Dehydrogenation catalyst, method for preparing and using the same, and method for dehydrogenating methylcyclohexane

Abstract

The present application relates to a dehydrogenation catalyst, its preparation method and application, and a methylcyclohexane dehydrogenation method, the catalyst comprising: Pt element, hydrocarbon complex and carrier; the hydrocarbon complex has a graphitization degree I D / I G = 1.9-1.2, wherein I D is the intensity of disordered carbon peak, and I G is the intensity of ordered carbon peak. It is proposed to introduce an organic compound in the reduction stage of catalyst preparation, and a dehydrogenation catalyst containing hydrocarbon complex is obtained. The organic compound is converted into hydrocarbon complex in situ during the reduction process of the catalyst, the high active sites in the catalyst are reasonably covered, the C-C bond activation ability of the active sites is weakened or eliminated, the C-H bond activation ability of the active sites is retained, and the dehydrogenation selectivity of the catalyst is improved without weakening the dehydrogenation activity of the catalyst.

Description

Technical Field

[0001] This invention relates to dehydrogenation catalysts, their preparation methods and applications, and a method for dehydrogenating methylcyclohexane. Background Technology

[0002] Organic hydrogen storage utilizes organic compounds such as cycloalkanes, polycycloalkanes, carbazoles, and N-heterocyclic compounds as media to achieve hydrogen storage and transportation through reversible chemical processes of hydrogenation and dehydrogenation without disrupting the main carbon-ring structure. Because the hydrogen storage medium can remain stable in a liquid state for extended periods at ambient temperature and pressure, it can be stored and transported safely like diesel fuel, enabling transoceanic, bulk, long-term storage, and convenient distribution of hydrogen. It is one of the most promising new hydrogen storage technologies currently available. Among various organic hydrogen storage media, methyl-methylcyclohexane is one of the most suitable systems for large-scale, long-distance, and long-term hydrogen transportation.

[0003] In CN115703064A, a highly selective dehydrogenation catalyst was obtained by controlling the chlorine element on the support; CN111725531B improved the catalytic selectivity by using copper as a second metal to dope platinum, thereby adjusting the electronic structure and catalytic activity of platinum. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of poor selectivity of existing catalysts for dehydrogenation target products, such as the dehydrogenation to toluene, and to provide a dehydrogenation catalyst and its preparation method, which has good dehydrogenation activity.

[0005] This invention proposes that platinum, a noble metal, is widely recognized as the most suitable catalyst for the dehydrogenation reaction of methylcyclohexane. However, during the reduction process, platinum forms various micro- and nano-structures, enabling it to activate not only CH bonds but also C / C bonds. This leads to hydrocracking and isomerization reactions in methylcyclohexane or toluene, reducing the selectivity of the dehydrogenation reaction, affecting the recycling of hydrogen storage media, and increasing the difficulty of hydrogen purification. Therefore, this invention proposes for the first time to introduce organic compounds into the reduction stage of catalyst preparation, resulting in a dehydrogenation catalyst containing hydrocarbon complexes. By utilizing the in-situ conversion of organic compounds into hydrocarbon complexes during the catalyst's reduction process, highly active sites in the catalyst are effectively covered, weakening or eliminating the C / C bond activation ability of active sites while retaining the CH bond activation ability. This improves the dehydrogenation selectivity without weakening the catalyst's dehydrogenation activity.

[0006] To achieve the above objectives, a first aspect of the present invention provides a dehydrogenation catalyst comprising: a Pt element, a hydrocarbon complex, and a support; wherein the hydrocarbon complex is graphitized to a degree of I. D / I G =1.9-1.2, where I DFor the intensity of disordered carbon peaks, I G The intensity of the ordered carbon peak; the molar ratio of carbon and hydrogen in the hydrocarbon complex is 3-7.

[0007] A second aspect of the present invention provides a method for preparing the dehydrogenation catalyst of the present invention, the method comprising: reducing a support loaded with Pt oxide in an atmosphere containing an organic compound and a reducing gas.

[0008] A third aspect of the present invention provides the application of the dehydrogenation catalyst described herein in dehydrogenation reactions, preferably in alkane dehydrogenation reactions.

[0009] A fourth aspect of the present invention provides a method for dehydrogenating methylcyclohexane, wherein methylcyclohexane is subjected to a dehydrogenation reaction in the presence of the dehydrogenation catalyst described in the present invention.

