Catalyst for selective reduction of nitrogen oxides in a gas, and use of the same.

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a novel catalyst for selectively reducing nitrogen oxides contained in a gas stream. In particular, the present invention relates to a method for catalytically reducing nitrogen oxides present in a gas stream with ammonia using this catalyst.

【0002】

In particular, many gaseous wastes such as automobile exhaust, waste gas from boilers and other fixed combustion units, waste gas from nitric acid production and general industrial waste gas are more or less nitrogen oxides (nitric oxide). Nitric oxide NO or nitric oxide NO₂ Can be). The oxides are usually NO_X It is called by the term.

【0003】

Nitrogen oxide NO released into the atmosphere_X Causes considerable acid rain and, along with hydrocarbons, causes photooxidative pollution, which is extremely harmful to the environment.

【0004】

Therefore, nitrogen oxide NO contained in the gas stream_X Is important to remove before it is released into the atmosphere.

【0005】

In this regard, various promulgated national legislative measures, in particular, nitrogen oxides (NO) contained in waste gas._X ) Is required to be low, not exceeding about 200vpm (0.02%).

【0006】

For this reason, the waste gas flow NO_X Many methods have been proposed to reduce the content to acceptable levels.

【0007】

Therefore, nitrogen oxide NO contained in the gas stream_X A catalyst capable of reducing the amount of water to nitrogen by ammonia was recommended by FR-A-2,450,784.

【0008】

The catalyst consists of a porous alumina carrier and a catalytically active phase with a catalytic content of 0.5-20% by weight. The catalyst has been found to be particularly effective against the reduction of nitrogen oxide waste formed during the synthesis of nitric acid by the oxygen oxidation of ammonia. The catalyst also has the advantage that it can be used at relatively low temperatures, such as 180-250 ° C, resulting in energy savings unless the gas stream to be processed needs to be heated. However, such catalysts have shown some drawbacks when used for catalytic reduction of nitrogen oxides contained in gas streams maintained at temperatures above 300 ° C. with ammonia.

【0009】

Nitrogen oxide NO_X Is reduced to high temperature with ammonia in the presence of the catalyst described in FR-A-2,450,784 and nitrous oxide N₂ It has been found to be accompanied by the formation of O, whose presence is also undesirable.

【0010】

In fact, recently it has been proposed that nitrous oxide is a gas that plays an important role in the greenhouse effect and the ozone destruction mechanism in the stratosphere.

【0011】

The presence of nitrous oxide may be due to a side reaction of ammonia oxidation by the following types of reactions: 2NH₃ + 2O₂ N₂ O + 3H₂ O (1) 4NH₃ + 4NO + 3O₂ 4N₂ O + 6H₂ O (2) [0012]

At high temperatures, further contamination with nitrous oxide continues, followed by consumption of ammonia by the simulated reaction (1).

【0013】

One object of the present invention is to selectively reduce nitrogen oxides contained in a gas stream with ammonia at 300 ° C or higher (350-450 ° C is advantageous), i.e., nitrogen oxides. It is to provide a catalyst which leads to recovery of a gas stream which does not contain.

【0014】

Another object of the present invention is to provide a catalyst that minimizes the formation of nitrous oxide during the selective reduction of nitrogen oxides at elevated temperatures.

【0015】

Another object of the present invention is conventional stoichiometry (nitrogen oxide NO)._X If the reduction of is carried out at a high temperature, the NO to be reduced_X It is to provide a catalyst that does not consume excessive ammonia as compared to 1 mol per mole).

【0016】

Now, we have found a catalyst (which constitutes the subject of the present invention) for reducing ammonia in a reduction step in which nitrogen oxides present in a gas stream are operated at a temperature of 300 ° C. or higher. The catalyst is a carrier of at least one inorganic oxide selected from alumina, aluminate, titanium oxide and zirconium oxide and at least one metal oxidation selected from oxides of vanadium and / or molybdenum and / or tungsten. It contains a catalytically active phase of the material and the carrier has a surface condition that chemically bonds with the metal elements V and / or Mo and / or W and V.₂ O₅ And / or MoO₃ And / or WO₃ It is characterized by not having a type crystal phase.

【0017】

One property of the catalyst of the present invention is the presence of the metal element M (M stands for V and / or Mo and / or W) bound on the carrier.

