A platinum-tin bimetallic supported catalyst for propane dehydrogenation and its preparation method

Abstract

The invention provides a propane dehydrogenation platinum-tin bimetallic supported catalyst and a preparation method thereof. The preparation method comprises the following steps: firstly preparing a mixed solution of cerium nitrate hexahydrate and urea, performing a two-stage step-by-step closed heating treatment, filtering a precipitate, and then roasting and grinding the precipitate to prepare a CeO2 carrier powder, and then adding the precipitate to a precursor solution prepared by preparing chloroplatinic acid hexahydrate and stannous chloride dihydrate, and removing water after fully stirring and mixing to obtain an oxidized PtSn x / CeO2, and finally calcined in air atmosphere and reducing gas atmosphere to prepare PtSn x / CeO2 catalyst. The catalyst ‑1 The propane yield at the air velocity can reach more than 25%. The preparation method has the characteristics of low cost, simple synthesis and industrial scale application, and has the prospect of industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts for the dehydrogenation of propane to propylene by CO 2 oxidation, and relates to a supported platinum-tin bimetallic catalyst for propane dehydrogenation and a preparation method thereof, and particularly relates to a supported platinum-tin bimetallic catalyst on cerium dioxide for the dehydrogenation of propane to propylene by CO 2 oxidation and a preparation method thereof. Background Art

[0002] As one of the basic raw materials for the three major synthetic materials, propylene is widely used in the production of important chemical products such as polypropylene, acrylic acid, acrylonitrile, and propylene oxide. With the continuous increase in the demand for propylene, the traditional steam cracking and catalytic cracking processes are difficult to meet the current production requirements for propylene. Therefore, exploring an efficient and green propylene production process has become the main problem faced by researchers.

[0003] In the context of the development of green chemistry, the development of shale gas has brought a large amount of natural propane gas, which makes the process of direct dehydrogenation of propane to propylene (PDH) more easily industrialized. However, this reaction is limited by the thermodynamic equilibrium, has high energy consumption, and low propylene selectivity. It has extremely high requirements for the reaction and requires frequent catalyst replacement. Introducing CO 2 as a weak oxidant, the introduced oxygen component helps propane dehydrogenation by consuming hydrogen, and at the same time can change the thermodynamic equilibrium of the reaction, reduce the reaction temperature, and improve propylene selectivity. It is considered an effective alternative to traditional methods.

[0004] Currently, the catalysts used for the dehydrogenation of propane to propylene by CO 2 oxidation mainly include metal oxide catalysts (such as CrO x , Ga 2 O 3 , Vo x , etc.), metal catalysts (such as Pt, Rh, etc.), bimetallic catalysts (such as PtFe, PtNi, NiFe, etc.), and polymetallic catalysts (such as PtCoIn ternary catalysts). Among them, metal catalysts have relatively high catalytic activity, and can be made more suitable for the complex reaction system of dehydrogenation of propane to propylene by CO 2 oxidation through the design of active components. Noble metal Pt-based catalysts have been widely studied by various researchers due to their excellent propane dehydrogenation performance. However, the Pt-based catalysts are prone to agglomeration, resulting in large-area dehydrogenation of propane, and then leading to low selectivity of the target product propylene and catalyst deactivation.

[0005] Therefore, there is currently a need for a hot catalyst for the dehydrogenation of propane to propylene by CO 2 oxidation, which has a relatively simple and reasonable preparation process, is suitable for industrial application, and can obtain a high propylene yield. Summary of the Invention

[0006] In order to solve the above problems in the prior art, the present invention provides a platinum-tin bimetallic supported catalyst for propane dehydrogenation and a preparation method thereof. The catalyst is a PtSn x / CeO 2 (X = 1.6 - 3.3) catalyst. The propane yield of this catalyst can reach more than 25% at a space velocity of 14,000 h -1 . Its preparation method has the characteristics of low cost, relatively simple synthesis and can be industrially scaled up for application, showing prospects for industrial production.

[0007] To achieve the above object, the present invention is realized by a technical solution composed of the following technical measures.

[0008] The present invention provides a preparation method of a platinum-tin bimetallic supported catalyst for propane dehydrogenation, mainly including the following steps:

[0009] (1) Dissolve cerium nitrate hexahydrate and urea in deionized water to prepare a mixed solution. Seal and heat it to 50 - 80 °C and maintain this temperature for 6 - 7 h, then continue to seal and heat it to 140 - 180 °C and maintain this temperature for at least 24 h. After cooling, filter to obtain a precipitate;

[0010] The concentration of cerium nitrate hexahydrate in the mixed solution is 0.04 - 0.05 g / ml, and the molar ratio of cerium nitrate hexahydrate to urea is 1:(1.8 - 2.2);

[0011] (2) Calcinate and grind the precipitate obtained in step (1) in sequence to prepare CeO 2 support powder;

[0012] (3) Dissolve chloroplatinic acid hexahydrate and stannous chloride dihydrate in deionized water to prepare a precursor solution. Weigh the CeO 2 support powder prepared in step (2) and add it to the precursor solution. After fully stirring and mixing evenly, remove the moisture to obtain the oxidized PtSn x / CeO 2 ;

[0013] The addition amount of chloroplatinic acid hexahydrate is calculated based on 1 - 1.2 wt% of the total amount of Pt element, Sn element and CeO x / CeO 2 in the oxidized PtSn 2 , and the molar ratio of Pt element to Sn element is 1:(1.6 - 3.3);

[0014] (4) Calcinate the oxidized PtSn x / CeO2 , calcined in an air atmosphere at 450 - 550 °C for at least 1 hour, and then calcined in a reducing gas atmosphere at 550 - 650 °C for at least 1 hour after cooling, thus obtaining a silver - gray PtSn x / CeO 2 catalyst, where X = 1.6 - 3.3.

