RU2609788C1 - Production method for nanowire catalyst - Google Patents

Abstract

FIELD: nanotechnologies.

SUBSTANCE: auxiliary layer, in which groove rows are formed of nanometer depth with vertical walls, is applied to a supporter; the layer of a catalyst material of nanometer thickness, on the top of which a photoresist mask with a pattern of narrow strips located aslant the grooves is formed, is applied; the layer of the catalyst material is removed by means of anisotropic etching up to the auxiliary layer retaining it on the side walls of the grooves and under the mask. The mask is removed. Supporters with nanowires are orderly allocated in a reactor.

EFFECT: increasing of end product output, consumption reducing of expensive catalyst material, and reducing of gas-dynamic resistance of the reactor.

4 cl, 1 dwg

Description

The invention relates to nanotechnology, can be used in the chemical industry to create effective catalysts.

Currently, nanowires are increasingly used. They are used in the manufacture of various electronic, optical and magnetic devices, in the creation of biological and chemical sensors and catalysts. These applications are based on the unique physical properties of various materials that manifest themselves at nanometer-sized samples.

The fundamental difference between nanoparticles and nanowires from bulk materials is that the number of atoms on their surface is commensurate with the number of atoms in the volume, and the radius of curvature of the surface is very small. It is generally accepted that precisely these features provide a high catalytic activity of nanostructured catalysts in comparison with their analogues based on bulk materials [1-3].

The key point in heterogeneous catalysis is the effective specific surface area of the catalyst — the surface of the catalyst particles involved in electrochemical processes, referred to the mass of the catalyst. That is why most of the catalysts studied in laboratories and used in technology contain nanoparticles whose size lies in the range of 1-100 nm.

To increase the yield of the final synthesis product, the gas flow rate relative to the catalyst should be high. In the synthesis of ethylene from a mixture of methane and oxygen at a temperature of 550 ° C on a catalyst using nanowires, the relative volumetric rate of the gas flow should be at least 20,000 per hour (20,000 gas volumes through 1 reactor volume) [1]. For an industrial reactor in the form of a column with a catalyst-coated filler several meters long and with a cross section of less than a meter, the flow rate should be several tens of meters per second, which is difficult to ensure, so many small reactors with lower flow rates must be used.

Porous substances such as zeolite and boehmite, which are coated with a thin layer of platinum, are usually used as filler [2]. Nanoparticles and nanowires form in the pores and cracks of these materials, but the area of these nano formations is small relative to the area of the continuous coating of the filler. Therefore, the effectiveness of such a catalyst is relatively small. The use of an array exclusively of nanowires would be more efficient.

For the manufacture of nanowires, various methods are currently used: mechanical [4], selective growth method [5], using nanodispersed particles of a crystal growth catalyst [6], focused ion beam [7], using the spacer formation process [8], standard photolithographic process [9] and many other methods.

Closest to the proposed invention, the technical solution is a method for the manufacture of nanowires, described in the patent [8]. It consists in the fact that an insulating layer is applied to the semiconductor substrate, on the surface of which grooves with vertical walls are formed by photolithography, a polysilicon layer is applied, which is then removed by anisotropic etching from horizontal surfaces to the insulating layer, leaving polysilicon nanowires on the side walls of the grooves.

The problem to which the invention is directed, is to obtain a catalyst consisting of substrates with an active surface in the form of a continuous ordered array of nanowires that will increase the yield of the final product, reduce the consumption of expensive catalytic material (e.g., platinum) and reduce the gasdynamic resistance of the reactor.

The problem is solved in a method comprising the following steps: applying an auxiliary layer to a substrate; the formation in it by the method of photolithography and anisotropic etching of rows of grooves of nanometer depth with vertical walls; application of a nanometer layer of the material on which the nanowires will be formed onto the surface of the substrate and the side walls of the grooves; anisotropic etching of the nanowire material layer to the auxiliary layer, characterized in that the material having the catalytic ability is used as the nanowire material, and before anisotropic etching on the substrate surface, the method Photolithography forms a mask of photoresist, which consists of narrow strips located perpendicular to the grooves.

As a substrate, a polished plate of silicon, glass, metal or polycor is used. As an auxiliary layer, silicon dioxide or silicon nitride is used. Noble metals Pt, Pd, Re, Ru, Rh, Os, Ir, Ag or metals of the Ni, Fe, Co, Cu group and their oxides are used as the material for nanowires.

Thus, the distinguishing features of the invention are: 1) the use of a catalytic material as a layer forming nanowires, 2) the use of a photoresist mask when etching a layer of catalytic material.

