JP2017042734A - Catalytic reaction control device - Google Patents

Abstract

Provided is a catalytic reaction control device capable of promoting and controlling catalytic activity by an external power source in a gas phase reaction. SOLUTION: A catalyst material, a counter electrode, a solid electrolyte layer disposed between the catalyst material and the counter electrode, and a voltage electrically connected to the catalyst material and the counter electrode are applied. The catalyst material is a dense film that does not conduct the constituent elements and constituent ion species of the electrolyte layer, and the thickness of the catalyst material is 12 nm or less. [Selection] Figure 1A

Description

  The present invention relates to a device for controlling and accelerating a catalytic reaction accompanied by a dissociation of polyatomic molecules in a gas phase reaction.

  In the gas phase reaction, there are many industrially important reactions such as chemical synthesis and exhaust gas purification reaction, and in order to increase the efficiency of the reaction, the development of catalyst materials has been energetically performed.

  The role of the catalyst in the gas phase reaction is to increase the reaction efficiency by forming adsorbed atoms or adsorbed molecules with high reaction activity as reaction intermediates by dissociating and adsorbing reactants, which are stable substances, on the catalyst surface. That is. Since the dissociative adsorption of the reactant dominates the reaction rate, the catalyst material is required to have characteristics that promote or control the dissociative adsorption. Since dissociative adsorption of the reactant is promoted by momentarily donating electrons from the catalyst material to the reactant, it is necessary to improve the electron donating ability of the catalyst material in order to improve the catalytic activity of the catalyst material. It is well known that there is a need to increase the electron concentration in the catalyst material (Non-patent Document 1). Thus, many developments have been made to increase the electron concentration of the catalyst material and improve the electron donating ability.

For example, in Patent Document 1 and Non-Patent Document 2, a catalyst such as iron or ruthenium is a 12CaO · 7Al ₂ O ₃ mayenite type compound having a high electron donating ability in order to improve the electron donating ability of the catalyst for ammonia generation. A catalyst structure to be supported on is disclosed. Patent Document 2 discloses a material in which molybdenum, rhenium, or niobium is added to a platinum catalyst to adjust the electron concentration of platinum in order to adjust the catalytic activity in the carbon monoxide shift reaction. In Non-Patent Document 3, by forming a platinum catalyst on the ferroelectric PbTiO ₃ , by changing the occupancy rate of electrons in platinum, that is, by changing the electron concentration, the adsorption energy of CO changes and the reaction rate changes. It is disclosed.

International Publication No. 2012/077658 JP 2004-97948 A

Surface Science 114, 527 (1982) Nature Chemistry 4,934 (2012) Physical Review Letters 98,166101 (2007)

  In catalytic reactions, reaction conditions such as temperature and reactant concentration, and catalyst surface conditions such as catalyst surface coverage of reaction intermediates vary temporally and spatially, so in order to obtain optimal catalyst activity, It is necessary to change the electron donating ability of the catalyst material according to the reaction conditions. However, in the prior art, since the electron donating ability was adjusted by material synthesis such as the mixing ratio and composition of the catalyst material, the electron concentration could not be controlled according to the change of reaction conditions, and the optimum catalyst activity was controlled. There was a problem that it was not possible.

The catalytic reaction control device of the present disclosure includes:
A device for promoting and controlling the catalytic ability of a gas phase reaction containing a molecule composed of two or more atoms as a reactant,
A catalyst material, a counter electrode, a solid electrolyte layer disposed between the catalyst material and the counter electrode, and an external power source that is electrically connected to the catalyst material and the counter electrode and can apply a voltage,
The catalyst material is a dense film that does not conduct constituent elements or constituent ion species of the electrolyte layer,
The catalyst material has a thickness of 12 nm or less.

  According to one aspect of the catalytic reaction control device of the present disclosure, by controlling the voltage applied to the catalyst material, the electron concentration and the electron donating ability in the catalyst material can be controlled, and the reaction conditions and the surface state of the catalyst can be controlled. Accordingly, a catalyst device exhibiting suitable catalytic activity can be realized.

