A Unique Titania-Based SCR NOx Catalyst for Diesel Exhaust Emission Control 2005-01-1859
The selective catalytic reduction (SCR) of nitrogen oxide (NOx) with ammonia (NH3) or urea ((NH2)2CO) as a reductant is becoming a promising method for near future diesel exhaust emission control. To achieve a higher conversion rate from NOx to nitrogen gas (N2) with less NH3 slip in the tail pipe, careful control of NH3 or urea dosage is necessary. For this purpose, a conventional SCR NOx catalyst usually needs an additional oxidation catalyst for the destruction of excess NH3. With an objective to destroy the excess NH3 as well as NOx within a single body of catalyst, a unique titania (TiO2)-based SCR NOx catalyst was developed, which can be fit into a space for an NOx only catalyst. A key mechanism of the destruction of excess NH3 without further formation of NOx is sort of a self-consuming action where the excess NH3 is partly converted to NO and this secondarily produced NO reacts with the remaining NH3 and finally is reduced to N2. Such a self-controlling feature can be applied to diesel engine vehicles or machines where load changes are frequently observed. In addition, a preliminary result on another TiO2-based SCR NOx catalyst, which does not contain vanadium (V) is also introduced.