Mayenite (12CaO·7Al 2 O 3 ) is a mesoporous calcium aluminum oxide, with a characteristic crystalline structure. The framework of mayenite is composed of interconnected cages with a positive electric charge per unit cell that includes two molecules [Ca 24 Al 28 O 64 ] 4+ , and the remaining two oxide ions O 2− , often labelled “free oxygen”, are trapped in the cages defined by the framework. Starting from mayenite structure se...