【0018】

The bond between the carrier metal element S (S stands for Al and / or Ti and / or Zr) and the metal element M is probably of the SOM type, although we do not want to be tied to or limited to any particular theory. These oxides are the surface MO of the tetrahedral structure bonded exclusively to the carrier.₄ Unit and MO₄ And / or MO₅ It is in the form of units of oligomers (these oligomers are attached to carriers), and they are V on the surface.₂ O₅ And / or MoO₃ And / or WO₃ It is considered that the metal oxide phase constituting the fully crystallized phase of is not contained.

【0019】

The characteristics of the catalyst of the present invention can be determined by Raman spectroscopic analysis under working conditions such that thermal decomposition of the catalyst does not occur under the influence of the excitation source of the spectroscope.

【0020】

Under these conditions, they are 850-980 cm, characteristic of vanadate, molybdate or tungstate (polymerized or other conditions).^-1And 220 ~ 370cm^-1Wavenumber range lines exist, 1000, 700, 535 and 400 cm^-1Crystals of vanadium oxide, 1000, 815, 665 and 280 cm^-1Crystalline molybdenum oxide and 810, 715 and 270 cm^-1It has a spectrum in which no characteristic line is present in the crystalline tungsten oxide.

【0021】

Applicants have found that this catalyst exhibits improved catalytic performance when it has the characteristics that appear in the Raman spectrum defined above.

【0022】

The first advantage of using such a catalyst in the step of reducing nitrogen oxides contained in the gas stream with ammonia is to reduce the nitrogen oxides to nitrogen at high temperatures while minimizing the formation of nitrous oxide. It is possible to do it.

【0023】

Another advantage obtained by utilizing the catalyst of the present invention is that the consumption of ammonia can be reduced.

【0024】

According to the present invention, the catalyst of the present invention is a carrier (alumina, aluminate, titanium oxide TiO).₂ And / or zirconia oxide ZrO known as zirconia₂ It results from some distribution of metal oxides that make up a catalytically active phase on top of it.

【0025】

Aluminate means a divalent transition metal aluminate having a small ionic radius (preferably not exceeding 0.08 nm).

【0026】

Examples of aluminates suitable for the present invention include aluminates of zinc, nickel, cobalt, magnesium and copper.

【0027】

Of the above-mentioned aluminates, nickel aluminate is preferable.

【0028】

The preferred catalyst according to the present invention has alumina or aluminate as a carrier.

【0029】

In the context of the present invention, for pores with a pore volume greater than 1000 Å in diameter, 25 cm.³ Larger than / 100g (especially 25 ~ 70cm)³ / 100g), 40cm for pores larger than 300Å in diameter³ Larger than / 100g (especially 43 ~ 70cm)³ / 100g), total pore volume is 80 ~ 120cm³ It is preferable to use a catalyst carrier based on alumina or aluminate, which is / 100 g.

【0030】

The surface area of the alumina-based carrier is preferably up to 160 m.² / g, more generally 90 ~ 150m² / g.

【0031】

Alumina that can be used usually has γ, θ, δ and α crystalline types (generally, γ, θ and δ types are predominant, so α type exists in a trace state).

【0032】

When titanium oxide is used, its anatase type is preferably used.

【0033】

The specific surface area of the carrier is 5 to 200 m.² / g (preferably 10-100m² / g) can vary over a very wide range. Total pore volume is 10-50 cm³ / 100g (preferably 20-40cm)³ / 100g).

【0034】

Zirconia is 5 ~ 200m as it is² It has a specific surface area of / g. Total pore volume is 10-70 cm³ / 100g (preferably 20-50cm³ / 100g).

【0035】

According to the present invention, a metal oxide of vanadium, molybdenum or tungsten, or a mixture thereof, can be added to V₂ O₅ And / or MoO₃ And / or WO₃ It adheres onto the carrier in such a way that no type crystal phase is formed (corresponding to the limited ratio of metal elements to the specific surface area of the carrier).

