CN114471667B - Catalyst for ammonia decomposition and preparation method thereof - Google Patents
Catalyst for ammonia decomposition and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a catalyst for ammonia decomposition and a preparation method thereof, relating to the field of catalysts, wherein the preparation method comprises the following steps: carrier pretreatment, carrier modification and loading; the catalyst comprises the following components in percentage by weight: 6.2 to 10.5 percent of nickel oxide, 7.2 to 8.4 percent of molybdenum trioxide, 1.1 to 1.5 percent of tungsten trioxide, 3.6 to 4.7 percent of cerium oxide and the balance of carrier. The catalyst prepared by the preparation method can realize excellent catalytic effect at the ammonia decomposition catalytic temperature lower than 500 ℃, and the initial ammonia conversion temperature is 322-331 ℃; the complete ammonia conversion temperature is 449-461 ℃; under the temperature condition of 450 ℃, the ammonia decomposition rate reaches 99.2 to 99.6 percent; the ammonia decomposition rate of the prepared catalyst can still reach 95.3 percent after the continuous catalysis for 3000 hours.
Description
Technical Field
The invention relates to the field of catalysts, and particularly relates to a catalyst for ammonia decomposition and a preparation method thereof.
Background
The ammonia decomposition catalyst is mainly applied to the field of environmental protection and the field of preparation of hydrogen and nitrogen. In the field of environmental protection, ammonia-containing waste gas of factories is decomposed under the catalytic action of an ammonia gas decomposition catalyst, so that the ammonia gas in the waste gas is decomposed into nontoxic hydrogen and nitrogen, and then the nontoxic hydrogen and nitrogen are recycled and utilized. So as to achieve the purpose of reducing pollution. In the field of hydrogen production, ammonia gas has the advantages of easy liquefaction, non-flammability, no toxicity at low concentration, high hydrogen storage density, mature production, storage and transportation technology, no carbon emission in the hydrogen production process and the like, so that the ammonia gas becomes a high-efficiency, clean and safe hydrogen storage carrier, and can be decomposed into hydrogen and nitrogen under the catalytic action of an ammonia gas decomposition catalyst when needed. Under the background of the large development trend of carbon emission reduction and carbon neutralization, the research on the ammonia gas decomposition catalyst becomes more important under the background that the clean energy hydrogen is increasingly emphasized.
Currently, in ammonia gas decomposition catalysis, noble metal catalysts represented by ruthenium and iridium and non-noble metal catalysts represented by iron and nickel are mainly used. Ruthenium-based catalysts are currently recognized to have the highest ammonia decomposition catalytic activity; the nickel-based catalyst has good ammonia decomposition catalytic performance under the high-temperature condition.
The inventor researches and discovers that most of nickel-based ammonia decomposition catalysts in the prior art can realize ammonia decomposition under low temperature conditions, but the nickel-based ammonia decomposition catalysts have low catalytic activity and unsatisfactory ammonia conversion rate under the low temperature conditions, and cannot meet the requirement of large-scale production. The nickel-based catalyst can realize excellent ammonia decomposition catalytic performance under the high temperature condition of at least 600 ℃, but the zero-valent metallic nickel as a catalytic active component has the phenomenon of agglomeration and sintering under the high temperature condition. The catalyst is catalyzed at a high temperature of over 500 ℃ for a long time, the catalytic activity of the catalyst gradually declines, the ammonia conversion rate gradually decreases, and finally the required catalytic performance cannot be achieved. Therefore, it is significant to develop an ammonia decomposition catalyst which can avoid the reduction of the activity of the catalyst and can realize better catalytic performance at a lower ammonia decomposition catalytic temperature.
