Catalysts for promoting the reaction of active metals with water and hydrogen production applications

Abstract

The application forms insoluble Al 3+ / TEMPO-CNFs complex nanostructure by adding 0.01-1wt% TEMPO-CNFs in water, plays the role of catalyst, effectively improves the reaction efficiency of aluminum / water, makes the reaction can be carried out at low temperature and room temperature, reduces the reaction energy consumption, improves the safety of the reaction process, makes the reaction more clean, low cost, high efficiency, and the by-products of the reaction, such as bell stone, can be reconverted into Al powder for reuse. The promoted Al powder / pure water reaction at less than 50 DEG C obtains a higher Al / H conversion rate, and the reaction can be scaled up for on-demand hydrogen production, has strong practicability and wide applicability.

Description

Technical Field

[0001] This invention relates to a catalyst and its application, specifically to a TEMPO-CNFs as a catalyst for promoting the aluminum / water reaction, belonging to the field of catalyst technology. Background Technology

[0002] The reaction of active metals with water is a promising technology for on-site hydrogen production. Theoretically, any active metal or metal alloy with a standard reduction potential below zero volts can react with water to produce hydrogen.

[0003] Aluminum has long been the preferred material for producing hydrogen through the reaction of active metals with water due to its high stability, low reduction potential (-1.662 to -2.33 V), excellent theoretical hydrogen production capacity (1 mol of aluminum can theoretically produce 1.5 mol of hydrogen), abundant reserves in the Earth's crust, and the fact that byproducts of its reaction with water (such as aluminum oxide and aluminum hydroxide) can be 100% reduced back to metallic aluminum.

[0004] However, under reaction conditions at low temperatures (temperatures equal to or lower than the boiling point of water), the reaction rate of aluminum with water is extremely slow, mainly due to the inert aluminum oxide film that forms naturally on the aluminum surface.

[0005] The most traditional solution is to add an alkaline chemical to the water. Among alkaline chemicals, caustic soda (sodium hydroxide) is the most effective alkaline additive; however, to completely convert aluminum into hydrogen, at least 1.5g of caustic soda is needed per gram of aluminum.

[0006] Sodium hydroxide has the following two functions: it dissolves and removes the inert alumina film through reaction 1, and promotes the reaction between aluminum and water through reactions 2 and 3, thereby accelerating the hydrogen production reaction and improving the aluminum-hydrogen conversion efficiency.

[0007] Al₂O₃ + 2Na + +2OH - +3H₂O→2Na + +2Al(OH)4 - (Reaction 1)

[0008] 2Al + 6H₂O + 2NaOH → 2NaAl(OH)₄ + 3H₂↑ (Reaction 2)

[0009] NaAl(OH)4→Al(OH)3↓+NaOH (Reaction 3)

[0010] In recent years, solid catalysts based on transition metal oxides, such as nickel-based catalysts, iron-based catalysts, and cobalt-nickel composite catalysts, have been developed to replace highly corrosive caustic soda. These solid catalysts catalyze the desorption reaction of molten aluminum based on the microcurrent derived between the solid catalyst and aluminum. Because there is a non-contact interface between the solid catalyst and aluminum (solid), the actual catalytic efficiency of solid catalysts is relatively low, and the required catalyst addition is as high as 10 wt%.

[0011] Increasing the reaction temperature, for example by using superheated water or superheated steam to react with aluminum, is also an effective method to promote hydrogen production via the aluminum / water reaction. For instance, using superheated water at 230-370°C to react with aluminum can convert aluminum powder with an average particle size of 70 μm to nearly 100% hydrogen in tens of seconds. Furthermore, a recent study demonstrated that using high-density supercritical water (>200 g L / L) at 382°C... -1 This method enables the production of hydrogen by reacting large-particle-size (average particle size of 3 mm) aluminum powder with water. In particular, if hot water steam exceeding 600°C is used to react with aluminum (aluminum powder particle size average 40 μm), the aluminum is evaporated to the atomic level. The atomic-level aluminum-water vapor-phase reaction produces hydrogen while also generating nano-sized alumina particles.

