A fiber-type noble metal catalyst and its preparation method

Abstract

This invention relates to a fiber-type noble metal catalyst and its preparation method, belonging to the field of functional polymer materials technology. The catalyst, for the first time, uses amine fibers as a support, on which noble metal elements platinum or gold are chemically adsorbed and loaded; the amine content in the amine fibers is 2.5 mmol / g to 3 mmol / g; the method uses amine fibers as a support and employs an adsorption-reduction approach, selectively fixing the noble metal elements to active sites on the fiber surface without aggregation or the formation of atomic clusters. The resulting catalyst not only has higher catalytic efficiency but also saves on the amount of noble metal used.

Description

Technical Field

[0001] This invention relates to a fiber-type noble metal catalyst and its preparation method, belonging to the field of functional polymer materials technology. Background Technology

[0002] Noble metal catalysts are precious metal materials that can alter the rate of chemical reactions without participating in the reaction to form the final products. They play a very important role in fields such as chemical engineering, petroleum refining, petrochemicals, pharmaceuticals, environmental protection, and new energy.

[0003] Noble metal catalysts can be broadly classified into two categories: homogeneous catalysis and heterogeneous catalysis. Heterogeneous catalysis accounts for 80% to 90% of all catalytic reactions. The vast majority of heterogeneous catalysts are supported on noble metals and can be further categorized into particulate, spherical, columnar, and honeycomb structures. Commonly used catalyst supports include Al₂O₃, SiO₂, porous ceramics, and activated carbon. Due to the scarcity and high cost of noble metal resources, researchers are continuously developing non-noble metal or low-noble metal catalysts.

[0004] In existing technologies, the preparation of catalysts using traditional supports (such as Al2O3, SiO2, activated carbon, etc.) to support noble metals has the following drawbacks: (1) Noble metals tend to agglomerate to form atomic clusters, which reduces the number of active sites and limits catalytic efficiency; (2) The precious metals are not evenly dispersed, and some precious metals are wrapped in the pores of the carrier, which prevents them from fully participating in the catalytic reaction, resulting in the waste of precious metals; (3) The carrier has limited specific surface area and surface active groups, resulting in poor loading capacity and fixation effect for precious metals, which affects the stability and service life of the catalyst.

[0005] Currently, some technologies exist that use fibers as carriers for precious metal catalysts, primarily conventional fibers such as carbon fiber and glass fiber. There are no reports of technologies using amine fibers as carriers for precious metal catalysts. Amine fibers are currently mainly used in the field of adsorption materials for treating wastewater containing heavy metal ions. Their core function is to achieve adsorption and separation by utilizing the chelation effect of amine groups with heavy metal ions. There are no technological inspirations for using them as catalyst carriers to load precious metals for catalytic reactions, nor are there any technological concepts related to improving catalytic efficiency or saving precious metal usage. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a fiber-type noble metal catalyst and its preparation method. The catalyst uses amine fiber as the catalyst support for the first time. The method uses amine fiber as the support and adopts an adsorption-reduction method to prepare the catalyst. The noble metal elements are selectively fixed on the active sites on the fiber surface without aggregation, and therefore no atomic clusters are generated. The catalyst prepared not only has higher catalytic efficiency, but also saves the amount of noble metal used.

[0007] To achieve the objectives of this invention, the following technical solutions are provided.

[0008] A fiber-type noble metal catalyst, wherein the catalyst uses amine-based fibers as a support on which noble metal elements are chemically adsorbed and loaded; The precious metal is platinum (Pt) or gold (Au).

[0009] Furthermore, preferably, the mass fraction of the precious metal is 0.1% to 0.5% based on the mass of the amino fiber as 100%.

[0010] The amino group content in the amino fiber is 2.5 mmol / g to 3 mmol / g.

