Process for the dehydrogenation of naphthenic compounds and dehydrogenation catalysts, methods for their preparation and use

Abstract

This invention provides a method for dehydrogenating cycloalkanes, a dehydrogenation catalyst, its preparation method, and its application. The catalyst comprises an alumina support and an active component platinum supported on the support; wherein the active component platinum is distributed on the outer surface of the support within a range of 0.2-0.7 times the support radius. When used for the dehydrogenation of cycloalkanes (methylcyclohexane), the catalyst of this invention exhibits excellent dehydrogenation performance (conversion > 95%, selectivity > 99%) at relatively low reaction temperatures (350°C).

Description

Technical Field

[0001] This invention relates to a dehydrogenation catalyst, its preparation method and application, as well as a method for dehydrogenating cycloalkane compounds, a dehydrogenation catalyst, its preparation method and application. Background Technology

[0002] Against the backdrop of a global effort to address climate change, the development of hydrogen energy has become a fundamental consensus in the international community. Currently, the bottleneck for the large-scale application of hydrogen lies in its efficient and safe storage and transportation. Organic liquid hydrogen storage is an emerging technology that utilizes the reaction of unsaturated liquid organic matter with hydrogen to form saturated hydrogenated organic matter, thereby achieving safe storage and transportation of hydrogen at room temperature and pressure.

[0003] The dehydrogenation process of hydrogen storage liquids requires a large amount of energy. Using highly active catalysts is beneficial for lowering the reaction temperature and reducing dehydrogenation energy consumption. Platinum-based catalysts are currently the mainstream dehydrogenation catalysts; however, the high price of platinum metal and limited surface reserves hinder the marketization of this hydrogen storage technology. Reducing the platinum content of the catalyst and increasing its utilization rate are the main technical approaches currently adopted. Nakaya et al. (ACS Catalysis, 2020, 10, 5163-5172) prepared various Pt alloy catalysts using SiO2 as a support, aiming to reduce the amount of the precious metal Pt used, and systematically studied the catalytic dehydrogenation performance of the catalysts on methylcyclohexane. The results showed that even with a Pt loading as high as 3 wt%, the catalytic dehydrogenation conversion rate of methylcyclohexane at 300 °C was only 70%.

[0004] CN112076748A discloses a dehydrogenation catalyst in which Pt element accounts for 1% to 3% of Al2O3 by weight in the active component. This catalyst has high activity and selectivity in organic liquid phase dehydrogenation process.

[0005] CN 115485064A discloses a method of achieving high dispersion of active metals on a support through support sulfidation modification, thereby improving the catalytic activity and selectivity of the catalyst. Summary of the Invention

[0006] The purpose of this invention is to provide a dehydrogenation catalyst with a rational distribution of active species on a support and its preparation method. By controlling the distribution of active species, this invention avoids the excessive aggregation of active species on the outer layer of the support, which would lead to the formation of a large number of large-sized, low-activity particles during calcination. Simultaneously, it avoids the active species being primarily located inside the support, thus reducing the internal diffusion resistance and increasing the availability of active species. This achieves the effect of reducing the amount of active metal used and improving catalytic performance.

[0007] During their research, the inventors of this invention discovered that, due to the large size of hydrogen storage liquid molecules, the dehydrogenation reaction preferentially occurs on the active metal on the catalyst surface. However, if the active metal is only loaded on the surface, it will result in poor dispersion and low catalytic activity. While loading the active metal inside the support can improve its dispersion, the impact of diffusion resistance within the catalyst particles on the availability of the active metal inside the support must be considered. Therefore, this invention proposes to regulate the catalyst preparation process to achieve a reasonable radial distribution of active species along the support, thereby obtaining a highly active dehydrogenation catalyst.

