Method for synthesizing ammonia by activating nitrogen through one-step method by directly taking water as hydrogen source

Abstract

The invention belongs to the technical field of catalysis, and discloses a method for synthesizing ammonia by activating nitrogen through a one-step method by directly taking water as a hydrogen source. The method for synthesizing ammonia by activating nitrogen with water as the hydrogen source comprises the following steps: by taking CO, N2 and H2O as raw materials, activating nitrogen with a one-step method under the action of a catalyst to synthesize ammonia, wherein the pressure of the reaction gas is 0.1-5 MPa, the molar ratio of CO to N2 to H2O is controlled to be (1-8): 1: (1-8), the reaction temperature is 100-300 DEG C, and the reaction time is 2-20 h. The catalyst provided by the invention has relatively high activity and good stability in the ammonia synthesis reaction of activating nitrogen by taking water as a hydrogen source.

Description

Technical Field

[0001] The invention belongs to the field of catalytic technology and relates to a method for synthesizing ammonia by activating nitrogen in one step directly using water as a hydrogen source. Background Art

[0002] The synthetic ammonia industry is one of the most important industrial processes. Ammonia is widely used in agriculture, industry, military and other fields as a chemical raw material. In agriculture, ammonia can be used as a nitrogen fertilizer to promote the growth of crops. It is understood that ammonia as a nitrogen fertilizer feeds 40% of the world's population (Nat. geo. 2008, 1, 636-639). With the increasing global greenhouse effect, the research and application of clean energy without carbon emissions has also received more and more attention and research. Ammonia, as a carbon-free energy, has zero carbon emissions during the application process, and has the advantages of high energy density and easy storage and transportation.

[0003] At present, the process flow of industrial synthetic ammonia is mainly based on the Haber-Bosch process. In the process, molten iron is used as a catalyst, and ammonia is synthesized at a high temperature of 450-600°C and a high pressure of 20-30MPa. The required raw materials are high-purity N2 and H2. The production of high-purity H2 requires a complex gasification process: steam reforming, water-gas shift, and carbon dioxide removal. The process is accompanied by high energy consumption.

[0004] Based on the above status of industrial ammonia synthesis, in order to avoid the complex industrial process and high energy consumption generated in the process of industrial ammonia synthesis, the present invention proposes a method for synthesizing ammonia by activating nitrogen in one step directly using water as a hydrogen source. Summary of the invention

[0005] The purpose of the present invention is to provide a method for synthesizing ammonia by activating nitrogen in one step directly using water as a hydrogen source.

[0006] The technical solution of the present invention:

[0007] A method for synthesizing ammonia by directly activating nitrogen in one step using water as a hydrogen source, using CO, N2 and H2O as raw materials, and activating nitrogen in one step to synthesize ammonia under the action of a catalyst; wherein the reaction gas pressure is 0.1-5 MPa, the molar ratio of CO, N2 and H2O is controlled to be (1-8):1:(20-30), the reaction temperature is 100-300°C, and the reaction time is 2-20 hours.

[0008] The catalyst is Rh / TiO2, Ru / TiO2, Au / TiO2, Rh / CeO2, Ru / CeO2, Au / CeO2, Rh / MoC, Ru / MoC or Au / MoC.

[0009] Beneficial effects of the present invention:

[0010] (1) Currently, industrial ammonia synthesis needs to be carried out at high temperatures of 450-600°C and high pressures of 20-30 MPa, and the preparation process of raw material H2 is complex and energy-intensive. Compared with the multi-step process and harsh reaction conditions of industrial ammonia synthesis, direct one-step activation of nitrogen using H2O as a hydrogen source to synthesize ammonia does not require the multi-step and high energy consumption of the above-mentioned traditional industrial ammonia synthesis. Under specific reaction conditions and the presence of a catalyst, CO and H2O can generate active H* species in situ on the catalyst surface. At this time, the active N* species adsorbed on the catalyst surface can undergo hydrogenation reaction with the active H* to achieve one-step ammonia synthesis.

[0011] (2) The catalyst used in the present invention has the characteristics of dual active sites, which can couple the complex hydrogen production process and the ammonia synthesis process, and realize the adsorption reaction of multiple reaction substrates on the same catalyst surface. The catalyst is mainly composed of a carrier and a supported metal species. During the reaction, the reaction substrate CO is mainly adsorbed and activated on the metal species supported on the catalyst surface, and N2 and H2O are mainly adsorbed and activated at the interface of the catalyst metal carrier. Through the synergistic effect of different active sites, in-situ H2O hydrogen production and N2 hydrogenation are realized.

[0012] (3) Traditional industrial ammonia synthesis needs to be carried out at high temperature (450-600°C) and high pressure (20-30MPa). During the experiment, the present invention found that N2 can activate ammonia synthesis at 100-300°C, and as the reaction temperature increases, the ammonia synthesis rate also increases.

