TWI430837B - Nano-metal particles dispersed in composite oxide catalyst and synthesizing method of the same - Google Patents

Description

Nano metal/composite oxide catalyst and synthesis method thereof

The present invention relates to a nano metal catalyst and a method for synthesizing the same, and in particular to a method of dispersing gold nanoparticles on a composite oxide support of a porous network structure, and a method for synthesizing the same.

In the past, gold particles have been considered to have no catalytic activity like copper or platinum, but in 1987, Dr. Masaaki Harada discovered that the catalyst made of nano-gold particles can catalyze carbon monoxide at minus 73 degrees Celsius. The oxidation reaction breaks the impression that gold is not active in the past.

In recent years, it has been found that the particle size of gold particles is less than 5 nm, especially 3 nm, which has the best catalytic effect on carbon monoxide reaction. It is suitable for use in masks, water heater exhaust pipes or exhaust pipes of steam locomotives. In the environment of carbon dioxide. At present, the methods for preparing the nano gold catalyst include an impregnation method, an ion exchange method, a coprecipitation method, a precipitation precipitation method, a vapor deposition method, a graft method, and the like.

However, gold particles having a particle size of 3 to 5 nm cannot be stably maintained in a dispersed state. At room temperature, the gold nanoparticles automatically aggregate into massive gold and lose the catalytic activity again. In order to maintain the dispersed state of the gold nanoparticles, a conventional technique is to coat the outer layer of the gold nanoparticles with a functional surfactant such as sodium citrate to prevent the gold nanoparticles from re-bonding. However, the gold nanoparticles are coated in the surfactant, and there is no way to exert the effect of the catalyst.

Later, it was developed to carry nano-gold particles in a unit oxide carrier, wherein the unit oxides may be titanium dioxide (TiO ₂ ), ferric oxide (Fe ₂ O ₃ ), etc., and are currently on the market. . However, the price of such a catalyst is very expensive, and it can reach 10,000 yuan per gram. Although titanium dioxide is a photocatalyst material, the environment of the exhaust pipe of a steam locomotive is not exposed to light, and the catalyst cannot be exerted. The catalytic effect is increased.

At present, the catalyst materials commonly used in exhaust pipes of steam locomotives are platinum, ruthenium and osmium three-way catalysts. The alumina ceramics are prepared into a porous structure, and the impregnation method is used to disperse and adhere platinum, ruthenium and osmium to alumina. However, the ternary catalyst can produce catalytic activity at a temperature above 250 °C. That is to say, when the steam locomotive is just started, the ternary catalyst can not effectively catalyze the oxidation reaction of toxic gases such as carbon monoxide or nitride, when the steam locomotive is parked. When it is in a confined space such as a basement parking lot, the exhaust gas discharged through the exhaust pipe still causes air pollution and endangers human health. Moreover, the price of the three-way catalyst is also very expensive.

Therefore, the present invention intends to develop a nano metal/oxide composite catalyst to achieve the following three requirements, including: (1) reducing the cost of the catalyst; and (2) simultaneously carrying the catalytic activity of the nano metal particles and the supported support. In order to improve the overall catalytic effect; (3) can also catalyze the oxidation of carbon monoxide at room temperature to replace the current three-way catalyst used in the exhaust pipe of steam locomotives.

In view of the above problems, the present invention provides a nano metal/composite oxide catalyst comprising a plurality of nano metal particles dispersed in a composite oxide support having a porous network structure, wherein the nano metal particles are selected from the group consisting of One of a group consisting of gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), and any combination thereof, wherein the composite oxide is a cuprite type, Expressed by the formula AxByOz.

The present invention also provides a method for synthesizing the foregoing nano metal/composite oxide catalyst, comprising: providing a composite oxide powder, wherein the composite oxide powder has a porous network structure, a surface area of at least greater than 10 m ² /g, and a composite oxide Representing the general formula AxByOz; preparing a composite oxide solution and a metal salt solution; mixing the composite oxide solution with the metal salt solution; placing the mixed solution in a photoreduction tank, irradiating with a light source for about 5 to 15 minutes to make the metal The salt is reduced to nano metal particles and distributed in the porous network structure of the composite oxide powder to form a nano metal/composite oxide catalyst; the nano metal/composite oxide catalyst and the solution are separated by centrifugal separation technique Separating; and evaporating excess water in the mixed solution to obtain the final product.

