Mechanistic Insights into Oxygen Dynamics in Soot
Combustion over Cryptomelane Catalysts in Tight and Loose Contact
Modes via 18O2/16O2 Isotopic
Variable Composition Measurements – A Hot Ring Model of the
Catalyst Operation
posted on 2021-07-16, 11:37authored byJoanna Gryboś, Monika Fedyna, Piotr Legutko, Bartosz Leszczyński, Janusz Janas, Anna Wach, Jakub Szlachetko, Xuehua Yu, Andrzej Kotarba, Zhen Zhao, Zbigniew Sojka
A cryptomelane K-OMS-2
model catalyst of a well-defined nanorod
morphology, dominated by the (100) and (110) planes, was synthesized,
and thoroughly examined by means of XRD, Raman, XPS, XAS, TEM/EDX/SAED,
and computed X-ray microtomography techniques. The catalyst oxidation
performance was elucidated in the tight (TC) and loose (LC) contact
modes using isotopic 18O2/16O2 mixtures of various compositions. A simple methodology disentangling
the relative involvement of the suprafacial (adsorbed/gas phase) and
intrafacial (surface/lattice) reactive oxygen species in the soot
oxidation was developed, allowing for straightforwardly unraveling
the mechanistic details of the LC and TC combustion of soot particles.
A functional “hot ring model” was established to rationalize
the catalyst operation. It was found that apart from the ROS generation
function, the catalyst acts in the TC mode as an igniter, whereas
in the LC mode as a booster that drives the combustion process until
the afterburning stage is reached. The obtained results were accounted
for by molecular DFT and atomistic thermodynamic modeling, justifying
the particular role of the surface di- (O2c) and tri-coordinated
(O3c) oxygen anions, located on the (100) and (110) planes
of the cryptomelane nanorods, in the ignition process.