[0013] (4) The catalyst provided in this article has good performance in catalyzing the synthesis of ammonia from N2, CO, and H2O, and the catalyst has good stability.

[0014] (5) The preparation method of the catalyst used in this article is simple and suitable for large-scale preparation. DETAILED DESCRIPTION

[0015] The specific implementation of the present invention is further described below in conjunction with the attached table and technical solutions.

[0016] Example 1

[0017] Preparation of Rh / TiO2 and evaluation of reaction activity: 1g of commercially purchased TiO2 was weighed and heated from room temperature to 500℃ in a muffle furnace at 10℃ / min, and calcined at 500℃ for 2h. 300mg of the calcined sample was weighed and placed in a 30mL glass bottle, and 1.88mL of 9.56mg / mL RhCl3 solution was added to it. After magnetic stirring for 1h, it was placed in a sand bath pot at 90℃ and stirred continuously until the solvent was completely evaporated. The solid powder was then reduced at 300℃ in a tubular furnace under hydrogen for 2h, and 2% O2 / Ar was purged for 2h after the temperature dropped to room temperature. When evaluating the catalyst, 30mg of the prepared catalyst was weighed and placed in a reactor, 5ml H2O was added, and then 3MPa CO / N2 mixed gas was flushed into the reactor, with a CO / N2O concentration ratio of 3:1. The reactor was then heated to 200℃ and reacted for 5h. After the reaction, the reaction solution was collected and measured by cation chromatography to calculate the ammonia generation rate.

[0018] Example 2

[0019] Preparation of Ru / TiO2 and evaluation of reaction activity: Refer to Example 1, except that the metal solution used in the catalyst preparation is RuCl3 solution.

[0020] Example 3

[0021] Preparation of Au / TiO2 and evaluation of reaction activity: Refer to Example 1, except that the metal solution used in the catalyst preparation is HAuCl4 solution.

[0022] Example 4

[0023] Preparation of Rh / CeO2 and evaluation of reaction activity: 0.87g Ce(NO3)3·6H2O and 0.79g NH4HCO3 were dissolved in 35mL distilled water. After stirring at room temperature for 1h, it was transferred to a 50mL stainless steel autoclave lined with Teflon and kept at 150℃ for 48h. After hydrothermal treatment, the resulting precipitate was filtered and washed several times with deionized water and anhydrous ethanol, and dried at 85℃ for 12h. Finally, the product was calcined in air at 500℃ for 5h to obtain a CeO2 carrier. Weigh 1g CeO2 and heat it from room temperature to 500℃ in a muffle furnace at 10℃ / min, and calcine it at 500℃ for 2h. Weigh 300 mg of the calcined sample and put it into a 30 mL glass bottle. Add 1.88 mL of 9.56 mg / mL RhCl3 solution to it. After magnetic stirring for 1 hour, place it in a sand bath at 90 ° C and continue stirring until the solvent evaporates completely. Then, reduce the solid powder in a tube furnace at 300 ° C for 2 hours under hydrogen. After the temperature drops to room temperature, purge it with 2% O2 / Ar for 2 hours. When evaluating the catalyst, weigh 30 mg of the prepared catalyst and put it into the reactor. Add 5 ml of H2O, and then flush 3 MPa of CO / N2 mixed gas into the reactor, with a CO / N2O concentration ratio of 3:1. Then heat the reactor to 200 ° C and react for 5 hours. After the reaction, collect the reaction solution and measure and calculate the ammonia generation rate using cation chromatography.

[0024] Example 5

[0025] Preparation of Ru / CeO2 and evaluation of reaction activity: Refer to Example 4, except that the metal solution used in the catalyst preparation is RhCl3 solution.

[0026] Example 6

[0027] Preparation of Au / CeO2 and evaluation of reaction activity: Refer to Example 4, except that the metal solution used in the catalyst preparation is HAuCl4 solution.

[0028] Example 7

[0029] Preparation of Rh / MoC and evaluation of reaction activity: MoO3 precursor was treated in 20% CH4 / H2 (100mL / min): the temperature was raised from 25°C to 700°C at 10°C / min, kept constant at 700°C for 2h, and cooled to room temperature. Then the sample was passivated with a 2% oxygen-argon mixed atmosphere at a flow rate of 100mL / min for 2h to obtain a MoC carrier. 300mg of MoC was weighed and placed in a 30mL glass bottle, and 1.88mL of 9.56mg / mL RhCl3 solution was added thereto. After magnetic stirring for 1h, it was placed in a sand bath at 90°C and stirred continuously until the solvent was completely evaporated. The obtained solid powder was then reduced at 300°C for 2h in a tubular furnace under hydrogen. After the temperature dropped to room temperature, it was purged with 2% O2 / Ar for 2h. When evaluating the catalyst, 30 mg of the prepared catalyst was weighed and placed in a reactor, 5 ml of H2O was added, and then 3 MPa of CO / N2 mixed gas was flushed into the reactor, with a CO / N2O concentration ratio of 3:1. The reactor was then heated to 200°C and reacted for 5 hours. After the reaction was completed, the reaction solution was collected and measured by cation chromatography to calculate the ammonia generation rate.

