Integral structure type ammonia decomposition catalyst based on metal honeycomb carrier, manufacturing method and application
By forming a dense nickel metal film layer on a metal honeycomb carrier, the monolithic structure of the ammonia decomposition catalyst solves the problems of high catalyst bed resistance and short service life, and achieves a highly efficient ammonia decomposition reaction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-11
- Publication Date
- 2026-04-03
AI Technical Summary
The reduction in size during the molding process of existing ammonia decomposition catalysts leads to high bed resistance, increasing system operating pressure and cost. Furthermore, the accumulation of small particles results in uneven bed resistance, affecting catalyst utilization and service life.
An integral structured ammonia decomposition catalyst based on a metal honeycomb support was prepared by forming a dense nickel metal film on the support surface through an oxidation-reduction treatment technique, and loading active metals and auxiliary metals.
It effectively reduces catalyst bed resistance, improves catalyst corrosion resistance and service life, and is suitable for high-space-velocity ammonia decomposition reactions.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of ammonia decomposition catalyst technology, specifically to an integral structure ammonia decomposition catalyst based on a metal honeycomb carrier, its preparation method, and its application. Background Technology
[0002] The ammonia decomposition reaction involves ammonia molecules undergoing adsorption, stepwise dehydrogenation, nitrogen atom recombination and desorption, and hydrogen atom recombination and desorption on a catalyst surface. Among these, the elementary reactions of ammonia molecule dissociation and nitrogen atom recombination and desorption have high activation energies and are potentially rate-determining steps. The role of the catalyst is to lower the activation energy of the elementary reactions and increase the reaction rate. Traditional ammonia decomposition typically occurs above 650℃, even reaching 800℃, to achieve ammonia conversion rates exceeding 99%. Traditional ammonia decomposition catalysts usually use non-precious metals such as Ni or Fe as the active component, loading them onto the surface of composite oxides to improve the dispersion of the active component and thus obtain good ammonia decomposition performance.
[0003] In recent years, the development of the hydrogen energy industry has been limited by the bottleneck problems of difficult and costly hydrogen storage and transportation. Ammonia, as an ideal hydrogen storage medium, has attracted much attention, and ammonia decomposition reaction has become a research hotspot. The research and development of low-temperature and high-efficiency ammonia decomposition catalysts is crucial. Theoretical studies have found that the noble metal Ru has a moderate Ru-N bond energy with the nitrogen atom (N) in ammonia molecules, which is conducive to promoting the adsorption, dehydrogenation, and reorganization and desorption of ammonia molecules. Therefore, Ru-based catalysts exhibit the highest ammonia decomposition activity among single metal catalysts. At temperatures as low as 450℃, some Ru-based catalysts (such as Ru / MgO(111)) can achieve an ammonia conversion rate of 98%~99%, which is significantly lower than the temperature required by traditional Ni-based catalysts.
[0004] Given Ru's noble metal properties, to reduce catalyst costs, it is common practice to highly disperse Ru on the support surface by selecting a suitable support, thereby reducing the amount of noble metal used. Materials with high specific surface area and good electronic conductivity, such as carbon supports, non-metallic oxides, and metal oxides, are often chosen as supports for Ru loading. Ammonia decomposition reactions utilize fixed-bed reactors. Considering both catalyst strength and the heat and mass transfer process of the materials, the catalyst needs to be shaped. Common fixed-bed catalysts include cylindrical, spherical, strip-shaped, Raschig ring, and honeycomb structures. Simultaneously, ammonia decomposition is a volume-increasing chemical reaction; reducing system pressure is beneficial for its progress. Therefore, ammonia decomposition reactions are usually carried out under near-atmospheric pressure conditions, with the chemical reaction occurring near the catalyst surface. To improve catalyst activity, the catalyst's shape is relatively small (millimeter-scale), resulting in higher bed resistance. Summary of the Invention
[0005] In existing technologies, reducing the catalyst size to improve catalyst quality leads to high catalyst bed resistance, which in turn increases system operating pressure, reactor processing costs, and equipment operating costs. Furthermore, the accumulation of small catalyst particles causes uneven bed resistance, resulting in channeling or wall flow, and the creation of central dead zones that affect catalyst utilization and lifespan. This paper provides a monolithic ammonia decomposition catalyst based on a metal honeycomb carrier, its manufacturing method, and its application. This effectively reduces the increase in catalyst bed resistance during the reaction process, thereby improving the corrosion resistance of the carrier surface and extending its service life.
