JPS6140460B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an exhaust gas purifying catalyst, a method for manufacturing the same, and a method for using the same. Specifically, the present invention relates to a catalyst for removing harmful components such as hydrocarbons, carbon monoxide, and nitrogen oxides contained in exhaust gas, a method for producing the same, and a method for using the same. More specifically, the invention provides that when an internal combustion engine is operated near the equivalence point of the air-to-fuel ratio, hydrocarbons in the exhaust gas,
The present invention relates to an exhaust gas purifying catalyst capable of stably and simultaneously removing carbon monoxide and nitrogen oxides, a method for producing the same, and a method for using the same. Some so-called three-way catalysts, which are catalysts that simultaneously remove the three components of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) from the exhaust gas of internal combustion engines, are already available. It is installed in commercially available car engines. Engines equipped with this three-way catalyst have a stoichiometric air-to-fuel ratio (A/
When operated in the vicinity of F), exhaust gas is said to be produced that most effectively purifies the above three components. However, in actual driving in the city or suburbs, a so-called unsteady mode of operation including acceleration, deceleration, etc. is performed. For this reason, a deviation from the set air-fuel ratio (A/F) occurs due to momentary changes in the engine condition, so a mechanism for quickly correcting this, that is, a feedback mechanism (or closed loop mechanism) is required. Specifically, it is necessary to equip the engine with, for example, an electronically controlled fuel injection system or a good ventilator carburetor, as well as a control mechanism that corrects the air-fuel ratio by means of a signal from an oxygen sensor installed in the exhaust pipe. However, even if such an A/F feedback mechanism is installed, the engine's A/F will inevitably have a considerable range around the stoichiometric A/F equilibrium value due to its control response time. It is also common knowledge that there are periodic fluctuations. When the range of such fluctuations is large, the performance of the three-way catalyst often deteriorates, that is, the A/F range that allows simultaneous removal of the three components at a high level (e.g., 80% or more) It is also true that situations may occur in which the window width (called the window width) becomes significantly narrower than at a static gas composition, or even disappears. To deal with this situation, a catalyst containing a metal such as rhenium, which has a high ability to temporarily absorb excess oxygen in the gas, is used to extend the operating range to the excess fuel (F) side of the A/F. Efforts to expand this have been proposed. However, this proposed method has problems such as the fact that the additive metal forms volatile oxides or is easily poisoned by sulfur contained in exhaust gas, or the window width is not wide enough to be practically satisfactory. There are problems such as not having one. One object of the present invention is to provide such periodic A/
The object of the present invention is to provide a catalyst composition that stably exhibits high three-component purification performance under fluctuations in F, and a method for producing the same. Another object of the present invention is to improve the catalyst containing rhodium (Rh) and platinum (Pt) as the main active components, which is currently receiving the highest evaluation as a three-way catalyst. An object of the present invention is to provide an improved catalyst capable of maintaining a high three-component purification level without narrowing the window width due to A/F fluctuations, and a method for manufacturing the same. Another object of the present invention is to minimize the amount of rhodium (Rh) used, which is resource-constrained and expensive, while still exhibiting a high level of three-component purification ability.
The objective is to provide a system catalyst. Generally, the natural production amount of rhodium (Rh) is extremely small (1/1 of platinum).
Estimated to be 9. ) for a weight ratio of Pt and Rh of 19:
For example, in a three-way catalyst containing Rh at a ratio of about 1 to 10:1,
It is difficult to maintain high purification performance over a distance of 50,000 km, especially since the oxygen concentration in the exhaust gas at a chemically equivalent air-fuel ratio is as low as 0.5 to 1%.
A notable drawback is the reduced ability to purify HC and CO. As a countermeasure for this, the catalyst is separated into two beds, the first bed supports the entire amount of Rh and a portion of Pt and Pd, then oxygen is added with secondary air, and then the second bed is loaded with oxygen.
