Theoretical insights into the surface growth of rutile TiO2
Adsorption of TiCl4 molecules on the reduced [1 1 0] surface of TiO2 is investigated using density functional theory with plane wave basis sets and pseudopotentials. Adsorption energies and barriers are calculated and discussed. The rate of this adsorption process is calculated using transition state theory with estimated vibrational frequencies. Derived activation energies are within error bounds of the experimental activation energy for surface growth, consistent with the hypothesis that TiCl4 adsorption is the rate limiting step to growth. However, quantitative predictions of the rate can not be made based on these theoretical calculations alone, due to sensitive dependence on the vibrational frequencies. Building on the theoretical work presented here and previous experimental results a new kinetic model is constructed consisting of a TiCl4 adsorption step followed by a secondary reaction with gaseous O2. Simulations of a plug flow reactor are used to fit the kinetic constants for the rate limiting adsorption step. Unlike the previous phenomenological models, this new Eley-Rideal model is under the theoretical limit at all conditions and contains a physically motivated dependence on gas phase concentrations.
- This paper draws from preprint 100: Theoretical insights into the surface growth of rutile TiO2