CN118384881A - Catalyst for producing hydrogen by ammonia decomposition, preparation method, application and coating process - Google Patents

Abstract

A catalyst for hydrogen production from ammonia decomposition, a preparation method, an application and a coating process, belonging to the field of hydrogen production technology. First, an ammonia decomposition hydrogen production catalyst carrier is prepared by using an alkaline solution, which is a composite of silicon oxide and rare earth metal oxides; then an active metal salt is added thereto, and an ammonia decomposition hydrogen production catalyst is obtained by reducing it with an alkaline solution of sodium borohydride. The obtained ammonia decomposition hydrogen production catalyst can show high activity and stability in catalyzing ammonia decomposition reactions at a relatively low temperature (400°C) and a high ammonia space velocity (17400mL·g _cat ^‑1 ·h ^‑1 ). The ammonia decomposition hydrogen production catalyst is further loaded on the surface of a honeycomb ceramic, which effectively solves the problem of low activity and poor stability of the ammonia decomposition hydrogen production catalyst at a relatively low temperature and poor stability when it is coated on the surface of a honeycomb ceramic. The preparation process of the present invention is simple, and the carrier used at the same time can increase the specific surface area of the ammonia decomposition hydrogen production catalyst in contact with the gas, which can effectively improve the performance of the catalyst.

Description

Ammonia decomposition hydrogen production catalyst, preparation method and application and coating process

Technical Field

The invention belongs to the technical field of hydrogen production, and specifically relates to an ammonia decomposition hydrogen production catalyst, a preparation method and application thereof, and a coating process for loading the catalyst on the surface of a honeycomb ceramic.

Background technique

Hydrogen can be produced from water cracking, fossil fuels, methanol decomposition and chemical hydrogen storage material decomposition. It only produces water after combustion. It is a green, renewable and clean energy and is considered to be one of the most promising energy sources in the future. According to the International Energy Agency, the global demand for "green hydrogen" and "blue hydrogen" will reach 75 million tons by 2040. However, due to the low volume energy density of hydrogen, its storage and transportation problems seriously restrict the development of the hydrogen energy industry.

Ammonia (NH ₃ ) is a widely used bulk chemical with wide applications in agriculture, chemical industry and energy industry. As an efficient hydrogen storage medium (mass fraction of hydrogen reaches 17.75wt%), ammonia has the advantages of easy liquefaction storage (only 8 atmospheres are needed under normal pressure), high safety and no carbon emission, which can solve the storage and transportation problems of hydrogen.

The key to developing ammonia decomposition hydrogen production technology lies in the development of ammonia decomposition hydrogen production catalysts with high hydrogen production activity and high catalytic stability at low temperatures. At present, the ammonia decomposition hydrogen production reaction mainly uses metal catalysts such as ruthenium (Ru), iridium (Ir), nickel (Ni), iron (Fe), cobalt (Co), and manganese (Mn). Among them, the hydrogen production performance of ruthenium-based catalysts is significantly higher than that of other metals, but the cost of precious metal ruthenium catalysts is relatively high, and the current ammonia decomposition hydrogen production catalysts generally have the problems of high ammonia decomposition temperature (≥500℃) and low low-temperature hydrogen production rate.

In order to realize the industrialization of ammonia decomposition technology, it is an effective means to load the ammonia decomposition hydrogen production catalyst on the surface of the honeycomb ceramic carrier by coating technology. The catalyst coating technology mainly includes dip coating, sol-gel method, pre-coating method and chemical vapor deposition method. The composition of the coating, the characteristics of the coating slurry and the loading amount of the ammonia decomposition hydrogen production catalyst on the honeycomb ceramic are important factors affecting the overall catalyst activity. Among them, the characteristics of the coating slurry such as pH, particle size and distribution on the honeycomb ceramic, loading amount and stability are also important factors affecting the subsequent ammonia decomposition hydrogen production efficiency.

Summary of the invention

The present invention aims to solve the relevant technical difficulties in the ammonia decomposition hydrogen production technology existing in the background technology to a certain extent. To this end, the purpose of the present invention is to propose an ammonia decomposition hydrogen production catalyst, a preparation method and application, and a coating process for loading it on the surface of honeycomb ceramics. The present invention solves the related problems of low activity and poor stability of ammonia decomposition hydrogen production catalyst at relatively low temperatures (≤400°C) and poor stability when coating it on the surface of honeycomb ceramics.

The ammonia decomposition hydrogen production catalyst prepared by the present invention can stably and efficiently convert ammonia into hydrogen and nitrogen at a high space velocity. The studied coating process is: the ammonia decomposition hydrogen production catalyst is coated on a cordierite honeycomb ceramic carrier to prepare an integral catalyst, which can be applied to the industrial production of ammonia hydrogen production. The integral catalyst comprises a carrier and an active component, the carrier is a cordierite honeycomb ceramic carrier, the active component is an ammonia decomposition hydrogen production catalyst, the loading amount of the active component on the catalyst carrier is 5-30wt%, and the loading amount = (mass of the active component/(mass of the active component + mass of the cordierite honeycomb ceramic carrier))*100%; in the integral catalyst, the ammonia decomposition hydrogen production catalyst is evenly distributed, has a high loading amount and good stability, and the thickness of the active component ammonia decomposition hydrogen production catalyst coating is 0.03-0.1mm.