[0008] To achieve the above objectives, this invention employs an acidic regulator to improve the catalyst preparation process, resulting in a dehydrogenation catalyst with a rationally distributed active species along the radial direction of the support (active components distributed on the outer surface of the support within a range of 0.2-0.7 times the support radius). When used for the dehydrogenation of cycloalkanes (methylcyclohexane), this catalyst exhibits excellent dehydrogenation performance (conversion > 95%, selectivity > 99%) at relatively low reaction temperatures (350°C).

[0009] The first aspect of the present invention provides a dehydrogenation catalyst comprising an alumina support and an active component platinum supported on the support; wherein the active component platinum is distributed on the outer surface of the support to a range of 0.2-0.7 times the radius of the support.

[0010] A second aspect of the present invention provides a method for preparing a dehydrogenation catalyst, the method comprising the following steps:

[0011] (1) Prepare an aqueous solution containing platinum ions such that the concentration of platinum ions is 5-20 mmol / L and the concentration of organic complex is 1-5 mmol / L;

[0012] (2) Add an acidity regulator to the ion dispersion in step (1) so that the pH value of the solution is 2.0-5.5;

[0013] (3) The solution obtained in step (2) is contacted with an alumina support source and dried to obtain a catalyst precursor;

[0014] (4) The above catalyst precursor is roasted and reduced.

[0015] A third aspect of the present invention provides a dehydrogenation catalyst obtained by the preparation method described herein.

[0016] The fourth aspect of this invention provides the application of the dehydrogenation catalyst described herein in the dehydrogenation of hydrocarbons, alcohols or ketones.

[0017] A fourth aspect of the present invention provides a method for dehydrogenating a cycloalkane compound, wherein the cycloalkane compound is dehydrogenated in the presence of a dehydrogenation catalyst, the dehydrogenation catalyst comprising the dehydrogenation catalyst described in the present invention.

[0018] In this invention, the above-mentioned technical effects are achieved by combining organic ligand chelation and acidity control of the impregnation solution. When the solution is highly acidic (pH > 5.5), during the impregnation process, only the outer surface of the support can undergo protonation, and the active ions can only be adsorbed on the outside of the support, resulting in the final calcined catalyst with the following cross-sectional morphology. Figure 1 As shown, no catalyst layer was observed inside the support. When the pH is between 2 and 5.5, chelation with organic ligands allows some free protons to diffuse into the support, protonating the inner surface and enabling the adsorption of active ions. By adjusting the pH of the solution, the degree of protonation on the inner surface of the support can be controlled, thereby achieving the goal of regulating the radial distribution of active species along the support and obtaining the desired catalyst (e.g., ...). Figure 2 (As shown). When the solution acidity is too low (pH < 2), the inner and outer surfaces of the support are fully protonated, and the active ions are adsorbed on both the inner and outer surfaces of the support, resulting in a catalyst with a homogeneous structure (as shown). Figure 3 (As shown).

[0019] The catalyst of the present invention has the advantage of a reasonable distribution of active species along the radial direction of the catalyst. Attached Figure Description

[0020] Figure 1 This is a cross-sectional view of the catalyst obtained in Comparative Example 2;

[0021] Figure 2 This is a cross-sectional view of the catalyst obtained in Example 1;

[0022] Figure 3 This is a cross-sectional view of the catalyst obtained in Comparative Example 1. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] This invention provides a dehydrogenation catalyst comprising an alumina support and an active platinum component supported on the support; wherein the active platinum component is distributed on the outer surface of the support within a range of 0.2-0.7 times the support radius, preferably distributed in steps on the outer surface of the support within a range of 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or 0.7 times the support radius.

[0025] According to a preferred embodiment of the present invention, the platinum content is 0.1%-1.2% based on the total mass of the catalyst, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, and 1.2%. The catalyst of the present invention can significantly reduce the platinum content and achieve high selectivity under conditions of lower platinum content.

[0026] According to a preferred embodiment of the present invention, the active component platinum exists in a metallic state.