[0006] The technical solution adopted by this invention to solve its technical problem is: a method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier, comprising the following steps: Step 1: Immersing a metal honeycomb carrier containing nickel metal in its components in an acidic solution to remove surface oxides; Step 2: Placing the metal honeycomb carrier immersed in the acidic solution in an oxidizing atmosphere to allow the nickel metal in the metal honeycomb carrier to undergo an oxidation reaction, generating nickel oxide; Step 3: Placing the oxidized metal honeycomb carrier in a hydrogen reducing atmosphere to reduce the nickel oxide to nickel metal, forming a dense nickel metal film layer on the surface of the metal honeycomb carrier; Step 4: Mixing the active metal component with an auxiliary metal salt to prepare a mixed slurry; Step 5: Immersing the reduced metal honeycomb carrier in the mixed slurry, thereby loading the active metal component and the auxiliary metal salt onto the metal honeycomb carrier; Step 6: Calcining the metal honeycomb carrier loaded with the active metal component and the auxiliary metal salt to obtain an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier.
[0007] Furthermore, in step one, the minimum mass percentage of nickel metal in the metal honeycomb carrier is 50%.
[0008] Furthermore, in step two, the oxidizing atmosphere is a mixture of argon and oxygen, with the oxygen volume percentage in the oxidizing atmosphere ranging from 5% to 10 vol%; the oxidation reaction temperature range is 300 to 500°C; and the oxidation time is 2 to 3 hours.
[0009] Furthermore, in step three, the hydrogen reduction atmosphere is a mixture of hydrogen and argon, with the volume percentage of hydrogen in the hydrogen reduction atmosphere ranging from 1% to 5%; the temperature range of the reduction reaction is 350 to 450°C; and the reduction time is 1 to 3 hours.
[0010] Furthermore, in step four, the active metal component is ruthenium metal or nickel metal; the auxiliary metal salt is an alkaline earth metal or a rare earth metal salt.
[0011] Furthermore, in step five, when the active metal component is ruthenium, the ruthenium loading accounts for 1 to 3% of the mass fraction of the loading component composed of the active metal and the auxiliary oxide; when the active metal component is nickel, the nickel loading accounts for 8 to 12% of the mass fraction of the loading component composed of the active metal and the auxiliary oxide.
[0012] Furthermore, in step six, the roasting temperature is 500–700 degrees Celsius, and the roasting time is 4–8 hours.
[0013] A method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb support. The integrally structured ammonia decomposition catalyst based on a metal honeycomb support comprises a metal honeycomb support, wherein the minimum nickel metal content in the metal honeycomb support is 50%; the surface of the metal honeycomb support is covered with a dense nickel metal film; an active metal and an auxiliary metal oxide are loaded on the metal honeycomb support; the active metal component and the auxiliary metal oxide are loaded on the nickel metal film; the active metal component is ruthenium or nickel metal, wherein when the active metal component is ruthenium metal, the ruthenium loading is 1-3%, and when the active metal component is nickel metal, the nickel loading is 8-12%.
[0014] An application of an integral structured ammonia decomposition catalyst based on a metal honeycomb carrier, wherein the integral structured ammonia decomposition catalyst based on a metal honeycomb carrier is used in the ammonia decomposition hydrogen production process.