Chinese patent CN110270340B discloses an ammonia decomposition catalyst, its preparation method and application, wherein the catalyst is prepared by using yttria stabilized zirconia carrier, loaded with active component nickel, auxiliary agent potassium oxide, etc. The patent has the disadvantages that the best catalytic performance can be realized only under the temperature condition of 650 ℃; meanwhile, when the catalyst is subjected to catalytic reaction at the temperature for a long time, the catalytic activity gradually declines, the ammonia conversion rate gradually decreases, and finally the required catalytic performance cannot be achieved.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a catalyst which can effectively avoid the problem that the catalytic activity of an ammonia decomposition catalyst is declined under the condition of long-term high temperature; the catalyst for ammonia decomposition can realize better catalytic performance at the ammonia decomposition catalysis temperature lower than 500 ℃ and the preparation method thereof.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a preparation method of a catalyst for ammonia decomposition comprises the following steps: carrier pretreatment, carrier modification and loading;
the carrier pretreatment method comprises the steps of putting the SBA-15 molecular sieve carrier into a predetermined part of first treatment liquid, heating to 60-70 ℃, and carrying out ultrasonic dispersion for 20-30min to obtain a mixed liquid; under the condition of stirring, dropwise adding a predetermined part of second treatment liquid into the mixed solution at a dropwise adding rate of 3-5 mL/min; after the second treatment solution is dropwise added, standing, naturally cooling to room temperature, and filtering out solids to obtain the SBA-15 molecular sieve carrier after secondary treatment; placing the SBA-15 molecular sieve carrier subjected to secondary treatment in a closed space, heating to 105-115 ℃ at the heating rate of 2-3 ℃/min, preserving heat and standing for 3-4h to finish the carrier pretreatment step to obtain the pretreated SBA-15 molecular sieve carrier;
preferably, the specification of the SBA-15 molecular sieve carrier is that the specific surface area is 550-600m2The grain diameter is 1.2-1.5 mu m, and the relative crystallinity is 92-95%.
Preferably, the ultrasonic dispersion method is that the ultrasonic dispersion frequency is 20-24KHz, and the ultrasonic dispersion power is 250-300W.
The first treatment liquid consists of the following raw materials: polydiallyl dimethyl ammonium chloride, polyethylene glycol laurate and deionized water; the weight ratio of the polydiallyl dimethyl ammonium chloride to the polyethylene glycol laurate to the deionized water is (10-12): 2-3: 120-150;
the second treatment liquid is 0.1-0.3mol/L nickel nitrate solution;
the SBA-15 molecular sieve carrier, the first treatment fluid and the second treatment fluid have the weight ratio of 1-2: 50-70: 250-300;
the carrier modification method comprises the steps of putting a predetermined part of nano alumina sol into deionized water, and uniformly stirring to prepare a modification solution; then adding a predetermined part of pretreated SBA-15 molecular sieve carrier into the modified liquid, carrying out micro-current treatment while carrying out ultrasonic dispersion, and leaching out solids after 20-30min of ultrasonic dispersion and micro-current treatment; placing the solid in an environment of 120-130 ℃, and naturally cooling after heat treatment for 30-40 min; leaching the solid by using 2-3 times of volume of modified liquid when the solid is naturally cooled to the temperature of 100-105 ℃; after leaching, processing the solid by intermittent microwave for 5-10 min; finally, heating the solid to 550-600 ℃, and preserving the heat for 1.5-2h to prepare a modified carrier;
the particle size of the nano alumina sol is 3-5 nm;
in the process of the intermittent microwave treatment, the temperature of the solid is kept within the range of 150 ℃ and 160 ℃;
the micro-current treatment is carried out with the micro-current intensity of 5-8 muA;
preferably, the ultrasonic dispersion method is that the ultrasonic dispersion frequency is 25-30KHz, and the ultrasonic dispersion power is 300-400W.
The weight ratio of the nano alumina sol, the pretreated SBA-15 molecular sieve carrier and the deionized water is 2-3: 5-6: 20-30 parts of;
the loading method comprises the steps of putting the modified carrier into a loading solution with the volume 8-10 times that of the modified carrier, and stirring for 2-3 hours; after stirring, centrifugally separating out the modified carrier loaded with the active ingredients, and standing for 2-3h at the temperature of 110-120 ℃; then heating to 400-500 ℃ at the heating rate of 6-10 ℃/min, calcining for 3-5h, and completing the loading step to obtain the catalyst for ammonia decomposition.
Preferably, the rotational speed of the centrifugal separation is 8000-9000 RPM.
The negative carrier liquid consists of the following components: ammonium heptamolybdate, ammonium metatungstate, cerium nitrate and deionized water;
the weight ratio of ammonium heptamolybdate, ammonium metatungstate, cerium nitrate and deionized water is 10-15: 2-3: 5-8: 120-150.
Further, the catalyst prepared by the preparation method comprises the following components in percentage by weight: 6.2 to 10.5 percent of nickel oxide, 7.2 to 8.4 percent of molybdenum trioxide, 1.1 to 1.5 percent of tungsten trioxide, 3.6 to 4.7 percent of cerium oxide and the balance of carrier.