[0012] High-temperature aluminum-water reaction for hydrogen production has advantages such as fast reaction rate and high hydrogen-aluminum conversion rate. On the other hand, it has not yet been used for large-scale industrial hydrogen production due to disadvantages such as high energy consumption, harsh reaction conditions, and strict requirements for equipment temperature and pressure resistance.

[0013] Processing aluminum into nanoscale aluminum powder can also achieve high-efficiency hydrogen production. For example, by reacting aluminum powder with an average particle size of 140 nm with deionized water, almost 100% of the aluminum can be converted into hydrogen under low-temperature reaction conditions of 50-75℃. However, the process of preparing nanoscale aluminum powder is complex and costly, and the inherent safety hazards of nanoscale aluminum, such as spontaneous combustion and explosion, still need to be addressed and overcome.

[0014] In fact, large-particle aluminum powder (with an average particle size of 20 μm or more), which exhibits high stability and safety, also shows certain reactivity in pure water. For example, as reported in the literature, after reacting aluminum powder with water at 100°C for 5 hours, nearly 60% of the aluminum can be converted into hydrogen gas. This preliminary study also pointed out that the byproducts of the aluminum powder / water reaction (mainly Bayerite, a special crystal structure of aluminum hydroxide) accumulate on the surface of the reacted aluminum powder, forming a shell / core structure. The formed Bayerite matrix shell blocks the diffusion of water molecules, thereby hindering the further reaction of the remaining aluminum powder with water.

[0015] When aluminum comes into contact with air, a thin, inert aluminum oxide film automatically forms on its surface. Previous studies have indicated that this aluminum oxide film is not completely inert; it undergoes hydrolysis upon contact with water or water vapor. However, without the addition of any chemicals, the hydrolysis of the aluminum oxide film is extremely slow.

[0016] Previous research by BCBunker et al. on the reaction mechanism of hydrolysis of alumina films showed that hydroxide ions are the main product of the hydrolysis reaction. Hydroxide ions produced by the hydrolysis reaction can diffuse and move within the unreacted alumina film, but their diffusion rate is extremely slow. Moreover, due to their combination with the trivalent positively charged conjugated aluminum ions produced in the hydrolysis reaction to form more stable aluminum hydroxide, the amount of free-state hydroxide ions provided by the hydrolysis reaction is usually negligible.

[0017] Therefore, it is necessary to provide a new catalyst to promote the reaction of active metals with water. Summary of the Invention

[0018] To address the shortcomings of existing technologies, the present invention aims to provide TEMPO-CNFs as catalysts for promoting aluminum / water reactions and hydrogen production applications.

[0019] To achieve the above objectives, the present invention adopts the following technical solution:

[0020] A catalyst for promoting the aluminum / water reaction, namely TEMPO-CNFs.

[0021] TEMPO-CNFs act as catalysts to promote the aluminum / water reaction.

[0022] The aforementioned TEMPO-CNFs are fibrous, with a length of less than 100 μm and a diameter of less than 100 nanometers.

[0023] The concentration of the above-mentioned TEMPO-CNFs in water is 0.01-1 wt%.

[0024] The reaction temperature of the aluminum / water above is below 50°C.

[0025] The particle size of the aluminum mentioned above is 2-200 μm.

[0026] TEMPO-CNFs serve as catalysts to promote the aluminum / water reaction for hydrogen production.

[0027] Aluminum / water reaction, including TEMPO-CNFs at a concentration of 0.01-1 wt%.

[0028] Furthermore, the temperature of the above reaction is below 50°C.

[0029] The hydrogen production reaction involves adding aluminum to an aqueous solution containing 0.01-1 wt% TEMPO-CNFs.

[0030] Furthermore, the temperature of the above reaction is below 50°C.

