Low-temperature efficient ammonia decomposition catalyst and preparation method thereof

Abstract

The invention discloses a low-temperature efficient ammonia decomposition catalyst and a preparation method thereof. The catalyst comprises a transition metal oxide modified carbon nitride carrier and active metal applied to the transition metal oxide modified carbon nitride carrier, by doping a certain amount of transition metal oxide in carbon nitride, the electron conduction performance of the carrier can be improved, the vacancy defect density in the carrier can be enhanced, and when the carrier is used, the electron density of active metal can be efficiently improved, the strong interaction between the active metal and the modified carrier can be improved, and the service life of the carrier is prolonged. And the doped metal oxide site can be used as a hydrogen overflow window hole to accelerate the hydrogen release rate, so that the purpose of improving the low-temperature ammonia decomposition activity and the stability of the catalyst is achieved. The catalyst is applied to catalytic ammonia decomposition hydrogen production reaction, and the ammonia decomposition rate and the hydrogen production rate are both remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic materials, and in particular relates to a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. Background Art

[0002] Ammonia has a large volumetric hydrogen storage density (more than 1.5 times the density of liquid hydrogen and nearly 3 times that of high-pressure hydrogen storage), a high boiling point, and is easy to liquefy, making it easier to store and transport. In addition, ammonia fuel has a high octane number (>130), good anti-knock performance, and can achieve zero carbon emissions. Therefore, low-temperature and efficient ammonia decomposition to produce hydrogen is one of the cleanest and most efficient key technologies that can replace fossil energy consumption in the future.

[0003] At present, active metals have high activity in low-temperature ammonia decomposition. Among the existing publicly available catalyst carriers, carbon nanotubes show better catalytic performance than MgO, ZrO2, Al2O3, TiO2 and other materials due to their excellent electronic conductivity. However, the synthesis cost of carbon nanotube materials is relatively high, making them difficult to mass produce on a large scale, and the methanation side reaction of carbon-based carrier catalysts will reduce their hydrogen production efficiency. The development of low-cost, side-reaction-free, low-temperature and high-efficiency carbon-based catalysts to replace carbon nanotube carriers has become one of the research hotspots. Existing catalysts are used in the ammonia decomposition hydrogen production reaction. At a low temperature of 450°C and a volume space velocity of more than 15,000 h -1 Under these conditions, the reaction activity is still low, the ammonia decomposition rate is ≤90%, and the hydrogen production rate is ≤15mmol / gcat / min. There are problems of high energy consumption and low hydrogen production efficiency, and it cannot have a broader application value in the downstream of hydrogen production. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof, so as to solve the problems of poor low-temperature activity of active metal ammonia decomposition hydrogen production catalysts containing carbon carriers in the prior art.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0006] A low-temperature and high-efficiency ammonia decomposition catalyst, the catalyst comprising a transition metal oxide-modified carbon nitride carrier and an active metal applied thereon;

[0007] The active metal includes noble metal elements and non-noble metal elements; the noble metal elements are one or two of ruthenium and platinum; the non-noble metal elements are one or two or more of nickel, cobalt, tungsten, zinc and gallium;

[0008] In the transition metal oxide modified carbon nitride carrier, the transition metal oxide is one or two or more of rhenium oxide, manganese oxide, molybdenum oxide and tin oxide.

[0009] The present invention also includes the following technical features:

[0010] Specifically, the noble metal elements in the active metal account for 1 to 5 wt% of the total weight of the catalyst; the non-noble metal elements in the active metal account for 10 to 25 wt% of the total weight of the catalyst;

[0011] The transition metal oxide accounts for 5 to 20 wt % of the total weight of the transition metal oxide modified carbon nitride carrier.

