JPS6242742A - Production of catalyst for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain the titled catalyst having large surface area and excellent mechanical strength and heat resistance by mixing at least one kind of a compd. selected from a tungsten compd. and a molybdenum compd. into colloidal orthotitanic acid and baking the mixture. CONSTITUTION:Orthotitanic acid is brought into sol and 5-40wt%, based on the titanium oxide, or a tungsten compd. and/or molybdenum compd. is added and mixed. The mixture is baked at >=800 deg.C. The tungsten compd. and the molybdenum compd. are the precursors forming oxides on baking. The baked product is the titanium oxide of an ungrown anatase type crystal and is appropriately used as a catalyst carrier or a catalyst. Furthermore, a metallic oxide having catalytic activity on removing nitrogen oxides can be deposited on the baked product. Those catalysts for removing nitrogen oxides maintain high activity for a long period. Moreover, the catalysts are practically and industrially excellent since the oxidation degree of sulfur dioxide is extremely low.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing a catalyst for removing nitrogen oxides (Prior Art) It is already known that a fired titanium oxide product is used as a carrier or a catalyst. Since the surface area, crystal shape, mechanical strength, heat resistance, etc. that have important effects on the carrier or catalyst function vary depending on the manufacturing method and the presence/absence, type, and amount of additives, various manufacturing methods have been proposed. has been done.

For example, it is already known that calcining orthotitanic acid yields anatase-type titanium oxide, which is a crystalline form generally preferred as a carrier or catalyst, although there are other factors as well.

(Problems to be Solved by the Invention) However, according to the method of adding additives such as silica to orthotitanic acid and firing, it is difficult to obtain a mixture with a uniform composition. When adding to titanic acid, since orthotitanic acid is in a gel state,
Additives cannot be uniformly dispersed in orthotitanic acid, and therefore, high performance supports and catalysts cannot be obtained.

The present invention solves these problems and proposes a method for producing an unprecedented and excellent catalyst for removing nitrogen oxides.

(Means for Solving the Problems) As a result of intensive research into the above manufacturing method, the present inventors found that they used a tungsten compound and/or a molybdenum compound as an additive, and made it into a sol to exist in 9-orthotitanic acid. By firing the orthotitanic acid, the crystal growth of titanium oxide is suppressed and the ungrown anatase crystals are made to be moat, resulting in a large surface area and improved mechanical strength and heat resistance. By discovering that it is possible to obtain a fired product and using it,
Alternatively, if this is used as a carrier and a certain metal oxide is supported, an unprecedentedly improved catalyst for removing nitrogen oxides can be obtained due to the synergistic effect of each oxide in the carrier and these metal oxides. This discovery led to the present invention.

That is, the present invention provides: (1) A method for producing a catalyst for removing nitrogen oxides, which comprises: (1) firing a sol-formed orthotitanic acid containing at least one compound selected from a tungsten compound and a molybdenum compound; At least 18 selected from tungsten compounds and molybdenum compounds! ! This invention relates to a method for producing a catalyst for removing nitrogen oxides, which comprises firing a sol-formed orthotitanic acid containing a compound of .

The tungsten compound used in the present invention is tungsten oxide and a precursor that forms tungsten oxide by firing, and examples of this precursor include ammonium paratungstate. Also,
Similarly, the molybdenum compound used in the present invention is molybdenum oxide and a precursor that gives molybdenum oxide by calcination, and examples of the precursor include ammonium molybdate.

In the present invention, preferably, orthotitanic acid is made into a sol, and at least one compound selected from the above-mentioned tungsten compound and molybdenum is added thereto and mixed,
Fire this.

Furthermore, after adding at least one compound selected from the above-mentioned tungsten compound and molybdenum to orthotitanic acid, the orthotitanic acid may be sol-formed and mixed.

In any case, it is necessary to make the above-mentioned compound exist in the orthotitanic acid which is partially or completely solized, so that it can be uniformly mixed with the above-mentioned compound orthotitanic acid.

The amount of the tungsten compound and/or molybdenum compound added is 5 to 50% by weight based on titanium oxide, and when the amount added is less than 5% by weight, the crystal growth of orthotitanic acid is inhibited during firing. On the other hand, if it exceeds 50% by weight, the mixture with the sol-formed orthotitanic acid will gel, making it difficult to mix uniformly, and this is not preferable since the above-mentioned effect will be inferior. .