【0036】

As an example, in the case of alumina or aluminate, this feature is satisfied and therefore the production of catalysts with the Raman spectrum defined above produces less vanadium and / or Y atoms per square nanometer of carrier. Correspondence to coating of alumina carrier with less molybdenum and / or tungsten is mentioned (X and Y are characterized by the following relationship: --X is 9 or less --Y is 6 or less --X is (1-Y / 6) x 9 or less --Y is (1-X / 9) x 6 or less).

【0037】

The numbers X and Y of atoms are expressed relative to the specific surface area of the carrier after calcination. The surface area is determined by measuring the specific surface area of the "finished" catalyst and is expressed in terms of the content of the catalyst carrier.

【0038】

The catalytically active phase according to the invention can consist of at least one metal oxide, such as an oxide of vanadium, molybdenum and / or tungsten.

【0039】

The content of the active phase of this catalyst can be 0.01 to 50% by weight (preferably 0.1 to 20% by weight) based on the total weight of the catalyst.

【0040】

A catalyst particularly well suited for this invention is vanadium oxide V.₂ O₅ Or, on the other hand, vanadium oxide V₂ O₅ On the other hand molybdenum oxide MoO₃ Or tungsten oxide WO₃ Consists of a catalytically active phase consisting of a mixture comprising. V₂ O₅ MoO₃ Or WO₃ The weight ratio to is preferably 1 to 0.01.

【0041】

The catalyst of the present invention can be produced using standard techniques for catalyst production.

【0042】

A well-suited method for their production is to impregnate the carrier with an aqueous solution containing the metal elements V and / or Mo and / or W, and then coat with V and / or Mo and / or W in subsequent steps. This is a method of subjecting the prepared carrier to heat treatment.

【0043】

In this method, in the first step, for example, a carrier in the form of beads, granules or an extruded product of any shape is impregnated with a solution of vanadium and / or molybdenum and / or a tungsten compound that produces a metal oxide upon firing. Become.

【0044】

It is also possible to precipitate the above compounds on a carrier.

【0045】

The starting vanadium compound can be a salt such as vanadium oxide, a vanadium complex (vanadium acetylacetate or vanadium oxyoxalate, etc.) or ammonium metavanadium or vanadium oxysulfate.

【0046】

The starting molybdate or tungsten compound can be an ammonium salt such as ammonium dimolybdate, ammonium heptamolybdate, ammonium metatungstate or ammonium paratungstate.

【0047】

The impregnating solution is generally an aqueous solution that may contain a metal salt that is a precursor to oxides of vanadium, molybdenum and / or tungsten.

【0048】

A water-soluble salt is used by the preferred method.

【0049】

The aqueous solution obtained by dissolving vanadium pentoxide in an oxalic acid solution can be used as an impregnating solution containing a vanadium compound.

【0050】

For molybdenum and / or tungsten compounds, ammonium salts are preferred.

【0051】

The catalyst of the present invention is produced, for example, by mixing an aqueous solution of a vanadium compound with an alumina or aluminate carrier for impregnation, and the vanadium compound does not exceed 9 vanadium atoms per square nanometer of carrier. It is used in such a ratio.

【0052】

If molybdenum and / or tungsten compounds are also present, their ratios are specified in consideration of the equations or inequalities given above.

【0053】

In the second step, a heat treatment consisting of firing the impregnated carrier is performed. However, although not essential, it is desirable to do so before the drying process.

【0054】

This drying is most often done in air at temperatures on the order of 100-150 ° C for about 1-12 hours.

【0055】

Then, in general, a firing operation is performed in air at an order of 300 to 800 ° C (preferably on the order of 350 to 600 ° C) for about 1 to 6 hours.

【0056】

The impregnation operation may be repeated once or more, and the firing operation may be performed after each operation.

【0057】

By a kneading step of the carrier in powder form with an oxide and / or salt of vanadium and / or molybdenum and / or tungsten in the presence of water and optionally an acid (eg, nitric acid) or base (eg, ammonia solution). It is also possible to produce the catalyst of the present invention.

【0058】

The resulting paste is extruded into any shape (eg, cylindrical or multilobular, ring, monolith, etc.).

【0059】

The obtained extruded product is appropriately dried and calcined as described above.

【0060】

Another subject of the present invention comprises a method of reducing nitrogen oxides present in a gas stream with ammonia using a catalyst as described above.

【0061】

The catalyst is generally introduced into a suitable reactor in the form of a fixed bed or a fluidized bed for use in the method of removing nitrogen oxides from the gas stream.

