The pivotal role of Ag species on porous nanosheets in the significant reduction of soot ignition temperature

Abstract

As a major technology, catalytic combustion is now widely used in reducing harmful soot emissions from diesel combustion. However, large amounts of soot are still emitted to atmosphere due to the lower exhaust temperature (below 200 °C) of diesel engines caused by frequent idling and cold start. Therefore, more and continued efforts are still needed to reduce the ignition temperature of T10 (at which 10 % of soot is converted) in terms of energy efficiency and environmental sustainability. In this work, an Ag-supported CoCe porous nanosheets catalyst was developed, through which a T10 < 230 °C was achieved under loose contact mode without the assistance of other atmosphere such as NOx. The detailed characterization of catalysts indicated that the motionless and mobile Ag particles, together with the regulation of valence state of Co ions by the abundant Ag+ species derived from Ag-Co interface are responsible for the ultra-low soot ignition temperature. Density functional theory (DFT) calculations proved that the electronic structure of Co can be tuned by the interactions between Ag and the support, which would promote the adsorption of O2. More importantly, the synergistic effect between Ag and Co, along with the formed interface can lower the dissociation energy barrier of O2, thus achieving a process with fast kinetics. In summary, the appropriate design of catalysts for soot combustion needs to consider both intrinsic activity and morphology, so that a significant reduction of soot emissions from vehicle exhaust can be achieved at low temperature.