[0015] The PtSn x / CeO 2 catalyst obtained by the above - mentioned preparation method can be used for the catalytic reaction of oxidative dehydrogenation of propane to propylene with CO 2 .

[0016] In this paper, the molar ratio of cerium nitrate hexahydrate to urea in step (1) is 1:(1.8 - 2.2), which is the optimal ratio confirmed by comparative experiments. Based on experimental facts, if the molar ratio of cerium nitrate hexahydrate to urea is lower than this ratio, the prepared CeO 2 support powder will be impure, while if the molar ratio is higher than this ratio, the prepared CeO 2 will have defects, affecting the crystal structure, both of which will have a significant impact on the synthetic morphology and performance of the finally prepared PtSn x / CeO 2 catalyst.

[0017] In this paper, the closed heating in step (1) can prevent the premature decomposition of urea. In addition, under the conditions of industrial implementation of the conversion amplification effect, it should be ensured that cerium nitrate hexahydrate and urea in the mixed solution are fully dissolved before heating; under the conditions of a larger preparation scale, it is advisable to choose to accompany stirring during closed heating.

[0018] It should be noted that in step (1), the closed heating is carried out to 50 - 80 °C and maintained at this temperature for 6 - 7 h, and then continued to be heated to 140 - 180 °C and maintained at this temperature for at least 24 h. The reason for adopting the two - stage step - type closed heating treatment is mainly based on experimental facts that urea is more likely to hydrolyze into NH 4+ and OCN - under lower - temperature conditions. Under neutral or weakly alkaline conditions, OCN - continues to react to generate CO 3 2- and NH 3 . Subsequently, with the synchronous increase of the closed - heating temperature and pressure, the urea hydrolysis rate increases, and Ce 3+ reacts with CO 3 2- and OH - to generate the CeCO 3 OH intermediate.

[0019] In this text, for the steps of calcining and grinding the precipitate obtained in step (1) as described in step (2), it is advisable to wash and dry the precipitate before calcining. However, those skilled in the art should be aware that the washing and drying of the filtered precipitate are conventional processes in chemical engineering, and those skilled in the art can select appropriate washing and drying methods according to common knowledge or conventional processes on their own.

[0020] To better illustrate the present invention and provide a reference technical solution, for the steps of calcining and grinding the precipitate obtained in step (1) as described in step (2), washing and drying the precipitate before calcining, the washing is carried out by alternately washing with deionized water and absolute ethanol at least 3 times to better remove the residual OH 3 in the precipitate (CeCO - OH intermediate), NH 4 + and CO 3 2- and other impurity ions.

[0021] In this text, for the steps of calcining and grinding the precipitate obtained in step (1) as described in step (2), calcining is to convert the metal components in the precipitate into oxides, specifically following the conventional calcining methods / parameters in chemical engineering, and those skilled in the art can directly refer to the conventional methods for calcining cerium dioxide for treatment.

[0022] In one technical solution, for the steps of calcining and grinding the precipitate obtained in step (1) as described in step (2), the specific process parameters of calcining are: heating at a heating rate of 1 - 1.2 °C / min to 550 - 560 °C, and holding for calcination for 4 - 4.5 h. After the time is reached, it is naturally cooled to room temperature. It should be noted that based on experimental facts, it is found that too high a heating rate during calcination is likely to cause changes in the CeO 2 structure. Therefore, the above heating rate is optimized.

[0023] In this text, for the steps of calcining and grinding the precipitate obtained in step (1) as described in step (2), grinding is a conventional process method for processing the calcined product into powder, following the conventional principles in chemical engineering, and those skilled in the art can carry out specific operations according to common knowledge.

[0024] In this text, the addition amount of chloroplatinic acid hexahydrate described in step (3) is based on the Pt element in the oxidation state of PtSn x / CeO 2 for the Pt element, Sn element and CeO 2Calculated based on 1 to 1.2 wt% of the total amount, and the molar ratio of Pt element to Sn element is 1:(1.6 - 3.3). Those skilled in the art can calculate the addition amount of chloroplatinic acid hexahydrate in the precursor solution according to the mass ratio of the Pt element, and at the same time, PtSn x / CeO 2 In which the value of X is the molar ratio of Pt element to Sn element, and then the addition amount of stannous chloride dihydrate in the precursor solution can be calculated. Since the solvent (deionized water) in the precursor aqueous solution will be removed, the addition amount of the deionized water generally does not affect the prepared product. In actual implementation, the addition of deionized water is based on being able to fully dissolve chloroplatinic acid hexahydrate and stannous chloride dihydrate and being suitable for removal treatment.

[0025] In this article, the removal of moisture in step (3) is one of the conventional processes for loading metal components by the impregnation method. For example, rotary evaporation treatment can be selected to remove moisture, and those skilled in the art can also use other methods for removing moisture in the impregnation method according to the existing instrument equipment.

[0026] In this article, in step (4), the oxidized PtSn x / CeO 2 obtained in step (3) is calcined in an air atmosphere at 450 - 550 °C for at least 1 hour. The purpose is to make the oxidized oxides of Pt and Sn more firmly loaded on the surface of the prepared CeO 2 surface, and at the same time remove the Cl ions in the precursor solution.

