One of the most challenging tasks in the environmental protection field is to reduce nitrogen oxide in the exhaust emissions. With the daily increasing of the usage amount of global automobile, the automobile exhaust has become one of the main sources of nitrogen oxides, which the governance has become particularly important. There are usually two methods to improve the denitration process of automobile exhaust, which are the methods of improving combustion process and flue gas denitrification. In the methods of improving combustion process, with the process changing, the NOx eliminate efficiency also will show a difference; however, it is denitration efficiency almost controlled among 50~60%. In the flue gas denitrification process, especially the using of catalytic method, its denitration efficiency can reach a relatively high level, and thus to have a widely application.

 

Denitration catalyst is the core part of the whole SCR system. Denitration catalyst is commonly using titanium dioxide as a carrier, and vanadium pentoxide as the active material which plays the role of oxidizing, otherwise, tungsten trioxide and other substances are added as the additives for enhancing its denitration performance. By controlling the amount of each component, we can get the high efficient of catalyst. Research has indicated that the SCR catalyst which is composed of a homogeneous mixture of titanium dioxide (80~90wt%), tungsten trioxide (6~10wt%) and vanadium pentoxide (highest of 3wt%), wherein the making up prescription may contain silica (0~ 10wt%), is a automobile exhaust denitration catalyst with a high activity.

 

In the tungsten trioxide denitration catalyst, titanium dioxide is used as an active carrier of high surface area to carry the active component of vanadium pentoxide, in which vanadium pentoxide decides the NOx reduction activity of the catalyst at a low or middle operating temperature. However, an excess of vanadium pentoxide will result in the sulfur dioxide gas being oxidized to sulfur trioxide. Therefore, for the purposes of the high sulfur content in the exhaust gas, the amount of vanadium pentoxide in the catalyst is supposed to be maintained at a low level (1wt% or even less), thus the catalyst can play a relatively high activity. Tungsten trioxide (or molybdenum trioxide) as the chemical additive or structural aid, can be used for extending the operating temperature range, and enhancing the anti-vulcanization property of the catalyst, thus effectively preventing the conversion of sulfur dioxide to sulfur trioxide. Silica is often used to improve the strength and stability of the catalyst.

 

With the expansion of SCR denitration projects, tungsten trioxide will have a very broad application prospect in the developing of catalyst and non-precious metal of the automobile exhaust denitration catalyst which is used under the lean-burn conditions.