Dehydrogenation catalyst, preparation thereof and methyl cyclohexane dehydrogenation method

Abstract

The invention provides a dehydrogenation catalyst, preparation thereof and a methyl cyclohexane dehydrogenation method. The dehydrogenation catalyst comprises Pt, alkaline earth metal oxide and a carrier, the carrier is selected from any one or more of Al2O3 (aluminum oxide), SiO2 (silicon dioxide), ZrO2 (zirconium dioxide) and TiO2 (titanium dioxide); the Pt and the alkaline earth metal oxide are loaded on the surface of the carrier; the content of the Pt in the dehydrogenation catalyst is 0.2 wt% to 1.2 wt%, and the content of the alkaline earth metal oxide in the dehydrogenation catalyst is 0.35 wt% to 2 wt%. When the dehydrogenation catalyst provided by the invention is applied to dehydrogenation of methylcyclohexane, the hydrogen release efficiency of 1000Nm < 3 >-H2 / h / Nm < 3 >-cat is realized, and the conversion rate of methylcyclohexane is gt; the toluene selectivity is gt; the stability of the catalyst at least reaches 120 hours, and the catalyst has commercial value.

Description

Technical Field

[0001] The present invention relates to, but is not limited to, the field of organic liquid hydrogen storage, and in particular to, but is not limited to, a dehydrogenation catalyst and its preparation and a dehydrogenation method. Background Art

[0002] Hydrogen is a clean energy source. Due to its low volume density and easy diffusion, the storage and transportation of hydrogen face challenges, and it is urgent to develop safe and efficient hydrogen storage technology. Methylcyclohexane is one of the commonly used organic liquid hydrogen storage media, but the lack of stable and efficient dehydrogenation catalysts limits the development of methylcyclohexane hydrogen storage technology. The existing catalyst problems are mainly reflected in carbon deposition and hydrogen production stability. Aiming at the main problems of Pt-based catalysts, the deactivation of active sites during the dehydrogenation reaction is solved by adding additives and the method of additive matching to achieve high methylcyclohexane conversion rate and toluene selectivity. The composition and key element content of the catalyst have a significant impact on the performance of the catalytic material. The activity and stability of the methylcyclohexane dehydrogenation reaction are controlled by the content of the dehydrogenation catalyst additive. Therefore, in order to obtain a stable and efficient dehydrogenation catalyst, it is necessary to determine the process conditions and methods suitable for the batch preparation of catalytic materials to accurately control the components of the catalytic materials to be in the optimal content range, and avoid the deactivation of the catalytic materials and the decrease in reaction stability caused by the deviation of the component control.

[0003] The dehydrogenation process of methylcyclohexane is an endothermic reaction. High temperature conditions are conducive to achieving higher dehydrogenation reaction activity. However, the dehydrogenation catalyst is easily deactivated under high temperature conditions, which makes the design of methylcyclohexane dehydrogenation catalysts challenging. Developing a dehydrogenation catalyst with high temperature stability is one of the important conditions for realizing methylcyclohexane hydrogen storage technology. Summary of the invention

[0004] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0005] The modified methylcyclohexane dehydrogenation catalyst provided by the present invention realizes safe, efficient and stable operation of the methylcyclohexane dehydrogenation step, and can still show high reaction activity for more than 120 hours at 400° C., thereby solving the problem of poor high-temperature stability of conventional methylcyclohexane dehydrogenation catalysts. At the same time, the modified methylcyclohexane dehydrogenation catalyst provided by the present invention has a simple preparation process and can be prepared in large quantities.

[0006] In some embodiments of the present disclosure, a dehydrogenation catalyst is provided, the dehydrogenation catalyst comprising Pt, an alkaline earth metal oxide, and a carrier;

[0007] The carrier is selected from Al 2 O 3 、SiO 2 、ZrO 2 and TiO2 Any one or more of the following;

[0008] The Pt and the alkaline earth metal oxide are loaded on the surface of the carrier;

[0009] The content of Pt in the dehydrogenation catalyst is 0.2 wt.% to 1.2 wt.%, and the content of the alkaline earth metal oxide is 0.35 wt.% to 2 wt.%.

[0010] In some embodiments provided in the present disclosure, the alkaline earth metal oxide may be selected from any one or more of magnesium oxide, calcium oxide, strontium oxide and barium oxide.