[0012] A method for preparing the low-temperature and high-efficiency ammonia decomposition catalyst comprises the following steps:

[0013] Step 1, mixing carbon and nitrogen-containing compounds and transition metal compounds according to the formula, melting and calcining for 4 to 10 hours, adding deionized water after cooling to room temperature, ultrasonically treating for 5 to 12 hours in a water bath, taking out and drying in a vacuum drying oven for 12 hours;

[0014] Step 2, placing the solid dried in step 1 in deionized water, adding a formula amount of active metals including compounds containing precious metal elements and compounds containing non-precious metal elements, stirring for 2 hours in a water bath, adding a precipitant dropwise, stirring for 8 hours, taking out, and aging at room temperature for 10 hours;

[0015] Step 3, washing, filtering and drying the solid obtained in step 2, and then calcining it in an argon atmosphere at 500-800° C. for 4-8 hours to obtain a catalyst.

[0016] Specifically, the carbon and nitrogen-containing compound is one or two or more of urea, melamine, amino acid, and p-dibenzonitrile.

[0017] Specifically, the transition metal-containing compound is one or two or more of ammonium perrhenate, manganese sulfate, ammonium molybdate, sodium molybdate, and tin tetrachloride.

[0018] Specifically, the compound containing precious metal elements is one or two or more of ruthenium chloride, triruthenium dodecacarbonyl, and platinum chloride;

[0019] The compound containing non-precious metal elements is one or two or more of nickel nitrate, nickel chloride, cobalt nitrate, cobalt chloride, ammonium metatungstate, zinc chloride and gallium chloride.

[0020] Specifically, the precipitant is one or two or more of ammonia water, sodium carbonate and sodium bicarbonate.

[0021] Specifically, the calcination temperature in step 1 is 600-800°C, the water bath temperature is 60°C, and the vacuum drying oven drying temperature is 100°C.

[0022] Specifically, in step 2, the water bath temperature is 50°C.

[0023] Specifically, in step 3, the calcination temperature is 500-800°C.

[0024] Compared with the prior art, the present invention has the following technical effects:

[0025] The catalyst obtained by the present invention is used in the catalytic ammonia decomposition hydrogen production reaction, the ammonia decomposition rate reaches 94.6%, and the hydrogen production rate is 18.7mmol / gcat / min, which has obvious advantages compared with the above-mentioned prior art. DETAILED DESCRIPTION

[0026] The present invention provides a low-temperature and high-efficiency ammonia decomposition catalyst, which comprises a transition metal oxide-modified carbon nitride carrier and an active metal applied thereon.

[0027] Active metals include precious metal elements and non-precious metal elements; the precious metal elements are one or both of ruthenium and platinum; preferably ruthenium; the non-precious metal elements are one or two or more of nickel, cobalt, tungsten, zinc, and gallium; preferably one or both of cobalt and zinc; more preferably zinc.

[0028] The noble metal elements in the active metal account for 1 to 5 wt% of the total weight of the catalyst.

[0029] The non-precious metal elements in the active metal account for 10 to 25 wt% of the total weight of the catalyst; when the non-precious metal elements are preferably one or two of cobalt and zinc, the corresponding preferred proportion is 15 to 20 wt% of the total weight of the catalyst; when zinc is preferred, the corresponding preferred proportion is 15 to 18 wt% of the total weight of the catalyst.

[0030] In the transition metal oxide modified carbon nitride carrier, the transition metal oxide is one or two or more of rhenium oxide, manganese oxide, molybdenum oxide and tin oxide; preferably rhenium oxide and manganese oxide, and more preferably rhenium oxide.

[0031] The transition metal oxide accounts for 5 to 20 wt% of the total weight of the transition metal oxide modified carbon nitride carrier; when rhenium oxide and manganese oxide are preferred, the corresponding preferred proportion is 5 to 15 wt% of the total weight of the transition metal oxide modified carbon nitride carrier; when rhenium oxide is preferred, the corresponding preferred proportion is 5 to 8 wt% of the total weight of the transition metal oxide modified carbon nitride carrier.

