Catalysts for NOX reduction employing h2 and a method of reducing NOX

Abstract

Disclosed is a catalyst composition for reducing NOx through two steps including reacting NOx with H2 thus producing ammonia which is then reacted with NOx, instead of direct NOx reduction by H2, and a method of reducing NOx using the catalyst composition.

Description

TECHNICAL FIELD[0001]As a system for reducing NOx from diesel exhaust gas, selective catalytic reduction (SCR) and NOx storage reduction (NSR) are known. In the SCR method, a reducing agent is continuously sprayed into exhaust gas and selectively reacted with NOx in a catalyst bed so that NOx is converted into N2. This method is classified into NH3-SCR, Urea-SCR, HC-SCR and H2-SCR depending on the type of reducing agent such as ammonia, urea, hydrocarbon and H2. On the other hand, in the NSR method, NOx is stored in an oxidation atmosphere and then desorbed in a reduction atmosphere formed through spray of fuel, thus reducing NOx.BACKGROUND ART[0002]Generally, NOx emitted from large-scale boilers or nitric acid plants can be effectively removed through NH3-SCR which supplies ammonia as a reducing agent to a catalyst bed composed of titania-supported vanadia or iron-containing zeolite. Ammonia is highly reactive and selective and is thus very effective for removing NOx from the exhau...

AI Technical Summary

Benefits of technology

[0021]According to the present invention, oxides of A metals including Cu, Fe, Co and Ni and oxides of B metals including Cr, Mn, Mo and V are co-precipitated and mixed, thus preparing mixed oxide catalysts and ternary mixed oxide catalysts. These catalysts exhibit superior activity for production of ammonia through selective reaction between NO2 and H2 even in the presence of 5% or 10% O2, and simultaneously, manifest very high NO2 and NO storage performance. Thereby, the catalysts can exhibit superior NOx reduction performance through injection of H2 even in the presence of O2. In particular, because NOx is removed via ammonia, the NOx removal performance is high. The catalysts according to the present invention have high Pt or Pd dispersability and high hydrothermal stability and poisoning resistance to sulfur and thus can significantly remove NOx from diesel exhaust gas. Also, the catalysts can be typically easily prepared from transition metal precursors which are inexpensive with high durability to water or heat and to sulfur poisoning.

Problems solved by technology

However, the use of ammonia to remove NOx from diesel exhaust gas is very dangerous because a diesel vehicle should be driven in a state of always being loaded with ammonia which is highly toxic.

Although the urea-SCR method is advantageous because NOx removal performance is high, it is problematic in that a tank for storing aqueous urea and a device for spraying such urea should be additionally mounted to a diesel vehicle.

As well, the urea-SCR method is difficult to apply to a diesel vehicle, due to problems including low solubility of urea, freezing, and ammonia slip.

However, it is difficult to construct the supply network of H2 and to load it into a vehicle.

Further, O2 in the diesel exhaust gas may first react with H2, undesirably lowering NOx selective removal efficiency by H2.

Thus, the application of the above method has not been considered to date.

In this case, however, a probability of reacting such H2 with O2 is increased, undesirably lowering the NOx removal efficiency.

Hence, limitations are imposed on applying the H2-SCR method to diesel vehicles.

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