Fundamental insight in soot oxidation over a Ag/Co₃O₄ catalyst by means of Environmental TEM

A novel Ag/Co₃O₄ catalyst for low-temperature soot oxidation has been studied by means of environmental TEM in order to get fundamental insight in the oxidation mechanism.
Soot particles generated in diesel engines are responsible for respiratory diseases, lung cancer and affect the climate both locally and globally. Removal of these particles from the exhaust gas is normally carried out by filtration through a ceramic filter. A major disadvantage of this technique is the need for periodic regenerations involving temperature increases in order to oxidize the collected soot. In an effort to minimize the filter regeneration temperature – ideally down to the normal temperature of the exhaust gas - a new catalyst for soot oxidation consisting of Ag nanoparticles supported on Co₃O₄ has been synthesized using flame spray pyrolysis and characterized using electron microscopy and X-Ray diffraction. Catalytic tests of the novel Ag/Co₃O₄ system carried out in a flow reactor show high conversion efficiencies. The temperature dependence of the soot oxidation rate for this new system cannot be directly described in terms of the activity of the single Ag and Co₃O₄ components, but is strongly dependent on preparation method, degree of contact with the soot and temperature range. In order to fully understand the role of the single constituents and the influence of different operating conditions in the overall catalytic activity, flow reactor experiments have been coupled with in situ soot oxidation in an Environmental TEM (ETEM) at different temperatures and gas compositions.