阅读说明：本技术 一种在温和条件下催化氮气氢气合成氨气的仿生催化剂制备方法 (Preparation method of biomimetic catalyst for catalyzing nitrogen and hydrogen to synthesize ammonia under mild condition ) 是由 丁辉 石佳慧 徐曦萌 于 2020-05-08 设计创作，主要内容包括：本发明公开了一种用于温和条件下催化氮气氢气合成氨气的人工仿生催化剂,该催化剂以碳纳米管和氧化铝为复合载体、铁为活性组分,活性组分以原子团簇或单原子的形式分散在复合载体内部,形成了独特的Fe/CNTs-Al2O3催化微反应器,其中低氧化态的Fe作为电子库调节整个过程的电荷转移、与Co-Mo协同作用模拟自然界生物固氮的高效氧化还原机制,以仿生结合加氢机制有效降低氮气的活化能垒,打破传统多相催化过渡金属表面直接解离机制的BEP关系限制,使合成氨反应能够在温和条件下驱动。(The invention discloses an artificial bionic catalyst for catalyzing nitrogen and hydrogen to synthesize ammonia under mild conditions, which takes carbon nano tubes and alumina as composite carriers and iron as active components, wherein the active components are dispersed in the composite carriers in the form of atomic clusters or monoatomic atoms to form a unique Fe/CNTs-Al2O3 catalytic microreactor, wherein Fe in a low oxidation state is taken as an electronic library to adjust charge transfer in the whole process, and the Fe and Co-Mo have synergistic effect to simulate a high-efficiency oxidation-reduction mechanism of biological nitrogen fixation in nature, so that the activation energy barrier of nitrogen is effectively reduced by a bionic combination hydrogenation mechanism, the BEP relation limitation of a traditional heterogeneous catalytic transition metal surface direct dissociation mechanism is broken through, and the synthetic ammonia reaction can be driven under mild conditions.)

1. An artificial bionic catalyst for catalyzing nitrogen and hydrogen to synthesize ammonia under mild conditions is characterized in that: the method comprises the following steps:

step one, Co-Mo/Al₂O₃Preparation of the catalytic carrier:

(1) industrial pure gamma-Al₂O₃Crushing, sieving with 12-16 mesh sieve, heating the sieved sample at 800 deg.C for 4h to convert into (theta) -Al₂O₃；

(2) First, 5g of (theta) -Al was taken after phase inversion₂O₃Placing in 50mL beaker, adding 10mL distilled water, soaking in 60 deg.C water bath for 40min to obtain (theta) -Al₂O₃Absorbing water, cooling to 25 deg.C, pouring out unabsorbed water, measuring the volume of poured water and recording as V, and calculating (theta) -Al₂O₃The saturated water absorption capacity of (A) is:

then, analytically pure Co (NO) with the mass ratio of 1: 1-5: 1₃)₂·6H₂O and analytically pure (NH)₄)₆Mo₇O₂₄·4H₂Dissolving O in (10-V) mL of distilled water to obtain a mixed solution, treating the mixed solution with ultrasonic wave until the solid component is completely dissolved, and adding 5g of phase-inverted (theta) -Al into the mixed solution₂O₃And continuously stirring the mixture under the baking of an infrared lamp until the solution is completely immersed into the (theta) -Al after phase inversion₂O₃In (theta) -Al after impregnation₂O₃Drying in an oven at 100-120 ℃ to obtain unreduced Co-Mo/Al₂O₃A catalytic support;

(3) mixing Co-Mo/Al₂O₃The catalytic carrier is placed in a constant temperature area of a quartz tube of a horizontal tube type resistance furnace, and in a mixed atmosphere of hydrogen and argon with the mass percent purity of 99.99%, the flow ratio of the two gases is controlled to be Ar: h₂80:20 mL/min-50 mL/min, heating to 500-550 ℃ at the speed of 5-10 ℃/min to reduce Co-Mo/Al₂O₃Catalyzing the carrier for 1-3 h to obtain reduced Co-Mo/Al₂O₃A catalytic support;

step two, CNTs-Al₂O₃Preparing a composite carrier:

