Selective catalytic reduction of nitric oxide with ammonia on vanadia/alumina catalysts - Influence of vanadia loading and secondary metal oxide additives

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 Bronsted acidity and reactivity of the V2O5/Al2O3 catalysts. Introducing additives that increased the Bronsted acidity, Mo oxide and W oxide, also increased the reactivity. Introducing additives that did not influence the Bronsted 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 Bronsted acid site. Consequently, increasing the surface vanadium oxide coverage and introducing additives that increase the surface concentration of Bronsted acid sites is beneficial for the SCR of NO with NH3.