JPH04363138A - Oxidation catalyst - Google Patents

Abstract

PURPOSE:To obtain a catalyst enabling oxidation of hydrocarbon, CO, etc., at, a low temp. CONSTITUTION:A transition metal is substd. for Mg in the structure of a double chain structure type clay mineral which has been made amorphous by heat treatment, and fine Pt or Pd particles are supported in a highly dispersed state to obtain an oxidation catalyst. Since the transition metal is substd. for Mg, it is highly dispersed without destructing the fine structure of the clay mineral and a carrier having excellent adsorbing characteristics is formed. Since the fine Pi or Pd particles are supported in a highly dispersed state, they act concertedly on adsorbed matter accordingly hydrocarbon and CO can be oxidized at a low temp. Since the clay mineral has been made amorphous, excellent heat resistance is ensured and the catalyst can be used as a catalyst for purification of exhaust gas.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for oxidizing hydrocarbons, carbon monoxide, etc. at low temperatures.

0002

2. Description of the Related Art Inorganic porous materials are commonly used as catalyst carriers. As the inorganic porous material, examples using a composite oxide consisting of titanium, nitrogen, zirconia, etc. (Japanese Patent Application Laid-Open No. 2-63552), examples using an aggregate of ceramic fibers (Japanese Patent Application Laid-Open No. 1-245850), and alumina, Examples using silica, titania or alumina-silica carriers (Japanese Patent Application Laid-open No. 62-201648), as well as A-type zeolite, 64-4220) has been disclosed. These methods focus on the solid acidity of the porous material or the size of the BET surface area. However, the oxidation performance of these is still not sufficient (the 50% conversion temperature of hydrocarbons is high as a performance evaluation standard), and for example, a catalyst with even higher activity is required for practical use as a catalyst for purifying automobile exhaust gas. was.

On the other hand, catalysts in which metals are supported on multi-chain clay minerals have excellent adsorption ability for gases and liquids, and have conventionally been used as catalysts for chemical reactions and purification adsorbents. It is also considered to be promising as a catalyst. However, "Catalyst for hydrotreating hydrocarbons" (Japanese Patent Application Laid-Open No. 53-34691)
), in which the structure of clay minerals is broken down with strong acids at low temperatures to support ions such as lanthanides and iron that serve as catalytic metals, the amount of supported metal ions is small and sufficient catalytic activity cannot be imparted. I couldn't do it.

[0004] Furthermore, in this method, there was a risk that the crystal structure of the double-chain clay mineral would be disrupted by the strong acid. Furthermore, since a strong acid is used, it is necessary to invest in manufacturing equipment and environmental purification, resulting in high manufacturing costs.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an oxidation catalyst having high activity as an oxidation catalyst for hydrocarbons and carbon monoxide.

In particular, it is an object of the present invention to provide an oxidation catalyst suitable for purifying exhaust gas from automobiles and the like.

[0007]

[Means for Solving the Problems] As a result of intensive research to achieve the above object, the present inventors have invented an oxidation catalyst using a double-chain clay mineral as a carrier as disclosed below.

[Configuration of the first invention] The oxidation catalyst of the first invention comprises a clay mineral with a double-chain structure that is at least partially amorphous at a temperature of 400° C. or higher and 800° C. or lower; It is characterized by consisting of platinum and/or palladium supported on clay minerals.

[0009] The structure of a double-chain clay mineral heat-treated at a temperature of 400°C or higher and 800°C or lower is a transitional structure that transitions from one crystal structure to the next. At least a portion of it appears to be in an amorphous state (hereinafter referred to as an amorphous state or an amorphous body for simplicity). In addition, fine particles of platinum and/or palladium are dispersed and supported via OH groups present on the asymmetric planes of amorphous clay minerals with a specific surface area of 120 m2/g or more, so they are at a high altitude close to the atomic state. It is in a dispersed state.

[0010] When treated at less than 400°C, the structure of the double-chain clay mineral is unstable and the structure is restored by absorbing water, so there is no amorphous part and the platinum and/or palladium It is difficult to support the particles in a highly dispersed manner. If the clay mineral is treated at a temperature exceeding 800°C, the structure of the double-chain clay mineral changes to an enstatite crystal structure and the OH groups in the structure disappear, making it impossible to support the platinum catalyst in a highly dispersed manner.

[Structure of the second invention] The oxidation catalyst of the second invention is a clay mineral with a double-chain structure that becomes at least partially amorphous at a temperature of 400°C or more and 800°C or less, and its constituent elements It is characterized by comprising a clay mineral in which at least a portion of certain magnesium and/or aluminum has been replaced with a transition metal element, and platinum and/or palladium supported on the clay mineral.