Compared with the prior art, the invention has the beneficial effects that:
(1) according to the preparation method of the catalyst for ammonia decomposition, the prepared catalyst can realize excellent catalytic effect at the ammonia decomposition catalytic temperature lower than 500 ℃, the initial ammonia conversion temperature is 322-331 ℃, and the low-temperature activity is good.
(2) According to the preparation method of the catalyst for ammonia decomposition, the prepared catalyst is used for ammonia decomposition catalysis, the complete ammonia conversion temperature is 449-461 ℃, the low-temperature catalysis performance is excellent, and the problem of activity degradation of the ammonia decomposition catalyst under the high-temperature condition is effectively avoided.
(3) The catalyst prepared by the preparation method for the catalyst for ammonia decomposition is used for ammonia decomposition catalysis, and the ammonia decomposition rate reaches 99.2-99.6% under the temperature condition of 450 ℃.
(4) According to the preparation method of the catalyst for ammonia decomposition, the prepared catalyst can achieve an ammonia decomposition rate of 95.3% after continuous catalysis for 3000 hours, and has excellent long-term performance.
Detailed Description
In order to more clearly understand the technical features, objects, and effects of the present invention, specific embodiments of the present invention will now be described.
Example 1
A preparation method of a catalyst for ammonia decomposition comprises the following specific steps:
1. pretreatment of the support
Adding the SBA-15 molecular sieve carrier into a predetermined part of first treatment liquid, heating to 60 ℃, and performing ultrasonic dispersion for 20min to obtain a mixed liquid; under the stirring condition of 80RPM, dropwise adding a predetermined part of second treatment liquid into the mixed liquid at a dropwise adding rate of 3 mL/min; after the second treatment solution is dropwise added, standing, naturally cooling to room temperature, and filtering out solids to obtain the SBA-15 molecular sieve carrier after secondary treatment; and (3) placing the SBA-15 molecular sieve carrier subjected to secondary treatment in a closed space, heating to 105 ℃ at the heating rate of 2 ℃/min, preserving heat and standing for 3 hours to finish the carrier pretreatment step.
Wherein the SBA-15 molecular sieve carrier has a specific surface area of 550m2(ii) g, pore diameter 7nm, particle diameter 1.2 μm, relative crystallinity 92%.
The first treatment liquid consists of the following raw materials: polydiallyl dimethyl ammonium chloride, polyethylene glycol laurate and deionized water. Wherein the weight ratio of the polydiallyl dimethyl ammonium chloride to the polyethylene glycol laurate to the deionized water is 10: 2: 120.
the second treatment liquid is 0.1mol/L nickel nitrate solution.
The ultrasonic dispersion method comprises the steps that the ultrasonic dispersion frequency is 20KHz, and the ultrasonic dispersion power is 250W.
The SBA-15 molecular sieve carrier comprises: first treatment liquid: the weight ratio of the second treating fluid is 1: 50: 250.
2. modification of supports
Putting a predetermined part of nano alumina sol into deionized water, and stirring at 30RPM for 10min to prepare a modified solution; then adding a predetermined part of SBA-15 molecular sieve carrier treated by the carrier pretreatment step into the modified liquid, carrying out micro-current treatment while carrying out ultrasonic dispersion, and draining solids after 20min of ultrasonic dispersion and micro-current treatment; placing the solid in an environment with the temperature of 120 ℃ and carrying out heat treatment for 30 min; naturally cooling the solid; when the solid is naturally cooled to 100 ℃, leaching the solid by using 2 times of the volume of the modifying liquid; after leaching, treating the solid for 5min by adopting intermittent microwave, and keeping the temperature of the solid within 150 ℃ in the intermittent microwave treatment process; and finally, heating the solid to 550 ℃, and preserving the heat for 1.5 hours to obtain the modified carrier.
Wherein the weight ratio of the nano alumina sol, the pretreated SBA-15 molecular sieve carrier and the deionized water is 2: 5: 20.
the particle size of the nano alumina sol is 3 nm.
The ultrasonic dispersion method comprises the steps that the ultrasonic dispersion frequency is 25KHz, and the ultrasonic dispersion power is 300W.
The micro-current processing is operated such that the micro-current intensity is 5 muA.
