Decoding the Reactivity Enhancement of LnCeO Compounds (Ln = Yb, Y, Tb, and Gd) for Soot Combustion: The Remarkable Contribution of Variable Valence A-Sites.

The impact of variable valence A-sites on the redox property and reactivity of LnCeO compounds in soot particulate combustion has been investigated. It was observed that YbCeO, YCeO, and GdCeO formed a rare earth C-type phase, while TbCeO formed a solid solution phase. Both TbCeO and YbCeO possess dual valence state A-sites, resulting in significantly more surface vacancies. Additionally, the advantageous solid solution phase structure of TbCeO leads to even more surface vacancies than YbCeO, which is crucial to generate active oxygen sites. Moreover, the introduction of NO into the reaction feed enhances combustion activity by producing active surface monodentate nitrates. A catalyst with higher numbers of surface vacancies exhibits improved NO oxidation ability and better NO utilization efficiency. Consequently, the TbCeO compound demonstrates not only the best soot combustion activity, but also an optimal NO-assistance effect. Therefore, it is concluded that variable valence A-site is the intrinsic factor to improve the reactivity of LnCeO catalysts.