The method of solization is not particularly limited, and for example, after orthotitanic acid is washed with water to remove most of the sulfuric acid groups, hydrochloric acid or nitric acid is added to partially or completely solize it. Or, especially if sulfate roots are not removed by washing with water, add chlorides of alkaline earth metals such as barium chloride, strontium chloride, calcium chloride, etc., or alkaline earth metals such as barium nitrate, strontium nitrate, calcium nitrate to orthotitanic acid. nitrate is added to fix the sulfate group as a water-insoluble barium salt, while partially or completely solizing the reaction mixture. The amount of these gelling agents added is appropriately selected depending on the degree to which the reaction mixture is to be made into a sol. In addition, since the orthotitanic acid sol gels at a pH of 1 to 2 or higher, it may be gelled if necessary, as long as the tungsten compound and/or the molybdenum compound are sufficiently uniformly mixed therein.

The mixture of orthotitanic acid thus obtained and the tungsten compound and/or molybdenum compound is dried, and then heated to 800° C. or lower, preferably at 70° C.
By firing at a temperature of 0 to 200°C and pulverizing, a powdered fired product is obtained.

In this case, according to the present invention, orthotitanic acid is used, resulting in anatase-type titanium oxide, which is preferable as a catalyst or carrier during calcination.

In addition, when the fired product is used as a carrier or catalyst in a predetermined shape such as a honeycomb shape, the dried product obtained by drying the above mixture can be processed by any conventionally known method, such as extrusion molding or rolling molding. It may also be fired after being formed by a method such as granulation. Further, the powdered fired product described above can be molded into a desired shape and then fired again. In this case, after molding into the desired shape, the temperature is again 800°C or lower, preferably 700°C or lower.
It may be fired at a temperature of 200°C. In this way, according to the present invention, a fired titanium oxide product can be obtained in the form of a powder or a molded product.

In addition, in the present invention, in any of the above cases,
By adding orthotitanic acid sol or gel to a powdered dry or fired product, molding it into the desired shape, and firing it, various physical properties such as mechanical strength, porosity, specific surface area, and pore distribution can be improved. can be improved, and the shrinkage rate during firing can be suppressed. In such cases, the amount of orthotitanic acid sol or gel added is 5% of the weight of the molded product in terms of titanium oxide.
~50% by weight is suitable.

In addition, it is of course possible to use conventionally known conventional molding aids, such as methyl cellulose (Asahi, Kasei (trade name: Avicel, manufactured by Q), etc. during molding.

In the present invention, the firing atmosphere is not limited at all, and may be air, combustion gas, inert gas, or the like.

As described above, the titanium oxide fired product obtained by the present invention is not limited by theory, but due to the presence of tungsten compounds and/or molybdenum compounds, titanium oxide crystals are produced during firing of orthotitanic acid. Since the growth is suppressed and the crystals remain as ungrown anatase crystals, the resulting fired product has a large surface area and has excellent mechanical strength and heat resistance, making it suitable as a catalyst carrier or as a catalyst as it is. It can be used for.

The fact that the fired product obtained by the present invention contains ungrown anatase is confirmed by its X-ray spectrum showing low and broad peaks, as shown in Figure 1; As shown in Figure 2, the X-ray spectrum of anatase-type titanium oxide has a high peak due to extremely well-grown crystals.
And sharp.

When using the fired titanium oxide product obtained as described above as a carrier, if the carrier is supported with an oxide known to have catalytic activity for removing nitrogen oxides, the fired product can be used as a carrier. Due to the unexpected synergistic effect with the constituent oxides, it is possible to obtain a nitrogen oxide removal catalyst with excellent selective catalytic reduction activity of nitrogen oxides using ammonia as a reducing agent.

In the present invention, an oxide of at least one element selected from vanadium, tungsten, molybdenum, copper, iron, chromium, manganese, and cerium is supported as the oxide. The method for supporting the above-mentioned oxide on the titanium oxide fired product can be any method conventionally used for preparing catalysts. For example, the above-mentioned oxide or its precursor is supported on the fired product formed into a predetermined shape. After impregnating or coating with a solution or dispersion containing , it may be fired to a predetermined temperature as necessary. Of course, the nitrogen oxide removal catalyst of the present invention can also be obtained by kneading the powdered calcined product with the solution or dispersion, molding it into a desired shape, and then calcining it to a predetermined temperature as necessary. can.

In order to remove nitrogen oxides from a mixed gas containing nitrogen oxides using the catalyst of the present invention, ammonia is added in an amount of 5 to 5 times the mole, preferably 1 to 2 times the mole of nitrogen oxides contained in the mixed gas. , this is passed through a reaction bed filled with a catalyst. Any of a moving bed, a fluidized bed, a fixed bed, etc. can be used as the reaction bed. Since the catalyst of the present invention contains at least one selected from tungsten compounds and molybdenum compounds and has excellent heat resistance, the reaction temperature may range from 200 to 600°C, but preferably from 300 to 500°C. . Also, the space velocity of the gas is 1,000 to 10
QOOOhr”, preferably 4000 to 3αOOOOhr
″″1 range.

