Application of a Ni / SrO-Sm2O3 catalyst in the production of hydrogen by thermal catalytic decomposition of ammonia

Abstract

The invention discloses an application of a Ni / SrO-Sm2O3 catalyst in thermal catalytic ammonia decomposition and hydrogen production. First, soluble Ni salt, Sr salt and Sm salt are dispersed in water and uniformly mixed, and a composite hydroxide is obtained by coprecipitation and hydrothermal treatment; then the composite hydroxide is pyrolyzed at high temperature to obtain a composite oxide nanorod; finally, the composite oxide nanorod is treated with high-temperature hydrogen to obtain a nanorod-shaped Ni / SrO-Sm2O3 catalyst. The catalyst has a stable structure, and Ni is uniformly dispersed in the catalyst. Ni serves as an active site in a thermal catalytic reaction, SrO serves as an alkaline carrier to improve the electronic state of Ni, and Sm2O3 serves as a hydrogen overflow carrier to alleviate hydrogen poisoning. The surface hydroxyl group promotes the generation of a new intermediate product (SmOH2), and the catalyst has excellent thermal catalytic activity in thermal catalytic ammonia decomposition and hydrogen production.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogen production by decomposing ammonia, and specifically relates to an application of a Ni / SrO-Sm2O3 catalyst in hydrogen production by thermal catalytic decomposition of ammonia. Background Art

[0002] The decomposition kinetics of NH3 on metals (denoted as M) depends on the strength of the MN bond. A stronger MN bond is conducive to the dissociation of NH in the NH3 molecule, but is not conducive to the desorption of N2 products on the catalyst surface; on the contrary, a weaker MN bond is conducive to the desorption of N2, but hinders the dissociation of the NH bond. Moderate MN bond strength, which is easy for NH dissociation and N2 desorption, is crucial to promote the decomposition of ammonia. Most of the current work is mainly aimed at solving the problem of MN bond strength. However, under high temperature and H2 atmosphere, active metals are easily poisoned by hydrogen to form stable MH bonds, resulting in catalyst deactivation. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide an application of a Ni / SrO-Sm2O3 catalyst in thermal catalytic ammonia decomposition to produce hydrogen. The catalyst has a stable structure and Ni is uniformly dispersed in the catalyst. Ni serves as an active site in the thermal catalytic reaction, SrO serves as an alkaline carrier to improve the electronic state of Ni, and Sm2O3 serves as a hydrogen overflow carrier to alleviate hydrogen poisoning. The hydroxyl groups on its surface promote the formation of a new intermediate product (SmOH2), and the catalyst has excellent thermal catalytic activity in thermal catalytic ammonia decomposition to produce hydrogen.

[0004] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0005] The invention discloses an application of a Ni / SrO-Sm2O3 catalyst in the production of hydrogen by thermal catalytic decomposition of ammonia. The preparation process of the Ni / SrO-Sm2O3 catalyst is as follows: firstly, soluble Ni salt, Sr salt and Sm salt are dispersed in water and uniformly mixed, and composite hydroxide is obtained by coprecipitation and hydrothermal treatment; then, the composite hydroxide is pyrolyzed at high temperature to obtain composite oxide nanorods; finally, the composite oxide nanorods are treated with high temperature hydrogen to obtain nanorod-shaped Ni / SrO-Sm2O3 catalyst; and then the catalyst is used for the production of hydrogen by thermal catalytic decomposition of ammonia.

[0006] Preferably, the soluble Ni salt, Sr salt and Sm salt are all nitrates of each other, and the molar ratio of the soluble Ni salt, the soluble Sr salt and the soluble Sm salt is 1:0.5-0.8:0.2-0.5.

[0007] Preferably, the alkali used in the coprecipitation process is one of sodium hydroxide, potassium hydroxide and ammonia water.

[0008] Preferably, the temperature of the hydrothermal treatment is 160-200°C and the time is 5-15h.

