Preparation method of core-shell structure composite molecular sieve with through hole

Abstract

The present application relates to the field of preparation of core-shell structure composite molecular sieve with through-pore channel. A kind of preparation method of core-shell structure composite molecular sieve with through-pore channel, ZSM-5 molecular sieve is dipped in nickel nitrate aqueous solution, then through drying, calcination forms ZSM-5 molecular sieve wrapped with nickel oxide;ZSM-5 molecular sieve wrapped with nickel oxide is reduced using hydrogen, forms ZSM-5 molecular sieve wrapped with nickel;ZSM-5 molecular sieve wrapped with nickel is placed in carbon fiber growth solution, induces carbon fiber to grow on ZSM-5 molecular sieve wrapped with nickel, forms carbon fiber, ZSM-5 molecular sieve wrapped with nickel. ZSM-5 molecular sieve or alumina material is wrapped in the outer layer of carbon fiber, ZSM-5 molecular sieve wrapped with nickel, forms core-shell structure ZSM-5 molecular sieve;Core-shell structure ZSM-5 molecular sieve is eliminated through calcination carbon fiber, forms core-shell structure composite molecular sieve with through-pore channel.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of preparation of core-shell structure composite molecular sieve with through-hole. BACKGROUND

[0002] Molecular sieve is an important inorganic porous material, which is widely used in adsorption and catalysis fields, and plays an irreplaceable important role in catalytic reaction processes such as cracking, hydrogenation, reforming, disproportionation, dehydrogenation, cyclization, and aromatization.

[0003] The catalytic action of molecular sieve cannot be separated from its regular and ordered pore structure. The pore structure of molecular sieve not only provides the positioning space of acid sites in the catalytic process, but also realizes the shape-selective effect through the size-limiting effect of pore size, so as to obtain the required catalytic products with high selectivity.

[0004] However, uniform and ordered pores also control the mass transfer and adsorption / desorption of reactants and products in the catalytic process, which is beneficial in some processes, but in other catalytic application scenarios, it limits the timely diffusion and rapid conversion of reactants, causing excessive reaction and accumulation of intermediate products and final products in the pores, which has adverse effects including decreased reaction selectivity, and pore blockage and deactivation of molecular sieve.

[0005] In view of this situation, researchers try to overcome it by reducing the diameter of molecular sieve particles and the length of internal pores. However, this method also brings problems such as a decrease in the crystallinity of molecular sieve and a change in the ratio of internal and external specific surface area, affecting the structural stability of molecular sieve and the selectivity of products.

[0006] On the contrary, another design idea for modifying molecular sieve is to construct a core-shell structure, using molecular sieve with target properties as the "core", and coating the molecular sieve with a material having a large pore structure on the outside to form a "shell", thereby realizing the modification of molecular sieve. The core-shell molecular sieve obtained by this method retains the relative advantage of the internal pore ratio of molecular sieve, while improving the mass transfer of reactants, thereby becoming an important direction of research on the modification of molecular sieve.

[0007] However, there is a difficult problem with core-shell structure molecular sieve, i.e., the blockage of pore structure penetration between core and shell. Generally, the shell layer grown outside the core will follow its own pore development law to form shell layer pores, which will produce a large number of shell-core pore misalignments, or even completely fail to penetrate, thereby making a large number of core layer pores with catalytic action unable to contact the reactants, causing a significant decrease in the activity of molecular sieve per unit weight. Therefore, it is of great significance to obtain a core-shell structure composite molecular sieve with through-hole by innovation of the preparation method, so as to fully exert the catalytic performance of molecular sieve and obtain high-performance modified molecular sieve. SUMMARY

[0008] The present application aims to provide a core-shell structure composite molecular sieve with through-pore and a preparation method thereof.

[0009] To achieve the above-mentioned application purposes, the present application adopts the following technical scheme: a core-shell structure composite molecular sieve with through-pore is prepared by loading metal components on a molecular sieve as a core, then inducing carbon fiber growth in a mixed atmosphere of hydrogen and carbon monoxide, and subsequently growing a shell layer to form the core-shell structure composite molecular sieve with through-pore.

[0010] The present application adopts the following technical scheme: a preparation method of a core-shell structure composite molecular sieve with through-pore, comprising the following steps

[0011] In step one, ZSM-5 molecular sieve is immersed in a nickel nitrate aqueous solution with a concentration of 0.1-0.5 g / ml for 6-24 h, and then dried and calcined to form ZSM-5 molecular sieve wrapped with nickel oxide.

[0012] In step two, the ZSM-5 molecular sieve wrapped with nickel oxide is reduced using hydrogen to form ZSM-5 molecular sieve wrapped with nickel.

[0013] In step three, the ZSM-5 molecular sieve wrapped with nickel is placed in a carbon fiber growth solution to induce carbon fiber growth on the ZSM-5 molecular sieve wrapped with nickel. Based on the principle that metal nickel does not match the crystal lattice of the molecular sieve, one end of the generated carbon fiber is connected to the ZSM-5 molecular sieve and the other end is connected to the metal nickel particles to form carbon fiber, ZSM-5 molecular sieve wrapped with nickel.