[0011] Furthermore, the amino-based fibers are preferably prepared by the following method: (1) The fiber is placed in an aqueous sodium hydroxide solution and hydrolyzed at 90 ℃ ~ 120 ℃ for 60 min ~ 90 min. It is then washed until neutral to obtain fiber containing carboxyl groups. Furthermore, when the mass fraction of the sodium hydroxide aqueous solution is preferably 0.5%, the mass ratio of fiber to sodium hydroxide aqueous solution is 1:20 to 1:50; (2) Soak the carboxyl-containing fiber in an aqueous solution of an amino group for 5 min to 10 min, squeeze and dehydrate to constant weight, and react at 70 ℃ to 105 ℃ for 30 min to 90 min under nitrogen or argon protection to obtain the amine-grafted fiber. The mass fraction of the amine in the aqueous solution is 5% to 20%; the mass ratio of the carboxyl-containing fiber to the aqueous solution of the amine is 1:10 to 1:20. (3) Soak the grafted amine fibers in the mixed solution for 5 min to 10 min, squeeze to dehydrate to constant weight, and react at 70 ℃ to 135 ℃ for 30 min to 90 min under nitrogen or argon protection to obtain solid amine fibers with high amine content. The mass ratio of the grafted amine-containing fiber to the mixed solution is 1:10 to 1:20; the mixed solution consists of amine-containing substances, crosslinking agents, and water, with the amine-containing substances comprising 5% to 20% of the total mass of the mixed solution, the crosslinking agent comprising 0.5% to 2% of the mass, and the remainder being water; the crosslinking agent is an aziridine crosslinking agent, an epoxy crosslinking agent, adipic acid, glutaric acid, or succinic acid; The amine substances in steps (2) and (3) are, respectively, polyethyleneamine, polyethyleneimine, triethylenetetramine or polyethylenepolyamine.

[0012] Furthermore, the fiber is polyester or acrylic.

[0013] A method for preparing the fibrous noble metal catalyst of the present invention, comprising the following steps: (1) The amino fiber is immersed in a noble metal solution with a mass fraction of 0.5% to 1% and statically adsorbed at 25℃ to 50℃. During the static adsorption process, the amino groups on the surface of the amino fiber undergo a chelation reaction with the noble metal ions. After adsorption for 2h to 4h, the fiber is taken out of the solution, washed with water to remove the unadsorbed free noble metal ions on the surface, and dried at 65℃ to 75℃ until the fiber weight no longer decreases, thus obtaining the dried fiber. (2) The dried fiber prepared in step (1) is soaked in a reducing agent solution with a mass fraction of 1% to 10% and the reduction reaction is carried out at 25 ℃ to 50 ℃ for 1 h to 2 h. The residual reducing agent is washed with water and dried to obtain a fiber-type noble metal catalyst. The reducing agent in the reducing agent solution is sodium borohydride or hydrazine hydrate.

[0014] Furthermore, in step (1): Wash with deionized water 3 to 5 times, each time for 5 to 10 minutes; dry in an oven for 2 to 3 hours until the fiber weight no longer decreases.

[0015] Furthermore, in step (2): Wash with deionized water 3 to 5 times to remove residual reducing agent; dry in an oven at 65 ℃ to 75 ℃ for 2 to 3 hours.

[0016] Beneficial effects (1) This invention provides a fiber-type noble metal catalyst. The catalyst creatively introduces amine fiber as a support for the first time. In the prior art, amine fiber is mainly used in the field of adsorption. Applying it to the catalyst support requires solving technical difficulties such as the effective binding of the active sites on the support surface with noble metal ions, the stable fixation of the reduced metal element and the control of dispersion. This invention successfully solves the above difficulties through specific amine fiber index requirements and loading methods. By loading noble metals such as platinum or gold on the fiber surface, metal atoms with high catalytic activity are obtained after reduction.

