CN104226330B - A kind of Au/Co (OH)2Nano array structure catalyst - Google Patents

Abstract

The invention discloses an Au/Co(OH) ₂ nano-array structured catalyst, belonging to the technical field of catalysis. Nano-arrays with rectangular flake-like morphology are directly grown on the foamed nickel substrate, and the formed nano-materials have a definite and orderly structure and can achieve high specific surface area. The microplatelets on the nickel foam substrate link the macroscale substrate and the nanoscale noble metal particles, which ensures sufficient adhesion and avoids leaching during the catalytic reaction. The average size of the monolithic square nanosheets is 1.5 micrometers wide, and the gold particles are 3‑5 nm in size. It can be effectively used for the hydrogenation reduction reaction of p-nitrophenol with a reaction rate of 30.8 s ^‑1 g ^‑1 , and the Au/Co(OH) ₂ nanoarray structured catalyst also has excellent cycle stability after 6 cycles After use, the morphology basically does not change, and more importantly, the catalytic performance also basically remains unchanged. It solves the problem of uneven distribution of active components of traditional monolithic catalysts, weak bonding with the carrier, and gradual decline in activity during the reaction.

Description

A Au/Co(OH)2 Nanoarray Structured Catalyst

technical field

The invention belongs to the technical field of catalysis, and in particular relates to an Au/Co(OH) ₂ nano-array structured catalyst with ordered structure and uniform size distribution grown on a nickel foam substrate and a preparation method thereof.

Background technique

With the rapid development of the national economy, China is facing the dual pressure of resource scarcity and environmental degradation, and the effective use of resources has become an urgent national major demand. Catalyst is a key step in industrial production, its research and development and application are closely related to all aspects of energy and chemical industry. Catalysts are divided into homogeneous catalysts and heterogeneous catalysts according to the phase state of the reaction system. In the current industrial application field, heterogeneous catalysts are mostly used. Heterogeneous catalysts, also known as heterogeneous catalysts, are used in catalytic reactions in different reaction phases, that is, the catalyst and the reactants are in different phase states. In recent years, in the field of heterogeneous catalysis research, a large amount of research work has mainly focused on the research of granular and powdery catalysts. However, the catalytic reactor filled with traditional granular catalysts usually has a large bed pressure drop, and the bed layer There is a large temperature gradient between them, and the reactants are unevenly distributed on the surface of the catalyst particles. In order to overcome these disadvantages, in recent years, the research of a new catalyst-structured catalyst in which the catalytic active components are composited with the monolithic catalyst support has attracted great attention. Compared with granular or powdered powder catalysts, this catalyst can strengthen the catalytic reaction process, improve catalytic efficiency, reduce energy consumption, and simplify the production process, and has been widely used in the fields of environmental protection, catalytic combustion, and catalytic distillation.

Structured catalysts usually consist of three parts: a structured substrate, a coating, and a catalytically active component. At present, the supports of structured catalysts mainly include ceramic base and metal base. The ceramic base support has poor shock resistance and short service life; the metal base support has the advantages of thin wall, large geometric area and porosity, good thermal conductivity, small heat capacity and high strength. , and analyzed from the simulation results of the metal base, it has good heat transfer capacity, extremely low pressure drop, and easy control of the structure, which will greatly improve the catalytic efficiency of the metal base, so it shows an excellent application prospect. At the same time, Yin Fengxiang and others proposed that the metal-based catalyst can be used as an integral component and applied to the direct coupling process of endothermic/exothermic reactions, which will improve the thermal efficiency of the reaction and realize the integration of resources, energy, equipment and processes. Strengthen the reaction process.