The first aspect of the present invention provides a method for preparing a catalyst for hydrogen production by decomposing ammonia, the steps of which are as follows (if not specifically stated, the solutions described in the present invention are all aqueous solutions):

(1) Mixing a carrier with deionized water, and ultrasonicating for 10 to 30 minutes to obtain a uniform mixed solution; adding a salt solution of a rare earth metal element to the uniform mixed solution under stirring, adding an alkaline solution to adjust the pH to 8 to 11, and continuing stirring for 10 to 60 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain a catalyst carrier for hydrogen production by decomposition of ammonia; the carrier is at least one of silicon oxide, aluminum oxide, magnesium oxide, molybdenum oxide, titanium oxide, zinc oxide, activated carbon, and carbon nanotubes; the molar ratio of deionized water, carrier, and rare earth metal element is 1000:0.5 to 5: 0.02～1; the concentration of the salt solution of the rare earth metal element is 0.1～10mol/L; the salt of the rare earth metal element is one or more of hydrated lanthanum nitrate, hydrated cerium nitrate, hydrated samarium nitrate, hydrated yttrium nitrate, and hydrated praseodymium nitrate; the alkaline solution is one of 0.1～10mol/L sodium hydroxide solution, 0.1～10mol/L potassium hydroxide solution, and 1～15mol/L ammonia solution; the drying temperature is 90～150℃, and the drying time is 2～8h; the calcination temperature is 300～700℃, and the calcination time is 1～12h;

(2) mixing the ammonia decomposition hydrogen production catalyst carrier, active metal salt and deionized water obtained in step (1), ultrasonically treating for 10 to 30 minutes to obtain a uniform solution, and continuing stirring at 20 to 70° C. for 1 to 5 hours to obtain a mixed solution; the feed mass ratio of the ammonia decomposition hydrogen production catalyst carrier, active metal salt and deionized water is 1:0.025 to 1:100 to 300, and the active metal salt is one or more of hydrated iron nitrate, hydrated cobalt nitrate, hydrated nickel nitrate, chloroplatinic acid, hydrated ruthenium chloride, and sodium chloropalladate;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution obtained in step (2) to reduce the active metal, continuing stirring for 1 to 5 hours, filtering and separating the product in the solution, and then drying to obtain ammonia decomposition hydrogen production catalyst powder; the alkaline sodium borohydride solution is a sodium hydroxide or potassium hydroxide solution (the concentration of sodium hydroxide or potassium hydroxide is 20 to 100 mmol/L) of sodium borohydride (the molar amount is 5 to 50 times the molar amount of the active metal salt), and the volume ratio of the alkaline sodium borohydride solution to the mixed solution obtained in step (2) is 20 to 100:100; the loading amount of the active metal in the ammonia decomposition hydrogen production catalyst is 0.5 to 50 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1).

The second aspect of the present invention provides a catalyst for hydrogen production by decomposing ammonia, which is prepared by the method described above.

The third aspect of the present invention provides use of the ammonia decomposition hydrogen production catalyst in preparing hydrogen by decomposing ammonia.

The ammonia decomposition hydrogen production catalyst is evaluated for ammonia decomposition performance in an ammonia decomposition fixed bed reactor: the ammonia decomposition hydrogen production catalyst is filled in a quartz tube in the fixed bed reactor; the quartz tube has an outer diameter of 8 mm and an inner diameter of 6 mm; the catalyst filling method is to weigh 10-100 mg of ammonia decomposition hydrogen production catalyst powder and 20-300 mesh quartz sand of 5-50 times the mass of the ammonia decomposition hydrogen production catalyst, grind and mix them evenly, fill them into the quartz tube, and then insert 0.5-2 cm of quartz wool at both ends to press them tightly to prevent the ammonia decomposition hydrogen production catalyst from being washed out of the quartz tube by the airflow; when the catalytic activity of the ammonia decomposition hydrogen production catalyst is tested, the catalytic reaction temperature is not higher than 400° C., and the reaction pressure is atmospheric pressure; the inlet gas composition is a mixture of ammonia and argon (ammonia accounts for 5-100% of the total volume of ammonia and argon), wherein the reaction space velocity of ammonia is controlled by an ammonia mass flowmeter to be 5000-70000 mL·g _cat ^-1 ·h ^-1 ; the activity test time of the catalyst is not less than 4 hours.

Compared with the prior art, the present invention has the following beneficial effects:

The ammonia decomposition hydrogen production catalyst prepared by the liquid phase synthesis method of the present invention has a small and uniform size of active metal particles loaded on the ammonia decomposition hydrogen production catalyst carrier (1-3 nm), and the rare earth metal oxide particles included in the ammonia decomposition hydrogen production catalyst carrier are slightly larger than the active metal particle size, which is 4-10 nm; the smaller size of the rare earth metal oxide can expose more active metal-carrier interfaces for loading active metals, resulting in stronger active metal-carrier interactions, which is beneficial to electron transfer during the reaction process, promotes the decomposition of ammonia on the surface, and thus increases the hydrogen production rate. The ammonia decomposition hydrogen production catalyst prepared by the method of the present invention exhibits high catalytic activity and excellent catalytic stability at a relatively low decomposition temperature (400°C).

The fourth aspect of the present invention provides a coating process for loading the ammonia decomposition hydrogen production catalyst on the surface of a cordierite honeycomb ceramic carrier, the steps of which are as follows:

(1) Pre-treating the cordierite honeycomb ceramic carrier: the pre-treatment process is to wash the cordierite honeycomb ceramic carrier with deionized water, then blow it with pressurized hot air to remove surface moisture, then put the cordierite honeycomb ceramic carrier into a glass container containing 0.1-5 mol/L nitric acid, and treat it at a constant temperature of 65-95° C. for 2-4 hours, and then wash the treated cordierite honeycomb ceramic carrier with deionized water and dry it; the cordierite honeycomb ceramic carrier has a pore density of 50-300 pores/square inch, a wall thickness of 0.5-0.9 mm, and a square channel size of (1.5-3.0)*(1.5-3.0) mm;