[0009] Preferably, the high temperature pyrolysis temperature is 600-700°C and the time is 4-6h.

[0010] Preferably, the atmosphere of the high temperature hydrogen treatment is a 6% H2 / Ar mixed atmosphere, the temperature is 550-650°C, and the time is 3-5h.

[0011] Advantages of the present invention:

[0012] The present invention realizes the loading of metal Ni on mixed oxide SrO-Sm2O3 through a co-precipitation hydrothermal method and high-temperature pyrolysis treatment in a reducing atmosphere to obtain Ni / SrO-Sm2O3. The composite material is a nanorod-like structure with uniform active centers and highly exposed active sites. SrO serves as an alkaline carrier to improve the electronic state of Ni. A large number of hydroxyl groups on the surface of Sm2O3 can serve as H overflow binding sites, promoting the transfer of hydrogen from active metal Ni to the surface hydroxyl groups of the Sm2O3 carrier, promoting the generation of a new intermediate product (SmOH2), effectively preventing hydrogen poisoning of the catalyst, and improving the TOF value of the catalyst. The obtained Ni / SrO-Sm2O3 has excellent thermal catalytic activity in thermal catalytic ammonia decomposition to produce hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The Ni / Sr prepared in Example 1 0.6 Sm 0.4 O x SEM images of

[0014] like Figure 1 As shown, Ni / Sr 0.6 Sm 0.4 O x The microscopic morphology is nanorod-like.

[0015] Figure 2 The XRD patterns of the catalysts prepared in Examples 1-3 and Comparative Examples 1-2;

[0016] like Figure 2 As shown, since SrO easily reacts with CO2 in the air, the composite catalyst is composed of SrCO3, Sm2O3 and Ni.

[0017] Figure 3 This is the high temperature XRD pattern of Ni / SrO prepared in Comparative Example 2;

[0018] like Figure 3 As shown, under the reaction conditions, Sr exists in the form of SrO, which indirectly indicates the successful preparation of the catalyst.

[0019] Figure 4 The Ni / Sr prepared in Example 1 0.6 Sm 0.4 O x XPS spectrum of

[0020] like Figure 4 As shown, the hydroxyl content on the catalyst surface is 59.61%, which contains a large amount of hydroxyl groups.

[0021] Figure 5 FTIR graphs of the catalysts prepared in Example 1 and Comparative Examples 1-2;

[0022] like Figure 5 As shown, the surfaces of the samples of Example 1 and Comparative Example 1 have hydroxyl groups, while the surface of the sample of Comparative Example 1 indicates that the hydroxyl groups on the surface of the material are mainly contributed by Sm2O3.

[0023] Figure 6 The Ni / Sr prepared in Example 1 0.6 Sm 0.4 O x In Situ FTIR spectrum;

[0024] like Figure 6 As shown, with the introduction of hydrogen, SmOH2 and hydroxyl species are gradually formed on the sample surface, indicating the generation of a new intermediate species SmOH2.

[0025] Figure 7 Ni / Sr prepared in Comparative Example 3 0.6 Sm 0.4 O x - XRD spectrum of bulk;

[0026] like Figure 7 As shown, the same as Example 1-3, is composed of SrCO3, Sm2O3 and Ni.

[0027] Figure 8 Ni / Sr prepared in Comparative Example 3 0.6 Sm 0.4 O x - SEM spectrum of the block;

[0028] like Figure 8 As shown, the microstructure of Comparative Example 3 is irregular blocks. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0030] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0031] Thermal catalytic ammonia decomposition to produce hydrogen:

[0032] Weigh 20 mg of catalyst and add it into a quartz reaction tube. Pass pure ammonia (99.999%) in the range of 400°C-600°C with a temperature gradient of 50°C. Test each temperature point for 40 minutes and detect the ammonia conversion rate by gas chromatography.