[0027] In this article, in step (4), after being cooled, it is calcined in a reducing gas atmosphere at 550 - 650 °C for at least 1 hour. The purpose is to reduce the oxidized oxides of Pt and Sn to the metallic state and use them as the active metals for the oxidative dehydrogenation of propane to propylene reaction. Among them, the reducing gas atmosphere is a hydrogen atmosphere or a mixed atmosphere of hydrogen and inert gas. 2 Among them, the reducing gas atmosphere is a hydrogen atmosphere or a mixed atmosphere of hydrogen and inert gas.

[0028] It should be noted that in step (4), after being cooled, it is calcined in a reducing gas atmosphere at 550 - 650 °C for at least 1 hour. After the calcination is completed, it is advisable to wait for the sample to cool naturally, and during this process, the reducing gas needs to be continuously introduced to prevent the re-oxidation of the Pt and Sn active metals.

[0029] Finally, the fresh PtSn x / CeO 2 catalyst is prepared by the above scheme. Under the conditions of 550 °C, 0.1 MPa, and 14000 h -1 for the oxidative dehydrogenation reaction of propane with CO 2 , a propylene yield of more than 30% can be achieved, where PtSn 1.6 / CeO 2 The catalyst focuses on a higher propane conversion rate, with PtSn 3.3 / CeO 2 focusing on propylene selectivity.

[0030] The inventive principle of the present invention lies in that Pt-based noble metal catalysts, which have high propane dehydrogenation activity, have always been the research focus of propane catalytic conversion and are widely considered to have good application prospects. However, the large-area dehydrogenation of propane caused by the easy agglomeration of Pt-based catalysts leads to low selectivity of the target product propylene and catalyst deactivation. Therefore, the inventors of the present invention attempt to prepare Pt and Sn bimetallic catalysts to solve the above-mentioned problems in the prior art.

[0031] The present invention attempts to modify the traditional Pt-based catalyst by introducing the inert metal Sn. The strong interaction between Sn and Pt can disperse the agglomerated Pt, reduce the excessive dehydrogenation of propane, increase the number of propane dehydrogenation sites, and improve the propane conversion rate. However, after retrieval and query, the Pt and Sn bimetallic catalysts reported in the prior art literature have good direct dehydrogenation effects on propane, but perform poorly in the oxidative propane dehydrogenation to propylene reaction. This may be due to the weak activation ability of the Pt and Sn bimetallic catalysts for CO 2 The oxidative propane dehydrogenation to propylene reaction shows poor performance, which may stem from the weak activation ability of the Pt and Sn bimetallic catalysts for CO 2 activation ability.

[0032] To solve these problems, on the one hand, the present invention attempts to use CeO 2 prepared by urea assistance as the catalyst support for Pt and Sn bimetallic loading. This CeO 2 support has excellent oxygen release ability, can help eliminate hydrogen components in the propane dehydrogenation step, and the formed oxygen vacancies can also be used for CO 2 capture and conversion. However, it is found in the actual experimental process that the process parameter variables in the CeO 2 support preparation process will greatly affect the synthetic morphology and performance of the finally prepared PtSn x / CeO 2 catalyst, and the above-mentioned process parameter variables have not been reported in the prior art literature, such as the molar ratio of cerium nitrate hexahydrate to urea and the two-stage stepped closed heating treatment; on the other hand, further explore the molar ratio between Pt and Sn bimetals through comparative experiments. Surprisingly, it is found that when the molar ratio of Pt to Sn is 1:(1.6 - 3.3), the prepared PtSn x / CeO 2 catalyst not only has a significantly higher propylene yield, but also has excellent propane conversion rate and better CO 2 conversion rate. In particular, it is worth noting that when the molar ratio of Pt to Sn is 1:1.6, that is, PtSn 1.6 / CeO 2 The propane conversion rate of the catalyst and CO 2 The conversion rate is close to 1:1, indicating that PtSn 1.6 / CeO 2 The catalyst can fully regulate CO 2 in the oxidative dehydrogenation reaction of propane.

[0033] In this article, the mixing, washing, and drying all follow the conventional principles in chemical engineering processes, and those skilled in the art can perform specific operations according to common general knowledge.

[0034] The present invention has the following beneficial effects:

[0035] 1. The present invention provides a platinum-tin bimetallic supported catalyst for propane dehydrogenation and its preparation method. It uses CeO 2 prepared by the urea-assisted method as the catalyst support for loading Pt and Sn bimetals, and prepares the PtSn x / CeO 2 catalyst by further regulating the molar ratio of Pt and Sn. It has excellent catalytic performance and, under the same test conditions, its catalytic activity is superior to similar products recorded in the existing literature in this field.

[0036] 2. The present invention provides a platinum-tin bimetallic supported catalyst for propane dehydrogenation and its preparation method. By forming a bimetal with inert metal Sn and Pt, the regulation of Sn on Pt disperses and increases the Pt active sites geometrically. The more stable bimetal can also reduce the agglomeration of Pt and increase the catalyst life. Further research finds that the special ratio of the molar ratio of Pt to Sn is 1:(1.6 - 3.3), which can better coordinate the interaction between Pt, Sn, and CeO 2 to obtain the highest propane conversion rate while having a relatively high propylene selectivity, directly improving the propylene yield.

[0037] 3. The overall process of the present invention is simple, easy to operate, and can be directly applied to the process of oxidative dehydrogenation of propane to propylene with CO 2 It has excellent practicability, low cost, and is easy to be promoted in the market as a superior product. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic flow chart in the process of preparing the PtSn 1.6 / CeO 2 catalyst in Example 1 of the present invention.

