Analysis of the mechanism of catalysis using computer simulation

Recent developments in computer hardware allow the extension of quantum chemical calculations to multi-atom systems. Quantum chemical calculations can analyze the mechanism of catalysis by modelling the molecular orbitals on the substrate, the electron states of the cluster formed on the active site, and the interactions between the substrate and the active site of the catalyst. The hydrorefining reaction, which includes hydrodesulfurization (HDS) and hydrodenitrogenation (HDN), proceeds via three discrete steps: adsorption of the sulfur or nitrogen species and hydrogen atoms at the active site of the catalyst; cleavage of the C-S or C-N bond by the addition of hydrogen atoms to the substrate; and desorption of the products from the active site. However, the specific details of the steps are largely unknown. In the present review, the mechanisms of the HDS of dibenzothiophene (DBT) and the HDN of acridine, a typical sulfur- and nitrogen-containing compound in middle distillate, were simulated based on molecular orbital calculations. Combination of the simulation and experimental data will allow more accurate evaluation of catalysis for hydrorefining.