A method for hydrogen production by ammonia cracking

Abstract

The application discloses a kind of methods for hydrogen production by ammonia cracking, belong to plasma catalysis and hydrogen energy technical field.The method uses iron-containing solid waste residue as catalyst, the iron-containing solid waste residue includes iron-containing compound, the iron-containing compound includes iron oxide and ferrite compound, the ferrite compound is composed of at least one element in calcium, aluminum and silicon and iron and oxygen element, the method of the application is under the action of plasma, catalyst surface active structure is enhanced, iron species may occur in situ phase transition, form active phase that is beneficial to ammonia molecular adsorption activation and N-H bond rupture, so that higher ammonia conversion rate and hydrogen production efficiency are realized under lower temperature conditions, while reducing the dependence on noble metal catalyst, realize the high-value utilization of industrial solid waste.

Description

Technical Field

[0001] This invention belongs to the field of plasma catalysis and hydrogen energy technology, and more specifically, relates to a method for producing hydrogen by ammonia cracking. Background Technology

[0002] Hydrogen energy, as a clean and efficient secondary energy source, holds significant promise for energy transition and low-carbon development. However, its storage and transportation suffer from low volumetric energy density, high cost, and poor safety, limiting its large-scale application. In contrast, ammonia possesses a high volumetric hydrogen storage density (approximately 121 kg-H2 / m³), is easily liquefied, and has mature storage and transportation conditions, making it considered a safe, green, and efficient hydrogen carrier. Therefore, hydrogen production through ammonia cracking has become one of the important technological pathways for hydrogen energy utilization.

[0003] Existing ammonia cracking hydrogen production technologies typically rely on high temperatures and highly active catalysts to achieve high ammonia conversion rates. Traditional thermocatalytic ammonia cracking reactions generally require temperatures of 500-900 °C and are often used in conjunction with precious metal catalysts such as ruthenium. This not only significantly increases the cost of hydrogen production but also easily leads to problems such as catalyst sintering and deactivation under high-temperature conditions, thus affecting the long-term stability and economic viability of the reaction.

[0004] Nonthermal plasma is a typical non-equilibrium system where the overall gas temperature can be maintained at a low level, while electrons possess high energy (typically 1-10 eV), enabling effective excitation and dissociation of stable molecular bonds. Therefore, nonthermal plasma can promote chemical reactions at relatively low apparent temperatures, providing a new approach to overcome the dependence of traditional thermocatalysis on high-temperature conditions. Furthermore, plasma reactions offer advantages such as fast reaction rates and rapid start-up and shutdown, showing potential benefits in coupling with renewable energy sources.

[0005] However, when using plasma alone for ammonia cracking, problems such as low energy utilization efficiency and limited utilization of active species often exist, making it difficult to achieve high-efficiency conversion while ensuring energy efficiency. Therefore, how to introduce suitable solid materials to form a synergistic effect with plasma to improve reaction efficiency and reduce dependence on noble metal catalysts remains a technical problem that urgently needs to be solved in the field of plasma-assisted ammonia cracking for hydrogen production.

[0006] The solid materials used in existing plasma-co-catalyzed research are mostly artificially synthesized catalysts or metal-supported materials. Their preparation process is complex, the raw material cost is high, and the reaction temperature is high, resulting in unsatisfactory hydrogen production from ammonia cracking. Summary of the Invention

[0007] 1. The problem to be solved To address the problem that the catalysts used in existing ammonia cracking hydrogen production technologies have low efficiency in ammonia cracking hydrogen production under plasma irradiation, the present invention aims to provide a method for ammonia cracking hydrogen production.

[0008] 2. Technical Solution To solve the above problems, the technical solution adopted by the present invention is as follows: This invention discloses a method for hydrogen production by ammonia cracking, which uses iron-containing solid waste residue as a catalyst to promote the activation and cracking of ammonia molecules under the action of plasma, so as to achieve hydrogen production.

[0009] The iron-containing solid waste residue includes iron-containing compounds, which include iron oxides and ferrite compounds. The ferrite compounds are composed of at least one element selected from calcium, aluminum, and silicon, along with iron and oxygen.

[0010] According to any embodiment of the method of the present invention, the iron-containing oxide includes one or more of ferrous oxide, ferric oxide, and magnetite.

[0011] According to any embodiment of the present invention, the ferrate compound is composed of at least one element selected from calcium, aluminum, and silicon, along with iron and oxygen elements, such as iron silicates, iron aluminates, iron aluminosilicates, iron calcium silicates, iron calcium aluminates, and calcium iron oxides.

[0012] The iron silicates include, but are not limited to, FeSiO3, Fe2SiO4, and Fe3Si2O5(OH)4; The iron aluminates include, but are not limited to, FeAl2O4 and Fe(AlO2)3; The iron aluminosilicates include, but are not limited to, Fe3Al2Si3O 12 ; The iron calcium silicate salts include, but are not limited to, CaFeSiO4 and CaFeSi2O6; The iron calcium aluminate salts include, but are not limited to, Ca4Al2Fe2O1, Ca2AlFeO5, and CaFeAlO4.

[0013] The calcium iron oxides include, but are not limited to, CaFe2O4 and Ca2Fe2O5.

[0014] According to any embodiment of the method of the present invention, the catalyst further includes an oxide or hydroxide of at least one element, such as calcium, aluminum, or silicon.

[0015] The oxides or hydroxides of at least one of calcium, aluminum, and silicon include one or more of the following: calcium oxides, calcium hydroxides, calcium silicates, aluminum oxides, aluminum hydroxides, and silicon oxides.

