CN113181957A - Low-temperature activation high-efficiency ammonia decomposition catalyst - Google Patents

Low-temperature activation high-efficiency ammonia decomposition catalyst Download PDF

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CN113181957A
CN113181957A CN202110174212.1A CN202110174212A CN113181957A CN 113181957 A CN113181957 A CN 113181957A CN 202110174212 A CN202110174212 A CN 202110174212A CN 113181957 A CN113181957 A CN 113181957A
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nickel
molecular sieve
roasting
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catalyst
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陈秉辉
廖泽凤
蔡钒
郑进保
谢建榕
张诺伟
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Xiamen University
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    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/65—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38, as exemplified by patent documents US4046859, US4016245 and US4046859, respectively
    • B01J29/66—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38, as exemplified by patent documents US4046859, US4016245 and US4046859, respectively containing iron group metals, noble metals or copper
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    • B01J37/0018—Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
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    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/04—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by decomposition of inorganic compounds, e.g. ammonia
    • C01B3/047—Decomposition of ammonia
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    • C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
    • C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
    • C01B39/04—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof using at least one organic template directing agent, e.g. an ionic quaternary ammonium compound or an aminated compound
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    • C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
    • C01B39/44—Ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38
    • C01B39/445—Ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38 using at least one organic template directing agent
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
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    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0266—Processes for making hydrogen or synthesis gas containing a decomposition step
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    • C01B2203/10—Catalysts for performing the hydrogen forming reactions
    • C01B2203/1041—Composition of the catalyst
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    • C01B2203/10—Catalysts for performing the hydrogen forming reactions
    • C01B2203/1041—Composition of the catalyst
    • C01B2203/1082—Composition of support materials
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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis

Abstract

The invention provides a low-temperature activation high-efficiency ammonia decomposition catalyst and a preparation method thereof, belonging to the field of ammonia decomposition catalysis. The catalyst is a nickel-containing FER molecular sieve, the molecular sieve takes a nickel-containing carbon material as a nickel source and a hard template agent, and metallic nickel is introduced into the FER molecular sieve in situ; the content of nickel in the nickel-containing molecular sieve is 0.1-5 wt.% in terms of nickel element; the invention also provides a preparation method of the catalyst, which specifically comprises the following steps: adding a nickel-containing carbon material, a silicon source, an aluminum source, an organic template agent, inorganic base and a solvent into a reactor according to a ratio, continuously stirring to obtain uniform sol, aging, transferring the sol to a hydrothermal reaction kettle for crystallization, filtering and washing a product after the reaction is finished, drying, roasting, performing hydrogen type transformation on the obtained molecular sieve, and finally roasting to obtain the nickel-containing FER molecular sieve. The catalyst has the advantages of rich microporous structure, short crystallization time, high catalyst activity and stability, greatly reduced temperature required by ammonia decomposition, and great industrial application potential.

Description

Low-temperature activation high-efficiency ammonia decomposition catalyst
Technical Field
The invention belongs to the technical field of ammonia decomposition catalysis, and particularly relates to a nickel-containing FER molecular sieve for effectively decomposing ammonia gas into hydrogen and nitrogen at low temperature and a synthesis method thereof.
Background
Hydrogen energy is the cleanest energy source, and its calorific value is much higher than other fuels, so it is one of the most promising alternative energy sources of future fossil energy. The hydrogen has high heat value in the combustion process, and can not generate COx and NOx emission, so the hydrogen can be used for fuel cell power generation and fuel cell electric vehicles. However, the volatility and low volumetric energy density of hydrogen make the generation, storage and transportation of hydrogen a great challenge, and the high cost of hydrogen in the storage and transportation process greatly restricts the development of hydrogen energy, for example, Mirai hydrogen fuel cell vehicles released in 2014 of toyota corporation, which use two high-pressure carbon fiber tanks to store about 120L of liquid hydrogen, the theoretical endurance under ideal conditions is 500 km, and the endurance of Mirai of the new generation released in the last year reaches 200 km, but due to the high cost of the tank equipment and the cost required for compressing hydrogen, the hydrogen energy electric vehicles have no advantage in price compared with lithium electric vehicles, and the sales of the hydrogen energy electric vehicles in north america in the past 10 years are not as high as one tesla month. Therefore, the instant hydrogen production technology becomes the most promising hydrogen energy solution.
Ammonia is a carbon-free hydrogen carrier, has a reasonably good volumetric and gravimetric energy density, and its storage and transportation processes are reasonably well established. The decomposition of ammonia to produce hydrogen avoids the storage and transportation of hydrogen and is therefore of great interest. The ammonia decomposition reaction is an endothermic reaction with an equilibrium conversion of 99.5% at 450 c, but the conversion efficiency of ammonia is not high due to kinetic limitations. The ammonia decomposition catalyst can obviously improve the reaction rate and the hydrogen production efficiency. Platinum, palladium, rhodium, ruthenium and iron were the earliest elements used as ammonia decomposition catalysts. Ganley et al examined the types of metals catalyzed by ammonia decomposition of different metals, the order of their activities being in order: ru > Ni > Rh > Co > Ir > Fe > Pt > Cr > Pd > Cu > Te, Se, Pb. The catalytic performance of ruthenium at the active temperature of ruthenium is far better than that of other metals, but the activity of ruthenium at a lower temperature is insufficient, and the conversion rate of the Ru/carbon nano tube at 450 ℃ is less than 50%. The addition of the promoter can improve the low-temperature activity of the ruthenium catalyst, for example, the alkali promoter modification of the Ru catalyst loaded on MgO or CNT can obviously improve the catalytic activity of the Ru catalyst at the temperature lower than 500 ℃. By stabilizing the Ru nanoparticles, e.g. embedding them in a stable porous oxide, and preventing their rapid deactivation by sintering, also the authors produced hydrogen gas at Cs-Ru/MWCNT below 317 ℃, which is a major breakthrough for ammonia decomposition reactions. Although these studies have improved the catalytic activity of Ru at low temperatures, it is difficult to apply ruthenium catalysts on a large scale in the automotive field since ruthenium is one of the rarest noble metals.