[0031] The advantages of this invention are:

[0032] This invention provides a chemical substance, TEMPO-CNFs, that can accelerate the hydrogen production rate and improve the aluminum-hydrogen conversion efficiency in the aluminum-water reaction, enabling hydrogen production under low-temperature conditions (room temperature to water boiling point). Unlike traditional caustic soda-based and transition metal-based catalysts, this invention achieves hydrogen production by adding 0.01-1 wt% TEMPO-CNFs to pure water, thereby forming insoluble Al... 3+ / TEMPO-CNFs, through their complexed nanostructures, act as catalysts, effectively improving the reaction efficiency of aluminum / water. This allows the reaction to proceed at both low and room temperatures, reducing energy consumption and enhancing the safety of the reaction process. The result is a cleaner, lower-cost, and more efficient reaction. Furthermore, the reaction byproduct, aluminum hydroxide, which is similar to bainite, can be converted back into Al powder for reuse.

[0033] The Al powder / pure water reaction promoted by this invention achieves a high Al / H conversion rate at temperatures below 50°C. The reaction can be scaled up for on-demand hydrogen production, demonstrating strong practicality and wide applicability. Attached Figure Description

[0034] Figure 1 This is a graph showing the hydrogen production versus reaction time in the aluminum molten metal reaction with and without TEMPO-CNFs.

[0035] Figure 2 This is a gas chromatogram of the gas produced by the reaction in Example 2.

[0036] Figure 3 This image shows the shape and constituent elements of the solid product generated after the reaction of molten aluminum using a scanning electron microscope equipped with elemental analysis.

[0037] Figure 4 The image shows the X-ray diffraction pattern of the solid product formed after the reaction of molten aluminum.

[0038] Figure 5 The X-ray diffraction pattern of the reactants in the reaction using sodium alginate as a catalyst is shown. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0040] TEMPO: 2,2,6,6-Tetramethylpiperidine-1-oxygen radical;

[0041] CNFs: Carbon nanofibers.

[0042] Aluminum powder: Three types of aluminum powder with a purity >99.9% and average particle sizes of 20um, 75um and 150um respectively, available commercially.

[0043] TEMPO-CNFs: A commercially available aqueous solution containing 2–2.4 wt% TEMPO-CNFs. Dilute with deionized water to obtain an aqueous solution with a lower TEMPO-CNFs content. TEMPO-CNFs are fibrous, less than 100 μm in length and less than 100 nm in diameter.

[0044] Example 1

[0045] The aqueous solution containing 2.0 wt% TEMPO-CNFs was diluted with deionized water to 0.2 wt%.

[0046] Pour 200 ml of an aqueous solution containing 0.2 wt% TEMPO-CNFs into a 500 ml wide-mouth glass bottle;

[0047] Weigh 0.66 g of aluminum powder with an average particle size of 20 μm and add it to a wide-mouth glass bottle; the reaction temperature is 45℃.

[0048] Connect a wide-mouthed glass bottle to a 50ml inverted burette using a rubber stopper with a glass tube inserted. The inverted burette is filled with about 25ml of water to remove any moisture that may be carried in the hydrogen gas produced by the aluminum molten metal reaction.

[0049] Connect the narrow end of an inverted burette to a water / gas displacement tube using a rubber tubing to track and measure the volume of hydrogen gas produced during the aluminum molten metal reaction. The measurement results of the hydrogen gas volume produced during the aluminum molten metal reaction are as follows: Figure 1 As shown.

[0050] Comparative experiment:

[0051] The above experiment was repeated using 200 ml of water without added TEMPO-CNFs and 0.66 g of aluminum powder with an average particle size of 20 μm, and the generated hydrogen gas was collected. The volume of hydrogen gas produced by the aluminum-water reaction versus the reaction time is shown in the figure below. Figure 1 As shown in the image.

