JPS6214337B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a honeycomb catalyst for exhaust gas purification. Specifically, it relates to a honeycomb catalyst for removing harmful components contained in exhaust gas, such as hydrocarbons (hereinafter referred to as HC), carbon monoxide (hereinafter referred to as CO), and nitrogen oxides (hereinafter referred to as NOx). More specifically, the present invention stably simultaneously removes HC, CO, and NOx from the exhaust gas when the internal combustion engine is operated with combustion near the stoichiometric equivalence point of the air-to-fuel ratio. This invention relates to a high-temperature durable monolithic catalyst for exhaust gas purification that is substantially harmless and exhibits little deterioration even when exposed to high temperatures of 800°C or higher. HC, CO and NOx3 in exhaust gas from internal combustion engines
Catalysts that simultaneously remove components using a single catalytic converter, so-called three-way catalysts, are installed in some cars that comply with the 1953 regulations, and recently, the number of cars equipped with three-way catalysts has increased, partly as a measure to improve fuel efficiency. are doing. In this case, the catalyst is often installed under the floor, and in some cases it is installed directly under the engine manifold. When an engine equipped with this three-way catalytic converter is operated near the stoichiometric air-fuel ratio (A/F), it will emit exhaust gas that has purified the three components mentioned above most effectively. In order to work more effectively, in addition to an electronically controlled fuel injection system that supplies fuel using an injection pump to maintain a constant A/F, a ventilator carburetor is used to control the air-fuel ratio. However, depending on the control method, the A/F may be quite wide from the stoichiometric equivalence point.
The catalyst may be exposed to the F range, and in the case of sudden changes in operation such as acceleration or deceleration, the fuel supply is partially or completely cut off to prevent the honeycomb catalyst from melting due to a sudden rise in temperature. may be exposed to lean atmospheres. In other words, the three-way catalyst is not always exposed to ideal exhaust gas during A/F operation, and when the catalyst is exposed to high temperatures under such conditions, the components contained in the catalyst, especially rhodium, Platinum is susceptible to thermal degradation. Therefore, there is a need for a three-way catalyst that exhibits stable purification performance even under a wide range of A/F operating conditions and that exhibits minimal deterioration. In addition, the temperature of the three-way catalyst mounted near the bottom of the floor is relatively lower than that of the tower mounted at the engine position, so it is necessary to increase the performance by increasing the catalyst capacity or the amount of precious metals supported. There are drawbacks to it. Therefore, if a three-way catalyst can be used in the high temperature range directly under the engine, the reaction rate will be high and the catalyst capacity can be made compact, which is advantageous in terms of cost. Therefore, there has been a desire for a three-way catalyst that can be stably used without deteriorating at high temperatures of 800 to 1000°C. An object of the present invention is to provide a catalyst composition that exhibits stable and high purification performance for CO, HC, and NOx3 components at high temperatures of 800° C. or higher over a wide range of A/F. The present invention can therefore be specified as follows. (1) A honeycomb carrier having an integral structure, at least one selected from the group consisting of activated alumina, ceria, neodymia, zirconia, iron oxide and nickel oxide, and at least one selected from the group consisting of platinum and palladium. A catalyst used for the simultaneous purification of hydrocarbons, carbon monoxide and nitrogen oxides in exhaust gas, which is made by supporting a carrier 1 and rhodium.
per unit, activated alumina 50-200g, ceria 5-30g
g, neodymia 2-15g, zirconia 1-8
g, 0 to 5 g as iron oxide Fe ₂ O ₃ , 0 to 10 g as nickel oxide NiO (however, Fe ₂ O ₃ +
0.5-10g as NiO), and a total of 0.1-10g of platinum group metals consisting of platinum and palladium.
and rhodium is supported in a range of 0.1 to 10 g, and the ceria content is greater than the neodymia content and the zirconia content, and the neodymia content is greater than the total content of iron oxide and nickel oxide. A honeycomb catalyst for exhaust gas purification that is characterized by The honeycomb carrier having a monolithic structure used in the present invention may be one commonly referred to as a ceramic honeycomb carrier, particularly cordierite, mullite, alpha alumina, zirconia, titania, titanium phosphate, aluminum titanate,
Honeycomb carriers made of petalite, spodium, aluminosilicate, magnesium silicate, etc. are preferred, and among them, cordierite is particularly preferred for use in internal combustion engines. In addition, a unitary structure made of oxidation-resistant heat-resistant metal such as stainless steel or FeClalloy is also used. These monolith carriers are manufactured by extrusion molding or rolling and compacting sheet-like elements.
