JPS6128455A - Catalyst for purifying exhaust gas and its preparation - Google Patents

Abstract

PURPOSE:To obtain a catalyst excellent in durability and catalytic capacity at high temp. and easy to prepare, by dispersing fine nickel oxide particles between the particles of the noble metal component of a purification catalyst. CONSTITUTION:In a purification catalyst wherein a noble metal such as platinum or palladium is supported by a catalyst carrier having a honeycomb structure, fine nickel oxide particles are dispersed between the particles of the noble metal component such as platinum or palladium. The dispersion of said nickel oxide is performed by bringing the catalyst carrier with a noble metal component-containing solution, to which a soluble nickel salt was added, to impregnate the same with said solution. Thus obtained catalyst is excellent in durability and catalytic capacity at high temp. and easy to prepare.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a catalyst for purifying exhaust gas, and more specifically, to a catalyst for purifying exhaust gas.
The present invention relates to an exhaust gas purifying catalyst having extremely excellent decomposition performance for converting nitrogen oxides (NOx) into harmless substances, and a method for producing the same.

Traditional technology: Three types of harmful substances emitted from internal combustion engines: CO and H.
Platinum (pt)-rhodium (Rh)-based catalysts have been put into practical use as so-called three-way catalysts that simultaneously convert C and NOx into harmless substances. This removal method using a catalyst controls the ratio of air to fuel (A/F ratio) to near the theoretical fuel efficiency to remove Co, HC, and other substances contained in exhaust gas.
The three components of NOx are removed simultaneously when the exhaust gas passes through the catalyst. The A/F control used in this system is normally carried out by detecting the amount of oxygen in the exhaust gas and feeding it back to the electronic fuel injection system via a computer to accurately control the ratio of fuel and air. In addition, noble metals such as platinum and rhodium are mainly used as the catalytic active components of the three-way catalyst used in this method, and various transitions such as iron, nickel, cobalt, cerium, and lanthanum are used to improve the dynamic catalytic effect and heat resistance. Many are used to which metals are added. Such conventional catalysts are mainly manufactured by the following methods. For example, (a) a wash-coated catalyst carrier is coated with a transition metal such as nickel, and then impregnated with a noble metal. (b) First, the catalyst carrier is wash-coated with a solution containing alumina as a main component, and then impregnated with a solution of a soluble nickel salt, and then impregnated with a noble metal component.

<Problems to be Solved by the Invention> Conventional purification catalysts exhibit suitable durability when used at relatively low temperatures, e.g., 500°C or lower, but when used at high temperatures, e.g., 700°C or higher, is becoming very heated.

There are also limits to catalyst performance. Furthermore, the manufacturing process is complicated and expensive.

Means for Solving the Problems> The present invention solves the above problems and provides an exhaust gas purifying catalyst that has excellent durability and catalytic performance under high temperatures and is easy to manufacture, and a method for manufacturing the same. The exhaust gas purification catalyst has a structure in which at least one of the noble metal components platinum, palladium, and rhodium is supported on a catalyst carrier having a honeycomb structure, and fine nickel oxide particles are present between the particles of the noble metal component. It is characterized by having particles dispersed therein, and its production method consists of: When at least one of the noble metal components of platinum, palladium, and rhodium is supported on a catalyst carrier having a honeycomb structure, a solution containing the noble metal component is prepared. A soluble nickel salt is added therein, the catalyst carrier is brought into contact with an iron solution to impregnate each component in the solution at the same time, and then heat treated.

As described above, the catalyst of the present invention has platinum (p
t) Precious metal components such as palladium (Pd) and rhodium (Rh) and soluble nickel salt are simultaneously impregnated and supported, and fine particles are formed between the supported noble metal components.

It is characterized by supporting nickel oxide with good dispersibility, and if necessary, it is impregnated with noble metal components and soluble cerium salts in addition to soluble nickel salts in order to increase heat resistance.