[0016] Wherein, the calcium oxide is preferably calcium oxide, and the calcium hydroxide is preferably calcium hydroxide; The aluminum oxide is preferably aluminum oxide, and the aluminum hydroxide is preferably aluminum hydroxide; The oxide of silicon is preferably silicon oxide; The calcium silicate is preferably one or more of calcium silicate and dicalcium silicate.

[0017] In the "ferrate compounds" described herein, Fe ions exist in a special environment of lattice distortion and coordination unsaturation. The center of its d-band is closer to the Fermi level, which allows for stronger adsorption with NH3 molecules. At the same time, oxygen vacancies are easily formed, which is accompanied by the occurrence of a homolytic dehydrogenation pathway: Fe-NH3 → Fe-NH2• + H•, generating NH2 radical intermediates and H• radicals. H• radicals can be adsorbed on oxygen vacancies or low-valence Fe active sites, further participating in subsequent reactions.

[0018] The iron-containing solid waste slag described herein exhibits a synergistic plasma interaction mechanism for ammonia cracking. Under plasma irradiation, ammonia is first excited and partially dissociated, generating high-energy electrons and reactive species such as NH3*, NH, H, and N. Iron oxides (Fe2O3, FeO), ferrate compounds, and iron-containing components in the RO solid solution phase of the iron-containing solid waste slag serve as key active sites for ammonia molecule adsorption activation and gradual dehydrogenation, thereby promoting NH4+ bond breaking. Possible hypothetical mechanisms include: (1) Plasma excitation and activation of NH3 Plasma can directly activate NH3 molecules through inelastic collisions of high-energy electrons. Ammonia is first excited and partially dissociated, generating high-energy electrons and reactive species such as NH3*, NH, H, and N. The bond energy of the NH bond is further reduced, making it easier to break. During this process, the plasma-induced NHx radical pool provides sufficient reactive intermediates for subsequent dehydrogenation reactions, reducing the reaction induction period, increasing the reaction rate, and working together with iron-containing active sites to enhance the activation ability of NH3 molecules.

[0019] (2) Adsorption and activation of ammonia molecules at iron-containing active sites The Fe element in the iron-containing component is mainly Fe 2+ Fe 3+The Fe ion, possessing an empty d orbital, can act as a Lewis acid center, coordinating with the N atom of the NH3 molecule containing a lone pair of electrons, thus achieving adsorption of the NH3 molecule at the iron-containing active site. This coordination rearranges the electron cloud density of the NH3 molecule, shifting the electron cloud of the N atom towards the Fe ion. This significantly reduces the electron cloud density of the NH bond in the NH3 molecule, slightly lengthens the bond, and effectively weakens the bond energy, transforming the NH3 molecule from a stable gaseous state to an adsorbed, activated state prone to dehydrogenation. Simultaneously, the lattice oxygen (O2) contained in the iron-containing solid waste... 2- The surface hydroxyl group (-OH) can form intermolecular hydrogen bonds with H atoms in the adsorbed NH3 molecule, further polarizing the NH bond, giving the H atom a partial positive charge, significantly increasing the reactivity of the NH bond, and promoting the removal of H atoms.

[0020] Based on this, the surface structure and electronic properties of iron-containing active sites are reconstructed under the induction of plasma, which promotes the dispersion of Fe active sites, avoids Fe aggregation, and increases the exposure of individual Fe sites. At the same time, it induces the generation of more oxygen vacancies on the surface of iron-containing waste slag, optimizes the coordination environment of Fe ions, makes the d-band center of Fe ions closer to the Fermi level, enhances the adsorption capacity of Fe sites for NH3 molecules and the dehydrogenation kinetics, and further reduces the reaction energy barrier for NH bond breaking.

[0021] (3) The gradual breaking and dehydrogenation process of NH bonds After adsorption and activation, NH3 molecules undergo a stepwise dehydrogenation reaction at iron-containing active sites, breaking three NH bonds in sequence. The first step of NH bond breaking and the further transformation and desorption of nitrogen-containing species on the surface may have a significant impact on the overall reaction rate. Plasma-induced active intermediates can significantly reduce the energy barrier of this step and accelerate the reaction.

[0022] (3) Realization of catalytic cycle The Fe element in the iron-containing active sites has Fe 2+ with Fe 3+ The variable valence states between these states can continuously exert a catalytic effect through redox cycles, ensuring the continuous adsorption and activation of NH3 molecules, dehydrogenation, and NH bond breaking. During the dehydrogenation reaction stage, Fe... 2+ Oxidized to Fe 3+ Fe releases electrons and provides empty orbitals to accept electrons from the N atom in the NH3 molecule, promoting heterolytic cleavage of the NH bond; in the subsequent removal of H species, Fe... 3+ Reduced to Fe 2+ This restores the activity of the Lewis acid center.

[0023] Meanwhile, lattice oxygen and oxygen vacancies in iron-containing solid waste participate in the oxygen transfer process, on the one hand for H... + It provides binding sites and, on the other hand, regulates the valence state changes of Fe ions, maintains the stability of the redox cycle, and enables the iron-containing active sites to catalyze the adsorption and activation of NH3 molecules and the breaking of NH bonds for a long time with high efficiency.

[0024] Plasma can accelerate the valence state cycle rate of Fe ions and promote Fe... 2 with Fe 3+ The interconversion between them, while also assisting the migration and renewal of surface lattice oxygen, provides H + Hydrogen species such as H• provide more binding sites, accelerate the removal of hydrogen species, and avoid catalytic deactivation caused by the accumulation of adsorbed hydrogen species on active sites; at the same time, plasma can etch in situ the inert impurities on the surface of iron-containing waste residue, further exposing active sites and avoiding catalyst poisoning.