The catalyst according to the invention can be used for the treatment of any gas containing nitrogen oxides, but in particular.

Boiler exhaust gas, i.e. 100-1000 ppm of nitrogen oxides, mainly nitrogen monoxide, as well as 200-200 ppm
0 ppm sulfur oxides, primarily sulfur dioxide, 1
~10 volume% oxygen, 5~20 volume carbon dioxide, 5~
It can be suitably used to remove nitrogen oxides from exhaust gas containing 20 volumes of water vapor.

(Function) As described above, in the method of the present invention, since the tungsten compound and the molybdenum compound are present in the sol-formed orthotitanic acid, these compounds are uniformly dispersed in the resulting mixture. At this time, the titanium oxide remains in the ungrown anatase crystal form due to the action of the above compound, so the fired product obtained has a large surface area and has significantly improved mechanical strength and heat resistance. Therefore, in a catalyst for removing nitrogen oxides made of such a fired product itself, or in a catalyst for removing nitrogen oxides obtained by supporting a metal oxide having catalytic activity for removing nitrogen oxides, the growth is suppressed. Due to the synergistic action of anatase-type titanium oxide and tungsten oxide and/or molybdenum oxide, or the synergistic action of these and the above metal oxides, it maintains high nitrogen oxide removal activity for a long period of time even under severe usage conditions. In addition, the oxidation rate of sulfur dioxide to sulfur trioxide is extremely low, making it an excellent practical and industrial nitrogen oxide removal catalyst.

(Examples) The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way.

Example 1 A titanium sulfate solution obtained from the titanium oxide manufacturing process using the sulfuric acid method was neutralized and hydrolyzed with aqueous ammonia to obtain orthotitanic acid, and 1 kg of this was taken as titanium oxide. ) 80f was added to form a sol, and the mixture was thoroughly stirred and mixed. Next, 250 g of a 10% methylamine solution containing 110 g of ammonium paratungstate was added, and after thorough stirring and mixing, 100 g of ammonium paratungstate was added.
It was dried at 500°C for 12 hours and then fired at 500°C for 5 hours. This baked product is pulverized using a sample mill, the particle size is adjusted, an appropriate amount of water is added, the mixture is kneaded, the extruder is used to extrude the product into a lattice-shaped product, and the product is heated from room temperature to 100°C to dry. Then, it was fired at 500°C for 5 hours to obtain a fired product according to the present invention. This is useful as a catalyst for removing nitrogen oxides, as described below.

The X-ray spectrum of the fired product obtained in this way was
As shown in the figure. Since the peak is low and broad, it is clear that the anatase crystal remains ungrown.

The X-ray spectra were obtained using an X-ray diffractometer RA manufactured by Rigaku Denki.
Measured using D-1[A, and the measurement conditions are as follows.

Scanning speed 1°/4 minutes Full scale 100Dcps Time constant 1 second Chart speed 10 days/minute Target Copper tube voltage 50 kV Flow through the tube 10 mA For comparison, the X-ray spectrum of the commercially available pigment anatase titanium oxide was As shown in the figure. The measurement conditions are the same as above except that the full scale is 4000 ape.

Example 2 The same orthotitanic acid as in Example 1 was taken out for 1 hour in terms of titanium oxide, barium chloride (dihydrate) 802 was added thereto to form a sol, and the mixture was thoroughly stirred and mixed. Next, ammonium molybdate 120? 500 ml of methylamine solution containing was added thereto, and baking was then carried out in exactly the same manner as in Example 1 to obtain a baked product. This is further extruded and
A calcined product that can be used as a catalyst for removing nitrogen oxides was obtained.

Example 3 To 1 kg of the baked product obtained in Example 1, an aqueous solution containing 10 f of ammonium metavanadate and 25 f of oxalic acid was added, and after thorough kneading, it was extruded into a lattice-shaped molded product using an extruder and heated from room temperature to The mixture was dried by heating to 100°C, and then calcined at 500°C for 3 hours to obtain a catalyst for removing nitrogen oxides.

Example 4 A catalyst for removing nitrogen oxides was obtained in exactly the same manner as in Example 3, except that the fired product obtained in Example 2 was used.

Example 5 After loading 5% by weight of manganese oxide on 1 kg of the powder fired product obtained in Example 1, a fired product in the form of a grid was obtained in exactly the same manner as in Example 1.