[0033] Example 1

[0034] Ni / Sr 0.6 Sm 0.4 O x :

[0035] (1) Dissolve 2mmolNi(NO3)2·6H2O, 1.2mmolSr(NO3)2, and 0.8mmolSm(NO3)3·6H2O in 360mLH2O, stir to dissolve, and then add 40mL1mol·L -1 KOH, after standing for 10 min, remove 320 mL of supernatant, transfer the remaining 80 mL of liquid and precipitate to a 100 mL hydrothermal autoclave, react at 180 °C for 10 h, cool and centrifuge, wash with water 3 times, and dry.

[0036] (2) The obtained precursor powder was heated in a muffle furnace at 5 °C min -1 The heating rate was increased to 650°C and then cooled to room temperature after keeping the temperature for 5 h.

[0037] (3) Then, the mixture was heated in a tube furnace (atmosphere of 6% H2 / Ar) at 5°C min -1 The heating rate was increased to 600°C and kept for 4 hours, and then the target catalyst was obtained after cooling to room temperature.

[0038] The prepared Ni / Sr 0.6 Sm 0.4 O x The catalyst is used for the thermal catalytic ammonia decomposition hydrogen production reaction. Under the conditions of 550℃ and pure NH3 (99.999%), the hydrogen production rate of the catalyst is 30.74mmolg (cat) -1 ·min -1 .

[0039] Example 2

[0040] Ni / Sr 0.5 Sm 0.5 O x :

[0041] (1) Dissolve 2mmolNi(NO3)2·6H2O, 1mmolSr(NO3)2, and 1mmolSm(NO3)3·6H2O in 360mLH2O, stir to dissolve, and then add 40mL1mol·L -1 KOH, after standing for 10 min, remove 320 mL of supernatant, transfer the remaining 80 mL of liquid and precipitate to a 100 mL hydrothermal autoclave, react at 180 °C for 10 h, cool and centrifuge, wash with water 3 times, and dry.

[0042] (2) The obtained precursor powder was heated in a muffle furnace at 5 °C min -1 The heating rate was increased to 650°C and then cooled to room temperature after keeping the temperature for 5 h.

[0043] (3) Then, the mixture was heated in a tube furnace (6% H2 / Ar atmosphere) at 5°C min -1 The heating rate was increased to 600°C and kept for 4 hours, and then the target catalyst was obtained after cooling to room temperature.

[0044] The prepared Ni / Sr 0.5 Sm 0.5 O x The catalyst is used for the thermal catalytic decomposition of ammonia to produce hydrogen. Under the conditions of 550°C and pure NH3 (99.999%), the hydrogen production rate of the catalyst is 29.39mmolg (cat) -1 ·min -1 .

[0045] Example 3

[0046] Ni / Sr 0.8 Sm 0.2 O x :

[0047] (1) Dissolve 2mmolNi(NO3)2·6H2O, 1.6mmolSr(NO3)2, and 0.4mmolSm(NO3)3·6H2O in 360mLH2O, stir to dissolve, and then add 40mL1mol·L -1 KOH, after standing for 10 min, remove 320 mL of supernatant, transfer the remaining 80 mL of liquid and precipitate to a 100 mL hydrothermal autoclave, react at 180 °C for 10 h, cool and centrifuge, wash with water 3 times, and dry.

[0048] (2) The obtained precursor powder was heated in a muffle furnace at 5 °C min -1 The heating rate was increased to 650°C and then cooled to room temperature after keeping the temperature for 5 h.

[0049] (3) Then, the mixture was heated in a tube furnace (6% H2 / Ar atmosphere) at 5°C min -1The heating rate was increased to 600°C and kept for 4 hours, and then the target catalyst was obtained after cooling to room temperature.

[0050] The prepared Ni / Sr 0.8 Sm 0.2 O x The catalyst is used for the thermal catalytic decomposition of ammonia to produce hydrogen. Under the conditions of 550°C and pure NH3 (99.999%), the hydrogen production rate of the catalyst is 29.86mmolg (cat) -1 ·min -1 .