[0025] In fact, in conventional thermocatalytic ammonia cracking, although iron-based active sites can exhibit high activity in the initial stage, the strong binding of nitrogen-containing species on the surface to iron active sites easily leads to their occupation and deactivation. In contrast, under the synergistic effect of plasma, Fe2O3, FeO, ferrate compounds, and some iron-containing components in the RO solid solution undergo structural reconstruction, forming Fe... x N and related phases, Fe x Nitrogen (N) is highly reactive and more easily dissociates. At the same time, reactive species such as NH3* and NH generated by plasma are beneficial to promoting the further transformation and desorption of nitrogen-containing intermediate species on the surface, thereby alleviating the poisoning effect caused by nitrogen accumulation on the surface and maintaining high ammonia cracking activity.

[0026] Furthermore, alkaline metal compounds such as CaO, Ca(OH)2, MgO, calcium silicates, and SiO2 in iron-containing solid waste can synergistically promote the adsorption and activation of ammonia molecules, the breaking of NH bonds, and the transformation of intermediate species by adjusting the acidity / alkalinity of the catalyst surface, the local electronic environment, and the adsorption / desorption behavior.

[0027] According to any embodiment of the method of the present invention, the catalyst includes one or more of steel slag and red mud.

[0028] According to any embodiment of the method of the present invention, the steel slag includes at least one of electric furnace slag, converter slag, and hot quenching slag.

[0029] According to any embodiment of the method of the present invention, the catalyst is steel slag, the steel slag comprising a multiphase structure and / or a solid solution phase structure formed by at least one element selected from iron, calcium, silicon, magnesium, aluminum, and manganese; and / or, The multiphase structure includes a phase composed of at least one element selected from calcium, silicon, magnesium, aluminum, and manganese, along with iron and oxygen; for example, iron silicates, iron aluminates, iron aluminosilicates, iron calcium silicates, iron calcium aluminates, manganese iron oxides, manganese iron silicates, and calcium iron oxides.

[0030] The solid solution structure includes an RO solid solution, which comprises at least two metal oxides selected from iron, calcium, magnesium, and manganese, for example, a solid solution formed from at least two metal oxides of FeO, MnO, MgO, and CaO.

[0031] The “RO solid solution phase” mentioned herein refers to a system formed from divalent metal oxides.

[0032] According to any embodiment of the method of the present invention, the steel slag further includes a compound composed of at least one element selected from calcium, silicon, magnesium, aluminum, and manganese and oxygen. For example, oxides of calcium, aluminum, silicon, magnesium, and manganese; and silicates of calcium, magnesium, and manganese, calcium-magnesium silicates, calcium-manganese silicates, and magnesium-manganese silicates; and aluminates of calcium, magnesium, and manganese, calcium-magnesium aluminates, calcium-manganese aluminates; and aluminosilicates of calcium, magnesium, and manganese.

[0033] The "RO solid solution phase" described herein can effectively disperse Fe active sites, increase the exposure of individual Fe sites, avoid the decrease in activity caused by Fe ion aggregation, and further improve the efficiency of NH bond breaking and dehydrogenation reaction; the coordination environment of Fe ions in ferrate compounds can regulate their electronic structure, optimize the adsorption strength and dehydrogenation kinetics of NH3 molecules, and synergistically promote NH bond breaking.

[0034] In the "RO solid solution phase" and "ferrate compounds" described herein, Fe ions are in a special environment of lattice distortion and coordination unsaturation. The center of its d-band is closer to the Fermi level, which can form a stronger adsorption with NH3 molecules. At the same time, oxygen vacancies are easily formed, which is accompanied by the occurrence of homolytic dehydrogenation pathway: Fe-NH3 → Fe-NH2• + H•, generating NH2 radical intermediates and H• radicals. H• radicals can be adsorbed on oxygen vacancies or low-valence Fe active sites, and further participate in subsequent reactions.

[0035] According to any embodiment of the present invention, the catalyst is steel slag, which comprises, by mass percentage: CaO 30%-60%, Fe2O3 10%-35%, SiO2 7%-20%, MgO 1%-15%, Al2O3 1%-8%, MnO 0.5%-5%, with the remainder being unavoidable impurities.

[0036] The aforementioned steel slag components achieve ammonia cracking under plasma irradiation. The mechanism involves the formation of a multiphase interface through the calcium-iron oxide mineral phase, calcium-silicate mineral phase, and RO solid solution phase in the steel slag. The compositional differences and interfacial coordination environment differences between the different phases facilitate the formation of interface regions with uneven electron distribution, thus providing favorable conditions for the adsorption and activation of ammonia molecules and the transformation of intermediate species. Simultaneously, the abundant calcium and magnesium basic components in the steel slag, such as CaO, Ca(OH)2, and MgO, can increase the alkalinity of the catalyst surface and regulate the local electronic environment around the iron-containing active sites, thus moderateing the interaction between nitrogen-containing intermediate species and active sites. Furthermore, the regulation of the local electronic environment and surface alkalinity helps reduce the site occupancy effect caused by excessive adsorption of nitrogen-containing intermediate species, promoting their further transformation and desorption, thereby alleviating the deactivation caused by the accumulation of nitrogen species on the surface and maintaining high ammonia cracking activity.