[0017] (2) The present invention provides a fiber-type noble metal catalyst, wherein the content of amino groups in the amine fibers of the catalyst is 2.5 mmol / g to 3 mmol / g. This range of amino group content is the key to achieving efficient loading of noble metals: if the content of amino groups is less than 2.5 mmol / g, there are insufficient active sites on the surface of the support, and the noble metal ions cannot be fully adsorbed, resulting in a low loading of noble metals and insufficient catalytic activity; if it is higher than 3 mmol / g, the mechanical strength of the amine fibers will decrease significantly, and they are prone to breakage and damage during subsequent adsorption, reduction and catalytic reactions, affecting the practicality and stability of the catalyst; furthermore, it is preferred that the amine fibers are prepared by the method of the present invention. The amine fibers prepared by this method have the advantages of high amine content, uniform distribution and good mechanical strength. Compared with other preparation methods, they can more effectively achieve uniform loading and stable fixation of noble metals. (3) The present invention provides a fiber-type noble metal catalyst. Platinum and gold are selected as noble metal components in the amine fiber of the catalyst because: they have excellent catalytic activity and can be applied to a variety of catalytic reaction scenarios (such as hydrogenation reaction, oxidation reaction, etc.); and platinum and gold ions have a strong chelating effect with the amine groups on the surface of the amine fiber, which can be easily loaded by chemical adsorption. After reduction, they can exist stably on the fiber surface and are not easy to agglomerate; other noble metals (such as palladium, silver, etc.) either have a weak chelating effect with the amine groups and poor loading effect; or they are easy to form atomic clusters after reduction, which cannot achieve the catalytic efficiency and noble metal saving effect of the present invention. The preferred loading of precious metals on the amine fiber support is 0.1wt% to 0.5wt%. This loading range can ensure catalytic efficiency while minimizing the amount of precious metals used. When the loading is less than 0.1wt%, there are insufficient active sites, and the catalytic efficiency is difficult to meet the actual requirements. When the loading is greater than 0.5wt%, the precious metals are prone to agglomeration and exceed the number of active sites required for the catalytic reaction, resulting in waste of precious metals. (4) This invention provides a fibrous noble metal catalyst, which, compared with traditional particulate and porous material catalysts, has the following advantages: ① Noble metal elements are fixed on the fiber surface and no atomic clusters are generated: The amino groups on the surface of the amino fiber form stable chelate bonds with the noble metal ions. After reduction, the metal element is uniformly dispersed on the fiber surface, avoiding the problem of noble metal agglomeration and atomic cluster formation in traditional carriers, and increasing the number of active sites. ② Higher catalytic efficiency: The fibrous support has a larger specific surface area, and all the noble metal active sites are exposed on the fiber surface, which can fully contact the reactants. Compared with the traditional porous support where some active sites are wrapped in pores, the catalytic efficiency is improved by 30% to 50% based on the test results of the examples. ③ Saves precious metal usage: Since the precious metals are uniformly dispersed and do not agglomerate, the precious metal loading of the present invention is only 60% to 70% of that of traditional catalysts to achieve the same catalytic efficiency, which significantly reduces the consumption of precious metals and alleviates the problem of scarce and expensive precious metal resources. (5) This invention provides a method for preparing a fiber-type noble metal catalyst, which uses an amine fiber and a solution containing noble metals to combine through static adsorption and then reduce with a reducing agent; wherein in step (1), a noble metal solution with a mass fraction of 0.5% to 1% is used. This mass fraction range is the key to achieving the target loading: if the mass fraction is less than 0.5%, the concentration of noble metal ions in the solution is insufficient, and even if the adsorption time is extended, it is difficult to achieve the required loading; if it is higher than 1%, the concentration of noble metal ions in the solution is too high, which can easily lead to the waste of unadsorbed noble metal ions and increase the difficulty of subsequent cleaning; The adsorption time is 2 h to 4 h, within which the noble metal ions can be fully adsorbed. If the adsorption time is less than 2 h, the adsorption is insufficient and the loading is too low; if it exceeds 4 h, the adsorption reaches saturation, and it is meaningless to continue to extend the time, but it will also increase the preparation cost. The chemical loading method is static adsorption. The advantages of static adsorption are that it is simple to operate, requires no additional equipment, and can ensure that the amine fiber and the noble metal solution are in full contact, thus ensuring uniform adsorption of noble metal ions. Compared with dynamic adsorption, static adsorption can avoid fiber damage caused by fluid scouring, and at the same time, it is more conducive to the full chelation reaction between amine groups and noble metal ions. The static adsorption temperature is 25℃~50℃, which can balance adsorption efficiency and energy consumption. When the temperature is below 25℃, the chelation reaction rate is slow and the adsorption time needs to be extended significantly. When the temperature is above 50℃, the noble metal solution is easy to volatilize and may cause the decomposition of amine groups on the surface of amine fibers, reducing the loading effect.

