Development of Mn-based perovskite materials: Chemical structure and applications

In this article, we summarize current progress on the bulk and surface characteristics of Mn-containing perovskite oxides known for their good catalytic activity in atmospheric pollutant abatement. These materials are emphasized as serious alternatives for noble metal-based catalysts (Pt, Rh, Pd) in many catalytic applications particularly in automotive exhaust catalytic converters, mainly due to their low cost, good thermal stability at high temperature and ease of preparation compared to supported noble metal catalysts. The success of such materials is mainly related to Mn³⁺ and Mn⁴⁺ mixed valence and the resulted point defects formed after incorporation of a large variety of metals with different size and charge in the perovskite structure. These parameters could also affect the Mn reducibility and oxygen species mobility considered as one of the most determining factors in catalytic activity. The effect of perovskite metallic composition on the surface Mn oxidation state and relative cations segregation as well as applications of Mn-containing perovskite oxides as catalysts for several deep oxidation reactions at low and high temperatures are presented. Particular attention is devoted to the solution combustion synthesis for Mn-containing perovskite catalysts due to its time and energy saving characteristics and high surface areas of the obtained products. These advantages open new attractive opportunities for the use of this economic process to prepare supported perovskite oxide catalysts with the aim to better control morphology and stability of both surface catalyst and supports.