A kind of preparation method who is used for the nickel-base catalyst of ammonia decomposition
Technical field
The present invention relates to the preparation method of the Ni-based ammonia decomposition catalyzer of a kind of efficient cryogenic, a kind of preparation method who is used for ammonia is decomposed into the nickel-base catalyst of hydrogen and nitrogen is provided specifically.
Background technology
Setting up the hydrogenation station that disperses is the development trend of following Hydrogen Energy in the fuel cell field extensive use, in recent years, has abroad begun to pay attention to carry out the corresponding techniques research and development for setting up the hydrogenation station.For example, Ri Ben Toho Gas company has built a hydrogenation station for fuel cell electric vehicle filling hydrogen in the Aichi laboratory.By the end of 2004, Japanese government set up 8 hydrogenation stations in Tokyo.According to current papers in 2003 (International Journal of HydrogenEnergy 28 (2003) 743-755), the U.S. is in order to satisfy the demand of fuel cell electric vehicle, and only the phase I just need be set up 4500~17700 hydrogenation stations.In addition, even territory and long-pending less Italy also need set up about 10000 hydrogenation stations (Journal ofPower Sources 106 (2002) 353-363).This shows that the market business opportunity and the economic interests of following Hydrogen Energy are very huge.A fuel cell bus special line is opened at a hydrogenation station surplus China also will be before 2008 Olympic Games builds 10 in Beijing simultaneously.
Utilizing liquefied ammonia to decompose on-the-spot hydrogen manufacturing is a kind of important selection of setting up the hydrogenation station future, is the problem that raw material not only can solve the fuel transport difficulty with liquefied ammonia, can also reduce cost of transportation.Adopt preparing hydrogen by ammonia decomposition in conjunction with the inoranic membrane isolation technics, not only can realize the production of High Purity Hydrogen, and can realize the production and the isolation integral of hydrogen, shortened process, the economy system investment also reduces production costs.Therefore, in recent years, preparing hydrogen by ammonia decomposition technology has caused domestic and international researcher's extensive concern again.
Except that following Hydrogen Energy field has wide application prospects, the application of ammonia decomposition reaction also comprises: the environmental protection deamination, electronics and metallurgy industry are with reducing gases and protect gas etc.
Yet the serviceability temperature of the ammonia decomposition catalyzer of present industrial application is too high, and generally more than 800 ℃, not only energy consumption is higher, and equipment corrosion is serious.Therefore, exploitation efficient cryogenic ammonia decomposition catalyzer is the important development direction.Document shows that the research of ammonia decomposition catalyzer mainly biases toward highly active ruthenium base of exploitation or nickel-base catalyst.Though ruthenium-based catalyst possesses higher ammonia degrading activity (Yin, et al., J.Catal.224,384,2004; Xu, et al., CN 1456491A), but content of metal generally higher (>5%) in the existing efficient ruthenium catalyst has increased the cost of catalyst.Carbon-based material such as active carbon, CNT is the optimum carrier of ruthenium, and methanation reaction takes place under the high temperature of ammonia decomposition reaction, rich hydrogen condition easily, has reduced the stability of ruthenium catalyst.Studies show that the nickel that reserves are abundant, the market price is low also is that a kind of ammonia preferably decomposes catalytic active component (Choudhary, et al., Catal.Lett.72,197,2001; Ganley, et al., Catal.Lett.96,117,2004).But the research and development of nickel-base catalyst for a long time lack than quantum jump, show that mainly the low temperature active of catalyst is poor, disposal ability is low.For example, document shows (A.S.Chellappa etal., Appl.Catal.A 227,231,2002), and several commercial ammonia decomposition catalyzers are being lower than under 700 ℃ the temperature, and the tool catalytic activity is all lower.
Catalyst |
Main chemical |
Producer |
Temperature (℃) |
Conversion ratio (%) |
G43-A 2800 146 |
Ni,Al,<1wt.%Pt 93.8%Ni,0.3%Fe,5.9%Al 0.5%Ru,Al |
United Catalyst Grace Davison Johnson Matthey |
500 600 600 700 550 600 |
14.5 78.1 18.8 81.6 12.9 23.6 |
At present, the preparation method of Ni-based ammonia decomposition catalyzer is based on the infusion process of routine, and the nickel species mainly exist with the free state form, with carrier interactions a little less than.Therefore, nickel crystallite in pre-treatment (roasting, the reduction etc.) process of catalyst very easily sintering grow up, this is to cause the active low main cause of existing nickel-base catalyst.In addition,, suppressed amino molecule and contacted, so cryogenic conditions is difficult to realize the high conversion of ammonia down with the catalyst activity component because the absorption occupy-place takes place on the catalyst activity component product hydrogen easily.