The features of the characterizing part of the claims provide the solution to the following functional problems. The use of a material with catalytic ability, in fact, provides a catalytic effect in the implementation of chemical reactions. The use of a photoresist mask when etching a layer of catalytic material ensures the formation of transverse strips (of the same material as nanowires) that fasten long nanowires, reducing the likelihood of them peeling off from the substrate when the reactor is heated and the catalyst is blown with a gas stream. Due to different coefficients of thermal expansion of materials, long conductors tend to peel off from the substrate when their width is less than the thickness.

The use of a large number of nanowires, of the order of 1000 per mm of substrate, allows to increase the yield of the final product with a smaller amount of catalyst. The use of a catalyst in the form of thin flat substrates with an active surface, which are arranged in an orderly manner at a small angle to the gas flow, can significantly reduce the gas-dynamic resistance of the reactor.

This combination of common and distinctive features ensures the achievement of a technical result, which consists in obtaining a catalyst in the form of thin plates with an active surface created by a grid consisting of rows of nanowires fastened by transverse strips of the same material. The catalyst plates are installed in the reactor orderly at a small distance from one another at a certain angle to the gas stream. The optimal number of substrates in the reactor, the distance between them and the angle with respect to the gas flow are determined experimentally for each specific process.

As an example, consider the use of this method of forming a grid of platinum nanowires for use as a catalyst. A silicon dioxide layer 0.5 μm thick is deposited on a silicon substrate with a diameter of 100 mm. Using photolithography and plasma etching methods, rows of grooves with a depth of 20-50 nm are formed in this layer. The width of the grooves and the distance between them are the same and equal to the minimum size reproduced by the equipment used, for example, 1 μm.

On this substrate by magnetron sputtering a platinum layer 10-30 nm thick is applied. To increase the adhesion of platinum to a layer of silicon dioxide, the deposition is carried out on a heated substrate.

A layer of photoresist is applied on top of this layer, which is illuminated by ultraviolet rays through the photo mask, which was used to form the grooves, but rotated 90 °, or another pattern with a rarer arrangement of strips. After exposure, the photoresist is processed in the developer and submerged. In this case, a photoresist mask is formed, which is used to locally remove the platinum layer in those places where it is not protected by a photoresist layer.

Carried out ion-plasma etching (spraying) of platinum with argon ions. After etching, the photoresist mask is removed. A network of 1000 nanowires per 1 mm fastened by strips 1 μm wide is formed on the substrate.

In FIG. Figure 1 shows a fragment of a nanowire network obtained on a silicon wafer, where A-A is the cross-section of the substrate along the strip fastening the nanowires, and BB is the cross-section of the substrate between the strips fastening the nanowires.

The practical feasibility of this method is ensured by the fact that all the techniques used in it individually have long been implemented in practice. The positive effect is provided by a large number of nanowires made of catalytic material on the surface of the plates (substrates).

Information sources

1. US patent No. 8962517.

2. RF patent No. 2529680.

3. RF patent No. 2528988.

4. RF patent No. 2529458.

5. RF patent No. 2437180.

6. RF patent No. 2526066.

7. RF patent No. 2457573.

8. US patent 8405168 B2.

9. Lee K.N., Jung S.W., Kim W.H., Lee M.H., Shin K.S., Seong W.K

Well controlled assembly of silicon nanowires by nanowire transfer method // Nanotechnology. - 2007. - No. 18 (44): 445302. - 7 pp.

Claims (4)

1. A method of manufacturing a catalyst from nanowires, comprising the following steps: applying an auxiliary layer to a substrate; the formation in it by the method of photolithography and anisotropic etching of rows of grooves of nanometer depth with vertical walls; the deposition of a nanometer layer of material on which the nanowires will be formed on the surface of the substrate and the side walls of the grooves, anisotropic etching of this layer to the auxiliary layer, characterized in that a material having catalytic ability is used as the material of the nanowires, before the anisotropic etching is formed on the substrate surface by photolithography mask made of photoresist, which consists of narrow strips located perpendicular to the grooves, and after anisotropic etching of the layer I nanowire mask is removed. 2. The method according to p. 1, in which a polished plate of silicon, glass, metal or polycor is used as a substrate. 3. The method of claim 1, wherein silica or silicon nitride is used as the auxiliary layer. 4. The method according to p. 1, in which, as a material having a catalytic ability, noble metals Pt, Pd, Re, Ru, Rh, Os, Ir, Ag or metals of the Ni, Fe, Co, Cu group and their oxides are used.

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