With the development of controllable synthesis technology of nanomaterials and the improvement of analytical methods, new opportunities have been brought for the development of high-performance catalysts. Due to its novel structure, unique photoelectric and catalytic properties, nano-array materials have great advantages and potentials in the field of nano-device fabrication and have attracted great attention. On the other hand, the miniaturization of the size of catalyst materials has been proved to be an effective way to improve the catalytic performance. By increasing the contact opportunities between the surface and reactive atoms such as gases and liquids, the activity is improved. For structured nanoarrays, the specific surface area of the overall catalyst material can be increased by reducing the size of the one-dimensional nanomaterials.

Supported gold catalysts have good low-temperature catalytic activity, good anti-poisoning performance and catalytic stability, and are widely used in the low-temperature oxidation of CO (Bond, G. C.; Thompson, D.T.Cat.Rev._Sci.Eng.1999, 41, 319 .), catalytic hydrogenation of aromatic amines (Chen, Y. Y.; Qiu, J.S.; Wang, X.K.; Xiu, J.H.J. Catal.2006, 242, 227.), oxidation of paraffins (Hughes, M.D.; Xu, Y. J.; Jenkins, P. Nature 2005, 437, 1132.), selective oxidation of polyols (Berndt, H. Appl. Catal., A: Chem. 2003, 244, 169.). Compared with other precious metals such as platinum and palladium, the price of gold is cheaper than these two, which makes gold catalysts more promising for practical industrial applications. However, even gold, a precious metal, is still expensive. The industrial cost of using precious metals as catalysts is too high. However, by loading precious metals on the carrier, the production cost will be greatly reduced and the utilization efficiency of precious metals will be greatly improved.

But so far, there are few researches on the application of nanoarrays to structured catalysts, which limits the industrial development and application of high-performance catalysts to a certain extent. Based on this, we propose to synthesize Au/Co(OH) ₂ nanoarray structured catalysts based on Co(OH) ₂ nanoarrays as the carrier. The problem of uneven distribution and weak adhesion with the carrier. Here we evaluated the performance of Au/Co(OH) ₂ nanoarray structured catalysts for the hydrogenation reduction reaction of p-nitrophenol.

Contents of the invention

The purpose of the present invention is to provide a design synthesis of Au/Co(OH) _2nano -array structured catalyst.

A kind of Au/Co(OH) _2nano -array structured catalyst provided by the present invention is to directly grow Co(OH) _2nanosheet arrays on the foamed nickel substrate, and then obtain Au/Co(OH) by reducing chloroauric acid in situ ₂ Nanoarray Catalysts.

The present invention provides the design and synthesis of the above-mentioned Au/Co(OH) ₂ nano-array structured catalyst, using in-situ hydrothermal synthesis technology to grow cobalt hydroxide rectangular micro-sheets on the foamed nickel substrate, and then reducing gold chloride in situ Au/Co(OH) ₂ nano-array structured catalyst with ordered structure, vertical and orderly growth on nickel foam substrate, and uniform size distribution. The specific preparation method is as follows:

a. Ultrasonic cleaning of 8 cm ² nickel foam substrates with hydrochloric acid for 5-10 minutes, then ultrasonic cleaning with absolute ethanol or acetone for 5-10 minutes, and then cleaning with deionized water to obtain foam nickel substrates for use;

b. Dissolve soluble cobalt salt, ammonium fluoride and urea in deionized water to form a solution, wherein the concentration of cobalt ions is 0.01-2mol/L, the ratio of ammonium fluoride to cobalt ions is 1:4, and urea The substance ratio with cobalt ion is 1:5;

c. Immerse the foamed nickel substrate obtained in step a into the mixed solution obtained in step b, and heat it in a reactor at 120° C. for 12 hours, and cool it to room temperature naturally after the reaction; the obtained substrate is washed with water and absolute ethanol to remove impurities. Dry in an oven at ℃ for 2-4h;

d. Soluble cobalt salt and urea are dissolved in deionized water to form a solution, wherein the concentration of cobalt ions is 0.025-2mol/L, and the mass ratio of urea and cobalt ions is 1: 10;

e. Immerse the substrate obtained in step c into the mixed solution obtained in step d, and heat it in a reaction kettle at 100°C for 10 hours, and cool it to room temperature naturally after the reaction; wash the obtained substrate with water and absolute ethanol to remove impurities, and heat it at 80°C Dry in oven for 2-4h;

f. Using NaBH ₄ to reduce 5-600 μL chloroauric acid in situ to obtain the Au/Co(OH) ₂ nano-array structured catalyst by the deposition precipitation method on the substrate obtained in step e.