A method that leads to a complete oxidation catalyst when Pt or Pd is supported is becoming promising. In the two-stage bed system considered so far, the carburetor is set so that the air-fuel ratio is on the fuel-added side, and only the NOx in the exhaust reducing gas is removed using a Rh catalyst, and then the secondary air is There was a method that led to the oxidation catalyst after addition, but this method had two drawbacks. In other words, with poor fuel efficiency and a reducing atmosphere,
A considerable proportion of NO was reduced to ammonia, which was returned to NO by the oxidation catalyst, leading to a decline in the overall NO purification ability. In contrast, the two-stage engine engine with air-fuel ratio control solves the above-mentioned drawbacks. In other words, the fuel efficiency is good because it is always operated at the chemical equivalence point, and since the NH ₃ byproduct is significantly suppressed during the reaction of exhaust gas near the chemical equivalence point, the overall NO purification rate can be maintained at a high level. As an example of such a two-tier floor type, there are currently 2 floors per vehicle.
Using a catalyst capacity of 1.5 g of Pt and 1.5 g of Pd,
When using 0.6g and 0.15g of Rh, and distributing Pt and Pd equally to the front and rear floors, the front floor is
Pt0.75g/, Pd0.3g/, Rh0.15g/ composition
The Pt/Rh ratio is 5/1. This ratio naturally means that the Rh ratio is higher than the Pt/Rh = 10/1 of a single bed three-way catalyst, and if we use the same idea to allocate 20% of Pt to the front bed and 80% to the rear bed. Front floor Pt/
It is also possible to set the Rh ratio to 2/1. but,
On the other hand, if attention is focused only on the first bed of a two-stage bed system, the reaction space velocity will be twice as high, so a two-way catalyst with higher activity will be required. Therefore, the object of the present invention additionally stated above is to provide a composition having a relatively low Pt/Rh ratio,
The object of the present invention is to provide a composition of a highly active three-way catalyst and at the same time provide an economical method for producing the same. More specifically, the catalyst of the present invention comprises Ce,
Fe, Pt, Pd, and Rh are used to convert exhaust gas from an engine with air-fuel ratio control into a single-bed type three-way catalyst, or as a front-stage three-way catalyst for a two-stage bed type catalytic converter to convert CO, HC, and NOx. The present invention relates to a catalyst composition that can be purified at a high level and is highly durable, and a method for producing the same. Specifically, the catalyst of the present invention is deposited on a refractory, porous, high surface area particulate support containing 1 to 20 g of cerium, 2.5 to 20 g of iron, and 0.05 g of atomic grams (g) per liter of finished catalyst.
~0.8g platinum, 0.02-0.3g palladium, 0.05
Carrying ~0.3g rhodium, 0~0.08g phosphorus,
and the weight ratio of Pt and Rh is 5:1 to 1:1, and Pt
This is a catalyst for the first bed of a single-bed system or a two-stage bed system, with a composition in which the ratio of The catalyst component is supported by the process, and in the first impregnation process, a final solution is prepared by adding and dissolving water-soluble salts of cerium and iron, a nitric acid acidic solution of dinitrodiamine platinum, a water-soluble salt of palladium, and phosphoric acid if necessary. A step of impregnating with a catalyst solution adjusted to a volume of about 0.5 to about 1.3 times, preferably 0.75 to 1.2 times the total water absorption amount of the carrier, and a second impregnation step of dissolving Rh in water. This production method is characterized by a step of impregnating Rh with an aqueous solution in which a salt is dissolved, adjusted to the same final liquid volume as the first-stage impregnation catalyst solution. As mentioned above, although the catalyst of the present invention has been defined, the role of each element constituting the catalyst of the present invention has not yet been completely elucidated. However, the present inventors have discovered the following fact. In other words, Ce and Fe have the ability to absorb and store oxygen in the reaction gas, and have the ability to minimize the range of air-fuel ratio fluctuations that are directly related to catalytic reactions. The effect of supporting the ohming reaction and, more importantly, the oxidizing ability of these elements themselves, CO and HC, and the oxidation ability of NOx.
It has the ability to reduce CO, H ₂ , HC, etc. Among these, Ce in particular affects the supporting depth of Rh that is later supported, and is used in the present invention.
