JPH0283039A - Catalyst for nitrogen oxide removal - Google Patents

Abstract

PURPOSE:To provide a catalyst having a high denitrifying activity at a high temperature and a long lifetime for Nox removal by dispersibly depositing the zeolite having a specified ratio of Al2O3 to SiO2, together with the oxide of W and Ce, on TiO2-SiO2. CONSTITUTION:The subject catalyst includes the oxide of W and/or Ce and Sn and the zeolite having the value of the ratio of Al2O3 to SiO2 not less than 8 in addition to the binary oxide of Ti and Si and/or the ternary oxide of Ti, Zr and Si in such proportions that the catalyst comprises the ternary oxide of 50-90wt.%, the oxide of W, etc., of 0.5-10wt.% and the zeolite of 5-50wt.% and that the binary and/or ternary oxide comprises Ti of 40-95wt.% and Si and/or Zr of 5-60wt.%. The catalyst prepared in this way has a high denitrifying activity at a temperature as high as 400 deg.C, capable of removing Nox for a long period of time with higher efficiency.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a catalyst for removing nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas discharged from boilers, gas turbines, diesel engines, and various industrial processes. Regarding.

In particular, the present invention adds ammonia as a reducing agent to exhaust gas containing NOx, and improves efficiency at high temperatures of 400°C or higher.
This invention relates to a highly durable catalyst that reduces x to harmless nitrogen and water.

<Prior art> Currently, there are 1 methods for removing NOx from exhaust gas.
Selective catalytic reduction methods that use ammonia as a reducing agent have become mainstream because NOx can be selectively removed even from exhaust gas containing 4 concentrations of oxygen, and a small amount of reducing agent is required, making it economical.

Many catalysts have been proposed for use in selective catalytic reduction methods using ammonia as a reducing agent, in which oxides such as vanadium, copper, tungsten, molybdenum, and iron are supported on carriers such as alumina, silica, zeolite, and titanium oxide. Among them, catalysts whose main component is titanium are not affected by SOx in exhaust gas, and
It is now widely put into practical use because of its low ability to oxidize from to S03. On the other hand, some exhaust gases, such as gas turbine exhaust gas and diesel engine exhaust gas, have exhaust gas temperatures exceeding 500°C, and catalysts for treating NOx in these high-temperature exhaust gases are disclosed in Japanese Patent Application Laid-Open No. 55-167044 and This has already been disclosed in Publication No. 127426/1983.

<Problems to be solved by the invention> However, at higher temperatures than the catalyst 4 described in the above publication, the oxidation (or decomposition) reaction of ammonia occurs at the same time as the reduction of NOx, so the denitrification activity is not sufficient. However, there are also problems with heat resistance, and the current situation is that it is by no means satisfactory as a practical catalyst.

<Object of the present invention> An object of the present invention is to provide a catalyst that has high denitrification activity at high temperatures of 400° C. or higher and can efficiently remove NOx over a long period of time.

Means for Solving the Problems> The present inventors have completed the present invention as a result of intensive studies to achieve the above object.

That is, the present invention uses titanium (Ti) and silicon (S) as a catalyst for catalytically reducing nitrogen oxides in exhaust gas by reacting them with ammonia at a temperature of 400 to 700°C.
i) and/or titanium (T
i), a ternary oxide consisting of zirconium (Zr) and silicon (Si) is used as the catalyst A component, and tungsten (
The catalyst B component is an oxide of at least one element selected from the group consisting of W), cerium (Ce), 15, and tin (Sn), and aluminum oxide (Aj!203
) contains a zeolite containing a ratio of silicon oxide (Si 02 ) to 8 or more as the tsC component, the catalyst A component is 50 to 95% by weight, and the catalyst component is 0.5% by weight.
~10 wt ω% and the catalyst C component is in the range of 5 to 50 wt%, and furthermore, the composition of the catalyst A component is 40 to 95 wt% of titanium (■1), silicon (Si) and /
Alternatively, the present invention provides a catalyst for removing nitrogen oxides, characterized in that the content of zirconium (Zr) is in the range of 5 to 60% by weight. The present inventors have developed a binary composite oxide consisting of titanium and silicon (hereinafter abbreviated as Ti 02-8i 02) and a ternary composite oxide consisting of titanium, zirconium and silicon (hereinafter referred to as Ti 02-Zr 02).
-8i 02) as a main component is proposed in Japanese Patent Application Laid-open No. 122293. In addition, a ternary composite oxide consisting of titanium, phosphorus, and silicon (hereinafter abbreviated as Ti 02-P205-8i 02) and a quaternary composite oxide consisting of titanium, phosphorus, zirconium, and silicon (hereinafter referred to as Ti 02 -P20s -Z
A catalyst containing r02-8i02 as a main component has already been proposed in JP-A-57-127426.

