EP0645466A1

EP0645466A1 - Catalyst material, based on a titanium-copper alloy and process for producing the same

Info

Publication number: EP0645466A1
Application number: EP94114639A
Authority: EP
Inventors: Tsuyoshi Masumoto; Akihisa Inoue; Katsutoshi Nosaki; Hideo Fukui
Original assignee: Honda Motor Co Ltd; YKK Corp
Current assignee: Honda Motor Co Ltd; YKK Corp
Priority date: 1993-09-29
Filing date: 1994-09-16
Publication date: 1995-03-29
Anticipated expiration: 2014-09-16
Also published as: DE69411483D1; DE69411483T2; EP0645466B1; JPH07163879A

Abstract

A Ti-Cu based alloy catalyst material having a composition including at least one element selected from the group consisting of V, Ni, Zr, Cr, Mn, Fe and Co as a partial substitute element for Ti and/or Cu in a composition represented by the general formula Ti_100-aCu_a, wherein "a" is, in atomic %, 30 ≦ a ≦ 50, 0.1 to 20 atomic % in the general formula Ti_100-aCu_a being substituted with said at least one element, in which a fine Ti-Cu intermetallic compound having a mean particle size of 10 nm or less is uniformly precipitated in an amorphous phase and/or α-Ti matrix. The alloy catalyst is produced by preparing an alloy of the above-specified composition having an amorphous phase and/or α-Ti matrix, and heating the alloy at a temperature of from the transformation temperature T_x of a non-equilibrium phase minus 50 K to the transformation temperature T_x plus 100 K so as to precipitate a fine Ti-Cu intermetallic compound in the matrix. The catalyst material is not only excellent in mechanical properties but also useful as a catalyst for various reactions.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention provides a highly hard and highly active Ti-Cu based alloy suitable for use as a catalyst material capable of catalyzing, for example, hydrogenation of carbon monoxide.