Summary of the invention
The object of the present invention is to provide a kind of preparation method who is used for the nickel-base catalyst of ammonia decomposition, have the characteristics of high activity, high stability, active component high dispersive by the nickel-base catalyst of the present invention's preparation
For achieving the above object, the preparation method who is used for the nickel-base catalyst of ammonia decomposition reaction provided by the invention, concrete steps are as follows:
The nitrate of active constituent Ni, carrier A l or Zr is made solution in the water-soluble or absolute ethyl alcohol, stoichiometric ammonium carbonate or carbonic hydroammonium are dissolved in water or the ethanol form solution.Above-mentioned two kinds of drips of solution are added in the same container, and the pH value of control solution is between 7~10.After charging finishes, stirred aging 2-6 hour, separate and remove mother liquor, spend the deionised water precipitation, dry back obtained the target catalyst at 400~900 ℃ of following roasting 4-8 hours, wherein the mass percent of active constituent Ni is 10-70%, is preferably 30-60%, preferred 40-60%.The present invention can also add auxiliary agent La or Ce, and its mass percent is 0-30%.
The present invention has following advantage:
1. strong, the good stability of catalyst activity height, disposal ability.Use the nickel-base catalyst of method preparation provided by the present invention, its key character is that catalytic activity is higher than the existing related Ni-based ammonia decomposition catalyzer of document.Because the present invention has used unconventional coprecipitation to prepare nickel-base catalyst, active component nickel is high dispersion state, and active component has less average grain diameter after the activation processing.Experimental result shows that the conversion ratio of ammonia can reach 99.8% when reaction temperature was 500 ℃.Reaction temperature is that 550 ℃, ammonia charging air speed are 20000h
-1The time, the conversion ratio of ammonia is up to 99.9%.Catalyst stability experiment shows, under 550 ℃, the reaction condition of 5atm, laboratory scale ammonia decomposition device safe handling is after 1000 hours, and conversion ratio maintains more than 99.9% all the time.This explanation, the nickel-base catalyst of method preparation provided by the present invention is a kind of efficient, stable ammonia decomposition catalyzer.
2. technology is simple.The present invention only needs general Preparation of Catalyst condition, and easy control of reaction and technical process are simple relatively, can satisfy the requirement that large-scale industrialization is produced fully.
3. preparation cost is low.The raw materials used cheapness of the present invention, preparation flow is short, and equipment requires simple.
Description of drawings
Fig. 1 is Ni/Al
2 O
31000 hours stability result of catalyst.
The specific embodiment
The present invention will be further described below in conjunction with embodiment.
Embodiment 1
155g nickel nitrate, 74g aluminum nitrate are dissolved in the 500ml deionized water, and it is standby to be configured to mixed liquor.Get stoichiometric ammonium carbonate and be dissolved in the 500ml deionized water, standby as precipitating reagent.Under stirring above-mentioned two drips of solution are added in the same vessel, the pH value of control solution is 8.After charging finishes, stirred aging 2 hours, centrifugation spends deionised water, obtains gel.After 120 ℃ of dryings, temperature programming to 600 ℃, roasting is 8 hours in air.Make nickel oxide content and be 80% Ni/Al
2O
3Catalyst.
According to the method described above, will feed intake changes 117g nickel nitrate, 147g aluminum nitrate into, makes nickel oxide content and be 63% Ni/Al
2O
3Catalyst.
According to the method described above, will feed intake changes 7.8g nickel nitrate, 280g aluminum nitrate into, makes nickel oxide content and be 5% Ni/Al
2O
3Catalyst.
Get above-mentioned each catalyst of 1.0g respectively and place stainless steel reactor, use 50%H
2-He reducing gases (100ml/min) feeds pure ammonia and carries out synthesis under normal pressure at 550 ℃ 600 ℃ of activation processing 3 hours, and the ammonia flow velocity is 333ml/min.Experimental result is as shown in table 1.
Table 1: nickel content is to the influence of catalytic activity
Numbering |
Nickel oxide (wt.%) |
Nickel/al atomic ratio |
550℃,20000h
-1Following ammonia conversion ratio (%)
|
Reduction back Ni
0Crystal grain d
XRD(nm)
|
1 2 3 |
80 63 5.0 |
2.8 1.2 0.04 |
90.2 91.3 17.6 |
5.9 3.6 - |
This shows that the nickel oxide percentage composition is 63% Ni/Al
2O
3Catalyst possesses the highest ammonia degrading activity.Select this catalyst to carry out the investigation of catalyst stability, setting the ammonia air speed is 5000h
-1, reaction temperature is 620 ℃, reaction pressure is 5atm.After the system steady running 1000 hours, the ammonia conversion ratio maintains (accompanying drawing 1) more than 99.9% all the time.The prepared Ni/Al of this explanation the present invention
2O
3Have good high temperature resistance stability, industrial prospect is wide.
