Enhanced NOx-assisted soot combustion by cobalt doping to weaken mullite Mn-O bonds for lattice oxygen activation

Abstract

Catalytic combustion is widely regarded as the most efficient technique for removing soot particulates from diesel engine exhaust, with its efficiency largely dependent on the performance of catalysts. In this study, a series of YMn_1-xCo_xO_5-ζ catalysts were synthesized using a hydrothermal method to investigate their catalytic properties in soot oxidation. Among these catalysts, YMCo-0.2 exhibited the highest catalytic activity, achieving 90% soot conversion at 392 °C and demonstrating robust tolerance in the presence of water vapour and SO₂. Structural characterisation revealed that Co doping did not alter the fundamental crystal structure of YMn₂O₅ mullite. Through some characterization comprehensive analysis, and DFT calculations further supported the experimental findings, indicate that Co substitution significantly increased the lattice oxygen mobility and surface active oxygen content. Compared to the surface lattice oxygens at other positions, the weakening of the Mn-O bond results in the lattice oxygens in the Co-O-Mn⁴⁺ sites in the catalysts exhibiting higher reactivity. Additionally, the catalyst displayed strong NO and O₂ adsorption and activation capabilities, indicating its potential for efficient NO_x-assisted soot combustion. This study provides insights for designing and optimizing mullite catalysts for soot combustion.

Environmental implications

The catalytic removal of soot particles from diesel exhaust is crucial for protecting both environmental quality and human health. In this work, cobalt (Co) doping into YMn₂O₅ mullite decreased the strength of Mn-O bond and increased the adsorption capacity of NO, which was beneficial to soot combustion reaction. This research enriches the application of mullite in the field of environmental catalysis.