In order to make the low concentration of Rh (0.3g/) work as effectively as possible in the reaction, it plays an effective role in supporting finely dispersed Rh near the surface of the carrier. In addition, when Ce is supported on a refractory such as alumina, Pt, Pd,
It has been found that noble metals such as Rh suppress the reaction with alumina and other substances at high temperatures, thereby contributing to improving the heat resistance stability of the catalyst. In addition, it is preferable that P, which can be used in the present invention, be supported as phosphoric acid at the same time as Pt and Pd, and its action is due to the strong adsorption property of phosphoric acid to alumina, so the amount of P added must be adjusted. By this, Pt and Pd can be supported at an arbitrary depth inside the carrier. Therefore, when there is a relatively large amount of Pt, such as when the Pt/Rh ratio is 5/1, P is added to lower the surface concentration of Pt, and in this way the Pt/Rh ratio on the catalyst surface is reduced. By lowering Pt−Rh
It is thought that undesirable alloying etc. can be considerably prevented. However, on the other hand, Pt/Rh=1/
In case 1, it is no longer preferable to support Pt deep into the carrier, and therefore the amount of phosphoric acid added becomes zero or substantially close to zero. According to the present inventors, the amount of phosphoric acid added is equal to the number of moles of Pt.
About 0.1 to 2 times the mole is good. It is thought that the phosphoric acid located on the surface of the carrier at an appropriate concentration is decomposed by the subsequent heat treatment and exists in the catalyst in an oxide state, but this P compound suppresses the ammonia by-product in the NO reduction reaction and makes it possible to release more nitrogen. It was also found that it has the effect of promoting the return of In addition to the basic elements constituting these catalysts, for example, rare earth elements other than Ce, such as lanthanum (La), praseodymium (Pr), neodymium, (Nd), and gadolinium (Gd), may be substituted for part of Ce. Fe
It is also possible to replace a part of nickel (Ni), barium (Ba), cobalt (Co), chromium (Cr), calcium (Ca), etc. The granular carrier used in the present invention is preferably one containing activated alumina as a main component, but other materials such as silica alumina, silica, magnesia, zirconia, and titania that have excellent heat resistance and sufficient strength as a carrier may also be used. It can be used even if some parts are mixed.
Further, as the particle shape, any of spheres, cylinders, and irregular cross-sectional shapes can be used. Also, in advance,
It is also possible to use an alumina carrier formed into granules containing a portion of Fe and Ce components. Support physical properties include BET surface area of 10 to 200 m ² /g, preferably
The ^total pore volume measured by mercury porosimetry is preferably 0.4 cc/g or more, preferably 0.5 to 1.3 cc/g, and the average pore diameter is 100 Å or more, preferably 150 Å or more. The catalyst raw materials used in the present invention are selected from compounds whose catalyst components can be activated into oxides or atoms through the activation treatment described below, and are usually inorganic salts, organic salts, metal acids, or compounds that can form an aqueous solution. That salt is fine. As a particularly preferable raw material,
For Fe, ferric nitrate and ferrous ammonium sulfate are good. For Ce, ceric nitrate and ceric ammonium nitrate are good. For P, phosphoric acid is good. As for Rh and Pd, their chlorides, nitrates, and other various water-soluble complex salts may be used. The most preferred platinum raw material is a nitric acid aqueous solution of dinitrodiaminoplatinum disclosed in US Pat. No. 3,953,369. The reason for this is that the first impregnating solution used in the production method of the present invention contains, for example, a large amount of cerium nitrate and iron nitrate ions together with Pt, so a Pt source such as ordinary chloroplatinic acid (H ₂ PtCl ₆ ) is not used. This is because if Pt is used, Pt penetrates deep into the carrier particles, sometimes even to the center of the granular carrier, and is supported, making it impossible to obtain a highly active catalyst. On the other hand, a nitric acid acidic solution of dinitrodiaminoplatinum has extremely strong adsorption to alumina, so it can be effectively supported near the surface of the carrier in a finely dispersed state even in the coexistence of the cerium nitrate and iron nitrate. At the same time, Pt/
In cases such as Rh=5/1, addition of phosphoric acid is useful as a means to arbitrarily control the carrier surface concentration of dinitrodiaminoplatinum. On the other hand, in order to prepare a catalyst having the composition of the present invention using chloroplatinic acid as a starting material, a good catalyst cannot be obtained by the two-stage impregnation method, and instead a three-stage impregnation method, that is, the first
A long manufacturing process is carried out in which Fe and Ce are supported in the first step, dried and fired, then Rh is supported in the second step, dried and fired, and then Pt and Pd are simultaneously supported with P in the third step, dried and activated. I have to take it.
