(696b) Identification of Active Site for Ethane Dehydrogenation on Platinum Catalysts Using Bayesian Analysis: Correction of DFT-Derived Enthalpy and Entropy

For improved design of platinum-based catalysts for ethane dehydrogenation (EDH), it is important to accurately identify the active site(s). Computational investigations using DFT methods are often inaccurate largely due to errors from the choice of functional and approximations used to compute entropy. Both errors significantly affect the Gibbs free energy (G), which affects the elementary rate constants. This study uses Bayesian modeling of microkinetic models (MKM) to correct Gibbs free energies and identify the active sites for the EDH between three Pt surface sites, i.e., Pt(100), Pt(111), and Pt(211). For each species, a normal distribution of SCF energies (E) was created from covariance matrix of 2000 BEEF ensemble energies and a chemical potential (Δµ) with upper and lower bounds of harmonic oscillator and free translator, respectively, was created. Here, G = E + Δµ. By sampling the E and Δµ space, MKM results were calibrated to five experimental studies at different reaction conditions and with varying numbers of reported observations, turnover frequency etc. We observed that the first dehydrogenation to CH₃CH₂ is rate controlling for ethylene production. On Pt(100) and Pt(111), two competitive second dehydrogenation steps to either CH₂CH₂ or CH₃CH decide if ethylene is produced or hydrogenolysis occurs. Methane production is crippled on Pt(100) and Pt(111) due to re-hydrogenation of dehydrogenated C2 species from CH₃CH, to CH₂CH₂. Ethylene is produced on all three facets, while acetylene and methane are largely produced on the Pt(111) and Pt(211) surfaces, respectively. It was observed that Pt(100), Pt(111), and Pt(211) surfaces are all active for EDH reaction and no evidence was found to support one surface site as the active site over the others. A CSTR Pt particle model was used to further investigate the effect of facet interaction on the EDH reaction.