1 is a cross-sectional view illustrating an embodiment of a catalytic reaction control device. 1 is a cross-sectional view illustrating an embodiment of a catalytic reaction control device. Process sectional drawing which shows an example of the manufacturing method of the catalytic reaction control device 101a of 1st Embodiment. Process sectional drawing which shows an example of the manufacturing method of the catalytic reaction control device 101a of 1st Embodiment. Process sectional drawing which shows an example of the manufacturing method of the catalytic reaction control device 101a of 1st Embodiment. Process sectional drawing which shows an example of the manufacturing method of the catalytic reaction control device 101b of 2nd Embodiment. Process sectional drawing which shows an example of the manufacturing method of the catalytic reaction control device 101b of 2nd Embodiment. Process sectional drawing which shows an example of the manufacturing method of the catalytic reaction control device 101b of 2nd Embodiment. Process sectional drawing which shows an example of the manufacturing method of the catalytic reaction control device 101b of 2nd Embodiment. Process sectional drawing which shows an example of the manufacturing method of the catalytic reaction control device 101b of 2nd Embodiment. The top view which shows the catalytic reaction control device 101b of an Example. Sectional drawing which shows the catalytic reaction control device 101b of an Example. The top view which shows the manufacturing method of the catalytic reaction control device 101b of an Example. Sectional drawing which shows the manufacturing method of the catalytic reaction control device 101b of an Example. The top view which shows the manufacturing method of the catalytic reaction control device 101b of an Example. Sectional drawing which shows the manufacturing method of the catalytic reaction control device 101b of an Example. The top view which shows the manufacturing method of the catalytic reaction control device 101b of an Example. Sectional drawing which shows the manufacturing method of the catalytic reaction control device 101b of an Example. The top view which shows the manufacturing method of the catalytic reaction control device 101b of an Example. Sectional drawing which shows the manufacturing method of the catalytic reaction control device 101b of an Example. The top view which shows the manufacturing method of the catalytic reaction control device 101b of an Example. Sectional drawing which shows the manufacturing method of the catalytic reaction control device 101b of an Example. The graph which shows the change of the electron density by the voltage application in the catalyst material 102 in Example 1-3 and Comparative Examples 1 and 2. 3 is a graph showing the responsiveness of changes in electron concentration in the catalyst material 102 with respect to voltage application in Example 1. The graph which evaluated the work function change of the electron in the catalyst material 102 by the voltage application in Example 1 using the X ray photoelectron spectroscopy. The graph which shows the change of the electron donating ability of the catalyst material 102 by Example 1-3 and Comparative Examples 1 and 2 by voltage application.

  As a result of intensive studies to obtain a catalytic reaction control device having a high electron donating ability, the present inventors have formed a dense and thin catalyst film on one surface of the solid electrolyte layer, and on the other surface of the solid electrolyte layer. It was found that the electron donating ability of the catalyst layer can be modulated by forming a counter electrode and applying a voltage between the counter electrode and the catalyst material.

(Embodiment)
The catalytic reaction control device of the first embodiment will be described with reference to the drawings.

  FIG. 1A is a schematic cross-sectional view of the catalytic reaction control device 101a of the first embodiment.

  The catalytic reaction control device 101 a includes a catalyst material 102, a counter electrode 104, and a solid electrolyte layer 103 disposed between the catalyst material 102 and the counter electrode 104. The solid electrolyte layer 103 is in contact with the catalyst material 102 and the counter electrode 104. In order to apply a voltage between the catalyst material 102 and the counter electrode 104, one end of the external power source 105 is electrically connected to the catalyst material 102, and the other end of the external power source 105 is electrically connected to the counter electrode 104. ing. At the time of electrical connection to the catalyst material 102, it is preferable to form a low resistance bus electrode 107 on the catalyst material 102 and to form an electrical connection to the bus electrode 107 in order to reduce the series resistance value. The bus electrode 107 is preferably formed in a grid shape so as not to greatly impair the surface area of the catalyst material 102.

  As shown in FIG. 1B, a counter electrode 104, a solid electrolyte layer 103, a catalyst material 102, and a bus electrode 107 are sequentially stacked on a substrate 106, and a DC power source 105 is connected between the catalyst material 102 and the counter electrode 104. May be.