This was used as a catalyst for removing nitrogen oxides.

Example 6 After loading 5% by weight of manganese oxide on 1 kg of the powder fired product obtained in Example 2, a catalyst for removing nitrogen oxides was obtained in exactly the same manner as in Example 2.

, Example 7 After loading 5% by weight of manganese oxide on the powder calcined product 17 obtained in Example 5, a catalyst for removing nitrogen oxides was obtained in exactly the same manner as in Example 3.

Comparative Example 1 The same orthotitanic acid as in Example 1 was taken out in terms of titanium oxide, and 80 tons of barium chloride (dihydrate) was added thereto to form a sol. After thorough stirring and mixing, the mixture was heated at 100°C.
The mixture was dried for 12 hours and then fired at a temperature of 500°C for 3 hours. This fired product was pulverized using a sample mill to adjust the particle size. Then, ammonium paratungstate 11
After adding 250° of a methylamine solution containing 02 and kneading, and further adding an appropriate amount of water and kneading, the mixture was extruded into a lattice shape in the same manner as in Example 1, and fired to form a nitrogen oxide removal catalyst. I got it.

Comparative Example 2 To the baked product 1 obtained in Comparative Example 1, an aqueous solution in which 102 ammonium orthovanadate and 125 t of ammonium orthovanadate were dissolved in water was added, and an appropriate amount of water was added and kneaded, followed by extrusion molding into a lattice shape. , dried at 100°C for 12 hours, and further dried for 5
The mixture was calcined at 00° C. for 3 hours to obtain a catalyst for removing nitrogen oxides.

Comparative Example 3 A fired product was obtained in exactly the same manner as in Example 1, except that siorthotitanic acid was not sol-formed with barium chloride.

Comparative Example 4 In Comparative Example 1, instead of ammonium paratungstate, a manganese nitrate solution whose concentration was adjusted to 5 weight as manganese oxide was added and kneaded, and then an appropriate amount of water was added and kneaded. It was extruded into a lattice shape and fired in the same manner as in Example 1 to obtain a catalyst for removing nitrogen oxides.

Comparative Example 5 Ammonium metavanadate 101F and oxalic acid 25% were added to 1 kg of the baked product obtained in Comparative Example 4. After adding an aqueous solution prepared by dissolving in water and further adding an appropriate amount of water and kneading, extrusion molding into a lattice shape, drying at 100°C for 12 hours, and further kneading at 500°C for 3 hours.
A catalyst for removing nitrogen oxides was obtained by firing for a period of time.

Comparative Example 6 A fired product was obtained in exactly the same manner as in Example 2 except that the siolum titanium/acid was not solified with barium chloride.

Each of the nitrogen oxide removal catalysts obtained in the above examples and comparative examples contained 200 ppm of nitrogen oxides and 200 ppm of ammonia.
, water vapor 10%, carbon dioxide 12%, sulfur dioxide 8D
A mixed gas with a composition of Oppm and the balance nitrogen was heated for 5 seconds.
The nitrogen oxide removal rate and sulfur dioxide (SOT) oxidation rate were measured by contacting at a space velocity of 5000 hr''.The results are shown in Table 2.The nitrogen oxide removal rate (% ) and sulfur dioxide oxidation rate (%) were calculated using the following formulas.

Nitrogen oxide removal rate (%) - (Catalyst waste inlet Box concentration - Catalyst layer outlet Box concentration) / (Catalyst layer inlet Hog concentration) xl
o.

Sulfur dioxide oxidation rate (%) - (Catalyst layer SO! concentration -
Concentration to catalyst layer outlet S)/(catalyst layer inlet (so, +803
) Concentration) During removal, the disadvantages due to the formation of sulfur trioxide can be eliminated.

[Brief explanation of the drawing]

FIG. 1 shows the X-ray spectrum of a titanium oxide fired product obtained by the method of the present invention, and FIG. 2 shows the X-ray spectrum of a titanium oxide pigment for comparison. Sub-Agents 1) Meifuku Agent Ryo Hagiwara − Sub-Agent Atsushi Anzai 2θ

Claims (2)

[Claims] (1) A method for producing a catalyst for removing nitrogen oxides, which comprises firing solized orthotitanic acid containing at least one compound selected from tungsten compounds and molybdenum compounds. (2) A sol-formed orthotitanic acid containing at least one compound selected from a tungsten compound and a molybdenum compound is fired, and a catalytic active component for removing nitrogen oxides is supported on the resulting fired product. Method for producing a catalyst for removing nitrogen oxides