Combination of Density Functional Theory and Microkinetic Study to the Mn-Doped CeO₂ Catalysts for CO Oxidation: A Case Study to Understand the Doping Metal Content

Abstract

CeO 2 doped with metal is employed in many catalytic reactions. Optimizing the content of metal is a routine step to improve the activity. In low doping metal content, the catalytic performance improves with the increase of the doping metal content. However, the catalytic performance decreases beyond the optimal doping metal content. To our best knowledge, the molecular level understanding to such phenomenon has never been reached. In the present study, Mndoped CeO 2 for CO oxidation has been taken as a case study toward this aim. Three different models, in which one, two, and three Mn atoms replace Ce atoms in CeO 2 (111) 3 × 3 supercell, were constructed. The oxidation state for all Mn atoms is +3. Because of charge imbalance, O 2 2− and O 2 − species would form spontaneously via a combination of lattice O on Mn 2 Ce x−2 O 2x (111) and Mn 3 Ce x−3 O 2x (111) surface, respectively. On all these three surfaces, CO oxidation follows the MvK mechanism which involves lattice oxygen atom. The main steps include CO physisorption, CO chemisorption, the formation and desorption of CO 2 , O 2 adsorption, a second CO adsorption and the reaction between CO and adsorbed O 2 − . Microkinetics simulations show that CO oxidation rates and optimal temperatures are different for these three surfaces. Optimal temperatures for CO oxidation depend on oxygen adsorption energy. The CO oxidation rate is highly influenced by the adsorption energy of the second CO molecule. This work provides insights into the influence of different Mn doping on the catalytic performance of CeO 2 .

Formation of superoxide and ozone-like species on Cu doped CeO2(111) and their CO oxidation reactivity: a DFT study

“…A new CO oxidation mechanism. It was generally recognized that the reaction process of CO on the CeO 2 surface followed the M-vK mechanism, [47][48][49][50] that was, CO adsorbed on the CeO 2 surface and interacted with the lattice oxygen to form CO 2 . When CO 2 was desorbed, free O 2 molecules filled the oxygen vacancies.…”

Mechanochemical Redox: Calcination‐free Synthesis of Ceria‐hybrid Catalyst with Ultra‐High Surface Area

“…Raman spectra together with XPS results claimed the presence of oxygen vacancies, which can be considered to be part of the active site for CO oxidation. [56,[75][76] Accordingly, the starting configuration was constructed by removing one O atom bonded with Cu from clean CeMnCuÀ M surface (Figure 9, state i, Supporting Information). Then, CO was firmly adsorbed on top of O v (O v -top) with adsorption energy of À 0.25 eV (Table S5).…”

Ethanol Steam Reforming on CexMyO2 (M: Cu, Zn, and Mn) Solid Solution Catalysts

“…Co 2 MnO 4 exhibited a desirable effect in ethanol steam reforming (ESR) and postponed catalyst deactivation 22. It was found that Mn in a Ce‐Mn composite as a catalyst in various reactions played an important role in water dissociation and easier CO oxidation 23–25. A highly favorable influence of Mn on CuZn at low temperature in ESR was also proved 26.…”