Research on Foamed Ceramic Monolith for Catalytic Purification of Exhaust Gases from Diesel Engine

Stringent environmental legislation in China has been made with an aim to reduce the harmful NOx especially through a successful auto exhaust control. Nevertheless, catalytic purification on exhaust of diesel engine still exist serious problems, for instance, the most widely used and commercialized catalyst system for this process is V2O5-WO3/TiO2along with a somewhat narrow window for operating temperature (350-400℃); the poor activity exhibiting at low temperatures is a fatal problem for its practical application, especially for a cold-start stage or a diesel engine, because the effluent gases must be heated up to ensure a required activity which leads to more energy consumption; high cost in loading precious metal. Therefore, indispensable efforts to seek for some highly SCR active catalysts in a broad-temperature zone, nice selectivity in N2, apply to high space velocity, simple and inexpensive to prepare into monolithic catalysts are thus necessary.Initially, two series of MnOx-YmOn/TiO2and V2O5-YmOn/TiO2were prepared and tested in NH3SCR of NO. MnOx-CeO2/TiO2and V2O5-WO3/TiO2were then respectively screened out based on their best performances in LT or HT zone, for the following combination. Combination of CC-B, V2O5-WO3/TiO2is set as the fore part while MnOx-CeO2/TiO2is separately set as the rear part, was both achieved LT and HT SCR performance during the NH3SCR of NO process, which obtained an outstanding SCR performance (NO conversion>85%, N2yield>70%) in a wide temperature window (from150℃to400℃). In this combination method, the sequence, volume ratio and component of the different catalytic parts were the key factors for an optimal activity.A combination principle can be concluded herein, that the catalytic component with better redox capacity had better be laid latterly in order to keep its ideal activity at low temperatures and to avoid the fatal depletion of reducing agent; while the other catalyst with poor LH but excellent HT activities should be set as the fore component in order to maintain its advantage in the combined catalyst. Moreover, MnOx-CeO2/TiO2had a better LT activity than V2O5-WO3/TiO2, which was ascribed to the excellent oxidation ability and the easy NO adsorption of the former to facilitate NO→NO2oxidation.