The gas passage opening (cell shape) may be hexagonal, square, triangular, or corrugated. Cell density (number of cells/unit cross-sectional area) is 150 to 600
A cell/inch of ² is sufficiently usable and gives good results. The activated alumina used in the present invention is preferably an activated alumina with a specific surface area of 50 to 180 m ² /g, and hydrated alumina in the state of aluminum hydroxide, boehmite, or precipitated boehmite is also supported on a honeycomb carrier and then fired to form the activated alumina. The crystalline forms of alumina in the finished catalyst can be γ, δ, θ, χ, κ, and η. Among these, particularly preferred aluminas are γ and δ type activated aluminas with a specific surface area of 70 to 160 m ² /g.
It is loaded in an amount between 50 and 200 g per portion. As the cerium source, cerium nitrate, cerium acetate, cerium oxalate, cerium carbonate, cerium hydroxide, and cerium oxide are preferably used. As neodymium sources, neodymium nitrate, neodymium acetate, neodymium oxalate, neodymium carbonate, neodymium hydroxide, and neodymium oxide are preferably used. As the zirconium source, zirconyl nitrate, zirconyl acetate, zirconyl hydroxide, and zirconium oxide are preferably used. As the iron source, iron nitrate, iron hydroxide, iron oxide, iron oxalate, and iron ammonium oxalate are preferably used. As the nickel source, nickel nitrate, nickel acetate, nickel carbonate, nickel hydroxide, and nickel oxide are preferably used. The content of cerium, neodymium, zirconium, iron, and nickel used in the present invention is as follows:
per unit, 5 to 30 g as ceria, 2 to 15 g as neodymia, 1 to 8 g as zirconia, 0 to 5 g of iron oxide as Fe ₂ O ₃ , 0 to 10 g of nickel oxide as NiO (however, 0.5 to 1 as Fe ₂ O ₃ + NiO) Ten
The ceria content is preferably greater than the neodymia content and zirconia content, and the neodymia content is preferably greater than the total content of iron oxide and nickel oxide. The reason for specifying this quantity relationship is that by containing less neodymia and zirconia than ceria and more neodymia than iron oxide and/or nickel oxide, CO and
It improves NOx purification properties and reduces deterioration even when exposed to high temperatures of 800℃ or higher.Furthermore, it improves the activity of NOx, CO, and HC near the A/F equivalence point, allowing temperatures of 800℃ or higher. This is because it is less susceptible to deterioration due to exposure to high temperatures and changes in the engine atmosphere. At the same time as possessing the above characteristics, it is resistant to oxidizing atmosphere on the lean side of A/F fuel.