[0015] This invention discloses an integral structure ammonia decomposition catalyst based on a metal honeycomb carrier, its preparation method, and its application. The prepared catalyst is an integral catalyst suitable for high space velocity ammonia decomposition reactions. By employing oxidation-reduction treatment technology, a dense nickel metal protective layer is formed on the surface of the metal carrier, effectively isolating the possible metal nitriding reaction between ammonia molecules and bulk metal atoms, thereby improving the catalyst's corrosion resistance and extending its service life. Detailed Implementation
[0016] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0017] The present invention discloses a method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier; comprising the following steps:
[0018] Step 1: Immerse the metal honeycomb carrier containing nickel in an acidic solution to remove surface oxides;
[0019] Step 2: The metal honeycomb carrier, after being soaked in the acidic solution, is placed in an oxidizing atmosphere, causing the nickel metal in the metal honeycomb carrier to undergo an oxidation reaction, generating nickel oxide;
[0020] Step 3: Place the oxidized metal honeycomb carrier in a hydrogen reducing atmosphere to reduce nickel oxide to nickel metal, forming a dense nickel metal film on the surface of the metal honeycomb carrier.
[0021] Step 4: Mix the active metal component with the auxiliary metal salt to form a mixed slurry;
[0022] Step 5: Immerse the reduced metal honeycomb carrier in the mixed slurry; so that the active metal components and auxiliary metal salts are loaded on the metal honeycomb carrier;
[0023] Step 6: Calcining the metal honeycomb support loaded with active metal components and auxiliary metal salts; obtaining an integral structural ammonia decomposition catalyst based on the metal honeycomb support.
[0024] In step one, during the preparation of the metal honeycomb carrier, nickel metal is mixed with other metal elements in a certain proportion to form a mixed alloy material for subsequent honeycomb carrier processing and molding. The minimum mass percentage of nickel metal in the metal honeycomb carrier is 50%, ensuring sufficient nickel for subsequent redox reactions and the formation of a nickel metal protective layer. In step two, the metal honeycomb carrier containing nickel metal is placed in an oxidizing atmosphere, such as a mixture of 5-10 vol% oxygen and argon, to undergo an oxidation reaction. Argon is incorporated into the atmosphere as a balancing gas to precisely reduce the partial pressure of the active gas, slowing down the reaction rate and allowing sufficient time for the heat released by the oxidation reaction to dissipate. This ensures that the entire catalyst bed reaches the target temperature uniformly and stably, achieving uniform heat distribution and preventing localized overheating or underheating, thus achieving overall uniform oxidation. This also prevents the metal honeycomb support from deforming, cracking, or sintering due to thermal stress caused by the exothermic oxidation reaction. The oxidation reaction temperature is 300–500℃, and the time is 2–3 hours, resulting in the oxidation of nickel metal within the metal honeycomb support to form nickel oxide. The specific reaction process is as follows:
[0025] 2Ni + O₂ = 2NiO
[0026] Because nickel metal has a relatively fast oxidation rate, and the nickel metal content in the metal carrier is at least 50%, a large amount of nickel oxide can be rapidly generated on the surface of the metal honeycomb carrier during the oxidation reaction. A nickel oxide film structure is formed and covers the corresponding surface of the metal honeycomb carrier, thereby preventing oxygen from further diffusing into the metal carrier. Specifically, the oxidation effect of the above oxidation reaction process is controlled by controlling the oxygen concentration and oxidation temperature during the oxidation process.