(2) preparing ammonia decomposition hydrogen production catalyst slurry for coating: the slurry is obtained by wet ball milling, and 10-100 g of zirconium balls, 5-50 mL of anhydrous ethanol, and polyvinyl alcohol, organic bentonite, polyvinyl pyrrolidone, B-98 (polyvinyl butyral) and ammonia decomposition hydrogen production catalyst in a mass ratio of 0.1-2:0.5-5:0.1-5:0.1-2:1-50 are weighed in sequence, and the mixture is put into a planetary ball mill for ball milling to obtain ammonia decomposition hydrogen production catalyst slurry, the rotation speed is set to 200-500 rpm, and the ball milling time is 5-24 h; wherein the amount of ammonia decomposition hydrogen production catalyst is 0.5-50 g, and the pH of the catalyst slurry is 5-7 (the pH is adjusted with ammonia water or dilute nitric acid with a concentration of 0.1-5 mol/L);

(3) using the coating slurry of step (2) to impregnate the cordierite honeycomb ceramic carrier pretreated in step (1), then blowing under pressure to make the slurry evenly distributed on the surface of the carrier and remove excess slurry, drying and calcining, so that the ammonia decomposition hydrogen production catalyst is loaded on the surface of the cordierite honeycomb ceramic carrier, and the loading amount of the active component ammonia decomposition hydrogen production catalyst on the cordierite honeycomb ceramic carrier is 5-30wt%; the impregnation time is 0.5-2h; the drying and calcining refers to placing the cordierite honeycomb ceramic carrier coated with the slurry with the pore direction perpendicular to the surface of the porcelain boat, drying and calcining, the drying temperature is 90-150°C, the drying time is 2-8h; the calcination temperature is 300-500°C, and the calcination time is 2-12h.

The coating process has the following advantages: simple operation. Compared with the method of pre-treating the catalyst and then compounding it with the carrier, the preparation process of the present invention is simpler. At the same time, the carrier used can increase the specific surface area of the ammonia decomposition hydrogen production catalyst in contact with the gas, which can effectively improve the performance of the catalyst. This method has low requirements for equipment, and the materials used are easy to obtain, which is suitable for industrial production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a TEM image (a) of the catalyst support for hydrogen production from ammonia decomposition and a particle size distribution diagram of rare earth metal cerium oxide on the surface of the support in Example 1 (b); it can be observed from the figure that the size distribution of the rare earth metal cerium oxide nanoparticles loaded on the surface of the catalyst support for hydrogen production from ammonia decomposition is relatively uniform, with an average size of about 5.78 nm;

FIG2 is a dark field TEM image (a) of the catalyst for hydrogen production by decomposition of ammonia after reaction and a particle size distribution diagram of active metal ruthenium nanoparticles (b) in Example 1; it can be observed from the figure that the size distribution of active metal ruthenium nanoparticles on the surface of the catalyst for hydrogen production by decomposition of ammonia in Example 1 after reaction is very uniform, about 1.72 nm;

FIG3 is a dark field TEM-EDS spectrum of the catalyst for hydrogen production from ammonia decomposition in Example 1 after reaction; it can be observed from the figure that the rare earth metal cerium oxide nanoparticles in the catalyst for hydrogen production from ammonia decomposition are uniformly grown on the surface of the support, while the active metal ruthenium is mainly distributed on the surface of the cerium oxide nanoparticles, proving the strong interaction between ruthenium and the rare earth metal cerium oxide;

FIG4 is a TEM image (a) of the catalyst for hydrogen production by decomposition of ammonia in Comparative Example 1 after the reaction and a particle size distribution diagram of active metal ruthenium nanoparticles (b); it shows that the active metal ruthenium nanoparticles loaded on the surface without rare earth metal oxides are obviously agglomerated after the ammonia decomposition reaction, and the particle size is significantly increased to about 3 to 5 nm;

FIG5 is a stability test curve of the ammonia decomposition hydrogen production catalyst in Example 1, Comparative Example 1 and Comparative Example 2; the results show that when the ammonia decomposition hydrogen production catalyst carrier includes both the carrier and the rare earth metal element oxide, the loaded active metal can exert efficient and stable catalytic activity, and at a relatively low decomposition temperature (400° C.) and a high ammonia gas space velocity (17400 mL·g _cat ^-1 ·h ^-1 ), after the catalytic reaction has lasted for 40 hours, the ammonia decomposition hydrogen production catalyst can still maintain a relatively high ammonia decomposition catalytic activity (ammonia conversion rate is about 70%);

FIG6 shows, from left to right, the cordierite honeycomb ceramic support before pretreatment (a), after pretreatment (b), and after loading the ammonia decomposition hydrogen production catalyst (c) in Example 9; it can be observed in the figure that the pretreatment process has no obvious change on the appearance of the cordierite honeycomb ceramic support, and after loading the ammonia decomposition hydrogen production catalyst on its surface, the ammonia decomposition hydrogen production catalyst interacts firmly with the cordierite honeycomb ceramic support and has excellent stability;

FIG7 shows, from left to right, SEM photographs of the cordierite honeycomb ceramic support before pretreatment (a), after pretreatment (b), and after loading the ammonia decomposition hydrogen production catalyst (c) of Example 9; it can be observed from the figure that the pretreatment process has no obvious change in the microscopic morphology of the cordierite honeycomb ceramic support, and after loading the ammonia decomposition hydrogen production catalyst on its surface, the ammonia decomposition hydrogen production catalyst is distributed more evenly on the surface of the cordierite honeycomb ceramic support.