The present inventors attempted to improve the denitrification activity of the above catalyst in the high temperature range, and found that TiO28102, Ti
02-Zr 02-8i By dispersing and supporting 02 with oxides such as tungsten, cerium, tin, etc., and further with zeolite having a ratio of SiO2 to A1203 of 8 or more, the denitrification activity is surprisingly significantly improved. It has been found that the denitrification activity is significantly improved at high temperatures of 400° C. or higher, and at the same time, the heat resistance is also significantly improved. The effect of the high-temperature activity improvement vIWJ of the catalyst of the present invention is not clear at present, but it is speculated as follows.

Catalyst A component molecular Al Ti 02-3i 02 OJ:UT
i 02-Zr 02-8i 02 as a solid acid.

It is well known that zeolides exhibit remarkable acidity that is not found in the individual oxides that they constitute, and that they also have a high specific surface area, while zeolides also have a large specific surface area and exhibit properties as solid acids. However, as with the catalyst of the present invention, <Ti
02-8i 02 and TiO2-Zr 02-8i
By adding zeolite to 02, the acidity of the finished catalyst can be optimally controlled and a favorable acid distribution can be obtained.As a result, NOX of NHs, which is said to normally occur at high temperatures of 400°C or higher, especially 450°C or higher, can be controlled. It is considered that the oxidation to N2 (or decomposition to N2) is suppressed as much as possible, and therefore the denitrification activity is significantly improved.

Ti 02-8i 02 or Ti which is catalyst A component
02-Zr 02-8i If the content of 02 is less than 50% by weight, the heat resistance will deteriorate, and if it exceeds 95% by weight, the
Since oxidation (or decomposition) of NH3 occurs at temperatures above .degree. C. and the denitrification activity decreases, in the present invention, the ratio of the catalyst A component to the total catalyst is preferably 50 to 95% by weight.

The composition of catalyst A component is 40-95% titanium in atomic percentage.
The content of silicon and/or zirconium is preferably in the range of 5 to 60%, and the specific surface area is 30 TIt/(1 or more, especially
50 nt/Q or more is preferable.

If the catalyst B component is less than 0.15% by weight, the denitrification activity will decrease, and if it exceeds 10 times, the denitrification activity cannot be expected to improve much, and the raw material cost of the catalyst will increase.
~10% by weight is preferred.

Also, touch! , the zeolite which is the C component is S1ω/
If the Δ1203 ratio is less than 8, SOx and Al2O3 in the exhaust gas
It is preferable that the Si 02 /Al2O3 ratio is 8 or more because not only does the structure of the Si 02 /Al2O3 ratio react, but the denitrification performance is also low.

Examples of the zeolite include mordenite, ferrierite, and ZSM-5. If the zeolite content is less than 5% by weight, the denitrification activity will be low, and if it exceeds 40% by weight, the heat resistance will be poor, and the moldability will also be poor.
A range of 40% by weight gives preferred results.

In order to prepare Ti 02-3i 02 used in the present invention, it is first necessary to select a titanium source from inorganic titanium compounds such as titanium chlorides and titanium sulfate, and organic titanium compounds such as titanium oxalate and tetraisopropyl titanate. The silicon source can be selected from inorganic silicon compounds such as colloidal silica, water glass, silicon tetrachloride, and organic silicon compounds such as tetraethyl silicate. Some of these raw materials contain trace amounts of impurities and contaminants, but this does not pose a problem as long as it does not significantly affect the physical properties of the Ti 02-8i 02 obtained.

A preferred method for preparing Ti 02-8i 02 includes the following method.

(2) A method in which titanium tetrachloride is mixed with silica sol, ammonia is added to form a precipitate, the precipitate is washed, dried, and then calcined at 300 to 650°C.

■ Add sodium silicate aqueous solution to titanium tetrachloride,
The reaction was carried out to form a precipitate, which was washed and dried for 300 min.
A method of firing at ~650°C.

■ Add ethyl silicate [(C21-1s 0)4Si ] to a water-alcohol solution of titanium tetrachloride to cause a hydrolysis reaction to form a precipitate, which was washed and dried for 30 minutes.
A method of firing at 0 to 650°C.

(2) A method in which ammonia is added to a water-alcohol solution of titanium oxide chloride (Ti OCj!2) and ethyl silicate to form a precipitate, which is washed and dried and then calcined at 300 to 650°C.

Among the above preferred methods, method (2) is particularly preferred, and this method is specifically carried out as follows. That is, the titanium source and silicon source compounds are replaced with Ti.
The molar ratio of 02 and SiO2 is set to a predetermined amount, and the concentration of titanium and silicon in terms of oxides is 1 to 100 (1/j!) in an acidic aqueous solution or sol state.
Keep at ~100℃.

