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


In a time when paradoxically coexist (i) the choice to restart coal-based powerplants, made by several European countries to address the present energy crisis; and (ii) the shared desire to reduce emissions, it is more than ever pivotal to dispose of air control technologies that allow the elimination of carbonaceous fine particulates (casually referred to as soot) before they are released into the atmosphere. Catalysts are known to have such potential. However, their formulations based on critical elements, namely noble metals (such as platinum, Pt) and/or rare earth elements (such as cerium, Ce), limit in a certain way their manufacture due to commercial and environmental reasons. In this context, Isaac Meza Trujillo, PhD student under the supervision of Prof. Eric Gaigneaux, has reported, in collaboration with a Polish group, on a novel family of catalysts essentially based on abundant, non-critical, and thus cheap elements (calcium, Ca and aluminum, Al), and eventually doped with tiny amounts of copper (Cu), a moderately expensive metal, titled “Cu-doped mayenite” (Cuₓ:C₁₂₋ₓAl₁₄O₃₃, abbreviated Cu-C12A7). Cu-C12A7 catalysts develop competitive performance compared to the currently employed expensive Pt- and Ce- based counterparts, providing a realistic alternative for the catalytic abatement of soot present as a pollutant in the air.

Precisely, 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.

Nature and role of Cu(II) species in doped C12A7 catalysts for soot oxidation
Isaac Meza-Trujillo a, Arnaud Mary a, Piotr Pietrzyk b, Zbigniew Sojka b, Eric M. Gaigneaux a,*
a  Institute of Condensed Matter and Nanosciences, UCLouvain, Place Louis Pasteur, 1, Box L4.01.09, 1348 Louvain-la-Neuve, Belgium
b  Faculty of Chemistry, Jagiellonian University, ul. Gronostajowa 2, 30-387 Krakow, Poland

Published on June 28, 2022