The researchers have extensively searched for the use of transition metal catalysts such as Fe, Co, Ni, etc. in ammonia decomposition reactions, for example, a nano-iron catalyst supported on carbon nanofibers, which shows an ammonia conversion of 92% at 550 ℃, but an iron-based catalyst is used at a relatively low temperature: (<No significant activity towards the decomposition of ammonia at 450 ℃. Okura et Al investigated Ni loading on Al2O3，CeO2，Y2O3And ammonia decomposition activity on other rare earth oxides, Ni/Y was found in all rare earth oxide supported Ni catalysts2O3Shows the highest ammonia conversion, Ni/Y2O3The conversion at 550 ℃ was 87% and was very stable over 50 h. Liu et Al chemically modified Ni with alumina and ceria, when Al3+/Ce3+For 9 days the effect is optimal, the ammonia conversion efficiency at 650 ℃ is greater than 99% at 100h reaction time. Cobalt as a single metal catalyst was also used for ammonia decomposition, with a Co/MWCNT conversion of 60.0% at 500 ℃. The addition of promoters such as calcium oxide, potassium oxide and aluminum oxide can make the cobalt oxide catalyst show 100% stable conversion rate at 525 ℃. Although Fe, Co and Ni are in the optimization of the carrierAnd alkali promoters, the decomposition temperature is improved significantly, but the conversion of these transition metals at around 450 ℃ is still behind that of Ru. Researchers have studied Fe, Ni, Co nanocatalysts supported on alumina prepared by coprecipitation, which, although having a considerable conversion rate at 500 ℃, could achieve 99% conversion rate only at 600 ℃. It has recently been found that nitrides and carbides of transition metals also exhibit catalytic activity for ammonia decomposition, but as single component catalysts they also far from achieving the targeted performance.
Both conventional high activity ruthenium catalysts and transition metal catalysts are required to achieve complete conversion of ammonia at high temperatures, even with 50% conversion at high activation temperatures. However, in the fuel cell application field, such as electric vehicles, there are great difficulties in designing, safety and cost to create a high temperature catalytic environment, so only the cheap ammonia decomposition catalyst with high low temperature decomposition rate (more than 50%) can be developed to really apply the hydrogen energy as a clean energy source in the fuel cell vehicle field! In order to increase the low temperature activity of ammonia decomposition catalysts, in recent years, developers have tried bimetallic ammonia decomposition catalysts, however, although bimetallic catalysts are better than single metal catalysts, the improvement is not sufficient to achieve the decomposition of ammonia below 450 ℃, and there have been reported nickel molybdenum nitride catalysts with the best performance, in which the initial temperature of ammonia conversion is reduced to 400 ℃, but the conversion rate is greatly increased to 550 ℃ or more.
The synergistic effect of the transition metal nitride-lithium imide composite material provides great hope for efficiently decomposing ammonia gas at low temperature, and NaNH is arranged at 530 DEG C2The ammonia conversion of (a) was 99.2%. Makepeach et al use lithium amide as a catalyst and achieve 90.7% ammonia conversion at 458 ℃. Amine/imide catalysts at relatively low temperatures: (<The accelerating effect on ammonia decomposition is larger when the temperature is 450 ℃. Recently, Ni-doped LiNH has been found2The conversion of 53% at 400 ℃ is achieved with/C. Guo et al impregnated LiNH with Fe2Above, with respect to Fe/CNT, Fe or Li alone2NH, its catalytic activity is greatly raised, and its activation temp. is as low as 350 deg.C.
FER molecular sieves are typical zeolites for commercial use,common FER molecular sieves include ferrierite, ZSM-35, Fu-9, NU-23, etc., wherein the ZSM-35 molecular sieve is a microporous ferrierite having a FER type framework structure, belonging to orthorhombic aluminosilicate. With an internal rim [010]8-membered ring in the direction (0.48 nm. times.0.35 nm) and along [001 ]]The directional 10-membered rings (0.54nm multiplied by 0.42nm) are mutually and vertically connected to form a two-dimensional channel structure, and meanwhile, six-membered rings parallel to ten-membered rings and eight-membered rings are intersected to form an elliptic FER cage. FER zeolite contains rich acid centers in uniform micropores, and can be used for skeletal isomerization of normal olefin, preparation of olefin from methanol and preparation of N2Decomposition of O and CO2The Ni/ZSM-35 catalyst can reduce the olefin content in the gasoline and increase the contents of isoparaffin and aromatic hydrocarbon. However, there are few reports of the use of ZSM-35 for ammonia decomposition catalysis.
In summary, in order to realize the wide application of hydrogen energy in the field of fuel cell electric vehicles, how to reduce the cost of the catalyst and how to improve the low-temperature conversion rate is still an urgent problem to be solved in the field of ammonia decomposition catalysts. The inventor unexpectedly finds that the framework Ni-ZSM-35 molecular sieve catalyst shows excellent performance in ammonia decomposition reaction, has excellent activity at low temperature and greatly promotes the industrialization of ammonia decomposition hydrogen fuel cells when researching the framework Ni-ZSM-35 molecular sieve catalyst.
