Dehydrogenation catalyst, preparation method and application thereof, and methylcyclohexane dehydrogenation method

Abstract

The invention relates to a dehydrogenation catalyst, a preparation method and application thereof and a methyl cyclohexane dehydrogenation method. The catalyst comprises a Pt element, a hydrocarbon compound and a carrier, the graphitization degree ID / IG of the hydrocarbon compound is 1.9-1.2, ID is the intensity of a disordered carbon peak, and IG is the intensity of an ordered carbon peak. An organic compound is introduced in the reduction stage of catalyst preparation, and the dehydrogenation catalyst containing the hydrocarbon compound is obtained. An organic compound is converted into a hydrocarbon compound in situ in the reduction process of the catalyst, high-activity sites in the catalyst are reasonably covered, the C-C bond activation capacity of the active sites is weakened or eliminated, the C-H bond activation capacity of the active sites is reserved, and the dehydrogenation selectivity of the catalyst is improved on the premise that the dehydrogenation activity of the catalyst is not weakened.

Description

Technical Field

[0001] The invention relates to a dehydrogenation catalyst, a preparation method and application thereof, and a methylcyclohexane dehydrogenation method. Background Art

[0002] Organic hydrogen storage is a technology that uses organic substances such as cycloalkanes, polycycloalkanes, carbazoles, and N-heterocyclic rings as media to achieve hydrogen storage and transportation through a reversible chemical process of hydrogenation and dehydrogenation without destroying the main structure of the carbon ring. Because its hydrogen storage medium can remain in a stable liquid state for a long period of time at room temperature and pressure, it can be safely stored and transported like diesel, and can achieve transoceanic transportation, bulk transportation, long-term storage, and convenient distribution of hydrogen. It is one of the most promising new hydrogen storage technologies. Among the many organic hydrogen storage media, methyl-methylcyclohexane is one of the most suitable systems for large-scale, long-distance, and long-term transportation of hydrogen.

[0003] In CN115703064A, a highly selective dehydrogenation catalyst was obtained by regulating the chlorine element on the carrier; CN111725531B doped platinum with a second metal copper to adjust the platinum electronic structure and its catalytic activity, thereby improving the catalytic selectivity. Summary of the invention

[0004] The purpose of the present invention is to overcome the problem of poor selectivity of catalysts in the prior art for dehydrogenation target products such as toluene produced by dehydrogenation, and to provide a dehydrogenation catalyst and a preparation method thereof, wherein the dehydrogenation catalyst has good dehydrogenation activity.

[0005] The present invention believes that the precious metal platinum is recognized as the most suitable catalyst for the dehydrogenation reaction of methylcyclohexane. However, the platinum element will form a variety of different micro-nanostructures during the reduction process, which makes it not only have the ability to activate CH bonds, but also have the ability to activate CC bonds, resulting in methylcyclohexane or toluene undergoing hydrocracking, isomerization and other reactions, reducing the selectivity of the dehydrogenation reaction, affecting the recycling of hydrogen storage media, and increasing the difficulty of hydrogen purification; thus, it is proposed for the first time to introduce organic compounds in the reduction stage of catalyst preparation, and obtain a dehydrogenation catalyst containing a hydrocarbon complex. By using the in-situ conversion of organic compounds into hydrocarbon complexes during the reduction process of the catalyst, the high-activity sites in the catalyst are reasonably covered, the CC bond activation ability of the active sites is weakened or eliminated, the CH bond activation ability of the active sites is retained, and the dehydrogenation selectivity of the catalyst is improved without weakening its dehydrogenation activity.

[0006] In order to achieve the above object, the present invention provides a dehydrogenation catalyst in a first aspect, the catalyst comprising: a Pt element, a hydrocarbon composite and a carrier; the hydrocarbon composite has a graphitization degree I D / I G =1.9-1.2, where I Dis the intensity of the disordered carbon peak, I G is the intensity of the ordered carbon peak; the molar ratio of carbon and hydrogen elements in the hydrocarbon complex is 3-7.

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

[0008] The third aspect of the present invention provides use of the dehydrogenation catalyst of the present invention in a dehydrogenation reaction, preferably in an alkane dehydrogenation reaction.

[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 of the present invention.

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

[0011] By introducing organic compounds in the reduction stage of catalyst preparation, a dehydrogenation catalyst containing hydrocarbon complexes is obtained. The present invention utilizes the in-situ conversion of organic compounds into hydrocarbon complexes during the reduction process of the catalyst, rationally covers the high active sites in the catalyst, weakens or eliminates the CC bond activation ability of the active sites, retains the CH bond activation ability of the active sites, and improves the selectivity of the catalyst for the target without weakening its dehydrogenation activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 These are the Raman curves of the catalysts prepared in Example 1, Example 2, and Example 3. DETAILED DESCRIPTION

[0013] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0014] The first aspect of the present invention provides a dehydrogenation catalyst, which comprises: a Pt element, a hydrocarbon composite and a carrier; the hydrocarbon composite has a graphitization degree of I D / I G =1.9-1.2, where I D is the intensity of the disordered carbon peak, I G is the intensity of the ordered carbon peak; the molar ratio of carbon and hydrogen elements in the hydrocarbon complex is 3-7.