3. Load(s)
Putting the modified carrier prepared in the modification step into a load solution with the volume 8 times that of the modified carrier, and stirring for 2 hours at 10 RPM; then, adopting 8000RPM centrifugal separation to obtain the modified carrier loaded with active ingredients, placing the modified carrier at the temperature of 110 ℃, and standing for 2 hours; and then heating to 400 ℃ at the heating rate of 6 ℃/min, calcining for 3h, and completing the loading step to obtain the catalyst.
The preparation method of the negative carrier liquid comprises the steps of putting ammonium heptamolybdate, ammonium metatungstate and cerium nitrate in predetermined parts into deionized water, and stirring at 300RPM for 10min to obtain the negative carrier liquid.
The weight ratio of ammonium heptamolybdate, ammonium metatungstate, cerium nitrate and deionized water is 10: 2: 5: 120.
in the catalyst, the nickel content is calculated by nickel oxide, the molybdenum content is calculated by molybdenum trioxide, the tungsten content is calculated by tungsten trioxide, the cerium content is calculated by cerium oxide, and the catalyst comprises the following components in percentage by weight: 6.2% of nickel oxide, 7.2% of molybdenum trioxide, 1.1% of tungsten trioxide, 3.6% of cerium oxide and the balance of a carrier.
Example 2
A preparation method of a catalyst for ammonia decomposition specifically comprises the following steps:
1. pretreatment of the support
Adding the SBA-15 molecular sieve carrier into a predetermined part of first treatment liquid, heating to 65 ℃, and ultrasonically dispersing for 25min to obtain a mixed liquid; dropwise adding a predetermined part of second treatment liquid into the mixed liquid at a dropwise adding rate of 4mL/min under the stirring condition of 90 RPM; after the second treatment solution is dropwise added, standing, naturally cooling to room temperature, and filtering out solids to obtain the SBA-15 molecular sieve carrier after secondary treatment; and (3) placing the SBA-15 molecular sieve carrier subjected to secondary treatment in a closed space, heating to 110 ℃ at a heating rate of 2.5 ℃/min, preserving heat and standing for 3.5 hours to finish the carrier pretreatment step.
Wherein the SBA-15 molecular sieve carrier has a specific surface area of 580m2(ii) g, pore diameter 8nm, particle diameter 1.3 μm, relative crystallinity 93%.
The first treatment liquid consists of the following raw materials: polydiallyl dimethyl ammonium chloride, polyethylene glycol laurate and deionized water. Wherein the weight ratio of the polydiallyl dimethyl ammonium chloride to the polyethylene glycol laurate to the deionized water is 11: 2.5: 135.
the second treatment liquid is 0.2mol/L nickel nitrate solution.
The ultrasonic dispersion method comprises the steps that the ultrasonic dispersion frequency is 22KHz, and the ultrasonic dispersion power is 270W.
The SBA-15 molecular sieve carrier, the first treatment fluid and the second treatment fluid have the weight ratio of 1.5: 60: 280.
2. modification of supports
Putting a predetermined part of nano alumina sol into deionized water, and stirring at 35RPM for 12min to prepare a modified solution; then adding a predetermined part of SBA-15 molecular sieve carrier treated by the carrier pretreatment step into the modified liquid, carrying out micro-current treatment while carrying out ultrasonic dispersion, and draining solids after 25min of ultrasonic dispersion and micro-current treatment; placing the solid in an environment at 125 ℃ and carrying out heat treatment for 35 min; naturally cooling the solid; when the solid is naturally cooled to 102 ℃, leaching the solid by using 2.5 times of modifying liquid; after leaching, treating the solid for 8min by adopting intermittent microwave, and keeping the temperature of the solid within 155 ℃ in the intermittent microwave treatment process; and finally, heating the solid to 580 ℃, and preserving the heat for 1.8 hours to obtain the modified carrier.
Wherein, the weight ratio of the nano alumina sol, the pretreated SBA-15 molecular sieve carrier and the deionized water is 2.5: 5.5: 25.
the particle size of the nano alumina sol is 4 nm.
The ultrasonic dispersion method comprises the steps that the ultrasonic dispersion frequency is 28KHz, and the ultrasonic dispersion power is 350W.
And (4) carrying out micro-current treatment, wherein the micro-current intensity is 6 muA.