[0011] In some embodiments provided in the present disclosure, the aluminum oxide may be α-Al 2 O 3 , β-Al 2 O 3 and γ-Al 2 O 3 Any one or more of; the SiO 2 The crystal form can be α-SiO 2 ,β-SiO 2 and γ-SiO 2 Any one or more of; the ZrO 2 The crystal form can be t-ZrO 2 、m-ZrO 2 and c-ZrO 2 Any one or more of; the TiO 2 The crystal form can be anatase, rutile, brookite, anatase / rutile composite phase and other heterogeneous structures formed by the aforementioned crystal forms; in the scheme provided in the present disclosure, there is no special requirement for the carrier crystal form.

[0012] On the other hand, some embodiments of the present disclosure provide a method for preparing the above-mentioned dehydrogenation catalyst. In order to construct alkaline earth metal oxide micro-regions instead of forming alkaline earth metal oxide particles, it is necessary to achieve fine control over the loading amount of the alkaline earth metal oxide. The preparation method comprises:

[0013] dissolving a soluble alkaline earth metal salt in water to obtain an alkaline earth metal salt solution;

[0014] Cooling the alkaline earth metal salt solution to 0°C ± 5°C;

[0015] Take the supernatant of the alkaline earth metal salt solution after cooling and mix it with Pt@Al 2 O 3 Stirring at 0°C ± 5°C to obtain a mixture;

[0016] The mixture is dried and then calcined to obtain the dehydrogenation catalyst;

[0017] The Pt@Al 2 O 3 The Pt content in the precipitate is 0.2 wt.% to 1.2 wt.%.

[0018] In some embodiments provided by the present disclosure, the soluble alkaline earth metal salt is selected from any one or more of chloride salts, dihydrogen phosphate salts, nitrates and hypochlorites of alkaline earth metals.

[0019] In some embodiments provided by the present disclosure, the soluble alkaline earth metal salt, the water and the Pt@Al 2 O 3 The weight ratio is (150 to 170):(190 to 200):(28 to 30).

[0020] In some embodiments provided by the present disclosure, the dissolving temperature is 15°C to 35°C.

[0021] In some embodiments provided in the present disclosure, the cooling is to cool the alkaline earth metal salt solution to 0°C±5°C in an ice water bath.

[0022] In some embodiments provided by the present disclosure, the drying is performed at 90° C. to 110° C. for 6 h to 8 h.

[0023] In some embodiments provided by the present disclosure, the calcination is calcined at 400° C. to 500° C. for 3 h to 6 h.

[0024] In another aspect, some embodiments of the present disclosure provide a second method for preparing the above-mentioned dehydrogenation catalyst, the preparation method comprising:

[0025] The Pt@Al 2 O 3 Mechanically mixing with the alkaline earth metal oxide to obtain the dehydrogenation catalyst;

[0026] The Pt@Al 2 O 3 The Pt content in the precipitate is 0.2 wt.% to 1.2 wt.%.

[0027] In some embodiments provided by the present disclosure, the mechanical mixing comprises ball milling, the rotation speed of the ball milling is 200 r / min to 300 r / min, and the ball milling time is 3 h to 4 h.

[0028] In some embodiments provided in the present disclosure, the ball-to-material ratio of the ball milling is (5 to 3):1.

[0029] In some embodiments provided in the present disclosure, the Pt@Al 2 O 3 The weight ratio of the alkaline earth metal oxide to the alkaline earth metal oxide is 40:(5 to 8).

[0030] In some embodiments provided in the present disclosure, the material of the grinding balls of the ball mill is selected from any one or more of ceramic, quartz, agate and zirconia.

[0031] In yet another aspect, the present disclosure provides a dehydrogenation catalyst prepared using any one of the two preparation methods described above.

[0032] In another aspect, the present disclosure provides a method for dehydrogenating methylcyclohexane using any one of the above-mentioned dehydrogenation catalysts, the dehydrogenation method comprising:

[0033] reducing the dehydrogenation catalyst in hydrogen;

[0034] The methylcyclohexane is preheated and then participates in the methylcyclohexane dehydrogenation reaction.

[0035] In some embodiments provided in the present disclosure, the temperature for reducing the dehydrogenation catalyst is 400° C. to 450° C.; the hydrogen space velocity is 150 h -1 Up to 450h -1 .

