Is fighting against pollutants possible with critical raw material free perovskites?

Abstract

Perovskites free of critical raw materials (noble metals and rare earths) of the type Ba1-ySryMn1−0.2-xMg0.2CuxO3 (y = 0.1, 0.5; x = 0.1, 0.2, 0.3) are developed for the abatement of pollutants in automotive exhaust, both gaseous (CO, NOx and HCs) and solid (carbon soot). The reactivity in oxidation and reduction is tuned through ad-hoc induced surface segregation phenomena and the promotion of specific Mn(III)/Mn(IV) and Cu/Mn atomic ratios. The insertion of Cu into the perovskitic cell, moves the crystalline structure from 2H-type toward a Mn-deficient one, in which Mn(III) is prevalent. The catalytic capability in abatement of pollutants was studied comparing the activity in the following reactions: CO oxidation, CO assisted NO reduction, and with a complex mixture simulating the composition of automotive exhausts in stoichiometric and rich conditions. CO oxidation is favored by surface segregation of Mn, Mg may play a role in CO coordination. Copper enhances the NO reduction activity of the catalysts in the CO + NO reaction and Ba0.9Sr0.1Mn0.5Mg0.2Cu0.3O3 is the more active, whereas in the complex mixture Ba0.9Sr0.1Mn0.7Mg0.2Cu0.1O3 and Ba0.9Sr0.1Mn0.6Mg0.2Cu0.2O3 are the more active suggesting a less relevant role of surface composition and a more active contribution of bulk ion mobility.