As mentioned above, the present invention uses noble metal components such as platinum, palladium,
In order to disperse fine nickel oxide between the noble metal component grains of rhodium, soluble N is added to the solution containing these noble metal components.
Use a solution to which i salt has been added. A wash-coated honeycomb structure catalyst carrier is brought into contact with the iron solution by immersion, etc., to impregnate the above-mentioned components simultaneously.

Here, the amount of the soluble nickel salt added is nickel oxide (
NiO) equivalent amount, 0.1 to 5 relative to the precious metal component.
About twice the molar amount is preferable. Addition of nickel at a molar ratio of 5 times or more to the noble metal does not produce any further effect, and is, on the contrary, unfavorable from the standpoint of heat resistance.

If the amount is less than 0.1 mole, the amount of nickel oxide is too small to fully exhibit the desired effect.

Furthermore, in the solution containing these precious metal components and soluble nickel salt, the total weight of the precious metal and the equivalent amount of nickel oxide! l
) It is possible to further improve the heat resistance by adding a soluble cerium salt (cerium nitrate, cerium acetate, etc.) of 10 to 150 weight (in terms of CeO) and simultaneously impregnating it with the three components.

Here, to explain the specific steps of the manufacturing method, the time for contacting the catalyst carrier with the above solution is the same as that of a commonly used carrier (surface area after wash coating: tstr?/gr or more, porosity: 0.10 bamboo r or more). If so, it is sufficient to soak the liquid for 3 to 5 hours, and there is no particular restriction on the temperature of the liquid used, and it can be used in a wide range from room temperature to 90°C. The temperature may drop to room temperature.

Next, this catalyst carrier was taken out from the above solution, washed with water, and then
It is dried at a temperature of ~450° C. for 1 to 3 hours, and subjected to a reducing heat treatment in order to fix the noble metal component and nickel in the solution to the catalyst carrier.

This treatment is carried out at 400-600℃ in a hydrogen stream at 30-60℃.
Heat for a minute. Through the above treatment, a catalyst body on which a predetermined noble metal component and Ni are supported is obtained. Next, if necessary, other noble metal components and Ni are simultaneously immersed in the same manner as described above, and the noble metal component and Ni of binary or ternary composition are immersed.
A catalyst having the following properties is obtained. It is also possible to obtain a catalyst similar to the above using an impregnating liquid containing a binary or ternary noble metal component and nickel at the same time.

The catalyst of the present invention obtained by the above production method has superior initial activity and heat resistance compared to conventional catalysts.

The reason for this is thought to be roughly as follows. That is, when observing the catalyst of the present invention from a transmission electron micrograph, it is found that the catalyst of the present invention is obtained by simultaneously impregnating and supporting noble metal components and nickel.

Compared to conventional catalysts obtained by wash-coating a support with an alumina-based composition and impregnating it with a soluble nickel salt and then supporting a noble metal, nickel oxide particles and noble metal particles as co-catalyst components are extremely It is confirmed that the particles are micronized (20A or less) and supported in a highly dispersed manner.

Incidentally, Figure 1) (b) shows electron micrographs of a conventional catalyst, and Figures 2 (a) and (b) show electron micrographs of the catalyst of the present invention.

Furthermore, if necessary, interposing cerium oxide (CeO) between the noble metal component and the nickel oxide particles has the effect of preventing grain growth of the noble metal or nickel oxide particles at high temperatures. As a result of the crystal particles of the precious metal component and the nickel oxide particles being supported in an extremely finely dispersed manner, the contact area with the exhaust gas is greatly increased and the number of active sites is increased, so that the catalyst performance is greatly improved.

Furthermore, heat resistance at high temperatures is improved. This is because the inclusion of Ni improves the dispersion of noble metal components, increases the surface area, and increases the number of active sites. Therefore, it is presumed to have heat resistance. Furthermore, it is thought that heat resistance is further improved by interposing CeO, and in some cases, suppressing the grain growth of noble metal components.