[0012] The structure of the double-chain clay mineral heat-treated at a temperature of 400°C or more and 800°C or less is a transitional structure that transitions from one crystal structure to the next, and as in the first invention, at least Part of it is in an amorphous state. The clay mineral in the second invention utilizes the fact that constituent elements such as aluminum and magnesium are easily replaced with other elements in an amorphous state.

[0013] The transition metal elements substituted with the constituent elements are highly dispersed in the multi-chain clay mineral, and fine particles of platinum and/or palladium are present on the asymmetric planes of the amorphous clay mineral. It is supported in a highly dispersed state close to an atomic state via OH groups.

[0014] At temperatures below 400°C, the structure of the double-chain clay mineral is not amorphous and there is little substitution of transition metals. Furthermore, at temperatures exceeding 800° C., the structure of the double-chain clay mineral changes to a stable enstatite crystal structure, making it difficult for transition metal substitution to occur.

[0015]

[Effect]

[Operation of the first invention] A multi-chain structure type clay mineral is not one large single crystal, but an aggregate of fine crystals, and has asymmetric surfaces at places where the crystal structure is cut. Hydroxyl groups are present on this asymmetric surface, and metal complexes such as platinum are easily adsorbed thereon.

[0016] By the way, double-chain structure type clay minerals are heated at 400°C.
When heat-treated at a temperature of 800° C. or lower, the crystal structure of the clay mineral collapses, resulting in a transitional amorphous state for transition to the next crystal structure. In this state, the original crystal structure is collapsed, and the number of asymmetric planes described above increases. For this reason, the OH groups present in the chiral plane increase and spread throughout the double-chain structure type clay mineral, resulting in a highly dispersed state.

[0017] Furthermore, since the amorphous double-chain structure type clay mineral has a high specific surface area (120 m2/g or more), it has excellent gas and liquid adsorption properties.

Since the platinum and/or palladium of the present invention is supported via the OH groups in this state, it does not aggregate and becomes highly dispersed. Therefore, the catalyst of the present invention becomes an oxidation catalyst with high activity.

[Operation of the second invention] In the second invention, since the structure is such that the binding strength of magnesium and aluminum in the amorphous clay mineral is reduced and replaced with transition metal elements, the substituted transition Metal elements are placed between the fibers or in channels (tunnels extending along the fiber direction with a cross-sectional width of about 1 to 0.6 nm that exist in the fibers) suitable for the diffusion and adsorption of hydrocarbons, carbon monoxide, etc. It can exist in a highly dispersed state without destroying the structure.

Furthermore, since the structure is such that platinum and/or palladium are supported in a highly dispersed manner as in the first invention using the double-chain structure type clay mineral substituted with the transition metal element as a carrier, platinum and/or palladium are supported in a highly dispersed manner. It is presumed that a concerted action occurs with the transition metal element. That is, a reaction occurs in which the transition metal adsorbs hydrocarbons, carbon monoxide, etc., and platinum and/or palladium in the vicinity oxidizes them.

[0021]

【Effect of the invention】

[Effects of the first invention] In the catalyst of the present invention, platinum and/or palladium are highly dispersed and supported, and combined with the adsorption properties of the amorphous support having a large specific surface area, it is possible to absorb hydrocarbons, carbon monoxide, etc. at low temperatures. It has excellent oxidation activity.

Furthermore, since the catalyst of the present invention is amorphous, there is no structural change due to the detachment of water, etc., which is conventionally retained, and the catalyst has excellent heat resistance. In addition, it is less susceptible to hydration reactions with water and poisoning by amines.

Therefore, the present invention can be used as an exhaust gas purification catalyst for internal combustion engines, etc.

[Effect of the second invention] The catalyst of the present invention has a high content of platinum and/or palladium on an amorphous double-chain structure type clay mineral carrier with a large specific surface area in which a transition metal is incorporated into the structure. Since it is supported in a dispersed state, the carrier,
Transition metals and platinum and/or palladium act in concert and have particularly excellent activity to oxidize hydrocarbons, carbon monoxide, etc. at low temperatures.

Therefore, the present invention can be used as an exhaust gas purification catalyst for internal combustion engines, etc.

[0026]

[Examples] The present invention will be explained in detail below using specific examples and examples.

(Specific Example 1) Sepiolite, palygorskite, and attapulgite can be used as the double-chain structure type clay mineral. Its composition is sepiolite is Si12Mg8
O30(OH2)4 ・8H2 O, attapulgite and palygorskite are (MgAl)5 (Si
Al)8O20(OH)2 .8H2O.

These are clay minerals whose main component is hydrated magnesium silicate and which has highly reactive hydroxyl groups on its surface. This clay mineral consists of fibers with a diameter of about 0.05 to 0.6 μm, and parallel to the fibers there are channels (channels) having a rectangular cross-sectional area of about 1 to 0.6 nm. It also has a large BET specific surface area of 350 to 400 m2/g.