CO and HC oxidation activities are also sufficiently maintained, thus NOx
It is possible to maintain high activity near the equivalence point and stable activity over a wide range of A/F without impairing the purification properties of. Therefore, it is important to contain the metal oxides within the ranges specified above to prevent deterioration of the finished catalyst when used at high temperatures. In addition to the above-mentioned basic elements constituting the catalyst of the present invention, lanthanum and praseodymium can be used together, but it is desirable that the amount of these used is less than the amount of neodymium used. As mentioned above, the platinum group metal used in the present invention essentially includes rhodium, and platinum and/or palladium are used, but the amount of platinum group metal used is between 0.1 and 10 g per catalyst, respectively,
and/or Pd ratios between 1:100 and 1:1 can be used. The method for producing the catalyst according to the present invention is carried out, for example, by the following method. (1) First, activated alumina is supported on a honeycomb carrier having an integral structure by a conventional method, and then cerium, neodymium, zirconium, and soluble salts of iron and/or nickel are supported in an aqueous solution, dried, and fired. Finally, an aqueous solution of a soluble salt of a platinum group metal is supported and dried, calcined, or reduced and calcined to obtain a finished catalyst. (2) An aqueous solution or dispersion of cerium, neodymium, zirconium, iron and/or nickel soluble salts or finely powdered hydroxides or oxides is added to activated alumina and mixed into a honeycomb carrier having an integral structure. , dried and calcined, and then supported again in the form of an aqueous slurry, dried and calcined, and finally supported with an aqueous solution of a soluble salt of a platinum group metal, dried, calcined or reduced and calcined to obtain a finished catalyst. (3) An aqueous solution or aqueous dispersion of activated alumina, soluble salts of cerium, neodymium, zirconium, iron and/or nickel and platinum group metals, or finely powdered hydroxides and oxides on a honeycomb carrier having an integral structure. After addition and mixing, drying and calcining, the slurry is made to support again and then dried or calcined if necessary to obtain a finished catalyst. (4) Add and mix an aqueous solution or aqueous dispersion of cerium, neodymium, zirconium, iron and/or nickel soluble salts or finely powdered hydroxides or oxides to activated alumina into a honeycomb carrier having an integral structure. After being fixed by drying and baking, an aqueous solution of a soluble salt of a platinum group metal is further mixed, and after drying, baking or reduction baking,
The slurry is again supported and then dried or, if necessary, calcined to obtain a finished catalyst. In these manufacturing methods, drying is carried out at a temperature of 200°C or lower and baking is carried out between 200 and 900°C, preferably between 400 and 800°C. Among these production methods, particularly preferred embodiments are (3) and (4). The present invention will be explained in more detail with reference to Examples below, but it goes without saying that the present invention is not limited only to these Examples. Example 1 Commercially available cordierite monolith support (N-
(manufactured by COR) to prepare a catalyst. The monolith carrier had about 300 gas flow cells per square inch in cross section, and when cut into a cylindrical shape with an outer diameter of 33 mm and a length of 76 mm, it had a volume of about 65 ml. Cerium nitrate [Ce(NO ₃ ) ₃・6H ₂ O] 17.6g,
100 ml of 20.2 g of ferric nitrate [Fe(NO ₃ ) ₃ 9H ₂ O], 5.6 g of zirconyl nitrate [ZrO(NO ₃ ) ₂ ], 13.0 g of neodymium nitrate [Nd(NO ₃ ) ₃ 6H ₂ O] Rhodium nitrate aqueous solution [Rh(NO ₃ ) ₃ .
2.3 ml of nH ₂ O] (Rh = 50 g/) and 11.2 ml of a nitric acid aqueous solution (Pt = 100 g/) of dinitrodiaminoplatinum [Pt(NH ₃ ) ₂ (NO ₂ ) ₂ ] were added and stirred. 120g of activated alumina powder with a surface area of 120m ² /g and an average particle size of 50μ was added to this aqueous solution while stirring, and after thorough mixing, it was dried at 150℃ for 5 hours, and then heated to 600℃ in 2 hours in an electric furnace. And at this temperature 2
Firing was continued for a certain period of time, after which it was gradually cooled and taken out from the furnace. This was mixed with dilute nitric acid water in a ball mill.
A slurry for coating was prepared by mixed pulverization for 30 hours. The honeycomb type carrier was immersed in this coating slurry for 30 seconds, then taken out from the slurry, and excess slurry in the cells was blown out with compressed air to remove clogging from all cells. This catalyst was dried in a dryer at 140°C for 5 hours to obtain a complete catalyst. In addition, when the coating amount of this catalyst was measured, it was 140 g/-catalyst. Also, the ratio to the total supported amount is approximately Al ₂ O ₃ /CeO ₂ /Fe ₂ O ₃ /
ZrO ₂ /Nd ₂ O ₃ =120/7/4/3/5.