【0062】

Typically, the gas stream to be purified by the present invention is a waste gas stream from a chemical process or fixed combustion unit, including in particular: - nitrogen, --Oxygen (usually 1-10% by volume), --Nitrogen oxide NO_X (Usually 0.01 to 1 volume% content), --Sulfur oxide SO_X (Usually 0 to 1% by volume content), --Water (usually 0.001 to 20% by volume).

【0063】

The catalyst, which is the subject of the present invention, is perfectly suitable for use in processes operating at temperatures above 300 ° C (preferably 300-550 ° C). The temperature of the gas flow to be treated is preferably 350 to 450 ° C.

【0064】

The hourly space velocity (HSV) of the gas to be treated depends on the temperature of the catalyst, the higher the temperature, the greater the HSV for a given result.

【0065】

HSV represents the volume of gas to be processed per hour per volume of catalyst. It is specified at standard temperature (0 ° C) and standard pressure (1 bar).

【0066】

More often, in the temperature range mentioned above, HSV is 2,000 to 150,000 h.^-1(Preferably 3,000-100,000h^-1).

【0067】

NH₃ / NO_X The molar ratio is NO in the gas stream_X Depends on the desired reduction in ammonia and the permissible emissions of ammonia in the treated stream (these two parameters are related).

【0068】

NO implemented by the present invention_X Selective reduction of is usually the desired degree of conversion and NO of the gas to be treated._X NH less than 1.1 depending on content₃ / NO_X A molar ratio (preferably 0.8-1) is required.

【0069】

Pressurizing the gas stream to be processed is NO_X N₂ It is convenient to convert to.

【0070】

It may be 1 to 20 bar (preferably 1 to 15 bar).

【0071】

A preferred embodiment of the method of reducing nitrogen oxides present in the gas stream is to adjust the amount of catalytic metal elements present on the surface of the catalyst according to the operating temperature of the method.

【0072】

In fact, it has been unexpectedly found that the amount can be reduced in proportion to the increase in reduction temperature.

【0073】

Therefore, the catalyst used has X vanadium atoms or Y molybdenum and / or tungsten atoms per square nanometer (decreases in proportion to the temperature rise of the gas stream to be treated).

【0074】

This property becomes even more apparent in the context of particularly advantageous catalyst examples (ie, catalysts based on alumina or aluminate coated with vanadium oxide). These catalysts do not substantially oxidize ammonia and significantly form nitrous oxide by ammonia, NO._X Can be efficiently decomposed exclusively into nitrogen and water at 300-550 ° C.

【0075】

Tolerance level is nitrogen oxide NO where the reaction enters the reactor_X It is thought to correspond to the amount of nitrous oxide formed before exceeding 1% of the amount of nitrous oxide.

【0076】

Therefore, the gas flow without water has a space speed of 8,000h.^-1And NO at the entrance₂ / NO_X It was found that the number X of vanadium atoms per square nanometer of alumina could decrease in proportion to the rise in temperature during treatment under an absolute pressure of 4 bar for a ratio of less than 0.5.

【0077】

If the temperature is less than or equal to 300 ° C, X is preferably less than or equal to 9. If the temperature is 350 ° C or less, X is preferably 7 or less. If the temperature is 400 ° C or less, X is preferably 4.5 or less. If the temperature is less than or equal to 500 ° C, X is preferably less than or equal to 1.

【0078】

Different values of X can be adjusted if the conditions are different, i.e. if water is present in the gas stream or if the pressure and contact time are different.

【0079】

Under these conditions, for example, for alumina and aluminate, the number X of vanadium atoms per square nanometer is 9 or less, the temperature T (Kelvin), and the contact time t._c (Seconds) (specified in relation to standard temperature and pressure conditions), pressure P (bar) and molar concentration of water C_H2O Depends on the value X₀ The following is specified and the value X₀ Is defined by the following formula: [Number 2]

X₀ =[-58.0+4.65×10⁴ × 1 / T] t_c^1.58 × p^0.26[1 + 5.2C_H2O ]^0.40(In the above formula, C_H2O Is the number of moles of water per mole of gas treated, 0-0.3 moles, t_c Is 0.1 to 1 second p is 1 ~ 15bar T is 580 ~ 800K).