  Hereinafter, each component will be described in detail.

(Catalyst material 102)
The catalyst material 102 may be any material that exhibits catalytic activity and has electron conductivity. In view of catalytic activity and electronic conductivity in various materials, a metal material containing a transition metal having 3d electrons, 4d electrons, and 5d electrons in the outermost shell, or an oxide, nitride or sulfide containing a transition metal is preferable. . More preferably, a material containing platinum, nickel, iron, cobalt, ruthenium, rhodium, palladium, copper, gold, or iridium as a main component is preferable.

  The catalyst material 102 is a dense material that does not conduct / permeate the conductive ion species of the solid electrolyte layer 103 and does not cause a redox reaction with the conductive ion species of the solid electrolyte layer 103.

  In the present invention, a chemical reaction occurring on the surface of the catalyst material 102 is promoted / controlled using a huge charge generated at the interface between the solid electrolyte 104 and the catalyst material 102. Therefore, the catalyst material 102 needs to be sufficiently thin in order for the influence of the electric charge generated on the interface side to affect the surface side. The thickness of the catalyst material 102 is preferably 12 nm or less, and more preferably 6 nm or less.

(Solid electrolyte layer 103)
The solid electrolyte layer 103 may be any material as long as it exhibits ionic conduction under catalytic reaction conditions. The specific value of the ionic conductivity may be about 10 ⁻⁷ S / cm or more. Examples of conductive ionic species include H ⁺ , H ⁻ , O ²⁻ , Li ⁺ , Na ⁺ , Mg ²⁺ , Ca ²⁺ , and Ag ⁺ , but are not limited to these ionic species. A typical material composing the solid electrolyte layer 103 is a proton conductor A (B _1-x C _x ) O _{3-x / 2} type perovskite oxide (A = alkaline earth metal such as Sr or Ba) B = tetravalent cation materials such as Zr and Ce, C = trivalent cation materials such as Y, In and Sc), yttrium-stabilized zirconia (YSZ) which is an oxygen ion conductor, and gadolinium-doped ceria (GDC). ), Lithium ion conductor (La _{2 / 3-x} Li _3x ) TiO ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , β-alumina, MAg ₄ I ₅ (monovalent alkali metal such as M = Rb) Etc.

  The thickness of the solid electrolyte layer 103 is not particularly specified, but is preferably 100 um or less in order to obtain a sufficiently high response speed (about 0.1 Hz or more) for performing catalytic reaction control. More preferably it is. On the other hand, if the thickness is too thin, electron leakage is likely to occur.

(Counter electrode 104)
The counter electrode 104 may be any electronic conductive material that does not cause a redox reaction with the solid electrolyte layer 103. For example, gold, platinum, copper, aluminum, strontium ruthenate, strontium titanate doped with Nb or La, and alloys containing these are preferable. Further, a material (titanium, nickel, chromium, cobalt, iridium, etc.) for increasing the adhesion strength at the interface with the solid electrolyte layer 103 may be sandwiched.

(Bus electrode 107)
The bus electrode 107 may be any material that is stable in the reaction atmosphere and exhibits good electron conductivity. For example, gold, silver, copper, platinum, nickel, aluminum and the like are preferable.

(Manufacturing method of catalytic reaction control device 101a)
Hereinafter, a method for manufacturing the catalytic reaction control device 101a of the first embodiment will be described with reference to FIGS. 2A to 2C.

  First, as shown in FIG. 2A, a solid electrolyte layer 103 is formed. For forming the solid electrolyte layer 103, for example, the material for forming the solid electrolyte layer 103 is sufficiently pulverized and mixed with a ball mill or the like, then press-molded, and then sintered in air at a high temperature of 1000 ° C to 1500 ° C. There is a way.

  Thereafter, in order to flatten the surface, it is preferable to polish both surfaces of the solid electrolyte layer 103.

  Next, as shown in FIG. 2B, the counter electrode 104 is formed on one main surface of the solid electrolyte layer 103, and the catalyst material 102 is formed on the other main surface of the solid electrolyte layer 103. For the formation of the counter electrode 104, for example, a sputter deposition method, a vacuum deposition method, a screen printing method, or the like can be used. Alternatively, the counter electrode 104 may be previously formed in a foil shape or a plate shape, and may be attached on the solid electrolyte 103.

