Cu/Mg/Al catalysts obtained by controlled calcination of hydrotalcite-type (HT) anionic clays may be new interesting and cheap catalysts for the selective catalytic reduction (SCR) of NO by NH3. In this paper the ammonia adsorption and oxidation on CuxMg0.710-xAl0.290 catalysts (x = 0.022, 0.046, and 0.072, as atomic ratio), obtained by calcination for 14 h at 923 K of HT precipitates, have been investigated and compared with those of the corresponding Mg0.710Al0.290 sample. The presence of copper strongly increases the SCR activity and the selectivity to nitrogen in ammonia oxidation, while the Mg/Al catalyst did not show SCR activity in these conditions and formed significant amounts of nitrogen oxides by ammonia oxidation. All samples adsorbed coordinatively ammonia on medium-week Lewis acid sites, while no Bronsted acidity was found, showing that protonic acidity is not necessary for both SCR and ammonia oxidation. With an increase in the copper content, the ammonia gave rise by oxidation to adsorbed hydrazine (likely via amide intermediates) and other adsorbed species, tentatively identified as imido or nitroxyl fragments and nitrogen anions. These surface species were probably involved in either selective or unselective ammonia oxidation, this last occurring via a Mars-van Krevelen-type mechanism. In order to have more information on the SCR activity of the Cu/Mg/Al catalysts, the NO adsorption also was investigated, showing that on the PI/Ig/Al-mixed oxide free surface, NO disproportionates to nitrogen dioxide and to a species identified as hyponitrite anions. On the other hand, over the Cu-containing centers NO gave rise mainly to surface nitrosyl, being also oxidized to nitrates. On the basis of these data, it was hypothesized that on the Cu/Mg/Al catalysts the SCR took place between NO or nitrosyls and amide species, which were likely common intermediates in either SCR and ammonia oxidation.