[0010] Through the above technical solution, the present invention has the following beneficial effects:

[0011] By introducing organic compounds during the reduction stage of catalyst preparation, a dehydrogenation catalyst containing hydrocarbon complexes was obtained. This invention utilizes the in-situ conversion of organic compounds into hydrocarbon complexes during the catalyst's reduction process, effectively covering highly active sites in the catalyst, weakening or eliminating the C / C bond activation ability of active sites, while retaining the CH bond activation ability, thereby improving the selectivity for target substances without weakening the catalyst's dehydrogenation activity. Attached Figure Description

[0012] Figure 1 These are Raman curves of the catalysts prepared in Examples 1, 2, and 3. Detailed Implementation

[0013] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0014] The first aspect of this invention provides a dehydrogenation catalyst comprising: a Pt element, a hydrocarbon complex, and a support; wherein the hydrocarbon complex is graphitized to a degree I. D / I G =1.9-1.2, where I D For the intensity of disordered carbon peaks, I G The intensity of the ordered carbon peak; the molar ratio of carbon and hydrogen in the hydrocarbon complex is 3-7.

[0015] According to a preferred embodiment of the present invention, Pt exists in a metallic state.

[0016] In this invention, the content of the active component elements can be selected from a wide range. According to a preferred embodiment of this invention, based on the total mass of the catalyst, the Pt element content is 0.05-0.9 wt%. In the examples, the Pt element content is 0.6 wt%, which is an example, but does not limit the scope of this invention.

[0017] In this invention, the content of element C can be selected within a wide range. According to a preferred embodiment of the invention, based on the total mass of the catalyst, the content of element C is 0.1 wt% or more, preferably 0.05-0.3 wt%. Using this preferred content range can further improve the dehydrogenation activity of the dehydrogenation catalyst.

[0018] In this invention, the carrier has no special requirements. According to a preferred embodiment of the invention, the carrier is selected from at least one of activated carbon, silicon dioxide, magnesium aluminum hydrotalcite and alumina carrier. In this invention, the alumina carrier is used as an example in the embodiments, but the invention is not limited to this scope.

[0019] All dehydrogenation catalysts with the aforementioned characteristics can be used in this invention, and there are no special requirements for their preparation methods.

[0020] According to a preferred embodiment of the present invention, a method for preparing a dehydrogenation catalyst includes: reducing a support loaded with Pt oxide in an atmosphere containing organic compounds and hydrogen.

[0021] In this invention, the organic compound is not specifically required. According to a preferred embodiment of the invention, the organic compound is selected from alkanes and / or alkenes, preferably C1-C5 alkanes and / or C2-C4 alkenes, with a mass ratio of alkane to olefin of 0.1-10:1. More preferably, the alkane is one or more of ethane, propane, butane, and isobutane; and the olefin is at least one of ethylene, propylene, and isobutene. Using the aforementioned preferred embodiments can improve the selectivity of the catalyst for the target analyte.

[0022] In this invention, the organic compound content in the reducing atmosphere, which includes hydrogen and organic compounds, can be selected within a wide range. According to a preferred embodiment of the invention, the organic compound content in the reducing atmosphere is 0.5v%-3v%. By adopting the aforementioned preferred embodiment, the selectivity of the catalyst for the target analyte can be improved.

[0023] In this invention, the content of Pt element in the carrier loaded with Pt oxide has a wide range of selectable values. According to a preferred embodiment of this invention, the content of Pt element in the carrier loaded with Pt oxide is 0.05-0.9% by weight, preferably 0.5-0.8% by weight. In the examples, the content of Pt element is 0.6% by weight as an example, but this invention does not limit the range.

[0024] In this invention, there are no special requirements for the reduction conditions.

[0025] According to a preferred embodiment of the present invention, the reduction temperature is 300-450°C. 350°C is used as an example in the embodiments, but this does not limit the scope of the present invention.

[0026] According to a preferred embodiment of the present invention, the reduction time is 4-8 hours. In the example, 4 hours is used as an example, but this does not limit the scope of the present invention.

[0027] According to a preferred embodiment of the present invention, the flow rate is 100-400 ml / min, with 300 ml / min used as an example in the embodiments, but this does not limit the scope of the present invention.

[0028] Through the aforementioned preferred embodiments, organic compounds are converted into hydrocarbon complexes in situ during the reduction process of the catalyst. By reasonably covering the highly active sites in the catalyst, the activation ability of the C-C bonds of the active sites is weakened or eliminated, while the activation ability of the CH bonds of the active sites is retained. This improves the selectivity of the catalyst for the target analyte without weakening its dehydrogenation activity.

[0029] In this invention, the preparation steps of the support loaded with Pt oxide include: contacting the Pt source with the support, drying, and calcining.