3. Load(s)
Putting the modified carrier prepared in the modification step into 9 times of volume of negative carrier liquid, and stirring at 15RPM for 2.5 h; then, centrifugally separating out the modified carrier loaded with the active ingredients at 8500RPM, placing at 115 ℃ and standing for 2.5 hours; and then heating to 450 ℃ at the heating rate of 8 ℃/min, calcining for 4h, and completing the loading step to obtain the catalyst.
The preparation method of the negative carrier liquid comprises the steps of putting ammonium heptamolybdate, ammonium metatungstate and cerium nitrate in preset parts into deionized water, and stirring at 350RPM for 12min to obtain the negative carrier liquid.
The weight ratio of ammonium heptamolybdate, ammonium metatungstate, cerium nitrate and deionized water is 12: 2.5: 7: 135.
in the catalyst, the nickel content is calculated by nickel oxide, the molybdenum content is calculated by molybdenum trioxide, the tungsten content is calculated by tungsten trioxide, the cerium content is calculated by cerium oxide, and the catalyst comprises the following components in percentage by weight: 8.4% of nickel oxide, 8.0% of molybdenum trioxide, 1.2% of tungsten trioxide, 4.1% of cerium oxide and the balance of a carrier.
Example 3
A preparation method of a catalyst for ammonia decomposition comprises the following specific steps:
1. pretreatment of the support
Adding the SBA-15 molecular sieve carrier into a predetermined part of first treatment liquid, heating to 70 ℃, and performing ultrasonic dispersion for 30min to obtain a mixed liquid; under the stirring condition of 100RPM, dropwise adding a predetermined part of second treatment liquid into the mixed liquid at a dropwise adding rate of 5 mL/min; after the second treatment solution is dropwise added, standing, naturally cooling to room temperature, and filtering out solids to obtain the SBA-15 molecular sieve carrier after secondary treatment; and (3) placing the SBA-15 molecular sieve carrier subjected to secondary treatment in a closed space, heating to 115 ℃ at the heating rate of 3 ℃/min, preserving heat and standing for 4h to finish the carrier pretreatment step.
Wherein the SBA-15 molecular sieve carrier has a specific surface area of 600m2(ii) g, pore diameter 9nm, particle diameter 1.5 μm, relative crystallinity 95%.
The first treatment liquid consists of the following raw materials: poly diallyl dimethyl ammonium chloride, polyethylene glycol laurate and deionized water. Wherein the weight ratio of the polydiallyl dimethyl ammonium chloride to the polyethylene glycol laurate to the deionized water is 12: 3: 150.
the second treatment liquid is 0.3mol/L nickel nitrate solution.
The ultrasonic dispersion method comprises the steps that the ultrasonic dispersion frequency is 24KHz, and the ultrasonic dispersion power is 300W.
The SBA-15 molecular sieve carrier comprises: first treatment liquid: the weight ratio of the second treating fluid is 2: 70: 300.
2. modification of supports
Putting a predetermined part of nano alumina sol into deionized water, and stirring at 40RPM for 15min to prepare a modified solution; then adding a predetermined part of SBA-15 molecular sieve carrier treated by the carrier pretreatment step into the modified liquid, carrying out micro-current treatment while carrying out ultrasonic dispersion, and draining solids after 30min of ultrasonic dispersion and micro-current treatment; placing the solid in an environment with the temperature of 130 ℃ and carrying out heat treatment for 40 min; naturally cooling the solid; when the solid is naturally cooled to 105 ℃, leaching the solid by using 3 times of volume of modified liquid; after leaching, treating the solid for 10min by adopting intermittent microwave, and keeping the temperature of the solid within 160 ℃ in the intermittent microwave treatment process; and finally, heating the solid to 600 ℃, and preserving the heat for 2 hours to obtain the modified carrier.
Wherein the ratio of parts by weight of the nano alumina sol, the SBA-15 molecular sieve carrier and the deionized water is 3: 6: 30.
the particle size of the nano alumina sol is 5 nm.
The ultrasonic dispersion method comprises the steps that the ultrasonic dispersion frequency is 30KHz, and the ultrasonic dispersion power is 400W.
And (4) carrying out micro-current treatment, wherein the micro-current intensity is 8 muA.
