JPS63119850A - Catalyst for cleaning up exhaust combustion gas - Google Patents

Abstract

PURPOSE:To efficiently remove CO, hydrocarbon, NOX, etc., in exhaust combustion gas by depositing a metal, metal oxide or metal salt on a carrier essentially consisting of zeolite thereby forming a catalyst for cleaning up the exhaust gas. CONSTITUTION:The metal or metal oxide or metal salt is deposited on the carrier essentially consisting of the zeolite of type A or X consisting of the sodium salt of alumino silicate (alumina silicate) to form the catalyst for cleaning up the exhaust combustion gas. The more specific example of the metal salt, etc., to be deposited includes simple substance metals such as Cu, Ni and Cr, metal oxides such as Fe2O3 and CuO or metal salts such as CuSO4, CuCl2 and LiCl. The catalyst permits dry NO2 cleaning-up of high activity simultaneously with the oxidation cleaning-up of CO and HC which are harmful components in the exhaust combustion gas of the atmosphere where oxygen exists.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a dry combustion exhaust gas purification catalyst that purifies nitrogen oxides, carbon oxides, unburned hydrocarbons, etc. contained in combustion exhaust gas in which oxygen coexists. It is related to.

Conventional technology The exhaust gas emitted from combustion equipment contains carbon dioxide (
co□), water (N20), nitrogen (N2), oxygen (0□
), -carbon oxides (CO), unburned hydrocarbons (fuel and its decomposition products), or nitrogen oxides (No and NO□: collectively called NOx) It is included.

CO is extremely toxic, with lethal effects at concentrations of several hundred ppm. Further, nitrogen oxides, especially No2, are harmful to the human body and are said to be a factor causing various respiratory diseases.

However, if we try to make this rain sound harmless at the same time, CO
must be oxidized to CO2, so the atmosphere must be in excess of 02, while NO□ must be reduced to CO2.
(preferably up to N2), a 02-free atmosphere is required. In contrast to these contradictory conditions, actual combustion exhaust gas usually contains a few percent to ten-odd percent of 0°, and even if a catalyst such as a metal or metal salt is used, CO and unburned carbonization are present. Although complete oxidation of hydrogen is relatively easy, it has a completely opposite effect on the reduction of NO□. In order to solve this problem, conventionally, for example, as seen in three-way catalysts for automobiles, combustion conditions are controlled to an air ratio of around 1 so that there is almost no surplus 02,
Here, a method was adopted in which NOX was reacted with CO or hydrocarbons (for example, Masanobu Hoshita, Masaru Ichiyo; "Homogeneous Catalyst and Heterogeneous Catalyst" Maruzen (1983) P, 183-184).

The reaction is 2GO+ 2NO= 2GO□10N2 4GO+2NO= 4C0□+N2 NOx + He −) N + CO2+H20(
HC: Hydrocarbon) etc. Alumina (Mu1□0.) is used as a catalyst.
Platinum (pt) and palladium (Pd) were added to this as a carrier.
), rhodium (Rh), etc. are often used (for example, Tatsuo Yamanaka; “Method for treating nitrogen oxides using catalysts”, Bessatsu Kagaku Kogyo 17-14, Kagaku Kogyosha (19
73) P, 177-208).

Alternatively, industrially, ammonia (NH3) is used as a reducing agent.
There is a catalytic reduction method of NOx using etc.

eNo + 4NH= 5N +1H206NO+8
Methods of causing reactions such as NH=7N +12H202S 2 have been widely put into practical use, and various metals and metal oxides have been proposed as catalysts (
For example, edited by the Air Pollution Research Association; ``Air Pollution Handbook (4) Combustors'' (1988), p. 258-266).

Problems to be Solved by the Invention In the above conventional method, the conditions under which an effective reaction can occur are limited to an extremely narrow range in the former (three-way catalyst method), and in order to satisfy this condition, the air and air during combustion are The fuel ratio needs to be tightly controlled. In the case of automobiles, this is actually controlled using equivalence ratio combustion (air ratio = 1
) However, since there is an excess of air in a general combustor, a large amount of 0□ remains in the exhaust gas, and even with this catalyst, it is impossible to completely process harmful gases. there were. On the other hand, in the latter (reduction method), the supplied reducing agent reacts with NOx to render it harmless.