[0030] In this invention, there are no special requirements for the method of providing the Pt source. According to a preferred embodiment of the invention, the Pt source is selected from water-soluble metal salts and / or acids of the corresponding element; preferably, the Pt source is selected from at least one of chloroplatinic acid, sodium chloroplatinate, dichlorotetraaminoplatinum, and tetraammineplatinum nitrate.

[0031] In this invention, there are no special requirements for the contact conditions between the Pt source and the support. According to a preferred embodiment of the invention, the dispersion of the Pt source is adsorbed onto the support by a solution impregnation method to obtain the catalyst precursor. This step is well known to those skilled in the art and can be performed with reference to the prior art.

[0032] In this invention, the drying conditions in the preparation step of the carrier loaded with Pt oxide are not particularly required and can be carried out with reference to the prior art. The example is exemplified by processing in an oven at 110°C for two hours, but this does not limit the scope of the invention.

[0033] The present invention does not have special requirements for the reduction environment or the reduction device used, and can be adapted to various devices. The embodiments use a tubular reactor to illustrate the advantages of the present invention.

[0034] In this invention, the calcination conditions in the preparation step of the Pt oxide-loaded support are not particularly required and can be carried out with reference to existing technology. This invention will not elaborate further here.

[0035] This invention provides the application of the dehydrogenation catalyst described herein in dehydrogenation reactions, preferably in alkane dehydrogenation reactions. The dehydrogenation catalyst of this invention, when applied to dehydrogenation reactions, can significantly improve the selectivity of the target analyte, especially in the dehydrogenation of methylcyclohexane, where it can significantly improve the selectivity of toluene.

[0036] This invention provides a method for dehydrogenating methylcyclohexane, wherein methylcyclohexane is subjected to a dehydrogenation reaction in the presence of the dehydrogenation catalyst described in this invention.

[0037] In this invention, there are no special requirements for the dehydrogenation conditions.

[0038] According to a preferred embodiment of the present invention, the dehydrogenation temperature is 400-500°C, with 450°C used as an example in the embodiments, but this does not limit the scope of the present invention.

[0039] According to a preferred embodiment of the present invention, the dehydrogenation mass hourly space velocity is 1-10 h⁻¹. -1 In the example, 2h -1 This is an illustrative example and is not intended to limit the scope of the invention.

[0040] According to a preferred embodiment of the present invention, the dehydrogenation pressure is 0-0.5 MPa. The examples use atmospheric pressure as an example, but this does not limit the scope of the present invention.

[0041] In this invention, Raman testing is performed using LabRAM ARAMIS laser Raman spectroscopy at a wavelength of 325 nm and a scanning range of 600-3200 cm⁻¹. -1 ;

[0042] In this invention, the content of each substance is obtained by ICP testing. The ICP testing method is a well-known technology in the art, and will not be described in detail here.

[0043] In this invention, the conversion rate of methylcyclohexane obtained by dehydrogenation of methylcyclohexane to produce hydrogen and the selectivity of toluene are well known in the art, and will not be described in detail here.

[0044] The present invention will be described in detail below through embodiments.

[0045] Example 1

[0046] (1) Chloroplatinic acid was prepared into an aqueous solution with a platinum ion concentration of 20 mg / mL. Platinum ions were loaded onto the surface of an alumina support using a solution impregnation process. The alumina support with the loaded precursor was then placed in an oven at 110°C for two hours and calcined in an air atmosphere at 500°C for 4 hours. The heating rate of the calcination furnace was 5°C / min, resulting in an alumina support loaded with Pt oxide (Pt content was 0.6% by weight).

[0047] (2) 2g of the calcined product was placed in a tubular reactor for reduction at a temperature of 350℃ for 4 hours at a flow rate of 300ml / min. The reducing gas was a mixture of hydrogen and ethane, with an ethane concentration of 2v%. The carbon and platinum content in the catalyst was determined by elemental analysis and ICP testing, and the carbon-hydrogen molar ratio is listed in Table 1. The degree of graphitization of the hydrocarbon complex in the catalyst (I0.05) was determined using Raman spectroscopy. D / I G The results of the characterization are shown in Table 1.

[0048] (3) Dehydrogenation of methylcyclohexane to produce hydrogen:

[0049] In a reaction tube, the catalyst and methylcyclohexane were reacted under a nitrogen atmosphere. The catalyst loading was 1 g, the reaction temperature was 450 °C, the pressure was atmospheric pressure, 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 96.7%, while the selectivity for toluene was 99.1%.

[0050] Example 2

[0051] (1) Sodium chloroplatinate was prepared into an aqueous solution with a platinum ion concentration of 20 mg / mL. Platinum ions were loaded onto the surface of an alumina support using a solution impregnation process. The alumina support with the loaded precursor was then placed in an oven at 110 °C for two hours and calcined in an air atmosphere at 550 °C for 4 hours at a heating rate of 5 °C / min to obtain an alumina support loaded with Pt oxide (Pt content was 0.6 wt%).

