Technical Report 100, c4e-Preprint Series, Cambridge

Authors: Raphael Shirley, Jethro Akroyd, Luke Miller, Oliver R. Inderwildi, Uwe Riedel, and Markus Kraft*

Reference: Technical Report 100, c4e-Preprint Series, Cambridge, 2011

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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.

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