JPS63158132A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To perform regeneration at low temp. while reducing the lowering in catalytic capacity, by substituting the specific element of an oxide particle represented by a specific general formula with Ni and mixing the substituted particle with MgO or oxide based on MgO or baking the resulting mixture. CONSTITUTION:A catalyst for purifying exhaust gas is formed by mixing an oxide catalyst, wherein the A-element of oxide represented by formula I (wherein A is at least one element selected from among Ca, Sr and Ba, Me is at least one element selected from among Mn, Cr, V and Fe, 0<=x<=1 and 0<=y<=1) is substituted with Ni, with MgO or oxide based on MgO or baking the resulting mixture. This catalyst for purifying exhaust gas is pref. formed by supporting the aforementioned oxide catalyst by a carrier composed of at least a metal selected from among Ni, Fe and Ti or an alloy based thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention converts harmful gases such as Go and HC contained in the exhaust gas of various combustion devices and internal combustion engines into harmless Co2 and H2O, and also converts them under a reducing atmosphere. No. 2 also concerns a catalytic body that can be purified.

Prior Art Conventionally, as this type of catalyst, noble metal catalysts such as Pt and Pd, and oxide catalysts such as Cu 2 O and M n O 2+ Co 304 have been used. The former is used as a three-way catalyst in an automobile exhaust gas purification catalyst and can perform NOx purification in an oxidizing or reducing atmosphere of Co, HC, etc., but is expensive. The latter is easily reduced at high temperatures and in a reducing atmosphere, reducing the catalytic activity, so Co,
It is used as an oxidation catalyst for HC, etc. On the other hand, the La1-ACol-yMyO,a-based oxide catalyst
It has high oxidation catalyst activity such as O, HC, is not easily reduced even at high temperatures and reducing atmosphere, and can purify No process in reducing atmosphere. Moreover, it is cheaper than noble metal catalysts such as Pt and Pd. It is an oxide catalyst.

Problems to be Solved by the Invention In oxides of the general formula La1-xAICol-, MyO3-, the alkaline earth element A easily converts into nitrate in an exhaust gas atmosphere containing a large amount of water vapor and No. catalytic performance decreases. In addition, when regenerating the catalyst, heating the nitrate to denitrify it will reduce the amount of Co in the atmosphere.
Since it is converted into carbonate by two gases, it requires a long-term high-temperature treatment comparable to the catalyst synthesis conditions.

Means for Solving the Problems In order to solve the above problems, the present invention replaces the element in La1-airAlCo1-yMyO3-δ-based oxide with Ni, and further uses MgO or MgO as the main component. A protective layer made of MgO was formed by mixing it with an oxide of MgO or by firing it.

Function: In the catalyst body according to the present invention, MgO acts as a base site,
It absorbs NOx in the atmosphere up to temperatures close to 400°C and produces nitrates or basic nitrates, but it decomposes and returns to its original state at temperatures above 400°C. For this reason, an oxide catalyst having a protective layer mainly composed of MgO or MqQ is less likely to react with No. oxide in the atmosphere and less likely to produce nitrate.

Further, even if nitrate is generated in the oxide catalyst, the nitrate ion is extracted by the strong alkaline action of MgO.

This allows catalyst regeneration at low temperatures. However, La
1-xAxCol-yMyO3-δ-based oxide catalyst (7)
A's 7/lzIf there is a large amount of potassium earth elements, MgO
Since de-nitrate ions by MgO are less likely to occur, the alkaline earth elements were replaced with Ni to enhance the de-nitrate ion effect by MgO.

Example In this example, "0.35Sr0.66" 0.7Fe0.
A case will be described in which an oxide consisting of 303J is used.

LaO,35SrO,65"0.7Fe0.303-1
5 is precipitated as oxalate and hydroxide using oxalic acid, amines and sodium hydroxide in an aqueous solution containing each metal salt, filtered, washed, dried, and then calcined in air at 800°C for 10 hours. Created by The above oxide powder was mixed with N1 (N
It was dispersed in an aqueous O3)2 solution, and part or all of the Sr was replaced with Ni. The amount of replacement is the liquid temperature.

It can be changed by the amount of hydrogen peroxide added.

Thereafter, it was filtered, washed, dried, and heat-treated in air at 400° C. for 1 hour.

An oxidation catalyst in which Sr was replaced with Ni was mixed with MgO at a ratio of 8:2, and the mixture was supported on a carrier made of a metallic Ni foam to prepare a measurement sample.

For evaluation of the catalyst, the catalyst was placed in a quartz glass tube passed through a tubular electric furnace, and the temperature was set at 300°C.
The oxidation rate of Co was measured by sending an oil stove exhaust gas containing 60 ppm of NOx, 60 ppm of H2O, and 7% of H2O. In addition, a cycle test was conducted in which the temperature of the catalyst was held at 300°C for 3 hours and at 600°C for 1 hour, and the Co oxidation rate at 300°C was measured.