[0052] (2) 2g of the calcined product was placed in a tubular reactor for reduction at a temperature of 350℃ for 4 hours at a flow rate of 300ml / min. The reducing gas was a mixture of hydrogen and propane, with a propane concentration of 2.9v%. The carbon and platinum content in the catalyst was determined by elemental analysis and ICP testing, and the carbon-hydrogen molar ratio is listed in Table 1. The degree of graphitization of the hydrocarbon complex in the catalyst (I0.05) was determined by Raman spectroscopy. D / I G The results of the characterization are shown in Table 1.

[0053] (3) Dehydrogenation of methylcyclohexane to produce hydrogen, refer to Example 1:

[0054] The conversion rate of methylcyclohexane was 96.3%, and the selectivity for toluene was 99.3%.

[0055] Example 3

[0056] (1) Prepare an aqueous solution of dichlorotetraaminoplatinum with a platinum ion concentration of 20 mg / mL. Load platinum ions onto the surface of an alumina support using a solution impregnation process. Then, place the alumina support loaded with the precursor in an oven at 110℃ for two hours; calcine it in an air atmosphere at 550℃ for 4 hours, with a heating rate of 5℃ / min, to obtain an alumina support loaded with Pt oxide (Pt content of 0.6 wt%).

[0057] (2) 2g of the calcined product was placed in a tubular reactor for reduction at a temperature of 350℃ for 4 hours at a flow rate of 300ml / min. The reducing gas was a mixture of hydrogen and isobutane, with the isobutane concentration being 0.6v%. The carbon and platinum content in the catalyst was determined by elemental analysis and ICP testing, and the carbon-hydrogen molar ratio is listed in Table 1. The degree of graphitization of the hydrocarbon complex in the catalyst (I0.05) was determined by Raman spectroscopy. D / I G The results of the characterization are shown in Table 1.

[0058] (3) Dehydrogenation of methylcyclohexane to produce hydrogen, refer to Example 1:

[0059] The conversion rate of methylcyclohexane was 96.9%, and the selectivity for toluene was 98.9%.

[0060] Figure 1 The Raman curves of the catalysts prepared in Examples 1, 2, and 3 are shown below; Figure 1 As can be seen, the G band (1600 cm⁻¹) of carbon can be detected in all samples. -1 ) and D-band (1350cm) -1 The presence of straight-chain alkanes during catalyst reduction indicates that carbon-containing species can be deposited on the catalyst surface. Simultaneously, the prominent D peak in the sample suggests that the graphitization of the deposited carbon is not high, and the hydrocarbon complex is a hydrocarbon compound.

[0061] Example 4

[0062] All conditions are the same as in Example 1, except that the reducing gas in step (2) is a mixture of hydrogen and n-pentane.

[0063] Elemental analysis and ICP testing were used to determine the carbon and platinum content and the carbon-hydrogen molar ratio in the catalyst, as shown in Table 1. Raman spectroscopy was used to determine the degree of graphitization (Ig) of the hydrocarbon complex in the catalyst. D / I G The results of the characterization are shown in Table 1.

[0064] The conversion rate of methylcyclohexane was 96.8%, and the selectivity for toluene was 98.5%.

[0065] Example 5

[0066] The method is the same as in Example 1, except that the reducing gas in step (2) is an ethylene-hydrogen mixer, wherein the concentration of ethylene is 2% (v).

[0067] Elemental analysis and ICP testing were used to determine the carbon and platinum content and the carbon-hydrogen molar ratio in the catalyst, as shown in Table 1. Raman spectroscopy was used to determine the degree of graphitization (Ig) of the hydrocarbon complex in the catalyst. D / I G The results of the characterization are shown in Table 1.

[0068] The conversion rate of methylcyclohexane was 96.1%, and the selectivity for toluene was 98.7%.

[0069] Example 6

[0070] The method is the same as in Example 1, except that the reducing gas in step (2) is a mixture of ethylene, ethane and hydrogen, wherein the concentration of ethylene is 1v% and the concentration of ethane is 1v%.

[0071] Elemental analysis and ICP testing were used to determine the carbon and platinum content and the carbon-hydrogen molar ratio in the catalyst, as shown in Table 1. Raman spectroscopy was used to determine the degree of graphitization (Ig) of the hydrocarbon complex in the catalyst. D / I G The results of the characterization are shown in Table 1.

