阅读说明：本技术 Ni@Au核壳型纳米催化剂及其合成与应用 (Ni @ Au core-shell type nano-catalyst and synthesis and application thereof ) 是由 苏党生 张晓奔 吴兆萱 杨冰 刘伟 于 2018-07-27 设计创作，主要内容包括：本发明公开了一种用于逆水煤气变换反应的Ni@Au核壳型纳米催化剂及其合成与应用,催化剂活性组分是以Ni为内核,Au为壳层的核壳型Ni@Au纳米颗粒。将镍的前体盐和金的前体盐溶于油胺中,在惰性气体保护条件下升温到200～300℃,得到哑铃型的NiAu纳米颗粒。利用有机溶剂充分洗涤该NiAu纳米颗粒去除残余的油胺分子后将之分散到乙醇、正己烷、DMF、乙腈、甲苯等溶剂中,然后将之浸渍负载到Al<Sub>2</Sub>O<Sub>3</Sub>、SiO<Sub>2</Sub>、TiO<Sub>2</Sub>等常用载体上,最后于还原性气氛中150～600℃下焙烧数个小时,即得Ni@Au核壳型纳米催化剂。此Ni@Au核壳型纳米催化剂用于CO<Sub>2</Sub>逆水气变换反应制CO,表现出优异的催化活性,产物CO的选择性接近100％,并且在接近真实体系的模拟中有较高的稳定性。(The invention discloses a Ni @ Au core-shell type nano catalyst for reverse water gas shift reaction and synthesis and application thereof. And dissolving nickel precursor salt and gold precursor salt in oleylamine, and heating to 200-300 ℃ under the protection of inert gas to obtain the dumbbell NiAu nano-particles. Fully washing the NiAu nano-particles by using an organic solvent to remove residual oleylamine molecules, dispersing the NiAu nano-particles into solvents such as ethanol, normal hexane, DMF, acetonitrile, toluene and the like, and then soaking and loading the NiAu nano-particles into Al 2 O 3 、SiO 2 、TiO 2 And the Ni @ Au core-shell type nano-catalyst is obtained by roasting the carrier on a common carrier for several hours at the temperature of 150-600 ℃ in a reducing atmosphere. The Ni @ Au core-shell type nano-catalyst is used for CO 2 The reverse water-gas shift reaction for preparing CO shows excellent catalytic activity, the selectivity of the product CO is close to 100 percent, and the product CO is connected with the catalystThe simulation of a near-real system has higher stability.)

The synthesis method of the Ni @ Au core-shell type nano-catalyst comprises the following steps:

1) dissolving a precursor salt of nickel and a precursor salt of gold in oleylamine;

2) introducing inert atmosphere gas into the solution obtained in the step 1) for protection;

3) heating the solution obtained in the step 2) to 200-300 ℃, keeping the temperature for a certain time, and then cooling to room temperature;

4) fully washing the suspension obtained in the step 3) by using an organic small molecular solvent, and collecting nanoparticles in the suspension;

5) dispersing the nano particles obtained in the step 4) into an organic solvent, impregnating and loading the organic solvent onto a corresponding carrier, and roasting the obtained powder in a reducing atmosphere to obtain a supported Ni @ Au core-shell nano catalyst; or roasting the nano particles obtained in the step 4) in a reducing atmosphere to obtain the Ni @ Au core-shell nano catalyst.

2. The method for synthesizing the Ni @ Au core-shell nanocatalyst of claim 1, wherein in step 1), the nickel precursor salt comprises one or more of nickel acetylacetonate, nickel chloride, nickel acetate, nickel nitrate, nickel sulfate and their corresponding hydrates; the gold precursor salt comprises one or more than two of chloroauric acid tetrahydrate, chloroauric acid trihydrate, chloroauric acid dihydrate, chloroauric acid monohydrate, gold acetate, gold potassium hydrocyanate and gold trichloride; the molar concentration of the precursor salt of nickel in the oleylamine is 50-200 millimoles per liter (preferably 80-120 millimoles per liter), and the atomic ratio of Ni to Au in the oleylamine is 20: 1-1: 1 (preferably 6: 1-8: 1).

3. The method for synthesizing a Ni @ Au core-shell nanocatalyst of claim 1, wherein in step 2), the inert atmosphere gas comprises one or more of nitrogen, argon or helium.