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

[0016] In the present invention, the optional range of the active component element content is relatively wide. According to a preferred embodiment of the present invention, based on the total mass of the catalyst, the Pt element content is 0.05-0.9wt%. In the embodiment, the Pt element content is 0.6wt% as an example, but the scope of the present invention is not limited thereto.

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

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

[0019] All dehydrogenation catalysts having the aforementioned characteristics can be used in the present invention, and there is no special requirement for their preparation methods.

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

[0021] In the present invention, there is no special requirement for the organic compound. According to a preferred embodiment of the present invention, the organic compound is selected from alkanes and / or alkenes, preferably C1-C5 alkanes and / or C2-C4 alkenes, and the mass ratio of alkanes to alkenes is 0.1-10:1. It is further preferred that the alkanes are one or more of ethane, propane, butane and isobutane; and the olefins are at least one of ethylene, propylene and isobutylene. The above preferred embodiments can improve the selectivity of the catalyst for the target.

[0022] In the present invention, the content of organic compounds in the reducing atmosphere including hydrogen and organic compounds can be selected in a wide range. According to a preferred embodiment of the present invention, the content of organic compounds in the reducing atmosphere is 0.5v%-3v%. The above preferred embodiment can improve the selectivity of the catalyst to the target.

[0023] In the present invention, the content of Pt element in the carrier loaded with Pt oxide can be selected in a wide range. According to a preferred embodiment of the present invention, the content of Pt element in the carrier loaded with Pt oxide is 0.05-0.9% by weight, preferably 0.5-0.8wt%. In the embodiment, the content of Pt element is 0.6wt% as an example, but the present invention is not limited to this range.

[0024] In the present invention, there is no special requirement for the reduction conditions.

[0025] According to a preferred embodiment of the present invention, the reduction temperature is 300-450° C., and 350° C. is used as an exemplary illustration in the examples, but the scope of the present invention is not limited thereby.

[0026] According to a preferred embodiment of the present invention, the reduction time is 4-8 hours. In the examples, 4 hours is used as an exemplary illustration, but the scope of the present invention is not limited thereby.

[0027] According to a preferred embodiment of the present invention, the flow rate is 100-400 ml / min. In the embodiment, 300 ml / min is used as an exemplary illustration, but the scope of the present invention is not limited thereby.

[0028] Through the aforementioned preferred implementation, organic compounds are converted into hydrocarbon complexes in situ during the reduction process of the catalyst, and the CC bond activation ability of the active sites is weakened or eliminated by reasonably covering the high activity sites in the catalyst, while retaining the CH bond activation ability of the active sites, thereby improving its selectivity for the target without weakening the dehydrogenation activity of the catalyst.

[0029] In the present invention, the steps of preparing the carrier loaded with Pt oxide include: contacting the Pt source with the carrier, drying, and calcining.

[0030] In the present invention, there is no special requirement for the method of providing the Pt source. According to a preferred embodiment of the present invention, the Pt source is selected from water-soluble metal salts and / or acids of the corresponding elements; preferably, the Pt source is selected from at least one of chloroplatinic acid, sodium chloroplatinate, tetraamine platinum dichloride and tetraamine platinum nitrate.

[0031] In the present invention, there is no special requirement for the contact conditions between the Pt source and the carrier. According to a preferred embodiment of the present invention, the dispersion of the Pt source is adsorbed on the carrier by solution impregnation to obtain a 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 the present invention, there is no special requirement for the drying conditions in the preparation step of the carrier loaded with Pt oxide, and it can be carried out with reference to the prior art. The embodiment is exemplified by treating in an oven at 110° C. for two hours, but the scope of the present invention is not limited thereto.

[0033] The present invention has no special requirements on the reduction device used in the reduction environment and can be adapted to various devices. The examples are conducted using a tubular reactor to illustrate the advantages of the present invention.

[0034] In the present invention, there is no special requirement for the calcination conditions in the preparation step of the carrier loaded with Pt oxide, and it can be carried out with reference to the prior art, and the present invention will not elaborate on it here.

[0035] The present invention provides the use of the dehydrogenation catalyst of the present invention in a dehydrogenation reaction, preferably in an alkane dehydrogenation reaction. The dehydrogenation catalyst of the present invention is applied to a dehydrogenation reaction to significantly improve the selectivity of the target product, especially when used for the dehydrogenation of methylcyclohexane, it can significantly improve the selectivity of toluene.