[0032] The transition metal oxide modified carbon nitride carrier provided by the present invention can improve the electronic conductivity of the carrier and enhance the vacancy defect density in the carrier by doping a certain amount of transition metal oxide in the carbon nitride. When used as a carrier, it can effectively improve the electron density of the active metal Ru and enhance the strong interaction between Ru and the modified carrier. The doped metal oxide sites can serve as hydrogen overflow windows to accelerate the hydrogen release rate, thereby achieving the purpose of improving the low-temperature ammonia decomposition activity and stability of the catalyst.

[0033] The present invention also provides a method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst, comprising the following steps:

[0034] Step 1, mixing carbon and nitrogen-containing compounds and transition metal compounds according to the formula amount, melting and calcining for 6 to 10 hours at a calcination temperature of 600 to 800° C., adding 100 mL of deionized water after cooling to room temperature, ultrasonically treating for 5 to 7 hours in a 60° C. water bath, taking out and placing in a 100° C. vacuum drying oven for 12 hours;

[0035] Step 2, placing the dried solid in step 1 in 50 mL of deionized water, adding a formula amount of active metals including compounds containing precious metal elements and compounds containing non-precious metal elements, stirring for 2 hours in a 50° C. water bath, adding a precipitant dropwise, stirring for 8 hours, taking out, and aging at room temperature for 10 hours;

[0036] Step 3, washing, filtering and drying the solid obtained in step 2, and then calcining it in an argon atmosphere at 500-800° C. for 4-8 hours to obtain a catalyst.

[0037] Specifically: the compound containing carbon and nitrogen is one or two or more of urea, melamine, amino acid, and para-dibenzonitrile; the compound containing transition metal is one or two or more of ammonium perrhenate, manganese sulfate, ammonium molybdate, sodium molybdate, and tin tetrachloride; the compound containing precious metal elements is one or two or more of ruthenium chloride, triruthenium dodecacarbonyl, and platinum chloride; the compound containing non-precious metal elements is one or two or more of nickel nitrate, nickel chloride, cobalt nitrate, cobalt chloride, ammonium metatungstate, zinc chloride, and gallium chloride.

[0038] The precipitant is one or two or more of ammonia water, sodium carbonate and sodium bicarbonate.

[0039] The selected non-precious metal salt needs to be soluble or highly dispersible in aqueous solution, and the amount of solvent used only needs to meet the solubility or sufficient dispersion requirements of the non-precious metal salt.

[0040] In the process of catalyst preparation, a one-step method is selected to synthesize transition metal oxide-modified carbon nitride, or a distribution method is used to first synthesize carbon nitride by melting method, and then a modified transition metal salt is used for deposition and calcination. In order to ensure the uniformity of crystallization of precious metals and non-precious metals on the carrier, the precipitant is added slowly, the water bath temperature should not be too high, the stirring speed should not be too fast, and the aging temperature can be selected at a constant temperature environment of less than 50°C.

[0041] The carrier and the final catalyst are calcined in steps under an inert atmosphere. The calcination operation can also be selected as a one-time calcination, that is, the active metal deposition is carried out after the carrier is dried. The preferred calcination temperature is 550-650°C.

[0042] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0043] The catalyst evaluation was carried out in a fixed bed reactor with a size of 550mm×Φ30mm×10mm. The reaction was carried out under normal pressure, with 1mL of catalyst loaded. After hydrogen in-situ reduction, ammonia mass flow meter was input into the reactor. The reactor was heated by three-stage electric heating, with a reaction temperature of 450℃ and a volume space velocity of 18000h-1. -1 After the reaction was stable for 2 h, online sampling and analysis were performed using a Fuli GC9720Plus gas chromatograph, a thermal conductivity cell detector, and a 5A molecular sieve filling column (3 m).

[0044] Embodiment 1:

[0045] This embodiment provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The catalyst preparation comprises the following steps:

[0046] 6.5 g of urea and 0.62 g of ammonium perrhenate were fully mixed to obtain a solid mixture A. Solid A was melted and calcined at 600°C for 6 hours to obtain a solid mixture B. After cooling to room temperature, B was added to 100 mL of deionized water, ultrasonically treated in a 60°C water bath for 5 hours, and then taken out and placed in a 100°C vacuum drying oven for 12 hours.