In the embodiment of the present invention, gold particles having a particle diameter of 3 to 5 nm are dispersed in a support of chromium chromium copper (CuCrO ₂ ) in this manner. Both the nano metal particles and the composite oxide as a support have catalytic activity and can catalyze the oxidation reaction of carbon monoxide at room temperature. In addition, the production method is simple, the cost is low, and it can be applied to the fields of masks, exhaust pipes of steam locomotives, gas masks or carbon monoxide detection, and has application potential.

In order to make the above objects, features and advantages of the present invention more comprehensible, the synthesis method of the nano metal/oxide composite catalyst according to the present invention is exemplified, and the preferred embodiment is combined with the related drawings. A detailed description is as follows.

The invention provides a nano metal/oxide composite catalyst and a synthesis method thereof, wherein the nano metal particles are dispersed on a support having a porous network structure composite oxide, and the nano metal particles and the support itself are Has a good catalytic activity.

According to an embodiment of the present invention, the nano metal particles may be selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), and any combination thereof. One type, wherein the particle diameter of the nano particles is preferably 20 nm or less, more preferably 10 nm or less. A more preferred embodiment is the choice of gold (Au) or platinum (Pt). Studies have shown that when the nanoparticle is gold (Au), the particle size is preferably 3 to 5 nm.

In the embodiment of the present invention, the composite oxide having a porous network structure has a crystal grain size of about 100 nm or less and a surface area of more than 10 m ² /g. The porous network structure and large surface area of the composite oxide can adhere to more nano metal particles, and the catalytic activity of the catalyst as a whole is greatly improved.

In the present embodiment, the composite oxide may be selected from the group consisting of a spinel type, a cuprite type, and a combination thereof, and is represented by the formula AxByOz. Further, the A system represents one selected from the group consisting of silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), and any combination thereof, and the B system is selected from the group consisting of aluminum (Al),钪(Sc), chromium (Cr), yttrium (Y), iron (Fe), indium (In), gallium (Ga), cobalt (Co), manganese (Mn), rhenium (Rh), nickel (Ni), One of a group consisting of lanthanum (La), yttrium (Nd), yttrium (Sm), europium (Eu), titanium (Ti), and any combination thereof. Among them, the B-site metal ion can also be doped with a divalent cation.

The present invention provides a method for synthesizing the above-mentioned nano metal catalyst. Referring to FIG. 1 , a flow chart of an embodiment of the present invention includes: providing a composite oxide (AxByOz) powder, as in step S100, in the embodiment of the present invention. The selected composite oxide is a porous network structure of chromium chromium copper (CuCrO ₂ ), and the composite oxide itself can be used as a catalyst and has catalytic activity at room temperature.

Next, a composite oxide solution and a metal salt solution are prepared, as by step S105. In one embodiment of the present invention, the composite oxide solution is mixed with 0.5 g of chromium oxide copper powder and 25 ml of deionized water, and the metal salt solution is 1.68 ml (0.85 mM) of tetrachloroauric acid with 75 ml. Mix and mix with deionized water.

Thereafter, the composite oxide solution is directly mixed with the metal salt solution, as by step S110. In another preferred embodiment, the weak base solution is formulated to produce hydroxide on the composite oxide support, and the contact portion of the metal salt solution and the support is made larger, for example, adjusting the pH of the mixed solution with ammonia or the like. Value, in the range of 6 to 12.

The mixed solution is placed in a photoreduction tank, and irradiated with a light source for a predetermined time to reduce the metal salt to nano metal particles, which are distributed in the porous network structure of the composite oxide powder to form a nano metal/oxidation. The composite catalyst is as in step S115. Among them, the length of the illumination time will affect the particle size of the nano metal particles, and therefore, the illumination time depends on the desired particle size of the nano metal particles. In one embodiment, the illumination time is approximately 1 to 30 minutes.

Because the cuprous iron-type composite oxide has the effect of photocatalyst, an electron-hole pair is generated after illumination. Taking CuCrO ₂ as an example, the hole and the Cu ⁺ ion in the solid lattice form Cu ²⁺ , electrons. Then, the metal ion M ²⁺ in the solution is reduced to the metal M, wherein M includes gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), and the like. The photon energy (h v ) emitted by the illumination source needs to be greater than the energy gap width (Eg) of the composite oxide. The energy gap width of the chromium oxide copper is about 1.28 eV, so in the present embodiment, after the solution is placed in the photoreduction tank, it is irradiated for 30 minutes at a speed of 600 rpm under a UV lamp to form a grain in the chromium oxide copper. Nano gold particles with a diameter of about 3 to 5 nm.