[0027] Catalysts possessing the aforementioned characteristics of this invention can achieve the objectives of this invention, and there are no special requirements for their preparation methods. In view of this invention, a method for preparing a dehydrogenation catalyst is provided, comprising the following steps:

[0028] (1) Prepare an aqueous solution containing platinum ions such that the concentration of platinum ions is 5-20 mmol / L and the concentration of organic complex is 1-5 mmol / L;

[0029] (2) Add an acidity regulator to the ion dispersion in step (1) so that the pH value of the solution is 2.0-5.5;

[0030] (3) The solution obtained in step (2) is contacted with an alumina support source and dried to obtain a catalyst precursor;

[0031] (4) The above catalyst precursor is roasted and reduced.

[0032] In this invention, the range of organic complexes that can be selected is relatively wide. For this invention, the organic complexes are preferably at least one of acetylacetone, oxalic acid, malonic acid and succinic acid.

[0033] In this invention, there are no special requirements for the calcination and reduction conditions. Commonly used calcination conditions in the prior art can be used in this invention. For example, the general calcination conditions in this invention include: air atmosphere, 500°C, and reaction for 6 hours. However, this embodiment is not limited to this one and is only used as an illustrative example.

[0034] Commonly used reduction conditions in the prior art can be used in this invention. For example, general reduction conditions include: hydrogen atmosphere, reaction at 350°C for 10 hours, but are not limited to this embodiment and are only used as an example.

[0035] According to a preferred embodiment of the present invention, step (3) includes: adsorbing the solution obtained in step (2) onto an alumina support by solution impregnation and drying to obtain a catalyst precursor.

[0036] In this invention, there are no special requirements for the type of Pt source. The Pt source described in this invention includes, but is not limited to, at least one of chloroplatinic acid, sodium chloroplatinate, and potassium chloroplatinate.

[0037] In this invention, the range of acidity regulators that can be selected is relatively wide. According to a preferred embodiment of this invention, the acidity regulator includes, but is not limited to, at least one of hydrochloric acid, nitric acid, citric acid, hydrobromic acid, perchloric acid and acetic acid, preferably acetic acid and / or perchloric acid.

[0038] For the present invention, it is preferred that the platinum-containing ion solution and the alumina carrier source be contacted under light-protected conditions for 8-12 hours, and the contact temperature is 40-60℃.

[0039] In this invention, there are no special requirements for drying conditions. For the purposes of this invention, the drying conditions for the catalyst precursor are exemplarily described as follows: temperature 80-150°C, time 12-24h, but this should not be construed as limiting the scope of this invention.

[0040] This invention provides a dehydrogenation catalyst obtained by the preparation method described herein.

[0041] The dehydrogenation catalyst obtained by the method of the present invention has the following characteristics.

[0042] The dehydrogenation catalyst prepared by the present invention comprises an alumina support and an active component platinum supported on the support; wherein the active component platinum is distributed on the outer surface of the support within a range of 0.2-0.7 times the support radius, preferably distributed in steps on the outer surface of the support within a range of 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, or 0.7 times the support radius.

[0043] The dehydrogenation catalyst prepared by this invention has a platinum content of 0.1%-1.2% based on the total mass of the catalyst, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, and 1.2%. The catalyst of this invention can significantly reduce the platinum content and achieve high selectivity under conditions of lower platinum content.

[0044] The dehydrogenation catalyst prepared in this invention has platinum as the active component in a metallic state.

[0045] This invention provides the application of the dehydrogenation catalyst described herein in the dehydrogenation of hydrocarbons, alcohols, or ketones, particularly cycloalkanes. The dehydrogenation catalyst of this invention has the advantage of high catalytic activity in the aforementioned dehydrogenation reactions.

[0046] This invention provides a method for dehydrogenating cycloalkane compounds, wherein the cycloalkane compounds are dehydrogenated in the presence of a dehydrogenation catalyst, the dehydrogenation catalyst comprising any one of the dehydrogenation catalysts described in this invention.