(1) reducing the Co-Mo/Al₂O₃Placing the catalytic carrier in a constant temperature area of a quartz tube of a horizontal tube type resistance furnace, and continuously heating to 550-750 ℃ in the mixed atmosphere of hydrogen and argon in the first step at the same flow ratio as that in the first step, wherein the heating rate is 5-10 ℃/min;

(2) introducing acetylene gas with the mass percent purity of 99.99% into the horizontal tubular resistance furnace, and simultaneously closing argon; at C₂H₂And H₂The flow ratio of (A) is 10:100 mL/min-100: 100mL/min, the reaction is carried out for 10-60 min under the reaction atmosphere, and the reduced Co-Mo/Al₂O₃Growing CNTs on a catalytic carrier in a catalytic manner, and stopping introducing acetylene gas into the horizontal tubular resistance furnace after the reaction is finished;

(3) continuously introducing mixed atmosphere of hydrogen and argon with the mass percent purity of 99.99% into the horizontal tubular resistance furnace, and controlling the flow ratio of the two gases to be Ar: h₂The CNTs are prepared by rapidly heating 80:20 mL/min-50: 50mL/min in the atmosphere to 700-800 ℃ for 1-3 h, and then cooling to 20-25 ℃ in the mixed atmosphere₂O₃A composite carrier;

(4) CNTs-Al₂O₃15-30% of H for composite carrier₂O₂Oxidizing for 6h, washing the treated sample to be neutral, and drying in a drying oven at the temperature of 60-80 ℃ to obtain the purified and modified CNTs-Al₂O₃A composite carrier;

step three, Fe/CNTs-Al₂O₃Preparing a biomimetic catalyst:

(1) taking 0.5000-5.0000 g FeCl₃Dissolving in 30mL of analytically pure acetone, and adding the purified and modified CNTs-Al₂O₃Stirring the composite carrier at 20-25 ℃ for 24-48h to load Fe, and carrying out Fe-loaded CNTs-Al₂O₃Filtering the composite carrier sample, washing with water, and slowly drying in an oven at 60-80 ℃;

(2) drying the CNTs-Al loaded with Fe₂O₃Placing a composite carrier sample in a constant temperature area of a quartz tube of a horizontal tube type resistance furnace, and controlling the flow ratio of two gases to be Ar: h₂20-50: 50mL/min, the heating rate is 5-10 ℃/min, the temperature is gradually increased to 350-750 ℃, then the calcination is carried out for 6-8 h, and then the temperature is reduced to 20-25 ℃ under the protection of the mixed atmosphere to prepare the Fe/CNTs-Al with atomic-level dispersion₂O₃A biomimetic catalyst.

Technical Field

The invention relates to a preparation method of a catalyst, in particular to a preparation method of a biomimetic catalyst for catalyzing nitrogen and hydrogen to synthesize ammonia under mild conditions.

Background

The Haber-Bosch process is a mainstream process for industrially producing ammonia at present, a traditional Haber-Bosch process is used for producing ammonia by utilizing nitrogen and hydrogen, a fused iron type catalyst is mostly used, although the preparation process is mature and the preparation cost is low, the process requires severe operating conditions of high temperature (300-550 ℃) and high pressure (15-25 MPa), 1-2% of energy supply in the world is consumed every year, and a large amount of greenhouse gas is released (1.87 tons of carbon dioxide is generated per ton of ammonia prepared). The second generation ruthenium-based ammonia synthesis catalyst can reduce the reaction temperature and pressure of ammonia synthesis to a certain extent, but ruthenium-based catalyst is a noble metal and has higher cost, thus preventing wide industrial popularization and application of the ruthenium-based catalyst.

