Chapter 11: Sustainable Catalysis by Manganese Compounds: From Heterogeneous Molecular Complexes to Manganese-based (Nano)Materials

Manganese is an Earth-abundant, environmentally friendly and low-priced element exhibiting a wide range of easily accessible oxidation states. It has a very rich oxide/hydroxide and coordination chemistry and participates in several biomolecules; manganese shows outstanding oxidative properties that makes it ubiquitous in the area of sustainable oxidative catalysis. This chapter aims to overview the variety of sustainable catalytic applications of manganese compounds, focusing predominantly in heterogeneous systems ranging from heterogeneous molecular complexes to manganese-based (nano)materials, for two major areas of high current impact: Fine Chemistry and Sustainable Energy & Environment Protection. In the first topic, the general methodologies used in heterogenisation of manganese complexes into solid supports are briefly described and examples of supported manganese complexes with salen and porphyrin ligands as heterogeneous catalysts in the epoxidation of alkenes are presented aiming to discuss the influence of the immobilisation strategy on their catalytic performance. The second topic reviews the role of manganese compounds in the water oxidation reaction, an alternative for sustainable fuels production, by chemically driven and electroassisted reactions. Furthermore, the role of manganese oxides as catalyst promotors in carbon-dioxide reforming of methane, a process for greenhouse gases mitigation and syngas production, is addressed. Finally, the application of manganese oxides as oxidants and recyclable catalysts for the degradation of anthropogenic organic pollutants found in water and wastewater is described.