(617gh) Kinetic Monte Carlo Simulation of Propylene Epoxidation with Au/TiO2/SiO2 Catalysts
We are currently exploring the use of Au-based bimetallic catalysts on oxide supports for direct propylene epoxidation (with H2 and O2) in order to achieve higher conversion, while maintaining selectivity. In order to do this, we are pursuing a combined computational and experimental investigation to clearly understand the structure/performance relationships of the catalyst material. The will allow us to identify the kinetically important steps in the propylene oxide formation mechanism, and consequently, the key step(s) involved in controlling product selectivity, stability, and overall activity.
Based on our on-going experimental work, a comprehensive atomistic model has been developed to quantify the underlying mechanisms which dictate the observed performance characteristics. The model is based on the kinetic Monte Carlo (KMC) simulation technique, which is well-grounded in the energetic and kinetic parameters extracted from DFT calculations. However, the kinetic rate parameters governing the steps in the reaction mechanism differ by several orders-of-magnitude, leading to stiffness in the traditional stochastic KMC approach. Thus, a multi-scale KMC technique is implemented, which is based on a quasi-steady state assumption of the fast system events. This allows rapid system propagation through time, and we are able to reach experimental time scales (while atomistic resolution is still preserved). Thus, we are able to make direction connections between the catalyst details (metal nanoparticle size, catalyst loading, etc.) and operating variables (temperature, partial pressure of gasses, etc.) and the resulting turnover frequency (TOF) of the catalyst for propylene epoxidation.