Next, as shown in step S120, "nano metal/composite oxide catalyst" is separated from the solution by a centrifugal separation technique. In this embodiment, the mixed solution was poured into a centrifuge tube, and a cycle was performed for 10 minutes at a low rotation speed of 20 rpm and a high rotation speed of 70 rpm for three cycles.

After centrifugation, a drying step, such as an oven or a hot plate, may be optionally employed to evaporate the "nano metal/composite oxide catalyst" water to obtain a final product, as in step S125.

2 is a transmission electron micrograph of a nano metal/oxide composite catalyst according to an embodiment of the present invention. As is apparent from the photograph, it is indeed possible to disperse the nano gold particles 11 having a particle diameter of only about 3 to 5 nm in the chromium chromium copper 10 (CuCrO ₂ ) support by the synthesis method provided by the present invention.

In the embodiment of the present invention, a method for preparing a composite oxide (AxByOz) powder having a porous network structure, please refer to one of the inventors' Taiwan patent applications, the application number is 099140875, and the invention name is nano-chietan iron ore type oxidation. Powder and its method of manufacture. The following is a brief description: First, a metal salt or an organometallic compound containing A ions and B ions is mixed and used as a metal precursor, and the metal precursor is dissolved in a solvent to form a metal precursor solution. Next, a fuel such as an amino acid fuel, oxalic acid or borane is added to the metal precursor solution to be mixed, and excess water in the metal precursor solution is evaporated (not completely dried) to form a colloid.

Finally, as long as the colloid is heated until it spontaneously reacts, the composite oxide powder for preparing the above composite catalyst can be obtained after completion of the reaction. The oxide powder prepared in the examples of the present invention has an average particle diameter of about 10 to 300 nm. Among them, the colloid is heated to a temperature at which the spontaneous combustion reaction is generated, which is about 150 to 250 °C.

A scanning electron micrograph of a copper-copper-iron composite oxide (CuCrO2) powder prepared in an embodiment of the present invention is shown in Fig. 3. As can be seen from the figure, the composite oxide powder 10 itself has a porous network structure. And the surface area of the chromium oxide copper (CuCrO ₂ ) powder is determined by the adsorption curve of nitrogen gas, about 30.4 m ² /g, and the same method can be used to prepare copper iron oxide (CuFeO ₂ ) and aluminum oxide copper (CuAlO ₂ ) in the same manner. Structure, and surface area of about 30 ~ 35 m ² / g.

In a preferred embodiment, the metal salt of the A ion and the B ion may be selected from the group consisting of a metal halide, a nitrate, an acetate, an oxalate, a sulfate, a carbonate, an organic acid salt, and any combination thereof. . Among them, nitrate or acetate is preferred because it is relatively low in cost.

The solvent used to dissolve the metal precursor is not particularly limited as long as it can be uniformly dissolved. Can be selected from water, alcohols (such as: methanol, ethanol, propanol, isopropanol, ethylene glycol, etc.), or ethers (such as: methyl ethyl ether, ethylene glycol methyl ether, ethylene glycol butyl ether, etc.) One of the groups consisting of any combination thereof.

The fuel may be selected from the group consisting of glycine, sarcosine, pyridine, aniline, oxalic acid, hydrazine, and borane. Since the amino acid fuel has a carboxyl group and an amine group and is capable of coordinating with a metal cation to form a stable colloid, in the preferred embodiment of the present invention, an amino acid fuel such as glycine or myoamine is used. Acid, pyridine, aniline, hydrazine, and the like. It is to be noted that the amount of fuel used is in the range of about 0.5 to 3 times the molar ratio of the total metal ions. Among them, it is preferably 1 to 2 times, more preferably 1.3 to 1.7 times, because in this range, the step of heat treatment after the combustion reaction can be omitted.

After the end of the auto-ignition reaction, the product after the reaction may be purified to reduce impurities, or a dispersion step may be performed to increase the dispersion of the cupronite-type oxide powder, or a separation step may be selectively performed to reduce The range of powder particle size distribution.

The nano metal/oxide composite catalyst prepared by the synthesis method of the embodiment of the invention can stably disperse the nano metal particles having a particle size of only 10 nm in the composite oxide carrier, thereby achieving the touch The effect of the media. Among them, both the nano metal particles and the composite oxide as a support have catalytic activity, and can exert the catalytic effect at room temperature or high temperature.

In addition, the composite oxide itself is simple in production and low in cost, and does not require the use of expensive vacuum equipment, high-pressure reactors, an inert gas atmosphere, and a dangerous hydrogen atmosphere, and does not require a high-temperature furnace exceeding 300 °C. In the future, it will have considerable development potential when used in the fields of masks, exhaust pipes for gas locomotives, gas masks or carbon monoxide detection.