The soluble cobalt salt in steps b and d is cobalt nitrate hexahydrate. The Au/Co(OH) nano _- array structured catalyst prepared above is applied to the reduction of p-nitrophenol to synthesize p-aminophenol, the reaction conditions are at room temperature, take (5-70ml) 0.625mM or 2.5mM For p-nitrophenol aqueous solution, add 0-65ml of water, blow nitrogen for 5-10min, stir magnetically, add 10-20mg of sodium borohydride, the color of the solution changes from light yellow to bright yellow, add an appropriate amount of catalyst (the size of nickel foam is 2*4cm ² ).

The present invention has the advantages of: (1) directly grow nano-arrays of rectangular plate shape on the foamed nickel substrate, and the nanomaterial structure formed is definite, orderly, and can realize high specific surface area; (2) the nano-arrays on the foamed nickel substrate The microsheets link the macroscale substrate and the nanoscale noble metal particles, which ensure sufficient adhesion and avoid leaching during catalytic reactions. (3) The nano-array structure has good electron transport performance and is conducive to the diffusion of active species; (4) the micro-sheet provides a stable support structure of the three-dimensional scaffold, so that the catalytic activity of the catalyst remains basically unchanged after six times of repeated use. Based on the above advantages, the Au/Co(OH) ₂ nanoarray structured catalyst exhibits excellent catalytic performance. The prepared structured catalyst can be effectively used in the hydrogenation reduction reaction of p-nitrophenol, and has high conversion rate of reactants and high product selectivity. In addition, it can also solve a series of problems caused by homogeneous catalysts and random particle catalysts, so that the process can meet the requirements of environmental protection and sustainable development. It can be effectively used in the hydrogenation reduction reaction of p-nitrophenol, the reaction rate is 30.8s ^-1 g ^-1 , the Au/Co(OH) ₂ nano-array structured catalyst also has excellent cycle stability, after 6 cycles After use, the morphology basically does not change, and more importantly, the catalytic performance also basically remains unchanged. It solves the problem of uneven distribution of active components of traditional monolithic catalysts, weak bonding with the carrier, and gradual decline in activity during the reaction. The design strategy of this array structured catalyst can be extended to the synthesis of other metal oxide nanoarrays on metal substrates, and provides a new idea for the design of new efficient structured catalysts.

Description of drawings

Fig. 1 is the XRD pattern of the structured catalyst prepared in embodiment 1;

Fig. 2 is the SEM figure of the structured catalyst prepared in embodiment 1;

Fig. 3 is the HRTEM figure of the structured catalyst prepared in embodiment 1;

Fig. 4 is the catalytic performance diagram of the structured catalyst prepared in embodiment 1;

Fig. 5 is the repeated use performance diagram of the structured catalyst prepared in embodiment 1;

Fig. 6 is the SEM figure of the structured catalyst prepared in embodiment 2;

detailed description

The present invention will be further described below in conjunction with specific embodiments.

Example 1:

a. Ultrasonic cleaning the 8 cm ² nickel foam substrate with hydrochloric acid for 5 minutes, then ultrasonic cleaning with absolute ethanol for 5 minutes, and then cleaning with deionized water to obtain the nickel foam substrate for use;

b. Dissolve 0.5820g of cobalt nitrate hexahydrate, 0.2963g of ammonium fluoride and 0.6000g of urea in 40mL of deionized water, stir evenly, and put it into a hydrothermal kettle;