<Example 1> Commercially available cordierite honeycomb carrier [manufactured by Nippon Insulator ~90
%φ x 110~L (300 cells/inch)] were first coated using various wash coating compositions A21~A-6 in Table 1, and after coating, the temperature was about 120°C. The sample was dried at 650° C. for 31 hours, and then baked at 650° C. for 3 hours. The above coating treatment, drying, and smoking were repeated three times to obtain carriers with various wash coating amounts shown in Table 1. Next, these carriers were made with an inner diameter of 92%φX
12 Load into a PVC cylinder or container of oXL size, and then add chloroplatinic acid (HtPtCAa 6H!o) 2- into pure water in an amount (approximately 509y) that is enough to submerge the honeycomb.
97 gr (carrier capacity υpt loading amount 1.6 V1
3 equivalent)) and prepare 6 pieces of dissolved solution, among which A-2 to A.
-6 contains nickel nitrate A/(Ni (NO3)2.6O) after being supported on the honeycomb.

The converted amounts were 0.1, 1.15° and 5.10 times the molar amount of pt, respectively, and solutions corresponding to each of A-1 to A-6 were added to the honeycomb inside the PVC cylinder. Injected from the top. After that, the honeycomb was left for 5 o'clock to adsorb PT, Ni, etc., and then the honeycomb was taken out from the tube, washed with water, and heated to 120℃ for 3 hours.
After drying for several hours, reduction treatment was performed at 500° C. for 30 minutes in a hydrogen stream.

Next, rhodium chloride, (RhC65-aH,o) 0.29 t (
Prepare 6 solutions in which the amount of Rh supported (o, equivalent to t6y-/-g per m body volume) is dissolved in approximately 5,001 ml of pure water.A-2~,A
In -6, nickel nitrate is added as NiO equivalent after supporting the honeycomb, as in the case of impregnating with chloroplatinic acid, and is 0.00% relative to the Rh molar amount.
1.1, 2.5, 5, 10 times the molar amount,
Each of the solutions corresponding to A-1 to A-6 was injected into the PVC cylinder using the same operation as for pouring the chloroplatinic acid solution described above, and the post-treatment after injection was also the same as the post-treatment of the chloroplatinic acid solution. Catalysts A-1 to A-6 supported on pt-1,6t/-13 and Rh-0,16t/J were obtained in exactly the same manner (A-2 to A-6).
-6 is Pt, Rh and Ni co-supported catalyst).

Next, in order to investigate the performance of the obtained various catalysts A-1 to A-6 as three-way catalysts, CO, The conversion performance of HC and NOx was measured.

The main measurement conditions are as follows.

Vehicle used: 2000cc passenger car manufactured by YJ Test catalyst: A-1 to A-6 (90φXll0L to 0.7J3) Catalyst installation position: Approximately IWt from the exhaust manifold outlet The performance of various catalysts from A-1 to A-6 is new. After measuring the performance of 8118FJ! in an electric furnace set at 950℃! The heat resistance performance of the heat-treated samples was also measured. The display of the results (rightmost column in Table 1) is the C when each catalyst was installed on the test vehicle.
o, HC, NOx 10 mode emissions (gr/km)
The conversion rate was calculated using the following equation based on the 10-mode emissions (gr/km) in the case of 10-mode emissions (gr/km2) and dummy (without catalyst installed).

The 10-mode emission values for dummy CO, HC, and NOx are as follows.

<Example 2> Three honeycomb carriers of the same type as used in Example 1 were prepared, and the wash coating was performed using the same composition as shown in Example 1 and the same operating method. Hereafter, palladium chloride (PdC6) was used instead of chloroplatinic acid.
, > in accordance with the operating method of Example 1 except that the solutions of B-1 to B-3 as shown in Table 2 were
A Rh-based catalyst was obtained (B-2 and B-3 are Pd, Rh and Ni
co-impregnated catalyst). Furthermore, the performance of these various catalysts as three-way catalysts was also measured using the same measurement conditions and method as shown in Example 1. The above results are shown in Table 2.

