A series of V₂O₅/Al₂O₃ catalysts have been examined for the selective catalytic reduction (SCR) of NO with NH₃ as a function of vanadia loading, metal oxide additives (Mo, W, Ni, Co), and reaction temperature. Increasing the vanadia loading, or surface vanadia coverage, increased the Brønsted acidity and reactivity of the V₂O₅/Al₂O₃ catalysts. Introducing additives that increased the Brønsted acidity, Mo oxide and W oxide, also increased the reactivity. Introducing additives that did not influence the Brønsted acidity, Ni oxide and Co oxide, did not affect the reactivity. However, the addition of Ni oxide and Co oxide increased the ratio of polymerized to isolated surface vanadium oxide species on alumina, which reveals that the SCR reaction is not sensitive to the surface vanadia structure on alumina. A model that explains these observations consists of a dual site: a surface redox site and an adjacent surface Brønsted acid site. Consequently, increasing the surface vanadium oxide coverage and introducing additives that increase the surface concentration of Brønsted acid sites is beneficial for the SCR of NO with NH₃.