[0036] In some embodiments provided by the present disclosure, the preheating is to preheat the methylcyclohexane to 150° C. to 300° C., and the mass flow rate of the methylcyclohexane is 0.5 h -1 Up to 2.6h -1 .

[0037] The beneficial effects of the present disclosure include at least:

[0038] Alkaline earth metal oxide micro-regions are constructed instead of forming alkaline earth metal oxide particles, and the loading amount of alkaline earth metal needs to be finely controlled. The method provided by the present disclosure has a high yield rate for preparing a dehydrogenation catalyst product, and the dehydrogenation activity of the product is stable and the conversion rate and selectivity are high. At the same time, the requirements for equipment and feed accuracy in the batch preparation process of high-performance catalysts are effectively reduced, and it is a low-cost preparation method for modified dehydrogenation catalysts.

[0039] The advantage of the present disclosure is that the Pt content in the catalyst is only 0.1wt.% to 0.35wt.%, which has the advantages of low cost, high performance and high stability. Compared with the Pt loading of 10wt.% to 20wt.% of commercial catalysts on the market, the catalyst has a significant cost advantage. At the same time, after the dehydrogenation performance test of 10g of catalyst, the methylcyclohexane conversion rate and toluene selectivity both reached more than 99%, with excellent performance and able to achieve 1000Nm 3 -H2 / h / Nm 3 -cat has a high hydrogen release efficiency and a catalyst stability of 120 hours, which is of commercial value.

[0040] The advantage of the present disclosure is that the catalyst preparation process does not need to consider the influence of acidic sites in conventional preparation methods, and can simply and efficiently prepare high-performance and stable methylcyclohexane dehydrogenation materials. The prepared catalyst can effectively suppress problems such as carbon deposition and catalyst deactivation under the set reaction process parameters, and is suitable for large-scale application scenarios of methylcyclohexane dehydrogenation.

[0041] The advantages of the present disclosure also lie in that the electron transfer between Pt atoms and methylcyclohexane molecules is enhanced through the synergistic effect of Pt and alkaline metal oxides, while the hydrogen spillover ability of Pt metal atoms is improved, the CH bond activation of methylcyclohexane molecules on the surface of Pt catalyst is promoted, and the dehydrogenation reaction activity of methylcyclohexane is improved.

[0042] Other features and advantages of the present disclosure will be described in the following description, and partly become apparent from the description, or be understood by implementing the present disclosure. Other advantages of the present disclosure can be invented and obtained by the schemes described in the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings are used to provide an understanding of the technical solution of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the technical solution of the present disclosure and do not constitute a limitation on the technical solution of the present disclosure.

[0044] Figure 1 This is a SEM morphology of the PCA catalyst prepared in Example 3 of the present disclosure. Figure 1 It can be seen that the CaO micro-region cannot be clearly marked due to the low Ca content; at the same time, the amount of Pt is also low, and the introduction of Ca and Pt does not significantly change the morphology of the catalyst. Figure 1 Ca / Pt / Al cannot be observed 2 O 3 The catalyst has a cotton-like morphology and Al 2 O 3 similar.

[0045] Figure 2 This is a comparison chart of the infrared absorption spectra of the PCA catalyst prepared in Example 3 of the present disclosure and CaO.

[0046] Figure 3 The PCA catalyst prepared in Example 3 of the present disclosure and Al 2 O 3 Crystal structure comparison diagram.

[0047] Figure 4 The PCA catalyst prepared in Example 3 of the present disclosure and Pt@Al 2 O 3 Surface chemical state analysis Pt4f peak comparison diagram.

[0048] Since the amount of Ca impregnation is very low, no obvious phase change can be observed in the crystal structure characterization of the material, indicating that no obvious CaO crystal phase is formed. Figure 2 Infrared absorption spectrum analysis shows that the functional groups on the surface of PCA catalyst can be compared to pure CaO phase, indicating that CaO micro-regions have formed on the surface of PCA catalyst. Figure 3 No CaO-related phases could be detected, but Figure 4 It can be seen that the oxidation state of Pt is suppressed. DETAILED DESCRIPTION

[0049] To make the purpose, technical solution and advantages of the present disclosure more clear, the embodiments of the present disclosure are described in detail below. It should be noted that the embodiments and features in the embodiments of the present disclosure can be combined with each other arbitrarily without conflict.