Aqueous ammonia was added dropwise as a neutralizing agent to the mixture while stirring, and 1
A coprecipitated compound consisting of titanium and silicon is formed at pH 2 to 10 for 0 minutes to 3 hours, separated by filtration and thoroughly washed, and then dried at 80 to 140°C for 1 to 10 hours.
T02-8i 02 is obtained by firing at 700° C. for 1 to 10 hours.

In addition, Ti 02-Zr 02-3i 02 is prepared in the same manner as Ti 02-3i 02, and zirconium chloride, zirconium chloride,
It can be selected from inorganic zirconium compounds such as zirconium sulfate and organic zirconium compounds such as zirconium oxalate.

That is, by treating a zirconium compound together with a titanium compound in the same manner as in the above method, Ti02Zr02
-8i 02 is easily prepared. And the existence range of this zirconium is TlO2+Zr 02 +
It is preferably within a range of up to 30% by weight in terms of zrO2 based on the total amount of Si02.

Next, Ti 02-8i 02 and Ti 02-
Starting materials for other catalyst components used together with Zr 02-8i 02 are appropriately selected from oxides, hydroxides, ammonium salts, silicates, halides, and the like.

An example of the method for preparing the catalyst of the present invention is to obtain a solution containing tungsten by adding a solution obtained by dissolving ammonium paratungstate to an aqueous solution containing monoethanolamine. Next, the Ti 02-8i02 powder and zeolite powder obtained by the above method are added to the obtained aqueous solution together with a molding aid, mixed and kneaded, and molded into a honeycomb shape using an extrusion molding machine. After drying the molded product at 50-120°C, it is heated at 400-100°C, preferably SOO-650°C for 1
The catalyst can be obtained by calcination in a stream of air for ~10 hours, preferably 2-6 hours. Alternatively, TiO2-5
iO2 powder and zeolite powder are made into a two-cam shape in advance,
A method of impregnating this with an aqueous solution containing tungsten and supporting it can also be adopted. It is also possible to use a coarse carrier. Examples of carriers that can be used include alumina, silica, silica alumina, bentonite, diatomaceous earth, silicon carbide, titania, zirconia, magnesia, copillite, mullite, pumice, and inorganic fibers. For example, granular silicon carbide and Ti
02-8i It can be prepared by making a slurry of 02, zeolite powder, and the catalyst component described above, and supporting the slurry by an impregnation method. Of course, the catalyst preparation method is not limited to these methods.

The shape of the catalyst is not limited to the above-mentioned honeycomb shape, but can be appropriately selected such as columnar, cylindrical, plate, ribbon, corrugated sheet, pipe, donut, lattice, and other integrally molded shapes. can.

The composition of the exhaust gas to be treated using the catalyst of the present invention is usually SOx O to 3000 ppm.

Oxygen 1-20% by volume, carbon dioxide 1-15% by volume, water vapor 5-15% by volume, soot 11-30% (+/N) and NOx (mainly NO) 20-11000pp
It contains to the extent of. Normal boiler exhaust gas falls within this range, but the gas composition is not particularly limited. This is because the catalyst of the present invention can also treat special exhaust gases such as NOXI-containing gas that does not contain SOx and NOX-containing exhaust gas that contains halogen compounds.

In addition, the processing conditions vary depending on the type and properties of the exhaust gas, but first, during the addition of ammonia (NH3), NOx
It is preferably 0.5 to 3 parts per part. For example, in the exhaust gas composition of a boiler, most of the NOx is No, so a molar ratio of No and NH3 of around 1:1 is particularly preferable. This is because care must be taken not to discharge excess NH3 as an unreacted component. Furthermore, if it is necessary to suppress unreacted NH3 as much as possible, NH3/NOx
It is preferable to use the molar ratio of 1 or less. Next, the reaction temperature is preferably 300 to 700°C, particularly 400 to 650°C, and the space velocity is 1000 to 100000 hr".
In particular, a range of 3000 to 30000 Hr-1 is suitable. The pressure is not particularly limited, but is preferably in the range of 0.01 to 10 kO/cj.

The type of reactor is not particularly limited, but common fixed bed, moving bed, fluidized bed, and other reactors can be used.

The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 Ti 02-8i 02 was prepared by the method described below.

Titanium tetrachloride (Ti Cj!4) in 80 Jl of water 11.
4 kg was added dropwise to each body under water-cooling and stirring, and then 2
Added 4.5k (l) (containing 0 to 21%). While maintaining the temperature at 30°C and stirring well, ammonia water was gradually added dropwise until the pH reached 7, and then left as it was. and aged for 2 hours.