4. The method for synthesizing the Ni @ Au core-shell nanocatalyst as claimed in claim 1, wherein in the step 3), the temperature rise rate of the solution is 10-20 ℃/min (preferably 10-12 ℃/min), and the retention time is 0.5-1.5 hours (preferably 1-1.5 hours).

5. The method for synthesizing a Ni @ Au core-shell nanocatalyst as claimed in claim 1, wherein in step 4), the small organic molecule solvent comprises: one or two or more mixed solvents of acetone, n-hexane, toluene, absolute ethyl alcohol, DMF, acetonitrile and isopropanol.

6. The method for synthesizing the Ni @ Au core-shell nanocatalyst according to claim 1, wherein in the step 5), the organic solvent comprises one or a mixture of two or more of acetone, n-hexane, toluene, absolute ethyl alcohol, DMF, acetonitrile and isopropanol; the carrier comprises one or more than two of silicon dioxide, aluminum oxide, titanium dioxide, cerium dioxide, molybdenum oxide, graphene and graphene oxide, and the mass load of Ni @ Au in the catalyst is 1% -10% (preferably 3-6%); the reducing atmosphere comprises: hydrogen and gas with hydrogen as main component, wherein the volume content is more than 5%, and the rest gas is one or more than two of nitrogen, argon and helium; the roasting temperature is 150-600 ℃ (preferably 300-400 ℃), and the roasting time is 1-5 hours (preferably 1.5-2 hours).

7. A supported Ni @ Au core-shell nanocatalyst or Ni @ Au core-shell nanocatalyst synthesized by the synthesis method of any of claims 1-6.

8. The Ni @ Au core-shell nanocatalyst of claim 7, wherein the Ni and Au are present in an atomic ratio of 20:1 to 1: 1; the configuration of the Ni @ Au core-shell type nano-catalyst is a core-shell type with Ni inside and Au outside, wherein the size of the core Ni is 10-30 nanometers, and the thickness of the Au shell layer is 1-10 Au atomic layers.

9. The application of the supported Ni @ Au core-shell nano-catalyst as claimed in claim 7 or 8, wherein the Ni @ Au core-shell nano-catalyst is applied to CO₂The CO is reduced to CO by reverse water-gas shift reaction.

10. The use of the supported Ni @ Au core-shell nanocatalyst of claim 9,

the application conditions are as follows: with CO₂And H₂The reaction temperature is 300-500 deg.C (preferably 300-400 deg.C).

Technical Field

The invention relates to a method for producing Ni @ Au core-shell nano-catalyst and synthesis and application thereof, in particular to a high-stability Ni @ Au core-shell nano-catalyst and synthesis and application thereof in CO₂The application in the reaction of converting the high-efficiency and high-selectivity reverse water-gas shift into CO.

Background

Gold has been known as a low catalytic activity material for many years. However, in 1987, the japanese scientist spring field (Haruta) and his research group found that gold has very good activity for CO oxidation at room temperature or even lower if its crystallites are less than 5nm and are supported on a reducible oxide support. Since then, the nano-gold catalyst has gradually become a focus and focus of research. The use of Au in a variety of reactions has been developed, for example: hydrogen dissociation reactions, formic acid decomposition reactions, water gas shift reactions, reverse water gas shift reactions, and selective or complete oxidation reactions of organic hydrocarbon molecules. Since the activity of the Au catalyst is sensitive to the size, and the Au catalyst has almost no activity when the size is larger than 5nm, the Au catalytic active phase of a sub-nanometer scale or even an atomic scale must be designed to realize the effective utilization of the gold catalyst. However, since Au atoms have high thermal mobility and very poor thermal stability, which leads to easy sintering deactivation at high temperature, if a stable sub-nanometer or even atomic Au catalyst can be constructed, the application thereof in real life, for example, CO low-temperature oxidation reaction, can be greatly promoted, thereby solving the environmental problem caused by automobile exhaust emission; by using CO₂The small molecules as resources react with hydrogen generated by industrial electrolyzed water to generate chemical raw materials CO and water through a reverse water-gas shift reaction path, thereby realizing greenhouse gas CO₂The resource utilization is realized.