[0037] According to any embodiment of the present invention, the steel slag may further contain associated components formed by slag-forming agents, deoxidizers, desulfurizers, fluxing agents or covering modifiers during the smelting process. The associated components may include one or more of CaO, Ca(OH)2, MgO, MnO, and SiO2. Among them, CaO, Ca(OH)2 and MgO can improve the surface alkalinity of the catalyst and regulate the local electronic environment around the iron-containing active sites. MnO can participate in the RO solid solution phase or affect the coordination environment around the iron-containing components. SiO2 can participate in the formation of multiphase interface structures and affect the surface adsorption / desorption behavior, thereby producing a synergistic effect with the calcium iron oxide mineral phase, calcium silicate mineral phase and iron-containing components in the RO solid solution phase of the steel slag, jointly promoting the adsorption and activation of ammonia molecules, the breaking of NH bonds and the transformation and desorption of nitrogen-containing intermediate species.

[0038] According to any embodiment of the method of the present invention, the red mud includes at least one of Bayer process red mud, sintering process red mud and combined process red mud.

[0039] According to any embodiment of the method of the present invention, the red mud comprises a multiphase structure formed by oxides of at least one element selected from iron, aluminum, silicon, sodium, titanium, and calcium; The multiphase structure comprises a phase composed of at least one element selected from calcium, silicon, aluminum, sodium, and titanium, along with iron and oxygen; and / or, A phase composed of at least one of the elements selected from calcium, silicon, aluminum, sodium, and titanium, and oxygen.

[0040] For example, one or more of the following: iron oxide phase, aluminum oxyhydride phase, silicon dioxide phase, titanium-containing phase, sodium-containing phase, and calcium-containing phase; The titanium-containing phase includes one or more of titanium dioxide and perovskite; The sodium-containing phase includes one or more of sodium aluminum silicate and sodium-containing oxide; The calcium-containing phase includes one or more of the following: calcium oxide phase, calcium silicate phase, and calcium-containing composite oxide phase formed by calcium and other elements.

[0041] According to any embodiment of the present invention, the red mud comprises, by mass percentage: 30%-60% Fe2O3, 10%-30% Al2O3, 3%-15% SiO2, 2%-10% Na2O, 1%-10% TiO2, and 1%-8% CaO.

[0042] Fe2O3 in red mud mainly participates in the adsorption and activation of ammonia molecules and the stepwise dehydrogenation process as an iron-containing active phase; AlO(OH) can regulate the acidity and alkalinity of the catalyst surface and the coordination environment around the iron-containing active sites, thus having a synergistic effect on the adsorption and activation of ammonia molecules; SiO2 can affect the surface adsorption / desorption behavior and the multi-phase interface structure, thus regulating the transformation process of intermediate species; TiO2, Na2O and CaO-related components can further regulate the local electronic environment and surface alkalinity, thereby enhancing the adsorption and activation capacity of iron-containing active sites for ammonia molecules and promoting the further transformation and desorption of nitrogen-containing intermediate species.

[0043] According to any embodiment of the present invention, the red mud may further contain associated components formed by alkaline media, limestone regulators and process aids added during the alumina extraction process. These associated components may include one or more of Na₂O, CaO, TiO₂ and aluminosilicate / sodium aluminosilicate species. Na₂O can increase the alkalinity of the catalyst surface and regulate the local electronic environment, affecting the adsorption / desorption behavior of ammonia molecules and nitrogen-containing intermediates at iron-containing active sites. CaO can regulate the surface alkalinity and the coordination environment around the iron-containing active components, synergistically promoting the adsorption activation of ammonia molecules and subsequent pyrolysis. TiO₂ can regulate the local electronic environment and surface properties near the multi-phase interface, promoting further transformation of intermediate species. The aluminosilicate / sodium aluminosilicate species can participate in the formation of the multi-phase interface structure and affect surface adsorption / desorption behavior, synergistically promoting the ammonia pyrolysis reaction with the main components in the red mud, such as Fe₂O₃, AlO(OH), and SiO₂.

[0044] According to any embodiment of the present invention, the catalyst may be in the form of powder, granules, porous blocks, coating, or a combination thereof, and its particle size may be selected according to the reactor loading method and discharge stability.

[0045] According to any embodiment of the method of the present invention, the particle size of the catalyst is 5 μm–10 mm, preferably, the particle size of the steel slag is 800 mesh. This selection is mainly to adapt to the reactor packing method and discharge stability. The particle size of the catalyst affects its porosity and specific surface area, further affecting the proportion of the catalyst that can interact with the plasma, and thus affecting the reaction rate. Smaller particle size steel slag can increase the specific surface area of ​​the catalyst, and a larger specific surface area can provide more active sites for contact with the reactants. This makes the contact efficiency between the catalyst and the reactants higher, and also facilitates a more complete interaction between the high-energy plasma particles and the catalyst surface.

[0046] According to any embodiment of the present invention, the steel slag is subjected to at least one of the following treatments before use: crushing, screening, washing, acid washing, alkali washing, heat treatment, or mechanical activation, in order to improve its interaction characteristics with plasma.

[0047] This invention discloses a plasma-assisted steel slag catalytic ammonia cracking method for hydrogen production: The process includes the following steps: placing iron-containing solid waste residue in a plasma reaction system, introducing ammonia gas under heating conditions, applying a high-frequency, high-voltage electric field to generate plasma, and achieving hydrogen production from ammonia through cracking.

[0048] According to any embodiment of the present invention, the discharge method is dielectric barrier discharge. Compared with other discharge methods, dielectric barrier discharge is more conducive to generating active species at lower apparent temperatures and enhancing the synergistic effect between plasma and catalyst bed.