[0050] In an embodiment of the present disclosure, a dehydrogenation catalyst is exemplarily provided, the dehydrogenation catalyst comprising Pt, an alkaline earth metal oxide and a carrier;

[0051] The carrier is selected from Al 2 O 3 、SiO 2 、ZrO 2 and TiO 2 Any one or more of the following;

[0052] The Pt and the alkaline earth metal oxide are loaded on the surface of the carrier;

[0053] The content of Pt in the dehydrogenation catalyst is 0.2 wt.% to 1.2 wt.%, and the content of the alkaline earth metal oxide is 0.35 wt.% to 2 wt.%.

[0054] Illustratively, the alkaline earth metal oxide may be selected from any one or more of magnesium oxide, calcium oxide, strontium oxide and barium oxide.

[0055] For example, the aluminum oxide may be α-Al 2 O 3 , β-Al 2 O 3 and γ-Al 2 O 3 Any one or more of; the SiO 2 The crystal form can be α-SiO 2,β-SiO 2 and γ-SiO 2 Any one or more of; the ZrO 2 The crystal form can be t-ZrO 2 、m-ZrO 2 and c-ZrO 2 Any one or more of; the TiO 2 The crystal form can be anatase, rutile, brookite, anatase / rutile composite phase and other heterogeneous structures formed by the aforementioned crystal forms; in the scheme provided in the present disclosure, there is no special requirement for the carrier crystal form.

[0056] Exemplarily, the alkaline earth metal oxide is arranged as little as possible on the Al 2 O 3 The Pt is arranged on the surface of the alkaline earth metal oxide in as small a amount as possible, and as little Pt@alkaline earth metal oxide phase as possible is formed in the dehydrogenation catalyst.

[0057] For example, the morphology of the dehydrogenation catalyst is a cotton-like morphology. Since the impregnation amount of Pt and alkaline earth metal is very low, the introduction of alkaline earth metal and Pt does not significantly change its morphology. The morphology of the dehydrogenation catalyst is similar to that of Al 2 O 3 Cotton-like morphology similar to the carrier.

[0058] For example, the Pt sites that are not directly supported on the alkaline earth metal oxide play a catalytic role, but the alkaline earth metal oxide around the Pt sites is effective in improving the Pt activity.

[0059] On the other hand, the present disclosure exemplarily provides a method for preparing the above-mentioned dehydrogenation catalyst in an embodiment. In order to construct alkaline earth metal oxide micro-regions instead of forming alkaline earth metal oxide particles, it is necessary to achieve fine control over the loading amount of the alkaline earth metal oxide. The preparation method comprises:

[0060] dissolving a soluble alkaline earth metal salt in water to obtain an alkaline earth metal salt solution;

[0061] Cooling the alkaline earth metal salt solution to 0°C ± 5°C;

[0062] Take the supernatant of the alkaline earth metal salt solution after cooling and mix it with Pt@Al 2 O 3 Stirring at 0°C ± 5°C to obtain a mixture;

[0063] The mixture is dried and then calcined to obtain the dehydrogenation catalyst;

[0064] The Pt@Al 2 O 3The Pt content in the precipitate is 0.2 wt.% to 1.2 wt.%.

[0065] Exemplarily, the soluble alkaline earth metal salt is selected from any one or more of chlorides, dihydrogen phosphates, nitrates and hypochlorites of alkaline earth metals.

[0066] Exemplarily, the soluble alkaline earth metal salt, the water and the Pt@Al 2 O 3 The weight ratio is (150 to 170):(190 to 200):(28 to 30).

[0067] Illustratively, the dissolving temperature is 15°C to 35°C.

[0068] Exemplarily, the cooling is to cool the alkaline earth metal salt solution to 0°C±5°C in an ice water bath.

[0069] Exemplarily, the drying is performed at 90° C. to 110° C. for 6 h to 8 h.

[0070] Illustratively, the calcination is performed at 400° C. to 500° C. for 3 h to 6 h.

[0071] In another aspect, the embodiments of the present disclosure exemplarily provide a second method for preparing the above-mentioned dehydrogenation catalyst, the preparation method comprising:

[0072] The Pt@Al 2 O 3 Mechanically mixing with the alkaline earth metal oxide to obtain the dehydrogenation catalyst;

[0073] The Pt@Al 2 O 3 The Pt content in the precipitate is 0.2 wt.% to 1.2 wt.%.