In traditional heterogeneous thermal catalysis, transition metal catalyst is mostly utilized to catalyze nitrogen and hydrogen to synthesize ammonia, and the rate-limiting step is N₂Direct dissociation activation of the molecule, but very stable due to the nitrogen-nitrogen triple bond (bond energy 946 kJ. mol)^-1)，N₂Is quite difficult to activate and is subject toRestrictions of the Evans-Polanyi (BEP) relationship, N₂There is a contradiction between the molecular activation barrier and the adsorption energy of reactive intermediate species. When N is present₂When the activation energy of the molecule is small, the adsorption energy of the intermediate species is strong; when the adsorption of the intermediate species is weak, N₂The activation energy of the molecule is again high, which results in a volcanic-type curve for the ammonia synthesis reactivity on the transition metal. An ideal ammonia synthesis catalyst should balance the energy relationship between the two, near the top of the volcano-type curve, and even if such a catalyst is found, it still requires relatively high temperatures and pressures to overcome N simultaneously₂Activation energy of (a) and adsorption energy of the intermediate species. Recently, Chen et al have developed a series of TM-LiH double-active center ammonia synthesis catalysts by introducing LiH as a second active center, and the ammonia synthesis activity of the composite catalysts does not present a volcano-type curve, which shows that the addition of hydride avoids the energy restriction relationship on a transition metal catalyst; li and the like in Fe₃/θ-Al₂O₃And Rh₁Co₃the/CoO (011) cluster is taken as a catalytic center, the synthesis of ammonia is realized by a hydrogen assisted dissociation mechanism similar to enzyme catalysis, and N adsorbed on an active site₂Is first hydrogenated to NNH, N₂ ^*Dissociation is NNH^*The dissociation is replaced by a lower barrier that can be driven under mild thermodynamic conditions.

In nature, the nitrogen-fixing microorganisms can utilize nitrogen-fixing enzymes in organisms to fix N under mild conditions₂Efficient reduction to NH₃Biological nitrogen fixation accounts for nitrogen fixed in the atmosphereMore than 60% of the total amount. The most abundant and characteristic nitrogenase is a molybdenum-dependent enzyme formed by the synergy of two essential metalloproteins, electron-donating ferritin (Fe-) and catalytic ferromolybdenum (MoFe-), which activates N₂The molecular properties are derived from the efficient redox cycling of Fe (II) and Fe (III) on the Mo-Fe-S-C cluster of the ferromolybdenum cofactor, through N₂The bound adsorption of (a) achieves hydrogenation rather than dissociative adsorption as in the Haber-Bosch process. Biological nitrogen fixation is not limited by the high-temperature high-pressure catalytic conditions of heterogeneous thermocatalytic ammonia synthesis, and N is reduced by preferentially combining a hydrogenation mechanism₂The activation energy barrier of the method and the limitation of BEP relation are avoided, so that the synthetic ammonia reaction can be efficiently carried out under mild conditions. But the biological nitrogen fixation amount in the nature is extremely small, and the requirement of human production and life can not be met.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a preparation method of a biomimetic catalyst for catalyzing nitrogen and hydrogen to synthesize ammonia under mild conditions, which effectively reduces the activation energy barrier of nitrogen, breaks through the BEP relation limitation of the traditional heterogeneous catalysis transition metal surface direct dissociation mechanism, enables the ammonia synthesis reaction to be driven under mild conditions, enables the active phase Fe to reach the atomic level dispersion level, forms a catalytic microreactor with a composite carrier, obviously improves the performance of the biomimetic catalyst, reduces the temperature and pressure of the traditional ammonia synthesis process, and reduces the energy consumption and pollution of the ammonia synthesis industry.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention relates to an artificial bionic catalyst for catalyzing nitrogen and hydrogen to synthesize ammonia under mild conditions, which comprises the following steps:

step one, Co-Mo/Al₂O₃Preparation of the catalytic carrier:

(1) industrial pure gamma-Al₂O₃Crushing, sieving with 12-16 mesh sieve, heating the sieved sample at 800 deg.C for 4h to convert into (theta) -Al₂O₃；

(2) First, 5g of (theta) -Al was taken after phase inversion₂O₃Placed in a 50mL beaker and 10mL of distilled water addedSoaking in water bath at 60 deg.C for 40min to obtain (theta) -Al₂O₃Absorbing water, cooling to 25 deg.C, pouring out unabsorbed water, measuring the volume of poured water and recording as V, and calculating (theta) -Al₂O₃The saturated water absorption capacity of (A) is:

then, analytically pure Co (NO) with the mass ratio of 1: 1-5: 1₃)₂·6H₂O and analytically pure (NH)₄)₆Mo₇O₂₄·4H₂Dissolving O in (10-V) mL of distilled water to obtain a mixed solution, treating the mixed solution with ultrasonic wave until the solid component is completely dissolved, and adding 5g of phase-inverted (theta) -Al into the mixed solution₂O₃And continuously stirring the mixture under the baking of an infrared lamp until the solution is completely immersed into the (theta) -Al after phase inversion₂O₃In (theta) -Al after impregnation₂O₃Drying in an oven at 100-120 ℃ to obtain unreduced Co-Mo/Al₂O₃A catalytic support;

(3) mixing Co-Mo/Al₂O₃The catalytic carrier is placed in a constant temperature area of a quartz tube of a horizontal tube type resistance furnace, and in a mixed atmosphere of hydrogen and argon with the mass percent purity of 99.99%, the flow ratio of the two gases is controlled to be Ar: h₂80:20 mL/min-50 mL/min, heating to 500-550 ℃ at the speed of 5-10 ℃/min to reduce Co-Mo/Al₂O₃Catalyzing the carrier for 1-3 h to obtain reduced Co-Mo/Al₂O₃A catalytic support;

step two, CNTs-Al₂O₃Preparing a composite carrier:

(1) reducing the Co-Mo/Al₂O₃Placing the catalytic carrier in a constant temperature area of a quartz tube of a horizontal tube type resistance furnace, and continuously heating to 550-750 ℃ in the mixed atmosphere of hydrogen and argon in the first step at the same flow ratio as that in the first step, wherein the heating rate is 5-10 ℃/min;

(2) acetylene gas with the mass percent purity of 99.99 percent is introduced into the horizontal tubular resistance furnaceSimultaneously closing the argon; at C₂H₂And H₂The flow ratio of (A) is 10:100 mL/min-100: 100mL/min, the reaction is carried out for 10-60 min under the reaction atmosphere, and the reduced Co-Mo/Al₂O₃Growing CNTs on a catalytic carrier in a catalytic manner, and stopping introducing acetylene gas into the horizontal tubular resistance furnace after the reaction is finished;

(3) continuously introducing mixed atmosphere of hydrogen and argon with the mass percent purity of 99.99% into the horizontal tubular resistance furnace, and controlling the flow ratio of the two gases to be Ar: h₂The CNTs are generated by rapidly heating to 700-800 ℃ for 1-3 h under the atmosphere at a ratio of 80:20 mL/min-50: 50mL/min, and then reducing to 20-25 ℃ under the protection of the mixed atmosphere to prepare the CNTs-Al₂O₃A composite carrier;

(4) CNTs-Al₂O₃15-30% of H for composite carrier₂O₂Oxidizing for 6h, washing the treated sample to be neutral, and drying in a drying oven at the temperature of 60-80 ℃ to obtain the purified and modified CNTs-Al₂O₃A composite carrier;

step three, Fe/CNTs-Al₂O₃Preparing a biomimetic catalyst:

(1) taking 0.5000-5.0000 g FeCl₃Dissolving in 30mL of analytically pure acetone, and adding the purified and modified CNTs-Al₂O₃Stirring the composite carrier at 20-25 ℃ for 24-48h to load Fe, and carrying out Fe-loaded CNTs-Al₂O₃Filtering the composite carrier sample, washing with water, and slowly drying in an oven at 60-80 ℃;

