阅读说明：本技术 一种用于费-托合成反应的高活性、高稳定性催化剂的制备方法 (Preparation method of high-activity and high-stability catalyst for Fischer-Tropsch synthesis reaction ) 是由 洪景萍 王博 李金林 张煜华 于 2019-09-05 设计创作，主要内容包括：本发明涉及纳米催化剂技术领域,尤其涉及一种用于费-托合成反应的高活性、高稳定性催化剂的制备方法。本发明的制备方法中预先在无机氧化物载体材料表面包覆CN纳米涂层,然后利用传统浸渍的方法将钴盐负载到制备的载体上,最后采用辉光放电等离子体技术分解钴盐前驱体,可以有效地控制所制备Co纳米颗粒尺寸以及钴-载体相互作用,有利于提高催化剂的稳定性、催化活性等与费-托合成反应相关的催化性能指标。通过将碳氮包覆和等离子体处理技术相结合,即提高了催化剂的活性,又使催化剂的反应稳定性得到提高。(The invention relates to the technical field of nano catalysts, in particular to a preparation method of a high-activity and high-stability catalyst for Fischer-Tropsch synthesis reaction. In the preparation method, the CN nano coating is coated on the surface of the inorganic oxide carrier material in advance, then the cobalt salt is loaded on the prepared carrier by using the traditional dipping method, and finally the glow discharge plasma technology is adopted to decompose the cobalt salt precursor, so that the size of the prepared Co nano particles and the cobalt-carrier interaction can be effectively controlled, and the stability, the catalytic activity and other catalytic performance indexes related to the Fischer-Tropsch synthesis reaction of the catalyst can be improved. By combining the carbon nitrogen coating and the plasma treatment technology, the activity of the catalyst is improved, and the reaction stability of the catalyst is improved.)

1. A preparation method of a high-activity and high-stability catalyst for Fischer-Tropsch synthesis reaction comprises the following steps:

(1) synthesis of the vector M @ CN: uniformly mixing a saturated aqueous solution of urea with inorganic oxide carrier M powder, drying at 90-120 ℃ for 9-15h, and roasting the dried sample at 500-550 ℃ for 2h to obtain a carrier M @ CN;

(2) preparation of Co/M @ CN by impregnation: taking a cobalt nitrate solution, impregnating the carrier M @ CN obtained in the step (1) by using an isometric impregnation method, then distilling under reduced pressure to remove water in the carrier M @ CN, and drying at 90-120 ℃ for 10-15h to obtain a Co/M @ CN precursor;

(3) plasma treatment of Co/M @ CN precursor:

(a) putting the Co/M @ CN precursor prepared in the step (2) into a plasma cavity sample cell of a glow discharge plasma device;

(b) vacuumizing the plasma cavity, introducing high-purity nitrogen into the plasma cavity, and adjusting a gas flowmeter to keep the vacuum degree in the cavity at 80-150 Pa;

(c) regulating the voltage of the glow discharge plasma device to be stable to 700V at 500-;

the inorganic oxide carrier M is TiO₂Or Al₂O₃The mass ratio of the inorganic oxide carrier M powder to the urea in the saturated aqueous solution of the urea is 1 (1-4).

2. The production method according to claim 1, wherein in the step (2), the loading amount of the Co element on the M @ CN support is 10 wt.%.

3. The method of claim 1, wherein the step (c) is: stabilizing the voltage of the glow discharge plasma device to 500V, adjusting the duty ratio to 20%, and treating for 2h under nitrogen to obtain the Co/M @ CN-p catalyst.

4. The preparation method according to claim 1, wherein the roasting process in the step (1) is as follows: the sample was placed in a muffle furnace at 10-20 ℃ C. min^-1The temperature is heated to 500-550 ℃, and then the mixture is roasted for 2h at 500-550 ℃.

5. The production method according to any one of claims 1 to 4, wherein the surface coating layer of the carrier M @ CN obtained in the step (1) is a carbon-nitrogen coating layer, and the thickness of the carbon-nitrogen coating layer is 0.50 to 1.5 nm.