[0039] Figure 2 It is the electron microscope morphology diagram of the CeO 2 support powder obtained in the preparation process of Example 1 of the present invention. It can be clearly seen that when prepared by the urea-assisted method, the obtained CeO2 The carrier particles are rod-shaped. Regular rod-shaped CeO 2 has more stable exposed crystal planes, providing better thermal stability to support the loading of the PtSn bimetal.

[0040] Figure 3 CeO obtained in the preparation process of Comparative Example 2 of the present invention 2 Electron microscopy morphology diagram of the carrier powder. It can be clearly seen that when sodium hydroxide is used as an aid in the preparation, the obtained CeO 2 The carrier particles are thin strips.

[0041] Figure 4 The catalysts prepared in Examples 1-2, Comparative Example 1, and Comparative Examples 3-5 of the present invention in the 2 Propylene yield comparison dot line graph in the oxidative dehydrogenation of propane to propylene reaction.

[0042] Figure 5 The catalysts prepared in Examples 1-2, Comparative Example 1, and Comparative Examples 3-5 of the present invention in the 2 Propane conversion comparison dot line graph in the oxidative dehydrogenation of propane to propylene reaction.

[0043] Figure 6 The catalysts prepared in Examples 1-2, Comparative Example 1, and Comparative Examples 3-5 of the present invention in the 2 CO in the oxidative dehydrogenation of propane to propylene reaction 2 Conversion rate comparison dot line graph.

[0044] Figure 7 The catalysts prepared in Examples 1-2, Comparative Example 1, and Comparative Examples 3-5 of the present invention in the 2 Propylene selectivity comparison dot line graph in the oxidative dehydrogenation of propane to propylene reaction.

[0045] Figure 8 The catalyst prepared in Comparative Example 2 of the present invention in the 2 Propane conversion rate dot line graph (left figure) and CO in the oxidative dehydrogenation of propane to propylene reaction 2 Conversion rate dot line graph (right figure).

[0046] Figure 9 Photo of the instrument scene when Example 1 of the present invention is being tested. Detailed implementation mode

[0047] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention. Those skilled in the art can draw on the content of this article and appropriately modify the process parameters to achieve. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and those related can obviously make changes or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Although it is believed that those of ordinary skill in the art are fully aware of the following terms, the following definitions are still stated to help illustrate the subject matter disclosed by the present invention.

[0048] A preparation method of a platinum-tin bimetal supported catalyst for propane dehydrogenation mainly includes the following steps:

[0049] (1) Cerium nitrate hexahydrate and urea are mixed and dissolved in deionized water to prepare a mixed solution, which is heated in a closed state to 50 - 80 °C and maintained at this temperature for 6 - 7 h, and then continuously heated in a closed state to 140 - 180 °C and maintained at this temperature for at least 24 h. After cooling, filtration is carried out to obtain a precipitate;

[0050] The concentration of cerium nitrate hexahydrate in the mixed solution is 0.04 - 0.05 g / ml, and the molar ratio of cerium nitrate hexahydrate to urea is 1:(1.8 - 2.2);

[0051] (2) The precipitate obtained in step (1) is calcined and ground in sequence to prepare CeO 2 support powder;

[0052] (3) Chloroplatinic acid hexahydrate and stannous chloride dihydrate are mixed and dissolved in deionized water to prepare a precursor solution. Weigh the CeO 2 support powder prepared in step (2) and add it to the precursor solution. After fully stirring and mixing evenly, the moisture is removed to obtain oxidized PtSn x / CeO 2 ;

[0053] The addition amount of chloroplatinic acid hexahydrate is calculated based on 1 - 1.2 wt% of the total amount of Pt element, Sn element and CeO x / CeO 2 in oxidized PtSn 2 with Pt element in the oxidized state, and the molar ratio of Pt element to Sn element is 1:(1.6 - 3.3);

[0054] (4) The oxidized PtSn x / CeO2 , calcined in an air atmosphere at 450 - 550 °C for at least 1 hour, and then calcined in a reducing gas atmosphere at 550 - 650 °C for at least 1 hour after cooling, thus obtaining silver - gray PtSn x / CeO 2 catalyst, and X = 1.6 - 3.3.

[0055] The PtSn x / CeO 2 catalyst obtained by the above - mentioned preparation method can be used for the catalytic reaction of oxidative dehydrogenation of propane to propylene with CO 2 .

[0056] In this article, the molar ratio of cerium nitrate hexahydrate to urea in step (1) is 1:(1.8 - 2.2), which is the optimal ratio confirmed through comparative experiments. Based on experimental facts, if the molar ratio of cerium nitrate hexahydrate to urea is lower than this ratio, the prepared CeO 2 support powder will be impure, while if the molar ratio is higher than this ratio, the prepared CeO 2 will have defects, affecting the crystal structure, both of which will have a significant impact on the synthetic morphology and performance of the finally prepared PtSn x / CeO 2 catalyst.

[0057] In this article, the closed heating in step (1) can prevent the premature decomposition of urea. In addition, in one of the implementation modes, under the conditions of industrial implementation and scale - up effect, it should be ensured that cerium nitrate hexahydrate and urea in the mixed solution are fully dissolved before heating; under the conditions of larger preparation scale, it is advisable to choose to accompany stirring while heating in a closed system.

[0058] It should be noted that the closed heating in step (1) is carried out to 50 - 80 °C and maintained at this temperature for 6 - 7 h, and then continued to be heated in a closed system to 140 - 180 °C and maintained at this temperature for at least 24 h. The reason for adopting the two - stage stepped closed heating treatment is mainly based on experimental facts that urea is more likely to hydrolyze into NH 4+ and OCN - under lower temperature conditions. Under neutral or weakly alkaline conditions, OCN - continues to react to generate CO 3 2- and NH 3 . Subsequently, with the synchronous increase of the closed heating temperature and pressure, the urea hydrolysis rate increases, and Ce 3+ reacts with CO 3 2- and OH - to generate the CeCO 3 OH intermediate.