[0074] Exemplarily, the mechanical mixing comprises ball milling, the rotation speed of the ball milling is 200 r / min to 300 r / min, and the ball milling time is 3 h to 4 h.

[0075] Exemplarily, the ball-to-material ratio of the ball milling is (5 to 3):1.

[0076] For example, the Pt@Al 2 O 3 The weight ratio of the alkaline earth metal oxide to the alkaline earth metal oxide is 40:(5 to 8).

[0077] Exemplarily, the material of the grinding balls of the ball mill is selected from any one or more of ceramic, quartz, agate and zirconia.

[0078] In yet another aspect, an embodiment of the present disclosure illustratively provides a dehydrogenation catalyst prepared using any one of the two preparation methods described above.

[0079] In another aspect, an embodiment of the present disclosure illustratively provides a method for dehydrogenating methylcyclohexane, using any one of the above-mentioned dehydrogenation catalysts, the dehydrogenation method comprising:

[0080] reducing the dehydrogenation catalyst in hydrogen;

[0081] The methylcyclohexane is preheated and then participates in the methylcyclohexane dehydrogenation reaction.

[0082] Exemplarily, the temperature for reducing the dehydrogenation catalyst is 400° C. to 450° C.; the hydrogen space velocity is 150 h -1 Up to 450h -1 .

[0083] Exemplarily, the preheating is to preheat the methylcyclohexane to 150° C. to 300° C., and the mass flow rate of the methylcyclohexane is 0.5 h -1 Up to 2.6h -1 .

[0084] In the embodiments and comparative examples disclosed herein, the Pt@Al 2 O 3 The catalyst powder was purchased from Beijing Tanqing Biotechnology Co., Ltd. and prepared by equal volume impregnation method. The content of Pt accounted for 1.3% of Pt@Al 2 O 3 0.25wt.%.

[0085] Example 1

[0086] Add 165g CaCl2 to 200ml water at room temperature (20°C) 2 ·2H 2 O, stir and dissolve until a clear and uniform solution is obtained, then place the beaker in an ice water bath and continue stirring for 2 hours. When the temperature of the solution in the beaker reaches 0°C, continue stirring for 1 hour, then filter with filter paper, take 50 ml of the upper clear liquid, and add it to the prepared Pt@Al 2 O 3 30g of catalyst powder was stirred at 0°C for 2 hours until the slurry was uniform, and then placed in a forced air drying oven at 105°C to 80°C for 6 hours until the water was completely dried. The catalyst was calcined at 450°C in a muffle furnace for 4.5 hours to obtain a PCA type modified dehydrogenation catalyst. The catalyst prepared in this example had a Pt content of 0.25wt% and a CaO content of 0.98wt%.

[0087] Example 2

[0088] Add 160g CaCl2 to 200ml water at room temperature (25°C) 2 ·2H 2 O, stir and dissolve until a clear uniform solution is obtained, then place the beaker in an ice water bath and continue stirring for 2 hours. When the temperature of the solution in the beaker reaches 2°C, continue stirring for 1 hour, then filter with filter paper, take 50 ml of the upper clear liquid, and add it to the prepared Pt@Al 2 O 3 28g of catalyst powder was stirred at 0°C for 2 hours until the slurry was uniform, and then placed in a forced air drying oven at 105°C for 6 hours until the water was completely dried. The catalyst was calcined at 450°C for 3 hours in a muffle furnace to obtain a PCA-type modified dehydrogenation catalyst. The catalyst prepared in this example had a Pt content of 0.26wt% and a CaO content of 1.03wt%.

[0089] Example 3

[0090] Add 170g CaCl2 to 200ml water at room temperature (30°C) 2 ·2H 2 O, stir and dissolve until a clear and uniform solution is obtained, then place the beaker in a water bath and continue stirring for 2 hours. When the temperature of the solution in the beaker reaches 0°C, continue stirring for 1 hour, then filter with filter paper, take 50 ml of the upper clear liquid, and add it to the prepared Pt@Al 2 O 3 30g of catalyst powder was stirred at 0°C for 2 hours until the slurry was uniform, and then placed in a forced air drying oven at 105°C for 6 hours until the water was completely dried. The catalyst was calcined at 450°C for 5 hours in a muffle furnace to obtain a PCA-type modified dehydrogenation catalyst. The catalyst prepared in this example had a Pt content of 0.25wt% and a CaO content of 1.05wt%.