Detailed ways

The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

Example 1

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) Mixing a magnesium oxide carrier with deionized water, and ultrasonicating for 20 minutes to obtain a mixed uniform solution; adding a hydrated cerium nitrate solution (2 mol/L) to the mixed uniform solution under stirring, then adding an ammonia solution (8 mol/L) to adjust the pH of the mixed solution to 10, and continuing stirring for 20 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain an ammonia decomposition hydrogen production catalyst carrier; wherein the molar ratio of deionized water, magnesium oxide carrier, and rare earth metal cerium element is 1000:1:0.1; the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 400°C, and the calcination time is 8 hours;

(2) mixing the dried ammonia decomposition hydrogen production catalyst support, active metal ruthenium salt (hydrated ruthenium chloride) and deionized water, ultrasonicating for 20 minutes to obtain a uniform solution, and continuing to stir at 50° C. for 3 hours; the feed mass ratio of the ammonia decomposition hydrogen production catalyst support, hydrated ruthenium chloride and deionized water is 1:0.08:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) to reduce the active metal, continuing stirring for 3 hours, filtering and separating the product in the solution, and then drying to obtain the ammonia decomposition hydrogen production catalyst powder; the alkaline sodium borohydride solution is a sodium hydroxide solution (50 mmol/L) of sodium borohydride (the molar amount of sodium borohydride is 10 times the molar amount of hydrated ruthenium chloride), and the volume ratio of the solution to the mixed solution in step (2) is 60:100; the loading amount of active metal ruthenium in the ammonia decomposition hydrogen production catalyst is 3 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1);

The TEM (transmission electron microscope) image of the ammonia decomposition hydrogen production catalyst carrier and the particle size distribution diagram of the rare earth metal cerium oxide on the carrier surface of the present embodiment are shown in FIG1 , the dark field TEM of the ammonia decomposition hydrogen production catalyst after a long-term stability test (40 h) and the particle size distribution diagram of the active metal ruthenium nanoparticles on the surface of the ammonia decomposition hydrogen production catalyst are shown in FIG2 , the dark field TEM-EDS energy spectrum of the ammonia decomposition hydrogen production catalyst after the reaction is shown in FIG3 , and the stability test results of the ammonia decomposition hydrogen production catalyst at a relatively low decomposition temperature (400° C.) and a high ammonia gas space velocity (17400 mL·g _cat ^-1 ·h ^-1 ) are shown in FIG5 .

Example 2

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) Mixing a silica carrier with deionized water, and ultrasonicating for 20 minutes to obtain a mixed uniform solution; adding a hydrated cerium nitrate solution (2 mol/L) to the mixed uniform solution under stirring, then adding an ammonia solution (8 mol/L) to adjust the pH of the mixed solution to 9, and continuing stirring for 20 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain an ammonia decomposition hydrogen production catalyst carrier; in the steps, the molar ratio of deionized water, silica carrier, and rare earth metal cerium element is 1000:1:0.1; the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 400°C, and the calcination time is 8 hours;

(2) mixing the dried ammonia decomposition hydrogen production catalyst support, active metal ruthenium salt (hydrated ruthenium chloride) and deionized water, ultrasonicating for 20 minutes to obtain a uniform solution, and continuing to stir at 50° C. for 3 hours; the feed mass ratio of the ammonia decomposition hydrogen production catalyst support, hydrated ruthenium chloride and deionized water is 1:0.08:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) to reduce the active metal, continuing stirring for 3 hours, filtering and separating the product in the solution and drying it to obtain the ammonia decomposition hydrogen production catalyst; the alkaline sodium borohydride solution is a sodium hydroxide solution (50 mmol/L) of sodium borohydride (the molar amount of sodium borohydride is 10 times the molar amount of hydrated ruthenium chloride), and the volume ratio of the solution to the mixed solution in step (2) is 60:100; the loading amount of active metal ruthenium in the ammonia decomposition hydrogen production catalyst is 5 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1).

Example 3

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) mixing an alumina carrier with deionized water, and ultrasonicating for 20 minutes to obtain a mixed uniform solution; adding a hydrated cerium nitrate solution (2 mol/L) to the mixed uniform solution under stirring, then adding an ammonia solution (8 mol/L) to adjust the pH of the mixed solution to 10, and continuing stirring for 20 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain an ammonia decomposition hydrogen production catalyst carrier; in the steps, the molar ratio of deionized water, alumina carrier, and rare earth metal cerium element is 1000:1:0.1; the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 400°C, and the calcination time is 8 hours;

(2) mixing the dried ammonia decomposition hydrogen production catalyst support, active metal ruthenium salt (hydrated ruthenium chloride) and deionized water, ultrasonicating for 20 minutes to obtain a uniform solution, and continuing to stir at 50° C. for 3 hours; the feed mass ratio of the ammonia decomposition hydrogen production catalyst support, hydrated ruthenium chloride and deionized water is 1:0.08:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) to reduce the active metal, continuing stirring for 3 hours, filtering and separating the product in the solution and drying it to obtain the ammonia decomposition hydrogen production catalyst; the alkaline sodium borohydride solution is a sodium hydroxide solution (50 mmol/L) of sodium borohydride (the molar amount of sodium borohydride is 10 times the molar amount of hydrated ruthenium chloride), and the volume ratio of the solution to the mixed solution in step (2) is 60:100; the loading amount of active metal ruthenium in the ammonia decomposition hydrogen production catalyst is 5 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1).