(2) drying the CNTs-Al loaded with Fe₂O₃Placing a composite carrier sample in a constant temperature area of a quartz tube of a horizontal tube type resistance furnace, and controlling the flow ratio of two gases to be Ar: h₂20-50: 50mL/min, the heating rate is 5-10 ℃/min, the temperature is gradually increased to 350-750 ℃, then the calcination is carried out for 6-8 h, and then the temperature is reduced to 20-25 ℃ under the protection of the mixed atmosphere to prepare the Fe/CNTs-Al with atomic-level dispersion₂O₃A biomimetic catalyst.

Compared with the prior art, the invention has the following advantages:

(1) the invention adopts a biological nitrogen fixation mechanism to realize the unification of heterogeneous catalysis and enzyme catalysis. The low oxidation state non-noble metal Fe is used as an electronic library to adjust charge transfer in the whole process, the high-efficiency oxidation reduction cycle of biological nitrogen fixation in nature is simulated by the synergistic effect of the Fe and Co-Mo, the activation energy barrier of nitrogen is effectively reduced by a bionic combination hydrogenation mechanism, the BEP relation limitation of a traditional heterogeneous catalysis transition metal surface direct dissociation mechanism is broken through, the reaction can be driven under a mild thermodynamic condition, and therefore the temperature and the pressure of the traditional Haber-Bosch ammonia synthesis process are remarkably reduced under the condition of no external light and electricity, and the ammonia synthesis reaction can be carried out under a mild condition.

(2) The invention realizes the atomic-level dispersion of the non-noble metal active phase Fe. Composite carrier CNTs-Al₂O₃The unique electronic confinement environment ensures that metal particles in the bionic catalyst are not easy to grow up, effectively avoids particle aggregation, and can also keep the stability of the particles in the bionic catalyst at higher temperature, thereby better resisting sintering, and the active phase Fe effectively keeps an atomic-level dispersion state, so that the bionic catalyst has excellent synthetic ammonia activity.

(3) The invention constructs a unique catalytic microreactor. CNTs-Al with macroscopic molding and microscopic adjustment₂O₃Is a composite carrier, takes the non-noble metal Fe dispersed in atomic level as an active phase to form Fe/CNTs-Al₂The O catalytic micro-reactor realizes the bionic high-efficiency catalytic synthesis of ammonia under mild conditions by utilizing the synergistic effect of the unique electronic confinement environment of the micro-reactor and the size effect of atomic-scale Fe.

Detailed Description

The present invention will be described in detail with reference to specific examples.

The invention relates to an artificial bionic catalyst for catalyzing nitrogen and hydrogen to synthesize ammonia under mild conditions, which comprises the following steps:

step one, Co-Mo/Al₂O₃Preparation of the catalytic carrier:

(1) industrial pure gamma-Al₂O₃Pulverizing, and sieving with 12-16 mesh sieveAnd (4) screening. Heating the screened sample at 800 ℃ for 4h to convert the phase into (theta) -Al₂O₃。

(2) First, 5g of (theta) -Al was taken after phase inversion₂O₃Placing in 50mL beaker, adding 10mL distilled water, soaking in 60 deg.C water bath for 40min to obtain (theta) -Al₂O₃Absorbing water, cooling to 25 deg.C, pouring out unabsorbed water, measuring the volume of poured water and recording as V, and calculating (theta) -Al₂O₃The saturated water absorption capacity of (A) is:

then, analytically pure Co (NO) with the mass ratio of 1: 1-5: 1₃)₂·6H₂O and analytically pure (NH)₄)₆Mo₇O₂₄·4H₂Dissolving O in (10-V) mL of distilled water to obtain a mixed solution, treating the mixed solution with ultrasonic wave until the solid component is completely dissolved, and adding 5g of phase-inverted (theta) -Al into the mixed solution₂O₃And continuously stirring the mixture under the baking of an infrared lamp until the solution is completely immersed into the (theta) -Al after phase inversion₂O₃In (theta) -Al after impregnation₂O₃Drying in an oven at 100-120 ℃ (usually for 24-46 h) to obtain unreduced Co-Mo/Al₂O₃A catalytic carrier.

