La1-x(Sr, Na, K)xMnO3 perovskites for HCHO oxidation: The role of oxygen species on the catalytic mechanism

A-site substituted perovskites were prepared and evaluated for formaldehyde oxidation. Based on the T-50, the catalytic activity ranking was: La0.8K0.2MnO3 > La0.8Na0.2MnO3 (LNMO) > La0.8Sr0.2MnO3 > LaMnO3. This improved activity is associated to (i) higher density of surface adsorption sites and (ii) higher bulk oxygen mobility. Stability tests, under humid and dry conditions, were also conducted. In dry conditions, a gradual deactivation of the substituted perovskites (from 50 % to 15 % HCHO conversion after 64 h, LNMO) was correlated to the loss of surface-active oxygen species and high-valence Mn4+. Besides, the presence of abundant adsorbed oxidation intermediates likely inhibited the reactivation of the catalyst surface. This inhibition was limited when humidity was added in the stream of gas, thus lowering the catalysts' deactivation, demonstrating the importance of OH surface groups on the catalyst surface in the oxidation mechanism. Consequently, this work highlights the design of perovskite-based catalysts with superior oxidation properties.

Automated summary

A-site substituted perovskites were prepared and evaluated for formaldehyde oxidation, with La0.8K0.2MnO3 showing the highest catalytic activity. Stability tests revealed gradual deactivation of the catalysts under dry conditions, while the addition of humidity in the gas stream led to reduced deactivation.