Technical Advantages of Vanadium SCR Systems for Diesel NOx Control in Emerging Markets 2008-01-1029
Selective catalytic reduction (SCR) is a promising technology for diesel aftertreatment to meet NOx emissions targets in several countries. In established markets such as the US and Europe, zeolite SCR systems are expected to be used due to their ability to survive the exhaust gas temperatures seen in an active diesel particulate filter regeneration. In emerging markets where the fuel sulfur level may be as high as 2000 parts per million, zeolite SCR catalysts may have durability issues. In these markets, low sulfur fuel is needed overall to meet emissions standards and to avoid high sulfate emissions, but the aftertreatment system must be durable to high sulfur levels because there is a risk of exposure to high sulfur fuel. Also, emissions standards may be met without a DPF in some applications, so that the exhaust system would not see temperatures of 600°C or higher. If a zeolite SCR system were used in this application, a diesel oxidation catalyst would be needed to regenerate the SCR after exposure to high sulfur fuel, adding cost to the system. Thus, a vanadium SCR system has several advantages for this application. This work shows experimental comparisons of state of the art vanadium SCR catalysts with base metal zeolite SCR catalysts. NOx conversion performance after exposure to sulfur is examined, as well as NOx conversion in the presence of hydrocarbons. Improvements in durability and performance of vanadium SCR catalysts are shown. Also, modeling results are presented demonstrating the ability of a vanadium SCR system to meet the NOx emissions targets for a Euro IV or Euro V standard. The thermal durability of current vanadium SCR catalysts is also evaluated. Based on these tests it is concluded that in markets where there is a risk of exposure to high sulfur fuel, vanadium SCR is the recommended technology.