2. Description of the Prior Art

Catalysts for use in the reaction in which carbon monoxide is hydrogenated to produce hydrocarbons and water have pretty widely been investigated, which include ruthenium-bearing alumina and Ti-Cu based alloy catalysts. However, it is often difficult to obtain a catalyst having a large specific surface area required for catalytic activity from crystalline alloys produced by the conventional processes because of their nonuniform chemical properties and brittleness.
On the other hand, it has recently become known that a microcrystalline structure having a size ranging from several tens of nanometers to several microns can be obtained by the heat treatment of an amorphous metal. Investigations of reinforced materials in which the above crystalline structure is utilized are being promoted, creating some results. A further refinement of the microcrystalline structure would lead to a further improvement of mechanical properties and a more effective exhibition of catalytic activities. However, it has been difficult to stably obtain a finer microcrystalline structure by the use of the conventional techniques.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a Ti-Cu based alloy suitable for use as a catalyst material having increased catalytic activity and improved mechanical properties by further refining the size of the microcrystalline structure and stabilizing the presence thereof in the Ti-Cu based alloy.
In a first aspect of the present invention, there is provided a Ti-Cu based alloy catalyst material having a composition including at least one element selected from the group consisting of V, Ni, Zr, Cr, Mn, Fe and Co as a partial substitute element for Ti and/or Cu in a composition represented by the general formula Ti_100-aCu_a, wherein "a" is, in atomic %, 30 ≦ a ≦ 50, 0.1 to 20 atomic % in the general formula Ti_100-aCu_a being substituted with said at least one element, in which a fine Ti-Cu intermetallic compound having a mean particle size of 10 nm or less is uniformly precipitated in an amorphous phase and/or an α-Ti matrix.
The above intermetallic compound is contained in the alloy catalyst in an amount of 5 to 90% by volume.
In a second aspect of the present invention, there is provided a process for producing the aforestated Ti-Cu based alloy catalyst material which comprises preparing an alloy having the above-specified Ti_100-aCu_a composition in which 0.1 to 20 atomic % thereof is substituted with at least one element selected from the group consisting of V, Ni, Zr, Cr, Mn, Fe and Co, the alloy having an amorphous phase and/or α-Ti matrix; and heating the alloy at a temperature ranging from the transformation temperature T_x of a non-equilibrium phase minus 50 K (i.e., T_x - 50 K) to the transformation temperature T_x plus 100 K (i.e., T_x + 100 K) so as to precipitate a fine Ti-Cu intermetallic compound in the matrix. Hereinafter, the transformation temperature T_x of a non-equilibrium phase is referred to "transformation temperature" or "T_x" unless otherwise specified.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a graph indicating the relationship between the particle size of the alloy of Ti_48.5Cu_48.5Mn₃ and the reaction rate measured in the hydrogenation of CO.
Fig. 2 is a graph indicating the relationship between the volume percentage of the intermetallic compound contained in the same alloy as in Fig. 1 and the reaction rate measured in the hydrogenation of CO.
Fig. 3 is a graph indicating the relationship between the heat treatment temperature applied in preparing the same alloy as in Fig. 1 and the particle size of the intermetallic compound.
Fig. 4 is a graph indicating the relationship between the heat treatment time taken in the heat treatment of the same alloy as in Fig. 1 at 400°C and the particle size of the intermetallic compound.
Fig. 5 is a micrograph showing the crystalline structure of the alloy of Ti_48.5Cu_48.5Zr₃ obtained by the present invention.
Fig. 6 is a micrograph showing the crystalline structure of the alloy of Ti_48.5Cu_48.5Mn₃ obtained by the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described above, in the Ti-Cu based alloy catalyst material of the present invention, Ti and/or Cu in the Ti_100-aCu_a composition is partially substituted with at least one additional element selected from the group consisting of V, Ni, Zr, Cr, Mn, Fe and Co in an amount of 0.1 to 20 atomic % of the composition. In the thus modified alloy material, fine particles of Ti-Cu intermetallic compound having a mean particle size of 10 nm or less are uniformly precipitated throughout an amorphous phase and/or α-Ti matrix.
Examples of the above intermetallic compounds include Ti₂Cu, TiCu, Ti₂Cu₃ and TiCu₃. It is requisite that the precipitated intermetallic compound have a mean particle size of 10 nm or less. When the mean particle size exceeds 10 nm, the mechanical performance and catalytic activity of the alloy catalyst would rapidly be deteriorated with the increase in the particle size. Fig. 1 shows a graph indicating the relationship between the particle size of the alloy of Ti_48.5Cu_48.5Mn₃ and the reaction rate measured in the hydrogenation of CO.
It is preferred that the intermetallic compound be contained in the matrix in an amount of 5 to 90% by volume. When the amount is less than 5% by volume, not only is it too small to cause the resultant catalyst to exhibit desired catalytic activity but also the mechanical strength of the alloy catalyst is likely to be poorer than in the range of 5 to 90% by volume. On the other hand, when the amount of the intermetallic compound exceeds 90% by volume, not only is it too large to cause the resultant catalyst to have desired catalytic activity improvement but also the activity lowering by sintering is likely to occur during the use of the catalyst.
Fig. 2 shows a graph indicating the relationship between the volume percentage of the intermetallic compound contained in the alloy of Ti_48.5Cu_48.5Mn₃ and the reaction rate measured in the hydrogenation of CO.
In the present invention, the matrix may be an amorphous phase, a fine Ti matrix phase or a phase of a mixture thereof. When the matrix is an amorphous phase, a structure in which fine Ti crystals and a Ti-Cu intermetallic compound have been precipitated would result. When the matrix consists of fine Ti crystals, a structure in which a Ti-Cu intermetallic compound has been precipitated therein would result.
According to the production process of the present invention, the above alloy having an amorphous phase and/or α-Ti matrix may be prepared by rapid solidification in which the cooling rate is 10⁴ to 10⁶ K/sec. When the cooling rate is lower than 10⁴ K/sec, any alloy having the composition according to the present invention and having the desired matrix cannot be obtained. The cooling rate exceeding 10⁶ K/sec cannot be attained by any industrial quenching means utilizing the currently available liquid quenching, etc.
The heat treatment for precipitating a Ti-Cu intermetallic compound must be conducted at a temperature ranging from the transformation temperature T_x minus 50 K to the transformation temperature T_x plus 100 K. When the alloy before the heat treatment is composed of an amorphous phase or includes an amorphous phase, the transformation temperature is the crystallization temperature of the amorphous phase. When the temperature is lower than the transformation temperature T_x minus 50 K, it is hard to attain precipitation of the Ti-Cu intermetallic compound which effectively acts in the catalytic activity desired in the present invention, so that the heat treatment takes a prolonged period of time. Thus, such a heat treatment is not practical and makes it difficult to form the intermetallic compound at a desirable volume percentage.
Fig. 3 shows a graph indicating the relationship between the heat treatment temperature applied in preparing the alloy of Ti_48.5Cu_48.5Mn₃ and the particle size of the intermetallic compound. When the heat treatment temperature exceeds the transformation temperature T_x plus 100 K, not only is the Ti-Cu intermetallic compound precipitated in excess but also the compound becomes coarse within a short period of time to thereby fail to effectively act as a catalyst in accordance with the object of the present invention. Further, when the heat treatment temperature exceeds the transformation temperature T_x plus 100 K, mechanically and chemically detrimental intermetallic compounds having been dissolved in the matrix are also precipitated so as to cause the alloy to become mechanically brittle and to have lowered catalytic activity.
Fig. 4 shows a graph indicating the relationship between the heat treatment time taken in the heat treatment of the alloy of Ti_48.5Cu_48.5Mn₃ at 400°C and the particle size of the intermetallic compound.
It is preferred that the heat treatment time be at least 0.01 hr. When the time is shorter than 0.01 hr, the heating must be conducted at a temperature of at least T_x plus 100 K for obtaining effective particle size. It is industrially difficult to achieve particle size control by uniformly heating within the above short period of time.
The reason for limiting the substitution with at least one additional element in the Ti_100-aCu_a composition to 0.1 to 20 atomic % is that an amorphous phase and/or α-Ti matrix required to form the desired microcrystalline structure can be obtained by the limitation, and that, outside the above range, it is difficult to stably obtain such a matrix.
Heating at 400°C in a vacuum for 1 hr converts a Ti-Cu based amorphous alloy to a crystalline structure of Ti-Cu intermetallic compound phase having a coarse particle size as large as about 1 to 2 µm. However, the addition of the above additional element to the amorphous alloy suppresses the growth of crystal grains, so that a crystalline structure results which has a size of about 1/10 to 1/1000 of that of the crystalline structure formed when no such additional element is added. This crystalline structure is a Ti-Cu intermetallic compound phase corresponding to the respective compositional proportions of Ti and Cu. The refining of the crystalline structure as indicated above catalytically activates and improves the properties of the alloy to thereby render the same excellent as a catalyst material.