Moreover, the present inventors have found that a catalyst produced by a two-stage impregnation method using a nitric acid solution of dinitrodiamine platinum has a higher reaction activity than a catalyst having the composition described in the present invention produced by a three-stage impregnation method using chloroplatinic acid. It has been found to be excellent in both durability. Although the reason for this has not been completely investigated, it is presumed that it is due to the Pt concentration in the extreme surface layer and the dispersion state of platinum (crystal fineness). The present inventors have also found that the NO purification rate is better when an appropriate ratio of Pt-Pd-Rh is used as a front-bed catalyst in a two-stage bed system than when only Rh is used due to the synergistic effect. In the method for preparing the catalyst of the present invention explained above,
The use of a polyoxyethylene nonionic surfactant in impregnating and supporting each component of Ce, Fe, Rh, Pt, Pd, and P is very useful for preparing the catalyst of the present invention. The presence of a polyoxyethylene-based nonionic surfactant generates appropriate foaming, which facilitates mutual contact between the catalyst component aqueous solution, carrier particles, and the wall of the preparation container, resulting in uniform and reproducible loading results. Furthermore, due to the low permeability of the surfactant, effective dispersion and loading on the surface and surface layer of the catalyst can be carried out, and a catalyst having the desired level of performance can be obtained with a minimum amount of loading. These advantages are particularly advantageous when preparing a large amount of catalyst. The surfactants used in the method of the present invention are as follows. Polyethylene glycol HO (C ₂ H ₄ O) _o H (n
= 11 to 900), polyoxyethylene glycol alkyl ether RO (C ₂ H ₄ O) _o H (R has 6 to 6 carbon atoms)
30 alkyl groups (n=3-30), "Pluronic" type, i.e. polyoxyethylene-polyoxypropylene-polyoxyethylene glycol
HO(C ₂ H ₄ O) _a (C ₃ H ₆ O) _b (C ₂ H ₄ O) _c H(a,
b, c are 1 or more, a+b+c=20-400)
general formula "Tetronic type nitrogen-containing nonionic surfactant (x ₁ to x ₄ , y ₁ to y ₄ are 1 or more, x ₁ +
x ₂ + x ₃ + x ₄ + y ₁ + y ₂ + y ₃ + y ₄ = 20-800), polyexyethylene alkyl allyl ether

[Formula] (R' is an alkyl group having 6 to 12 carbon atoms, n = 3 to 30), polyoxyethylene alkyl ester R-COO (C ₂ H ₄ O) _o H
or R−COO(C ₂ H ₄ O) _o−1 −CH ₂ CH ₂ COO−R
(R is an alkyl group having 6 to 24 carbon atoms, and n=3 to
30), polyoxyethylene alkylamine (R is an alkyl group having 6 to 30 carbon atoms, and n, n ₁ and n ₂ are 3 to 30), polyoxyethylene alkylamide R-CONH-(C ₂ H ₄ O) _o H or

[Formula] (R is an alkyl group having 6 to 30 carbon atoms, and n, n ₁ and n ₂ are 3 to 30), fatty acid ester of polyoxyethylene sorbitan (R is an alkyl group having 6 to 24 carbon atoms, and n is 3 to
30) Among these polyoxyethylene nonionic surfactants, those having an average molecular weight of 500 or more, particularly 1000 or more are preferred. This is because if the average molecular weight is less than 500, the permeability will increase, and the catalyst components (particularly the noble metal components) will be uniformly supported and distributed inside the carrier, making it necessary to increase the amount supported. This surfactant is 0.05 to 1 per carrier.