[0059] In one of the embodiments, in step (1), the enclosure is heated to 50 - 80°C and maintained at this temperature for 6 - 7 h, and then continuously heated to 140 - 180°C and maintained at this temperature for at least 24 h; where the heating to 50 - 80°C, for example, is 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C or any range or point value between them; the continuous heating to 140 - 180°C, for example, is 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C or any range or point value between them; the maintaining at this temperature for at least 24 h, for example, is 24 h, 25 h, 26 h, 27 h, 28 h, 29 h, 30 h, 31 h, 32 h or any range or point value between them.

[0060] In one of the embodiments, in step (1), the molar ratio of cerium nitrate hexahydrate to urea is 1:(1.8 - 2.2), for example, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2 or any range or point value between them.

[0061] In this text, in step (2), the precipitate obtained in step (1) is successively calcined and ground. It is advisable to wash and dry the precipitate before calcination. However, those skilled in the art should know that the washing and drying of the filtered precipitate are conventional processes in chemical engineering, and those skilled in the art can select appropriate washing and drying methods according to common knowledge or conventional processes.

[0062] To better illustrate the present invention and provide a reference embodiment, in step (2), the precipitate obtained in step (1) is successively calcined and ground. Before calcination, the precipitate is washed and dried. The washing is carried out by alternately washing with deionized water and absolute ethanol at least 3 times to better remove the residual OH 3 in the precipitate (CeCO - OH intermediate), NH 4 + and CO 3 2- and other impurity ions.

[0063] In this text, in step (2), the precipitate obtained in step (1) is successively calcined and ground. The calcination is to convert the metal components in the precipitate into oxides, specifically following the conventional calcination methods / parameters in chemical engineering. Those skilled in the art can directly refer to the conventional methods for calcining cerium dioxide for treatment.

[0064] In one of the embodiments, in step (2), the precipitate obtained in step (1) is successively calcined and ground. The specific process parameters for calcination are as follows: heating to 550 - 560 °C at a heating rate of 1 - 1.2 °C / min, and holding for 4 - 4.5 h. After the time is up, it is naturally cooled to room temperature. It should be noted that based on experimental facts, it is found that too high a heating rate during calcination is likely to cause changes in the CeO 2 structure. Therefore, the above heating rate is optimized.

[0065] In this article, in step (2), the precipitate obtained in step (1) is successively calcined and ground. Among them, grinding is a conventional process method for processing the calcined product into powder, following the conventional principles in chemical engineering. Those skilled in the art can perform specific operations according to common knowledge.

[0066] In this article, the addition amount of chloroplatinic acid hexahydrate in step (3) is calculated based on 1 - 1.2 wt% of the total amount of Pt element, Sn element and CeO x / CeO 2 in the form of oxidized Pt in PtSn 2 / CeO x / CeO 2 . The molar ratio of Pt element to Sn element is 1:(1.6 - 3.3). Those skilled in the art can calculate the addition amount of chloroplatinic acid hexahydrate in the precursor solution according to the mass ratio of Pt element. At the same time, the value of X in PtSn

[0067] / CeO

[0068] is the molar ratio of Pt element to Sn element, and then the addition amount of stannous chloride dihydrate in the precursor solution can be calculated. Since the solvent (deionized water) in the precursor aqueous solution will be removed, the addition amount of deionized water usually does not affect the prepared product. In actual implementation, the addition of deionized water is based on being able to fully dissolve chloroplatinic acid hexahydrate and stannous chloride dihydrate and being suitable for removal treatment. x / CeO 2 obtained in step (3) is calcined in an air atmosphere at 450 - 550 °C for at least 1 hour. The purpose is to make the oxidized oxides of Pt and Sn more firmly loaded on the surface of the prepared CeO 2 , and at the same time remove the Cl ions in the precursor solution.

[0069] In this article, after cooling, it is calcined in a reducing gas atmosphere at 550 - 650°C for at least 1 hour. The purpose is to reduce the oxidized oxides of Pt and Sn to the metallic state and use them as the active metals for the oxidative dehydrogenation of propane to propylene. Among them, the reducing gas atmosphere is a hydrogen atmosphere or a mixed atmosphere of hydrogen and inert gas. 2 It should be noted that after cooling, it is calcined in a reducing gas atmosphere at 550 - 650°C for at least 1 hour. After the calcination is completed, it is advisable to wait for the sample to cool naturally. During this process, the reducing gas needs to be continuously introduced to prevent the re-oxidation of the Pt and Sn active metals.

[0070] In one implementation, the oxidized PtSn

[0071] obtained in step (3) is calcined in an air atmosphere at 450 - 550°C for at least 1 hour, and after cooling, it is calcined in a reducing gas atmosphere at 550 - 650°C for at least 1 hour; among them, at 450 - 550°C in an air atmosphere, such as 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C or any range or point value between them; at 550 - 650°C in a reducing gas atmosphere, such as 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C or any range or point value between them; the calcination for at least 1 hour, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours or any range or point value between them. x / CeO 2 Finally, the fresh PtSn

[0072] / CeO x catalyst is prepared through the above scheme. Under the conditions of 550°C, 0.1 MPa, and 14000 h 2 , for the oxidative dehydrogenation reaction of propane with CO -1 , a propylene yield of more than 30% can be achieved. Among them, the PtSn 2 / CeO 1.6 catalyst emphasizes a higher propane conversion rate, and the PtSn 2 / CeO 3.3 emphasizes the propylene selectivity. 2

[0073] The inventive principle of the present invention lies in that Pt-based noble metal catalysts, which have relatively high propane dehydrogenation activity and have always been the research focus of propane catalytic conversion, are widely considered to have good application prospects. However, the large-area dehydrogenation of propane caused by the easy agglomeration of Pt-based catalysts leads to low selectivity of the target product propylene and catalyst deactivation. Therefore, the inventors of the present invention attempt to prepare Pt-Sn bimetallic catalysts to solve the above problems in the prior art.