[0018] In addition, the static adsorption chemical loading method is simple to operate, low in cost, and can ensure uniform dispersion of precious metals. It does not require complex equipment and is suitable for large-scale production. (6) This invention provides a method for preparing a fiber-type noble metal catalyst, which adopts a process of combining amine-based fibers with a solution containing noble metals through static adsorption and then reducing them with a reducing agent; wherein in step (2), the reducing agent is sodium borohydride or hydrazine hydrate. The reason for choosing these two reducing agents is that they have strong reducing power and can efficiently reduce noble metal ions to metal elements under mild conditions, and the reduction products are environmentally friendly and will not introduce harmful impurities; other reducing agents (such as formaldehyde) have low reduction efficiency or produce toxic byproducts during the reduction process, which affect the purity and safety of the catalyst. The reduction reaction is carried out at a temperature of 25 ℃ ~ 50 ℃. This temperature range ensures that the reduction reaction proceeds efficiently: when the temperature is below 25 ℃, the reduction reaction rate is too slow and the reduction is incomplete; when the temperature is above 50 ℃, the reducing agent is prone to decomposition and failure, and may cause the loaded noble metal element to agglomerate, forming atomic clusters and reducing catalytic activity. The mass fraction of the reducing agent solution is 1% to 10%, which ensures the reduction effect. If the mass fraction is less than 1%, the reducing agent concentration is insufficient and the reduction reaction is incomplete. If it is more than 10%, the reducing agent is excessive and the reduction product is likely to adhere to the fiber surface, affecting the exposure of the catalyst active sites. The reduction reaction takes 1 to 2 hours. Within this time range, the adsorbed noble metal ions can be fully reduced to the metal element. If the reaction time is less than 1 hour, the reduction is insufficient, and some noble metal ions are not converted into active metal elements, resulting in low catalytic efficiency. If the reaction time exceeds 2 hours, the reduction is complete, and further extending the time is meaningless. (7) The present invention provides a method for preparing a fiber-type noble metal catalyst. The method has a short preparation process, low energy consumption, and environmental friendliness. The preparation cost is reduced by 20% to 30% compared with traditional catalysts, and it has significant industrial application value. Detailed Implementation

[0019] The present invention will be described in detail below with specific embodiments, but these are not intended to limit the scope of the present invention.

[0020] Example 1 A method for preparing a fibrous noble metal catalyst, comprising the following steps: (1) Place 10 g of acrylic fiber into 300 g of sodium hydroxide aqueous solution with a mass fraction of 0.5%, heat at 100°C for 75 min to hydrolyze, and wash with deionized water until neutral to obtain fiber containing carboxyl groups; The carboxyl-containing fiber was immersed in a 10% (w / w) polyethyleneimine aqueous solution for 8 min, squeezed to dehydrate to constant weight, and heated at 90 °C for 60 min under nitrogen protection to obtain amine-grafted fiber; wherein the mass ratio of the carboxyl-containing fiber to the polyethyleneimine aqueous solution was 1:15. The cellulose grafted with amine groups was immersed in a mixed solution for 8 minutes, squeezed to dehydrate to constant weight, and then heated at 100°C for 60 minutes under nitrogen protection to obtain amine-based fibers. The mass ratio of the fiber cloth grafted with amine groups to the mixed solution is 1:15; the mixed solution consists of 10% polyethyleneimine, 1% aziridine crosslinking agent, and water. The content of amino groups in the amino fiber was determined to be 2.5 mmol / g using an acid-base titration method and an automatic potentiometric titrator.

[0021] (2) Place 2 g of the amino fiber prepared in step (1) into 200 ml of chloroauric acid solution, the mass fraction of gold in the chloroauric acid solution is 1%, and perform static adsorption reaction at 50 °C for 3 h; take out the fiber, wash it with deionized water 5 times, each time for 10 min, to remove the unadsorbed free gold ions on the surface; heat and dry it in an oven at 75 °C for 3 h until the weight of the fiber no longer decreases, and obtain the dried fiber.