The present invention has been described above by way of a preferred example, but it is not intended to limit the spirit of the invention and the inventive subject matter. Those who are familiar with the technology can easily understand and utilize other components or methods to produce the same effect. Modifications made without departing from the spirit and scope of the invention are intended to be included within the scope of the appended claims.

S100, S105, S110, S115, S120, S125. . . Synthetic method flow step

10. . . Composite oxide

11. . . Nano gold particles

1 is a flow chart showing the manufacture of a nano metal/oxide composite catalyst according to an embodiment of the present invention;

2 shows a transmission electron micrograph of a nano gold particle/composite oxide (CuCrO ₂ ) powder prepared in an embodiment of the present invention;

Fig. 3 is a scanning electron micrograph showing a powder of a cupronite-type composite oxide (CuCrO ₂ ) according to an embodiment of the present invention.

10. . . Composite oxide

11. . . Nano gold particles

Claims (10)

A nano metal/composite oxide catalyst comprising a plurality of nano metal particles dispersed in a composite oxide support selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), and ruthenium One of the group consisting of (Ru), rhodium (Rh) and any combination thereof, the composite oxide support has a porous network structure, and has a crystal grain size of 100 nm or less and a surface area of 10 m ² /g or more. It is represented by the general formula AxByOz. The nano metal/composite oxide catalyst according to claim 1, wherein the nano metal particles have a particle diameter of 3 to 5 nm. The nano metal/composite oxide catalyst according to claim 1, wherein the nano metal particles are gold (Au) or platinum (Pt). The catalyst according to claim 1, wherein the A-form of the composite oxide support AxByOz is selected from the group consisting of silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), and any One of the groups consisting of combinations, the B system is selected from the group consisting of aluminum (Al), strontium (Sc), chromium (Cr), yttrium (Y), iron (Fe), indium (In), gallium (Ga), Cobalt (Co), manganese (Mn), rhenium (Rh), nickel (Ni), lanthanum (La), niobium (Nd), niobium (Sm), europium (Eu), titanium (Ti) and any combination thereof One of the groups. The catalyst according to claim 1, wherein the composite oxide support is selected from the group consisting of a spinel type, a cuprite type, and a combination thereof. A method for synthesizing a nano metal/composite oxide catalyst, wherein the nano metal/composite oxide catalyst comprises a plurality of nano metal particles dispersed in a composite oxide support, comprising: providing a composite oxide powder, wherein The composite oxide powder has a porous network structure, a surface area of at least greater than 10 m ² /g, and the composite oxide is represented by the general formula AxByOz; preparing the composite oxide solution and a metal salt solution; and the composite oxide solution and the metal The salt solution is mixed, wherein the metal salt is a metal salt containing gold, palladium or platinum; the mixed solution is placed in a photoreduction tank and irradiated with a light source for a predetermined time, depending on the desired particle size of the nano metal particles, so that The metal salt is reduced to nano metal particles, distributed in the porous network structure of the composite oxide powder to form a nano metal/composite oxide catalyst; and the nano metal is separated from the solution by centrifugal separation technology/ Composite oxide catalyst. The synthesis method according to claim 6, wherein the mixed oxide solution and the metal salt solution are further mixed, and the pH of the mixed solution is adjusted to be in the range of 6 to 12. The synthesis method according to claim 6, wherein when the mixed solution is placed in the photoreduction tank, the photon energy (hv) emitted by the light source for irradiating the solution is greater than the energy gap of the composite oxide. Width (Eg). The synthesis method according to claim 6, wherein the method for providing the composite oxide powder AxByOz comprises: providing a metal salt or an organometallic compound containing A ions and B ions, respectively, and mixing them as a metal precursor; The metal precursor is dissolved in a solvent to form a metal precursor solution; Adding a fuel to the metal precursor solution, wherein the fuel is selected from the group consisting of an amino acid fuel, oxalic acid or borane; evaporating excess water in the metal precursor solution to form a colloid; and heating the colloid to make the colloid A self-ignition reaction is generated to obtain the oxide AxByOz powder after the reaction is completed, wherein the colloid is heated to a temperature at which the colloid produces a self-ignition reaction of about 150 to 250 °C. The synthesis method according to claim 9, wherein the metal precursor solution is mixed with the fuel, and the molar ratio of the fuel to the total metal ion ranges from about 0.5 to 3 times.