[0074] The present invention attempts to modify the traditional Pt-based catalyst by introducing the inert metal Sn. The strong interaction between Sn and Pt can disperse the agglomerated Pt, reduce the excessive dehydrogenation of propane, increase the number of propane dehydrogenation sites, and improve the propane conversion rate. However, through retrieval and query, it is found that the Pt-Sn bimetallic catalysts reported in the prior art literature have good direct dehydrogenation effect on propane, but perform poorly in the oxidative propane dehydrogenation to propylene reaction. This may be due to the weak activation ability of the Pt-Sn bimetallic catalyst for CO 2 The oxidative propane dehydrogenation to propylene reaction performs poorly, which may stem from the weak activation ability of the Pt-Sn bimetallic catalyst for CO 2 and.

[0075] To solve these problems, on the one hand, the present invention attempts to use urea-assisted prepared CeO 2 as the catalyst support for Pt-Sn bimetallic loading. This CeO 2 support has excellent oxygen release ability, can help eliminate hydrogen components in the propane dehydrogenation step, and at the same time the formed oxygen vacancies can also be used for the capture and conversion of CO 2 . However, it is found in the actual experimental process that the variable process parameters in the preparation process of the CeO 2 support will greatly affect the synthetic morphology and performance of the finally prepared PtSn x / CeO 2 catalyst, and the above process parameter variables have not been reported in the prior art literature, such as the molar ratio of cerium nitrate hexahydrate to urea and the two-stage stepped closed heating treatment; on the other hand, further exploration of the molar ratio between Pt and Sn bimetals is carried out through comparative experiments. In this process, it is surprisingly found that when the molar ratio of Pt to Sn is 1:(1.6-3.3), the prepared PtSn x / CeO 2 catalyst not only has a significantly higher propylene yield, but also has excellent propane conversion rate and better CO 2 conversion rate. In particular, it is worth noting that when the molar ratio of Pt to Sn is 1:1.6, that is, PtSn 1.6 / CeO 2 catalyst has a propane conversion rate and a CO 2 conversion rate close to 1:1, indicating that the PtSn 1.6 / CeO 2 catalyst can fully regulate CO2 Propane dehydrogenation reaction.

[0076] In this text, the mixing, washing, and drying all follow the conventional principles in chemical engineering processes, and those skilled in the art can perform specific operations according to common general knowledge.

[0077] The present application will be further explained in detail with reference to the embodiments below. However, those skilled in the art should understand that these embodiments are provided for illustrative purposes only and are not intended to limit the present application.

[0078] Embodiments

[0079] The implementation schemes of the present application will be described in detail below in combination with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those embodiments where specific conditions are not indicated, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments where the manufacturer is not indicated, they are all conventional products that can be obtained through commercial purchase. The present application should not be construed as being limited to the specific embodiments described.

[0080] 1. Raw materials

[0081] Material Name Concentration Manufacturer <![CDATA[H 2 PtCl 6 ·6H 2 O]]> AR, Pt ≥ 37.5% Shanghai Macklin Biochemical Co., Ltd. <![CDATA[SnCl·2H 2 O]]> Analytical Reagent Chengdu Kelong Chemical Co., Ltd. <![CDATA[Ce(NO 3 ) 3 ·6H 2 O]]> Analytical Reagent Chengdu Kelong Chemical Co., Ltd. <![CDATA[H 2 NCONH 2 > ≥99.5％ Shanghai Aladdin Biochemical Technology Co., Ltd. <![CDATA[C 3 H 8 > 99.99％ Chengdu Xuyuan Chemical Co., Ltd. <![CDATA[CO 2 > 99.99％ Chengdu Xuyuan Chemical Co., Ltd. <![CDATA[C 3 H 8 , CO 2 mixed gas]]> 99.99％ Chengdu Xuyuan Chemical Co., Ltd. Ar 99.999％ Chengdu Xuyuan Chemical Co., Ltd. <![CDATA[10% H 2 / Ar]]> 99.99％ Chengdu Xuyuan Chemical Co., Ltd.

[0082] 2. Test method

[0083] After compacting and sieving the sample, samples with a size of 20 - 40 mesh are prepared. Weigh 0.2 g of the sample and mix it with 0.8 g of quartz sand (20 - 40 mesh), and then put the mixture into a quartz fixed-bed reactor with an inner diameter of 8 mm. The carrier gas used for the reaction is high-purity nitrogen (purity ≥ 99.999%). The reaction conditions are as follows: temperature 550 °C, reaction pressure 0.1 MPa, reaction space velocity 14000 h -1 , where the gas flow rate of propane and CO 2 is 1:1.

[0084] C 3 H 8 and the conversion rate calculation formula of CO 2 is as follows:

[0085]

[0086]

[0087] C x H y The selectivity calculation formula is as follows:

[0088]

[0089] C 3 H 6The yield calculation formula is as follows:

[0090]

[0091] Wherein, in represents the input value of the corresponding gas component, and out represents the output value of the corresponding gas component.