[0047] The dried solid B was placed in 50 mL of deionized water, and 0.079 g of ruthenium trichloride and 1.41 g of nickel nitrate hexahydrate were added. After stirring at a rate of 300 rpm in a 50 ° C water bath for 2 hours, a suspension C was obtained. A 1.0 mol / L ammonia solution was added dropwise to the suspension C until the pH value reached 9. After stirring for 8 hours, the suspension was taken out and aged at room temperature for 10 hours.

[0048] The obtained solid was washed, filtered and dried at 110° C., and then calcined at 500° C. in an argon atmosphere for 4 hours to obtain Catalyst I.

[0049] Embodiment 2:

[0050] This embodiment provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The catalyst preparation comprises the following steps:

[0051] 3.12 g of melamine and 0.58 g of ammonium perrhenate were fully mixed to obtain a solid mixture A. Solid A was melt-calcined at 600°C for 6 hours to obtain a solid mixture B. After cooling to room temperature, B was added to 100 mL of deionized water, ultrasonically treated in a 60°C water bath for 5 hours, and then taken out and placed in a 100°C vacuum drying oven for 12 hours.

[0052] After drying, solid B was placed in 50 mL of deionized water, and 0.079 g of ruthenium trichloride and 1.41 g of nickel nitrate hexahydrate were added. After stirring at a rate of 300 rpm for 2 hours in a 50°C water bath, a suspension C was obtained. A 1.0 mol / L ammonia solution was added dropwise to C until the pH value reached 9. After stirring for 8 hours, the suspension was taken out and aged at room temperature for 10 hours.

[0053] The obtained solid was washed, filtered and dried at 110° C., and then calcined at 500° C. in an argon atmosphere for 4 hours to obtain Catalyst II.

[0054] Embodiment 3:

[0055] This embodiment provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The catalyst preparation comprises the following steps:

[0056] 6.04 g of terephthalonitrile and 2.42 g of manganese sulfate were fully mixed to obtain solid mixture A. Solid A was melt-calcined at 700°C for 6 hours to obtain solid mixture B. After cooling to room temperature, B was added to 100 mL of deionized water, ultrasonically treated in a 60°C water bath for 10 hours, and then taken out and placed in a 100°C vacuum drying oven for 12 hours.

[0057] The dried solid B was placed in 50 mL of deionized water, and 0.114 g of ruthenium trichloride and 1.76 g of anhydrous zinc chloride were added. The suspension C was obtained after stirring at 300 rpm in a 50 °C water bath for 2 hours. 1.0 mol / L sodium bicarbonate solution was added dropwise to C, and the suspension was taken out after stirring for 8 hours and aged at room temperature for 10 hours.

[0058] The obtained solid was filtered, washed, dried at 110°C, and then calcined at 650°C in an argon atmosphere for 5 hours to obtain Catalyst III.

[0059] Embodiment 4:

[0060] This embodiment provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The catalyst preparation comprises the following steps:

[0061] 4.63 g of amino acid and 0.45 g of tin tetrachloride were fully mixed to obtain solid mixture A. Solid A was melt-calcined at 700°C for 5 hours to obtain solid mixture B. After cooling to room temperature, B was added to 100 mL of deionized water, ultrasonically treated in a 60°C water bath for 5 hours, and then taken out and placed in a 100°C vacuum drying oven for 12 hours.

[0062] The dried solid B was placed in 50 mL of deionized water, and 0.047 g of platinum tetrachloride and 2.55 g of gallium chloride were added. After stirring at 300 rpm for 2 hours in a 50°C water bath, a suspension C was obtained. 1.0 mol / L sodium carbonate solution was added dropwise to C, and after stirring for 8 hours, the suspension was taken out and aged at room temperature for 10 hours.