6. The preparation method of any one of claims 1 to 4, wherein the cobalt nanoparticles on the surface of the Co/M @ CN-p catalyst obtained in the step (3) have a particle size of 1 to 4 nm.

Technical Field

The invention relates to the technical field of nano catalysts, in particular to a preparation method of a high-activity and high-stability catalyst for Fischer-Tropsch synthesis reaction.

Background

Fischer-Tropsch synthesis (FTS) is catalyzed by a catalystSynthesis gas (CO and H) under oxidation₂) Heterogeneous catalytic processes for the conversion of hydrocarbons can be used to produce clean fuels and specialty chemicals free of nitrogen and sulfur. The raw material synthesis gas of the FTS can be converted from coal, natural gas and biomass, and the adoption of the FTS can efficiently utilize carbon resources or renewable resources with relatively rich reserves in China, promote the sustainable development of carbon cycle and further relieve the situation of energy shortage in China.

The FTS catalyst is influenced by three factors of active metal, auxiliary agent and carrier, so the research on the structure-activity relationship of the catalyst is helpful to screen the FTS catalyst with excellent performance. Oxides, composite oxides, molecular sieves, carbon materials, and the like are commonly supported on FTS catalysts. Since the active metal and the inorganic oxide support easily form a strong interaction, a metal-support composite oxide such as CoSiO which is difficult to reduce is formed₃、CoAlO₂、CoTiO₃And the like, a higher reduction temperature is needed to reduce the active metal, and a higher heat treatment temperature causes sintering of the active component, so that the traditional oxide carrier-supported cobalt-based catalyst usually needs to add a noble metal auxiliary agent to simultaneously take high dispersity and high reduction performance of cobalt into consideration.

The carbon material has the characteristics of surface chemical inertness, high purity, good conductivity, high thermal stability, large specific surface area and the like, and can be used as a potential catalyst carrier, however, the interaction between the active metal and the carbon material carrier is weak, and the metal nanoparticles are easy to agglomerate and sinter in the reaction process, so that the catalytic activity of the catalyst is limited. The regulation and control of the carrier structure of the catalyst are beneficial to obtaining a high-performance FTS catalyst, and Liu et al wrap glucose in TiO by using a hydrothermal method₂On top of that, TiO is formed₂Taking carbon as a core-shell structure carbon-titanium material of a core and carbon as a shell, and then taking the carbon-titanium composite material as a carrier to prepare the cobalt-based FTS catalyst, wherein TiO is weakened by coating of a carbon layer_xAnd the exposed cobalt active sites are more stably existed due to the migration to the cobalt metal surface in the reduction process, so that better catalytic activity is obtained. However, the carbon layer is easily consumed in the reaction process, and the service life of the catalyst is seriously influenced. Hong et al utilize glow discharge plasmaDaughter prepared CoPt/TiO with noble metal assistant Pt₂The catalyst, a cobalt-based catalyst with high reduction performance, although achieving better reaction activity, is obtained due to cobalt and TiO₂The phenomenon of catalyst deactivation still occurs in the reaction process due to the strong interaction between carriers. In addition, the precious metal auxiliary agent has limited reserves and high price, and if the precious metal auxiliary agent can be replaced by a simple method, the industrial application cost of the catalyst can be obviously reduced.

In the preparation process of the catalyst, the metal salt precursor loaded on the surface of the carrier is decomposed by a common roasting method, and the roasting condition has important influence on the structure of the catalyst; because the metal salt generally needs to be decomposed at a relatively high temperature to form an oxide, the high temperature causes sintering of the active metal and increases the interaction between the carrier and the active component, and in addition, the roasting process has the problems of long time consumption, high power consumption and the like.