[0091] Example 4

[0092] Add 150g CaCl2 to 200ml water at room temperature (25°C) 2 ·2H 2 O, stir and dissolve until a clear and uniform solution is obtained, then place the beaker in an ice water bath and continue stirring for 2 hours. When the temperature of the solution in the beaker reaches 0°C, continue stirring for 1 hour, then filter with filter paper, take 50 ml of the upper clear liquid, and add it to the prepared Pt@Al 2 O 3 28g of catalyst powder was stirred at 0°C for 2 hours until the slurry was uniform, and then placed in a forced air drying oven at 105°C for 8 hours until the water was completely dried. The catalyst was calcined at 450°C for 4.5 hours in a muffle furnace to obtain a PCA-type modified dehydrogenation catalyst. The catalyst prepared in this example had a Pt content of 0.26wt% and a CaO content of 0.96wt%.

[0093] Example 5

[0094] 850 g of CaCl 2 ·2H 2 O, stir and dissolve in 1L water until a clear and uniform solution is obtained, then place the beaker in an ice water bath and continue stirring for 4 hours. When the temperature of the solution in the beaker reaches 0°C, continue stirring for 1 hour, then filter with filter paper, take 250ml of the upper clear liquid, and add it to the prepared Pt@Al 2 O 3 150 g of catalyst powder was stirred at 0°C for 2 hours until the slurry was uniform, and then placed in a forced air drying oven at 105°C for 8 hours until the water was completely dried. The mixture was calcined in a muffle furnace at 450°C for 5 hours to obtain a PCA-type modified dehydrogenation catalyst.

[0095] The catalyst prepared in this example has a Pt content of 0.25 wt % and a CaO content of 1.05 wt %.

[0096] Example 6

[0097] The CaO and Pt@Al 2 O 3 The catalyst was mechanically mixed (ball milling speed was 200 r / min, ball milling time was 4 h), CaO and Pt@Al 2 O 3 The weight ratio of the catalyst is 1:5. The grinding balls are zirconium oxide balls, and the ball-to-material ratio is 5:1. The catalyst prepared in this comparative example has a Pt content of 0.2wt% and a CaO content of 2wt%.

[0098] Comparative Example 1

[0099] The difference between Comparative Example 1 and Example 1 is that the preparation process does not involve CaCl 2 ·2H 2 O, and other raw materials and preparation processes are exactly the same. The Pt content of the catalyst prepared in this comparative example is 0.25wt%.

[0100] Comparative Example 2

[0101] The Pt@CaO catalyst was prepared by impregnating calcium oxide with chloroplatinic acid. The catalyst did not show dehydrogenation catalytic activity. The preparation method was as follows: 30g of CaO powder was impregnated into 204ml of 0.01mg / ml chloroplatinic acid acetone solution, stirred for 6 hours, dried at 70℃ for 6 hours, and calcined at 450℃ for 4 hours to prepare the Pt@CaO catalyst. The Pt content of the catalyst prepared in this comparative example was 0.25wt%.

[0102] Comparative Example 3

[0103] This comparative example is a dehydrogenation catalyst prepared under non-water bath conditions.

[0104] 850 g of CaCl 2 ·2H 2 O, stir and dissolve in 1L water until a clear and uniform solution is obtained, continue stirring at room temperature (20°C to 30°C) for 3 hours, take 250ml of the solution and add it to the prepared Pt@Al 2 O 3 The catalyst powder was stirred at room temperature (20-30°C) for 2 hours until the slurry was uniform, and then placed in a forced air drying oven at 105°C for 8 hours until the water was completely dried. The catalyst powder was calcined in a muffle furnace at 450°C for 5 hours to obtain a non-water bath prepared PCA-type modified dehydrogenation catalyst.

[0105] The catalyst prepared in this comparative example has a Pt content of 0.25 wt % and a CaO content of 2.5 wt %.

[0106] Comparative Example 4

[0107] 10% Pt-Al 2 O 3 Commercial catalyst, Shaanxi Ruike New Materials Co., Ltd.