Regarding platinum and rhodium, Pt=1.12 g/-catalyst and Rh=0.11 g/-catalyst (hereinafter expressed similarly) were supported, respectively. Example 2 Catalysts with different compositions were prepared in the same manner as in Example 1. That is, the ratio of amounts of cerium nitrate, ferric nitrate, zirconyl nitrate, neodymium nitrate and activated alumina powder was changed. In addition, as a noble metal source, chloroplatinic acid [H ₂ PtCl ₆ ] was used instead of dinitrodiaminoplatinum, and rhodium chloride aqueous solution [RhCl ₃ .nH ₂ O] was used instead of rhodium nitrate aqueous solution to prepare a finished catalyst. The coating amount of this catalyst was measured and was 146g/
-It was a catalyst. Also, the ratio to the total supported amount is approximately Al ₂ O ₃ /CeO ₂ /Fe ₂ O ₃ /ZrO ₂ /Nd ₂ O ₃ =
It was 120/15/3/2/5. Regarding platinum and rhodium, Pt was supported at 1.12 g/Rh and Rhodium was supported at 0.11 g/Rh. Example 3 Cerium acetate [Ce(CH ₃ COO) ₃ ] 18.4 g, Iron oxide powder [Fe ₂ O ₃ ] 2 g, Zirconyl acetate [ZrO
(CH ₃ COO) ₂ ] 9.1 g, neodymium acetate [Nd
(CH ₃ COO) ₃ ] 15.3 g was dissolved in 100 ml of water. 120 g of activated alumina powder was added to this aqueous solution with stirring. After thorough mixing, the mixture was dried at 150°C for 5 hours, and then fired in an electric furnace at 600°C for 2 hours. On the other hand, rhodium nitrate aqueous solution (Rh=50g/)
Add 2.3 ml and 11.2 ml of dinitro-diaminoplatinum nitric acid aqueous solution (Pt = 100 g/), dilute with water.
Add the powder to 150 ml while stirring, and add 60 ml.
Stirring was continued for a minute. After that, Example 1
A finished catalyst was prepared by drying, calcination, and slurry formation using the same method as above. When the coating amount of this catalyst was measured, it was 146g/, and the ratio to the total supported amount was approximately Al ₂ O ₃ /CeO ₂ /
Fe ₂ O ₃ /ZrO ₂ /Nd ₂ O ₃ =120/10/2/5/8. For platinum and rhodium, Pt=1.12g/
, Rh=0.11g/supported. Example 4 Nickel or lanthanum was added using the same method as in Example 1. Namely, cerium, iron, zircon, neodymium nitrates and nickel nitrate [Ni
(NO ₃ ) ₂・6H ₂ O] or lanthanum nitrate [La
(NO ₃ ) _{3.6H 2} O] was simultaneously dissolved and charged to prepare a finished catalyst. The catalyst composition is shown below.

[Table] Example 5 A catalyst was prepared in the same manner as in Example 1. However, instead of platinum, the same amount of palladium was supported as the noble metal. A nitric acid aqueous solution of palladium nitrate [Pd(NO ₃ ) ₂ ] was used as a palladium source. As in Example 1, a rhodium nitrate aqueous solution was used to prepare the finished catalyst. When the coating amount of this catalyst was measured, it was 140g/. Moreover, the ratio to the total supported amount is approximately Al ₂ O ₃ /CeO ₂ /Fe ₂ O ₃ /
ZrO ₂ /Nd ₂ O ₃ =120/7/4/3/5.