【0080】

The catalysts of the present invention find particularly good applications in the treatment of waste gas streams obtained as emissions from the process of producing nitric acid by oxidizing ammonia.

【0081】

It's NO_X It is also suitable for the treatment of any waste gas, including waste gas from boilers and other fixed combustion units.

【0082】

The following examples illustrate the invention, but without limitation.

【0083】

[Example]

Example 1 Production of catalyst A (representative of the present invention) For the production of catalyst A, alumina is used in the form of beads with a diameter of 3 mm, such as: --Specific surface area is 152m² / g --Total pore volume is 100 cm³ / 100g --For pores larger than 1000 Å in diameter, the pore volume is 27 cm.³ / 100g --For pores larger than 300 Å in diameter, the pore volume is 46 cm.³ / 100g.

【0084】

100 g of this carrier is impregnated with 100 ml of an aqueous solution of vanadium oxyhydrate obtained by dissolving 17.6 g of vanadium pentoxide in a oxalic acid solution (a stoichiometric amount relative to vanadium pentoxide).

【0085】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0086】

The resulting catalyst A contains 15% by weight vanadium pentoxide (uniformly distributed in alumina beads, equal to 7.7 vanadium atoms per square nanometer), expressed in% by weight relative to the carrier.

【0087】

Example 2 Production of catalyst B (representative of the present invention) The alumina carrier described in Example 1 is used for the production of catalyst B.

【0088】

100 g of this carrier is impregnated with 100 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 13 g of vanadium pentoxide in an oxalic acid solution.

【0089】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0090】

The resulting catalyst B contains 11.5% by weight vanadium pentoxide (uniformly distributed in alumina beads, equal to 5.6 vanadium atoms per square nanometer), expressed in% by weight relative to the carrier.

【0091】

Example 3 Production of catalyst C (representative of the present invention) The alumina carrier described in Example 1 is used for the production of catalyst C.

【0092】

100 g of this carrier is impregnated with 100 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 11.1 g of vanadium pentoxide in an oxalic acid solution.

【0093】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0094】

The resulting catalyst C contains 10% by weight vanadium pentoxide (uniformly distributed in alumina beads, equal to 4.8 vanadium atoms per square nanometer), expressed in% by weight relative to the carrier.

【0095】

Example 4 Production of catalyst D (representative of the present invention) The alumina carrier described in Example 1 is used for the production of catalyst D.

【0096】

100 g of this carrier is impregnated with 100 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 4.2 g of vanadium pentoxide in an oxalic acid solution.

【0097】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0098】

The resulting catalyst D contains 4% by weight vanadium pentoxide (uniformly distributed in alumina beads, equal to 1.8 vanadium atoms per square nanometer), expressed in% by weight relative to the carrier.

【0099】

Example 5 Catalyst E^* Manufacturing (comparative test) Catalyst E^* The alumina carrier described in Example 1 is used for the production of.

【0100】

100 g of this carrier is impregnated with 100 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 17.6 g of vanadium pentoxide in an oxalic acid solution.

【0101】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0102】

100 g of this product is impregnated with 100 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 11.6 g of vanadium pentoxide in an oxalic acid solution.

【0103】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0104】

The resulting catalyst E^* Contains 25% by weight vanadium pentoxide (uniformly distributed in alumina beads, equal to 13.9 vanadium atoms per square nanometer), expressed in% by weight relative to the carrier.

【0105】

Example 6 Catalyst F^* Manufacturing (comparative test) Catalyst F^* For the production of, use titanium dioxide in the form of a three-lobed extruded product with a diameter of 3 mm, such as: --Specific surface area is 155m² / g --Total pore volume is 30 cm³ / 100g --For pores larger than 1000 Å in diameter, the pore volume is 6 cm³ / 100g --For pores larger than 300 Å in diameter, the pore volume is 17 cm.³ / 100g.

【0106】

100 g of this carrier is impregnated with 30 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 4.4 g of vanadium pentoxide in an oxalic acid solution.

【0107】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0108】

The resulting product is impregnated with 30 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 4.4 g of vanadium pentoxide in an oxalic acid solution.

