Cerium Zirconium Tungsten Composite Oxide Catalyst

With the increasing shortage of global petroleum resources and the pressure of CO₂ emission reduction, diesel vehicles with good fuel economy and strong power are paid more and more attention. The trend of "diesel" of global automotive power has become increasingly evident. However, compared with gasoline vehicles equipped with three-way catalysts with relatively mature technology, the NO_x and PM in the exhaust of diesel vehicles using lean burn technology have become the bottleneck restricting their popularization and application.

The development of new vanadium-free SCR catalysts is of great environmental significance. In order to solve the shortcomings of metal oxide catalyst system, such as narrow operating temperature window, poor low activity at low temperature, low selectivity of N₂ and sensitivity to reaction space velocity, etc. A cerium zirconium tungsten composite oxide catalyst has been proposed by some scholars. Its catalytic activity and high temperature sintering resistance have been greatly improved. It can be used as a mobile source represented by diesel exhaust and a fixed source represented by coal-fired power plant flue gas for catalytic purification of NO_x. The synthesis process includes the following steps:

(1)A mixed solution of cerium source, zirconium source and tungsten source is prepared. In the mixed solution, the molar ratio of cerium to zirconium is 0.1-10.0, and the molar ratio of cerium to tungsten is 0.1-10.0.

(2)Adding excessive urea to the mixed solution as precipitant can complete the precipitation of cerium, zirconium and tungsten ions.

(3)The precipitated products were filtered and washed to obtain filter cake.

(4)Ce-Zr-W composite oxide catalyst was prepared by drying and roasting filter cake.

The specific operation is as follows:
Ammonium tungstate was dissolved in oxalic acid solution (the mass ratio of ammonium tungstate to oxalic acid was 1:1). Cerium nitrate and zirconium nitrate were added to the solution. The solution with Ce/Zr/W molar ratio of 1:0.1:1 was prepared and mixed evenly. Excess urea was added to the solution and stirred continuously for 12 hours at 90 ℃. Then the solution was filtered and washed. The filter cake was dried in an oven at 100 ℃ for 12 hours, and then calcined in air at 500 ℃ for 5 hours in a muffle oven to prepare powdered cerium zirconium tungsten composite oxide catalyst.

The operating temperature window of cerium zirconium tungsten composite oxide catalyst is wide, and it is suitable for the application environment where the temperature of motor vehicle tail gas varies greatly. It is expected to be used in fixed source flue gas denitrification after flue gas desulfurization and dust removal in order to improve the service life of SCR catalyst.

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