For palladium and rhodium, Pd=1.12g/
, Rh=0.11g/supported. Example 6 A coated carrier was obtained in the same manner as in Example 1 except that the rhodium nitrate aqueous solution and the dinitrodiaminoplatinum aqueous solution were not added. Furthermore, this catalyst was calcined at 600°C for 2 hours. Next, the catalyst was immersed in an aqueous solution containing rhodium trichloride and chloroplatinic acid for 1 hour, taken out, and dried at 140° C. for 5 hours to obtain a finished catalyst. In addition, when the coating amount of this catalyst was measured, it was 140g/. Moreover, the ratio to the total supported amount is approximately Al ₂ O ₃ /CeO ₂ /
Fe ₂ O ₃ /ZrO ₂ /Nd ₂ O ₃ =120/10/2/3/4. For platinum and rhodium, Pt=1.12g/
, Rh=0.11g/supported. Example 7 The following finished catalyst was prepared in a manner similar to Example 1. When the coating amount of this catalyst was measured, it was 141g/. Also, the ratio to the total supported amount is Al ₂ O ₃ /CeO ₂ /Fe ₂ O ₃ /ZrO ₂ /Nd ₂ O ₃ =
It was 120/10/2/5/3. Regarding platinum and rhodium, Pt was supported at 1.12 g/Rh and Rh was supported at 0.11 g/Rh. Comparative Example 1 A catalyst having a composition not containing iron was prepared. That is, Example 1 except that ferric nitrate was not added.
The finished catalyst was prepared in a similar manner. When the coating amount of this catalyst was measured, it was 136 g/. Also, the ratio to the total supported amount is Al ₂ O ₃ /
CeO ₂ /Fe ₂ O ₃ /ZrO ₂ /Nd ₂ O ₃ =120/7/0/
It was 3/5. For platinum and rhodium, Pt=
1.12g/, Rh=0.11g/. Comparative Example 2 A catalyst was prepared that supported a larger amount of neodymia than ceria. Further, a finished catalyst was prepared in the same manner as in Example 2 except that the amounts of iron and zirconium were changed. When we measured the amount of coating on this catalyst,
It was 143g/. Also, the ratio to the total supported amount is Al ₂ O ₃ /CeO ₂ /Fe ₂ O ₃ /ZrO ₂ /Nd ₂ O ₃ = 120/
It was 7/4/3/10. Regarding platinum and rhodium, Pt was supported at 1.12 g/Rh and Rh was supported at 0.11 g/Rh. Comparative Example 3 A catalyst was prepared in which the amount of neodymia supported was smaller than the amount of iron oxide supported. Further, a finished catalyst was prepared in the same manner as in Example 3 except that the amount of zirconium was changed. When we measured the amount of coating on this catalyst,
It was 140g/. Also, the ratio to the total supported amount is Al ₂ O ₃ /CeO ₂ /Fe ₂ O ₃ /ZrO ₂ /Nd ₂ O ₃ = 120/
It was 10/4/3/2. Regarding platinum and rhodium, Pt was supported at 1.12 g/Rh and Rh was supported at 0.11 g/Rh. Comparative Example 4 A coating carrier containing only activated alumina, ceria, and neodymia was produced using the honeycomb carrier used in Example 1 in the same manner as in Example 6.
It was fired at 600℃. Next, rhodium and platinum were supported in the same manner as in Example 6 and dried at 140°C.
A completed catalyst was obtained by calcining at ℃ for 2 hours. The coating amount of this catalyst was measured and was found to be 141 g/kg. Also, the ratio to the total supported amount is Al ₂ O ₃ /
CeO ₂ /Nd ₂ O ₃ =120/10/10. For platinum and rhodium, Pt = 1.12g/, Rh = 0.11g/
was carrying it. Comparative Example 5 A catalyst containing no neodymia was prepared. First, only activated alumina was supported on the honeycomb carrier used in Example 1, dried, and fired at 700°C for 2 hours. Then, this alumina-coated carrier was impregnated with an aqueous solution in which cerium nitrate, zirconyl nitrate, and iron nitrate were dissolved. It was dried and baked at 700°C for 2 hours. This coated carrier was further loaded with rhodium and platinum in the same manner as in Example 6, dried at 140°C, and calcined at 500°C for 2 hours to obtain a finished catalyst.