c. Immerse the foamed nickel substrate obtained in step a into the mixed solution obtained in step b, and heat it with water at 120°C for 12 hours in a reaction kettle, and cool it to room temperature naturally after the reaction; the obtained substrate is washed with water and absolute ethanol to remove impurities. Dry in an oven at ℃ for 2 hours;

d. Soluble cobalt salt and urea are dissolved in deionized water to form a solution, wherein the concentration of cobalt ions is 0.025mol/L, the addition is 0.296g, and the substance ratio of urea and cobalt ions is 1: 10;

e. Immerse the substrate obtained in step c into the mixed solution obtained in step d, and heat it in a reaction kettle at 100°C for 10 hours, and cool it to room temperature naturally after the reaction; wash the obtained substrate with water and absolute ethanol to remove impurities, and heat it at 80°C Dry in oven for 2h;

f. The substrate obtained in step e was subjected to in-situ reduction of 200 μL of chloroauric acid with NaBH ₄ to obtain an Au/Co(OH) ₂ nanoarray structured catalyst by deposition precipitation method. The average size of the monolithic square nanosheets is 1.5 micrometers wide and 5 nm thick, and the gold particle size is 3-5 nm.

The XRD pattern of the prepared structured catalyst is shown in Fig. 1 (before and after loading gold), the SEM pattern is shown in Fig. 2, and the HRTEM pattern is shown in Fig. 3.

The prepared Au/Co(OH) ₂ nano-array structured catalyst was applied to the reduction of p-nitrophenol to synthesize p-aminophenol. The reaction conditions are as follows: at room temperature, take 70ml of 2.5mM p-nitrophenol aqueous solution, pass nitrogen gas for 5-10min, stir magnetically, add 20mg of sodium borohydride, the color of the solution changes from light yellow to bright yellow, add the Au/ Co(OH) ₂ Nanoarray Structured Catalysts.

The catalytic performance diagram is shown in Figure 4 (which also includes the comparison with the conventional nanowire Co ₃ O ₄ as a catalyst), and the repeated use performance diagram is shown in Figure 5 .

Example 2:

a. Ultrasonic cleaning of 8 cm ² nickel foam substrates with hydrochloric acid (1mol/L) for 5 minutes, then ultrasonic cleaning with absolute ethanol for 5 minutes, and then cleaning with deionized water to obtain iron substrates for later use;

b. Dissolve 1.164g of cobalt nitrate hexahydrate and 0.56g of hexamethylenetetramine in 40mL of deionized water, stir evenly, and put it into a hydrothermal kettle;

c. Immerse the foamed nickel substrate obtained in step a into the mixed solution obtained in step b, and heat it with water at 100°C for 10 hours in a reaction kettle, and cool it to room temperature naturally after the reaction; the obtained substrate is washed with water and absolute ethanol to remove impurities. Dry in an oven at ℃ for 2 hours;

d. The substrate obtained in step c was subjected to in situ reduction of 200 μL of chloroauric acid with NaBH ₄ to obtain an Au/Co(Oh) ₂ nanoarray structured catalyst by deposition precipitation method. The thickness of the nanosheets is about 10 nanometers, and the size of the gold particles is 3-5nm.

The SEM image of the prepared structured catalyst is shown in Figure 6.

Claims (6)

1. a kind of Au/Co (OH)₂Nano array structure catalyst, it is characterised in that be grown directly upon in foam nickel base It is also loaded on sheet-like morphology cobalt hydroxide film micron film, cobalt hydroxide film micron film by prepared by deposition-precipitation method urging Change active component gold grain；

Its preparation method comprises the following steps：

A. by 8cm²Foam nickel base clean 5min with hydrochloric ultrasonic wave, then be cleaned by ultrasonic 5-10min with absolute ethyl alcohol or acetone, Cleaned up again with deionized water, obtain foam nickel base standby；

B. soluble cobalt, ammonium fluoride and urea are dissolved into wiring solution-forming in deionized water, the concentration of wherein cobalt ions is The amount ratio of the material of 0.01-2mol/L, ammonium fluoride and cobalt ions is 1: 4, and the amount ratio of the material of urea and cobalt ions is 1: 5；

