Mechanism of the Cyclo‐Oligomerisation of C₂H₂ on Anatase TiO₂ (101) and (001) Surfaces and Their Reduction: An Electron Paramagnetic Resonance and Density Functional Theory Study

Abstract

Dehydroxylated, hydroxylated and hydrated anatase TiO2 samples have been exposed to acetylene at room temperature. The interaction leads to the formation of polycyclic aromatic hydrocarbons (PAHs) and is accompanied by the appearance of Ti3+ ions, as shown by electron paramagnetic resonance (EPR) spectra. Fully or partly dehydroxylated samples show higher reactivity, whereas the hydrated samples are chemically inert. The experimental results point towards a crucial role of the more reactive (001) facets of anatase nanoparticles. Density functional theory calculations show that acetylene physisorbs on the anatase (101) surface without activation of the C−H bond. The reduced (101) surface (O vacancies) leads to acetylene activation but not to dissociative adsorption. In contrast, the dehydroxylated (001) anatase surface is very active and leads to the spontaneous splitting of the C−H bond with formation of Ti−C2H and OH groups. This is followed by subsequent additions of C2H2 molecules with formation of PAHs. During the dissociation of C2H2, radical species do not form and electrons are not transferred to the surface because direct Ti−C covalent bonds form on the surface. However, the ring closure in the formation of the aromatic compounds leaves behind hydrogen atoms that donate their valence electrons to the oxide. This results in the appearance of EPR‐active Ti3+ centres.

Molecules and heterostructures at TiO2 surface: the cases of H2O, CO2, and organic and inorganic sensitizers

“…[139] The validity of the reaction pathways proposed in Refs. [138,139] and summarized in the above schemes has been recently supported by DFT (density functional theory) simulations of the interaction of acetylene with the (101) and the less stable (001) surfaces of anatase [140]. Both the faces result to be fully inactive when saturated with OH groups, while after dehydroxylation they gain the ability to adsorb the acetylene molecules through dispersive forces (physical adsorption).…”

Elucidation of polyethylene glycol adsorption at the solid–H2O(l) interfaces of anatase TiO2(101) using density functional theory and molecular dynamics simulations

“…[66][67][68] Also, we applied the Hubbard U = 3.0 eV for the 3d orbitals of Ti based on existing literature, to account for the self-interaction errors of d-block metals. [69][70][71] In the geometry optimization, criteria for self-consistent convergence of the energy and force on each atom were set to 10 −4 eV and 0.05 eV Å −1 , respectively.…”

Drought and Flood Disaster Control of Agricultural Land and Optimization Method of Planting Structure to Avoid Disaster

“…The "output" refers to the result of disaster losses without further expansion in affected regions. The larger the input-output ratio, the more reparable disaster losses are, and the stronger disaster prevention ability will be (Chen et al, 2016). There are many kinds of agricultural disasters.…”