Characteristics of Soot Oxidation at the Interface between Soot and Silicon-Oxy-Carbide with Embedded Single Nanosized Pt Particles 2013-01-0516

A diesel particulate membrane filter (DPMF) offers good trapping efficiency of soot and reduces the pressure loss through the soot-trapping process. We found that one specific design of DPMF has the effect of reducing the apparent activation energy of the soot oxidation. The membrane is made of SiC nanoparticles with a diameter of 10-100 nm, which are covered with a thin silicon-oxy-carbide layer with a thickness of about 5 nm. The apparent activation energy of soot oxidation on the DPMF was reduced by 30-40 kJ/mol than conventional SiC-DPF. Furthermore, the light-off temperature of soot oxidation on the DPMF (with single nanosized Pt) is about 100°C lower than that of the DPMF (without Pt). The single nanosized Pt particles are embedded in the silicon-oxy-carbide layer. The formation of additional Pt is different from that which takes place in a conventional catalyzed soot filter (CSF). In a conventional CSF, the surface of the Pt particles is exposed to the atmosphere. The reaction path of soot oxidation on the DPMF is likely to be different from that of a conventional CSF. In this report, an inspection of the reducing effect of the light-off temperature of soot oxidation on a DPMF was evaluated. In addition, we sought to ascertain the characteristics of the reaction path of the soot oxidation. The characteristics of soot oxidation were investigated using three methods: environmental transmission electron microscope (ETEM), temperature programmed oxidation (TPO), thermal desorption spectroscopy (TDS). From the ETEM observation of the soot oxidation on SiC nanoparticles, it looks like the soot reacts on the surface of silicon-oxy-carbide layer. The results of TPO and TDS showed that there are two reaction paths of soot oxidation. First, the soot directly reacts with the oxygen in that exhaust gas at temperatures over 550-600°C. Second, the soot is oxidized at the interface between the soot and the silicon-oxy-carbide layer by the adsorbed oxygen on the surface of the SiC nanoparticles.