[0108] The PCA modified dehydrogenation catalysts prepared in the examples and comparative examples were reduced in hydrogen at 400°C with a hydrogen volume flow space velocity of 300 h -1 The dehydrogenation reaction was carried out at 400 °C. Methylcyclohexane was preheated at 230 °C in a preheater before entering the catalyst reaction bed. The mass flow rate of methylcyclohexane was 1.8 h / min. -1 .

[0109] Table 1: Comparative Examples and Examples, Drug Dosage, Methylcyclohexane Conversion Rate and Toluene Selectivity Test Results

[0110]

[0111] In Table 1, the conversion rate and selectivity refer to the methylcyclohexane conversion rate and toluene selectivity detected after 1 hour of reaction, respectively, and the performance retention rate after 10 hours of reaction refers to the product of the percentage of the conversion rate and selectivity after 10 hours of reaction relative to the conversion rate and selectivity after the first hour.

[0112] It is difficult for the methylcyclohexane dehydrogenation catalyst in the prior art to achieve a conversion rate and selectivity of >99% at the same time and achieve a long-term stability effect.

[0113] The comparative examples and implementation of the examples show that the catalyst has excellent catalytic dehydrogenation activity and stability.

[0114] It can be seen from Comparative Example 1 and Example 1 that the presence of the Ca phase can significantly improve the stability of the catalyst, and the methylcyclohexane conversion rate and toluene selectivity are also improved. This may be because the presence of the Ca phase can achieve the Al2 O 3 Ca-Al-Pt can form a stable activation of the CH bond of the methylcyclohexane molecule, which is a more stable structure. Comparative Example 1 Under the same conditions, pure Pt@Al without CaO 2 O 3 The catalyst had an initial conversion rate of only 68% and deactivated rapidly.

[0115] It can be seen from Comparative Example 2 and Example 1 that Pt directly supported on CaO cannot effectively activate the CH bond of methylcyclohexane, so methylcyclohexane exhibits a low conversion rate, indicating that the Ca-related phase can both promote and inhibit the catalytic activity of the Pt site.

[0116] It can be seen from Example 6 and Example 1 that the presence of Ca actually creates a Ca-MCH-Pt synergistic environment (MCH: methylcyclohexane), and the presence of CaO can significantly promote the Pt-Al 2 O 3 The dehydrogenation activity of the site stabilizes the CH bond activation of Pt towards the methylcyclohexane molecule.

[0117] It can be seen from Comparative Example 2 and Example 1 that the Pt site on CaO itself inhibits the CH dissociation of the MCH molecule. That is, excessive Ca impregnation or Pt impregnated with CaO particles will inhibit CH bond dissociation. Direct loading of Pt on CaO particles will inhibit the CH bond dissociation activity of Pt, while the CaO microregion near the Pt site will promote the CH bond dissociation activity of the Pt site.

[0118] By comparing Comparative Example 3 with Example 5, it can be seen that the catalyst of Example 5 exhibits high methylcyclohexane conversion (99.6%) and toluene selectivity (99.5%). The catalyst of Comparative Example 3 exhibits high toluene selectivity (99.6%) and low methylcyclohexane conversion (87.3%), but as the reaction time is extended to 5-10 h, the conversion gradually decreases to 60%.

[0119] More benzene was produced in the product of Comparative Example 4. This was because the excessively high Pt loading of the catalyst without proper Ca fine-tuning resulted in rapid thermal decomposition of methylcyclohexane at the test temperature. Although the conversion rate of methylcyclohexane was high, the yield of the toluene product was reduced.

[0120] It can be seen that the alkaline earth metal oxide micro-region environment constructed by a small amount of alkaline earth metal impregnation has a significant promoting effect on the Pt active site, promoting the CH dissociation of Pt to MCH molecules, thereby achieving significantly enhanced MCH dehydrogenation activity. The present disclosure innovatively uses a simple two-step temperature-controlled impregnation method to accurately control the alkaline earth metal content in the catalyst based on the limitation of the solubility of the alkaline earth metal salt, constructs the alkaline earth metal oxide micro-region, rather than the alkaline earth metal oxide particle phase, to ensure that the Pt-Al 2 O 3 Based on the catalyst activity, the alkaline earth metal oxide micro-region relative to Pt-Al 2 O 3 The promoting effect of catalytic activity.

