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

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 Pb _x Mn₈O₁₆ 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.