to useful fuels and chemicals has gained great attention in the past decades; yet the challenge persists due to the inert nature of CO₂ and the wide range of products formed. Pd-based catalysts are extensively studied to facilitate CO₂ hydrogenation to methanol via a reverse water gas shift (rWGS) pathway or formate pathway where formic acid may serve as an intermediate species. Here, we report the selective production of formic acid on the stable Pd(111) surface phase under CO₂ hydrogenation conditions, which is fully covered by chemisorbed hydrogen, using combined Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC) simulations. The results show that with the full coverage of hydrogen, instead of producing methanol as reported for Pd(111), the CO₂ activation is highly selective to formic acid via a multi-step process involving the carboxyl intermediate. The high formic acid selectivity is associated with surface hydrogen species on Pd(111), which not only acts as a hydrogen reservoir to facilitate the hydrogenation steps, but also enables the formation of confined vacancy sites to facilitate the production and removal of formic acid. Our study highlights the importance of reactive environments, which can transform the surface structures and thus tune the activity/selectivity of catalysts.

Unravelling the role of oxophilic metal in promoting the deoxygenation of catechol on Ni-based alloy catalysts

Increasing the content of oxophilic Fe alloyed greatly enhances deoxygenation performance in catechol HDO on nickel-based alloy catalysts.