Investigation of lattice capacity effect on Cu2+-doped SnO2 solid solution catalysts to promote reaction performance toward NO -SCR with NH3

To understand the effect of the doping amount of Cu 2+ on the structure and reactivity of SnO 2 in NO x -SCR with NH 3 , a series of Sn-Cu-O binary oxide catalysts with different Sn/Cu ratios have been prepared and thoroughly characterized. Using the XRD extrapolation method, the SnO 2 lattice capacity for Cu 2+ cations is determined at 0.10 g CuO per g of SnO 2 , equaling a Sn/Cu molar ratio of 84/16. Therefore, in a tetragonal rutile SnO 2 lattice, only a maximum of 16% of the Sn 4+ cations can be replaced by Cu 2+ to form a stable solid solution structure. If the Cu content is higher, CuO will form on the catalyst surface, which has a negative effect on the reaction performance. For samples in a pure solid solution phase, the number of surface defects increase with increasing Cu content until it reaches the lattice capacity, as confirmed by Raman spectroscopy. As a result, the amounts of both active oxygen species and acidic sites on the surface, which critically determine the reaction performance, also increase and reach the maximum level for the catalyst with a Cu content close to the lattice capacity. A distinct lattice capacity threshold effect on the structure and reactivity of Sn-Cu binary oxide catalysts has been observed. A Sn-Cu catalyst with the best reaction performance can be obtained by doping the SnO 2 matrix with the lattice capacity amount of Cu 2+ . Doping the SnO 2 matrix with the lattice capacity amount of Cu 2+ gives an optimal Sn–Cu catalyst for NO x -SCR with NH 3 by maximizing surface active oxygen and acidic sites.