[0014] In step four, the outer layer of the carbon fiber, ZSM-5 molecular sieve wrapped with nickel is wrapped with ZSM-5 molecular sieve or alumina material to form a core-shell structure ZSM-5 molecular sieve.

[0015] In step five, the core-shell structure ZSM-5 molecular sieve is calcined to eliminate the carbon fiber to form a core-shell structure composite molecular sieve with through-pore.

[0016] In step one, the calcination temperature is 300-400℃ and the calcination time is 2-10 h.

[0017] When reducing the ZSM-5 molecular sieve wrapped with nickel oxide using hydrogen, the treatment temperature is 400-500℃ and the reduction time is 2-10 h.

[0018] When inducing carbon fiber growth on the ZSM-5 molecular sieve wrapped with nickel, it is performed in a mixed atmosphere of hydrogen and carbon monoxide, the volume ratio of hydrogen to carbon monoxide is 3:1-1:1, and the carbon fiber induction growth time is 6-48 h.

[0019] In the formation of carbon fiber, ZSM-5 molecular sieve wrapped with nickel, the length of the carbon fiber is 8-20 nm and the diameter is 0.5-5.5 nm.

[0020] The thickness of the shell layer ZSM-5 molecular sieve or the aluminum oxide material in the core-shell structure ZSM-5 molecular sieve is 30% to 80% of the average length of the carbon fiber.

[0021] In the fifth step, when the core-shell structure ZSM-5 molecular sieve is calcined, the calcination atmosphere is hydrogen or carbon dioxide, the flow atmosphere, the calcination temperature is 450 to 550 DEG C, and the calcination time is 6 to 12 hours.

[0022] The beneficial effects of the present application are: (1) the core-shell molecular sieve structure is synthesized, the relative advantage of the internal pore channel ratio of the molecular sieve is retained, and the mass transfer of the reactants is improved. (2) The metal component is loaded on the "core" molecular sieve, and then the carbon fiber is induced to grow in the hydrogen and carbon monoxide mixed atmosphere, and then the "shell layer" is grown, so that the core-shell structure molecular sieve with through-pore channels is formed. DETAILED DESCRIPTION

[0023] The specific embodiments of the present application are further described in detail below through specific examples. Example 1

[0024] ZSM-5 molecular sieve is used as the "core" of the core-shell molecular sieve. By the method of immersion, nickel nitrate is immersed on the ZSM-5 molecular sieve, and the loading is completed through the process of drying and calcination. The concentration of the nickel nitrate solution is 0.3 g / ml, and the immersion time is 12 hours. The calcination temperature is 400 DEG C, and the calcination time is 6 hours. The above-mentioned intermediate "core" is reduced in a hydrogen atmosphere, the reduction temperature is 400 DEG C, and the reduction time is 6 hours. The loading amount of nickel in the obtained reduced intermediate is 10 wt%. The above-mentioned intermediate is induced to grow carbon fiber in a hydrogen and carbon monoxide mixed atmosphere, the volume ratio of hydrogen and carbon monoxide is 2:1, and the carbon fiber induction growth time is 8 hours. The length of the formed carbon fiber is 10 nm, the diameter of the carbon fiber is 1.5 nm, and the above-mentioned core is coated with an aluminum oxide material (which can be immersed by the method) to form a "shell layer". The thickness of the "shell layer" is 50% of the average length of the carbon fiber. Then, the carbon fiber is removed by calcination in a flowing carbon dioxide atmosphere, the calcination temperature is 500 DEG C, and the calcination time is 6 hours.

[0025] It is determined that the through-pore channel ratio of the composite molecular sieve is 98%, the internal surface ratio of the ZSM-5 molecular sieve is 95%, the propane conversion rate in the propane aromatization reaction is 93%, and the aromatic hydrocarbon selectivity is 85%. Example 2

[0026] ZSM-5 zeolite was used as the "core" of the core-shell zeolite. Nickel nitrate was impregnated on the ZSM-5 zeolite by the impregnation method, and the loading was completed through the processes of drying and calcination. The concentration of the nickel nitrate solution was 0.2 g / ml, the impregnation time was 8 h, the calcination temperature was 380°C, and the calcination time was 6 h. The above-mentioned intermediate "core" was subjected to reduction treatment in a hydrogen atmosphere, the reduction temperature was 400°C, and the reduction time was 6 h. The loading amount of nickel in the obtained reduced intermediate was 10 wt%. The above-mentioned intermediate was subjected to carbon fiber induced growth in a mixed atmosphere of hydrogen and carbon monoxide, the volume ratio of hydrogen to carbon monoxide was 2:1, and the carbon fiber induced growth time was 8 h. The length of the formed carbon fiber was 10 nm, the diameter of the carbon fiber was 2 nm, ZSM-5 zeolite material was coated on the above-mentioned core (which can be synthesized by hydrothermal synthesis) to form a "shell layer". The thickness of the "shell layer" was 60% of the average length of the carbon fiber. Subsequently, the carbon fiber was removed by calcination in a flowing carbon dioxide atmosphere, the calcination temperature was 500°C, and the calcination time was 6 h.