LaO, 35SrO, 66”0.7Fe0.3o3-J prepared in the same manner for comparison
A similar test was also conducted on an oxide catalyst in which the same weight was supported on a carrier made of metallic Ni foam in the same manner.

CC020pp for the 11th sword, No 50ppm,
The results of measuring the oxidation rate of Co when kerosene stove exhaust gas containing 7% H2 was continuously sent to a catalyst set at 300C are shown. From this result, it was confirmed that by providing a protective layer made of MgO, the catalytic performance did not deteriorate even if the catalyst was left in an exhaust gas atmosphere containing NOx and water vapor for a long time. Furthermore, the catalyst body with the MgO protective layer, which had decreased in catalytic ability, was left at room temperature for a day and night, and the Co oxidation rate at 300° C. was measured, and as a result, recovery of the catalytic ability was observed.

Figure 2 shows Co 20 ppm, No, 60 ppm.
A cycle test was conducted in which kerosene stove exhaust gas containing H2O7 was continuously fed, and the catalyst body was alternately held at 300℃ for 3 hours → eoo℃ for 1 hour.
o Changes in oxidation rate are shown.

It was found that by providing a protective layer made of MgO, the catalyst was almost regenerated at a temperature of 60Q°C, so that the decrease in catalytic performance was extremely small.

Furthermore, NO! Regarding reduction, the catalyst body with a protective layer made of MgO can be reduced by N in a C○ reducing atmosphere, similar to the oxide catalyst body consisting of "ao, 5sSro, es"o, 7"o, 303-δ only.
It was recognized that Ox was reduced.

A catalyst body in which a catalyst with an Mq○ protective layer was supported on a ceramic carrier such as cordierite or mullite was heat treated in air at 600°C for 100 hours, and the Co oxidation rate was measured at 300°C, but the catalytic performance decreased. was not recognized. This is La0.35” ro, 65 coo, 7 Fe
In the catalyst body consisting only of 0.303-B, Co is 3i or A.
Although the catalytic ability was reduced by reacting with S
MgO, which is a solid base for i, 02 and Al2O3
protects the catalyst.

As described above, the exhaust gas purifying catalyst of the present invention shows little decrease in catalytic performance even in an exhaust gas atmosphere containing a large amount of water vapor and NO, and can be easily obtained using general combustion equipment at 600°C. It is a catalyst that can be regenerated at temperature.

Furthermore, in the embodiment, the case where A is Sr and M is Fe is described, but the present invention is not limited to this. A is Ca, Ba, M is Mn,
Similar effects were obtained in the case of Cr and V.

Still, a metallic Ni foam was used as the carrier, but Fe.

Similar effects were obtained using Ti or a metal support mainly composed of Ni, Fe, or Ti.

By adding a noble metal of the PT group to such an oxide catalyst, it was possible to obtain the same level of catalytic performance as in the conventional PT group catalyst with the addition of an extremely small amount of the PT group element.

Effects of the Invention The present invention provides an oxide protective layer mainly composed of MgO or M(JO) on an oxide catalyst in which alkaline earth elements are replaced with Ni, so that MgO acts as a strong basic point,
In addition to preventing other metal oxides from turning into nitrates, the denitrification effect from nitrates is also stronger than Ni○, and therefore water vapor and N
The catalytic performance hardly decreases in response to exhaust gas containing a large amount of O-trium, and an inexpensive catalyst body can be obtained.

[Brief Description of the Drawings] Fig. 1 is a characteristic diagram showing the stability of the Co oxidation rate of a catalyst body according to an embodiment of the present invention with respect to exhaust gas containing water vapor and No Continuously sends exhaust gas containing No. It is a characteristic diagram showing the stability of the Co oxidation rate at 300° C. in a cycle test in which the temperature of the catalyst body was held at 300° C. for 3 hours and then held at 60° C. for 1 hour. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure HA Time M (static)

Claims (4)

[Claims] (1) General formula La_1_-_x_A_xCo_1_-_
yM_yO_3_-_δ (A is at least one element selected from Ca, Sr, Ba, M is M_n, Cr, V, F
At least one element selected from e, 0≦x≦1, 0≦y≦
A catalyst body for exhaust gas purification, which is an oxide represented by 1), which is obtained by mixing or calcining an oxide catalyst in which element A is replaced with Ni, with MgO or an oxide whose main component is MgO. (2) Claim 1, characterized in that the oxide catalyst is supported on a carrier made of a metal made of at least one element selected from Ni, Fe, and Ti, or an alloy made of the metal as a main component. Catalyst for exhaust gas purification. (3) The catalyst body for exhaust gas purification according to claim 1, characterized in that an oxide catalyst is supported on a ceramic carrier. (4) Claims 1, 2, or 3 are characterized in that at least one element of the Pt group is added.
Catalyst body for exhaust gas purification as described in .