Disclosure of Invention
Based on the purpose, the invention provides a low-temperature activation high-efficiency ammonia decomposition catalyst which is characterized in that the catalyst is a nickel-containing FER molecular sieve, a nickel-containing carbon material is used as a nickel source and a hard template agent for the nickel-containing FER molecular sieve, and metal nickel is introduced into the FER molecular sieve in situ; the content of nickel in the nickel-containing FER molecular sieve is 0.1-5 wt.%.
The FER molecular sieve is ZSM-35, Fu-9, NU-23 or other synthetic molecular sieves with FER structures.
The nickel-containing carbon material is one or more of nickel-containing activated carbon, carbon nanotubes, carbon black, graphene and biochar. The nickel-containing carbon material can be a commercial carbon material or a freshly synthesized carbon material, and the nickel content in the nickel-containing carbon material is 5-15 wt.%.
The invention also provides a preparation method of the low-temperature activation high-efficiency ammonia decomposition catalyst, which comprises the following steps:
(1) adding a nickel-containing carbon material, a silicon source, an aluminum source, an organic template agent, inorganic base and a solvent into a container according to a proportion, continuously stirring to obtain uniform sol, and aging to obtain gel;
(2) transferring the gel obtained in the step (1) to a hydrothermal reaction kettle for crystallization to obtain a crystallized product;
(3) and (3) filtering and washing the crystallized product obtained in the step (2), drying and roasting to obtain the nickel-containing FER molecular sieve.
The nickel-containing carbon material in the step (1) is a commercial nickel-containing carbon material or a freshly synthesized carbon material, and the content of nickel in the nickel-containing carbon material is 5-15 wt.%.
In the preparation method, in the step (1), the silicon source is one or more of white carbon black, silica gel, silica sol or water glass; the aluminum source is one or more of sodium aluminate, aluminum sulfate, aluminum chloride or aluminum nitrate; the organic template agent is one or more of n-butylamine, ethylenediamine, cyclohexylamine or pyrrolidine; the inorganic base is one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide; the solvent is deionized water; the inorganic alkali, the silicon source, the aluminum source, the organic template agent and the solvent are prepared according to the following molar ratio: (0.5-1.8): (10-100) SiO2:1Al2O3:(2-20)Py:(100-1000)H2O; the mass ratio of the using amount of the nickel-containing carbon material to the aluminum source is 1:0.4-1:20, preferably 1:0.8-1: 8.
The preparation method of the invention comprises the step (1) of preparing the FER molecular sieve by a conventional method in the field, preferably adding an inorganic alkali, an aluminum source and a solvent into a reactor, and stirring until the solution is clear; adding nickel-containing carbon material, ultrasonically treating, dropwise adding silica sol, continuously stirring until the mixture is in a uniform sol state, dropwise adding a template agent, stirring, standing and aging.
The stirring time of the step (1) of the preparation method is not less than 30 min; the aging time is 1-4 h, preferably 2 h.
In the step (2) of the preparation method, the crystallization temperature is 120-; the crystallization time is preferably 24-72 h; more preferably 36-48 h.
In the preparation method, deionized water and ethanol are alternately and repeatedly washed for multiple times in the washing process in the step (3); the drying is vacuum drying, the drying temperature is 60-100 ℃, and the drying time is not less than 6 hours; the roasting process adopts temperature programmed roasting, and the roasting conditions are as follows: the heating rate is 5-10 ℃/min, the roasting temperature is 500-650 ℃, and the roasting time is 4-10 h.
The preparation method of the invention can also comprise a subsequent molecular sieve transformation treatment step, which comprises the steps of putting the molecular sieve obtained in the step (3) into an ammonium salt solution for ammonium ion exchange, drying after the exchange is finished, and then roasting to obtain the Ni-HFER molecular sieve.
The ammonium salt solution used for ammonium ion exchange in the transformation step is one of aqueous solutions of ammonium chloride, ammonium nitrate and ammonium carbonate, and the concentration of the ammonium salt solution is 0.1-2.0 mol/L; the ion exchange conditions are as follows: the temperature is 60-90 ℃, the time is 2-10h, and the solid-to-liquid ratio is 1g:20-100 mL; the temperature is preferably 65 ℃, the time is 3h, and the solid-to-liquid ratio is 1g:50 mL. The roasting process in the molecular sieve transformation treatment step adopts temperature programming roasting, and the roasting conditions are as follows: the heating rate is 5-10 ℃/min, the roasting temperature is 500-650 ℃, and the roasting time is 4-10 h.
The synthesis method of the nickel-containing carbon material in the step (1) of the preparation method comprises the following steps: placing one or more of pretreated activated carbon, carbon nano tubes, carbon black, graphene and biochar in a soluble nickel salt solution, drying after loading, and then roasting in a protective atmosphere.
The nickel salt in the soluble nickel salt solution is one or more of nickel nitrate, nickel sulfate, nickel chloride and nickel acetate; the concentration of the nickel salt solution is 0.1-1 mol/L. The load adopts the modes of precipitation, impregnation, heating reflux and the like; the drying temperature is 60-80 ℃, and the drying time is 8-24 h; the protective atmosphere in the roasting process is nitrogen, inert gas or one or more of the combination of nitrogen and inert gas; the roasting process adopts temperature programming, the temperature rising rate is 5-10 ℃/min, the roasting temperature is 500-700 ℃, and the roasting time is 2-6 h.
