Tuning the K⁺ Concentration in the Tunnels of α-MnO₂ To Increase the Content of Oxygen Vacancy for Ozone Elimination

Abstract

α-MnO is a promising material for ozone catalytic decomposition and the oxygen vacancy is often regarded as the active site for ozone adsorption and decomposition. Here, α-MnO nanowire with tunable K concentration was prepared through a hydrothermal process in KOH solution. High concentration K in the tunnel can expand crystal cell and break the charge balance, leading to a lower average oxidation state (AOS) of Mn, which means abundant oxygen vacancy. DFT calculation has also proven that the samples with higher K concentration exhibit lower formation energy for oxygen vacancy. Due to the enormous active oxygen vacancies existing in the α-MnO nanowire, the lifetime of the catalyst (corresponding to 100% ozone removal rate, 25 °C) is increased from 3 to 15 h. The FT-IR results confirmed that the accumulation of intermediate oxygen species on the catalyst surface is the main reason why it is deactivated after long time reaction. In this work, the performance of the catalyst has been improved because the abundant active oxygen vacancies are fabricated by the electrostatic interaction between oxygen atoms inside the tunnels and the introduced K, which offers us a new perspective to design a high efficiency catalyst and may promote manganese oxide for practical ozone elimination.

Experimental and Theoretical Investigation of the Effect of Oxygen Vacancies on the Electronic Structure and Pseudocapacitance of MnO2

“…However, the diffraction peaks became weaker and wider with increasing reaction time, indicating a decrease in crystallinity, which can provide more channels for ion permeation . Moreover, compared with pure MnO 2 , the peaks located at 2 θ =36.2 and 65.5° slightly shifted toward lower angles for the ROV‐ m samples and weakened or even disappeared for the OOV‐ n samples, indicating the existence of lattice distortion caused by oxygen vacancies …”

“…[39] Moreover,c ompared with pure MnO 2 ,t he peaks located at 2q = 36.2 and 65.58 slightly shifted toward lower angles for the ROV-m samples and weakened or even disappeared for the OOV-n samples, indicating the existence of lattice distortion causedb yo xygen vacancies. [40] To analyze the local structure of MnO 2 ,R aman spectroscopy was employed owing to its high sensitivity for the examination of the crystal microstructure. [41] As showni nF igure1b-c, all spectra had similar characteristicc urves, in which the band at 554 cm À1 was attributed to the MnÀOs tretching vibration in the basal plane of the MnO 6 sheet and the band at 620 cm À1 was assigned to the symmetric stretching vibration of the MnÀ Ob ond in the MnO 6 groups.…”

The Role of Alkali Metal in α‐MnO2 Catalyzed Ammonia‐Selective Catalysis

“…To uncover the atomic role of K + for K‐α‐MnO 2 , the chemical adsorption of NH 3 and dissassociation of N−H bond was calculated based on DFT method (Figure ). Experimentally, NH 3 molecules mainly adsorbed on Lewis acid sites provided by unsaturated coordinative Mn atoms with or without oxygen vacancies . Therefore, two aspects were considered for building the models (Figure a,b; Supporting Information, Figures S17 and S18): 1) The adsorption of NH 3 at the original formed five‐coordinated unsaturated Mn cations (Mn 5c , the Lewis acid site) on the (001) surface of K‐α‐MnO 2 and α‐MnO 2 , respectively (Figure a); 2) an oxygen vacancy is introduced by removing a two‐coordinated bridge oxygen (O bri ) atom, then forming a new Mn 5c site on the surface with original Mn 5c site coexisted (Figure b).…”

Gram-scale synthesis of ultra-fine Cu2O for highly efficient ozone decomposition

“…The catalytic activity of Cu 2 O-1 : 2.5 is compared with those of some recently reported catalysts ( Table 2). [35][36][37][38][39][40][41][42][43][44][45] It is noted that the reaction rate (mol g À1 h À1 ) of Cu 2 O-1 : 2.5 is one of the highest in the list, especially under high humidity. In order to make a more reasonable comparison, the reaction rate is normalized to the catalyst specic area, i.e., the surface-specic catalytic rate (SA, the number of moles of decomposed ozone per square meter per hour, mol m À2 h À1 ).…”