[0027] In step three, the metal honeycomb support with a nickel oxide coating formed on its surface after oxidation is placed in a hydrogen reducing atmosphere; wherein the hydrogen reducing atmosphere is a mixture of hydrogen and argon; the volume percentage of hydrogen is 1-5% and the reduction temperature is 350-450℃; the reduction time is 1-3 hours; specifically, the metal honeycomb support with nickel oxide coating on its surface undergoes the following reaction in the hydrogen reducing atmosphere:
[0028] NiO + H₂ → Ni + H₂O
[0029] Therefore, nickel oxide on the carrier surface forms a metallic nickel film under the reduction of hydrogen gas. Due to the small size, strong diffusion ability, and fast diffusion rate of hydrogen molecules, during the reduction reaction, hydrogen molecules can quickly pass through the nickel metal protective layer and react with the nickel oxide inside the film. This ensures that the reduction reaction does not only occur on the surface of the film, achieving a thorough reduction of the nickel oxide film from the surface inwards. The nickel oxide formed during the oxidation process is fully reduced to metallic nickel. When the oxygen in the nickel oxide film is completely removed, the reduced metallic nickel atoms rearrange and stack, forming a continuous and complete dense nickel metal protective layer. Similarly, hydrogen molecules diffused into the nickel oxide film combine with oxygen atoms to form water molecules. These water molecules can then travel along the original hydrogen gas path. The reverse diffusion path of the molecules fully expels the formed water molecules, thereby completely metallizing the surface NiO and forming a complete and continuous dense nickel metal protective layer. This improves the corrosion resistance of the catalyst and extends its service life. Similarly, the hydrogen reduction atmosphere is a mixture of hydrogen and argon. By mixing hydrogen and argon as the reducing gas, the reduction rate is reduced compared to pure hydrogen, effectively controlling the reduction process. During the reduction process, argon helps to evenly distribute heat, avoiding local high or low temperatures and ensuring stable temperature during the reduction process. In the above reduction reaction process, the reduction effect of hydrogen on nickel oxide is comprehensively controlled by controlling the hydrogen concentration, reduction temperature, and process parameters, such as heating rate and distribution reduction.
[0030] In step four, an active metal component, such as a ruthenium or nickel metal salt, is mixed with an auxiliary metal salt, such as an alkaline earth metal oxide or a rare earth metal oxide, to prepare a slurry for subsequent loading of the active metal component and auxiliary on the metal honeycomb carrier. In step five, the reduced metal honeycomb carrier is immersed in the mixed slurry containing the active metal component and auxiliary metal salt prepared in step four, so that the active metal component and auxiliary metal salt are loaded on the metal honeycomb carrier, realizing the loading of the active metal component and auxiliary metal salt on the metal honeycomb carrier. Loading on a honeycomb support; wherein, when the active metal component is ruthenium metal, the ruthenium loading is 1-3% (by mass ratio of the active metal and the auxiliary oxide), and when the active metal component is nickel metal, the nickel loading is 8-12% (by mass ratio of the active metal and the auxiliary oxide); in step six: the metal honeycomb support loaded with the active metal component and the auxiliary metal salt is calcined; to obtain an integral structural ammonia decomposition catalyst based on the metal honeycomb support, wherein the calcination temperature is 500-700 degrees Celsius and the calcination time is 4-8 hours.
[0031] The following examples further illustrate the preparation method of the monolithic ammonia decomposition catalyst based on a metal honeycomb support disclosed in this application.
[0032] Example 1
[0033] Step 1: Immerse the metal honeycomb carrier containing nickel in an acidic solution to remove surface oxides; the nickel content of the metal honeycomb carrier is 50%.
[0034] Step 2: The metal honeycomb carrier with a nickel metal content of 50% after being soaked in acidic solution is placed in a mixed atmosphere of oxygen and argon, where the volume percentage of argon is 5 vol%, and oxidized at 300°C for 2 hours, so that the nickel metal in the metal honeycomb carrier undergoes an oxidation reaction to form a nickel oxide film layer.
[0035] Step 3: Place the oxidized metal honeycomb carrier in a mixed atmosphere containing hydrogen and argon, where the volume percentage of hydrogen is 1%; reduce it at 350℃ for 1 hour to reduce the nickel oxide on the surface of the metal honeycomb carrier to nickel metal, forming a dense nickel metal film on the surface of the metal honeycomb carrier.
[0036] Step 4: Mix the active metal component with the auxiliary metal salt to form a mixed slurry; wherein the active metal component is ruthenium metal salt, and the auxiliary metal salt is an alkaline earth metal or rare earth metal oxide;
[0037] Step 5: Immerse the reduced metal honeycomb carrier in the mixed slurry; so that the active metal components and auxiliary metal salts are loaded on the metal honeycomb carrier; wherein the ruthenium metal loading is 1%;
[0038] Step 6: The metal honeycomb support loaded with active metal components and auxiliary metal salts is calcined at 500°C for 4 hours to obtain an integral ammonia decomposition catalyst based on the metal honeycomb support.