(Specific Example 2) A metal consisting of platinum and/or palladium supported in a highly dispersed state is present in a raft-like structure or in a monoatomic state with a small number of metal atoms in the metal cluster, and the metal is supported in a highly dispersed state. The amount is 0.1wt% or more1
It is desirable that the content be 0 wt% or less. When the amount is less than 0.1 wt%, the catalytic effect is almost lost. If it exceeds 10 wt%, the metal clusters will become coarse and the catalytic activity will decrease. Moreover, since the amount of metal supported becomes large, the cost increases.

(Specific Example 3) The transition metals include V, Mn,
Fe, Co, Ni and Cu are suitable.

[0031] The appropriate amount of these transition metals to be ion-exchanged is 5 to 10 wt% relative to magnesium and/or aluminum in the clay mineral.

[0032] If the amount is more than this, the activity as an oxidation catalyst decreases because diffusion paths and adsorption sites such as between fibers and channels existing in the double-chain clay mineral are crushed. If the amount is less than this, the amount of concerted reaction between the transition metal and platinum and/or palladium will decrease, resulting in a decrease in activity as an oxidation catalyst.

(Specific Example 4) The method for producing an oxidation catalyst of the present invention involves heat-treating a double-chain structure type clay mineral at a temperature of 400°C or higher and 800°C or lower to change the structure of the clay mineral and at least partially a heat treatment process to amorphize the
A substitution step in which magnesium and/or aluminum ions in the clay mineral are ion-exchanged with transition metal ions, and platinum and/or palladium ions are reacted on the ion-exchanged double-chain structure clay mineral to form platinum and/or palladium ions.
Alternatively, it consists of a supporting step of supporting palladium. However, in the first invention, the substitution step may be omitted.

[0034] The heat treatment temperature in the heat treatment step is 400
℃~800℃. If the temperature is lower than 400°C, the structure of the clay mineral cannot be changed sufficiently. Temperatures exceeding 800° C. are not preferred because the structure of the clay mineral changes to enstatite-type crystals, making it difficult to support metal elements and causing pores to disappear. When the pores disappear, it becomes impossible to secure gas adsorption sites and effective passages for gas diffusion. Heat treatment can make the structure of the clay mineral amorphous and reduce the bonding strength between magnesium or aluminum and oxygen.

[0035] When the heat treatment is carried out, first, zeolite water and crystalline water present in the tunnels in the structure of the clay mineral are removed. At the same time, the crystal structure changes, and the Mg that makes up the crystal
The Mg-O bond strength of the octahedron of the O layer decreases, and magnesium becomes ionized and easily eluted in water. This also applies to aluminum replacing magnesium.

[0036] The heat treatment temperature is particularly preferably 600°C to 700°C, where amorphization is large and ion exchange is most likely to occur.

[0037] In the step of replacing magnesium and/or aluminum in the clay mineral with at least one selected from transition elements in the amorphous double-chain structure type clay mineral,
Clay minerals are first dispersed in water to create a suspension. The amount of water at this time is preferably 10 times the weight or more. If the amount is less than this, the clay mineral will be poorly suspended, and it will be difficult to uniformly replace magnesium and/or aluminum with the transition metal. The transition metals replacing magnesium and/or aluminum are preferably introduced in salt form. In this step, these metal salts are added to the suspension and mixed.

[0038] When transition metal ions are allowed to act in water, magnesium and/or aluminum, which has a reduced binding strength, of the clay mineral is ionized and can be easily ion-exchanged with transition metal ions. By replacing transition metal ions with high catalytic activity with magnesium and/or aluminum ions and introducing them into the structure of the clay mineral,
These transition metals are strongly and highly dispersed.

[0039]Although double-chain structure type clay minerals heat-treated at 400°C to 800°C have a BET specific surface area of 120 m2/g or more, the specific surface area does not decrease due to ion substitution. Rather, it becomes a strong and stable structure, and the specific surface area also increases.

Furthermore, in the supporting step of supporting a metal consisting of platinum and/or palladium, a compound of platinum and/or palladium is added to the solution in which the transition metal-substituted double-chain clay mineral produced in the above step is suspended. Alternatively, a solution of the compound is added to support platinum and/or palladium.

(Example 1) As the double-chain structure type clay mineral, sepiolite powder from Turkey was used. This sepiolite powder was placed in an alumina crucible and heated to 400℃ in a nichrome furnace.
Heat treatment was carried out by holding the sample in a temperature range of 800° C. for 4.5 hours. 20g of sepiolite heat-treated at each predetermined temperature from 400℃ to 800℃ was collected, and platinum was 0.4 to 10%.
wt% dinitrodiamine platinum nitric acid solution. After dipping, the mixture was stirred on a heating stirrer, and excess water was evaporated at a temperature of 110° C. to 120° C. under uniform stirring using a heater. Thereafter, excess moisture was evaporated in a dryer at 110°C. After evaporating all the water, it was heated at 350℃ in a nichrome furnace for 3 hours.
The oxidation catalyst of this example was prepared by firing for a period of time.