Example 4

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) mixing a molybdenum oxide carrier and an aluminum oxide carrier with deionized water, and ultrasonicating for 20 minutes to obtain a mixed uniform solution; adding a hydrated cerium nitrate solution (2 mol/L) to the mixed uniform solution under stirring, then adding an ammonia solution (8 mol/L) to adjust the pH of the mixed solution to 10, and continuing stirring for 20 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain an ammonia decomposition hydrogen production catalyst carrier; in the steps, the molar ratio of deionized water, molybdenum oxide carrier, and rare earth metal cerium element is 1000:0.8:0.8:0.1; the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 400°C, and the calcination time is 8 hours;

(2) mixing the dried ammonia decomposition hydrogen production catalyst support, active metal ruthenium salt (hydrated ruthenium chloride) and deionized water, ultrasonicating for 20 minutes to obtain a uniform solution, and continuing to stir at 50° C. for 3 hours; the feed mass ratio of the ammonia decomposition hydrogen production catalyst support, hydrated ruthenium chloride and deionized water is 1:0.08:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) to reduce the active metal, continuing stirring for 3 hours, filtering and separating the product in the solution and drying it to obtain the ammonia decomposition hydrogen production catalyst; the alkaline sodium borohydride solution is a sodium hydroxide solution (50 mmol/L) of sodium borohydride (the molar amount of sodium borohydride is 10 times the molar amount of hydrated ruthenium chloride), and the volume ratio of the solution to the mixed solution in step (2) is 60:100; the loading amount of active metal ruthenium in the ammonia decomposition hydrogen production catalyst is 5 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1).

Example 5

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) mixing a titanium oxide carrier with deionized water, and ultrasonicating for 20 minutes to obtain a mixed uniform solution; adding a hydrated cerium nitrate solution (2 mol/L) to the mixed uniform solution under stirring, then adding an ammonia solution (8 mol/L) to adjust the pH of the mixed solution to 10, and continuing stirring for 20 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain an ammonia decomposition hydrogen production catalyst carrier; in the steps, the molar ratio of deionized water, titanium oxide carrier, and rare earth metal cerium element is 1000:1:0.1; the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 400°C, and the calcination time is 8 hours;

(2) mixing the dried ammonia decomposition hydrogen production catalyst support, active metal ruthenium salt (hydrated ruthenium chloride) and deionized water, ultrasonicating for 20 minutes to obtain a uniform solution, and continuing to stir at 50° C. for 3 hours; the feed mass ratio of the ammonia decomposition hydrogen production catalyst support, hydrated ruthenium chloride and deionized water is 1:0.08:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) to reduce the active metal, continuing stirring for 3 hours, filtering and separating the product in the solution and drying it to obtain the ammonia decomposition hydrogen production catalyst; the alkaline sodium borohydride solution is a sodium hydroxide solution (50 mmol/L) of sodium borohydride (the molar amount of sodium borohydride is 10 times the molar amount of hydrated ruthenium chloride), and the volume ratio of the solution to the mixed solution in step (2) is 60:100; the loading amount of active metal ruthenium in the ammonia decomposition hydrogen production catalyst is 5 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1).

Example 6

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) Mixing a silicon oxide carrier, a magnesium oxide carrier and deionized water, and ultrasonicating for 20 minutes to obtain a mixed uniform solution; adding a hydrated cerium nitrate solution (2 mol/L) to the mixed uniform solution under stirring, then adding an ammonia solution (8 mol/L) to adjust the pH of the mixed solution to 10, and continuing stirring for 20 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain an ammonia decomposition hydrogen production catalyst carrier; in the steps, the molar ratio of deionized water, silicon oxide carrier, magnesium oxide carrier, and rare earth metal cerium element is 1000:0.5:0.5:0.1; the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 400°C, and the calcination time is 8 hours;

(2) mixing the dried ammonia decomposition hydrogen production catalyst carrier, active metal ruthenium salt (hydrated ruthenium chloride), active metal nickel salt (hydrated nickel nitrate) with deionized water, ultrasonicating for 20 minutes to obtain a uniform solution, and continuing stirring at 50° C. for 3 hours; the feed mass ratio of the ammonia decomposition hydrogen production catalyst carrier, hydrated ruthenium chloride, hydrated nickel nitrate and deionized water is 1:0.04:1:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) to reduce the active metal, continuing stirring for 3 hours, filtering and separating the product in the solution and drying it to obtain the ammonia decomposition hydrogen production catalyst; the alkaline sodium borohydride solution is a sodium hydroxide solution (100 mmol/L) of sodium borohydride (the molar amount of sodium borohydride is 30 times the molar amount of hydrated ruthenium chloride and hydrated nickel nitrate), and the volume ratio of the solution to the mixed solution in step (2) is 60:100; in the ammonia decomposition hydrogen production catalyst, the loading amount of active metal ruthenium is 1.5 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1), and the loading amount of active metal nickel is 18 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1).

Example 7

The preparation method of the catalyst for hydrogen production by decomposing ammonia comprises the following steps:

(1) Mixing a magnesium oxide carrier with deionized water, and ultrasonicating for 20 minutes to obtain a mixed uniform solution; under stirring, sequentially adding a hydrated cerium nitrate solution (2 mol/L) and a hydrated samarium nitrate solution (2 mol/L) to the mixed uniform solution, then adding an aqueous sodium hydroxide solution (8 mol/L) to adjust the pH of the mixed solution to 10, and continuing stirring for 20 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain an ammonia decomposition hydrogen production catalyst carrier; in the steps, the molar ratio of deionized water, silicon oxide carrier, magnesium oxide carrier, rare earth metal cerium element, and rare earth metal samarium element is 1000:0.5:0.5:0.1:0.1; the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 400°C, and the calcination time is 8 hours;

(2) mixing the dried ammonia decomposition hydrogen production catalyst carrier, active metal ruthenium salt (hydrated ruthenium chloride), active metal cobalt salt (hydrated cobalt nitrate) with deionized water, ultrasonicating for 20 minutes to obtain a uniform solution, and continuing stirring at 50° C. for 3 hours; the feed mass ratio of the ammonia decomposition hydrogen production catalyst carrier, hydrated ruthenium chloride, hydrated cobalt nitrate and deionized water is 1:0.04:1.5:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) to reduce the active metal, continuing stirring for 3 hours, filtering and separating the product in the solution and drying it to obtain the ammonia decomposition hydrogen production catalyst; the alkaline sodium borohydride solution is a potassium hydroxide solution (100 mmol/L) of sodium borohydride (the molar amount of sodium borohydride is 30 times the molar amount of hydrated ruthenium chloride and hydrated cobalt nitrate), and the volume ratio of the solution to the mixed solution in step (2) is 60:100; in the ammonia decomposition hydrogen production catalyst, the loading amount of active metal ruthenium is 1.5 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1), and the loading amount of active metal cobalt is 26 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1).