The pretreatment process of the carbon material comprises the following specific steps: condensing and refluxing 1-10mol/L nitric acid at 60-100 ℃ for 2-8h with a solid-to-liquid ratio of 1g:2-20mL, drying at 100-120 ℃, and grinding to 120 meshes or above.
The invention provides an application of a nickel-containing FER molecular sieve, which is characterized in that the nickel-containing FER molecular sieve is used for ammonia decomposition catalytic reaction, and ammonia is pure ammonia or a mixed gas of ammonia and one or more of nitrogen and inert gases.
The reaction conditions of the ammonia decomposition reaction are as follows: the space velocity of ammonia gas is 6000-50000ml/g-1·h-1The reaction temperature is 150-400 ℃.
The invention has the following effective effects:
1. the invention adopts nickel-containing carbon material as nickel source, effectively solves the technical problem that metal nickel is difficult to be introduced in situ in the preparation process of the molecular sieve, common water-soluble nickel salt can immediately form nickel hydroxide precipitate with inorganic base in the preparation process of the molecular sieve raw material, influences the subsequent crystallization process of the molecular sieve, causes low crystallinity of the molecular sieve, and even is difficult to obtain the molecular sieve with stable crystal form structure, adopts nickel-containing carbon material with proper granularity to form uniform gel with alkaline silicon source, aluminum source, inorganic base, soft template agent and molecular sieve raw material, and nickel-carbon material can enter the molecular sieve framework in the crystallization process;
2. the method adopts a hydrothermal dynamic synthesis method, utilizes double templates to synthesize the Ni-HFER molecular sieve, wherein a nickel-containing carbon material is used as a hard template, an organic template agent is used as a soft template, the addition of the hard template agent can effectively shorten the crystallization time on the premise of not influencing the crystallinity, and meanwhile, the addition of the carbon material can reduce the thickness of a single-layer lamella of the molecular sieve, reduce the stacking degree of the molecular sieve to different degrees and is beneficial to improving the catalytic stability of the molecular sieve; meanwhile, the carbon material can generate a pore system in the roasting process, so that the function of improving the pore connectivity can be achieved, and the catalytic performance and the stability of the molecular sieve are effectively improved;
3. the Ni-HFER molecular sieve obtained by the invention uses a nickel-containing carbon material as a nickel source to introduce metallic nickel in situ of the molecular sieve, so that the microporous structure of the FER molecular sieve is not damaged, and simultaneously the concentration of ammonia at an active site is improved by using the microporous aggregation effect of the molecular sieve, so that the purpose of improving the ammonia decomposition activity of the catalyst is achieved, and the activation temperature of the ammonia decomposition catalyst is reduced (ammonia can be catalytically decomposed at 200 ℃), the conversion rate of the catalyst at 250 ℃ can reach 50%, and the conversion rate of ammonia at 350 ℃ reaches more than 90%.
Drawings
FIG. 1 is a signal diagram of the ammonia decomposition products of the molecular sieve obtained in example 1 of the present invention;
FIG. 2 is a scanning electron micrograph of the molecular sieve obtained in example 1 of the present invention;
FIG. 3 is a scanning electron micrograph of the molecular sieve obtained in example 2 of the present invention;
FIG. 4 is a scanning electron micrograph of the molecular sieve obtained in example 3 of the present invention;
FIG. 5 is a scanning electron micrograph of a molecular sieve obtained in comparative example 1 of the present invention;
FIG. 6 is an XRD pattern of the molecular sieve obtained in example 4 of the present invention;
FIG. 7 is an XRD pattern of the molecular sieve obtained in comparative example 2 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples.
The invention provides a preparation method of a low-temperature activated ammonia decomposition catalyst, which specifically comprises the following steps:
(1) adding a nickel-containing carbon material, a silicon source, an aluminum source, an organic template agent, inorganic base and a solvent into a reactor according to a ratio, continuously stirring to obtain gel, and aging for later use;
(2) transferring the gel obtained in the step (1) to a hydrothermal reaction kettle for crystallization to obtain a crystallized product;
(3) filtering the crystallized product obtained in the step (2), washing, drying and roasting to obtain a Ni-FER molecular sieve;
(4) and (4) placing the Ni-FER molecular sieve obtained in the step (3) in an ammonium salt solution for ammonium ion exchange, drying after the exchange is finished, and roasting to obtain the Ni-HFER molecular sieve.
The preparation process of the nickel-containing carbon material comprises the following steps:
(1) pretreatment of the carbon material: putting the carbon material in nitric acid, condensing and refluxing for a period of time, drying and grinding;
(2) loading nickel to obtain a nickel-containing carbon material: placing one or more of pretreated activated carbon, carbon nano tubes, carbon black, graphene and biochar in a soluble nickel salt solution, drying after loading, and then roasting in a protective atmosphere.
