JPS63305940A - Catalytic body for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To prevent catalytic activity from being deteriorated with NOx by mixing a catalyst consisting of oxide shown in a specified general formula with MgO or oxide contg. MgO as a main component or calcining this mixture and forming a catalyst for purifying exhaust gas. CONSTITUTION:A catalyst consisting of oxide shown in a formula I (Ln shows at least one kind of element selected from among La, Ce, Pr and Na, M shows at least one kind of element selected from among Cr, Mn, Fe, Ni and V, A shows at least one kind of element selected from among Ca, Sr and Ba, 0<=x<=1, 0<=y<=1, delta shows defective number of oxygen) is formed. A catalytic body for purifying exhaust gas is obtained by mixing the catalyst consisting of oxide with MgO or oxide contg. MgO as a main component or calcining this mixture. In this catalytic body, its catalytic capacity is not almost deteriorated even in the atmosphere of exhaust gas contg. large amounts of steam and NOx.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention converts harmful gases such as Go and HC contained in the combustion exhaust gas of various combustion devices and internal combustion engines into harmless Co2. H2O
This invention relates to a catalyst body that can change NOx and also purify NOx under a reducing atmosphere.

BACKGROUND OF THE INVENTION Conventionally, noble metal catalysts such as Pt and Pd, and oxide catalysts such as CuO, MnO2, and Ga2O3 have been used as catalysts of this type. 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 degrading atmosphere of Go, HC, etc., but is expensive. The latter is easily reduced at high temperatures and in a reducing atmosphere, reducing the catalytic activity, so Go is mainly used in the presence of an acid curtain.
It is used as an oxidation catalyst 37, -7° for , HC, etc. On the other hand, Lnl-xAx
The co4 yMy05B-based oxide catalyst has high oxidation activity for Go, HC, etc., is resistant to reduction even at high temperatures and in a reducing atmosphere, and can purify NOx in a reducing atmosphere. It is an oxide catalyst that is cheaper than precious metals.

Problems to be Solved by the Invention In the oxide catalyst represented by the general formula Ln1xAxCO1yMy03-δ, human alkaline earth elements easily convert into nitrates in an exhaust gas atmosphere containing a large amount of water vapor and NOx, and the catalytic ability decreases. descend.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides the general formula Ln1
XAXcoj-yMyo3-δ (Ln is La, Ce
, Pr.

At least one element selected from Nd, A is Ca.

At least one element selected from Sr and Ba, M is O
At least one element selected from r, Mn, Fe, Ni, and V, ○iX≦1. MgO or an oxide containing MgO as a main component is mixed or calcined with an oxide catalyst represented by ○y<1, δ is the number of oxygen vacancies).

Function: In the catalyst of the present invention, MgO acts as a basic site.
Q: Absorbs NOx in the atmosphere up to temperatures close to ○°C, and decomposes and returns to its original state at temperatures above 400°C. For this reason, M
By mixing or firing with an oxide whose main component is gO or MgO, the catalytic activity of the oxide catalyst is prevented from decreasing due to NOx.

Example In this example, LaO, 5Sro, 5Coo 3-
A case where an oxide consisting of δ is used will be described. La
O,5Sr O,5Coo 3-δ is precipitated as a mixture of metal oxalate and metal hydroxide using a solution containing the metal salts of each component and a mixture of oxalic acid, amines or caustic alkali, 800 in air after filtration, washing and drying
It was created by firing at ℃ for 10 hours.

MgO was mixed with the above oxide catalyst at a weight ratio of 7:3, and the mixture was supported on a carrier made of metal Ni foam to prepare a measurement sample.

As a characteristic evaluation of the catalyst body, the catalyst body was placed in a tubular electric furnace 5-・-
・ Place it in a quartz glass tube passed through the tube, set the temperature to 300℃, and add CC02opp, NOlsOppm, and H2O7%.
The oxidation rate of CO was measured by sending kerosene stove combustion exhaust gas. In addition, as a cycle life test, while sending kerosene stove exhaust gas with the same composition as above, the temperature of the catalyst body was alternately maintained at 300 ° C for 3 hours and at 6Q○ ° C for 1 hour, and this was carried out 500 times as one cycle. The CO oxidation rate at 300°C for each cycle was measured.

For comparison purposes, a similar test was also conducted on a catalyst body in which La O, 5Sr O, 5Co O3-δ prepared by the same method was supported on a metal N1 foam of the same weight.

