Nature and role of Cu(II) species in doped C12A7 catalysts for soot oxidation

Abstract

Two series of copper-doped mayenite catalysts (Cuₓ:C₁₂₋ₓA₇) were synthesized by one-pot-assisted solution combustion at different Cu loadings (0.06 ≤x ≤ 1) with the aim to correlate their performances in soot combustion and the nature and abundance of the different copper species present. The atmosphere composition influence, precisely of the presence of water, was also studied. It appears that Cu(II) interacted with the C12A7 matrix in three structurally different forms: isolated-Cu²⁺, clustered-Cu²⁺, and bulky CuO particles. Cu-C12A7 catalysts exhibited enhanced activity over bare-C12A7, both in terms of soot oxidation at low temperatures and CO₂ selectivity. The control over the dispersion of Cu, the texture, and superoxide concentration of the Cu-C12A7 catalysts achieved by adjusting the Cu loading and calcination temperature, appeared crucial in promoting the catalytic performance. We concluded that the well-dispersed clustered Cu²⁺ is the most likely active species responsible for the improved activity both under dry and wet conditions.