An oxidation activity test was conducted on this catalyst as follows. First, the prepared oxidation catalyst was
After press-molding at a pressure of m2, it was crushed with a cutter knife and classified into sizes of 6 to 10 mesh. Weigh out 7 cc of this crushed grain, fill it in a quartz tube with an inner diameter of 15 mm, and use gas containing 500 ppm of C3H6 as a hydrocarbon and 1% of carbon monoxide CO as a carbon oxide, at a temperature that allows 50% conversion of these. I looked into it. The results are shown in Table 1 (A
1 to A11).

[0043]

[Table 1]

Table 1 also shows comparative examples where the heat treatment temperature is less than 400°C and those where the heat treatment temperature is over 800°C (R1 to
R6), and one using θ-alumina as a carrier (
R7) results are shown. The 50% conversion temperature of the catalyst of this example is lower than that of the catalyst of the comparative example prepared at temperatures below 400°C and above 800°C and the catalyst using alumina as a carrier, and its activity as an oxidation catalyst is extremely high. . For the catalysts used in this example, 10 mesh particles were used.

(Example 2) 30 g of Turkish sepiolite heat-treated at 650° C. and 900 cc of ion-exchanged water were placed in a household mixer and operated for 10 minutes to fully disperse the sepiolite in the ion-exchanged water. After dispersion, chlorides of Co, Ni, Fe, Mn, and V as transition metal compounds were added in an amount equivalent to 3 mol of metal atoms per 1 mol of sepiolite, and dissolved using a mixer to prepare a solution of each transition metal compound. Sepiolite was added to this solution and stirred for 30 minutes using a Dispa to ion-exchange the magnesium in the sepiolite with each transition metal element. After that, suction filtration is repeated several times to thoroughly wash away chlorine ions, etc.
Removed. Thereafter, it was dried at 100° C. for 15 hours, and 4 wt % of platinum was supported thereon in the same manner as in Example 1 to obtain the oxidation catalyst of this example.

The oxidation activity of the obtained catalyst was determined in the same manner as in Example 1. The results are shown in Table 2 (A12 to A16).

[0047] As a comparative example, below 400°C and 8°C
A catalyst (R8
~R12) was used. As is clear from Table 2, the 50% conversion temperature of the catalyst of this example is much lower than that of the catalyst of Comparative Example, and is also lower than that of the catalyst of Example 1, making it suitable as an oxidation catalyst. It has particularly excellent activity.

[0048]

[Table 2]

(Example 3) Sepiolite 10 from Turkey
Put the powder of 0 mesh or less into an alumina crucible, and
Heat treatment was performed by holding at a predetermined temperature in the temperature range of 00 to 800°C for 4.5 hours. After the heat treatment, the sepiolite was ground into powder of 100 mesh or less in an alumina mortar. 20g of this sepiolite powder was collected and palladium was 0.1~
It was immersed in a dinitrodiamine palladium nitric acid solution corresponding to 10 wt%. Excess water was evaporated by a heater while stirring the immersed mixed suspension on a heating stirrer. Furthermore, it was dried in a dryer at 110°C. After completely removing moisture, it was fired in a nichrome furnace at a temperature of 350° C. for 3 hours to prepare the oxidation catalyst of this example.

The oxidation activity of the obtained catalyst was determined in the same manner as in Example 1. The results are shown in Table 3 (A17-A28).

[0051] Also, as a comparative example, below 400°C and 8°C
Catalysts (R13 to R18) prepared in exactly the same manner as in this example using sepiolite heat-treated at a temperature exceeding
) was used. Further, catalysts (R19, R20) prepared using alumina as a carrier and otherwise prepared in the same manner as in this example were used. As is clear from Table 3, 50% of the catalyst of this example
The % conversion temperature is much lower than that of the catalyst of the comparative example, and it has particularly excellent activity as an oxidation catalyst.

[0052]

[Table 3]

Claims (2)

[Claims] [Claim 1] Consisting of a double-stranded clay mineral that is at least partially amorphized at a temperature of 400°C or more and 800°C or less, and platinum and/or palladium supported on the double-stranded clay mineral. An oxidation catalyst characterized by: 2. A clay mineral with a double-chain structure that is at least partially amorphous at a temperature of 400° C. or higher and 800° C. or lower, in which at least a portion of the constituent elements magnesium and/or aluminum are transition metal elements. An oxidation catalyst characterized by comprising a clay mineral substituted with , and platinum and/or palladium supported on the clay mineral.