SELECTIVE CATALYTIC REDUCTION OF NITRIC-OXIDE WITH AMMONIA ON VANADIAALUMINA 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 load ing, 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. Intr oducing additives that increased the Bronsted acidity, Mo oxide and W oxide, also increased the reactivity. Introducing additives that did n ot influence the Bronsted acidity, Ni oxide and Co oxide, did not affe ct the reactivity. However, the addition of Ni oxide and Co oxide incr eased the ratio of polymerized to isolated surface vanadium oxide spec ies on alumina, which reveals that the SCR reaction is not sensitive t o the surface vanadia structure on alumina. A model that explains thes e observations consists of a dual site: a surface redox site and an ad jacent surface Bronsted acid site. Consequently, increasing the surfac e vanadium oxide coverage and introducing additives that increase the surface concentration of Bronsted acid sites is beneficial for the SCR of NO with NH3.