The coating amount of this catalyst is 115g/
The ratio to the total supported amount is Al ₂ O ₃ /CeO ₂ /
ZrO ₂ /Fe ₂ O ₃ = 100/4/6/4, and for platinum and rhodium, Pt = 1.12g/, Rh = 0.11
g/ was supported. Example 8 The ternary characteristics of the catalysts from Example 1 to Example 7 and the catalysts from Comparative Example 1 to Comparative Example 5 were evaluated using engine exhaust gas. The engine used in this experiment was a commercially available electronically controlled 4-cylinder 1800c.c., and the test method used was a method that modeled the A/F status of an actual closed-loop engine. Forcibly vibrate in ±0.5 A/F units (i.e. A/F14.0 to A/F15.0) for 1 hour, and then change the center by 0.2 from A/F = 15.1 to 14.1.
Measure the purification rates of CO, HC, and NO components by varying the amount of water, plot the purification rates of the three components on the vertical axis, plot the center point of A/F on the horizontal axis, and use the resulting graph to determine the three components. The catalytic reaction characteristics were compared. That is,
The intersection point of the CO and NO purification rate curves [called the crossover point (COP)] is the criterion for a good catalyst.
In terms of the height of COP and the A/F width that can achieve a purification rate of 80% or more at the same time, the one with the higher value of the former (COP) and the one with the higher value of the latter (A/F width) are selected. The reaction was carried out by filling the catalyst into a bench multi-converter. Evaluation conditions are inlet gas temperature 400℃, SV
= approximately 90000Hr ^-1 (STP), catalyst volume = 65ml. The evaluation results are shown in Table 1, and all of the catalysts of the present invention have a high intersection point (crossover point) of the conversion rate curves of NO and CO, and also have a high A/F value width (80% window) that can simultaneously remove 80% or more. ) was also wide. On the other hand, the comparative example had a low crossover point and a narrow window width.

【table】

[Table] Example 9 The catalyst whose initial activity was evaluated in Example 8 was subjected to endurance running using an engine bench test device. The engine used was a commercially available electronically controlled 8-cylinder engine.
4400c.c., and its durability operation method adopted a mode operation method using a program setter. i.e. 60
Engine speed per second 3000 rpm x boost pressure (-
300mmHg), then return the throttle for 7 seconds to turn off the fuel. After 7 seconds, the engine speed will be approximately
It becomes 1800rpm. During this deceleration, the inlet oxygen concentration reaches 19% to 20%, causing rapid deterioration of the catalyst. The catalyst is packed in a multi-converter, and during steady running, the inlet temperature is 850℃ and the space velocity (SV) is approximately 350000Hr ^-1 (STP) A/F =
14.65 for 100 hours, and the ternary characteristics were evaluated again using the same evaluation method as in Example 6.
The evaluation results are shown in Table 2. The catalyst of the present invention had a very high level of crossover point and an effective window, but the catalysts of the comparative examples all had a low crossover point and almost no window.

【table】

【table】 [Brief explanation of the drawing]

Figure 1 shows the new A/F of Example 1.
A graph showing changes in CO, HC, and NO purification rates (%) is shown.

Claims (1)

[Claims] 1. Activated alumina, ceria, neodymia, zirconia and
Oxidation of hydrocarbons, carbon monoxide, and nitrogen in exhaust gas by supporting at least one selected from the group consisting of iron oxide and nickel oxide, and at least one selected from the group consisting of platinum and palladium, and rhodium. A catalyst used for the simultaneous purification of substances, containing 50 to 200 g of activated alumina, 5 to 30 g of ceria, and 2 g of neodymia per carrier.
~ _15g , 1-8g of zirconia, 0-5g as iron oxide _Fe2O3 , 0-10 as nickel oxide NiO
g (however, 0.5 to 10 g as Fe ₂ O ₃ + NiO), platinum group metals consisting of platinum and palladium in a total range of 0.1 to 10 g, and rhodium in a total range of 0.1 to 10 g.
The exhaust gas is further characterized in that the ceria content is greater than the neodymia content and the zirconia content, and the neodymia content is greater than the total content of iron oxide and nickel oxide. Honeycomb catalyst for gas purification.