  For the formation of the catalyst material 102, a sputtering vapor deposition method, a vacuum vapor deposition method, a chemical vapor deposition method (hereinafter referred to as a CVD method), a pulse laser deposition method (hereinafter referred to as a PLD method), a sol-gel method, or the like can be used.

  Thereafter, as shown in FIG. 2C, a bus electrode 107 is formed. For the formation of the bus electrode 107, a sputter deposition method, a vacuum deposition method, a screen printing method, or the like can be used.

  Finally, one end of the external power source 105 and the bus electrode 107 are electrically connected, the other end of the external power source 105 and the counter electrode 104 are electrically connected, and a voltage is applied.

(Manufacturing method of catalytic reaction control device 101b)
Hereinafter, a method for manufacturing the catalytic reaction control device 101b of the second embodiment will be described with reference to FIGS. 3A to 3E.

  First, as shown in FIG. 3A, the counter electrode 104 is formed on the surface of the substrate 106 prepared in advance. The counter electrode 104 can be formed by sputtering, vacuum deposition, CVD, PLD, sol-gel, or the like.

  Next, as shown in FIG. 3B, the solid electrolyte layer 103 is formed on the counter electrode 104. For example, a thin film forming method such as a sputter deposition method, a vacuum deposition method, a CVD method, a PLD, or a sol-gel method can be used.

  Subsequently, as shown in FIG. 3C, the catalyst material 102 is formed on the solid electrolyte layer 103. For the formation of the catalyst material 102, a sputter deposition method, a vacuum deposition method, a CVD method, a PLD method, a sol-gel method, or the like can be used.

  Thereafter, as shown in FIG. 3D, the bus electrode 107 is formed. For the formation of the bus electrode 107, a sputter deposition method, a vacuum deposition method, a screen printing method, or the like can be used.

  Finally, as shown in FIG. 3E, one end of the external power source 105 and the bus electrode 107 are electrically connected, the other end of the external power source 105 and the counter electrode 104 are electrically connected, and a voltage is applied.

(Example)
The result of producing the catalytic reaction control device 101b and evaluating the device performance will be described.

Example 1
(Production of catalytic reaction control device)
In Example 1, in order to measure the change in the electron concentration of the catalyst material 102 due to voltage application and the change in the electron donating ability, as shown in FIGS. 4A and 4B, the catalyst material 102 is formed in a channel shape, The bus electrode 107 was formed so as to intersect with both ends thereof.

First, as shown in FIGS. 5A and 5B, an SrTiO ₃ (100) substrate was used as the substrate 106, and an SrRuO ₃ film was formed on the substrate 106 as the counter electrode 104 by the PLD method. A SrRuO ₃ sintered body was used as a target. The film forming conditions by the PLD method were as follows.

Laser pulse energy: 100 mJ
Pulse frequency: 5Hz
Oxygen partial pressure: 10 Pa
Substrate temperature: 700 ° C
Distance between target and substrate: 40mm
In order to form a pattern of the counter electrode 104 at the time of film formation, the counter electrode 104 was formed through a hard mask in which a through hole was formed in a 100-um thick SUS plate. The thickness of the obtained counter electrode 104 was about 100 nm.

Next, as shown in FIGS. 5C and 5D, a solid electrolyte layer 103 made of La _0.56 Li _0.33 TiO ₃ was formed using the PLD method. A sintered body having a composition of La _0.56 Li _0.43 TiO ₃ was used as a target. The film formation conditions by PLD were as follows.

Laser pulse energy: 50 mJ
Pulse frequency: 10Hz
Oxygen partial pressure: 10 Pa
Substrate temperature: 800 ° C
Distance between target and substrate: 40mm
In order to form a pattern of the solid electrolyte layer 103 at the time of film formation, the solid electrolyte layer 103 was formed through a hard mask in which a through hole was formed in a SUS plate having a thickness of 100 μm. The thickness of the obtained solid electrolyte layer 103 was about 300 nm.