[0039] Example 2
[0040] Step 1: Immerse the metal honeycomb carrier containing nickel in an acidic solution to remove surface oxides; the nickel content of the metal honeycomb carrier is 50%.
[0041] Step 2: The metal honeycomb carrier with a nickel metal content of 60% after being soaked in acidic solution is placed in a mixed atmosphere of oxygen and argon, where the argon volume percentage is 8 vol%, and oxidized at 400℃ for 3 hours, so that the nickel metal in the metal honeycomb carrier undergoes an oxidation reaction to form a nickel oxide film layer.
[0042] Step 3: Place the oxidized metal honeycomb carrier in a mixed atmosphere containing hydrogen and argon, where the volume percentage of hydrogen is 3%; reduce it at 400℃ for 2 hours to reduce the nickel oxide on the surface of the metal honeycomb carrier to nickel metal, forming a dense nickel metal film on the surface of the metal honeycomb carrier.
[0043] Step 4: Mix the active metal component with the auxiliary metal salt to form a mixed slurry; wherein the active metal component is ruthenium metal salt, and the auxiliary metal salt is alkaline earth metal or rare earth metal salt;
[0044] Step 5: Immerse the reduced metal honeycomb carrier in the mixed slurry; so that the active metal components and auxiliary metal salts are loaded on the metal honeycomb carrier; wherein the ruthenium metal loading is 2%;
[0045] Step 6: The metal honeycomb support loaded with active metal components and auxiliary metal salts is calcined at 600℃ for 5 hours to obtain an integral ammonia decomposition catalyst based on the metal honeycomb support.
[0046] Example 3
[0047] Step 1: Immerse the metal honeycomb carrier containing nickel in an acidic solution to remove surface oxides; the nickel content of the metal honeycomb carrier is 50%.
[0048] Step 2: The metal honeycomb carrier with a nickel metal content of 80% after being soaked in acidic solution is placed in a mixed atmosphere of oxygen and argon, where the argon volume percentage is 10 vol%, and oxidized at 500℃ for 3 hours, so that the nickel metal in the metal honeycomb carrier undergoes an oxidation reaction to form a nickel oxide film layer.
[0049] Step 3: Place the oxidized metal honeycomb carrier in a mixed atmosphere containing hydrogen and argon, where the volume percentage of hydrogen is 5%; reduce it at 400℃ for 2 hours to reduce the nickel oxide on the surface of the metal honeycomb carrier to nickel metal, forming a dense nickel metal film layer on the surface of the metal honeycomb carrier.
[0050] Step 4: Mix the active metal component with the auxiliary metal salt to form a mixed slurry; wherein the active metal component is a nickel metal salt, and the auxiliary metal salt is an alkaline earth metal or a rare earth metal salt;
[0051] Step 5: Immerse the reduced metal honeycomb carrier in the mixed slurry; so that the active metal components and auxiliary metal salts are loaded on the metal honeycomb carrier; wherein the nickel metal loading is 12%;
[0052] Step 6: The metal honeycomb support loaded with active metal components and auxiliary metal salts is calcined at 600°C for 5 hours to obtain an integral structural ammonia decomposition catalyst based on the metal honeycomb support.
[0053] An integral ammonia decomposition catalyst based on a metal honeycomb support is prepared by the method described above. The catalyst comprises a metal honeycomb support containing at least 50% nickel metal; a dense nickel metal film covering the metal honeycomb support; an active metal component and an auxiliary metal oxide loaded on the metal honeycomb support; the active metal component and the auxiliary metal oxide loaded on the nickel metal film; the active metal component is ruthenium or nickel metal, wherein when the active metal component is ruthenium, the ruthenium loading is 1–3%; and when the active metal component is nickel, the nickel loading is 8–12%.
[0054] An application of an integral structured ammonia decomposition catalyst based on a metal honeycomb carrier, wherein the integral structured ammonia decomposition catalyst based on a metal honeycomb carrier is used in an ammonia decomposition hydrogen production process.