<Example 3> Seven honeycomb carriers of the same type as used in Example 1 were prepared, and the carriers with the wash coating amount shown in Table 3 were obtained by the same operation as shown in Example 1. Then palladium chloride PdCg, 2.1? Seven pieces were prepared by dissolving this in a 18 t/13 urea solution of about 500 ml. (C-
1 to C-7: Pd supported amount per carrier capacity 1.8 SIL/A
equivalent), then nickel chloride (Ni(J
, 2H, O) 1.13 gr (Equivalent to Pd%/L/
amount) Add cerium acetate A (Ce) to KC-1 to C-7.
(CH3COO), H,0) respectively 0°21,
0.42, 2.11, 4.21.

6.32, 8.42 gr (CeO, equivalent to 5, 10, 50° 100.150, 200 wt per weight of (Pd+Ni0) as a converted amount, respectively) were added. These seven solutions were added to Example 1. Supporting treatment was performed in the same manner as shown above.After reduction treatment at 500°C for 30 minutes, calcination was performed in an electric furnace at 650°C for 1 hour to obtain each catalyst. Performance measurement was carried out under the same measurement conditions and measurement method as in Examples 1 and 2. The above results are shown in Table 3.

Comparative Example> Three non-nicum carriers of the same type as those used in Examples 1 to 3 were prepared, and various wash coating compositions of A-0, B-o, and Co shown in Table 4 were applied. Examples 1 to 3 using
The procedure was carried out in the same manner as described above to obtain carriers with various wash coating amounts shown in Table 4. Next, the noble metal supporting method shown in Examples 1 and 2.3 was applied to these three carriers, respectively.
However, the addition of Ni salt to the precious metal solution is excluded),
Support each precious metal, Ni or N 1 /
CeO! P t/Rh and P d/Rh prepared by including them in a wash coating composition.

A Pd-based catalyst was obtained. The CO, HC, and NO conversion performance of these catalysts was measured by the method shown in Example 1. The results are shown in Table 4.

<Effects of the Invention> As is clear from the test results of Examples and Comparative Examples, the catalyst of the present invention described above has high catalytic performance at high temperatures.
In particular, in Examples 2 and 3, the co, I (c conversion rate) at high temperatures was almost 80% to 90% or more, whereas in the comparative examples, most of the conversions were around 60 to 70%, which is different from the present invention. It can be seen that the catalyst of the invention exhibits excellent catalytic performance at high temperatures.

[Brief explanation of drawings]

Figure 1 (a) and (b) are electron micrographs of conventional convergence.
FIGS. 2(a) and 2(b) are electron micrographs of the catalyst of the present invention. Note that each figure (a) shows the fiber-combined state of the catalyst at a magnification of 20,000 times, and each figure Φ) shows the state of the fibers at a magnification of 150,000 times.

Claims (4)

[Claims] (1) In a purification catalyst in which at least one of the noble metal components of platinum, palladium, and rhodium is supported on a catalyst carrier having a honeycomb structure, fine nickel oxide particles are dispersed between the particles of the noble metal component. Features of exhaust gas purification catalyst (2) When supporting at least one noble metal component such as platinum, palladium, or rhodium on a catalyst carrier having a honeycomb structure, a soluble nickel salt is added to a solution containing the noble metal component, and the catalyst carrier is brought into contact with the solution. A method for producing a catalyst for exhaust gas purification, characterized by impregnating each component in a solution at the same time and heat-treating the same. (3) In claim 2, the soluble nickel salt is expressed as a precious metal component 1 in terms of nickel oxide (NiO).
A method for producing an exhaust gas purifying catalyst, characterized by using a solution containing 0.1 to 5 moles per mole. (4) In claim 2 or 3, soluble cerium salt is contained in an amount of 10 to 150% by weight in terms of cerium oxide (CeO_2) based on the total amount of the noble metal component and the amount in terms of nickel oxide. A method for producing an exhaust gas purifying catalyst characterized by using a solution of