[0049] According to any embodiment of the method of the present invention, in the heating conditions, the temperature of the reaction zone is controlled at 0-550°C to form a synergistic effect of thermal action and plasma action. Under the same or lower external heating temperature conditions, higher ammonia conversion efficiency can be achieved through the synergistic effect of steel slag and plasma.

[0050] According to any embodiment of the method of the present invention, the plasma discharge power of the high-frequency high-voltage electric field is 10-50W; the average discharge voltage of the electric field is 2.5-3.5kV, and the average current is 3-4mA.

[0051] According to any embodiment of the present invention, the ammonia flow rate is 10-50 ml / min.

[0052] According to any embodiment of the present invention, the actual amount of catalyst added is adjusted according to factors such as ammonia flow rate, preferably 0.2 g, with an ammonia flow rate of 20 ml / min, in which case the amount of ammonia used per unit mass of catalyst is 6000 ml g. -1 ·h -1 .

[0053] According to any embodiment of the method of the present invention, the heating method is electric heating or other physical heat exchange heating methods, such as resistance heating, tube furnace heating, heating jacket heating, infrared heating, induction heating, or a combination thereof. In one feasible embodiment, the heating method is external resistance furnace heating to achieve overall temperature rise of the reaction bed.

[0054] High-energy electrons can be generated in a gas using dielectric barrier discharge, with an average electron energy of 1-10 electron volts. These high-energy electrons efficiently transfer electrical energy to ammonia molecules through inelastic collisions, thereby exciting, dissociating, and ionizing the ammonia molecules under mild conditions, producing ammonia plasma rich in reactive species. In the ammonia plasma, the NH bonds in the ammonia molecules are activated and broken to varying degrees.

[0055] When solid waste slag containing iron oxide, such as steel slag, is filled into a dielectric barrier discharge region, the steel slag particles, as a high dielectric constant medium, can induce a local electric field enhancement effect, further increasing the electron temperature at particle contact points and pores, thereby generating high-density micro-discharge channels. This strong physical field environment is deeply coupled with the active components on the surface of the steel slag: on the one hand, high-energy electrons and active nitrogen species induce in-situ chemical reconstruction of calcium ferrite and iron oxide components in the steel slag, generating highly active iron nitride (FexN) species and calcium oxide. It should be noted that, unlike in thermocatalytic ammonia cracking, the generation of iron nitride (FexN) means catalyst poisoning, that is, the active sites in the iron-containing catalyst are occupied. Under the action of plasma, the generation of iron nitride is conducive to promoting the activation and bond breaking of ammonia; on the other hand, the calcium, magnesium and other alkaline components rich in steel slag act as electron aids, which can transfer electrons to the active center, weaken the Fe-N bond strength, and thus significantly accelerate the rate-determining step (rate-determining step) of the recombinant desorption of adsorbed nitrogen atoms into free nitrogen gas.

[0056] Therefore, in the presence of dielectric barrier discharge, the ammonia decomposition activity of the catalyst is significantly improved, and the reaction temperature can be greatly reduced. Furthermore, the heating effect generated by the dielectric barrier discharge can provide the reaction temperature for the steel slag catalyst, supplying heat to the endothermic ammonia cracking reaction, thus creating energy coupling between the dielectric barrier discharge and the steel slag catalyst, which is more conducive to energy saving.

[0057] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention utilizes the continuous action of plasma to stimulate the catalytic activity of iron-containing solid waste residue. Together with the iron-containing solid waste residue, it exhibits a significant catalytic promoting effect in the ammonia cracking reaction. A high ammonia conversion rate can be achieved under relatively low temperature conditions, reducing the dependence on precious metal catalysts and high temperature conditions. (2) The iron-containing solid waste residue added in this invention also contains associated components. These associated components and the active components in the iron-containing solid waste residue produce a synergistic effect under the action of plasma, which is conducive to improving the adsorption and activation capacity of ammonia molecules, promoting the breaking of NH bonds and the transformation of intermediate species, thereby improving the ammonia cracking efficiency. (3) This invention realizes the high-value utilization of iron-containing solid waste residue, which has good economic and environmental benefits. Attached Figure Description

[0058] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that these drawings are designed for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless specifically indicated, these drawings are intended only to conceptually illustrate the structural construction described herein and are not necessarily drawn to scale.

[0059] Figure 1 This is a schematic diagram of the plasma reactor. Figure 2 The results show the variation of ammonia conversion rate with power in the catalytic ammonia cracking of steel slag under different temperature conditions. Figure 3 The results show the variation of ammonia conversion rate with power in red mud catalytic ammonia cracking under different temperature conditions; Figure 4 The results show the change in ammonia conversion rate with power under different catalyst conditions for ammonia cracking. Figure 5 The image shows the XRD pattern of steel slag before reaction. In the image, Fresh steel slag is the steel slag before reaction, and Spent steelslag is the steel slag after reaction. Detailed Implementation

[0060] The following detailed description of exemplary embodiments of the invention is taken with reference to the accompanying drawings, which form part of the description and illustrate exemplary embodiments in which the invention may be practiced. While these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from the spirit and scope thereof. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and not restrictive of the description of the features and characteristics of the invention, to suggest the best mode for carrying out the invention, and is sufficient to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is defined only by the appended claims.