[0052] The hydrogen-aluminum conversion efficiency (Y) is calculated using the following formula:

[0053] Y=V / ((W / 27)*1.5*24.45)*100%

[0054] In the formula, V is the total amount of hydrogen produced from the start of the aluminum-water reaction to the reaction time t, W is the total amount of aluminum powder reacting, 1 mole of aluminum theoretically produces 1.5 moles of hydrogen, and 24.45 (liters) is the standard volume of 1 mole of hydrogen at standard temperature and 1 atmosphere.

[0055] To ensure thorough mixing during the reaction, the reaction flask was kept in an open ultrasonic generator throughout the entire process.

[0056] like Figure 1 As shown, the addition of 0.2 wt% TEMPO-CNFs shortened the start time of the aluminum molten metal reaction from 90 minutes to 60 minutes and increased the hydrogen generation rate from 0.7 ml / min to 5.77 ml / min (the linear reaction range for hydrogen production is 100–220 minutes).

[0057] Furthermore, after 220 minutes, the total amount of hydrogen produced by the aluminum-water reaction containing 0.2 wt% TEMPO-CNFs was 758 ml, while the total amount of hydrogen produced by the aluminum-water reaction without TEMPO-CNFs was 111 ml. This means that after 220 minutes, the hydrogen-aluminum conversion rate of the aluminum-water reaction containing 0.2 wt% TEMPO-CNFs was as high as 84.5% (758 ml / 897 ml), while the hydrogen / aluminum conversion rate of the aluminum-water reaction without TEMPO-CNFs was only 12.4%. That is, the conversion rate increased by 6.8 times.

[0058] Example 2: Qualitative and quantitative analysis of hydrogen gas generated during the aluminum molten metal reaction.

[0059] Pour approximately 800 ml of an aqueous solution containing 0.2 wt% TEMPO-CNFs into a 1000 ml wide-mouth glass beaker;

[0060] Weigh 40.4 grams of aluminum powder with an average particle size of 20 μm and add it to a wide-mouth glass beaker;

[0061] Place the wide-mouthed glass beaker in a water bath at 36°C and stir continuously with a stirrer at a speed of 150–300 rpm.

[0062] Place the wide-mouth side of the funnel over the mouth of the wide-mouth glass beaker, and draw gas from the narrow-mouth side of the funnel using a 100ml syringe.

[0063] The collected gas was injected into a gas chromatograph for qualitative and quantitative analysis of the gas components generated during the aluminum molten metal reaction.

[0064] Measurement results as follows Figure 2As shown, since the sampling was conducted in an open environment, in addition to the hydrogen peak, chromatographic peaks corresponding to oxygen and nitrogen from the air were also observed in the chromatography. After the aluminum water reaction had proceeded for 60, 90, 105, 135, 165, and 195 minutes, the hydrogen content (volume ratio) in the gas samples taken were 1.55%, 11.81%, 17.92%, 11.3%, 7.11%, and 5.01%, respectively.

[0065] Gas chromatography was performed using a GL Science 990GC, with a separation column temperature of 100℃, a sampling injection temperature of 80℃, and argon as the mobile phase gas.

[0066] Example 3: Physical and structural analysis of byproducts generated from the aluminum molten metal reaction

[0067] The liquid in the milky white slurry generated after the aluminum water reaction in Example 2 was separated by vacuum filtration to obtain a milky white solid substance.

[0068] The milky white solid substance was placed in a constant temperature oven at 60°C and dried for more than 72 hours to remove the remaining moisture.

[0069] The microstructure of the solid material was tested and analyzed using a scanning electron microscope equipped with elemental analysis and an X-ray diffraction analyzer.

[0070] like Figure 3 As shown, when TEMPO-CNFs are present in the aluminum-water reaction system, the aluminum powder masterbatch reacts completely with water, and the resulting substance contains oxygen and aluminum elements. Furthermore, the aluminum powder masterbatch with an average particle size of 20 μm before the reaction is decomposed into tiny particles with a particle size of tens to hundreds of nanometers.

