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.