[0047] According to a preferred embodiment of the present invention, preferably, the cycloalkane compound is at least one selected from methylcyclohexane, cyclohexane, dimethylcyclohexane, ethylcyclohexane, tetrahydronaphthalene, and decahydronaphthalene.

[0048] The present invention will be described in detail below through examples. In the following examples, the metal content parameters were measured by ICP method; the specific surface area of ​​the catalyst was obtained by nitrogen adsorption-desorption tester; and the alumina support was a commercially available product.

[0049] The distribution of the catalyst along the radial direction of the support was detected using an optical microscope.

[0050] Example 1

[0051] (1) A certain amount of chloroplatinic acid was prepared into an aqueous solution with a platinum ion concentration of 15 mmol / L and a succinic acid concentration of 3 mmol / L. Hydrochloric acid aqueous solution was added to make the pH of the platinum-containing solution 2.6. Then, the platinum-containing solution was placed in contact with the alumina support at 40°C in the dark for 10 h. Subsequently, the alumina support carrying the precursor was placed in an oven at 110°C for 14 h.

[0052] (2) The above-mentioned precursor containing metal elements was placed in an air atmosphere at 450°C for 4 hours, and the heating rate of the calcining furnace was 5°C / min.

[0053] (3) Take 5g of the roasted product and place it in a tubular reactor for reduction. The reduction temperature is 350℃ and the reduction time is 4h.

[0054] The obtained catalyst, as determined by ICP testing, contains 0.7 wt% platinum and the active components are distributed on the outer surface of the support up to 0.5 times the radius of the support.

[0055] Dehydrogenation of methylcyclohexane to produce hydrogen:

[0056] In the reaction tube, the catalyst loading was 1 g, the reaction temperature was 350 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 2 h⁻¹. -1 The product after 12 hours of reaction was analyzed, and the conversion rate of methylcyclohexane was 96.8%, while the selectivity for toluene was 99.3%.

[0057] Figure 2 This is a cross-sectional view of the catalyst obtained in Example 1. The white area represents the alumina support, and the gray area represents the supported active metal. The active components are distributed on the outer surface of the support up to 0.5 times the radius of the support.

[0058] Example 2

[0059] (1) A certain amount of sodium chloroplatinate was prepared into an aqueous solution with a platinum ion concentration of 19 mmol / L and an oxalic acid concentration of 4.9 mmol / L. Nitric acid aqueous solution was added to make the pH of the platinum-containing solution 2.0. Then, the platinum-containing solution was placed in contact with the alumina support at 55°C in the dark for 8 hours. Subsequently, the alumina support carrying the precursor was placed in an oven at 140°C for 18 hours.

[0060] (2) The above-mentioned precursor containing metal elements was placed in an air atmosphere at 450°C for 4 hours, and the heating rate of the calcining furnace was 5°C / min.

[0061] (3) Take 5g of the roasted product and place it in a tubular reactor for reduction. The reduction temperature is 350℃ and the reduction time is 4h.

[0062] The obtained catalyst, as determined by ICP testing, contains 0.7 wt% platinum and the active components are distributed on the outer surface of the support up to 0.7 times the radius of the support.

[0063] Dehydrogenation of methylcyclohexane to produce hydrogen:

[0064] In the reaction tube, the catalyst loading was 1 g, the reaction temperature was 350 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 2 h⁻¹. -1 The product after 12 hours of reaction was analyzed, and the conversion rate of methylcyclohexane was 96.3%, while the selectivity for toluene was 99.1%.

[0065] Example 3

[0066] (1) A certain amount of potassium chloroplatinate was prepared into an aqueous solution with a platinum ion concentration of 6 mmol / L and an acetylacetone concentration of 1 mmol / L. Acetic acid aqueous solution was added to make the pH of the platinum-containing solution 5.4. Then, the platinum-containing solution was placed in contact with the alumina support at 44℃ in the dark for 12 h. Subsequently, the alumina support loaded with the precursor was placed in an oven at 100℃ for 24 h.