Example 1
(1) Carbon material pretreatment: placing 5g of carbon nano tube in 50mL of 1mol/L nitric acid, condensing and refluxing for 6h at 65 ℃, drying at 110 ℃, and grinding to be more than 120 meshes;
(2) synthesis of nickel-containing carbon material: 1g of the pretreated carbon nanotube was placed in a 10mL, 0.2mol/L Ni (NO)3)2Fully soaking in the solution, drying at 65 ℃ for 24h, then roasting in a nitrogen atmosphere, and adopting a temperature programming roasting process, wherein the specific roasting conditions are as follows: the heating rate is 5 ℃/min, the roasting temperature is 550 ℃, and the heat preservation time is 6h, so that Ni-CNT with the Ni loading of 10% is obtained;
(3) synthesis of molecular sieve precursor: under the condition of room temperature, adding 0.2g of sodium hydroxide, 0.8g of sodium metaaluminate and 30mL of deionized water into a 50mL beaker, and stirring until the solution is clear; then adding 0.1g of Ni-CNT, carrying out ultrasonic treatment for 2h, dropwise adding 15g of alkaline silica sol (30 wt.%), continuously stirring for 1h until the alkaline silica sol is in a uniform sol state, dropwise adding 5ml of pyrrolidine, stirring for 30min, standing and aging for 2h to obtain gel;
(4) synthesis of Ni-FER molecular sieve: transferring the gel into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, placing the hydrothermal reaction kettle into a homogeneous reactor for crystallization, wherein the crystallization temperature is 190 ℃, the crystallization time is 36 hours, after crystallization is finished, repeatedly washing a solid product with absolute ethyl alcohol and deionized water, then transferring the solid product into an oven, drying the solid product at 80 ℃ for 6 hours, and then transferring the solid product into a muffle furnace for temperature programmed roasting, wherein the roasting conditions are as follows: heating up at a rate of 10 ℃/min, keeping the roasting temperature at 550 ℃ for 6h to obtain about 4g of Ni-FER molecular sieve;
(5) synthesis of Ni-HFER molecular sieve: adding the obtained Ni-FER molecular sieve into 200mL of ammonium chloride solution with the concentration of 1mol/L for ion exchange, wherein the exchange time is 3h, and the exchange temperature is 65 ℃. Then transferring the mixture into a drying oven at 120 ℃ for drying for 8 hours to obtain Ni-NH4And transferring the FER molecular sieve into a muffle furnace to carry out temperature programming roasting, wherein the roasting conditions are as follows: heating to 550 ℃ at the temperature of 10 ℃/min, and preserving the heat at 550 ℃ for 6h to finally obtain the Ni-HFER molecular sieve, wherein the nickel content in the obtained molecular sieve is about 0.25 wt.% calculated by nickel.
The ammonia decomposition activation temperature of the Ni-HFER molecular sieve obtained in example 1 was determined, and the results are shown in FIG. 1. The ammonia decomposition activation temperature adopts a microphone adsorption instrument. The test process is as follows: putting a certain amount of catalyst into a U-shaped quartz tube filled with quartz wool at two ends, heating to 300 ℃ at a heating rate of 10 ℃/min in a helium atmosphere, and then preserving heat for 1 h; then the temperature is reduced to 120 ℃, and 10 percent NH is introduced3-He adsorbs for 30min and purge with helium gas until baseline is flat. And finally, carrying out temperature programmed desorption from 120 ℃ to 600 ℃ at a temperature rise rate of 10 ℃/min, and detecting desorbed species by adopting an MS detector.
It can be seen from figure 1 that there is a signal of desorbed hydrogen and nitrogen gas at 200 c, indicating that ammonia gas has started to decompose by the molecular sieve catalyst at 200 c.
Example 2
The difference between this example 2 and example 1 is that CNTs were replaced with graphene of equal mass, and the other preparation processes were the same as in example 1.
Example 3
This example 3 is different from example 1 in that CNTs were replaced with activated carbon of equal mass, and the other preparation processes were the same as example 1.
Comparative example 1
This comparative example is different from example 1 in that CNT is omitted and other preparation processes are the same as example 1.
The crystallinity and pore structure properties of the molecular sieve catalysts prepared in examples 1-3 and comparative example 1 were determined and the results are shown in table 1. The molecular sieve texture property of the invention adopts an ASAP 2460 type physical adsorption instrument, and nitrogen is used as adsorbate to carry out micro/mesoporous full static adsorption. The pretreatment procedure is as follows: and (3) carrying out vacuum pretreatment for 3h at 300 ℃. The BET specific surface area and the volume in the analysis result are measured by a multipoint method, the micropore specific surface area and the volume are measured by a t-plot method, and the mesopore specific surface area and the volume are measured by a BJH method.
TABLE 1 crystallinity and texture characteristics of the molecular sieve catalysts obtained in examples 1-3 and comparative example 1
Figure BDA0002940047450000071
The hf (hierarchy factor) index quantitatively describes the fractionation characteristics of the mesoporous molecular sieve. The formula for HF is defined as follows:
Figure BDA0002940047450000072
wherein VmicroRepresents the mesopore volume; vporeRepresents the total pore volume; (ii) a SmesoRepresents the mesoporous surface area; sBETRepresenting the total surface area. The higher the HF index is, the less the damage of mesoporous formation to micropores is, the better the pore channel connectivity of the molecular sieve is, and the faster the diffusion rate of the product is. As shown in Table 1, the HF index of the FER molecular sieves obtained in examples 1 to 3 is about 0.116, which is higher than that of the molecular sieve obtained in comparative example 1, and the effect of improving the pore connectivity due to the addition of the carbon material is probably because the carbon material is partially wrapped by the molecular sieve during the growth process, and the carbon material generates a pore system during the calcination process.
Fig. 2 to 5 are scanning electron micrographs of the molecular sieve catalysts obtained in examples 1 to 3 and comparative example 1, respectively, and the scanning electron microscopy characterization of the present invention employs a Field Emission Scanning Electron Microscope (FESEM), and the sample preparation process: placing a small amount of powder sample in ethanol solution, performing ultrasonic treatment for 30min until the powder sample is completely dispersed, sucking 1 drop of the mixed solution by using a liquid transfer gun and dripping the mixed solution on a silicon wafer, and finally drying the silicon wafer. As can be seen from fig. 2 to 5, the molecular sieve without the carbon material hard template agent has a bulk stacking morphology with a width of about 1.2 μm, and the molecular sieve added with the carbon material hard template agent has a substantially non-stacking, more three-dimensional spatial structure, and is beneficial to product diffusion.