[0071] X-ray diffraction analysis results ( Figure 4 The results show that the main component of the solid product formed after the reaction of molten aluminum is aluminum hydroxide, which is similar to bel lith. The numbers in parentheses in the figure represent the lattice coordinates of aluminum hydroxide corresponding to the X-ray diffraction peak.

[0072] Example 4

[0073] To further demonstrate the excellent performance of TEMPO-CNFs in promoting hydrogen production from aluminum hydrate in this invention, sodium alginate was selected as a substitute for TEMPO-CNFs, and its catalytic effect on hydrogen production from aluminum hydrate was verified.

[0074] Alginic acid and TEMPO-CNFs have similar structures, both being linear polysaccharides formed by monosaccharides linked by 1,4 glycosidic bonds, and both carrying negatively charged carboxyl groups. The structural difference lies in the fact that sodium alginate units, namely β-D-mannuronic acid and α-L-guluronic acid (G), both contain carboxyl groups, thus sodium alginate is completely soluble in water.

[0075] Experimental steps:

[0076] Pour 800 ml of a deionized aqueous solution containing 0.2 wt% sodium alginate into a 1000 ml wide-mouth glass beaker;

[0077] Weigh 40.4 g of aluminum powder with an average particle size of 20 μm and add it to a wide-mouth glass beaker;

[0078] Place the wide-mouthed glass beaker in a water bath at 36°C and stir continuously with a stirrer at a speed of 150–300 rpm.

[0079] During the reaction, about 20 ml of reactants containing aluminum powder were taken out. The solution was separated by centrifugation, the solid components were recovered, and the remaining water was removed in a constant temperature oven at 60°C to obtain the powder.

[0080] The powder was tested and analyzed using an X-ray diffractometer, such as... Figure 5 The X-ray diffraction pattern shows that even after 30 hours of aluminum-water reaction, with sodium alginate replacing TEMPO-CNFs, metallic aluminum remains the main component. This means that the catalytic performance of sodium alginate in the aluminum-water hydrogen production reaction is far inferior to that of TEMPO-CNFs.

[0081] Reaction principle:

[0082] In the presence of TEMPO-CNFs, a certain amount of TEMPO-CNFs adheres to Al2O3 on the aluminum surface, forming a condensed network carrying a large number of negative charges (carboxylates) on the Al2O3 layer.

[0083] The hydration of the Al2O3 layer will produce Al 3+ and OH - Two initial ions, of which Al 3+ By forming insoluble Al 3+ / TEMPO-CNFs are trapped in the complexed nanostructure, OH - It is pushed toward Al2O3 by electrostatic repulsion.

[0084] The highly alkaline environment generated by OH- ions destroys the Al2O3 layer through the following reaction:

[0085] Al₂O₃ + 2OH⁻ - +3H₂O→2Al(OH)₄ -

[0086] Exposed Al reacts with water via OH-, as shown in the following equation:

[0087] 2Al + 6H₂O + 2OH⁻ - →2Al(OH)- 4+3H2↑

[0088] Al(OH)4 - →Al(OH)3↓+OH - .

[0089] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. The application of TEMPO-CNFs as a catalyst for promoting the aluminum / water reaction, characterized in that, The TEMPO is a 2,2,6,6-tetramethylpiperidine-1-oxy radical; The aluminum / water reaction is used to produce hydrogen. The TEMPO-CNFs are fibrous, with a length of less than 100 μm and a diameter of less than 100 nanometers; The concentration of the TEMPO-CNFs in water is 0.01-1 wt%; The reaction temperature of the aluminum / water reaction is below 50°C.

2. The application according to claim 1, characterized in that, The aluminum has a particle size of 2-200 μm.

3. A hydrogen production reaction, characterized in that, Aluminum is added to an aqueous solution containing 0.01-1 wt% TEMPO-CNFs; The TEMPO is a 2,2,6,6-tetramethylpiperidine-1-oxy radical; The TEMPO-CNFs are fibrous, with a length of less than 100 μm and a diameter of less than 100 nanometers; The reaction temperature of the aluminum / water reaction is below 50°C.

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