Example

An alloy having a given composition was prepared by the use of an arc melting furnace. The alloy was inserted into a silica tube having a small opening at its tip, and heated to melt the alloy. The silica tube was placed just above a 200-mm roll, and the molten alloy was injected through the small opening of the silica tube under an argon pressure of 0.7 kg/cm² while rotating the roll at a speed as high as 4000 rpm so as to cause the injected alloy to contact the roll surface, thereby effecting quench solidification of the alloy. Thus, a thin ribbon having a width of about 1 mm was obtained. The thin ribbon was heated at 400°C for 1 hr in a vacuum to thereby crystallize the same. Thus, a fine crystalline structure phase was obtained. This grain-refinement of the crystal not only has a marked effect on the mechanical properties of the thin ribbon but also ensures effective action as a catalyst in chlorofluorocarbon decomposition, benzene hydrogenation, carbon monoxide hydrogenation, alcohol dehydration and other reactions. Comparative data with respect to mechanical properties on the alloy having the above microcrystalline structure relative to the TiCu alloy not containing any additional element and thus consisting of coarse crystal grains are shown in Table 1. Figs. 5 and 6 show the fine intermetallic compound structures of Ti_48.5Cu_48.5Zr₃ and Ti_48.5Cu_48.5Mn₃ obtained by the present invention, respectively. Table 1