[0092] 3. Preparation method

[0093] (1) Mix 2.17 g of cerium nitrate hexahydrate with 0.6 g of urea and dissolve them in 50 ml of deionized water to prepare a mixed solution. Heat it in a closed container to 60 °C and maintain this temperature for 6 h, then continue to heat it in a closed container to 150 °C and maintain this temperature for 24 h. After cooling, filter to obtain a precipitate;

[0094] (2) Wash, dry, calcine, and grind the precipitate obtained in step (1) in sequence to prepare CeO 2 support powder;

[0095] The specific process parameters of the calcination are as follows: heat it to 550 °C at a heating rate of 1 °C / min, and keep it calcined for 4 h. After the time is up, cool it naturally to room temperature;

[0096] (3) Mix chloroplatinic acid hexahydrate and stannous chloride dihydrate and dissolve them in deionized water to prepare a precursor solution. Weigh 500 mg of the CeO 2 support powder prepared in step (2) and add it to the precursor solution. After stirring and mixing evenly, perform rotary evaporation treatment (at 50 °C, under negative pressure conditions) to remove water, and thus obtain oxidized PtSn x / CeO 2 ;

[0097] The addition amount of the chloroplatinic acid hexahydrate is calculated based on 1 wt% of the total amount of Pt element, Sn element, and CeO x / CeO 2 in the oxidized PtSn 2 / CeO x (4) Calcinate the oxidized PtSn 2 / CeO x obtained in step (3) in an air atmosphere at 500 °C for 1 h. After cooling, calcine it again in a hydrogen-argon mixed gas atmosphere at 600 °C for 1 h, and thus prepare a silver-gray PtSn 2 / CeO 1.6 catalyst, and X = 1.6 - 3.3.

[0099] Example 1

[0100] In this example, PtSn 1.6 / CeO 2 catalyst was prepared according to the above "3. Preparation method", that is, when X = 1.6, the addition amounts of chloroplatinic acid hexahydrate and stannous chloride dihydrate in the precursor solution needed to be adjusted correspondingly.

[0101] The prepared PtSn 1.6 / CeO 2 catalyst was tested according to the above "2. Test method". As Figures 4 - 7 shown, the PtSn 1.6 / CeO 2 catalyst could achieve a propane conversion rate of over 40% in the first 2 h. As the reaction time increased, after some carbon deposition or sintering caused catalyst deactivation (2 - 6 h), it could still achieve a propane conversion rate of over 30%. At the same time, the ratio of CO 2 conversion rate to propane conversion rate was close to 1:1, indicating that the PtSn 1.6 / CeO 2 catalyst could fully regulate the oxidative dehydrogenation reaction of propane with CO 2 .

[0102] The results showed that the PtSn 1.6 / CeO 2 catalyst obtained in Example 1 had obvious effects on the oxidative dehydrogenation of propane with CO 2 to produce propylene, and the propylene yield could reach over 25% under the reaction conditions.

[0103] It should be emphasized that the above test conditions were carried out under laboratory conditions, and the catalytic activity was better than that of similar products recorded in the existing literature in this field.

[0104] Example 2

[0105] In this example, PtSn 3.3 / CeO 2 catalyst was prepared according to the above "3. Preparation method", that is, when X = 3.3, the addition amounts of chloroplatinic acid hexahydrate and stannous chloride dihydrate in the precursor solution needed to be adjusted correspondingly.

[0106] The prepared PtSn 3.3 / CeO 2 catalyst was tested according to the above "2. Test method". As Figures 4 - 7 shown, in the activity test from 0 to 6 h, the catalyst showed a lower propane conversion rate than that in Example 1, basically fluctuating in the range of 28 - 40%; at the same time, the CO 2 conversion rate was relatively low, only 20 - 30%, but it was also found that although its CO 2The activation effect is lower, but it has higher propylene selectivity. However, due to the decrease in propane conversion, the overall propylene yield is still slightly lower than that of PtSn 1.6 / CeO 2 catalyst.

[0107] The results show that different from the different molar ratios of Pt and Sn, the regulation effects on the oxidative propane dehydrogenation reaction are also different. The catalyst obtained in Example 2 has better performance in the oxidative propane dehydrogenation to propylene, but it is still slightly inferior to that in Example 1. 2 The results show that different from the different molar ratios of Pt and Sn, the regulation effects on the oxidative propane dehydrogenation reaction are also different. The catalyst obtained in Example 2 has better CO 2 oxidative propane dehydrogenation to propylene performance, but it is still slightly inferior to that in Example 1.

[0108] Comparative Example 1

[0109] In this comparative example, only Pt metal was loaded, that is, only chloroplatinic acid hexahydrate was added in step (3) of the above "3. Preparation method", and stannous chloride dihydrate was not added. The other steps were the same as those in "3. Preparation method" to obtain Pt / CeO 2 catalyst.

[0110] The prepared Pt / CeO 2 catalyst was tested according to the above "2. Test method". As Figures 4 - 7 shown, the catalyst has the worst effect on the oxidative propane dehydrogenation to propylene. During the reaction time of 0-6 h, the catalyst shows a low propane conversion rate, which basically fluctuates in the range of 25-45%, but the CO 2 conversion rate is relatively high (50-60%). This indicates that pure platinum has poor regulation on the oxidative propane dehydrogenation to propylene reaction. The too high CO 2 conversion rate makes the overall oxidation of the reaction too strong, which directly leads to the over-oxidation of propane to produce by-products such as CO, that is, the dry reforming reaction is prone to occur. 2 The results show that the Pt / CeO 2 catalyst obtained in Comparative Example 1 has very poor reaction activity for the oxidative propane dehydrogenation when the second-phase metal Sn is not added.