[0063] The obtained solid was washed, filtered and dried at 110° C., and then calcined at 600° C. in an argon atmosphere for 8 hours to obtain Catalyst IV.

[0064] Embodiment 5:

[0065] The present embodiment provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The catalyst preparation comprises the following steps: 3.12 g of melamine and 1.17 g of ammonium molybdate are fully mixed to obtain a solid mixture A, the solid A is melt-calcined at 700° C. for 10 hours to obtain a solid mixture B, after cooling to room temperature, B is added to 100 mL of deionized water, ultrasonically treated in a 60° C. water bath for 5 hours, and taken out and placed in a 100° C. vacuum drying oven for 12 hours.

[0066] After drying, solid B was placed in 50 mL of deionized water, and 0.182 g of ruthenium trichloride and 3.22 g of anhydrous zinc chloride were added. After stirring at 300 rpm for 2 hours in a 50 ° C water bath, a suspension C was obtained. 1.0 mol / L ammonia solution was added dropwise to C until the pH value reached 9. After stirring for 8 hours, the suspension was taken out and aged at room temperature for 10 hours.

[0067] The obtained solid was washed, filtered and dried at 110° C., and then calcined at 600° C. in an argon atmosphere for 5 hours to obtain Catalyst V.

[0068] Embodiment 6:

[0069] This embodiment provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The catalyst preparation comprises the following steps:

[0070] 6.5 g of urea, 1.29 g of ammonium perrhenate and 0.27 g of tin tetrachloride were fully mixed to obtain a solid mixture A. Solid A was melted and calcined at 500°C for 6 hours to obtain a solid mixture B. After cooling to room temperature, B was added to 100 mL of deionized water, ultrasonically treated in a 60°C water bath for 5 hours, and then taken out and placed in a 100°C vacuum drying oven for 12 hours.

[0071] The dried solid B was placed in 50 mL of deionized water, and 0.042 g of ruthenium trichloride, 0.019 g of platinum tetrachloride and 1.67 g of anhydrous zinc chloride were added. After stirring at 300 rpm for 2 hours in a 50 ° C water bath, a suspension C was obtained. A 1.0 mol / L ammonia solution was added dropwise to C until the pH value reached 9. After stirring for 8 hours, the suspension was taken out and aged at room temperature for 10 hours.

[0072] The obtained solid was washed, filtered and dried at 110° C., and then calcined at 600° C. in an argon atmosphere for 6 hours to obtain Catalyst VI.

[0073] Embodiment 7:

[0074] This embodiment provides a low-temperature and high-efficiency ammonia decomposition catalyst and a preparation method thereof. The catalyst preparation comprises the following steps:

[0075] 7.33 g of melamine, 0.34 g of manganese sulfate and 0.49 g of ammonium molybdate were fully mixed to obtain a solid mixture A. Solid A was melt-calcined at 600°C for 6 hours to obtain a solid mixture B. After cooling to room temperature, B was added to 100 mL of deionized water, ultrasonically treated in a 60°C water bath for 5 hours, and then taken out and placed in a 100°C vacuum drying oven for 12 hours.

[0076] After drying, solid B was placed in 50 mL of deionized water, and 0.052 g of ruthenium trichloride, 0.028 g of platinum tetrachloride and 2.51 g of cobalt nitrate hexahydrate were added. After stirring at a rate of 300 rpm for 2 hours in a 50°C water bath, a suspension C was obtained. 1.0 mol / L ammonia solution was added dropwise to C until the pH value reached 9. After stirring for 8 hours, the suspension was taken out and aged at room temperature for 10 hours.

[0077] The obtained solid was washed, filtered and dried at 110° C., and then calcined at 600° C. in an argon atmosphere for 6 hours to obtain Catalyst VII.

[0078] Catalyst performance evaluation

[0079] Catalysts I, II, III, IV, V, VI, and VII obtained in Examples 1 to 7 were respectively loaded into a fixed bed reactor for catalyst evaluation; the reaction results are shown in Table 1.