[0067] (2) The above-mentioned precursor containing metal elements was placed in an air atmosphere at 450°C for 4 hours, and the heating rate of the calcining furnace was 5°C / min.

[0068] (3) Take 5g of the roasted product and place it in a tubular reactor for reduction. The reduction temperature is 350℃ and the reduction time is 4h.

[0069] The obtained catalyst, as determined by ICP testing, contains 0.7 wt% platinum and the active components are distributed on the outer surface of the support up to 0.2 times the radius of the support.

[0070] Dehydrogenation of methylcyclohexane to produce hydrogen:

[0071] In the reaction tube, the catalyst loading was 1 g, the reaction temperature was 350 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 2 h⁻¹.-1 The product after 12 hours of reaction was analyzed, and the conversion rate of methylcyclohexane was 95.5%, while the selectivity for toluene was 99.3%.

[0072] Example 4

[0073] (1) A certain amount of chloroplatinic acid was prepared into an aqueous solution with a platinum ion concentration of 15 mmol / L and a succinic acid concentration of 3 mmol / L. Perchloric acid aqueous solution was added to make the pH of the platinum-containing solution 3.0. Then, the platinum-containing solution was placed in contact with the alumina support at 40°C in the dark for 10 h. Subsequently, the alumina support carrying the precursor was placed in an oven at 110°C for 14 h.

[0074] (2) The above-mentioned precursor containing metal elements was placed in an air atmosphere at 450°C for 4 hours, and the heating rate of the calcining furnace was 5°C / min.

[0075] (3) Take 5g of the roasted product and place it in a tubular reactor for reduction. The reduction temperature is 350℃ and the reduction time is 4h.

[0076] The obtained catalyst, as determined by ICP testing, contains 0.65 wt% platinum and the active components are distributed on the outer surface of the support up to 0.4 times the radius of the support.

[0077] Dehydrogenation of methylcyclohexane to produce hydrogen:

[0078] In the reaction tube, the catalyst loading was 1 g, the reaction temperature was 350 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 2 h⁻¹. -1 The product after 12 hours of reaction was analyzed, and the conversion rate of methylcyclohexane was 97.1%, while the selectivity for toluene was 99.4%.

[0079] Example 5

[0080] (1) A certain amount of chloroplatinic acid was prepared into an aqueous solution with a platinum ion concentration of 15 mmol / L, a succinic acid concentration of 2 mmol / L, and an acetylacetone concentration of 1 mmol / L. Perchloric acid aqueous solution was added to make the pH of the platinum-containing solution 3.0. Then, the platinum-containing solution was placed in contact with the alumina support at 40°C in the dark for 10 h. Subsequently, the alumina support carrying the precursor was placed in an oven at 110°C for 14 h.

[0081] (2) The above-mentioned precursor containing metal elements was placed in an air atmosphere at 450°C for 4 hours, and the heating rate of the calcining furnace was 5°C / min.

[0082] (3) Take 5g of the roasted product and place it in a tubular reactor for reduction. The reduction temperature is 350℃ and the reduction time is 4h.

[0083] The obtained catalyst, as determined by ICP testing, contains 0.65 wt% platinum and the active components are distributed on the outer surface of the support up to 0.6 times the radius of the support.

[0084] Dehydrogenation of methylcyclohexane to produce hydrogen:

[0085] In the reaction tube, the catalyst loading was 1 g, the reaction temperature was 350 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 2 h⁻¹. -1 The product after 12 hours of reaction was analyzed, and the conversion rate of methylcyclohexane was 97.3%, while the selectivity for toluene was 99.4%.

[0086] Comparative Example 1

[0087] The method is the same as in Example 1, except that an aqueous hydrochloric acid solution is added to make the pH of the platinum-containing solution 1.5.

[0088] The obtained catalyst, as determined by ICP testing, contains 0.7 wt% platinum and the active components are uniformly distributed on the support.

[0089] The conversion rate of methylcyclohexane was 93.9%, and the selectivity for toluene was 98.6%.

