Catalytic oxidation of NO over SmMn2O5 nanostructures derived from different Mn precursors

Mn-Based Mullites for Environmental and Energy Applications

Mn-based mullite oxides AMn2O5 (A = lanthanide, Y, Bi) is a novel type of ternary catalyst in terms of their electronic and geometric structures. The coexistence of pyramid Mn3+-O and octahedral Mn4+-O makes the d-orbital selectively active toward various catalytic reactions. The alternative edge- and corner-sharing stacking configuration constructs the confined active sites and abundant active oxygen species. As a result, they tend to show superior catalytic behaviors and thus gain great attention in environmental treatment and energy conversion and storage. In environmental applications, Mn-based mullites have been demonstrated to be highly active toward low-temperature oxidization of CO, NO, volatile organic compounds (VOCs), etc. Recent research further shows that mullites decompose O3 and ozonize VOCs from -20 °C to room temperature. Moreover, mullites enhance oxygen reduction reactions (ORR) and sulfur reduction reactions (SRR), critical kinetic steps in air-battery and Li-S batteries, respectively. Their distinctive structures also facilitate applications in gas-sensitive sensing, ionic conduction, high mobility dielectrics, oxygen storage, piezoelectricity, dehydration, H2O2 decomposition, and beyond. A comprehensive review from basic physicochemical properties to application certainly not only gains a full picture of mullite oxides but also provides new insights into designing heterogeneous catalysts.

Promoted Carbon Monoxide Sensing Performance of a Bi2Mn4O10-Based Mixed-Potential Sensor by Regulating Oxygen Vacancies

The YSZ-based mixed-potential sensor has exhibited promising application prospects for in situ carbon monoxide (CO) monitoring owing to its excellent thermal stability. However, the way to further enhance the sensitivity and selectivity of the sensor remains challenging due to the limitation of the sensing material. In the present work, we proposed a strategy of introducing moderate oxygen vacancies in the transition metal oxide sensing material to enhance CO sensing performance. More importantly, the oxygen vacancies of the sensing electrode were regulated by adjusting the volatilization of the Bi element at different sintering temperatures. Meanwhile, the stable mullite structure and variable valency of Mn were also exploited to maintain the phase structure stability and charge balance brought by the loss of Bi. The relationship between CO sensing properties and the proportion of both Mn³⁺/Mn⁴⁺ and oxygen vacancies was elucidated from XPS and EIS measurements. By contrast, the 800 °C-sintered Bi₂Mn₄O₁₀ possesses the highest oxygen vacancy content and thus exhibits preferable sensing performance including a lower detecting limit (10 ppm), swifter response/recovery processes, and enhanced CO sensitivity (-70.47 mV/decade operated at 450 °C) with satisfactory selectivity and stability, indicating a promising prospect for CO monitoring under exhaust environments.