Although CO and hydrocarbons contained in the exhaust gas can also be purified by acting as a reducing agent, it is necessary to supply the reducing agent, and in order to cause an effective reaction, the reducing agent must be supplied in excess. There is a risk of secondary pollution due to chemical leakage. Or GO or He for NOx
If they are present in excess, they are directly exhausted and purification of the exhaust gas cannot be completed. When the reducing agent is NH, even in an atmosphere where 02 coexists, the supplied NH,
selectively reacts with NOx and renders it harmless, but NH,
In general, reducing agents preferentially react with oxygen in the exhaust gas, except in cases where the reducing agent reacts preferentially with the oxygen in the exhaust gas, so a huge amount of reducing agent is required to treat combustion exhaust gas with an oxygen concentration of several percent.

Furthermore, the equipment also becomes larger due to the addition of a reducing agent supply means.

It is not suitable for small exhaust gas generating equipment (for example, household combustion equipment).

The present invention overcomes the above-mentioned conventional drawbacks, and eliminates the need for supply of reducing agent or strict control of combustion conditions, and allows the production of GO1 hydrocarbons in exhaust gas in the presence of oxygen in a dry process.

The present invention provides a catalyst that makes it possible to remove harmful motions such as NOx.

Means for Solving the Problems The technical means used in the present invention to solve the above-mentioned conventional problems consists of a combustion exhaust gas purifying catalyst in which a metal, a metal oxide, or a metal salt is supported on zeolite. It is.

Function The present invention purifies NOx (particularly NO□) and aO1 hydrocarbons (HCj) that are selectively adsorbed on the zeolite carrier by reducing or oxidizing them, respectively, by the action of supported metal salts, etc., by the above-mentioned means. It is something to do. That is, zeolite is composed of crystalline aluminosilicate hydrated metal salt, and has a basic composition of M2. nO・mu120.・xsio□・7H2
For example, synthetic zeolites Molecular Sheep 4M and Molecular Sheep 13X are represented by the following formulas.

4m: Na1□ [cm102), 2 (SiO□), 2]
・2TH2013X: Na, 6 ((mu10°), 6
(Sin□),. 6) a276 H2O The metal cations (here, Na ions) present in the crystal lattice act to electrostatically attract the negative terminals of polar molecules,
In a multicomponent system in which any molecule can enter the pores, molecules with stronger polarity (larger dipole moment) will be more strongly adsorbed. The dipole moment of the main molecules is 0
□=0, whereas Co=Q, 112, N0=0.
158. No2=0.316 is given and C unit:
(115b76, Nippon Kagaku Kinsen; "Chemical Handbook Basic Edition ■'", Maruzen (1968), P, 1227).As is clear from these values, the adsorption surface of zeolite is
O, Co, and No□ act to displace 0□ and are adsorbed, and therefore, even though the exhaust gas coexists with 0□, an atmosphere is maintained on the zeolite surface as if 0□ were absent. If a metal or a metal salt is used here, due to its catalytic action, some of the carbon is
An oxidation/reduction reaction between O or He and NOx purifies both of them, or even in an atmosphere with excess NOx, a reaction occurs in which NO2, which is more strongly adsorbed, is decomposed into NO and 02, which have weaker adsorption power, and is discharged. It becomes possible. Thus 0□
In the exhaust gas where there is an excessive amount of G
o, H(, NOx (especially No2) are both Co
HO, No (or up to N2.0□) will be purified.

Examples Examples of the present invention will be shown below. A dry mixed gas was used as the reaction gas, and the ratio was set to 0□=6 to match the combustion exhaust gas.

GO□=10%, CO=O~200ppm, N
.

20~1100pp, NO□=o~10opp! 11
The balance is N2. Space velocity (s
v) was reacted at 2000011''.

Example 1 Commercially available Molecular Sheep 6mu (Mu type zeolite)/Na
-Ca type) 1/16 inch (diameter) pellet with oxidized steel (
GO=100p on a catalyst supporting 6% by weight of CuO)
pII, No = 50 ppml, go2 = 8
The reaction was carried out at 500° C. by passing a mixed gas of 0 ppm.

Example 2 Commercially available Molecular Sheep 4M (Mu type zeolite/N&
mold) 1/16 inch (diameter) pellet with oxidized steel (CuO
A gas having the same composition as in Example 1 was passed through a catalyst supporting 6% by weight of ) to react at soo°C.

Example 3 Commercially available Molecular Sheep 13x (X-type zeolite/N
a type) 1/16 inch (diameter) pellet copper oxide (CuO
A gas having the same composition as in Example 1 was passed through a catalyst carrying 5% by weight of 5% by weight of 20% by weight, and the reaction was carried out at tso o'C.