The thus obtained Ti 02-8i 02 gel was filtered, washed with water, dried at 120°C for 10 hours, further washed with water, and then fired at 600°C for 3 hours. The composition of the obtained powder is Ti 02 /Si 02 = 4 (molar ratio) as an oxide.
So, the BET surface area is 18G? 7f/! It was II.

The powder obtained here is hereinafter referred to as TS-1.

Monoethanolamine 21ai! was mixed with water 210Id, and ammonium paratungstate 58.3σ
Add and dissolve to make a homogeneous solution. Furthermore, this solution was mixed with the above powder (T 5-1) 6500 and Toyo Soda H
Type zeolite TSZ620HOA (Si 02 /A
1203=10) In addition to 300a, the mixture was thoroughly mixed and kneaded using a kneader while adding an appropriate amount of water, and then molded into pellets with a diameter of 4 sφ and a length of 5 trta L using an extrusion molding machine. It was then dried at 60°C and fired at 600°C for 5 hours under air circulation. The content of TS-1, H-type zeolite and WO3 in the obtained finished catalyst was 6% by weight, respectively.
They were 5%, 30%, and 5%.

Example 2 Titanium tetrachloride 11.41 (g, zirconium acid chloride [Z
Ti 02-Zr 02-8i 02 was prepared according to Example 1 except that r 0Cf2-8t-42071,2Kg and Snowtex-03,4Kg were used. The composition of the obtained powder was Ti 02 :Zr as an oxide.
O2:Si02 =80:5:15(T-/L/
ratio) and the SET surface area was 210Td/(l. The obtained powder was called TZS-1, and this TZS-
A catalyst having a similar composition was prepared in the same manner as in Example 1 using No. 1. The content of ZS-1, H-type zeolide and WO3 in the obtained finished catalyst was 65% by weight, respectively.
They were 30% and 5%.

Examples 3 to 7 Ti 02-8i 02 powder obtained in Example 1 (TS
A catalyst was prepared according to Example 1 using WO3, Ce 02 , Sn 02 and H-type zeolite using 1). The resulting catalyst composition, expressed in fiffi%, is as follows.

Comparative Examples 1 to 3 Ti 02-8i 02 powder obtained in Example 1 (T
A catalyst was prepared according to Example 1 using 5-1) and changing the composition of WO3 and H-type zeolite.

The resulting catalyst composition, expressed in m%, is as follows.

The denitrification rate was determined for each catalyst of Examples 1 to 7 and Comparative Examples 1 to 3 by the following method.

Touch 120. ml! 116. A quartz reaction tube was filled, and a synthesis gas having the following composition was introduced into the catalyst layer. The NOx concentration before and after the reactor was measured using a chemiluminescent NOx meter (model ECL-77A) manufactured by Yanagimoto Seisakusho, and the denitrification rate was calculated according to the following formula.

Denitrification rate (%) = Inlet NOx concentration - Outlet NOx concentration Reaction gas condition gas ffi 3.33 N 1 /
1lin space velocity a (SV) 100OO
Hr -1NH3/NOX (molar ratio) 1.0 Gas composition N Ox 100100pp 1
5% 802 200ppm) 120 10% N2 The results are shown in Table 1.

Further, a heat resistance test was conducted on each of the catalysts of Examples 1, 5.6 and Comparative Example 1.3 using the following method.

Heat exposure was performed at 500°C using an electric furnace, and changes in the denitrification rate at 500°C with elapsed time were investigated. The results obtained are shown in Table 2.

Table (Denitrification rate %) Table 1 (Denitrification rate %) <Effects of the invention> The catalyst of the present invention has high denitrification performance at high temperatures of 400°C or higher and is a catalyst that can efficiently remove NOx for a long period of time. It is.

Claims (1)

[Claims] (1) Nitrogen oxides in exhaust gas together with ammonia
A binary oxide consisting of titanium (Ti) and silicon (Si) and/or titanium (Ti), zirconium (Zr) and silicon (Si) as a catalyst for catalytic reduction by reaction at a temperature of ~700°C The catalyst A component is a ternary oxide consisting of tungsten (W), cerium (C
e) and an oxide of at least one element selected from the group consisting of tin (Sn) as the catalyst B component;
The catalyst C component is a zeolite containing SiO_2) at a ratio of 8 or more, and the catalyst A component is 50 to 95% by weight, the catalyst B component is 0.5 to 10% by weight, and the catalyst C component is 5 to 50% by weight. Furthermore, the composition of the catalyst A component is 40 to 95% by weight of titanium (Ti) and 5 to 95% of silicon (Si) and/or zirconium (Zr) in atomic percentage.
A catalyst for removing nitrogen oxides, characterized in that the content is in the range of 60% by weight.