[0111] The results show that the Pt / CeO 2 catalyst obtained in Comparative Example 1 has very poor reaction activity for the oxidative propane dehydrogenation when the second-phase metal Sn is not added. 2 The results show that the Pt / CeO

[0112] Comparative Example 2

[0113] In this comparative example, the CeO 2 support prepared without the assistance of urea was not used, and only Pt metal was loaded. That is, in step (1) of the above "3. Preparation method", 1.736 g of cerium nitrate hexahydrate and 19.2 g of sodium hydroxide were mixed and dissolved in 50 ml of deionized water, and then only chloroplatinic acid hexahydrate was added in step (3), and stannous chloride dihydrate was not added. The other steps were the same as those in "3. Preparation method" to obtain Pt / CeO 2Catalyst.

[0114] The prepared Pt / CeO 2 catalyst was tested according to the above "2. Test method". As Figure 8 shown, in the activity test for 2 - 6 h, the propane conversion rate was only stable at about 15%, and the CO 2 conversion rate was 30 - 40%. Both data were further inferior to the catalyst prepared in Comparative Example 1.

[0115] The results showed that CeO 2 prepared by sodium hydroxide assistance in Comparative Example 2 as the catalyst support had further inferior activity than that in Comparative Example 1.

[0116] Comparative Example 3

[0117] In this comparative example, the PtSn 0.5 / CeO 2 catalyst was prepared according to the above "3. Preparation method", that is, X = 0.5, and the addition amounts of chloroplatinic acid hexahydrate and stannous chloride dihydrate in the precursor solution needed to be adjusted correspondingly.

[0118] The prepared PtSn 0.5 / CeO 2 catalyst was tested according to the above "2. Test method". As Figures 4 - 7 shown.

[0119] Comparative Example 4

[0120] In this comparative example, the PtSn 1 / CeO 2 catalyst was prepared according to the above "3. Preparation method", that is, X = 1, and the addition amounts of chloroplatinic acid hexahydrate and stannous chloride dihydrate in the precursor solution needed to be adjusted correspondingly.

[0121] The prepared PtSn 1 / CeO 2 catalyst was tested according to the above "2. Test method". As Figures 4 - 7 shown, although it showed a propane conversion rate close to that of the catalyst in Example 1, the CO 2 conversion rate was significantly higher, resulting in a significantly lower propylene yield than that in Example 1.

[0122] Comparative Example 5

[0123] In this comparative example, the PtSn 4.9 / CeO 2 catalyst was prepared according to the above "3. Preparation method", that is, X = 4.9, and the addition amounts of chloroplatinic acid hexahydrate and stannous chloride dihydrate in the precursor solution needed to be adjusted correspondingly.

[0124] The prepared PtSn 4.9 / CeO 2 catalyst was tested according to the above "2. Test Method", as Figures 4 - 7 shown.

[0125] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing a propane dehydrogenation platinum-tin bimetallic supported catalyst, characterized in that The main steps include: (1) dissolving cerium nitrate hexahydrate and urea in deionized water to prepare a mixed solution, heating the solution to 50-80° C. and maintaining the temperature for 6-7 hours, and then heating the solution to 140-180° C. and maintaining the temperature for at least 24 hours, cooling the solution, and filtering the solution to obtain a precipitate; The concentration of cerium nitrate hexahydrate in the mixed solution is 0.04-0.05 g / ml, and the molar ratio of cerium nitrate hexahydrate to urea is 1:(1.8-2.2); (2) calcining and grinding the precipitate obtained in step (1) to prepare CeO2 carrier powder; (3) Dissolve chloroplatinic acid hexahydrate and stannous chloride dihydrate in deionized water to prepare a precursor solution, weigh the CeO2 carrier powder prepared in step (2) and add it to the precursor solution, stir and mix thoroughly, and remove water to obtain oxidized PtSn x / CeO2; The amount of chloroplatinic acid hexahydrate added is PtSn with Pt element as oxidation state. x / 1-1.2 wt% of the total amount of Pt element, Sn element and CeO2 in CeO2, and the molar ratio of Pt element to Sn element is 1:(1.6-3.3); (4) PtSn in the oxidized state obtained in step (3) x / CeO2, calcined at 450-550℃ in air atmosphere for at least 1 hour, and then calcined at 550-650℃ in reducing gas atmosphere for at least 1 hour after cooling, to obtain silver-gray PtSn x / CeO2 catalyst, and X=1.6~3.

3.

2. The preparation method according to claim 1, characterized in that: In step (2), the precipitate obtained in step (1) is sequentially roasted and ground, and the precipitate is washed and dried before roasting, wherein the washing is performed by alternately washing with deionized water and anhydrous ethanol for at least 3 times.

3. The preparation method according to claim 1, characterized in that: In step (2), the precipitate obtained in step (1) is successively roasted and ground, wherein the specific process parameters of the roasting are: heating to 550-560°C at a heating rate of 1-1.2°C / min, and roasting at this temperature for 4-4.5h, and naturally cooling to room temperature after the time is up.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the Pt element to the Sn element in step (3) is 1.6 or 3.

3.

5. A PtSn prepared by the method for preparing a propane dehydrogenation platinum-tin bimetallic supported catalyst according to claim 1 x / CeO2 catalyst.

6. PtSn as claimed in claim 5 x / Application of CeO2 catalyst in the field of CO2 oxidation of propane to produce propylene.

7. The use according to claim 6, characterized in that: The catalytic reaction of CO2 oxidation of propane to produce propylene is carried out at a temperature of at least 550°C.

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