Example 4 Commercially available Molecular Sheep 13X (X type zeolite/N
type a) 1/16 inch (diameter) pellet with cupric chloride (
A gas having the same composition as in Example 1 was passed through a catalyst supporting 6% by weight of CuC1□) to react at 500°C.

Example 6 Chromium chloride (0r
C1,) was supported at 6% by weight, and the reaction was carried out under the same conditions as in Example 4.

Example 6 Lithium chloride (L
iC1) was supported at 6% by weight and reacted under the same conditions as in Example 4.

Example 7 Catalyst of Example 4 (CuCl2/Molecular Sheep 13
x), GO=o, NO20, NO□=1oO
pp! A mixed gas of 1.0 liters was passed through the reactor, and the reaction was carried out at soo'c.

Example 8 In the above Example 6, GO=100ppI11,
5 by contacting the mixed gas with No = O and No2 = O.
The reaction was carried out at 00'C.

Example 9 Under the same reaction conditions as in Example 4 above, only the carrier was
The reaction was carried out using a catalyst substituted with activated alumina (Mu1□03) from sheep.

The reaction results for the above 8 Examples are shown in the table below. The conversion rate in each reaction is a stable value after passing for 1 hour.

(Left space below) As seen in the results shown in the table above, when a metal salt exhibiting oxidizing activity is used in an oxidizing atmosphere in which 6% 0□ coexists, Although the oxidation reaction of Go proceeds relatively easily, purification of NO□ cannot be expected. However, when this is supported on zeolite, under the influence of the selective adsorption effect described above, the oxidation reaction of CO and the reduction reaction of N02 proceed simultaneously, making it possible to simultaneously purify harmful gases.

Moreover, unlike conventional three-way catalysts and ammonia reduction methods, as in Examples 7 and 8, it effectively acts on Go and NO□, each of which exists singly, without impairing the activity. Therefore, Go (and HC) in exhaust gas
Therefore, it is possible to provide a catalyst that can purify harmful components at a high efficiency at a relatively low temperature of 600°C, regardless of the abundance ratio of NO2 and NO2.

In Examples 1 to 3, the zeolite used as a carrier has a higher activity in the sodium type 4M and 13X than in the calcium (Ca) substituted type molecular sheep 5M. This is clear from the results (and other experimental results not shown), and this is due to the fact that the electrical adsorption ability of polar molecules is stronger in alkali metals than in alkaline earth metals. Therefore, in this method that utilizes electroselective adsorption of harmful molecules, high activity can be achieved by using Molecular Sheep 4 or 13x, which are sodium type zeolites.

In addition, the supported metal salts include copper (Cu) and nickel (
Metals such as Ni ), chromium (Or), diiron trioxide (Fe2O, ), and the oxidized steel used in Examples 1 to 3 (
Metal oxides such as sulfuric acid steel (Cu5O4) and various chlorinating agents (Curl□) used in the above examples.

Although various metal salts such as 0ral, , LiC1) can be prepared and used, transition metal halides, which have high activity at low temperatures, are more preferred. Especially CuC1
In □, the oxidation activity of CO reaches 100% at 600°C, and the reduction activity of NO□ also reaches 93~ (Example 4)
, has shown extremely excellent performance.

Moreover, although Cu C1□ alone is an unstable substance at high temperatures with a melting point of 498°C, it is stabilized by being supported on zeolite. That is, the metal ions in the zeolite lattice act electrically on CuC1□ here as well.

Even when heated to a temperature of 100°C in an air stream, it is maintained without causing any changes such as evaporation or oxidation.

In this way, the zeolite carrier not only contributes to the zoning of harmful gases, but also has the effect of stabilizing the supported metal salts.
This enables unprecedented selectivity, activity, and stability.

Effects of the Invention As described above, the present invention enables oxidative purification of CO and HC, which are harmful components, in combustion exhaust gas in an atmosphere where oxygen coexists, as well as highly active dry NO2 purification that does not require a reducing agent, which was previously not possible. Moreover, it is stable even when exposed to high temperatures.

It is possible to provide a catalyst for purifying combustion exhaust gas that is extremely effective in preventing air pollution and can be easily put to practical use.

Claims (3)

[Claims] (1) A combustion exhaust gas purifying catalyst in which a metal, metal oxide, or metal salt is supported on a carrier mainly composed of zeolite. (2) The catalyst for purifying combustion exhaust gas according to claim 1, wherein the carrier is mainly composed of A-type or X-type zeolite made of sodium (Na) salt of aluminosilicate (alumina silicate). (3) The combustion exhaust gas purifying catalyst according to claim 1 or 2, wherein a transition metal halide is used as the metal salt.