3. Load(s)
Putting the modified carrier prepared in the modification step into a loading solution with the volume 10 times that of the carrier, and stirring for 3 hours at 20 RPM; then, centrifugally separating out the modified carrier loaded with the active ingredients at 9000RPM, placing at 120 ℃, and standing for 3 hours; and then heating to 500 ℃ at the heating rate of 10 ℃/min, calcining for 5h, and completing the loading step to obtain the catalyst.
The preparation method of the negative carrier liquid comprises the steps of putting ammonium heptamolybdate, ammonium metatungstate and cerium nitrate in preset parts into deionized water, and stirring at 400RPM for 15min to obtain the negative carrier liquid.
The weight ratio of ammonium heptamolybdate, ammonium metatungstate, cerium nitrate and deionized water is 15: 3: 8: 150.
in the catalyst, the nickel content is calculated by nickel oxide, the molybdenum content is calculated by molybdenum trioxide, the tungsten content is calculated by tungsten trioxide, the cerium content is calculated by cerium oxide, and the catalyst comprises the following components in percentage by weight: 10.5% of nickel oxide, 8.4% of molybdenum trioxide, 1.5% of tungsten trioxide, 4.7% of cerium oxide and the balance of a carrier.
Comparative example 1
The preparation method of the catalyst for ammonia decomposition described in example 2 was used, except that: omitting the carrier pretreatment step in the first step, and adopting the SBA-15 molecular sieve with the same specification as a carrier to replace the SBA-15 molecular sieve carrier treated by the carrier pretreatment step. Meanwhile, adding nickel nitrate into the load solution in the third loading step, which specifically comprises the following steps: the preparation method of the negative carrier liquid comprises the steps of putting nickel nitrate, ammonium heptamolybdate, ammonium metatungstate and cerium nitrate in predetermined parts into deionized water, and stirring at 300-400RPM for 10-15min to obtain the negative carrier liquid. The nickel nitrate: ammonium heptamolybdate: ammonium metatungstate: cerium nitrate: the weight ratio of the deionized water is 35: 12: 2.5: 7: 135.
comparative example 2
The preparation method of the catalyst for ammonia decomposition described in example 2 was used, except that: the step of modifying the carrier in the second step is omitted, and the step of loading in the third step is directly carried out after the carrier in the first step is prepared.
Comparative example 3
The preparation method of the catalyst for ammonia decomposition described in example 2 was used, with the difference that: in the third step of loading, the loading liquid omits ammonium metatungstate and cerium nitrate.
The catalysts prepared in examples 1 to 3 and comparative examples 1 to 3 were used in the ammonia decomposition catalytic process, and the ammonia decomposition performance of each catalyst was examined. Specifically, examples 1 to 3 and comparative example 1 were reduced with hydrogen gas-3, the reduction temperature is 500 ℃, the reduction pressure is 0.3Mpa, and the space velocity is 1500h-1Reducing for 30 min; then filling the reduced catalyst into a quartz reaction tube for detection, wherein the filling amount of the catalyst is 1 g; pure ammonia gas is adopted as raw material gas for detection, the reaction pressure is 0.2MPa, and the ammonia gas volume space velocity is 6000h-1。
The catalysts prepared in examples 1 to 3 and comparative examples 1 to 3 were tested as follows:
further, the catalysts obtained in examples 1 to 3 and comparative examples 1 to 3 were tested for ammonia decomposition rate at 450 deg.C, 550 deg.C and 600 deg.C, respectively, under the experimental conditions described above. Wherein, the calculation method of the ammonia decomposition rate comprises the following steps: ammonia decomposition rate = (initial ammonia content-treated ammonia content)/initial ammonia content x100%, results are given in the following table:
further, under the temperature condition of 450 ℃, the volume space velocity of ammonia gas is 6000-1The catalysts obtained in examples 1-3 were tested for life under the following conditions, and the catalytic reaction of each catalyst in examples 1-3 after 3000h of continuous catalysis was examined, and the test results are as follows:
all percentages used in the present invention are mass percentages unless otherwise indicated.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments described above, or equivalents may be substituted for elements thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (5)
1. A preparation method of a catalyst for ammonia decomposition is characterized by comprising the following steps: carrier pretreatment, carrier modification and loading;