[0061] The main components of steel slag typically include various metal oxides such as CaO, Fe2O3, SiO2, MgO, and Al2O3. The mineral phases already formed in the slag mainly include calcium ferrite, calcium silicate, ferrous oxide, and metal solid solution phases (iron oxide, magnesium oxide, and aluminum oxide). Existing research indicates that metal oxides may undergo surface defect generation, valence state changes, and local structural reconstruction under plasma irradiation, thereby affecting plasma discharge behavior and the conversion process of active species. However, as a widely available and extremely low-cost solid waste, whether steel slag can be activated under plasma irradiation and exhibit catalytic promoting effects, especially in the ammonia cracking hydrogen production reaction, remains a subject of systematic research and lacks effective technical solutions.

[0062] Therefore, developing a method that can utilize plasma to stimulate the potential catalytic activity of steel slag and achieve synergistic promotion of ammonia cracking for hydrogen production by plasma and steel slag is of great technical significance and application value for reducing hydrogen production costs, reducing dependence on precious metal catalysts, and realizing the high-value utilization of industrial solid waste.

[0063] The purpose of this invention is to utilize steel slag, a widely available and inexpensive industrial solid waste, to stimulate its potential catalytic activity under the action of plasma. This transforms the steel slag from a low-activity solid waste into a catalytic medium with reaction-promoting capabilities during the reaction process. Thus, under heating conditions, the synergistic effect of plasma and steel slag material can efficiently promote the ammonia cracking reaction to produce hydrogen, reduce the dependence of the hydrogen production process on precious metal catalysts, and improve the efficiency of ammonia cracking for hydrogen production.

[0064] This invention provides a method for hydrogen production by ammonia cracking using non-thermal plasma to continuously excite the catalytic activity of industrial solid waste steel slag, achieving efficient hydrogen production under medium and low temperature conditions and significantly reducing catalytic costs.

[0065] The ammonia cracking hydrogen production method of the present invention is carried out in a plasma reactor, the structure of which is as follows: Figure 1 As shown, it includes: The plasma reactor includes a corundum tube, a high-voltage electrode, a grounding electrode, a catalyst bed, quartz wool, an inlet, an outlet, and an external heating device.

[0066] The high-voltage electrode is located inside the corundum tube, and the grounding electrode is located outside the corundum tube; the catalyst bed is filled inside the corundum tube and supported and fixed by quartz wool located on its upper and lower sides. The air inlet is located at the upper end of the corundum tube, and the air outlet is located at the lower end of the corundum tube. The raw material gas enters from the air inlet, flows through the plasma discharge area and the catalyst bed, and is discharged from the air outlet. The heating device is located outside the reactor and is used to heat the reactor externally.

[0067] The gas composition before and after the reaction was detected using gas chromatography. Under the same injection volume and detection conditions, the relative content of ammonia was characterized by the chromatographic peak area. The ammonia conversion rate was calculated using the following formula:

[0068] in, For ammonia conversion rate, This represents the chromatographic peak area of ​​ammonia in the raw gas. This represents the chromatographic peak area of ​​ammonia in the tail gas after the reaction.

[0069] Example 1 The plasma-assisted steel slag catalytic ammonia cracking hydrogen production method in this embodiment: The steps include: placing 0.2 g of steel slag in a plasma reaction system at a reaction temperature of 450°C, introducing ammonia gas, applying a high-frequency high-voltage electric field to generate plasma, and realizing the cracking of ammonia to produce hydrogen.

[0070] The composition of the steel slag is shown in Table 1: Table 1. Composition of steel slag in Example 1

[0071] The steel slag has a particle size of 800 mesh.

[0072] The multi-mineral / solid solution structure in steel slag provides favorable conditions for the adsorption and activation of ammonia molecules and the transformation of intermediates. The phase composition of the steel slag before and after the reaction is as follows: Figure 5 As shown. Before the reaction, the steel slag mainly consisted of Ca2SiO4, Ca(OH)2, CaFe2O4, and RO solid solution phase, wherein the RO solid solution phase was mainly a solid solution formed by FeO, MgO, and MnO. After the reaction, the diffraction characteristics of Ca2SiO4, Ca(OH)2, and the RO solid solution phase could still be observed in the sample, and iron-based nitrides (Fe2O4, Ca(OH)2, and RO solid solution phases also appeared. x The new characteristic peaks of Fe(N) were observed. Compared with the pre-reaction state, the diffraction peaks of some iron-containing phases weakened, disappeared, or became less distinct, indicating that the iron-containing components in the steel slag underwent significant structural reconstruction under the synergistic effect of dielectric barrier discharge plasma, forming a Fe / Fe... x N is the characteristic dynamic working state; among which, Fe-related active sites realize the adsorption and stepwise dehydrogenation of ammonia molecules, and the generated Fe x Nitrogen species may further promote the activation and dissociation of ammonia molecules and the generation of hydrogen by regulating the electronic structure around iron sites and the nitrogen binding environment.

[0073] In the high-frequency, high-voltage electric field that generates plasma, the plasma discharge power is 50W, the average discharge voltage of the electric field is 3.2kV, and the average current is 4.0mA. In actual experiments, the current and voltage fluctuate, and the discharge process of this application can be achieved by controlling them within this range.

[0074] The plasma-generating discharge method is dielectric barrier discharge.

[0075] The ammonia flow rate is 20 ml / min.

[0076] The final ammonia conversion results are shown in Figure 2 And Table 2.

[0077] Comparative Example 1 This comparative example is basically the same as Example 1, except that no plasma was applied, the average discharge voltage of the electric field was 2.5 kV, and the average current was 2.8 mA. The final ammonia conversion results are shown in [the table below]. Figure 2 And Table 2.