[0027] It was determined that the through-pore channel proportion of the composite zeolite was 97%, the internal surface proportion of the ZSM-5 zeolite was 96%, the propane conversion rate in the propane aromatization reaction was 95%, and the aromatic hydrocarbon selectivity was 91%.

[0028] Comparative Example 1

[0029] ZSM-5 zeolite was used as the "core" of the core-shell zeolite. Alumina material was coated on the above-mentioned core to form a "shell layer". Subsequently, calcination was performed in a flowing carbon dioxide atmosphere, the calcination temperature was 500°C, and the calcination time was 6 h.

[0030] It was determined that the through-pore channel proportion of the composite zeolite was 12%, the internal surface proportion of the ZSM-5 zeolite was 91%, the propane conversion rate in the propane aromatization reaction was 33%, and the aromatic hydrocarbon selectivity was 75%.

[0031] Comparative Example 2

[0032] ZSM-5 zeolite was used as the "core" of the core-shell zeolite. Alumina material was coated on the above-mentioned core to form a "shell layer". Subsequently, calcination was performed in a flowing carbon dioxide atmosphere, the calcination temperature was 500°C, and the calcination time was 6 h.

[0033] It was determined that the through-pore channel proportion of the composite zeolite was 98%, the internal surface proportion of the ZSM-5 zeolite was 46%, the propane conversion rate in the propane aromatization reaction was 93%, and the aromatic hydrocarbon selectivity was 15%.

Claims

1. A method for preparing a core-shell structure composite molecular sieve having a through-pore channel, characterized by: It comprises the following steps: Step one, ZSM-5 molecular sieve is immersed in a nickel nitrate aqueous solution with a concentration of 0.1-0.5 g / ml for 6-24 hours, and then a nickel oxide coated ZSM-5 molecular sieve is formed through drying and calcination; Step two, the nickel oxide coated ZSM-5 molecular sieve is reduced using hydrogen to form a nickel coated ZSM-5 molecular sieve; Step three, the nickel coated ZSM-5 molecular sieve is placed in a carbon fiber growth solution to induce the growth of carbon fibers on the nickel coated ZSM-5 molecular sieve, based on the principle that metal nickel does not match the molecular sieve lattice, the generated carbon fibers are connected to the ZSM-5 molecular sieve at one end and to the metal nickel particles at the other end, forming carbon fibers, nickel coated ZSM-5 molecular sieve; Step four, the carbon fiber, nickel coated ZSM-5 molecular sieve is coated with ZSM-5 molecular sieve or alumina material on the outer layer to form a core-shell structure ZSM-5 molecular sieve; Step five, the core-shell structure ZSM-5 molecular sieve is calcined to eliminate the carbon fibers, forming a through-pore core-shell structure composite molecular sieve.

2. The method for preparing a core-shell composite molecular sieve with interconnected channels according to claim 1, characterized in that: In step one, the calcination temperature is 300-400°C, and the calcination time is 2-10 hours.

3. The method for preparing a core-shell composite molecular sieve with interconnected channels according to claim 1, characterized in that: When reducing the nickel oxide coated ZSM-5 molecular sieve using hydrogen, the treatment temperature is 400-500°C, and the reduction time is 2-10 hours.

4. The method of claim 1, wherein the method further comprises: providing a mixture of a first zeolite and a second zeolite; and calcining the mixture to form the composite zeolite. When inducing the growth of carbon fibers on the nickel coated ZSM-5 molecular sieve, it is carried out in a mixed atmosphere of hydrogen and carbon monoxide, the volume ratio of hydrogen to carbon monoxide is 3:1-1:1, and the carbon fiber induction growth time is 6-48 hours.

5. The method for preparing a core-shell composite molecular sieve with interconnected channels according to claim 1, characterized in that: In the formation of carbon fibers, nickel coated ZSM-5 molecular sieve, the length of the carbon fibers is 8-20 nm, and the diameter is 0.5-5.5 nm.

6. The method of claim 5, wherein the method further comprises: In the core-shell structure ZSM-5 molecular sieve, the thickness of the shell ZSM-5 molecular sieve or alumina material is 30%-80% of the average length of the carbon fibers. ​ 7. The method for preparing a core-shell composite molecular sieve with interconnected channels according to claim 1, characterized in that: In step five, when calcining the core-shell structure ZSM-5 molecular sieve, the calcination atmosphere is hydrogen or carbon dioxide, the flow atmosphere, the calcination temperature is 450-550°C, and the calcination time is 6-12 hours.