Surface diffusion control of the photocatalytic oxidation in air/TiO2 heterogeneous reactors

TL;DR

This paper investigates how surface diffusion of superoxide radicals on TiO2 catalysts influences photocatalytic oxidation, revealing a resonant dependence on lattice parameters that affects reaction efficiency.

Contribution

It provides a theoretical analysis of diffusion mechanisms on TiO2 surfaces, highlighting the impact of lattice parameters and vibrational effects on diffusion rates.

Findings

Diffusivity depends resonantly on TiO2 lattice parameters.

Rotation and surface-normal vibrations significantly influence diffusion.

Bond vibrations of superoxide anions have negligible effect on diffusivity.

Abstract

The diffusion of superoxide radical anions on the surface of TiO2 catalysts is theoretically considered as an important step in the kinetics of photocatalytic oxidation of toxic pollutants. A detailed analysis is performed to discriminate the effects of rotation, anion and adsorption bonds vibrations on the diffusion coefficient. A resonant dependence of the diffusivity on the lattice parameters of the TiO2 surface is discovered showing that the most rapid diffusion takes place when the lattice parameters are twice larger than the bond length of the superoxide radical anions. Whereas the rotation and vibrations normal to the catalyst surface are important, the anion bond vibrations do not affect the diffusivity due to their low amplitudes as compared to the lattice parameters.