[0051] Comparative Example 1

[0052] Ni / Sm2O3:

[0053] (1) Dissolve 2mmolNi(NO3)2·6H2O and 2mmolSm(NO3)3·6H2O in 360mLH2O, stir to dissolve, and then add 40mL1mol·L -1 KOH, after standing for 10 min, remove 320 mL of supernatant, transfer the remaining 80 mL of liquid and precipitate to a 100 mL hydrothermal autoclave, react at 180 °C for 10 h, cool and centrifuge, wash with water 3 times, and dry.

[0054] (2) The obtained precursor powder was heated in a muffle furnace at 5 °C min -1 The heating rate was increased to 650°C and then cooled to room temperature after keeping the temperature for 5 h.

[0055] (3) Then, the mixture was heated in a tube furnace (atmosphere of 6% H2 / Ar) at 5°C min -1 The heating rate was increased to 600°C and kept for 4 hours, and then the target catalyst was obtained after cooling to room temperature.

[0056] The prepared Ni / Sm2O3 catalyst was used for the thermal catalytic decomposition of ammonia to produce hydrogen. Under the conditions of 550℃ and pure NH3 (99.999%), the hydrogen production rate of the catalyst was 11.02mmolg (cat) -1 ·min -1 .

[0057] Comparative Example 2

[0058] Ni / SrO:

[0059] (1) Dissolve 2mmolNi(NO3)2·6H2O and 2mmolSr(NO3)2 in 360mLH2O, stir to dissolve, and then add 40mL1mol·L -1KOH, after standing for 10 min, remove 320 mL of supernatant, transfer the remaining 80 mL of liquid and precipitate to a 100 mL hydrothermal autoclave, react at 180 °C for 10 h, cool and centrifuge, wash with water 3 times, and dry.

[0060] (2) The obtained precursor powder was heated in a muffle furnace at 5 °C min -1 The heating rate was increased to 650°C and then cooled to room temperature after keeping the temperature for 5 h.

[0061] (3) Then, the mixture was heated in a tube furnace (6% H2 / Ar atmosphere) at 5°C min -1 The heating rate was increased to 600°C and kept for 4 hours, and then the target catalyst was obtained after cooling to room temperature.

[0062] The prepared Ni / SrO catalyst was used for the thermal catalytic decomposition of ammonia to produce hydrogen. Under the conditions of 550°C and pure NH3 (99.999%), the hydrogen production rate of the catalyst was 8.18 mmol / g (cat) -1 ·min -1 .

[0063] Comparative Example 3

[0064] Ni / Sr 0.6 Sm 0.4 O x - Blocky:

[0065] (1) Add 2 mmol Ni(NO3)2·6H2O, 1.2 mmol Sr(NO3)2, 0.8 mmol Sm(NO3)3·6H2O, and 4.8 mmol citric acid to 80 mL water and stir vigorously in an 80 °C water bath until the water evaporates. The resulting precursor is dried at 100 °C overnight.

[0066] (2) The obtained precursor powder was heated in a muffle furnace at 5 °C min -1 The heating rate was increased to 600°C and kept at this temperature for 5 h before being lowered to room temperature.

[0067] (3) Then, the mixture was heated in a tube furnace (6% H2 / Ar atmosphere) at 5°C min -1 The heating rate was increased to 600°C and kept for 4 hours, and then the target catalyst was obtained after cooling to room temperature.

[0068] The prepared Ni / SrO catalyst was used for the thermal catalytic decomposition of ammonia to produce hydrogen. Under the conditions of 550°C and pure NH3 (99.999%), the hydrogen production rate of the catalyst was 17.70 mmol / g (cat) -1 ·min -1 .

[0069] Comparative Example 4

[0070] Ni / Mg 0.6 Sm 0.4 O x :

[0071] (1) Dissolve 2mmolNi(NO3)2·6H2O, 1.2mmolMg(NO3)2, and 0.8mmolSm(NO3)3·6H2O in 360mLH2O, stir to dissolve, and then add 40mL1mol·L -1 KOH, after standing for 10 min, remove 320 mL of supernatant, transfer the remaining 80 mL of liquid and precipitate to a 100 mL hydrothermal autoclave, react at 180 °C for 10 h, cool and centrifuge, wash with water 3 times, and dry.