Example 8

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) mixing a carbon nanotube carrier, a magnesium oxide carrier and deionized water, and ultrasonicating for 20 minutes to obtain a mixed uniform solution; under stirring, sequentially adding a hydrated praseodymium nitrate solution (2 mol/L) and a hydrated samarium nitrate solution (2 mol/L) to the mixed uniform solution, then adding an aqueous potassium hydroxide solution (8 mol/L) to adjust the pH of the mixed solution to 10, and continuing stirring for 20 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain an ammonia decomposition hydrogen production catalyst carrier; in the steps, the molar ratio of deionized water, carbon nanotube carrier, magnesium oxide carrier, rare earth metal praseodymium element, and rare earth metal samarium element is 1000:0.2:0.8:0.1:0.1; the drying temperature is 120°C, the drying time is 6 hours, the calcination temperature is 300°C, and the calcination time is 8 hours;

(2) mixing the dried ammonia decomposition hydrogen production catalyst carrier, active metal ruthenium salt (hydrated ruthenium chloride), active metal ruthenium salt (hydrated ferric nitrate), active metal nickel salt (hydrated nickel nitrate) with deionized water, ultrasonicating for 20 minutes to obtain a uniform solution, and continuing stirring at 50° C. for 3 hours; the feed mass ratio of the ammonia decomposition hydrogen production catalyst carrier, hydrated ruthenium chloride, hydrated ferric nitrate, hydrated nickel nitrate and deionized water is 1:0.04:1.25:1.25:200;

(3) adding an alkaline sodium borohydride solution dropwise into the mixed solution in step (2) to reduce the active metal, continuing stirring for 3 hours, filtering and separating the product in the solution and drying it to obtain the ammonia decomposition hydrogen production catalyst; the alkaline sodium borohydride solution is a potassium hydroxide solution (100 mmol/L) of sodium borohydride (the molar amount of sodium borohydride is 30 times the sum of the molar amounts of hydrated ruthenium chloride, hydrated ferric nitrate and hydrated nickel nitrate), and the volume ratio of the solution to the mixed solution in step (2) is 60:100; in the ammonia decomposition hydrogen production catalyst, the loading amount of active metal ruthenium is 1.5 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1), the loading amount of active metal iron is 22 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1), and the loading amount of active metal nickel salt is 20 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier in step (1).

Comparative Example 1

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) Weigh 1 g of magnesium oxide support and mix it with 500 mL of deionized water, and ultrasonicate it for 20 min to obtain a mixed uniform solution;

(2) adding ruthenium chloride hydrate to the mixed solution of step (1), ultrasonicating for 10 minutes to obtain a uniform solution, and continuing stirring at 50° C. for 2 hours; wherein the mass ratio of the magnesium oxide carrier, ruthenium chloride hydrate and deionized water is 1:0.08:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) (the volume ratio of the solution to the mixed solution in step (2) is 60:100, the amount of sodium borohydride added is 10 times the amount of metal ruthenium, wherein the alkaline solution refers to sodium hydroxide solution (50 mmol/L)), to reduce the active metal, and continuing stirring for 5 hours, filtering and separating the product in the solution, and vacuum drying at room temperature for 12 hours to obtain ammonia decomposition hydrogen production catalyst.

TEM and surface active ruthenium nanoparticle size distribution of the ammonia decomposition catalyst of Comparative Example 1 after 8 hours of ammonia decomposition test are shown in FIG4 . The stability test results at a lower decomposition temperature (400° C.) and a high ammonia space velocity (17400 mL·g _cat ^-1 ·h ^-1 ) are shown in FIG5 .

Comparative Example 2

The preparation method of the catalyst for producing hydrogen by decomposing ammonia comprises the following steps:

(1) Weigh 1 g of cerium oxide support and mix it with 500 mL of deionized water, and ultrasonicate it for 20 min to obtain a mixed uniform solution;

(2) adding hydrated ruthenium chloride to the mixed solution of step (1), ultrasonicating for 10 minutes to obtain a uniform solution, and continuing stirring at 50° C. for 2 hours; wherein the mass ratio of the cerium oxide carrier, the active metal ruthenium salt and the deionized water is: 1:0.08:200;

(3) adding alkaline sodium borohydride solution dropwise into the mixed solution in step (2) (the volume ratio of the solution to the mixed solution in step (2) is 60:100, the amount of sodium borohydride added is 10 times the amount of metal ruthenium, wherein the alkaline solution refers to sodium hydroxide solution (50 mmol/L)) to reduce the active metal, and continuing stirring for 5 hours, filtering and separating the product in the solution, and vacuum drying at room temperature for 12 hours to obtain an ammonia decomposition hydrogen production catalyst.

The stability test results of the ammonia decomposition hydrogen production catalyst described in Comparative Example 2 at a relatively low decomposition temperature (400° C.) and a high ammonia space velocity (17400 mL·g _cat ^-1 ·h ^-1 ) are shown in FIG5 .