  Subsequently, as shown in FIGS. 5E and 5F, a catalyst material 102 made of gold was formed on the solid electrolyte layer 103 by a sputtering method. A lift-off method was used to form the pattern of the catalyst material 102. The resulting catalyst material 102 had a thickness of 3 nm.

  Thereafter, as shown in FIGS. 5G and 5H, a bus electrode 107 having a titanium / platinum laminated structure was formed by a sputtering method. A lift-off method was used to form the bus electrode 107 pattern.

  Finally, as shown in FIGS. 5I and 5J, the external power source 105 was electrically connected to the bus electrode 107 and the counter electrode 104, and the bus electrode 107 was grounded.

(Evaluation of electron concentration change by voltage application)
Next, the change in the electron concentration in the catalyst material 102 of the catalytic reaction control device 101b of Example 1 produced by the above method was evaluated.

A voltage (V _G ) was applied using the external power source 105, and the resistance value of the catalyst material 102 at different V _G was evaluated. Application of the DC voltage V _G, and the measurement of the resistance of the catalyst material 102, a semiconductor parameter analyzer (Agilent Co., HP4156B) was used. Evaluation of resistance using a four-terminal method, the conversion of the electronic density change [Delta] n _e from the resistance value, using the following formula.

_{Δn e = (ρ (V G} ) -ρ (V G = 0) / ρ (V G = 0) × n e, Au
ρ (V _G ) = R (V _G ) × w × t / L
Here, R (V _G ) is the resistance measurement value of the catalyst material 102 at the voltage V _G , w is the channel width of the catalyst material 102, t is the thickness of the catalyst material 102, and L is between the voltage measurement terminals in the four-terminal measurement. The length of ρ _e , _Au is the electron concentration of gold, and ρ _e , _Au = 5.9 × 10 ²² / cm ³ .

In Example 1, the change in the electron concentration by applying the voltage (V _G ) of the catalyst material 102 is as shown in FIG. By applying a voltage of +1.0 V, the electron concentration of 3.5 × 10 ²⁰ / cm ³ increased, and by applying a voltage of −1.5 V, the electron concentration of 3 × 10 ²⁰ / cm ³ decreased.

Next, in Example 1, the response speed with respect to voltage application of the electron concentration change of the catalyst material 102 was evaluated. FIG. 7 shows time responses of changes in electron concentration when the applied voltage V _G is sequentially changed to 0V, + 1V, 0V, −1V, and 0V.

(Evaluation of change in electron donating ability of catalyst material 102 with voltage application)
In Example 1, the change in the electron donating ability of the catalyst material 102 with voltage application was evaluated. For the evaluation of the electron donating ability change, the work function change of the catalyst material 102 was measured using X-ray photoelectron spectroscopy (SPring-8, BL16XU).

The result of measuring the change in the electron work function of the catalyst material 102 is as shown in FIG. The work function change ΔΦ due to the application of the voltage V _G corresponds to Φ (V _G ) −Φ (V _G = 0) in FIG. 8, and ΔΦ = 150 meV. A positive ΔΦ indicates a decrease in work function and an improvement in electron donating ability.

(Example 2)
A catalytic reaction control device of Example 2 was produced in the same manner as in Example 1 except that the thickness of the catalyst material 102 was changed. In Example 2, the obtained catalyst material 102 had a thickness of 6 nm.

In Example 2, the change in the electron concentration of the catalyst material 102 at V _G = + 1 V was about 2 × 10 ²⁰ / cm ³ , and the work function change amount was a decrease of 80 meV.

(Example 3)
A catalytic reaction control device of Example 3 was produced in the same manner as in Example 1 except that the thickness of the catalyst material 102 was changed. In Example 3, the obtained catalyst material 102 had a thickness of 12 nm.

In Example 3, the change in the electron concentration of the catalyst material 102 at V _G = + 1 V was about 1 × 10 ²⁰ / cm ³ , and the work function change amount was a decrease of 60 meV.

(Comparative Example 1)
A catalytic reaction control device of Comparative Example 1 was produced in the same manner as in Example 1 except that the thickness of the catalyst material 102 was changed. In Comparative Example 1, the thickness of the obtained catalyst material 102 was 20 nm.

