Interaction of CO Molecule with Au/MOR Catalyst: ONIOM-PM6 Study, Active Sites, Thermodynamic and Vibrational Frequencies

Abstract

ONIOM calculations have been carried out to determine geometries, adsorption energies, and vibrational frequencies of CO on a model for Au-exchanged mordenite catalysts, Au/MOR. The CO-calculated vibrational frequencies (upsilon(CO)) are in good agreement with the reported experimental values. We proposed to interpret the frequency results. CH(3)COCH(3) and CH(3)SH adsorption enthalpy calculations on Au/MOR model show that the Au/MOR catalyst behaves like a soft acid according to Pearson's rule. A higher structural deformation degree of the mordenite was found in the calculations with PM6 than with universal force field approach approach. A new pseudopotential (ACEP-121) was developed to improve the Au-Au distance, and Au ionization potential.

Nitrogen oxides and SO2 adsorption on Au/MOR catalyst: Adsorption sites, thermodynamic and vibrational frequencies. ONIOM study

“…T1 and T4 sites were chosen because they are located at the main channel, where Au aggregates have enough space to grow. On the other hand, according to the literature [38,54], the acid Brønsted site is located preferentially at T4 followed by T2 > T1 > T3. Even though, stability of T1 is lower than T2, its acidity (measured as NH 3 adsorption energy) is higher than T2 and similar to T4 [38].…”

“…LANL2DZ basis set and its corresponding pseudopotentials for H, Si, Al, and O atoms belonging to the MOR model were employed. The re-adjusted small-core relativistic compact effective potential ACEP-121 [38] with its corresponding basis set was employed for Au. For the NO, NO 2 , SO 2 and N 2 O molecules the full-electron 6-31+G(d,p) basis set was used.…”

“…These cationic species replace the H acidic of the H-MOR. The T1 and T4 models have been used previously by us in the CO adsorption study on Au/MOR [38]. The Au + as well as Au 3 + ions are included in the high level calculations.…”

“…This result is a consequence of the site strength. It has been shown in the literature [38] that the Au + species are stronger soft acids than the [Au 3 ] + species consequently; the SO 2 interaction with the Au/T sites will be more favorable than the interaction with the Au 3 /T sites.…”

Adsorption of CO<sub>2</sub> and H<sub>2</sub> on Cu and Zn Micro-Cluster Surfaces Studied by Quantum Chemistry and Theory of Absolute Reaction Rates

“…As PM6 covers open shell calculations, reaction intermediates or radicals can also be treated using the same framework. PM6 has already been used for the study of molecular properties such as polycyclic aromatic hydrocarbons and fullerenes [15], molecular orbital study of the interaction between MgATP and the myosin motor domain [16], and frontier orbital theory study of some aminopyrimidine derivatives and their interaction with an iron surface [17].…”