Selective Formation of Cu Active Sites with Different Coordination States on Pseudospinel CuAl₂O₄ and Their NO Reduction Catalysis

Abstract

In the spinel framework, copper (Cu) in two distinct coordination states exhibits catalytic activity for NO reduction through different mechanisms. However, detailed exploration of their respective catalytic properties, such as the redox behavior of Cu and substrate molecule adsorption, has been challenging due to difficulties in their separate formation. In this study, we present the controlled formation of pseudospinel CuAl 2 O 4 , containing exclusively tetrahedrally or octahedrally coordinated Cu, achieved by manipulating aging temperature and O 2 concentration. Through these materials, we observed that in the CO−NO reaction, the step primarily determining the rate differs: NO reduction dominates with octahedrally coordinated Cu, whereas carbon monoxide (CO) oxidation is prominent with tetrahedrally coordinated Cu. The lower coordination number of Cu significantly benefits NO reduction but negatively impacts the CO−NO reaction, albeit positively influencing NO reduction in three-way catalytic reactions.