Enhanced oxidative ability, recyclability, water tolerance and aromatic resistance of α-MnO2 catalyst for room-temperature formaldehyde oxidation via simple oxalic acid treatment

Alpha-MnO2 catalyst with high formaldehyde oxidation and moisture resistance by joint cerium modification and phosphoric acid post-treatment

Moisture is one prevalent interfering component during toxic formaldehyde treatment. Herein, Ce0.2Mn-P was synthesized through Ce incorporation and H3PO4 post-treatment, thereby enhancing the activity and water tolerance of α-MnO2. Removal efficiencies for ∼315 mg/m3 formaldehyde are ∼52 %, ∼54 %, ∼88 % and ∼85 % over MnO2, MnO2-P, Ce0.2Mn and Ce0.2Mn-P, respectively. Various analyses have shown that Ce modification is the primary factor enhancing catalytic oxidation. Besides, under two humidities (1.8 and 3.0 vol%), the inactivation rate of Ce0.2Mn-P is below 20 %, which was much lower than that of MnO2-P and Ce0.2Mn. Obviously, the enhancement of the moisture resistance of the catalyst is attributed to the joint action of Ce modification and H3PO4 post-treatment. XRD, isothermal N2 adsorption-desorption, SEM, mapping, (HR)TEM, Raman, ATR, DRS, XPS, CO-TPR, O2-TPD, O2-TPO, water contact angle, H2O-TPD are performed for characterizations. Ce modification populates surface hydroxyls, which play a crucial role in the complete oxidation of formaldehyde. In addition, Ce modification and H3PO4 pretreatment can not only suppress the adsorption of water on the catalyst surface but also mitigate the impact of water on the polarity of the Mn-O bond. which is conducive to the improvement of the moisture resistance of the catalyst.

Synergistic strategy of solute environment and phase control of Pb-based anodes to solve the activity-stability trade-off

The contradiction between the activity and stability of metal anodes exists extensively, especially in acid electrooxidation under industrial-level current density. Although the anode modification enhanced the initial activity of anodes, its long-term activity is limited by anode slime accumulation. Herein, a synergistic strategy, coupling the solute environment with the phase control of anodes, is proposed to achieve the trade-off between activity and stability of Pb-based anodes in concentrated sulfuric acid electrolysis. Non-exogenous Mn2+ motivated a series of positive behaviours of reactive-oxygen-species capture, anode reconstruction and corrosion-dependent activity alleviation. The synergistic effects, which are crystal phase-dependent, mainly benefit from the continuous self-healing ability of the specific crystal phase of MnO2 on the anodes by the coexisted Mn2+. Compared with Mn2+/α-MnO2, Mn2+/γ-MnO2 exhibited outperformed activity and stability in boosting oxygen evolution reaction (OER) and reducing hazardous pollutants, which resulted from the energy difference in the rate-determining step of OER and in the selectivity priority of Mn2+/MnO2 oxidation pathway. Interestingly, the pre-coated γ-MnO2 on the anode also presents excellent inheritance, guaranteeing the unchanged crystal phase of MnO2 and the high performance in ultra-low hazardous slime generation in subsequent Mn2+ oxidation. The sustainability of Mn2+/γ-MnO2 was proved in the operating hydrometallurgy conditions on Pb-based anodes. This strategy offers a promising approach for this common issue in electrooxidation-related areas.