[0080] Table 1 Reaction results

[0081] catalyst Ammonia decomposition rate / % Hydrogen production rate / (mmol / gcat / min) I 91.7 16.1 II 91.9 16.4 III 92.5 17.5 IV 90.6 15.3 V 91 15.8 VI 94.6 18.7 VII 93.8 17.6

[0082] Conclusion: The catalyst of the present invention is used to catalyze the decomposition of ammonia to produce hydrogen at a reaction temperature of 450°C and a volume space velocity of 18000 h -1 Under these conditions, the ammonia decomposition rate can reach 94.6% and the hydrogen production rate can reach 18.7mmol / gcat / min.

Claims

1. A low-temperature and high-efficiency ammonia decomposition catalyst, characterized in that: The catalyst comprises a transition metal oxide modified carbon nitride carrier and an active metal applied thereon; The active metal includes noble metal elements and non-noble metal elements; the noble metal elements are one or two of ruthenium and platinum; the non-noble metal elements are one or two or more of nickel, cobalt, tungsten, zinc and gallium; In the transition metal oxide modified carbon nitride carrier, the transition metal oxide is one or two or more of rhenium oxide, manganese oxide, molybdenum oxide and tin oxide.

2. The low-temperature and high-efficiency ammonia decomposition catalyst according to claim 1, characterized in that: The noble metal elements in the active metal account for 1 to 5 wt% of the total weight of the catalyst; the non-noble metal elements in the active metal account for 10 to 25 wt% of the total weight of the catalyst; The transition metal oxide accounts for 5 to 20 wt % of the total weight of the transition metal oxide modified carbon nitride carrier.

3. A method for preparing the low-temperature and high-efficiency ammonia decomposition catalyst according to claim 2, characterized in that: The following steps are involved: Step 1, mixing carbon and nitrogen-containing compounds and transition metal compounds according to the formula, melting and calcining for 4 to 10 hours, adding deionized water after cooling to room temperature, ultrasonically treating for 5 to 12 hours in a water bath, taking out and drying in a vacuum drying oven for 12 hours; Step 2, placing the solid dried in step 1 in deionized water, adding a formula amount of active metals including compounds containing precious metal elements and compounds containing non-precious metal elements, stirring for 2 hours in a water bath, adding a precipitant dropwise, stirring for 8 hours, taking out, and aging at room temperature for 10 hours; Step 3, washing, filtering and drying the solid obtained in step 2, and then calcining the solid in an argon atmosphere at 500-800° C. for 4-8 hours to obtain a catalyst.

4. The method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst according to claim 3, characterized in that: The carbon and nitrogen-containing compound is one or two or more of urea, melamine, amino acid and p-dibenzonitrile.

5. The method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst according to claim 3, characterized in that: The transition metal-containing compound is one or two or more of ammonium perrhenate, manganese sulfate, ammonium molybdate, sodium molybdate, and tin tetrachloride.

6. The method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst according to claim 3, characterized in that: The compound containing precious metal elements is one or two or more of ruthenium chloride, triruthenium dodecacarbonyl, and platinum chloride; The compound containing non-precious metal elements is one or two or more of nickel nitrate, nickel chloride, cobalt nitrate, cobalt chloride, ammonium metatungstate, zinc chloride and gallium chloride.

7. The method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst according to claim 3, characterized in that: The precipitant is one or two or more of ammonia water, sodium carbonate and sodium bicarbonate.

8. The method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst according to claim 3, characterized in that: The calcination temperature in step 1 is 600-800°C, the water bath temperature is 60°C, and the vacuum drying oven drying temperature is 100°C.

9. The method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst according to claim 3, characterized in that: In step 2, the water bath temperature is 50°C.

10. The method for preparing a low-temperature and high-efficiency ammonia decomposition catalyst according to claim 3, characterized in that: In the step 3, the calcination temperature is 500-800°C.