With the deep space exploration in China, how to effectively prolong the time required by spacemen in space exploration is of great importance. The method not only relates to the smoothness of the detection task, but also relates to how to effectively increase the load capacity of the spacecraft, and further directly relates to the life safety of the astronauts. Reverse water gas shift Reaction (RWGS) using CO₂Reacting with hydrogen to form CO and H₂Reaction of O, as it isThe synthesis gas is prepared by the existing non-fossil energy route, so that the synthesis gas becomes CO₂The important part of resource utilization technology. In space stations, water is a valuable resource for producing life activities, and people can breathe without separating oxygen produced by electrolyzing water. By using CO exhaled by human body₂With exhaust gas H generated by electrolysis of water₂By this reaction H can be achieved₂The recycling of O, thereby greatly reducing the aerospace cost; china officially repeated the Mars detection plan in 2016, and in the future, the abundant CO in the Mars atmosphere is utilized₂By-product H obtained in solar energy hydrolysis of water to oxygen₂H necessary for carrying out reactions to complete life activities₂The circulation of O and the acquisition of fuel CO are expected to establish a permanent human residence point on Mars, and the method has strategic significance. Therefore, by means of nano synthesis and advanced modern characterization technology, the catalytic mechanism of RWGS reaction is deeply researched and understood, the efficient and high-stability RWGS reaction catalyst is scientifically designed and prepared, and the development of space exploration industry is facilitated.

At present, the mechanism of the reverse water-gas shift reaction mainly has the following two viewpoints: one is the redox mechanism on the surface of the catalyst; the second is the intermediate species decomposition mechanism. A report from the teaching group of R.J. Behm of Ulm university, Germany in 2013 showed that they conducted a real-time product analysis (TAP) reactor on Au/CeO₂The mechanism of the catalyst used in the RWGS reaction is researched, and the result shows that CO is generated₂The preliminary reduction activation on the catalyst surface is a prerequisite for the RWGS reaction to proceed, and it is thus well documented that Au/CeO is involved in the reaction₂The RWGS reaction proceeds via a redox mechanism. However, a large number of researchers have suggested that CO is₂Firstly, a hydrogen-assisted activation process is carried out on a catalyst to form carbonate, formate or carboxyl intermediate species with higher activity, and then the intermediate species are decomposed in time to generate CO and H₂And O. For example, Cu/Al₂O₃Catalyst system, Pt/CeO₂Catalytic system, Ru/Al₂O₃Catalytic systems, and the like. However, the traditional synthesis strategies such as an impregnation method, a coprecipitation method and the like are adopted for the catalyst aiming at the RWGS at present, and the catalyst obtained by the method has active speciesThe structure is complex, the configuration is various, and the influence caused by crystal face effect, size effect, carrier effect and the like cannot be eliminated in the mechanism research, so that the design and construction of the catalyst with uniform structure and uniform particle size is the most effective means for deeply understanding the generation mechanism of the inverse water-gas shift and regulating and controlling the reaction to be carried out towards the direction of high activity, high selectivity and high stability.

Disclosure of Invention

The invention aims to provide a Ni @ Au core-shell nano-catalyst, a synthesis method thereof and application thereof in reverse moisture-gas conversion. The catalyst prepared by the invention shows excellent catalytic activity, CO selectivity close to 100% and good stability in reverse water-gas shift reaction.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the synthesis method of the Ni @ Au core-shell type nano-catalyst comprises the following steps:

1) dissolving a precursor salt of nickel and a precursor salt of gold in oleylamine;

2) introducing inert atmosphere into the solution obtained in the step 1) for protection;

3) heating the solution obtained in the step 2) to 200-300 ℃, keeping the solution at the highest temperature for a certain time, and then cooling to room temperature;

4) fully washing the suspension obtained in the step 3) by using an organic small molecular solvent, and collecting nanoparticles in the suspension;

5) dispersing the nano-particles obtained in the step 4) into an organic solvent, impregnating and loading the organic solvent onto a corresponding carrier, and roasting the carrier for 1-5 hours at the temperature of 200-500 ℃ in a reducing atmosphere to obtain the Ni @ Au core-shell nano-catalyst.

In the step 1), the nickel precursor salt includes nickel acetylacetonate, nickel chloride or a hydrate thereof, nickel acetate or a hydrate thereof, nickel nitrate or a hydrate thereof, and nickel sulfate or a hydrate thereof; the gold precursor salt comprises chloroauric acid tetrahydrate, chloroauric acid trihydrate, chloroauric acid dihydrate, chloroauric acid monohydrate, gold acetate, gold potassium hydrocyanate and gold trichloride;

in the step 2), the inert atmosphere comprises nitrogen, argon or helium;

in the step 3), the temperature rising speed of the solution is 10-20 ℃/min, and the retention time at the highest temperature is 0.5-1.5 hours;

