La-based perovskites are catalytically active owing to the oxygen vacancies, redox metal centers of B sites and surface hydroxyl groups. Nevertheless, the insights into these active centers on environmental catalysis are still insufficient. In this study, hierarchical mixed oxides perovskite microspheres were synthesized for catalytic ozonation over oxalic acid and benzotriazole. LaMn 4 O x , with LaMnO 3-δ as the dominant crystal phase, demonstrated superior catalytic activity to Mn 2 O 3 and LaMnO 3 synthesized from citric acid sol-gel method. Temperature-programmed desorption of NH 3 (NH 3 -TPD) and pyridine-Fourier transform infrared spectroscopy (pyridine-FTIR) tests proved Lewis acid as the main acid type. Temperature-programmed reduction of H 2 (H 2 -TPR), O 2 -TPD and X-ray photoelectron spectroscopy (XPS) analysis indicated the presence of oxygen vacancies and mixed valences of Mn in the crystal structure facilitated the catalytic process. Moreover, the content of oxygen vacancy was calculated by iodometric titration method. With the aid of theoretical calculations, oxygen vacancies were found to exhibit a strong affinity toward ozone adsorption, where ozone molecules spontaneously dissociated into reactive oxygen species (ROS) such as O 2 − and 1 O 2 . The B site of Mn facilitated ozone decomposition by extending the O O bond of ozone due to the electron transfer from Mn 3+ /Mn 4+ redox cycle. In-situ EPR and quenching tests confirmed the contribution of O 2 − and 1 O 2 in benzotriazole degradation along with OH. This study stepped further to unveil the ozone adsorption/decomposition and ROS generation on nanoscale perovskite-based composites.
Ruipeng Yuan,Jinyu Zhao,Xu Chen,Xiaoming Qiu,Xiaomin Wang
Cobalt-nitrogen-carbon (CoN x C) materials are regarded as promising low-cost electrocatalysts for the oxygen reduction reaction (ORR). However, their susceptibility to deactivation and poor stability in acidic media limits their practical applications. In this study, we develop cobalt (Co) and manganese (Mn) embedded in nitrogen-doped carbon (CoMnN x C) dual-site catalysts by incorporating Mn into CoN x C and leverage a synergistic dual-catalysis strategy to optimize both activity and stability. The dynamic evolution of *OOH intermediate on the catalyst surface is monitored via in situ Raman spectroscopy, confirming that Mn introduction modulates the reaction pathway. Due to electron transfer from Mn to the Co-N x center in CoMnN x C, *OOH activation on the surface is enhanced, and the two-electron ORR process is inhibited. Consequently, the CoMnN x C catalyst exhibits excellent ORR activity (E 1/2 = 0.76 V vs. reversible hydrogen electrode) and a very low hydrogen peroxide (H 2 O 2 ) yield (<2.9 %) in acidic electrolyte. Additionally, the dynamic evolution of *OH on the Mn-N x site confirms that Mn-N x can serve as a potential catalytic site for the hydrogen peroxide reduction reaction (HPRR), facilitating H 2 O 2 decomposition. Differential electrochemical mass spectrometry (DEMS) demonstrates that this parallel catalytic pathway effectively weaks the oxidative corrosion of H 2 O 2 on the carbon carrier. The results indicate that the negative half-wave potential shift of CoMnN x C catalysts in acidic electrolyte after 10,000 accelerated durability tests (ADT) is only 11 mV. The synergistic dual-catalytic strategy proposed in this work offers a novel approach for designing high-efficiency and stable transition metal-nitrogen-carbon catalysts.
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