Theoretical ONIOM2/DFT study of Pd/ZSM-5 catalyst: CO and NO adsorption

In this study, we carried out two-layer ONIOM(DFT: MM) calculations to determine the adsorption enthalpies and vibrational frequencies of NO and CO molecules, on palladium exchanged zeolite (Pd/ZSM-5) catalyst. The results reveal that the local Al distribution near to Pd+2 influence the stretching frequencies as well as the adsorption enthalpies. The nine possible Al distributions studied can be gathered in two groups. One responsible for high CO and NO frequencies (v(CO) = 2146 cm(-1) and v(NO) = 1880 cm(-1)) and the other one responsible for the low frequencies (v(CO) = 2127 cm-1 and v(NO) = 1840 cm-1). In general, the adsorption enthalpy of the CO is similar to the NO therefore; there is not a preferential adsorption of CO over the NO molecule.