Ammonia decomposition performance test

The ammonia decomposition hydrogen production catalyst is evaluated for its ammonia decomposition performance in an ammonia decomposition fixed bed reactor: the ammonia decomposition hydrogen production catalyst is filled in a quartz tube in the fixed bed reactor; the quartz tube has an outer diameter of 8 mm and an inner diameter of 6 mm; the catalyst filling method is to weigh 30 mg of ammonia decomposition hydrogen production catalyst powder and 200 mesh quartz sand of 20 times the mass of the ammonia decomposition hydrogen production catalyst, grind and mix them evenly, fill them into the quartz tube, and then insert 1.0 cm of quartz wool at both ends to press them tightly to prevent the ammonia decomposition hydrogen production catalyst from being washed out of the quartz tube by the airflow; when the catalytic activity of the ammonia decomposition hydrogen production catalyst is tested, the catalytic reaction temperature is 400°C and the reaction pressure is atmospheric pressure; the inlet gas composition is a mixed gas of ammonia and argon (the volume fraction of ammonia in the total of ammonia and argon is 25%), wherein the reaction space velocity of ammonia is controlled by an ammonia mass flowmeter to be 17400 mL·g _cat ^-1 ·h ^-1 ; the activity test time of the catalyst is 8 hours. The catalytic ammonia decomposition activity test results (ammonia conversion rate) of the ammonia decomposition hydrogen production catalyst are shown in Table 1. The results in Table 1 show that the catalysts for hydrogen production by decomposing ammonia prepared in Examples 1-8 of the present invention have good stability and can exhibit high catalytic activity at low temperatures.

Table 1: Ammonia conversion rate (%) obtained from the test of ammonia decomposition hydrogen production catalyst at 400°C and ammonia space velocity of 17400 mL·g _cat ^-1 ·h ^-1

Example 1 Example 2 Example 3 Example 4 Example 5 69 75 82 87 81 Example 6 Example 7 Example 8 Comparative Example 1 Comparative Example 2 75 91 98 53 64

Example 9

The coating process of coating the active component ammonia decomposition hydrogen production catalyst on the surface of the carrier cordierite honeycomb ceramic includes:

(1) Pre-treating a cordierite honeycomb ceramic carrier; the pre-treatment process comprises washing the cordierite honeycomb ceramic carrier with deionized water, then blowing the cordierite honeycomb ceramic carrier with pressurized hot air to remove surface moisture, placing the cordierite honeycomb ceramic carrier in a glass container containing 1 mol/L nitric acid, and treating the cordierite honeycomb ceramic carrier at a constant temperature of 85° C. for 4 h, then washing the treated cordierite honeycomb ceramic carrier with deionized water and drying the cordierite honeycomb ceramic carrier; the cordierite honeycomb ceramic carrier has a pore density of 160 pores/square inch, a wall thickness of 0.7 mm, and a square channel size of 2*2 mm;

(2) preparing a coating catalyst slurry; the slurry is obtained by wet ball milling; the wet ball milling specifically comprises: weighing 50 g of zirconium balls, 50 mL of anhydrous ethanol, and polyvinyl alcohol, organic bentonite, polyvinyl pyrrolidone, B-98 and the ammonia decomposition hydrogen production catalyst prepared in Example 7 in a mass ratio of 0.5:0.5:1:1:8 in sequence, and putting them into a planetary ball mill for ball milling at a speed of 200 rpm for 24 h; wherein the amount of the ammonia decomposition hydrogen production catalyst is 10 g; the pH of the coating catalyst slurry is 5.7 (the pH is adjusted with ammonia water having a concentration of 1 mol/L);

(3) using the coating slurry described in step (2) to impregnate the cordierite honeycomb ceramic carrier pretreated in step (1), wherein the mass ratio of the active component ammonia decomposition hydrogen production catalyst to the cordierite honeycomb ceramic carrier is 1.5:10; blowing under pressure to make the surface slurry evenly distributed and removing excess slurry before drying and calcining; the impregnation time is 2 hours; the drying and calcining process refers to placing the coated cordierite honeycomb ceramic carrier on a porcelain boat with its pore direction perpendicular to the surface of the porcelain boat and drying and calcining, the drying temperature is 120°C, the drying time is 8 hours, the calcination temperature is 500°C, and the calcination time is 12 hours.

The photos of the cordierite honeycomb ceramic carrier before and after pretreatment and after coating the active component ammonia decomposition hydrogen production catalyst on the surface of the carrier cordierite honeycomb ceramic are shown in Figure 6 from left to right, and the SEM photos of the cordierite honeycomb ceramic carrier before and after pretreatment and after coating the active component ammonia decomposition hydrogen production catalyst on the surface of the carrier cordierite honeycomb ceramic are shown in Figure 7 from left to right. In the final monolithic catalyst, the loading amount of the active component ammonia decomposition hydrogen production catalyst is 21%; the ammonia decomposition hydrogen production catalyst is evenly distributed, has a high loading amount and good stability, and the thickness of the coated catalyst is about 0.05mm.

