JPH08988A - Chemical reaction control method - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] To provide a novel method for improving the conventional chemical reaction control method using a catalyst. [Structure] A chemical reactivity is controlled by changing an adsorption state of a molecule by changing an electronic state of a metal cluster supported on the support or a surface of the support. Specifically, it is composed of a surface composed of the carrier 3 and the metal cluster 2, and a metal electrode 1 installed near the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for improving a chemical reaction control method using a conventional catalyst.

[0002]

2. Description of the Related Art A typical conventional industrial catalyst is a supported metal catalyst in which one or more kinds of active metal clusters are supported on a carrier made of an oxide such as alumina. From such combinations, catalysts with higher selectivity and higher reaction activity have been searched for and prepared. The performance of these catalysts, once prepared, is constant or deteriorates with time, and the performance cannot be controlled during the reaction. Further, it is conventionally known that an electric circuit is controlled by applying an electric field with a metal electrode such as a MOS type semiconductor to form an electronic circuit. However, it is known to control the reactivity of molecules by applying an electric field. It has not been applied in the past.

[0003]

DISCLOSURE OF THE INVENTION In the present invention, the charge distribution on the surface of an active metal cluster or a carrier is determined by
Partially subtly changing provides a reaction system with higher selectivity and higher activity.

[0004]

According to the present invention, the electronic state of the surface of an active metal cluster or carrier is changed by applying an electric field from outside or inside the surface, or directly from an electrode formed on the surface. It is possible to control the activity and selectivity of the reaction delicately by putting in and out. Here, the number of metal electrodes is one or more, and each electrode does not necessarily have the same potential. In addition, the size and type of the metal cluster whose respective electrodes change the charge may be different. Further, as a method of controlling the electronic state of the surface of the cluster or the carrier, it is possible to apply a magnetic field or to form a temporary excited state by light irradiation, in addition to applying an electric field. When transferring charges to and from metal clusters,
The carrier is preferably an insulator or a semiconductor. The type and size of the metal cluster are arbitrary, but small clusters of 10 nm or less with many steps or kink structures on the surface are preferable.

[0005]

The energy of the highest occupied level of electrons is changed by increasing or decreasing the charge on the surface of the active metal cluster or carrier, or by irradiating a magnetic field or light to change the amount of charge transfer to the adsorbed molecule. Can be controlled to change the adsorption state such as dissociative adsorption of molecules. As a result of controlling the adsorption state of molecules, the reaction activity and the selectivity of reaction products can be increased. That is, in principle, by applying an external electric field / magnetic field, injecting charges, or partially irradiating light to the metal cluster supported on the carrier, the substantial work function (electron The active point can be increased or decreased by changing the energy level of the highest occupied level. This can change the activity or selectivity of the reaction.

[0006]

【Example】

Example 1 As shown in FIG. 1, Pd clusters 2 were formed on the surface of carrier alumina 1 by vapor deposition. Deposition amount is 5 × 10 ¹⁴ atom
At s / cm ² , it was confirmed that Pd clusters having a diameter of ˜2 nm were formed. The metal electrode 3 was brought close to this sample and an electric field was applied. Metal electrode 4 on the back side of the carrier alumina
And an electric field is created between the metal electrodes 1 and 4. By changing the potential of the metal electrode 3, a positive or negative electric dipole was induced on the sample surface.

FIG. 2 shows the relaxation process of the induced dipole after extinguishing this electric field. When CO gas is exposed to this sample, molecular dissociation occurs when the sample surface is negative, and when the sample surface is positive, it is observed that it is adsorbed as a molecule as a change in surface work function or potential. It was
This state is shown in FIG.

When the sample surface is uniformly charged positively and negatively with an electron beam and argon ions, the dissociation of CO molecules occurs at least in the range of negative charge density of 0.1 to 1 × 10 ⁹ electrons / cm ² , Molecular adsorption is at least positive charge density 0.
It was confirmed that this occurs in the range of 1 to 1 × 10 ⁹ electrons / cm ² . The higher the CO gas pressure, the faster the dissociation rate. In addition, even when this sample was exposed to NO, SO ₂ , and CO ₂ gas, dissociation of molecules occurred when the sample surface was negative, and when the sample surface was positive, it was adsorbed as molecules. C
When H ₂ gas is caused to flow at the same time as the O gas, the dissociated C reacts with H ₂ when the sample surface is negative, so that CH ₄
Was generated, and in the case of a positive value, molecularly adsorbed CO and H ₂ reacted to generate CH ₃ OH.

Example 2 As shown in FIG. 4, metal electrodes 3 and 3'were formed on the surface of carrier alumina 1 by a lithographic method, and Pd clusters were further formed by a vapor deposition method. By changing the potential of the metal electrode, the sample surface around the electrode was positively or negatively charged. This sample is used for CO, NO, SO ₂ , C
When exposed to O ₂ gas, dissociation of molecules occurred when the sample surface was negative, and when the sample surface was positive, it was adsorbed as molecules, as in Example 1. When H ₂ gas was flowed at the same time as CO gas, CH ₄ was produced when the sample surface was negative, and CH ₃ OH was produced when it was positive.

Example 3 As shown in FIG. 5, first, an insulating film was formed by oxidizing the surface on which a plurality of metal (Al) electrodes 3, 3 ′ were formed by a lithography method. Pd clusters were formed on this surface by vapor deposition. By changing the potentials of the plurality of metal electrodes, an electric field was generated between the external electrode 5 and the metal electrodes 3, 3 ', and a positive or negative dipole was induced on the sample surface. This sample is CO,
When exposed to NO, SO ₂ and CO ₂ gases, dissociation of molecules occurred in the place where the sample surface was negative, and was adsorbed as molecules in the place where it was positive. When H ₂ gas was caused to flow at the same time as CO gas, CH ₄ was produced at a place where the sample surface was negative and CH ₃ OH was produced at a place where the sample surface was positive.

[0011]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a reaction system having higher selectivity and higher activity by partially and subtly changing the electronic states of the active metal clusters and the carrier surface after the catalyst preparation. You can

[Brief description of drawings]

FIG. 1 is a perspective view of a sample surface and electrodes in Example 1.

FIG. 2 is a state of relaxation of dipoles induced when an electric field is applied in Example 1.

FIG. 3 shows C in Example 1 when the surface is positive or negative.
This is a change in surface potential due to adsorption of O molecules.

FIG. 4 is a perspective view of a sample surface and electrodes in Example 2.

5 is a perspective view of a sample surface and electrodes in Example 3. FIG.

[Explanation of symbols]

1 ... Carrier, 2 ... Metal cluster, 3 ... Metal electrode, 3 '... Metal electrode, 4 ... Metal electrode, 5 ... Metal electrode.

Claims (4)

[Claims] 1. A chemical reaction control method comprising controlling a chemical reaction by changing the charge distribution of a metal cluster or a metal thin film supported on a solid surface or the charge distribution on a supported solid surface. 2. An electric field is applied to the charge distribution on the surface of the metal cluster or the charge distribution on the surface of the supported solid by applying one or more metal electrodes inside or outside the solid, or by using one or more metal electrodes on the surface of the solid. The chemical reaction control method according to claim 1, wherein the control is performed by directly taking in and out electrons. 3. The chemical reaction control method according to claim 1, wherein the charge distribution on the surface of the metal cluster or the charge distribution on the surface of the supported solid is changed by applying a magnetic field from the outside. 4. The method for controlling a chemical reaction according to claim 1, wherein the charge distribution on the surface of the metal cluster or the charge distribution on the surface of the supported solid is changed by irradiating light from the outside.