【0109】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0110】

The resulting product is impregnated with 30 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 4.4 g of vanadium pentoxide in an oxalic acid solution.

【0111】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0112】

The resulting product is impregnated with 30 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 4.4 g of vanadium pentoxide in an oxalic acid solution.

【0113】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0114】

The resulting catalyst F^* Is 70m² 15% by weight vanadium pentoxide (uniformly distributed in titanium dioxide extrude, equal to 17 vanadium atoms per square nanometer) with a specific surface area of / g and expressed in% by weight relative to the carrier Including.

【0115】

Example 7 Production of catalyst G (typical of the present invention) The titanium dioxide carrier described in Example 6 is used for the production of catalyst G.

【0116】

100 g of this carrier is impregnated with 30 ml of an aqueous solution of vanadium oxyoxalate obtained by dissolving 4.2 g of vanadium pentoxide in an oxalic acid solution.

【0117】

After 30 minutes of contact, the resulting product is dried in a furnace at 120 ° C for 4 hours and then calcined in air at 450 ° C for 4 hours.

【0118】

The resulting catalyst G is 88m² 4 wt% vanadium pentoxide (uniformly distributed in titanium dioxide extrude, equal to 3.1 vanadium atoms per square nanometer) with a specific surface area of / g and expressed in% by weight relative to the carrier. Including.

【0119】

Example 8 Characteristic display of catalyst Catalysts A, B, C, D, E produced by the above example^* , G and F^* Is characterized by Raman spectroscopy.

【0120】

Raman spectra of the catalysts were recorded using a Ramonor HG2S apparatus under the following conditions: --Excitation wavelength: 514.5nm --Laser power: 300mW --Spectrum range: 800.0 ~ 1200.0cm^-1--Slit width: 400 μm --Spectral slit width: 3.49 cm^-1--Scanning speed: 130cm^-1/ Minute --Time constant: 6 --Number of scans: 3.

【0121】

Catalyst E manufactured for comparison purposes^* And F^* In the spectrum of 1000, 700, 535 and 400 cm^-1The presence of lines characteristic of the microcrystalline vanadium oxide is observed. These lines do not exist in the case of the catalysts A to D and G that represent the present invention.

【0122】

Example 9 Catalysts A, B, C, D, E^* And G^* Evaluation of NO, NO with controlled pressure and flow rate by testing the catalysts described in the above example₂ , NH₃ , H₂ O and N₂ NO in equipment with a source of_X Removal efficiency and N₂ Measure the formation of O. 25 cm of gas flow from the gas mixture³ A volume of catalyst is housed and fed to a reactor placed in a temperature controlled chamber, which is then chemiluminescently NO._X And by gas chromatography N₂ Pass it through a device that measures O.

【0123】

NO_X The efficiency of removal is measured by the following formula: [Number 3]

NO_X Degree of removal (%) = (entrance NO_X -Exit NO_X ) / Entrance NO_X× 100 (During the ceremony, entrance NO_X = NO entering the reactor_X Concentration of Exit NO_X = NO from the reactor_X Concentration).

【0124】

The results obtained using a gas mixture containing the following are shown in Table I (the gas being processed has a space velocity of 8000 h / h).^-1, 4bar with absolute gas pressure): --0.2 Volume% NO_X-10 at the exit^-4NH by volume less than%₃ Variable amount of NH adjusted to obtain concentration₃ (0.195 ~ 0.600 volume%) - 3 Volume% O₂--Remaining nitrogen.

【0125】

Table II shows the amount of ammonia introduced at 420 ° C, and Table III shows the catalysts A, B, C, D, E at 370 and 420 ° C.^* , F^* And N formed by G₂ Indicates the amount of O.

[table 1]

<img file="JP2651981B2_D0001.tif" />[Table 2]

<img file="JP2651981B2_D0002.tif" />[Table 3]

<img file="JP2651981B2_D0003.tif" />【0126】

The results in Table I show that the catalyst according to the invention is NO._X It is shown that the removal performance is as good as that of the catalyst produced for comparative purposes.

【0127】

The results in Table II show that the catalyst according to the invention consumes much less ammonia than the catalyst for comparative purposes.

【0128】

The results in Table III show that the catalyst according to the invention is N compared to the catalyst prepared for comparison.₂ O is shown to be much less formed.