[0078] Example 2 This embodiment is basically the same as Embodiment 1, except that the plasma power is 10W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0079] Example 3 This embodiment is basically the same as Embodiment 1, except that the plasma power is 20W, the average discharge voltage of the electric field is 2.7kV, and the average current is 3.1mA. The final ammonia conversion result is shown in [the figure]. Figure 2 And Table 2.

[0080] Example 4 This embodiment is basically the same as Embodiment 1, except that the plasma power is 30W, the average discharge voltage of the electric field is 2.8kV, and the average current is 3.7mA. The final ammonia conversion result is shown in [the figure]. Figure 2 And Table 2.

[0081] Example 5 This embodiment is basically the same as Embodiment 1, except that the plasma power is 40W, the average discharge voltage of the electric field is 3.0kV, and the average current is 3.8mA. The final ammonia conversion result is shown in [the figure]. Figure 2 And Table 2.

[0082] Example 6 This embodiment is basically the same as Example 1, except that the reaction temperature is 400℃. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0083] Comparative Example 2 This comparative example is basically the same as Example 6, except that no plasma is applied. The final ammonia conversion result is shown in [Figure 6]. Figure 2 And Table 2.

[0084] Example 7 This embodiment is basically the same as Embodiment 6, except that the plasma power is 10W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0085] Example 8 This embodiment is basically the same as Embodiment 6, except that the plasma power is 20W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0086] Example 9 This embodiment is basically the same as Embodiment 6, except that the plasma power is 30W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0087] Example 10 This embodiment is basically the same as Embodiment 6, except that the plasma power is 40W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0088] Example 11 This embodiment is basically the same as Example 1, except that the reaction temperature is 25°C. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0089] Comparative Example 3 This comparative example is basically the same as Example 11, except that no plasma is applied. The final ammonia conversion result is shown in [Figure 11]. Figure 2 And Table 2.

[0090] Example 12 This embodiment is basically the same as Embodiment 11, except that the plasma power is 10W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0091] Example 13 This embodiment is basically the same as Embodiment 11, except that the plasma power is 20W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0092] Example 14 This embodiment is basically the same as Embodiment 11, except that the plasma power is 30W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0093] Example 15 This embodiment is basically the same as Embodiment 11, except that the plasma power is 40W. The final ammonia conversion result is shown in [reference needed]. Figure 2 And Table 2.

[0094] Table 2 Ammonia conversion rates of Examples 1-15 and Comparative Examples 1-3

[0095] The final ammonia conversion results obtained in Examples 1-15 and Comparative Examples 1-3 are as follows: Figure 2 As shown, the reaction process was carried out under heating conditions, with the reaction temperature controlled at 25℃, 400℃, and 450℃. The plasma was excited by a high-voltage power supply, and the catalyst was placed in the plasma discharge region so that the plasma acted on the steel slag material during the reaction. Figure 2 It can be seen that under the conditions of plasma-assisted steel slag catalysis, the ammonia conversion rate generally shows an upward trend with the increase of plasma discharge power and reaction temperature.

[0096] Specifically, at a reaction temperature of 450 °C and a plasma discharge power of 50 W, the ammonia conversion rate can reach 90%. With further increases in reaction temperature, a higher ammonia conversion rate can also be obtained under lower plasma discharge power conditions, demonstrating a significant synergistic promoting effect between plasma and steel slag materials.

[0097] Examples 16-30 Examples 16-30 are basically the same as Examples 1-15, except that the catalyst is replaced with red mud.

[0098] Comparative Examples 4-6 are basically the same as Comparative Examples 1-3, except that the catalyst is replaced with red mud.

[0099] The composition of the red mud is shown in Table 3: Table 3. Composition of red mud in Examples 16-30 and Comparative Examples 4-6

[0100] In the high-frequency, high-voltage electric field that generates plasma, the plasma discharge power is 0-50W.

[0101] In the high-frequency, high-voltage electric field that generates plasma, the average discharge voltage of the electric field is 2.5-3.5kV and the average current is 3-4mA. In actual experiments, the current and voltage fluctuate, and the discharge process of this application can be achieved by controlling them within this range.

[0102] The plasma-generating discharge method is dielectric barrier discharge.

[0103] The ammonia flow rate is 20 ml / min.

[0104] The final ammonia conversion results are shown in Figure 3 By varying the reaction temperature and plasma power, the final ammonia conversion rate differs, specifically as follows: Figure 3 And Table 4.

[0105] Table 4 Ammonia conversion rates of Examples 16-30 and Comparative Examples 4-6

[0106] The superior catalytic effect of red mud compared to steel slag is mainly attributed to the deep coupling effect of its unique "iron-aluminum-titanium-alkali" multi-metal system in the plasma field: First, the strong alkaline component (Na2O / K2O) remaining in red mud has a stronger electron donor capacity than the calcium-based component in steel slag, significantly reducing the electron work function of the iron active center and greatly accelerating the rate-determining step (nitrogen desorption) of the ammonia cracking reaction; Second, the unique titanium dioxide (TiO2) semiconductor component in red mud has a higher dielectric constant, inducing stronger local electric field distortion and high-density micro-discharge in the reaction bed than steel slag. Combined with the alumina (Al2O3) matrix providing a framework with a high specific surface area, it ensures the high dispersion and stability of the in-situ generated iron nitride active phase under the plasma thermal effect, thereby achieving ultra-high catalytic activity at low temperature.

[0107] Comparative Examples 7-12 Comparative Examples 7-12 are essentially the same as Examples 1-5, except that the catalyst is replaced with CaO. The final ammonia conversion results are shown in the figure. Figure 4 See Table 5.