in the step 4), the organic small molecule solvent includes: acetone, n-hexane, toluene, anhydrous ethanol, DMF, acetonitrile, isopropanol, or a mixed solvent thereof;

in the step 5), the organic solvent comprises acetone, n-hexane, toluene, absolute ethyl alcohol, DMF, acetonitrile, isopropanol or a mixed solvent thereof; the carrier comprises silicon dioxide, aluminum oxide, titanium dioxide, cerium dioxide, molybdenum oxide, graphene and graphene oxide; the reducing atmosphere comprises: hydrogen gas and a gas containing hydrogen as a main component; the roasting temperature is 150-600 ℃, and the roasting time is 1-5 hours.

The invention provides a Ni @ Au core-shell type nano-catalyst synthesized by the method.

Further, the Ni @ Au core-shell nano-catalyst is characterized in that the atomic ratio of Ni to Au is larger than that of Au;

further, the Ni @ Au core-shell type nano-catalyst is characterized in that the Ni @ Au core-shell type nano-catalyst is in a core-shell type with Ni inside and Au outside, wherein the size of the core Ni is 10-20 nanometers, and the thickness of a shell layer of Au is 1-10 Au atomic layers;

furthermore, the Ni @ Au core-shell nano-catalyst is characterized in that the Ni @ Au core-shell nano-catalyst is applied to CO₂The method is applied to the reaction of reducing the reverse water-gas shift into CO.

The technical advantages of the invention are as follows:

1. the invention creates a novel catalyst for reverse water-gas shift reaction, which is structurally characterized in that an inner core is Ni, and an outer shell layer is Au. The characteristic can realize stable atomic-level dispersion of the active metal Au, and is beneficial to realizing high activity of the catalyst; meanwhile, the catalyst is a catalyst with a single active phase structure, which is beneficial to accurately constructing the structure-effect relationship in catalysis, thereby realizing the high selectivity of the catalyst; further, since the catalyst active phase is Au, it can form an insoluble alloy with Ni, and thus can have high stability.

2. The catalyst shows excellent catalytic performance in reverse water-gas shift reaction. TOF value is as high as 0.202molCO₂·molCat.^-1·s^-1Higher than the common reports of the same type; meanwhile, the selectivity of the product CO is close to 100 percent, so that the cost of later-stage product separation is greatly saved; in addition, stability experiments at 400 ℃ show that the catalyst has higher stability under the condition close to a real system.

Therefore, the method has excellent performance in solving the problem that the Au is difficult to prepare in a sub-nanometer or even atomic scale, and has wide application prospect in the actual reverse moisture-gas conversion reaction.

Drawings

FIG. 1 is a reaction tube used for evaluating the performance of a catalyst in example 7 of the present invention;

FIG. 2 is a Scanning Transmission Electron Microscope (STEM) photograph of dumbbell-shaped NiAu nanoparticles of a precursor of the catalyst in example 1 of the present invention, the average particle size being 13.5 nm, and Ni and Au components being distributed at both ends of the particles in a dumbbell shape;

FIGS. 3(a) and 3(b) are low magnification annular dark field-scanning transmission electron microscope (HADDF-STEM) images of the catalyst in example 1 of the present invention, which shows that the particles are converted into Ni @ Au core-shell structures on the basis of better size uniformity and dispersibility;

FIG. 4 is an atom-resolved HADDF-STEM plot of the catalyst of example 1 of the present invention, showing that the particle has a standard Ni core and Au shell configuration, wherein the Au shell is only 2 atomic layers;

FIG. 5 is a graph of activity data for the catalyst of example 1 of the present invention.

Detailed Description

The invention is further illustrated by the following examples, which do not limit the scope of the invention in any way.

The synthesis method of the Ni @ Au core-shell type nano-catalyst comprises the following steps: dissolving a precursor salt of nickel and a precursor salt of gold in oleylamine; introducing inert atmosphere into the obtained solution for protection; heating to 200-300 ℃, keeping a certain time at the highest temperature, and cooling to room temperature; centrifugally washing the obtained suspension by using an organic small molecular solvent, and collecting nano particles in the suspension; dispersing the obtained nano particles into an organic solvent, soaking and loading the nano particles on a corresponding carrier, blowing and drying at the temperature of 30-60 ℃, and finally roasting the obtained solid for 1-5 hours at the temperature of 200-500 ℃ in a reducing atmosphere to obtain the Ni @ Au core-shell nano catalyst.