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Method for treating a gas containing nitrogen oxides (NOx), using as nox trap a composition based on zirconium oxide and praseodymium oxide

A technology of nitrogen oxides and zirconium oxides, applied in metal/metal oxide/metal hydroxide catalysts, chemical instruments and methods, physical/chemical process catalysts, etc., can solve problems such as low efficiency

Inactive Publication Date: 2008-11-19
RHODIA OPERATIONS SAS +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0004] However, known NOx traps still have certain drawbacks
Their ability to capture or store NOx is optimal at high temperatures (that is, typically around 400°C), while they exhibit inefficiency at lower temperatures

Method used

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  • Method for treating a gas containing nitrogen oxides (NOx), using as nox trap a composition based on zirconium oxide and praseodymium oxide

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0067] This example concerns the preparation of a first compound that can be incorporated into a composition that can be used in the methods of the invention. This compound is based on oxides of cerium, zirconium and praseodymium, expressed in proportions by mass of oxides of 55%, 15% and 30% respectively.

[0068] The ceric nitrate solution, the praseodymium nitrate solution and the zirconium nitrate solution are mixed in the stoichiometric ratios required to obtain the above mixed oxides. This zirconium solution is obtained by etching zirconium carbonate with concentrated nitric acid. Such a solution is such that the amount of base required to reach the equivalence point during an acid / base titration of this solution obeys the condition OH - / Zr molar ratio = 1.14.

[0069] Acid / base titrations are performed in a known manner. To make it work under optimal conditions, the concentration expressed in elemental zirconium can be titrated to approximately 3x10 -2 mol / liter so...

Embodiment 2

[0073] This example concerns the preparation of a second compound that can be incorporated into a composition that can be used in the method of the invention. This compound is based on 60% zirconium and 40% praseodymium, these proportions are based on the oxide ZrO 2 and Pr 6 o 11 expressed as a mass percentage.

[0074] 500 ml of zirconium nitrate (120 g / l) and 80 ml of praseodymium nitrate (500 g / l) were introduced into the stirring beaker. It was subsequently replenished with distilled water to obtain 1 liter of nitrate solution.

[0075]224 ml of an aqueous ammonia solution (12 mol / l) were introduced into the stirred reactor and subsequently replenished with distilled water to obtain a total volume of 1 liter.

[0076] The nitrate solution was introduced into the continuously stirred reactor over 1 hour.

[0077] The obtained solution was placed in a stainless steel autoclave equipped with a stirrer. The temperature of the medium is brought to 150° C. under stirring ...

Embodiment 3

[0084] This example concerns the preparation of a third compound that can be incorporated into compositions that can be used in the methods of the invention. This compound is based on 90% zirconium and 10% praseodymium, these proportions are based on the oxide ZrO 2 and Pr 6 o 11 expressed as a mass percentage.

[0085] The operating steps were carried out in the same manner as in Example 2, and the nitrate solution was mixed to obtain the stoichiometric ratio required for the above-mentioned mixed oxide. The specific surface area after calcination is 70m 2 / g.

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Abstract

The invention concerns a method for treating a gas containing nitrogen oxides (NOx) characterized in that it consists in using as NOx trap a composition based on a catalyst for oxidizing NOx into NO2 and a compound based on zirconium oxide and praseodymium oxide in a proportion of praseodymium oxide ranging between 5 wt. % and 50 wt. % of oxide. Said compound may further comprise cerium oxide. The inventive method can be used for treating exhaust gas of a Diesel or lean mixture gasoline internal combustion engine.

Description

technical field [0001] The present invention relates to a method for treating NOx-containing gases by using a composition based on zirconium oxide and praseodymium oxide as nitrogen oxide (NOx) trap. Background technique [0002] It is known that environmental standards are increasingly demanding the reduction of nitrogen oxide (NOx) emissions from the exhaust of motor vehicle engines, especially diesel engines or gasoline engines operating under lean burn conditions, "ternary" Catalysts are not suitable for these engines. [0003] Systems known as NOx traps have been proposed as catalyst types that can meet this requirement. They are systems that are able to partially oxidize and then store the nitrogen oxides present in the lean gas and to release and reduce them to nitrogen when the surrounding mixture is rich. [0004] However, known NOx traps still have certain drawbacks. Their ability to capture or store NOx is optimal at high temperatures (that is, typically around...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): B01D53/86B01D53/94
CPCB01D53/9422B01D2255/20715B01D2255/2065B01D2255/2066B01D53/94F01N3/10B01J23/10B01J21/06
Inventor G·布兰查德E·罗阿尔Y·朗德勒斯F·特罗内尔X·库尔图瓦D·迪普雷S·埃尔伯厄扎伊P·马里科特
Owner RHODIA OPERATIONS SAS
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