Effect of various admixtures on the properties of Mn-substituted cordierite

Resumo

The effect of various admixtures (graphite, sawdust, mullite–silica fiber, vermiculite, boric acid, different size fractions of cordierite, corundum microspheres) in the cordierite stock (mixture of talc, clay, manganese oxide, and aluminum hydroxide) on the formation of Mn-substituted cordierite has been investigated. The admixtures exert an effect on the degree of cordierite formation, on the impurity phase content of the product (including its Mn₂O₃ content), on the surface concentration of manganese cations, on their oxidation state, on the texture of the catalysts, and on their ammonia oxidation activity. The highest NO_x yield is observed with the catalysts containing a coarse fraction of cordierite and corundum microspheres, which are characterized by a high surface concentration of oxidized manganese cations and have large transport pores.