[0036] The present invention provides a methylcyclohexane dehydrogenation method. In the presence of the dehydrogenation catalyst of the present invention, methylcyclohexane is subjected to a dehydrogenation reaction.

[0037] In the present invention, there is no special requirement for the dehydrogenation conditions.

[0038] According to a preferred embodiment of the present invention, the dehydrogenation temperature is 400-500° C., and 450° C. is used as an exemplary embodiment, but the scope of the present invention is not limited thereto.

[0039] According to a preferred embodiment of the present invention, the dehydrogenation mass space velocity is 1-10h -1 In the embodiment, 2h -1 This is intended to be an illustrative description, but 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. In the examples, normal pressure is used as an exemplary illustration, but the scope of the present invention is not limited thereby.

[0041] In the present invention, the Raman test was performed on a LabRAM ARAMIS laser Raman spectrometer with a Raman wavelength of 325 nm and a scanning range of 600-3200 cm -1 ;

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

[0043] In the present invention, the conversion rate of methylcyclohexane obtained by dehydrogenating methylcyclohexane to produce hydrogen and the toluene selectivity are well known in the art and will not be elaborated herein.

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

[0045] Example 1

[0046] (1) Take chloroplatinic acid and prepare an aqueous solution with a platinum ion concentration of 20 mg / mL. Use a solution impregnation preparation process to load platinum ions on the surface of an alumina carrier. Then place the alumina carrier loaded with the precursor in an oven at 110°C for two hours, and roast it in an air atmosphere at 500°C for 4 hours. The heating rate of the roasting furnace is 5°C / min, and an alumina carrier loaded with Pt oxide (the content of Pt element is 0.6% by weight) is obtained.

[0047] (2) 2 g of the calcined product was placed in a tubular reactor for reduction at a temperature of 350°C, a reduction time of 4 h, a flow rate of 300 ml / min, and a reduction gas of hydrogen and ethane mixed gas, wherein the concentration of ethane was 2% by volume. The carbon element, platinum element content, and carbon-hydrogen element molar ratio in the catalyst were determined by elemental analysis and ICP test, respectively, and are listed in Table 1. The graphitization degree (I D / I G ) were characterized and the results are listed in Table 1.

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

[0049] In a reaction tube, the catalyst and methylcyclohexane were reacted in a nitrogen atmosphere. The catalyst loading was 1 g, the reaction temperature was 450 ° C, the pressure was normal pressure, and the mass space velocity of methylcyclohexane was 2 h -1 The product after 12 hours of reaction was analyzed, and the conversion rate of methylcyclohexane was 96.7%, and the toluene selectivity 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. The platinum ions were loaded on the surface of the alumina carrier by a solution impregnation preparation process. The alumina carrier loaded with the 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, with a heating rate of 5°C / min in the calcination furnace, to obtain an alumina carrier loaded with Pt oxide (the content of Pt element was 0.6 wt%).

[0052] (2) 2 g of the calcined product was placed in a tubular reactor for reduction at a temperature of 350°C, a reduction time of 4 h, a flow rate of 300 ml / min, and a reduction gas of hydrogen and propane mixed gas, wherein the concentration of propane was 2.9 v%. The carbon element, platinum element content, and carbon-hydrogen element molar ratio in the catalyst were determined by elemental analysis and ICP test, respectively, and are listed in Table 1. The graphitization degree (I D / I G ) were characterized and the results are listed in Table 1.

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

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

[0055] Example 3

[0056] (1) Take tetraaminoplatinum dichloride and prepare an aqueous solution with a platinum ion concentration of 20 mg / mL. Use a solution impregnation preparation process to load platinum ions on the surface of an alumina carrier. Then place the alumina carrier loaded with the precursor in an oven at 110°C for two hours; calcine at 550°C in an air atmosphere for 4 hours, with a heating rate of 5°C / min in the calcination furnace, to obtain an alumina carrier loaded with Pt oxide (the content of Pt element is 0.6% by weight).

[0057] (2) 2 g of the calcined product was placed in a tubular reactor for reduction at a temperature of 350°C, a reduction time of 4 h, a flow rate of 300 ml / min, and a reduction gas of hydrogen and isobutane mixed gas, wherein the concentration of isobutane was 0.6 v%. The carbon element, platinum element content, and carbon-hydrogen element molar ratio in the catalyst were determined by elemental analysis and ICP test, respectively, and are listed in Table 1. The graphitization degree (I D / I G ) were characterized and the results are listed in Table 1.

