SU941284A1 - Catalyst for reducing nitrogen dioxide into nitrogen oxide - Google Patents

Description

(FOR) CATALYST FOR RESTORING NITROGENIUM DIOXIDE TO NITROGENIUM OXIDE

one

The invention relates to gas analysis measurements and can be used in the construction of chemiluminescent gas analyzers for nitrogen oxides.

In order to use a chemiluminescent primary transducer, which uses a specific reaction of nitric oxide with ozone, to measure nitrogen dioxide concentrations, the latter must be reduced (converted) to nitric oxide.

The operation of the gas measuring instrument imposes a number of requirements on the catalyst, the main ones of which are to maintain high speed and conversion efficiency (at least 95%) for a very long time of continuous operation.

Known catalyst, which is a glassy carbon, heated to a temperature of 200-600 ° F.

However, at elevated temperatures and in an atmosphere containing oxygen, glassy carbon releases an excessive amount of nitric oxide, which introduces an error in the measurement.

The closest to the proposed technical essence and achievable result is a graphite-based catalyst with molybdenum or tungsten deposited on its surface. Operating temperature "5 i 50-550c 2.

A disadvantage of the known catalyst for the reduction of nitrogen dioxide to nitric oxide is a limited service life (up to 30 days).

20

The purpose of the invention is to increase the service life of the catalyst.

The goal is achieved by adding sodium or potassium to a catalyst containing 9 grlfits, molybdenum or tungsten in the following ratio of components, weightD: Molybdenum or tungsten 0.2-1.2 Sodium or potassium0, 06-0.2 Graphite Else passing a gas mixture with N02 through such a catalyst ensures sufficiently effective (96-98%) and fast (several seconds) conversion to nitric oxide at a temperature. The service life of the catalyst exceeds 60 days. The proposed catalyst is characterized by an increased service life, which reduces the cost of maintenance of the gas analyzer, the absence of the influence of other nitrogen-containing compounds due to the decrease in the operating temperature of the catalyst; the absence of decomposition of nitric oxide into components, which ensures high accuracy in measuring the concentration of nitrogen oxides. An example. The catalyst is prepared from chipped granules of graphite of industrial production of the brand MG-OOCH. The average granule size is 2x3x3 mm. The granules are treated with an aqueous solution of ammonium molybdate or ammonium tungstate. Sodium or potassium hydroxide is added to the solution so that the alkali metal content is 10-30 wt.% Of the molybdenum (tungsten) content. After removing the excess solution and drying, the graphite is heated at 600-700 ° C in a stream of hydrogen. The catalyst test is carried out in a flow type converter. The volume of the working chamber is 25 cm. The rate of the analyzed gas mixture is about 1 l / min. To the input of the converter from the nitrogen dioxide generator a gas mixture N02 + air with NOj content equal to 0,.% 80.0 79.0 87.0 95.5 98.5 98.0 97.0 78.5 77.5 36, is supplied, 3 97.0 96.5 97.5 E3.5 4 The concentration of dioxide and nitrous oxide in the converter inlet and outlet is measured using an APNA2000 (Horib) Japan gas analyzer. The temperature of the working chamber of the converter is 200-20C. The change in the degree of reduction of: -, nitrogen dioxide in the course of the continuous operation of a carbon-based catalyst with different contents of molybdenum or tungsten is given in Table 1. From the data table. 1, it follows that when the content of Mo or W is less than 0.2% by weight of graphite, the catalyst has a low conversion degree, which decreases sharply after 10-15 days of continuous operation. When the content of Mo or W is more than 1.2% by weight, the catalyst also detects a decrease in conversion efficiency during continuous operation. Thus o6pa30Mj the optimal content of Mo, W is in the range of 0.2-1.2 weight. In the table. Figures 2 and 3 present data reflecting the change (in the course of continuous operation) of the degree of reduction of nitrogen dioxide on a catalyst containing 0.6 wt. Mo (Table 2) or W (Table 3), with different content of alkali metal (Na or K). From the table it can be seen that when the alkali metal content is less than O, O, and more than 0.2 wt.%, The degree of conversion N0 on the catalyst decreases to the level of 90% after 15-30 days of continuous operation. A catalyst containing an alkali metal in an amount of 0.06 - 0.2 Ae. Retains a high degree of conversion during the entire test period. Thus, the optimum alkali metal content is 0.06–0.2 wt.%) The proposed catalyst has a rather long service life and ensures high accuracy in measuring the concentration of nitrogen oxides. Table f 96.5 98.0 95.0 97.0 97.5 98.0

The change in the degree of reduction (PP 100%) of nitrogen dioxide in the process of continuous operation of the carbon catalyst,

containing 0.6 ppm of molybdenum with different content of alkali metal (sodium or potassium)

Continued table. one

-Table 2

, N0

 NOi

The change in the degree of reduction (sh 100%) of nitrogen dioxide in the process of continuous operation of the carbon catalyst containing 0.6 weight. molybdenum with different content of alkali metal (sodium or potassium) 32 85.5 84.0 93.0 97.0 9b, 5 84.5 81.5 95.0 96.5 97.5

Uh

8 Continued table. 2

Table 3

, N0 9,597,096,0 93,096,595,5 95,59,593,0 97,092;, 5 95,089,087,0 96,085,08i, 5 9,586,082,0 95,0 9b, 5 97,582,579,0 9,0 96,0 97,081,5 / 6,5

52 81.0 82.0 atiS 93.5 65 76.0 78.5 96.0 96.5 70 71.0 73.0 97.5 97.0

Formula inventions

A catalyst for reducing nitrogen dioxide to nitrous oxide containing graphite coated with molybdenum or tungsten on its surface, characterized in that, in order to increase the service life of the catalyst, it additionally contains sodium or potassium in the following ratio of components.

95.5 93.0 98.0 96.0 82.0 77.5 97.0 96.0 9.5 9.5 79.0 73.0 93.5 95.5 95.0 97.0 77.0 7 ,five

Molybdenum or

tungsten 0,2-1,2

Sodium or

potassium 0.06-0.2

Goafit Else

Sources of information taken into account in the examination

1. US Patent If, cl. 23-232, 197t.

2. US patent number 3730686.kl.23-232, 1973.

Claims (1)

Claim A catalyst for the reduction of nitrogen dioxide to nitric oxide, containing graphite with molybdenum or tungsten deposited on its 20 surface, characterized in that, in order to increase the life of the catalyst, it additionally contains sodium or potassium with the following ratio of components, weight. % Molybdenum or tungsten 0.2-1.2 Sodium or potassium 0.06-0.2 Graphite Else