[0072] The conversion rate of methylcyclohexane was 96.3%, and the selectivity for toluene was 99.0%.

[0073] Comparative Example 1

[0074] The method of Example 1 was followed, except that the reducing atmosphere in step (2) was a hydrogen atmosphere. The carbon and platinum content and the carbon-hydrogen molar ratio in the catalyst were determined by elemental analysis and ICP testing, and are listed in Table 1. The degree of graphitization (Ig) of the hydrocarbon complex in the catalyst was determined using Raman spectroscopy. D / I G The results of the characterization are shown in Table 1.

[0075] The conversion rate of methylcyclohexane was 97.5%, and the selectivity for toluene was 93.2%.

[0076] Comparative Example 2

[0077] The method is the same as in Example 1, except that the reducing gas in step (2) is a mixture of hydrogen and ethane, wherein the concentration of ethane is 20% v%.

[0078] Elemental analysis and ICP testing were used to determine the carbon and platinum content and the carbon-hydrogen molar ratio in the catalyst, as shown in Table 1. Raman spectroscopy was used to determine the degree of graphitization (Ig) of the hydrocarbon complex in the catalyst. D / I G The results of the characterization are shown in Table 1.

[0079] The conversion rate of methylcyclohexane was 83.2%, and the selectivity for toluene was 94.5%.

[0080] Table 1

[0081]

[0082]

[0083] 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 technical features in any other suitable manner. 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 dehydrogenation catalyst, characterized in that, The catalyst comprises: Pt element, hydrocarbon complex, and support; the hydrocarbon complex is graphitized to a degree I. D / I G = 1.9-1.2, where I D For the intensity of disordered carbon peaks, I G The intensity of the ordered carbon peak; the molar ratio of carbon and hydrogen in the hydrocarbon complex is 3-7.

2. The catalyst according to claim 1, wherein, Pt exists in the metallic state; and / or Based on the total mass of the catalyst, the Pt element content is 0.05-0.9 wt%; and / or the C element content is 0.1 wt% or more.

3. The catalyst according to claim 2, wherein, Based on the total mass of the catalyst, the Pt element content is 0.5-0.8 wt%; and / or the C element content is 0.05-0.3 wt%.

4. The catalyst according to claim 1, wherein, The carrier is selected from at least one of activated carbon, silicon dioxide, magnesium aluminum hydrotalcite, and alumina carrier.

5. A method for preparing a dehydrogenation catalyst according to any one of claims 1-4, characterized in that, The method includes reducing a support loaded with Pt oxide in an atmosphere containing organic compounds and hydrogen.

6. The method according to claim 5, wherein, The organic compound is selected from alkanes and / or alkenes; and / or The organic compound content in the reducing atmosphere, which includes hydrogen and organic compounds, is 0.5v%-3v%; and / or The Pt element content in the support containing Pt oxide is 0.05-0.9% by weight.

7. The method according to claim 6, wherein, The organic compound is selected from C1-C5 alkanes and / or C2-C4 alkenes; and / or The Pt element content in the support loaded with Pt oxide is 0.5-0.8 wt%.

8. The method according to claim 7, wherein, When the organic compound is a mixture of alkanes and olefins, the mass ratio of alkanes to olefins is 0.1-10:

1.

9. The method according to claim 8, wherein, The alkane is one or more of ethane, propane, butane, and isobutane; the olefin is at least one of ethylene, propylene, and isobutene.

10. The method according to claim 5, wherein, The reduction conditions include: The temperature is 300-450℃; and / or the reduction time is 4-8h; and / or the flow rate is 100-400ml / min.

11. The method according to claim 5, wherein, The preparation steps of the support loaded with Pt oxide include: contacting the Pt source with the support, drying, and calcining; The Pt source is selected from water-soluble metal salts and / or acids of the corresponding elements.

12. The method according to claim 11, wherein, The Pt source is selected from at least one of chloroplatinic acid, sodium chloroplatinate, dichlorotetraaminoplatinum, and tetraammineplatinum nitrate.

13. The use of the dehydrogenation catalyst according to any one of claims 1-4 in a dehydrogenation reaction.

14. The use of the dehydrogenation catalyst according to any one of claims 1-4 in the dehydrogenation reaction of alkane.

15. A method for dehydrogenating methylcyclohexane, characterized in that, Methylcyclohexane is subjected to a dehydrogenation reaction in the presence of the dehydrogenation catalyst according to any one of claims 1-4.

16. The method according to claim 15, wherein, The dehydrogenation conditions include: Temperature 400-500℃; and / or Mass hourly space velocity (MHSV) is 1-10 h -1 ; and / or Pressure 0-0.5MPa.

Images