[0121] Different from the direct impregnation method used in the comparative literature, the present disclosure promotes the formation of alkaline earth metal oxide microphases, effectively avoiding the loss of Pt active sites caused by the formation of alkaline earth metal oxide particle phases.

[0122] Ball milling can also be used as an alternative method to improve the activity of the catalyst. Although it is impossible to completely eliminate the alkaline earth metal oxide particles, the alkaline earth metal oxides close to the Pt site of the catalyst may form a micro-region-like effect, thereby improving the dehydrogenation performance of the catalyst.

[0123] The mechanical stirring method is an important control example to illustrate the importance of the presence of alkaline earth metal oxides. As described in this paragraph, the presence of alkaline earth metal oxides can promote CH activation and stabilization, but the content of alkaline earth metal oxides needs to be precisely controlled. The mechanical mixing method can achieve a certain effect of alkaline earth metal oxides on the improvement of Pt catalytic activity.

Claims

1. A dehydrogenation catalyst, characterized in that The dehydrogenation catalyst comprises Pt, an alkaline earth metal oxide and a carrier; The carrier is selected from any one or more of Al2O3, SiO2, ZrO2 and TiO2; The Pt and the alkaline earth metal oxide are loaded on the surface of the carrier; The content of Pt in the dehydrogenation catalyst is 0.2 wt.% to 1.2 wt.%, and the content of the alkaline earth metal oxide is 0.35 wt.% to 2 wt.%.

2. The method for preparing a dehydrogenation catalyst according to claim 1, characterized in that: The preparation method comprises: dissolving a soluble alkaline earth metal salt in water to obtain an alkaline earth metal salt solution; Cooling the alkaline earth metal salt solution to 0°C ± 5°C; The supernatant of the alkaline earth metal salt solution after cooling is taken and stirred with Pt@Al2O3 at 0°C±5°C to obtain a mixture; The mixture is dried and then calcined to obtain the dehydrogenation catalyst; The Pt content in the Pt@Al2O3 is 0.2wt.% to 1.2wt.%.

3. The preparation method according to claim 2, characterized in that: The weight ratio of the soluble alkaline earth metal salt, the water and the Pt@Al2O3 is (150 to 170):(190 to 200):(28 to 30).

4. The preparation method according to claim 2 or 3, wherein the dissolution temperature is 15°C to 35°C; Optionally, the cooling is to cool the alkaline earth metal salt solution to 0°C ± 5°C in an ice water bath; Optionally, the drying is performed at 90° C. to 110° C. for 6 to 8 hours; Optionally, the calcination is carried out at 400° C. to 500° C. for 3 h to 6 h.

5. The method for preparing a dehydrogenation catalyst according to claim 1, characterized in that: The preparation method comprises: Mechanically mixing the Pt@Al2O3 and the alkaline earth metal oxide to obtain the dehydrogenation catalyst; The Pt content in the Pt@Al2O3 is 0.2wt.% to 1.2wt.%; Optionally, the mechanical mixing comprises ball milling, the rotation speed of the ball milling is 200 r / min to 300 r / min, and the ball milling time is 3 h to 4 h.

6. The preparation method according to claim 5, characterized in that: The ball-to-material ratio of the ball mill is (5 to 3):1; Optionally, the weight ratio of the Pt@Al2O3 to the alkaline earth metal oxide is 40:(5 to 8).

7. The method for preparing a dehydrogenation catalyst according to claim 5 or 6, characterized in that: The grinding ball material of the ball mill is selected from any one or more of ceramic, quartz, agate and zirconia.

8. A method for dehydrogenating methylcyclohexane, characterized in that: Using the dehydrogenation catalyst according to claim 1 or 2, the dehydrogenation method comprises: reducing the dehydrogenation catalyst in hydrogen; The methylcyclohexane is preheated and then participates in the methylcyclohexane dehydrogenation reaction.

9. The method according to claim 8, characterized in that The temperature for reducing the dehydrogenation catalyst is 400°C to 450°C; the hydrogen space velocity is 150h -1 Up to 450h -1 .

10. The method according to claim 8 or 9, characterized in that: The preheating process is to preheat the methylcyclohexane to 150° C. to 300° C., and the mass flow rate of the methylcyclohexane is 0.5 h -1 Up to 2.6h -1 .

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