50 g, preferably 0.1 to 20 g, is used, and when added to the catalyst component aqueous solution, it is used in a range of 0.005 to 10% by weight, preferably 0.01 to 5% by weight. Example 1 Surface area 105m ² /g, apparent specific gravity 0.5g/cc, diameter 3
mm, cylindrical alumina carrier 100c.c. with an average length of 4mm,
Cerous nitrate [Ce(NO ₃ ) ₃・6H ₂ O] 3.10g
and ferric nitrate [Fe(NO ₃ ) ₃・9H ₂ O] 7.2g and 0.019
g of 85% phosphoric acid (H ₃ PO ₄ ) and a nitric acid acidic solution containing 0.124 g of dinitrodiaminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ], 0.065 g of palladium nitrate and 0.05 g of Pluronic type nonionic Surfactant [average molecular weight
A block copolymer of 11,000 propylene oxide (PO) and ethylene oxide (EO) with 80 EO in the entire molecule.
Weight%. ], then dissolved with water to make a total volume of 57 c.c., immersed in a solution, concentrated to dryness on a warm bath to support the above components, dried at 150°C for 2 hours, and then dissolved in hydrogen (H ₂ ) 10% - remaining in nitrogen (N ₂ ) stream
Reduction treatment was performed at 350°C for 2 hours. then 0.038g
After dissolving rhodium trichloride (Rh・Cl ₃・3H ₂ O) and 0.05 g of the same surfactant as above in water to make a total amount of 57 c.c., Rh was impregnated and supported using the same method as above. After that, it was dried at 180°C for 3 hours and used as a catalyst. In this catalyst, the amount of each component supported per liter of the finished catalyst, expressed in atomic grams, was as follows. Ce:Fe:P:Pt:Pd:Rh=10:10:0.05:
0.75:0.3:0.15 Example 2 The following catalyst was prepared using the same starting materials as in Example 1 and using the same supporting technique. However, Ce,
550 instead of Fe, P, Pt, Pd supported drying and reduction firing
Oxidation calcination was performed at 350°C for 3 hours, and after drying the Rh supported, reduction calcination was performed at 350°C in H ₂ /N ₂ to obtain the following catalyst. Ce:Fe:P:Pt:Pd:Rh=15:7.5:0.02:
0.3:0.25:0.1 Example 3 Using the same loading method as in Example 1 and using the same starting materials, a catalyst having the following composition was prepared. however,
After Rh supporting drying, reduction firing was performed again at 350° C. in a H ₂ /N ₂ gas flow. Ce:Fe:P:Pt:Pd:Rh=7.5:2.5:0.005:
0.1:0.4:0.1 Examples 4 to 6 The following catalysts with different amounts of phosphoric acid added were prepared in the same manner as in Example 2. Example 4 Ce:Fe:P:Pt:Pd:Rh=5:
5:0:0.15:0.06:0.1 Example 5 Ce:Fe:P:Pt:Pd:Rh=5:
5:0.005:0.15:0.06:0.1 Example 6 Ce:Fe:P:Pt:Pd:Rh=5:
5:0.05:0.15:0.06:0.1 Comparative Example 1 A catalyst was prepared in the same manner as in Example 5, except that it did not contain Ce or Fe. Ce:Fe:P:Pt:Pd:Rh=0:0:0.005:
0.15:0.06:0.1 Example 7 The catalysts of Examples 1 to 6 and the catalyst of Comparative Example 1 were evaluated for their purification performance using a bench engine test device. The test method was an air-fuel ratio oscillation method roughly similar to that described in SAE770371. That is, commercially available 4
A 1Hz sine wave potential generated by an oscillator is introduced into the control unit into the cylinder 1800c.c. engine (EFI), and the equivalent of ±1.0A/F (for example, A/F =
The amplitude was determined to give an air-fuel ratio oscillation of 13.5 to 15.5). The catalyst was packed into a stainless steel multi-reactor, and the reaction conditions were set at an inlet temperature of 550°C and a SV of 120000 Hr ^-1 . Table 1 shows the evaluation of performance when new. In this table, the actual NO purification rate is the most important item, and other
The CO and HC purification rates are considered as reference values here, as they are further purified by the oxidation catalyst installed afterwards. After the catalyst had been evaluated when new, the engine speed was raised to 3000 rpm and the catalyst was aged near the chemical equivalence point in closed-loop operation for 100 hours, and its performance was evaluated again under the same conditions as when it was new. The gasoline used was standard unleaded gasoline, and the actual lead content was less than 0.003 gPb/gal. Table 2 shows the performance evaluation results after running for 100 hours. Comparative Example 1 does not contain Fe or Ce.