Disclosure of Invention

Aiming at the defects of the existing traditional oxide-supported cobalt-based catalyst, the invention aims to provide the preparation method of the cobalt-based Fischer-Tropsch synthesis catalyst which does not need to add a noble metal auxiliary agent, has simple and controllable operation, saves energy consumption and can obtain high catalytic activity and stability.

The technical scheme of the invention is to provide a preparation method of a high-activity and high-stability catalyst for Fischer-Tropsch synthesis reaction, which comprises the following steps:

(1) synthesis of the vector M @ CN: uniformly mixing a saturated aqueous solution of urea with inorganic oxide carrier M powder, drying at 90-120 ℃ for 9-15h (preferably drying at 100 ℃ for 12h), and roasting the dried sample at 500-550 ℃ for 2h to obtain carrier M @ CN;

(2) preparation of Co/M @ CN by impregnation: taking a cobalt nitrate solution, impregnating the carrier M @ CN obtained in the step (1) by using an isometric impregnation method, then distilling under reduced pressure to remove water in the carrier M @ CN, and drying at 90-120 ℃ for 10-15h (preferably drying at 100 ℃ for 10h) to obtain a Co/M @ CN precursor;

(3) plasma treatment of Co/M @ CN precursor:

(a) putting the Co/M @ CN precursor prepared in the step (2) into a plasma cavity sample cell of a glow discharge plasma device;

(b) vacuumizing the plasma cavity, introducing high-purity nitrogen into the plasma cavity, and adjusting a gas flowmeter to keep the vacuum degree in the cavity at 80-150Pa (preferably 120 Pa);

(c) regulating the voltage of the glow discharge plasma device to be stable to 700V at 500-;

the inorganic oxide carrier M is TiO₂Or Al₂O₃The mass ratio of the inorganic oxide carrier M powder to urea in the saturated aqueous solution of urea is 1 (1-4), preferably 1: 1.

Further, the step (c) is: and regulating the voltage of the glow discharge plasma device to be stabilized to 500V, regulating the duty ratio to be 20%, and treating for 2h under nitrogen to obtain the Co/M @ CN-p catalyst.

Further, the roasting process in the step (1) is as follows: the sample was placed in a muffle furnace at 10-20 ℃ C. min^-1Is heated to 500-550 ℃ and then is roasted at 500-550 ℃ for 2h, and preferably, the sample is placed in a muffle furnace at 15 ℃ min^-1Heated to 550 ℃ and then calcined at 550 ℃ for 2 h.

Further, in the step (2), the loading amount of the Co element on the M @ CN support is 10 wt.% based on the mass of the support M @ CN.

Further, the surface coating of the carrier M @ CN obtained in the step (1) is a carbon-nitrogen coating, and the thickness of the carbon-nitrogen coating is 0.50-1.5 nm.

Further, the particle size of the cobalt nanoparticles on the surface of the Co/M @ CN-p catalyst obtained in the step (3) is 1-4 nm.

The plasma provides a new approach for preparing a high-dispersion high-efficiency catalyst in a green and energy-saving way, active species which are high in energy and unstable, including high-energy electrons, ions, molecules and the like, exist in a plasma field, and if a solid material is placed in the plasma field, the high-energy active species are contacted with the solid material, the active species act on the surface of the solid material, and the property of the surface of an object is changed. According to the effect, the plasma technology is applied to the catalyst preparation process, and the plasma technology can be found to effectively decompose metal salt precursors (such as nitrate, hydroxide, hydrous oxide and the like) to obtain metal oxide catalysts or supported catalysts. Therefore, the invention adopts the technical means of plasma and the cheaper means of carrier modification to combine to obtain the cobalt-based Fischer-Tropsch synthesis catalyst with high dispersion, high activity and high stability.

The invention applies the plasma technology to the preparation of the catalyst, determines a proper operation process which can be suitable for the preparation of the Fischer-Tropsch synthesis catalyst through a large number of creative experiments, and can prove that the conversion rate of carbon monoxide of the catalyst obtained by the invention in the Fischer-Tropsch synthesis reaction can reach 20.7 percent through the test of the catalytic performance.