[0030] Example 8

[0031] Preparation of Ru / MoC and evaluation of reaction activity: Refer to Example 7, except that the metal solution used in the catalyst preparation is RuCl3 solution.

[0032] Example 9

[0033] Preparation of Au / MoC and evaluation of reaction activity: Refer to Example 7, except that the metal solution used in the catalyst preparation is HAuCl4 solution.

[0034] Example 10

[0035] The preparation of Ru / CeO2 was the same as that of Example 4. The difference was that the reaction substrate ratio was changed in the catalyst evaluation. CO / N2 was 5:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 5 h.

[0036] Embodiment 11

[0037] The preparation of Ru / CeO2 was the same as that of Example 4. The difference was that the reaction substrate ratio was changed in the catalyst evaluation. CO / N2 was 8:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 5 h.

[0038] Example 12

[0039] The preparation of Ru / CeO2 is consistent with Example 4. The difference is that the amount of the reaction substrate H2O is changed in the catalyst evaluation. CO / N2 is 3:1, the reaction pressure is 3MPa, 8mL H2O, the reaction temperature is 200℃, and the reaction time is 5h.

[0040] Embodiment 13

[0041] The preparation of Ru / CeO2 is consistent with Example 4. The difference is that the amount of the reaction substrate H2O is changed in the catalyst evaluation. CO / N2 is 3:1, the reaction pressure is 3MPa, 10mL H2O, the reaction temperature is 200℃, and the reaction time is 5h.

[0042] Embodiment 14

[0043] The preparation of Rh / TiO2 was the same as in Example 1. The difference was that the reaction temperature was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 100°C, and the reaction time was 5 h.

[0044] Embodiment 15

[0045] The preparation of Rh / TiO2 was the same as in Example 1. The difference was that the reaction temperature was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 300°C, and the reaction time was 5 h.

[0046] Example 16

[0047] The preparation of Rh / TiO2 was the same as in Example 1. The difference was that the reaction time was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 2 h.

[0048] Embodiment 17

[0049] The preparation of Rh / TiO2 was the same as in Example 1. The difference was that the reaction time was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 8 h.

[0050] Embodiment 18

[0051] The preparation of Rh / TiO2 was the same as in Example 1. The difference was that the reaction time was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 10 h.

[0052] Embodiment 19

[0053] The preparation of Rh / TiO2 was the same as in Example 1. The difference was that the reaction time was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 15 h.

[0054] Embodiment 20

[0055] The preparation of Rh / TiO2 was the same as in Example 1. The difference was that the reaction time was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 3 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 20 h.

[0056] Embodiment 21

[0057] The preparation of Rh / TiO2 was the same as in Example 1. The difference was that the reaction pressure was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 1 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 2 h.

[0058] Embodiment 22

[0059] The preparation of Rh / TiO2 was the same as that in Example 1. The difference was that the reaction pressure was changed in the catalyst evaluation. CO / N2 was 3:1, the reaction pressure was 5 MPa, 5 mL H2O, the reaction temperature was 200°C, and the reaction time was 2 h.

[0060] Table 1 Summary of performance of different catalysts for direct one-step activation of nitrogen to ammonia synthesis using water as hydrogen source

[0061]

[0062]

[0063] From the above table, it can be concluded that Rh / TiO2, Ru / TiO2, Au / TiO2, Rh / CeO2, Ru / CeO2, Au / CeO2, Rh / MoC, Ru / MoC or Au / MoC all have certain activity in catalyzing this reaction, among which TiO2 loaded with metal Rh has the highest activity, and the ammonia production rate can reach 56umol / g / h. When the same catalyst is used and other reaction conditions are the same, when the proportion of CO in the reactants is increased, it helps to increase the ammonia production rate, and reducing or increasing the amount of water is not conducive to the reaction. Increasing the temperature will obviously increase the reaction rate. Reducing the reaction time will increase the ammonia production rate, but the total amount of production will decrease, and increasing the reaction time has the opposite effect. The higher the reaction pressure, the higher the ammonia production rate.

Claims

1. A method for synthesizing ammonia by activating nitrogen in one step directly using water as a hydrogen source, characterized in that: CO, N2 and H2O are used as raw materials, and nitrogen is activated in a one-step process to synthesize ammonia under the action of a catalyst; wherein the reaction gas pressure is 0.1-5MPa, the molar ratio of CO, N2 and H2O is controlled to be (1-8):1:(20-30), the reaction temperature is 100-300°C, and the reaction time is 2-20h.

2. The method according to claim 1, characterized in that: The catalyst comprises active components and a carrier, wherein the active components are Rh, Ru and Au, the carrier is TiO2, CeO2 and MoC, and the content of the active components is 1-20wt%.

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