[0108] Comparative Examples 13-18 Comparative Examples 13-18 are essentially the same as Examples 1-5, except that the catalyst is replaced with Fe2O3. The final ammonia conversion results are shown in [Figure 1]. Figure 4 See Table 5.

[0109] Comparative Examples 19-24 Comparative Examples 19-24 are essentially the same as Examples 1-5, except that no catalyst is added. The final ammonia conversion results are shown in [Figure 1]. Figure 4 See Table 5.

[0110] In comparison, the iron oxide content in steel slag is only 23.3%, but its catalytic ammonia cracking effect is comparable to that of pure Fe2O3 catalyst. Moreover, preferably, when the plasma power is 20-40W, the ammonia conversion rate is slightly higher than that of Fe2O3 and much higher than that of CaO, indicating that the components in steel slag and red mud have a synergistic effect with plasma and have obvious advantages.

[0111] Table 5 Ammonia conversion rate of Comparative Example 7-24

[0112] This invention stimulates the potential catalytic activity of steel slag, an industrial solid waste, through plasma action, enabling it to exhibit significantly enhanced reaction-promoting ability during the reaction process, thereby achieving a high ammonia conversion rate under relatively low temperature and low energy consumption conditions.

[0113] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0114] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A method for producing hydrogen by ammonia cracking, characterized in that, Iron-containing solid waste residue was used as a catalyst to carry out ammonia cracking reaction under the action of plasma to produce hydrogen. The iron-containing solid waste residue includes iron-containing compounds, which include iron oxides and ferrite compounds. The ferrite compounds are composed of at least one element selected from calcium, aluminum, and silicon, along with iron and oxygen.

2. The method for producing hydrogen from ammonia via cracking according to claim 1, characterized in that, The iron oxide includes one or more of ferrous oxide, ferric oxide, and magnetite; and / or, The ferrate compounds include one or more of the following: iron silicates, iron aluminates, iron aluminosilicates, iron calcium silicates, iron calcium aluminates, and calcium iron oxides.

3. The method for producing hydrogen from ammonia via cracking according to claim 1, characterized in that, The catalyst further includes an oxide or hydroxide of at least one element, such as calcium, aluminum, or silicon; and / or, The oxides or hydroxides of at least one of calcium, aluminum, and silicon include one or more of the following: calcium oxides, calcium hydroxides, calcium silicates, aluminum oxides, aluminum hydroxides, and silicon oxides.

4. The method for producing hydrogen from ammonia via cracking according to claim 1, characterized in that, The catalyst includes one or more of steel slag and red mud.

5. The method for producing hydrogen from ammonia via cracking according to claim 4, characterized in that, The catalyst is steel slag, which comprises a multiphase structure and / or a solid solution phase structure formed by at least one element selected from iron, calcium, silicon, magnesium, aluminum, and manganese; and / or, The multiphase structure comprises a phase composed of at least one element selected from calcium, silicon, magnesium, aluminum, and manganese, along with iron and oxygen; and / or, The solid solution structure includes an RO solid solution, which includes at least two metal oxides selected from iron, calcium, magnesium, and manganese.

6. The method for producing hydrogen from ammonia via cracking according to claim 5, characterized in that, The steel slag also includes compounds composed of at least one element selected from calcium, silicon, magnesium, aluminum, and manganese, and oxygen.

7. The method for producing hydrogen from ammonia via cracking according to claim 5, characterized in that, The steel slag comprises, by mass percentage: CaO 30%-60%, Fe2O3 10%-35%, SiO2 7%-20%, MgO 1%-15%, Al2O3 1%-8%, MnO 0.5%-5%, with the remainder being unavoidable impurities.

8. The method for producing hydrogen from ammonia via cracking according to claim 4, characterized in that, The catalyst is red mud, which contains a multiphase structure formed by oxides of at least one element selected from iron, aluminum, silicon, sodium, titanium, and calcium. The multiphase structure comprises a phase composed of at least one element selected from calcium, silicon, aluminum, sodium, and titanium, along with iron and oxygen; and / or, A phase composed of at least one of the elements selected from calcium, silicon, aluminum, sodium, and titanium, and oxygen.

9. The method for producing hydrogen by ammonia cracking according to claim 8, characterized in that, The red mud comprises, by mass percentage: Fe2O3 30%-60%, Al2O3 10%-30%, SiO2 3%-15%, Na2O 2%-10%, TiO2 1%-10%, CaO 1%-8%, with the remainder being unavoidable impurities.

10. The method for producing hydrogen by ammonia cracking according to claim 1, characterized in that: The catalyst is subjected to at least one of the following treatments before use: crushing, screening, washing, acid washing, alkali washing, heat treatment, or mechanical activation.

11. The method for producing hydrogen from ammonia via cracking according to claim 10, characterized in that, The process includes the following steps: placing the catalyst in a plasma reaction system, introducing ammonia gas under heating conditions, applying a high-frequency, high-voltage electric field to generate plasma, and achieving hydrogen production from ammonia through cracking.

12. The method for producing hydrogen from ammonia via cracking according to claim 11, characterized in that, The discharge method is dielectric barrier discharge.

13. The method for producing hydrogen by ammonia cracking according to claim 11, characterized in that, The discharge power of the high-frequency, high-voltage electric field is 10-50W; the temperature of the reaction zone is controlled at 0-550℃; and / or, The average discharge voltage is 2.5-3.5kV, and the average current is 3-4mA.

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