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

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

[0060] Figure 1 is the Raman curve of the catalyst prepared in Example 1, Example 2, and Example 3; Figure 1 It can be seen that the G band of carbon (1600cm -1 ) and D belt (1350cm -1 ), indicating that the introduction of straight-chain alkanes during the catalyst reduction process can cause the deposition of carbon-containing species on the catalyst surface; at the same time, the D peak in the sample is obvious, indicating that the graphitization degree of the deposited carbon is not high, and the hydrocarbon complex is a hydrocarbon.

[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] The carbon content, platinum content, and carbon-hydrogen molar ratio in the catalyst were determined by elemental analysis and ICP test, as shown in Table 1. The graphitization degree (I D / I G ) were characterized and the results are listed in Table 1.

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

[0065] Example 5

[0066] The method of Example 1 is followed, except that the reducing gas in step (2) is an ethylene / hydrogen mixer, wherein the concentration of ethylene is 2% by volume.

[0067] The carbon content, platinum content, and carbon-hydrogen molar ratio in the catalyst were determined by elemental analysis and ICP test, as shown in Table 1. The graphitization degree (I D / I G ) were characterized and the results are listed in Table 1.

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

[0069] Example 6

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

[0071] The carbon content, platinum content, and carbon-hydrogen molar ratio in the catalyst were determined by elemental analysis and ICP test, as shown in Table 1. The graphitization degree (I D / I G ) were characterized and the results are listed in Table 1.

[0072] The conversion of methylcyclohexane was 96.3%, and the selectivity of 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 element, platinum element content, and carbon-hydrogen element molar ratio in the catalyst were determined by elemental analysis and ICP testing, as shown in Table 1. The graphitization degree (I D / I G ) were characterized and the results are listed in Table 1.

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

[0076] Comparative Example 2

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

[0078] The carbon content, platinum content, and carbon-hydrogen molar ratio in the catalyst were determined by elemental analysis and ICP test, as shown in Table 1. The graphitization degree (I D / I G ) were characterized and the results are listed in Table 1.

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

[0080] Table 1

[0081]

[0082]

[0083] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A dehydrogenation catalyst, characterized in that The catalyst comprises: a Pt element, a hydrocarbon composite and a carrier; the hydrocarbon composite has a graphitization degree of I D / I G =1.9-1.2, where I D is the intensity of the disordered carbon peak, I G is the intensity of the ordered carbon peak; the molar ratio of carbon and hydrogen elements in the hydrocarbon complex is 3-7.

2. The catalyst according to claim 1, wherein The Pt element exists in a metallic state; and / or Based on the total mass of the catalyst, the Pt content is 0.05-0.9wt%, preferably 0.5-0.8wt%; and / or the C content is above 0.1wt%, preferably 0.05-0.3wt%.

3. The catalyst according to claim 1 or 2, wherein The carrier is selected from at least one of activated carbon, silicon oxide, magnesium aluminum hydrotalcite and aluminum oxide carriers.

4. A method for preparing a dehydrogenation catalyst according to any one of claims 1 to 3, characterized in that: The method comprises: reducing a carrier loaded with Pt oxide in an atmosphere containing an organic compound and hydrogen.

5. The method according to claim 4, wherein: The organic compound is selected from alkanes and / or alkenes, preferably C1-C5 alkanes and / or C2-C4 alkenes. When alkanes and olefins are mixed, the mass ratio of alkanes to olefins is preferably 0.1-10:1; It is further preferred that the alkane is one or more of ethane, propane, butane and isobutane; the olefin is at least one of ethylene, propylene and isobutylene; and / or The reducing atmosphere including hydrogen and organic compounds contains 0.5v% to 3v% of organic compounds; and / or In the carrier loaded with Pt oxide, the content of Pt element is 0.05-0.9 wt %, preferably 0.5-0.8 wt %.

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

7. The method according to any one of claims 4 to 6, wherein: The steps of preparing the carrier loaded with Pt oxide include: contacting the Pt source with the carrier, drying, and calcining; The Pt source is selected from water-soluble metal salts and / or acids of the corresponding elements; Preferably, the Pt source is selected from at least one of chloroplatinic acid, sodium chloroplatinate, tetraamine platinum dichloride and tetraamine platinum nitrate.

8. Use of the dehydrogenation catalyst according to any one of claims 1 to 3 in a dehydrogenation reaction, preferably in an alkane dehydrogenation reaction.

9. A method for dehydrogenating methylcyclohexane, characterized in that: In the presence of the dehydrogenation catalyst according to any one of claims 1 to 3, methylcyclohexane is subjected to a dehydrogenation reaction.

10. The method according to claim 9, wherein: The dehydrogenation conditions include: A temperature of 400-500°C; and / or Mass space velocity is 1-10h -1 ; and / or Pressure 0-0.5MPa.

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