Morphology effects in MnCeOx solid solution-catalyzed NO reduction with CO: Active sites, water tolerance, and reaction pathway

Morphological effects of nanoparticles are crucial in many solid-catalyzed chemical transformations. We herein prepared two manganese-ceria solid solutions, well-defined MnCeO x nanorods and MnCeO x -nanocubes, exposing preferentially (111) and (100) facets of ceria, respectively. The incorporation of Mn dopant into ceria lattice strongly enhanced the catalytic performance in the NO reduction with CO. MnCeO x (111) catalyst outperformed MnCeO x (100) counterpart due to its higher population density of oxygen vacancy defects. In-situ infrared spectroscopy investigations indicated that the reaction pathway over MnCeO x and pristine CeO 2 is similar and that besides the direct pathway, an indirect pathway via adsorbed hyponitrite as an intermediate cannot be ruled out. X-ray photoelectron and Raman spectroscopies as well as first-principles density functional theory (DFT) calculations indicate that the enhanced catalytic performance of MnCeO x can be traced back to its “Mn—O L (VÖ)—Mn—O L (VÖ)—Ce” connectivities. The Mn dopant strongly facilitates the formation of surface oxygen vacancies (VÖ) by liberating surface lattice oxygen (O L ) via CO* + O L → CO 2 * + VÖ and promotes the reduction of NO, according to NO* + VÖ → N* + O L and 2N* → N 2 . The Mn dopant impact on both the adsorption of CO and activation of O L reveals that a balance between these two effects is critical for facilitating all reaction steps.