[0090] Figure 3 The image shows a cross-sectional view of the catalyst obtained in Comparative Example 1. The white area represents the alumina support, and the gray area represents the supported active metal. The active components are uniformly distributed on the support.

[0091] Comparative Example 2

[0092] The method is the same as in Example 2, except that an aqueous hydrochloric acid solution is added to make the pH of the platinum-containing solution 6.3.

[0093] The obtained catalyst, as determined by ICP testing, contains 0.7 wt% platinum and the active components are distributed on the outer surface of the support.

[0094] The conversion rate of methylcyclohexane was 93.5%, and the selectivity for toluene was 98.5%.

[0095] Figure 1 The image shows a cross-sectional view of the catalyst obtained in Comparative Example 2. The white area represents the alumina support, and the gray area represents the supported active metal. The active components are mainly located on the outer surface of the support.

[0096] Comparative Example 3

[0097] The method described in Example 1 was followed, except that succinic acid was not added; all other conditions remained the same.

[0098] The obtained catalyst, as determined by ICP testing, contains 0.7 wt% platinum and the active components are distributed on the outer surface of the support up to 0.18 times the radius of the support.

[0099] Dehydrogenation of methylcyclohexane to produce hydrogen:

[0100] In the reaction tube, the catalyst loading was 1 g, the reaction temperature was 350 °C, and the mass hourly space velocity (WHSV) of methylcyclohexane was 2 h⁻¹. -1 The product after 12 hours of reaction was analyzed, and the conversion rate of methylcyclohexane was 94.0%, and the selectivity of toluene was 98.7%.

[0101] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for dehydrogenating a cycloalkane compound, wherein the cycloalkane compound is dehydrogenated in the presence of a dehydrogenation catalyst, characterized in that, The catalyst comprises an alumina support and platinum as the active component supported on the support; wherein the platinum active component is distributed on the outer surface of the support to a range of 0.2-0.7 times the radius of the support; and the platinum content is 0.1%-1.2% based on the total mass of the catalyst. The cycloalkane compound is at least one selected from methylcyclohexane, dimethylcyclohexane, ethylcyclohexane, tetrahydronaphthalene, and decahydronaphthalene.

2. The method according to claim 1, wherein, The active component, platinum, exists in a metallic state.

3. The method according to claim 1, wherein, The preparation method of the dehydrogenation catalyst includes the following steps: (1) Prepare an aqueous solution containing platinum ions such that the concentration of platinum ions is 5-20 mmol / L and the concentration of organic complex is 1-5 mmol / L, wherein the organic complex is at least one of acetylacetone, oxalic acid, malonic acid and succinic acid; (2) Add an acidity regulator to the ion dispersion in step (1) to make the pH of the solution 2.0-5.5; (3) Contact the solution obtained in step (2) with the alumina support source and dry it to obtain the catalyst precursor; (4) The above catalyst precursor is roasted and reduced.

4. The method according to claim 3, wherein, Step (3) includes: adsorbing the solution obtained in step (2) onto the alumina support by solution impregnation and drying to obtain the catalyst precursor.

5. The method according to claim 3, wherein, The Pt source is selected from at least one of chloroplatinic acid, sodium chloroplatinate, and potassium chloroplatinate; and / or The acidity regulator is selected from at least one of hydrochloric acid, nitric acid, citric acid, hydrobromic acid, perchloric acid, and acetic acid.

6. The method according to claim 5, wherein, The acidity regulator is acetic acid and / or perchloric acid.

7. The method according to any one of claims 3-6, wherein, In step (3), the solution is in contact with the alumina carrier source for 8-12 hours under light-protected conditions, and the contact temperature is 40-60℃.

8. The method according to any one of claims 3-6, wherein the drying conditions for the catalyst precursor include: Temperature 80-150℃, time 12-24h.

9. The dehydrogenation catalyst obtained by the method of any one of claims 3-8.

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