Embodiment 2
46g nickel nitrate, 59g aluminum nitrate, 9g lanthanum nitrate are dissolved in the 200ml deionized water, and it is standby to be mixed with mixed liquor.Get stoichiometric ammonium carbonate and be dissolved in the 200ml deionized water, standby as precipitating reagent.Under stirring above-mentioned two drips of solution are added in the same vessel, the pH value of control solution is 8.After charging finishes, stirred aging 6 hours, centrifugation spends deionised water, obtains gel.After 120 ℃ of dryings, temperature programming to 600 ℃, roasting is 4 hours in air.Making the nickel al atomic ratio is 1.2, and the lanthanum nickle atom is than the Ni/La-Al that is 0.22
2O
3Catalyst.
According to the method described above, will feed intake changes 46g nickel nitrate, 59g zirconium nitrate, 11g cerous nitrate into, and making the nickel al atomic ratio is 1.2, and the cerium nickle atom is than the Ni/Ce-ZrO that is 0.23
2Catalyst.
Get above-mentioned each catalyst of 1.0g respectively and place stainless steel reactor, use 50%H
2-He reducing gases (100ml/min) feeds pure ammonia and carries out synthesis under normal pressure at 550 ℃ 600 ℃ of activation processing 3 hours, and the ammonia flow velocity is 333ml/min.Experimental result is as shown in table 2.
Table 2: auxiliary agent is to the influence of catalytic activity
Numbering |
Catalyst |
Nickel/al atomic ratio |
Nickel/auxiliary agent atomic ratio |
550℃,20000h
-1Ammonia conversion ratio (%)
|
1 2 3 |
Ni/Al
2O
3 Ni/La-Al
2O
3 Ni/Ce-ZrO
2 |
1.2 1.2 1.2 |
- 0.22 0.23 |
91.3 99.9 96.8 |
As shown in Table 2, add rare-earth elements of lanthanum, cerium can effectively improve the ammonia degrading activity of nickel-alumina catalyst, and it is active best wherein to add lanthana.Therefore, The effect Ni/La-Al
2O
3The activity of catalyst under the differential responses condition.Experimental result is as shown in table 3.
Table 3:Ni/La-Al
2O
3Ammonia decomposition reaction conversion ratio (%) on the catalyst
Reaction temperature (℃) |
Ammonia charging air speed (h
-1)
|
1000 |
2000 |
5000 |
10000 |
20000 |
400 450 500 550 |
51.9 97.4 99.9 >99.9 |
37.5 91.9 99.8 >99.9 |
21.5 67.3 99.4 >99.9 |
14.1 51.4 95.3 >99.9 |
9.6 37.0 78.0 99.9 |
Embodiment 3
According to embodiment 2 described preparation methods, change ammonium carbonate into carbonic hydroammonium, making the nickel al atomic ratio is 1.2, the lanthanum nickle atom is than the Ni/La-Al that is 0.21
2O
3Catalyst.
Get this catalyst of 1.0g, carry out activity rating according to the condition described in the embodiment 2.Experimental result: 550 ℃, when the ammonia flow velocity was 333ml/min, the ammonia conversion ratio was 99.7%.
Ni/La-Al with gained among the embodiment 2
2O
3Catalyst is compared, and selects for use carbonic hydroammonium or ammonium carbonate suitable as the prepared catalyst activity of precipitating reagent.This explanation prepares the Ni-based ammonia decomposition catalyzer technology of high activity for coprecipitation, and ammonium carbonate and carbonic hydroammonium all are precipitating reagents preferably.
Embodiment 4
46g nickel nitrate, 59g aluminum nitrate, 9g lanthanum nitrate are dissolved in the 200ml absolute ethyl alcohol, and it is standby to be mixed with mixed liquor.Get stoichiometric ammonium carbonate and be dissolved in 200ml ethanol water (1: the 1) solution, standby as precipitating reagent.Under stirring above-mentioned two drips of solution are added in the same vessel, the pH value of control solution is 8.After charging finishes, stirred aging 4 hours, centrifugation spends deionised water, obtains gel.After 120 ℃ of dryings, temperature programming to 600 ℃, roasting is 6 hours in air.Making the nickel al atomic ratio is 1.2, and the lanthanum nickle atom is than the Ni/La-Al that is 0.22
2O
3Catalyst.
Get the above-mentioned catalyst of 1.0g and place stainless steel reactor, use 50%H
2-He reducing gases (100ml/min) feeds pure ammonia and carries out synthesis under normal pressure at 550 ℃ 600 ℃ of activation processing 3 hours, and the ammonia flow velocity is 333ml/min.Experimental result: the ammonia conversion ratio is 98.9%.
Ni/La-Al with gained among the embodiment 2
2O
3Catalyst is compared, and the catalyst activity of present embodiment gained is suitable.