Claims (10)

1. A method for preparing a catalyst for hydrogen production by decomposing ammonia, comprising the following steps: (1) mixing a carrier with deionized water, and ultrasonicating for 10 to 30 minutes to obtain a uniform mixed solution; adding a salt solution of a rare earth metal element to the uniform mixed solution under stirring, adding an alkaline solution to adjust the pH to 8 to 11, and continuing stirring for 10 to 60 minutes; then filtering and separating the precipitate in the solution, drying and calcining to obtain a catalyst carrier for hydrogen production by decomposition of ammonia; the molar ratio of deionized water, carrier, and rare earth metal element is 1000:0.5 to 5:0.02 to 1, and the concentration of the salt solution of the rare earth metal element is 0.1 to 10 mol/L; (2) mixing the catalyst support for hydrogen production from ammonia decomposition, the active metal salt and deionized water obtained in step (1), ultrasonically treating for 10 to 30 minutes to obtain a uniform solution, and continuing stirring at 20 to 70° C. for 1 to 5 hours to obtain a mixed solution; the feed mass ratio of the catalyst support for hydrogen production from ammonia decomposition, the active metal salt and the deionized water is 1:0.025 to 1:100 to 300; (3) adding alkaline sodium borohydride solution dropwise into the mixed solution obtained in step (2) to reduce the active metal, continuing stirring for 1 to 5 hours, filtering and separating the product in the solution, and then drying to obtain ammonia decomposition hydrogen production catalyst powder; the molar amount of sodium borohydride used is 5 to 50 times the molar amount of the active metal salt used, and the volume ratio of the alkaline sodium borohydride solution to the mixed solution obtained in step (2) is 20 to 100:100; the loading amount of the active metal in the ammonia decomposition hydrogen production catalyst is 0.5 to 50 wt% of the mass of the ammonia decomposition hydrogen production catalyst carrier described in step (1). 2. The method for preparing a catalyst for hydrogen production by decomposing ammonia as claimed in claim 1, characterized in that: in step (1), the carrier is at least one of silicon oxide, aluminum oxide, magnesium oxide, molybdenum oxide, titanium oxide, zinc oxide, activated carbon, and carbon nanotubes; the salt of a rare earth metal element is one or more of hydrated lanthanum nitrate, hydrated cerium nitrate, hydrated samarium nitrate, hydrated yttrium nitrate, and hydrated praseodymium nitrate; and the alkaline solution is one of 0.1-10 mol/L sodium hydroxide solution, 0.1-10 mol/L potassium hydroxide solution, and 1-15 mol/L ammonia solution. 3. The method for preparing a catalyst for hydrogen production by decomposing ammonia as claimed in claim 1, characterized in that: in step (1), the drying temperature is 90-150° C. and the drying time is 2-8 h; the calcination temperature is 300-700° C. and the calcination time is 1-12 h. 4. The method for preparing a catalyst for hydrogen production by decomposing ammonia as claimed in claim 1, characterized in that: the active metal salt in step (2) is one or more of hydrated iron nitrate, hydrated cobalt nitrate, hydrated nickel nitrate, chloroplatinic acid, hydrated ruthenium chloride, and sodium chloropalladate. 5. The method for preparing a catalyst for hydrogen production by decomposing ammonia as claimed in claim 1, characterized in that the alkaline sodium borohydride solution in step (3) is a sodium hydroxide or potassium hydroxide solution of sodium borohydride, and the concentration of the sodium hydroxide or potassium hydroxide solution is 20 to 100 mmol/L. 6. A catalyst for hydrogen production by decomposing ammonia, characterized in that it is prepared by the method described in any one of claims 1 to 5. 7. Use of the ammonia decomposition hydrogen production catalyst as claimed in claim 6 in the preparation of hydrogen by ammonia decomposition. 8. A coating process for loading ammonia decomposition hydrogen production catalyst on the surface of a cordierite honeycomb ceramic carrier, the steps of which are as follows: (1) Pre-treating the cordierite honeycomb ceramic carrier: washing the cordierite honeycomb ceramic carrier with deionized water, then blowing with pressurized hot air to remove surface moisture, then placing the cordierite honeycomb ceramic carrier in a glass container containing 0.1 to 5 mol/L nitric acid, and treating at a constant temperature of 65 to 95° C. for 2 to 4 h, and then washing the treated cordierite honeycomb ceramic carrier with deionized water and drying; (2) preparing ammonia decomposition hydrogen production catalyst slurry for coating: weighing 10-100 g of zirconium balls, 5-50 mL of anhydrous ethanol, and polyvinyl alcohol, organic bentonite, polyvinyl pyrrolidone, polyvinyl butyral and ammonia decomposition hydrogen production catalyst in a mass ratio of 0.1-2:0.5-5:0.1-5:0.1-2:1-50 in sequence, and putting them into a planetary ball mill for ball milling, wherein the amount of ammonia decomposition hydrogen production catalyst is 0.5-50 g, and the pH of the catalyst slurry is 5-7; (3) The cordierite honeycomb ceramic carrier pretreated in step (1) is impregnated with the coating slurry described in step (2), and then the slurry is evenly distributed on the carrier surface and excess slurry is removed. The carrier is dried and calcined to load the ammonia decomposition hydrogen production catalyst on the surface of the cordierite honeycomb ceramic carrier. The loading amount of the active component ammonia decomposition hydrogen production catalyst on the cordierite honeycomb ceramic carrier is 5 to 30 wt %, and the thickness of the active component ammonia decomposition hydrogen production catalyst coating is 0.03 to 0.1 mm. 9. A coating process for loading an ammonia decomposition hydrogen production catalyst on the surface of a cordierite honeycomb ceramic carrier as described in claim 8, characterized in that: in step (1), the pore density of the cordierite honeycomb ceramic carrier is 50 to 300 pores/square inch, the wall thickness is 0.5 to 0.9 mm, and the size of the square channel is (1.5 to 3.0)*(1.5 to 3.0) mm. 10. A coating process for loading an ammonia decomposition hydrogen production catalyst on the surface of a cordierite honeycomb ceramic carrier as described in claim 8, characterized in that: step (3) drying and calcining refers to placing the cordierite honeycomb ceramic carrier coated with the slurry on a porcelain boat with its pore direction perpendicular to the surface of the porcelain boat, drying and calcining, the drying temperature is 90-150°C, the drying time is 2-8h; the calcination temperature is 300-500°C, and the calcination time is 2-12h.