Surface modification of γ-alumina by NaNO2, NaNO3, HNO2, HNO3 and H2SO4: A DFT-D approach

In this study, the dissociative adsorption of NaNO2, NaNO3, HNO2, HNO3 and H2SO4 over (1 1 0) surface of γ-alumina non-spinel model were investigated through the dispersion corrected density functional theory (DFT-D) at PBE-D/DNP level of calculation. It was found that all of the species are dissociated to their ionic forms after adsorption and relaxation over the surface, i.e. Na+NO2−, Na+NO3−, H+NO2−, H+NO3−, H+HSO4− and 2H+SO42−. The Lewis acidity of alumina surface by addition of HNO2, HNO3 and H2SO4 is increased, while in the presence of NaNO2 and NaNO3, the acidity of catalyst is decreased. Theoretical calculations predict stronger dissociative adsorption of H2SO4 over the surface in compared to other compounds. The HNO2 and HNO3 mineral acids are better adsorbed over the surface than NaNO2 and NaNO3 salts. The better adsorption of nitrites than nitrates is due to the stronger electrostatic attractions. The order of NaNO3 < NaNO2 < HNO3 < HNO2 < H2SO4 for the dissociative adsorption energy of the title compounds is predicted.