In Comparative Example 1, the work function change amount at V _G = + 1 V was 10 meV or less, and no significant difference was observed.

(Comparative Example 2)
A catalytic reaction control device of Comparative Example 2 was produced in the same manner as in Example 1 except that the material of the solid electrolyte layer 103 was changed to SiO ₂ . The SiO ₂ film was formed by sputtering under the following conditions.

RF power 200W
Substrate temperature 300 ° C
Oxygen partial pressure 1Pa
In Comparative Example 2, there was no significant change in the electron concentration of the catalyst material 102 due to the application of the voltage V _G , and the work function change amount at V _G = + 1 V was 10 meV or less, and no significant difference was observed.

(Results and Discussion)
The results of Examples 1 to 3 and Comparative Examples 1 and 2 described above are shown in FIGS.

From the results of FIG. 6, in Examples 1-3, the catalyst material 102 is formed over the solid electrolyte layer 103, by applying a voltage V _G, the electron concentration in the catalyst material 102 is 10 ²⁰ / cm ³ It changed with the order. The amount of change in the electron concentration changes with respect to the value of the applied voltage and can be controlled. On the other hand, as shown in the result of Comparative Example 2, when SiO ₂ , which is a dielectric material that does not conduct ions, is used for the solid electrolyte layer 103, the electron concentration of the catalyst material 102 did not change. From the above results, it can be seen that the electron concentration of the catalyst material 102 can be controlled by forming the catalyst material 102 on the solid ion conductor and applying a voltage.

  From the results shown in FIG. 7, the response speed of the change in the electron concentration of the catalyst material 102 due to voltage application is on the order of 1 sec. It was.

From the results of FIG. 9, in Examples 1 to 3, the work function was decreased by applying the voltage V _G , but in Comparative Example 1, no change in the work function was observed. This is a phenomenon in which a change in electron concentration due to voltage application occurs in the vicinity of the interface between the solid electrolyte layer 103 and the catalyst material 102, and a change in electron concentration in the vicinity of the interface results in a work function change, that is, the amount of electrons on the surface It shows that the thickness of the catalyst material 102 needs to be 12 nm or less in order to contribute to the Fermi level change.

  The catalytic reaction control device disclosed in the present application can promote and control the catalytic reaction in the gas phase reaction by applying voltage, such as ammonia generation / decomposition reaction, hydrocarbon generation from synthesis gas, carbon monoxide oxidation reaction, etc. It is useful as an application.

101a Catalytic reaction control device of the first embodiment 101b Catalytic reaction control device of the second embodiment 102 Catalytic material 103 Solid electrolyte 104 Counter electrode 105 DC power source 106 Substrate 107 Bus electrode

Claims (4)

A device for promoting and controlling the catalytic ability of a gas phase reaction containing a molecule composed of two or more atoms as a reactant,
A catalyst material, a counter electrode, a solid electrolyte layer disposed between the catalyst material and the counter electrode, and an external power source that is electrically connected to the catalyst material and the counter electrode and can apply a voltage,
The catalyst material is a dense film that does not conduct constituent elements or constituent ion species of the electrolyte layer,
A device having a thickness of the catalyst material of 12 nm or less. The catalytic reaction control device according to claim 1,
The catalyst reaction control device, wherein the catalyst material contains platinum or gold. The device of claim 2, comprising:
The said solid electrolyte is an oxide containing La, Li, and Ti. The catalytic reaction control device characterized by the above-mentioned. The catalytic reaction control device according to claim 3, wherein
The gas phase reaction is an ammonia generation reaction containing nitrogen gas and hydrogen gas as reactants;
Ammonia decomposition reaction containing ammonia as a reactant,
Water-gas shift reaction that produces hydrogen and carbon dioxide using carbon monoxide and water as reactants,
A reaction that produces hydrocarbons using carbon monoxide and hydrogen as reactants,
A catalytic reaction control device, characterized in that it is one of exhaust gas purification reactions containing any or all of carbon monoxide, nitrogen oxides and hydrocarbons as reactants.

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