Example 4
(1) Carbon material pretreatment: placing 5g of carbon nano tube in 50mL of 1mol/L nitric acid, condensing and refluxing for 6h at 65 ℃, drying at 110 ℃, and grinding to be more than 120 meshes;
(2) synthesis of nickel-containing carbon material: 1g of the pretreated carbon nanotube was placed in a 10mL, 0.2mol/L Ni (NO)3)2Drying the solution at 65 ℃ for 24h, then roasting the solution in a nitrogen atmosphere, and adopting a temperature programming roasting process, wherein the specific roasting conditions are as follows: the heating rate is 5 ℃/min, the roasting temperature is 550 ℃, and the heat preservation time is 6 h;
(3) synthesis of molecular sieve precursor: under the condition of room temperature, adding 0.2g of sodium hydroxide, 0.8g of sodium metaaluminate and 30mL of deionized water into a 50mL beaker, and stirring until the solution is clear; then adding 0.2gNi-CNT, carrying out ultrasonic treatment for 2h, dropwise adding 15g of alkaline silica sol (30 wt.%), continuously stirring for 1h until the alkaline silica sol is in a uniform sol state, dropwise adding 5ml of pyrrolidine, stirring for 30min, standing and aging for 2h to obtain gel;
(4) synthesis of Ni-FER molecular sieve: transferring the gel into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, placing the hydrothermal reaction kettle into a homogeneous reactor for crystallization, wherein the crystallization temperature is 180 ℃, the crystallization time is 1h, 6h, 12h, 24h, 30h, 36h and 48h respectively, after crystallization is finished, repeatedly washing a solid product by absolute ethyl alcohol and deionized water, then transferring the solid product to an oven, drying the dried product for 6h at the temperature of 80 ℃, transferring the dried product to a muffle furnace, and carrying out temperature programmed roasting, wherein the roasting conditions are as follows: heating up at a rate of 10 ℃/min, keeping the roasting temperature at 550 ℃ for 6h to obtain the Ni-FER molecular sieve;
(5) synthesis of Ni-HFER molecular sieve: adding the obtained Ni-FER molecular sieve into 200mL of ammonium chloride solution with the concentration of 1mol/L for ion exchange, wherein the exchange time is 3h, and the exchange temperature is 65 ℃. Then transferring the mixture into a drying oven at 120 ℃ for drying for 8 hours to obtain Ni-NH4And transferring the FER molecular sieve into a muffle furnace to carry out temperature programming roasting, wherein the roasting conditions are as follows: heating to 550 ℃ at a temperature of 10 ℃/min, and preserving heat for 6h at 550 ℃ to finally obtainThe molecular sieves are respectively marked as C-FER-1h, C-FER-6h, C-FER-12h, C-FER-24h, C-FER-30h, C-FER-36h and C-FER-48 h. And (3) measuring the XRD of the molecular sieve prepared in different crystallization time, wherein the XRD test conditions are as follows: cu target Ka radiation; the current is 30 mA; voltage 40kV, using high speed array detector, scan speed is: 10 degree/min, detection range is: detecting in the range of 5 degrees < 2 theta < 60 degrees.
Comparative example 2
Comparative example 2 and example 4 are different in that the use of carbon nanotubes is omitted, and the crystallization time t of the molecular sieve in step (4) is adjusted to 12h, 24h, 36h, 42h and 48h, respectively, and the obtained molecular sieves are respectively designated as FER-12h, FER-24h, FER-36h, FER-42h and FER-48h, and then XRD of the obtained molecular sieves are respectively measured.
FIGS. 6 and 7 show XRD patterns of the molecular sieve catalysts obtained in example 4 and comparative example 2 at different crystallization times, respectively, from which it can be seen that the addition of the hard template can shorten the crystallization time of the molecular sieve, the molecular sieve is completely crystallized in about 24h and completely crystallized in 36h, while the molecular sieve without the hard template is still in an amorphous state in 36 h.
Example 5
This example is different from example 1 in that 0.1g of Ni-CNT in step (3) is replaced with 0.2g of Ni-CNT, and the other preparation processes are the same as example 1.
Example 6
This example is different from example 1 in that 0.1g of Ni-CNT in step (3) is replaced with 0.4g of Ni-CNT, and the other preparation processes are the same as example 1.
Example 7
This example is different from example 1 in that 0.1g of Ni-CNT in step (3) is replaced with 1g of Ni-CNT, and the other preparation processes are the same as example 1.
Example 8
This example is different from example 1 in that 0.1g of Ni-CNT in step (3) is replaced with 2g of Ni-CNT, and the other preparation processes are the same as example 1.
Example 9
This example is different from example 1 in that 0.1g of Ni-CNT in step (3) is replaced with 0.04gNi-CNT, and the other preparation processes are the same as example 1.