(3) Mixing Co-Mo/Al₂O₃The catalytic carrier is placed in a constant temperature area of a quartz tube of a horizontal tube type resistance furnace, and in a mixed atmosphere of hydrogen and argon with the mass percent purity of 99.99%, the flow ratio of the two gases is controlled to be Ar: h₂80:20 mL/min-50 mL/min, heating to 500-550 ℃ at the speed of 5-10 ℃/min to reduce Co-Mo/Al₂O₃Catalyzing the carrier for 1-3 h to obtain reduced Co-Mo/Al₂O₃A catalytic carrier.

Step two, CNTs-Al₂O₃Preparing a composite carrier:

(1) reducing the Co-Mo/Al₂O₃The catalytic carrier is arranged in a constant temperature area of a quartz tube of the horizontal tube type resistance furnace, and the hydrogen and the argon are mixed in the step oneAnd (4) continuously heating in the atmosphere and at the same flow ratio as that in the first step, wherein the heating rate is 5-10 ℃/min, and the temperature is increased to 550-750 ℃.

(2) And (3) introducing acetylene gas with the mass percent purity of 99.99% into the horizontal tubular resistance furnace, and closing argon. At C₂H₂And H₂The flow ratio of (A) is 10:100 mL/min-100: 100mL/min, the reaction is carried out for 10-60 min under the reaction atmosphere, and the reduced Co-Mo/Al₂O₃And (3) catalytically growing Carbon Nano Tubes (CNTs) on the catalytic carrier, and stopping introducing acetylene gas into the horizontal tubular resistance furnace after the reaction is finished.

(3) Continuously introducing mixed atmosphere of hydrogen and argon with the mass percent purity of 99.99% into the horizontal tubular resistance furnace, and controlling the flow ratio of the two gases to be Ar: h₂The CNTs are prepared by rapidly heating 80:20 mL/min-50: 50mL/min in the atmosphere to 700-800 ℃ for 1-3 h, and then cooling to 20-25 ℃ in the mixed atmosphere₂O₃And (3) a composite carrier.

(4) CNTs-Al₂O₃15-30% of H for composite carrier₂O₂Oxidizing for 6h, washing the treated sample to be neutral, drying in an oven at 60-80 ℃ (usually for 24-48 h) to obtain the purified and modified CNTs-Al₂O₃And (3) a composite carrier.

Step three, Fe/CNTs-Al₂O₃Preparing a biomimetic catalyst:

(1) taking 0.5000-5.0000 g FeCl₃Dissolving in 30mL of analytically pure acetone, and adding the purified and modified CNTs-Al₂O₃Stirring the composite carrier at 20-25 ℃ for 24-48h to load Fe, and carrying out Fe-loaded CNTs-Al₂O₃And filtering the composite carrier sample, washing with water, and slowly drying in an oven at 60-80 ℃ (usually for 24-48 h).

(2) Drying the CNTs-Al loaded with Fe₂O₃Placing a composite carrier sample in a constant temperature area of a quartz tube of a horizontal tube type resistance furnace, and controlling the flow ratio of two gases to be Ar:H₂20-50: 50mL/min, the heating rate is 5-10 ℃/min, the temperature is gradually increased to 350-750 ℃, then the calcination is carried out for 6-8 h, and then the temperature is reduced to 20-25 ℃ under the protection of the mixed atmosphere to prepare the Fe/CNTs-Al with atomic-level dispersion₂O₃A biomimetic catalyst.