[0022] (3) The dried fiber was soaked in a 10% hydrazine hydrate solution and reduced at 50°C for 1.5 h. The fiber was washed 5 times with deionized water and dried in an oven at 75°C for 3 h to obtain the fiber-type gold catalyst.

[0023] Catalytic performance test: Test method: A micro fixed-bed reactor was used. 2g of the fibrous gold catalyst prepared in this example was loaded into a glass reaction tube. 1% carbon monoxide was introduced, and the equilibrium gas was 99% air. The gas flow rate was 50 ml / min, and the reaction temperature was 25 ℃. The volume fraction of carbon monoxide before and after the reaction was tested using a YT-1200H-S tester. Test results: The volume fraction of carbon monoxide before the reaction was 1.0%, and the volume fraction of carbon monoxide at the outlet after the reaction was 0.4%, with a carbon monoxide conversion rate of 60%. Comparative test: Using a catalyst with gold supported on a traditional activated carbon carrier, the gold loading was the same as in this example, with a mass fraction of 0.45%. Under the same test conditions, the carbon monoxide conversion rate was 35%. Conclusion: The fibrous gold catalyst prepared in this embodiment has a catalytic efficiency that is 71.4% higher than that of the traditional activated carbon supported gold catalyst.

[0024] Example 2 A method for preparing a fibrous noble metal catalyst, comprising the following steps: (1) Place 10 g of acrylic fiber into 400 g of sodium hydroxide aqueous solution with a mass fraction of 0.5%, heat at 110 °C for 80 min to hydrolyze, and wash with deionized water until neutral to obtain fiber containing carboxyl groups; The above-mentioned carboxyl-containing fibers were soaked in a 15% (w / w) polyethyleneamine aqueous solution for 10 min, squeezed to dehydrate to constant weight, and heated at 100 °C for 70 min under argon protection to obtain amine-grafted fibers; the mass ratio of carboxyl-containing fibers to polyethyleneamine aqueous solution was 1:20. The cellulose grafted with amine groups was immersed in a mixed solution for 10 min, squeezed to dehydrate to constant weight, and heated at 120°C for 70 min under argon protection to obtain amine-based cellulose. The mass ratio of the grafted amine-group fiber to the mixed solution is 1:20; the mixed solution consists of 15% polyethyleneamine, 1.5% epoxy crosslinking agent, and water. The content of amino groups in the amino fiber was determined to be 3.0 mmol / g using an acid-base titration method and an automatic potentiometric titrator.

[0025] (2) Place 2 g of the amino fiber prepared in step (1) into 200 ml of chloroplatinic acid solution, the mass fraction of platinum in the chloroplatinic acid solution is 0.5%, and statically adsorb at 25 ℃ for 2 h; take out the fiber, wash it with deionized water 4 times, each time for 8 min, to remove the unadsorbed free platinum ions on the surface; heat and dry it in an oven at 70 ℃ for 2.5 h until the fiber weight no longer decreases, and obtain the dried fiber.

[0026] (3) The dried fiber was soaked in a 1% sodium borohydride solution and reduced at 25°C for 1 h. The fiber was washed 4 times with deionized water and dried in an oven at 70°C for 2.5 h to obtain the fiber-type platinum catalyst.

[0027] Catalytic performance test: Test method: A micro fixed-bed reactor was used. 2 g of the fibrous platinum catalyst prepared in this example was loaded into a glass reaction tube. Hydrogen gas with a volume fraction of 1% was introduced, and nitrogen gas with a volume fraction of 99% was used as the equilibrium gas. The gas flow rate was 50 ml / min, and the reaction temperature was 25 ℃. The volume fraction of hydrogen gas before and after the reaction was tested using a GC-950 micro hydrogen analyzer manufactured by Shanghai Haixin Chromatography Instrument Co., Ltd. Test results: The hydrogen gas fraction before the reaction was 1.0%, and the hydrogen gas fraction at the outlet after the reaction was 0.6%, with a hydrogen conversion rate of 40%. Comparative test: Using a conventional Al2O3 support to support platinum catalyst, with the same platinum loading as in this example (0.15% by mass), and under the same conditions, the hydrogen conversion rate was 25%. Conclusion: The fibrous platinum catalyst prepared in this embodiment has a catalytic efficiency that is 60% higher than that of the traditional Al2O3 supported platinum catalyst.