Figure 1 shows Go 20 ppm and NOX 50 ppm.
, kerosene stove combustion exhaust gas containing 7% H2O
The measurement results of the CO oxidation rate when continuously fed to the catalyst body set at 00'C are shown. From this result, it was confirmed that by mixing MgO, the catalytic performance did not deteriorate even if the catalyst was left in an exhaust gas atmosphere containing water vapor and NOx for a long time. In addition, the catalyst body mixed with MgO whose catalytic ability had decreased was left at room temperature for one day, and the CO oxidation rate at 300° C. was measured at 6 H. As a result, recovery of the catalytic ability was observed. This is Mg
This is because the basicity of O pulls out NO2+ and NO3- from the portions that have been damaged by NOx.

In Figure 2 (1020ppm, No) (50ppm
, shows the change in CO oxidation rate at 300°C in a 500 cycle life test in which kerosene stove combustion exhaust gas containing 7% H2O was sent and the catalyst body was alternately held at 300°C for 3 hours and 600°C for 1 hour. From this result, by mixing MgO, the amount of MgO that has absorbed NOx is 600
NOx of the oxide catalyst to completely return to the original MgO at ℃
It was observed that there was very little decrease in catalytic ability due to

Furthermore, in a NOx reduction test under a reducing atmosphere, Mg
Regarding the catalyst body mixed with O, La O, 5Sr Q,
It was observed that the catalyst reduced NOx similarly to the catalyst containing only 5 Coo 5-δ.

A catalyst body in which a catalyst mixed with MgO is supported on a ceramic carrier such as cordierite or mullite is heated in air at 60Q°C.
After heat treatment for 00 hours, the oxidation rate of 7/-7° CO was measured at 300°C, and there was almost no decrease in catalytic performance. This is Lao, 5 Sr o, s Coo
With a catalyst containing only 3-δ, CO reacted with 5102 and Ag2O3, resulting in a decrease in catalytic performance, but with a catalyst containing MgO, MgO reacted with the catalyst with 5102 and kA! This is to prevent reaction with zos.

As described above, the catalyst body for exhaust gas purification according to the present invention shows almost no decrease in catalytic performance even in an exhaust gas atmosphere containing a large amount of water vapor and NOx, and still maintains a temperature of 600°C, which is easily obtained even with general combustion equipment. It is a catalyst body that can be regenerated at temperatures that can be used.

Furthermore, in the examples, only the case where Ln is La and A is Sr is described, but when La contains Ce, Pr, Nd or two or more of La, Ce, Pr, Nd, A is Ca, Ba or Sr. , Ca, and Ba, M is Or.

Similar effects were obtained with oxidation catalysts containing Mn, Fe, Ni, V, or two or more thereof.

Further, although only the case where the metal N1 foam is used as the carrier has been described, the same effect can be obtained even when a metal carrier containing Fe, Ti, or Ni, Fe, or Ti as a main component is used.

When a PT group noble metal catalyst is added to such an oxide catalyst, it is possible to obtain the same level of catalytic performance with the addition of an extremely small amount of the PT group noble metal catalyst compared to a catalyst body using a conventional PI group noble metal catalyst. .

Effects of the Invention According to the present invention, by mixing or calcining an oxide catalyst represented by Ln1-xAxCO1-yMyO3-δ with an oxide containing MgO or Mho as a main component,
Even in an exhaust gas atmosphere containing a large amount of water vapor and NOx, the catalytic performance hardly decreases, and an inexpensive catalyst body can be obtained.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the stability of the CO oxidation rate with respect to exhaust gas containing water vapor and NOx at 300°C of the catalyst body of one example of the present invention, and Figure 2 is a characteristic diagram showing the stability of the CO oxidation rate with respect to exhaust gas containing water vapor and NOx of the catalyst body of an embodiment of the present invention.
Continuously send exhaust gas containing x to raise the catalyst temperature to 30
9 is a characteristic diagram showing the stability of the CO oxidation rate at 300°C when a cycle life test was performed in which the samples were held alternately at 0°C for 3 hours and 600°C for 1 hour. Name of agent: Patent attorney Toshio Nakao (1 or 1 person Figure 1)

Claims (4)

[Claims] (1) General formula Ln_1_-_xA_xCo_1_-_y
M_yO_3_-_δ (Ln is La, Ce, Pr, Nd
At least one element selected from A is Ca, Sr, Ba
At least one element selected from, M is Cr, Mn, Fe
, Ni, at least one element selected from V, 0≦x≦1
, 0≦y≦1, δ is the number of oxygen vacancies) and MgO or an oxide whose main component is MgO, mixed or fired. (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 whose main component is the metal. 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) The exhaust gas purifying catalyst body according to claim 1, 2, or 3, wherein at least one element from the Pt group is added.