Comparative example 3
(1) Carbon material pretreatment: placing 5g of carbon nano tube in 50mL of 1mol/L nitric acid, condensing and refluxing for 6h at 65 ℃, drying at 110 ℃, and grinding to be more than 120 meshes;
(2) synthesis of molecular sieve precursor: under the condition of room temperature, adding 0.2g of sodium hydroxide, 0.8g of sodium metaaluminate and 30mL of deionized water into a 50mL beaker, and stirring until the solution is clear; then adding 0.1g of CNT, carrying out ultrasonic treatment for 2 hours, dropwise adding 15g of alkaline silica sol (30 wt.%), continuously stirring for 1 hour until the alkaline silica sol is in a uniform sol state, dropwise adding 5ml of pyrrolidine, stirring for 30 minutes, standing and aging for 2 hours to obtain gel;
(3) synthesis of NaFER molecular sieve: transferring the gel into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, placing the hydrothermal reaction kettle into a homogeneous reactor for crystallization, wherein the crystallization temperature is 190 ℃, the crystallization time is 36 hours, after crystallization is finished, repeatedly washing a solid product with absolute ethyl alcohol and deionized water, then transferring the solid product into an oven, drying the solid product at 80 ℃ for 6 hours, and then transferring the solid product into a muffle furnace for temperature programmed roasting, wherein the roasting conditions are as follows: heating up at a rate of 10 ℃/min, keeping the temperature at 550 ℃ for 6h to obtain the NaFER molecular sieve;
(4) synthesis of HFER molecular sieve: adding the obtained NaFER molecular sieve into 200mL of 1mol/L ammonium chloride solution for ion exchange, wherein the exchange time is 3h, and the exchange temperature is 65 ℃. Then transferring the mixture into a drying oven at 120 ℃ for drying for 8 hours to obtain NH4And transferring the FER molecular sieve into a muffle furnace to carry out temperature programming roasting, wherein the roasting conditions are as follows: heating to 550 ℃ at the temperature of 10 ℃/min, and preserving the heat for 6h at 550 ℃ to obtain the HFER molecular sieve.
Comparative example 4
(1) Carbon material pretreatment: placing 5g of carbon nano tube in 50mL of 1mol/L nitric acid, condensing and refluxing for 6h at 65 ℃, drying at 110 ℃, and grinding to be more than 120 meshes;
(2) synthesis of molecular sieve precursor: under the condition of room temperature, adding 0.2g of sodium hydroxide, 0.8g of sodium metaaluminate and 30mL of deionized water into a 50mL beaker, and stirring until the solution is clear; then adding 0.1g of CNT, carrying out ultrasonic treatment for 2 hours, dropwise adding 15g of alkaline silica sol (30 wt.%), continuously stirring for 1 hour until the alkaline silica sol is in a uniform sol state, dropwise adding 5ml of pyrrolidine, stirring for 30 minutes, standing and aging for 2 hours to obtain gel;
(3) synthesis of NaFER molecular sieve: transferring the gel into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, placing the hydrothermal reaction kettle into a homogeneous reactor for crystallization, wherein the crystallization temperature is 190 ℃, the crystallization time is 36 hours, after crystallization is finished, repeatedly washing a solid product with absolute ethyl alcohol and deionized water, then transferring the solid product into an oven, drying the solid product at 80 ℃ for 6 hours, and then transferring the solid product into a muffle furnace for temperature programmed roasting, wherein the roasting conditions are as follows: the heating rate is 10 ℃/min, the roasting temperature is 550 ℃, and the temperature is kept for 6 h;
(4) synthesis of HFER molecular sieve: adding the obtained NaFER molecular sieve into 200mL of 1mol/L ammonium chloride solution for ion exchange, wherein the exchange time is 3h, and the exchange temperature is 65 ℃. Then transferring the mixture into a drying oven at 120 ℃ for drying for 8 hours to obtain NH4And transferring the FER molecular sieve into a muffle furnace to carry out temperature programming roasting, wherein the roasting conditions are as follows: heating to 550 ℃ at a speed of 10 ℃/min, and preserving the heat at 550 ℃ for 6h to obtain the HFER molecular sieve;
(5) synthesis of Ni-HFER molecular sieve: the molecular sieve was adjusted to 10mL, 0.2mol/L Ni (NO)3)2Soaking in the solution, drying at 65 ℃ for 24h, then roasting in nitrogen atmosphere, and adopting a temperature programming roasting process, wherein the specific roasting conditions are as follows: the heating rate is 5 ℃/min, the roasting temperature is 550 ℃, and the heat preservation time is 6 h; the nickel content of the resulting molecular sieve was about 0.25 wt.%, calculated as nickel.
Example 10
The molecular sieve catalyst obtained in the above example was used in ammonia decomposition reaction, and the catalyst evaluation system was as follows:
the activity of the catalyst was evaluated by ammonia decomposition hydrogen production reaction. The evaluation of the catalyst activity was carried out in a fixed-bed reactor at normal pressure, the reactor diameter being 6 mm. The amount of catalyst used was 200 mg. The catalyst is firstly purged by inert gas for 1h, then is switched to feed gas ammonia gas, and reacts after the temperature is raised, wherein the test airspeed is 10000 ml/g.h, and the reaction temperature is 300 ℃. Reaction product H2And N2Analyzed by Shimadzu GC gas chromatograph. The gas chromatography TCD detector temperature and column box temperature were 110 ℃, and the chromatography carrier gas was argon. Detection of ammonia slip at different decomposition temperaturesThe results of the conversion and the ammonia conversion are shown in Table 2.
The ammonia conversion rate calculation formula is as follows:
conversion rateNH3Is equal to (input NH)3Total amount-output NH3Total)/input NH3The total amount is multiplied by 100 percent;
the hydrogen production rate calculation formula is as follows:
hydrogen generation Rate V (mmol. g)-1·min-1) (ammonia flow rate/22.4 Xconversion)NH3) X 1.5/catalyst mass.