Claims

1. A fibrous noble metal catalyst, characterized in that: The catalyst uses amine fibers as a support, on which precious metal elements platinum or gold are chemically adsorbed and loaded; the amine content in the amine fibers is 2.5 mmol / g ~ 3 mmol / g.

2. The fiber-type noble metal catalyst according to claim 1, characterized in that: Based on the mass of 100% amine fiber, the mass fraction of the precious metal is 0.1% to 0.5%.

3. A fibrous noble metal catalyst according to claim 1 or 2, characterized in that: The amino-based fiber was prepared using the following method: (1) The fiber is placed in an aqueous sodium hydroxide solution and hydrolyzed at 90 ℃ ~ 120 ℃ for 60 min ~ 90 min. It is then washed until neutral to obtain fiber containing carboxyl groups. (2) Soak the carboxyl-containing fiber in an aqueous solution of an amino group for 5 min to 10 min, squeeze and dehydrate to constant weight, and react at 70 ℃ to 105 ℃ for 30 min to 90 min under nitrogen or argon protection to obtain the amine-grafted fiber. (3) Soak the amine-grafted fiber in the mixed solution for 5 min to 10 min, squeeze to dehydrate to constant weight, and react at 70 ℃ to 135 ℃ for 30 min to 90 min under nitrogen or argon protection to obtain amine-based fiber; The mixed solution is composed of an amine substance, a crosslinking agent, and water. Based on the total mass of the mixed solution as 100%, the mass fraction of the amine substance is 5% to 20%, the mass fraction of the crosslinking agent is 0.5% to 2%, and the remainder is water. The crosslinking agent is an aziridine crosslinking agent, an epoxy crosslinking agent, adipic acid, glutaric acid, or succinic acid.

4. A fiber-type noble metal catalyst according to claim 3, characterized in that: In step (1), when the mass fraction of the sodium hydroxide aqueous solution is 0.5%, the mass ratio of the fiber to the sodium hydroxide aqueous solution is 1:20 to 1:50; the fiber is polyester or acrylic fiber. In step (2), the mass fraction of the amine substance in the aqueous solution is 5% to 20%; the mass ratio of the carboxyl-containing fiber to the aqueous solution of the amine substance is 1:10 to 1:

20. In step (3), the mass ratio of the amine-grafted fiber to the mixed solution is 1:10 to 1:20; In steps (2) and (3), the amine substances are, respectively, polyethyleneamine, polyethyleneimine, triethylenetetramine or polyethylenepolyamine.

5. A method for preparing a fibrous noble metal catalyst as described in any one of claims 1 to 4, characterized in that: (1) Immerse the amino fiber in a noble metal solution with a mass fraction of 0.5% ~ 1% and perform static adsorption chelation reaction at 25 ℃ ~ 50 ℃ for 2 h ~ 4 h. Remove the fiber from the solution, wash it with water, and dry it at 65 ℃ ~ 75 ℃ until the fiber weight no longer decreases, to obtain the dried fiber. (2) The dried fiber is soaked in a reducing agent solution with a mass fraction of 1% to 10% and the reduction reaction is carried out at 25℃ to 50℃ for 1 h to 2 h. The fiber is washed with water and dried to obtain a fiber-type noble metal catalyst. The reducing agent in the reducing agent solution is sodium borohydride or hydrazine hydrate.

6. The method for preparing a fibrous noble metal catalyst according to claim 5, characterized in that: In step (1), the fiber is washed 3 to 5 times with deionized water, each time for 5 to 10 minutes; drying is done in an oven for 2 to 3 hours until the fiber weight no longer decreases.

7. The method for preparing a fibrous noble metal catalyst according to claim 5, characterized in that: In step (2), the residual reducing agent is removed by washing with deionized water 3 to 5 times; drying is carried out in an oven at 65 ℃ to 75 ℃ for 2 h to 3 h.