the carrier pretreatment method comprises the steps of putting the SBA-15 molecular sieve carrier into a predetermined part of first treatment liquid, heating to 60-70 ℃, and carrying out ultrasonic dispersion for 20-30min to obtain a mixed liquid; under the condition of stirring, dropwise adding a predetermined part of second treatment liquid into the mixed solution at a dropwise adding rate of 3-5 mL/min; after the second treatment solution is dropwise added, standing, naturally cooling to room temperature, and filtering out solids to obtain the SBA-15 molecular sieve carrier after secondary treatment; placing the SBA-15 molecular sieve carrier subjected to secondary treatment in a closed space, heating to 105-115 ℃ at the heating rate of 2-3 ℃/min, preserving heat and standing for 3-4h to finish the carrier pretreatment step to obtain the pretreated SBA-15 molecular sieve carrier;
the specification of the SBA-15 molecular sieve carrier is that the specific surface area is 550-2G, the aperture is 7-9nm, the grain diameter is 1.2-1.5 mu m, and the relative crystallinity is 92-95%;
the first treatment liquid consists of the following raw materials: polydiallyl dimethyl ammonium chloride, polyethylene glycol laurate and deionized water; the weight ratio of the polydiallyl dimethyl ammonium chloride to the polyethylene glycol laurate to the deionized water is (10-12): 2-3: 120-150;
the second treatment liquid is 0.1-0.3mol/L nickel nitrate solution;
the SBA-15 molecular sieve carrier, the first treatment fluid and the second treatment fluid have the weight ratio of 1-2: 50-70: 250-300;
the carrier modification method comprises the steps of putting a predetermined part of nano alumina sol into deionized water, and uniformly stirring to prepare a modification solution; then adding a predetermined part of pretreated SBA-15 molecular sieve carrier into the modified liquid, carrying out micro-current treatment while carrying out ultrasonic dispersion, and leaching out solids after 20-30min of ultrasonic dispersion and micro-current treatment; placing the solid in an environment of 120-130 ℃, and naturally cooling after heat treatment for 30-40 min; leaching the solid by using 2-3 times of volume of modified liquid when the solid is naturally cooled to the temperature of 100-105 ℃; after leaching, processing the solid by intermittent microwave for 5-10 min; finally, heating the solid to 550-600 ℃, and preserving the heat for 1.5-2h to prepare a modified carrier;
the particle size of the nano alumina sol is 3-5 nm;
in the process of the intermittent microwave treatment, the temperature of the solid is kept within the range of 150 ℃ and 160 ℃;
the micro-current treatment is carried out with the micro-current intensity of 5-8 muA;
the weight ratio of the nano alumina sol, the pretreated SBA-15 molecular sieve carrier and the deionized water is (2-3): 5-6: 20-30 parts of;
the loading method comprises the steps of putting the modified carrier into a loading solution with the volume 8-10 times that of the modified carrier, and stirring for 2-3 hours; after stirring, centrifugally separating out the modified carrier loaded with the active ingredients, and standing for 2-3h at the temperature of 110-120 ℃; then heating to 400-500 ℃ at the heating rate of 6-10 ℃/min, calcining for 3-5h, and completing the loading step to prepare the catalyst for ammonia decomposition;
the negative carrier liquid consists of the following components: ammonium heptamolybdate, ammonium metatungstate, cerium nitrate and deionized water;
the weight ratio of ammonium heptamolybdate, ammonium metatungstate, cerium nitrate and deionized water is 10-15: 2-3: 5-8: 120-150.
2. The method for preparing a catalyst for ammonia decomposition as defined in claim 1, wherein in the carrier pretreatment step, the ultrasonic dispersion is carried out at an ultrasonic dispersion frequency of 20-24KHz and an ultrasonic dispersion power of 250-300W.
3. The method for preparing a catalyst for ammonia decomposition as defined in claim 1, wherein in the step of modifying the support, the ultrasonic dispersion is carried out at an ultrasonic dispersion frequency of 25-30KHz and an ultrasonic dispersion power of 300-400W.
4. The method for preparing a catalyst for ammonia decomposition according to claim 1, wherein the rotation speed of the centrifugal separation is 8000-9000 RPM.
5. A catalyst for ammonia decomposition, which is produced by the production method according to any one of claims 1 to 4; the catalyst comprises the following components in percentage by weight: 6.2 to 10.5 percent of nickel oxide, 7.2 to 8.4 percent of molybdenum trioxide, 1.1 to 1.5 percent of tungsten trioxide, 3.6 to 4.7 percent of cerium oxide and the balance of carrier.
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