First principles investigation of NO2and SO2adsorption on γ-Al2O3supported mono- and diatomic metal clusters

NOx storage/reduction catalysts have been developed in the 1990's to minimize the emission of harmful NO and NO2 gases as a result of lean burning in diesel engines. Sulfur poisoning of the catalyst occurs when SOx (x = 2-3) species present in the fuel react aggressively with both the storage and the precious metal redox components. In the present work, DFT calculations within the plane wave, pseudopotential GGA framework were performed to study NO2 and SO2 adsorption on mono and diatomic clusters of Pt and Rh supported on the gamma-Al2O3 (100) surface. The most stable adsorption geometries for the clusters on the surface were identified and used as anchoring points for the adsorption of NO2 and SO2 molecules. Binding energies of a large number of NO2 and SO2 adsorption geometries were reported. In all cases where direct comparison between NO2 and SO2 binding geometries was possible, NO2 binding energies were observed to be larger than SO2 binding energies, in some cases by more than 1 eV.