Compared with the prior art, the invention has the advantages and beneficial effects that:

1. the invention coats a CN nano coating on the surface of an inorganic oxide carrier material in advance, then uses a traditional dipping method to load cobalt salt on a prepared carrier, and finally adopts a plasma technology to decompose a cobalt salt precursor, thereby effectively controlling the size of the prepared Co nano particles and the cobalt-carrier interaction, and being beneficial to improving the stability, catalytic activity and other catalytic performance indexes related to the Fischer-Tropsch synthesis reaction of the catalyst.

2. The support for the catalyst prepared in the present invention includes, but is not limited to, Al₂O₃、TiO₂The powder has wide application range, simple operation process in the reaction process and energy saving.

3. The invention not only applies the CN nano coating pre-treatment to the carrier to the preparation of the catalyst for Fischer-Tropsch synthesis for the first time, the cobalt salt precursor is decomposed by matching with the plasma technology, the carrier modification treatment is skillfully combined with the plasma technology, the two preparation methods have synergistic effect, the matching of the plasma technology and the carrier modification ensures that the performance of the prepared catalyst generates unexpected effect, the catalytic performance and stability of the catalyst exceed those of the catalyst prepared by the common conventional method and the plasma technology, the reaction performance of the Co/carrier @ CN-p catalyst obtained in the way is obviously superior to that of the catalyst prepared by the traditional roasting method in the Fischer-Tropsch synthesis, by studying the mechanism of catalytic action of the fischer-tropsch synthesis reaction on the catalyst, the development of cheaper catalyst preparation techniques can be driven.

4. The carbon-nitrogen coating and the plasma treatment technology are combined, so that the activity of the catalyst is improved, the reaction stability of the catalyst is improved, the interaction between an active component and a carrier on the catalyst is usually enhanced to prevent the catalyst from being inactivated due to sintering, but the strong interaction can reduce the reduction performance of active metal, further reduce the reaction activity, and the initial reaction activity is reduced although the reaction stability of the catalyst is improved by the pure carbon-nitrogen coating. After the plasma treatment is combined, the reaction activity is greatly improved while high reaction stability is kept.

Drawings

FIG. 1 shows the TiO support prepared in example 1₂@1CN (i.e. TiO)₂@CN)、TiO₂@1.5CN、TiO₂@2CN、TiO₂TEM image of @3 CN;

TiO with four different urea/P25 titanium dioxide mass ratios₂@ CN support, in which TiO₂@1CN、TiO₂@1.5CN、TiO₂@2CN、TiO₂The urea/titanium dioxide mass ratios on @3CN are 1:1, 1.5:1, 2:1 and 3:1, respectively. The surface coating layer-carbon nitrogen coating layer was found to have a thickness of 0.80 to 1.4nm, and the thickness of the carbon nitrogen coating layer increased as the amount of urea added increased.

FIG. 2 shows the Co/TiO catalysts prepared in example 1 and comparative example₂@CN-p、Co/TiO₂、Co/TiO₂TEM image and surface cobalt particle size distribution of @ CN, it can be seen that Co/TiO₂The particle size of the cobalt nano-particles on the surface of the @ CN-p catalyst is 3.4 +/-0.5 nm, and the particle size is obviously smaller than that of the cobalt particles in the catalyst prepared by the comparative example.

FIG. 3 is a drawing showingCo/TiO catalyst prepared in example 1 and comparative example₂@CN-p、Co/TiO₂、Co/TiO₂H of @ CN₂-a TPR map.

FIG. 4 shows the Co/TiO catalysts prepared in example 1 and comparative example₂@CN-p、Co/TiO₂、Co/TiO₂Graph of the activity of @ CN in catalyzing the Fischer-Tropsch synthesis reaction as a function of time.

Detailed Description

In order to make the objects, technical solutions, advantages and beneficial effects of the present invention more apparent, the technical solutions of the present invention are further described in detail below with reference to specific embodiments.