C. foam nickel base obtained by step a is immersed into mixed solution obtained by step b, and 120 DEG C of temperature hydro-thermals in reactor 12h, reaction naturally cools to room temperature after terminating；Gained substrate is washed with water and absolute ethyl alcohol, removes impurity, in 80 DEG C of baking ovens Dry 2-4h；

D. soluble cobalt and urea are dissolved into wiring solution-forming in deionized water, the wherein concentration of cobalt ions is 0.025- The amount ratio of the material of 2mol/L, urea and cobalt ions is 1: 10；

E. gained substrate in step c is immersed into mixed solution obtained by step d, and 100 DEG C of temperature hydro-thermal 10h in reactor, instead Room temperature is naturally cooled to after should terminating；Gained substrate is washed with water and absolute ethyl alcohol, removes impurity, and 2- is dried in 80 DEG C of baking ovens 4h；

F. substrate obtained by step e is used into NaBH by deposition-precipitation method₄In-situ reducing 5-600 μ L gold chlorides obtain Au/Co (OH)₂Nano array structure catalyst.

2. Au/Co (OH) according to claim 1₂Nano array structure catalyst, it is characterised in that can in step b, d Dissolubility cobalt salt is cabaltous nitrate hexahydrate.

3. a kind of Au/Co (OH) according to claim 1₂The preparation method of nano array structure catalyst, its feature exists In comprising the following steps：

A. by 8cm²Foam nickel base clean 5min with hydrochloric ultrasonic wave, then be cleaned by ultrasonic 5-10min with absolute ethyl alcohol or acetone, Cleaned up again with deionized water, obtain foam nickel base standby；

B. soluble cobalt, ammonium fluoride and urea are dissolved into wiring solution-forming in deionized water, the concentration of wherein cobalt ions is The amount ratio of the material of 0.01-2mol/L, ammonium fluoride and cobalt ions is 1: 4, and the amount ratio of the material of urea and cobalt ions is 1: 5；

C. foam nickel base obtained by step a is immersed into mixed solution obtained by step b, and 120 DEG C of temperature hydro-thermals in reactor 12h, reaction naturally cools to room temperature after terminating；Gained substrate is washed with water and absolute ethyl alcohol, removes impurity, in 80 DEG C of baking ovens Dry 2-4h；

D. soluble cobalt and urea are dissolved into wiring solution-forming in deionized water, the wherein concentration of cobalt ions is 0.025- The amount ratio of the material of 2mol/L, urea and cobalt ions is 1: 10；

E. gained substrate in step c is immersed into mixed solution obtained by step d, and 100 DEG C of temperature hydro-thermal 10h in reactor, instead Room temperature is naturally cooled to after should terminating；Gained substrate is washed with water and absolute ethyl alcohol, removes impurity, and 2- is dried in 80 DEG C of baking ovens 4h；

F. substrate obtained by step e is used into NaBH by deposition-precipitation method₄In-situ reducing 5-600 μ L gold chlorides obtain Au/Co (OH)₂Nano array structure catalyst.

4. Au/Co (OH) according to claim 3₂The preparation method of nano array structure catalyst, it is characterised in that Soluble cobalt is cabaltous nitrate hexahydrate in step b, d.

5. a kind of Au/Co (OH) according to claim 1 or 2₂Nano array structure catalyst is applied to p-nitrophenol Reduction synthesis para-aminophenol.

6. application according to claim 5, it is characterised in that reaction condition is at ambient temperature, to take 5-70mL 2.5mM's The p-nitrophenol aqueous solution, adds 0-65mL water, leads to nitrogen 5-10min, and magnetic agitation adds sodium borohydride 10-20mg, solution Color becomes glassy yellow by faint yellow, adds proper catalyst, and nickel foam size is 2*4cm²。