Composition of alloy Crystal particle size Vickers hardness (Hv)

Ti₅₀Cu₅₀ 1-2 µm 578

Ti_48.5Cu_48.5Zr₃ 10 nm 685

Ti_48.5Cu_48.5Mn₃ 5 nm 712

Further, comparative data with respect to the catalytic performance in carbon monoxide hydrogenation at 280°C are shown in Table 2.

Table 2

Composition of alloy	Reaction rate at 280°C
Ti₅₀Cu₅₀	2.0x10⁻¹⁰mol/g·s
Ti_48.5Cu_48.5Zr₃	5.2x10⁻⁴mol/g·s
Ti_48.5Cu_48.5Mn₃	1.9x10⁻⁷mol/g·s
Note: CO/H₂ = 4, total pressure = 1 atm.

Tables 1 and 2 show data on the catalysts in which Zr and Mn were employed as the additional elements. The use of at least one member selected from the group consisting of the other additional elements, i.e., V, Ni, Cr, Fe and Co in place of Zr and Mn or together with either one or both of them gives similar results.
The present invention provides a Ti-Cu based alloy catalyst material which is excellent in mechanical properties and catalytic activity. The Ti-Cu based alloy catalyst effectively catalyzes chlorofluorocarbon decomposition, benzene hydrogenation, carbon monoxide hydrogenation, alcohol dehydration and other reactions.

Claims

A Ti-Cu based alloy catalyst material having a composition including at least one element selected from the group consisting of V, Ni, Zr, Cr, Mn, Fe and Co as a partial substitute element for Ti and/or Cu in a composition represented by the general formula Ti_100-aCu_a, wherein "a" is, in atomic %, 30 ≦ a ≦50, 0.1 to 20 atomic % in the general formula Ti_100-aCu_a being substituted with said at least one element, in which a fine Ti-Cu intermetallic compound having a mean particle size of 10 nm or less is uniformly precipitated in an amorphous phase and/or α-Ti matrix.
The Ti-Cu based alloy catalyst material according to claim 1, in which said Ti-Cu intermetallic compound is finely and uniformly dispersed in the matrix and contained in an amount of 5 to 90% by volume.
A process for producing a Ti-Cu based alloy catalyst material which comprises preparing an alloy having a composition including at least one element selected from the group consisting of V, Ni, Zr, Cr, Mn, Fe and Co as a partial substitute element for Ti and/or Cu in a composition represented by the general formula Ti_100-aCu_a, wherein "a" is, in atomic %, 30 ≦ a ≦ 50, 0.1 to 20 atomic % in the general formula Ti_100-aCu_a being substituted with said at least one element, said alloy having an amorphous phase and/or α-Ti matrix; and heating the alloy at a temperature ranging from the transformation temperature T_x of a non-equilibrium phase minus 50 K to the transformation temperature T_x plus 100 K so as to precipitate a fine Ti-Cu intermetallic compound in the matrix.
The process for producing a Ti-Cu based alloy catalyst material according to claim 3, in which said transformation temperature T_x is the crystallization temperature.
The process for producing a Ti-Cu based alloy catalyst material according to claim 3, in which said alloy having an amorphous phase and/or α-Ti matrix is prepared by rapid solidification at a cooling rate of 10⁴ to 10⁶ K/sec.
The process for producing a Ti-Cu based alloy catalyst material according to claim 3, in which said precipitated fine Ti-Cu intermetallic compound has a mean particle size of 10 nm or less.
The process for producing a Ti-Cu based alloy catalyst material according to claim 3, in which said Ti-Cu intermetallic compound is uniformly precipitated in the matrix in an amount of 5 to 90% by volume.