[0055] When the mass of the active metal and auxiliary oxide loaded on the metal honeycomb carrier is 0.3 g, in 10000 mL.g -1 .h -1 At space velocity, the ammonia decomposition conversion rates of the monolithic ammonia decomposition catalysts based on metal honeycomb carriers prepared in Examples 1-3 at different evaluation temperatures are as follows;
[0056]
[0057] Although the above embodiments have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the above descriptions are merely embodiments of the present invention and do not limit the scope of patent protection of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.
Claims
1. A method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier, characterized in that: Includes the following steps: Step 1: Immerse the metal honeycomb carrier containing nickel in an acidic solution to remove surface oxides; Step 2: The metal honeycomb carrier, after being soaked in the acidic solution, is placed in an oxidizing atmosphere, causing the nickel metal in the metal honeycomb carrier to undergo an oxidation reaction, generating nickel oxide; Step 3: Place the oxidized metal honeycomb carrier in a hydrogen reducing atmosphere to reduce nickel oxide to nickel metal, forming a dense nickel metal film on the surface of the metal honeycomb carrier. Step 4: Mix the active metal component with the auxiliary metal salt to form a mixed slurry; Step 5: Immerse the reduced metal honeycomb carrier in the mixed slurry; so that the active metal components and auxiliary metal salts are loaded on the metal honeycomb carrier; Step 6: Calcining the metal honeycomb support loaded with active metal components and auxiliary metal salts; obtaining an integral structural ammonia decomposition catalyst based on the metal honeycomb support.
2. The method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier according to claim 1, characterized in that: In step one, the minimum mass percentage of nickel metal in the metal honeycomb carrier is 50%.
3. The method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier according to claim 1, characterized in that: In step two, the oxidizing atmosphere is a mixture of argon and oxygen, with the oxygen volume percentage in the oxidizing atmosphere ranging from 5% to 10 vol%; the oxidation reaction temperature range is 300 to 500°C; and the oxidation time is 2 to 3 hours.
4. The method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier according to claim 1, characterized in that: In step three, the hydrogen reduction atmosphere is a mixture of hydrogen and argon, and the volume percentage of hydrogen in the hydrogen reduction atmosphere ranges from 1% to 5%; the temperature range of the reduction reaction is 350 to 450°C; and the reduction time is 1 to 3 hours.
5. The method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier according to claim 1, characterized in that: In step four, the active metal component is ruthenium metal or nickel metal; the auxiliary metal salt is an alkaline earth metal or a rare earth metal salt.
6. The method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier according to claim 5, characterized in that: In step five, when the active metal component is ruthenium, the ruthenium loading accounts for 1 to 3% of the mass fraction of the loading component composed of the active metal and the auxiliary oxide; when the active metal component is nickel, the nickel loading accounts for 8 to 12% of the mass fraction of the loading component composed of the active metal and the auxiliary oxide.
7. The method for preparing an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier according to claim 1, characterized in that: In step six, the roasting temperature is 500–700 degrees Celsius, and the roasting time is 4–8 hours.
8. A monolithic ammonia decomposition catalyst based on a metal honeycomb support prepared by the method for preparing a monolithic ammonia decomposition catalyst based on a metal honeycomb support according to any one of claims 1 to 7, comprising a metal honeycomb support, characterized in that: The minimum nickel metal content in the metal honeycomb carrier is 50%; the surface of the metal honeycomb carrier is covered with a dense nickel metal film; the metal honeycomb carrier is loaded with an active metal and an auxiliary metal oxide; the active metal component and the auxiliary metal oxide are loaded on the nickel metal film; the active metal component is ruthenium or nickel metal, and when the active metal component is ruthenium metal, the ruthenium loading is 1-3%, and when the active metal component is nickel metal, the nickel loading is 8-12%.
9. An application of an integrally structured ammonia decomposition catalyst based on a metal honeycomb carrier, characterized in that: The monolithic ammonia decomposition catalyst based on a metal honeycomb carrier is used in the ammonia decomposition hydrogen production process.