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DFT and kinetic evidences of the preferential CO oxidation pattern of manganese dioxide catalysts in hydrogen stream (PROX)
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DOI：10.1016/j.apcatb.2021.120715.png)
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Abstract
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The oxidation functionality of Mn(IV) sites has been assessed by density functional theory (DFT) analysis of adsorption and activation energies of CO, H-2 and O-2 on a model Mn4O8 cluster. DFT calculations indicate that Mn (IV) atoms prompt an easy CO conversion to CO2 via a reaction path involving both catalyst and gas-phase oxygen species, while much greater energy barriers hinder H-2 oxidation. Accordingly, a MnCeOx catalyst (Mn-at/Ce-at, 5) with large exposure of Mn(IV) sites shows a remarkable CO oxidation performance at T >= 293 K and no H-2 oxidation activity below 393 K. Empiric kinetics disclose that the catalyst-oxygen abstraction step determines both CO and H-2 oxidation rate, although different activation energies favor the preferential oxidation (PROX) pattern of the studied catalyst (353-423 K). Conversion-selectivity of 100%, high stability during 72 h reaction time and moderate inhibiting effects of water and CO2 feeding reveal the potential of MnO2 materials as efficient, low-cost and robust PROX catalysts.
Keywords:
DFT analysis
H-2 and CO oxidation
Manganese dioxide catalyst
Reaction mechanism and kinetics
Preferential CO oxidation
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