TABLE 2 Performance of the molecular sieve catalysts obtained in the examples in the decomposition reaction of ammonia
Figure BDA0002940047450000111
As can be seen from Table 2, the Ni-HFER molecular sieve catalysts obtained in the examples of the present invention all have good ammonia decomposition catalytic activity, and can achieve about 50% conversion rate at 250 ℃, and the ammonia decomposition conversion rate at 350 ℃ can achieve more than 90%, and meanwhile, the comparative examples and comparative examples can find that the Ni-HFER molecular sieve prepared by the impregnation method has low activity, and the effective ammonia conversion rate at low temperature (< 350 ℃) can not be obtained by trying to adjust the preparation process, the Ni introduced by the impregnation method can easily block micropores, while the microporous structure of the FER molecular sieve can not be damaged by introducing Ni in situ, and the microporous structure of the FER molecular sieve can be damaged by the impregnation method, so that the activity of the catalyst can be reduced.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the invention, and it should be understood by those skilled in the art that various modifications and changes in equivalent structure or equivalent flow, or direct or indirect application to other related fields without creative efforts based on the technical solutions of the present invention may be made within the scope of the present invention.

Claims (10)

1. The catalyst is a nickel-containing FER molecular sieve, wherein the nickel-containing FER molecular sieve takes a nickel-containing carbon material as a nickel source and a hard template agent, and metallic nickel is introduced into the FER molecular sieve in situ; the content of nickel in the nickel-containing FER molecular sieve is 0.1-5 wt.%.
2. The ammonia decomposition catalyst according to claim 1, characterized in that: the nickel-containing carbon material is one or more of nickel-containing activated carbon, carbon nanotubes, carbon black, graphene and biochar; the nickel content in the nickel-containing carbon material is 5-15 wt.%.
3. The method for preparing a high-efficiency ammonia decomposition catalyst with low temperature activation according to any one of claims 1 to 2, characterized by comprising the steps of:
(1) adding a nickel-containing carbon material, a silicon source, an aluminum source, an organic template agent, inorganic base and a solvent into a container according to a proportion, continuously stirring to obtain uniform sol, and aging to obtain gel;
(2) transferring the gel obtained in the step (1) to a reactor for crystallization to obtain a crystallization product, wherein the crystallization temperature is 120-220 ℃, and the crystallization time is 24-72 h;
(3) and (3) filtering and washing the crystallized product obtained in the step (2), drying and roasting to obtain the nickel-containing FER molecular sieve.
4. The method according to claim 3, wherein: the synthesis method of the nickel-containing carbon material in the step (1) comprises the following steps: placing one or more of pretreated activated carbon, carbon nano tubes, carbon black, graphene and biochar in a soluble nickel salt solution, drying after loading, and then roasting in a protective atmosphere.
5. The method according to claim 4, wherein: the soluble nickel salt is one or more of nickel nitrate, nickel sulfate, nickel chloride and nickel acetate; the concentration of the soluble nickel salt solution is 0.1-1 mol/L; the load adopts the modes of precipitation, impregnation, heating reflux and the like; the drying temperature is 60-80 ℃, and the drying time is 8-24 h; the protective atmosphere in the roasting process is one or a combination of nitrogen and inert gas; the roasting process adopts temperature programming, the temperature rising rate is 5-10 ℃/min, the roasting temperature is 500-700 ℃, and the roasting time is 2-6 h.
6. The method according to claim 3, wherein:
the silicon source in the step (1) is one or more of white carbon black, silica gel, silica sol or water glass; the aluminum source is one or more of sodium aluminate, aluminum sulfate, aluminum chloride or aluminum nitrate; the organic template agent is one or more of n-butylamine, ethylenediamine, cyclohexylamine or pyrrolidine; the inorganic base is one or more of sodium hydroxide, potassium hydroxide and lithium hydroxide; the solvent is deionized water; the inorganic alkali, the silicon source, the aluminum source, the organic template agent and the solvent are prepared according to the following molar ratio: (0.5-1.8): (10-100) SiO2:1Al2O3:(2-20)Py:(100-1000)H2O; the mass ratio of the nickel-containing carbon material to the aluminum source is 1:0.4-1:20, preferably 1:0.8-1: 8.
7. The method according to claim 3, wherein: the crystallization temperature in the step (2) is preferably 170-200 ℃, and the crystallization time is preferably 36-48 h; in the step (3), the roasting adopts temperature programming roasting, and the roasting conditions are as follows: the heating rate is 5-10 ℃/min, the roasting temperature is 500-650 ℃, and the roasting time is 4-10 h.
8. The method according to claim 3, wherein: and (3) carrying out transformation treatment on the nickel-containing FER molecular sieve obtained in the step (3), specifically, putting the nickel-containing FER molecular sieve obtained in the step (3) into an ammonium salt solution for ammonium ion exchange, drying after the exchange is finished, and finally roasting to obtain the Ni-HFER molecular sieve.
9. The method of claim 8, wherein: the ammonium salt solution is one of aqueous solutions of ammonium chloride, ammonium nitrate and ammonium carbonate, and the concentration of the ammonium salt solution is 0.1-2.0 mol/L; the ion exchange conditions are as follows: the temperature is 60-90 ℃, the time is 2-10h, and the solid-to-liquid ratio is 1g:20-100 mL.
10. The use of any one of the low temperature activated high efficiency ammonia decomposition catalysts of claims 1-2, wherein: the catalyst is used for ammonia decomposition catalytic reaction, and the ammonia is pure ammonia or a mixed gas of the ammonia and one or more of nitrogen and inert gases.
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