It is clear that the actual NO purification rate is low. In addition,
For reference, Figures 1-1, 1-2 (Example 1 above), Figures 2-1, 2-2 (Example 5), and Figures 3-1, 3-2 (Comparative Example 1) ) is shown below.

【table】

【table】

【table】

[Table] Example 8 Catalyst 900c.c. of Example 5 and prepared by normal manufacturing method
Pt0.85g/, Pd0.34g/supported oxidizing acid medium 900c.c.
A two-bed catalytic converter was created by combining the two. This catalytic converter was installed on the 1800 c.c.
After running for a certain period of time, performance was examined using the same evaluation method as in Example 7. Table 3 shows the performance evaluation results of this converter.
Compare with.

【table】 [Brief explanation of the drawing]

FIG. 1-1 is a diagram of the catalytic activity of the catalyst of Example 1 when new, and FIG. 1-2 is a diagram of the catalytic activity of the catalyst of Example 1 after running for 100 hours. Figure 2-1 and Figure 2
-2 indicates the catalytic activity of the catalyst of Example 5 when new and after running for 100 hours. 3-1 and 3-2 show similar catalytic activity of the catalyst of Comparative Example 1.

Claims (1)

[Claims] 1. Using a refractory porous granular carrier having a high surface area, () dissolving water-soluble compounds of cerium (Ce) and iron (Fe) in an aqueous medium, and dissolving dinitroinol into this solution. It was impregnated with a catalyst solution prepared by adding an acidic solution of diaminoplatinum in nitric acid and then an aqueous solution containing palladium (Pd).
After drying at 120°C to 600°C, it is calcined in air or in a hydrogen atmosphere, and then () the calcined catalyst is impregnated with a catalyst solution containing a water-soluble compound of rhodium (Rh), and then at 120 to 180°C. Dry or further in air or hydrogen atmosphere for 250
obtained by calcination at ~600°C, and contains 1 to 20 g, expressed in atomic grams, per liter of finished catalyst.
Ce, 2.5~20g Fe, 0.05~0.8g Pt, 0.02~
It supports 0.3 g of Pd and 0.05 to 0.3 g of Rh, and the weight ratio of Pt:Rh is 5:1 to 5, Pt:
A method for producing an exhaust gas purifying catalyst capable of simultaneously removing carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) in exhaust gas in a weight ratio of Pd in the range of 1:0.2 to 5. 2 Using a refractory porous granular carrier with a high surface area, () dissolve the water-soluble compounds of cerium (Ce) and iron (Fe) in an aqueous medium, and add to this solution a nitric acid acidic solution of dinitrodiaminoplatinum. , then impregnated with an aqueous solution containing palladium (Pd) and a catalyst solution prepared by adding phosphoric acid,
Then, after drying at 120-180℃, firing at 250-600℃ in air or hydrogen atmosphere, and then ()
The calcined catalyst was impregnated with a catalyst solution containing a water-soluble compound of rhodium (Rh), and then
obtained by drying at 180°C or further calcining at 250-600°C in air or hydrogen atmosphere, and containing 1-20 g of Ce, 2.5-20 g of Ce, expressed in atomic grams, per liter of finished catalyst. Fe, 0.05~0.8
g of Pt, 0.02 to 0.3 g of Pd, 0.05 to 0.3 g of Rh, and 0.005 to 0.08 g of phosphorus, and
Carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides ( A method for manufacturing an exhaust gas purification catalyst that can simultaneously remove NOx).