Soot combustion improvement in diesel particulate filters catalyzed with ceria nanofibers

摘要

Ceria nanofibers were prepared and deposited on SiC diesel particulate filters (DPFs), aiming at improving the soot-catalyst contact conditions and promote soot combustion at lower temperatures than in the noncatalytic case. In particular, the nanofibers have been found to be very active with respect to other ceria catalyst morphologies, due to their arrangement in a network which enhances the number of soot-fiber contact points. This effect was initially elucidated in a series of tests of soot temperature programmed combustion, which were carried out on the catalysts powders mixed with soot in loose contact conditions: a specific sub-set of nanofibers exhibited a 112 °C anticipation of the onset oxidation temperature (10% of total soot combustion) with respect to the non-catalytic test, and 38 °C with respect to ceria nanopowders obtained with the so-called Solution Combustion Synthesis (SCS). The nanofibers were then supported on Alumina washcoated DPFs, which were loaded with soot for 1 h, and subsequently subjected to a progressive temperature increase to induce soot ignition. Both CO2 concentration in the outlet gas, and the pressure drop, were recorded during these tests. The main advantage given by the nanofiber catalyzed DPF, with respect to the other investigated morphologies, was not related to the maximum rate of soot oxidation, which was similar for all ceria catalysts, but again to the onset temperature. In fact, the pressure drop curve started to decrease more than 50 °C before the DPF catalyzed with ceria through in situ SCS. This behavior could greatly improve the soot oxidation activity especially for DPF passive regeneration purposes.