Life cycle of single atom catalysts: a Mössbauer study on degradation and reactivation of tetrapyrrolic Fe-N-C powders.

The degradation of a single-site atomically dispersed, model Fe-N-C powder catalyst with high activity is investigated using cryo-Mössbauer spectroscopy. The results indicate a degradation initiated by an Fe 2+ to Fe 3+ oxidation due to coordination of oxygen to tetrapyrrolic Fe-N 4 sites at atmospheric conditions (change between characteristic doublets) before iron(III) oxide is formed (sextet). Thermal reactivation can be used to restore substantial catalytic activity of aged Fe-N-C powders.