[0072] (2) The obtained precursor powder was heated in a muffle furnace at 5 °C min -1 The heating rate was increased to 650°C and then cooled to room temperature after keeping the temperature for 5 h.

[0073] (3) Then, the mixture was heated in a tube furnace (atmosphere of 6% H2 / Ar) at 5°C min -1 The heating rate was increased to 600°C and kept for 4 hours, and then the target catalyst was obtained after cooling to room temperature.

[0074] The prepared Ni / Mg 0.6 Sm 0.4 O x The catalyst is used for the thermal catalytic decomposition of ammonia to produce hydrogen. Under the conditions of 550°C and pure NH3 (99.999%), the hydrogen production rate of the catalyst is 21.38mmolg (cat) -1 ·min -1 .

[0075] Comparative Example 5

[0076] Ni / Sr 0.6 Y 0.4 O x :

[0077] (1) Dissolve 2mmolNi(NO3)2·6H2O, 1.2mmolSr(NO3)2, and 0.8mmolY(NO3)3·6H2O in 360mLH2O, stir to dissolve, and then add 40mL1mol·L -1 KOH, after standing for 10 min, remove 320 mL of supernatant, transfer the remaining 80 mL of liquid and precipitate to a 100 mL hydrothermal autoclave, react at 180 °C for 10 h, cool and centrifuge, wash with water 3 times, and dry.

[0078] (2) The obtained precursor powder was heated in a muffle furnace at 5 °C min -1The heating rate was increased to 650°C and then cooled to room temperature after keeping the temperature for 5 h.

[0079] (3) Then, the mixture was heated in a tube furnace (atmosphere of 6% H2 / Ar) at 5°C min -1 The heating rate was increased to 600°C and kept for 4 hours, and then the target catalyst was obtained after cooling to room temperature.

[0080] The prepared Ni / Sr 0.6 Y 0.4 O x The catalyst is used for the thermal catalytic decomposition of ammonia to produce hydrogen. Under the conditions of 550°C and pure NH3 (99.999%), the hydrogen production rate of the catalyst is 25.05mmolg (cat) -1 ·min -1 .

Claims

1. Application of Ni / SrO-Sm2O3 catalyst in the production of hydrogen by thermal catalytic decomposition of ammonia, characterized in that: The preparation process of the Ni / SrO-Sm2O3 catalyst is as follows: firstly, soluble Ni salt, Sr salt and Sm salt are dispersed in water and uniformly mixed, and composite hydroxide is obtained by coprecipitation and hydrothermal treatment; then, the composite hydroxide is pyrolyzed at high temperature to obtain composite oxide nanorods; finally, the composite oxide nanorods are treated with high temperature hydrogen to obtain nanorod-shaped Ni / SrO-Sm2O3 catalyst; and then the catalyst is used for thermal catalytic decomposition of ammonia to produce hydrogen; The soluble Ni salt, Sr salt and Sm salt are all their respective nitrates, and the molar ratio of the soluble Ni salt, the soluble Sr salt and the soluble Sm salt is 1:0.5-0.8:0.2-0.

5.

2. The use according to claim 1, characterized in that: The alkali used in the coprecipitation process is one of sodium hydroxide, potassium hydroxide and ammonia water.

3. The use according to claim 1, characterized in that: The temperature of the hydrothermal treatment is 160-200°C and the time is 5-15h.

4. The use according to claim 1, characterized in that: The temperature of the high temperature pyrolysis is 600-700°C and the time is 4-6h.

5. The use according to claim 1, characterized in that: The atmosphere of the high temperature hydrogen treatment is a 6% H2 / Ar mixed atmosphere, the temperature is 550-650°C, and the time is 3-5h.

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