Incorporating Pb²⁺ Templates into the Crystalline Structure of MnO₂ Catalyst Supported on Monolith: Applications in H₂O₂ Decomposition

Abstract

Several MnO2 catalysts, promoted with Pb2+ ions and supported on a wash-coated monolith (WMon), briefly, xPbyMn-WMon (x = 0, 0.5, 1.0, 1.5, 2, and 2.5 and y = 8 wt %), were prepared. The presence of Pb2+ affects the manganese oxidation state, crystalline phase, thermal resistance, metal dispersion, and catalytic performance. According to XPS spectra, XRD patterns and HRTEM images, manganese was dispersed on the monolith surface as Mn3+ and Mn4+ species in both α and β crystalline phases. The ratios of Mn4+/Mn3+ states and α/β phases were highly enhanced, and the desired PbxMn8O16 phase (coronadite) was formed. Concentrations of the defect oxygen (Mn–O–H) and oxygen vacancies, which improve the catalyst reducibility and the MnO2 reduction temperature, were also increased. Further, based on the H2 chemisorption analysis, the Pb2+ template would increase the manganese dispersion and the reaction sites. Meanwhile, the average MnO2 crystallite size was decreased from 13.26 to 8.15 nm. The optimum catalyst 1.5Pb8Mn-WMon exhibited an activity 149% more than the manganese-only catalyst in decomposition of H2O2. Evaluation of catalyst stability in the presence of Pb2+ after 10 recycles showed only a 6.8% decrease. The catalytic reaction was evaluated based on different criteria.

Complete Removal of Organoarsenic by the UV/Permanganate Process via HO• Oxidation and in Situ-Formed Manganese Dioxide Adsorption

“…To further study the adsorption mechanism of in situ formed MnO 2 , the O 1s XPS spectra of pure MnO 2 and MnO 2 after roxarsone treatment in the UV/permanganate process were compared (Figure c). The O 1s spectra could be deconvoluted into three species: lattice oxygen, hydroxyl surface groups of metal oxides, and molecular water. , The binding energies of lattice oxygen, hydroxyl groups, and molecular water were 529.4, 531, and 532.4 eV, respectively . The obvious increase at a binding energy of 531 eV after roxarsone treatment was likely attributable to the formation of hydroxylated arsenate surface complexes (Figure c) .…”

“…49,50 The binding energies of lattice oxygen, hydroxyl groups, and molecular water were 529.4, 531, and 532.4 eV, respectively. 51 The obvious increase at a binding energy of 531 eV after roxarsone treatment was likely attributable to the formation of hydroxylated arsenate surface complexes (Figure 3c). 50 Thus, the adsorption of arsenic by in situ formed MnO 2 occurred due to the generation of arsenate complexes on the MnO 2 hydroxyl surface.…”

Nanometer effect promoting arsenic removal on α-MnO2 nano-surface in aqueous solution: DFT+U research

“…4f~h). And the H + ions will adsorb on MnO2 surface layer to form Mn-O-H clusters (Hasanpour et al 2019), whose bonds are equal to 1.002 Å (Fig. 4f), 1.005 Å(Fig.…”