NO reduction with CO over CuOx/CeO2 nanocomposites: influence of oxygen vacancies and lattice strain†
CuOx/CeO2 catalysts were prepared by depositing CuOx clusters onto ceria nanoparticles with different morphologies, including rods, polyhedra, and cubes. These catalysts were evaluated for the reduction of NO with CO. Depending on their morphology these nanoparticles exposed different ceria faces on the surface. Nanorods and nanopolyhedra exposed primarily the (111) faces, while nanocubes showed the (100) faces. The catalytic performance of these catalysts depended strongly on the morphology of the support, that is on the exposed ceria faces and was highest for CuOx supported on nanorods and nanopolyhedra, while on the nanocubes it was lowest. The focus of our study was the influence of oxygen vacancy defects and their role in the reaction mechanism. The morphology-dependent concentration of oxygen vacancy defects on these catalysts was examined using electron paramagnetic resonance, X-ray photoelectron spectroscopy, and Raman spectroscopy. Among the evaluated CuOx/CeO2 catalysts the one based on ceria polyhedra exhibited the best performance, affording full conversion of NO and CO with nearly 100% selectivity to N2 over 150 h on-stream at 250 °C and a gas hourly space velocity of 36 000 mL g−1 h−1. First-principles calculations indicate that with increasing lattice strain the formation of oxygen vacancies is favored on ceria(111) compared to ceria(100) and shed some light on the crucial role of oxygen vacancy defects in the reaction mechanism.