Effect of MnO2 Polymorphs? Structure on Low-Temperature Catalytic Oxidation: Crystalline Controlled Oxygen Vacancy Formation

MnO2 polymorphs (alpha-, beta-, and epsilon-MnO2) were synthesized, and their chemical/physical properties for CO oxidation were systematically studied using multiple techniques. Density functional theory (DFT) calculations and temperature-programmed experiments reveal that beta-MnO2 shows low energies for oxygen vacancy generation and excellent redox properties, exhibiting significant CO oxidation activity (T-90 = 75 degrees C) and stability even under a humid atmosphere. For the first time, we report that the specific reaction rate for beta-MnO2 (0.135 moleculeCO.nm(-2).s(-1) at 90 degrees C) is roughly approximately 4 and 17 times higher than that of epsilon-MnO2 and alpha-MnO2, respectively. The specific reaction rate order (beta-MnO2 > epsilon-MnO2 > alpha-MnO2) is not only in good agreement with reduction rates (CO-TPSR measurements) but also agrees with the DFT calculation. In combination with in situ spectra and intrinsic kinetic studies, the mechanisms of CO oxidation over various crystal structures of MnO2 were proposed as well. We believe the new insights from this study will largely inspire the design of such a kind of catalyst.

Automated summary

Different MnO2 polymorphs were studied for their properties in CO oxidation, with beta-MnO2 showing higher activity and stability. The mechanism of CO oxidation over MnO2 was proposed based on in situ spectra and intrinsic kinetic studies.