First-Principles-Based Microkinetic Simulations of CO₂ Hydrogenation to Methanol over Intermetallic GaPd₂: Method Development to Include Complex Interactions between Surface Adsorbates

To computationally design efficient solid catalysts, density functional theory (DFT) calculations are widely used in combination with microkinetic modeling (MKM). However, MKM results are often biased due to the overestimation of adsorption strength in DFT calculations that are usually performed at an arbitrary low coverage of surface intermediates. We hereby developed a new iterative approach focusing on the main species present on the catalyst at the steady state, hence allowing adsorption energy calculation only in the presence of relevant intermediates. In this way, the complex parametrization process to determine scaling relations between adsorption energies and coverages is avoided, which will increase the efficiency and accuracy of the iteration process. When applying this approach to CO2 hydrogenation over GaPd2, we found within few iterations that only when running DFT calculations using the surface with both CO and HCOO precovered, the coverage of surface species obtained from MKM analysis can be consistent with that used in DFT calculations. It stems from our theoretical study that all the species coverages must be self-consistent in order to predict methanol selectivity in fair agreement with experiment.