Platinum-carbon catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of propane dehydrogenation, and discloses a platinum-carbon catalyst and a preparation method and application thereof.The preparation method of the platinum-carbon catalyst comprises the steps that 1, in the presence of a hydrogen-containing atmosphere, a carbon material is modified, and a modified carbon carrier is obtained; (2) introducing a platinum precursor onto the modified carbon carrier, and then carrying out gas phase reduction; wherein the ratio of sp2 carbon to sp3 carbon on the surface of the carbon material is 0.2-1.5; the surface of the carbon material only contains two oxygen-containing groups, namely C-OH / C-O-C and O-C = O. The platinum-carbon catalyst provided by the invention has relatively high stability in a propane dehydrogenation reaction.

Description

Technical Field

[0001] The invention relates to the technical field of propane dehydrogenation, and in particular to a platinum-carbon catalyst and a preparation method and application thereof. Background Art

[0002] As an important organic chemical raw material and petrochemical intermediate, propylene can be used to produce polypropylene, polyacrylonitrile, acrylic acid, synthetic detergents, propylene oxide and cumene, etc. It is an important bridge for the traditional refining industry to transform into an integrated refining and chemical industry.

[0003] Direct dehydrogenation of propane is an important way to produce propylene, and the key lies in the catalyst. Industrial direct dehydrogenation catalysts for propane are mainly Pt-based catalysts and CrOx-based catalysts, among which CrOx-based catalysts are easily deactivated and require frequent regeneration. Pt-based catalysts have better direct dehydrogenation performance for propane, but due to the presence of acidic sites on the surface of alumina carriers commonly used in Pt-based catalysts, side reactions such as cracking, deep dehydrogenation and olefin polymerization are easily induced, reducing the stability of the catalyst. In addition, Pt metal reserves are low and expensive, so it is necessary to reduce the Pt loading and increase the utilization rate of Pt atoms. In summary, it is of great significance to develop efficient, green, stable and highly dispersed propane dehydrogenation catalysts.

[0004] Carbon materials have excellent properties such as low acidity, pore structure and adjustable surface properties, making Pt / carbon catalyst one of the propane dehydrogenation catalysts with potential for industrial application. Since propane dehydrogenation reaction is a reversible endothermic reaction, its thermodynamic equilibrium conversion rate increases with increasing temperature. However, the reaction temperature is high, the energy consumption is high, and at high reaction temperature, CC bonds are easier to break than CH bonds. When the reaction temperature exceeds a certain value, the thermal reaction intensifies, carbon deposits are generated, and the catalyst is deactivated. In addition, due to the weak interaction between the metal active component and the carbon carrier, when reacting at high temperature, the Pt / carbon catalyst will be deactivated due to the sintering of the active component Pt. In particular, the smaller the particle size of Pt, the easier it is to sinter. Volykin Andrey et al. (TopCatal, 2015, 58: 854-865) prepared Pt / carbon black with a Pt loading of 0.82 wt%, and the average particle size of Pt was 1.6 nm according to the transmission electron microscopy results. When the catalyst catalyzes the direct dehydrogenation of propane at 500°C, the propane conversion rate drops from ~13.5% to ~9.1% during the reaction from 10min to 60min, that is, the propane conversion rate decreases by 32.59%. Yin et al. (Nature Communication, 2021, 12: 4865.) prepared Pt / XC-72R with a Pt loading of 1 wt%. During the 500min propane dehydrogenation evaluation process, it showed high stability, but the active component Pt in the catalyst is also not mainly present in the form of single atoms or small-sized atomic clusters, that is, the utilization rate of Pt atoms is relatively low. Therefore, the preparation of Pt / carbon catalysts with high stability and high dispersion is crucial to promote their industrial application.

[0005] From the perspective of catalyst carriers, the main methods to improve the high-temperature stability of platinum-carbon catalysts include element doping, defect modification, and morphology control. Yin et al. (Nature Communications, 2021, 12: 3135.) used 2,2'-dithiophene as a precursor and SiO2 as a template to prepare sulfur-doped carbon material (SC) by a template method. It was prepared into Pt / SC and applied to the direct dehydrogenation reaction of propane, showing excellent performance. However, the Pt loading in Pt / SC is 1wt%, and Pt mainly exists in the form of Pt nanoclusters of ~1nm. The utilization rate of Pt atoms is lower than that of single atoms or atomic clusters. In addition, the preparation process of SC is complicated and costly, which is not conducive to its industrial application. Liu et al. (ACS Catalysis, 2017, 7: 3349-3355.) subjected nanodiamonds to high temperature annealing (1100°C) to obtain graphene-coated nanodiamond materials (ND@G), which were prepared into Pt / ND@G with a Pt loading of 0.5wt%, which also showed high stability. However, the Pt particle size is mainly distributed in the range of 1.1 to 1.5nm, and ND@G needs to be obtained through high temperature annealing, which is not conducive to its industrialization. Morphology control is usually based on confinement means, which will sacrifice catalyst activity.

[0006] It can be seen that although progress has been made in improving the stability of Pt / carbon catalysts for direct dehydrogenation of propane, the particle size of the active component Pt in the Pt / carbon catalyst is large, and the preparation method of stable Pt / carbon catalysts is cumbersome or energy-intensive. Therefore, it is challenging to develop a simple method to prepare Pt / carbon catalysts with high stability and highly dispersed active components. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems in the prior art that the method for improving the stability of Pt / carbon catalyst is complicated, difficult to industrialize and the utilization rate of Pt still needs to be improved, and to provide a platinum-carbon catalyst and its preparation method and application. The platinum-carbon catalyst provided by the present invention has high stability in the propane dehydrogenation reaction.

[0008] In order to achieve the above object, the first aspect of the present invention provides a method for preparing a platinum-carbon catalyst, the method comprising the following steps:

[0009] (1) modifying the carbon material in the presence of a hydrogen-containing atmosphere to obtain a modified carbon support;

[0010] (2) introducing a platinum precursor onto the modified carbon support and then performing gas phase reduction;

[0011] Wherein, the surface sp of the carbon material 2 Carbon and sp 3The ratio of carbon is 0.2-1.5;

[0012] The surface of the carbon material contains only two oxygen-containing groups, namely C-OH / COC and OC=O.

[0013] Preferably, the oxygen-containing groups OC═O on the surface of the carbon material account for 40-60% by weight of the total surface oxygen content.

[0014] Preferably, the modification treatment conditions include: a temperature of 450-600°C, preferably 480-520°C, and a time of 30-130 min, for example, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min or 130 min, preferably 40-90 min.

[0015] Preferably, the carbon carrier and the platinum precursor are used in such an amount that the platinum metal loading in the prepared platinum-carbon catalyst is 0.20-0.55 wt %, preferably 0.25-0.48 wt %, based on the total amount of the platinum-carbon catalyst.

[0016] The second aspect of the present invention provides a platinum-carbon catalyst prepared by the preparation method provided in the first aspect.

[0017] The third aspect of the present invention provides use of the platinum-carbon catalyst described in the second aspect in a propane dehydrogenation reaction.

[0018] The method provided by the present invention utilizes a carbon carrier with specific surface properties, and utilizes a hydrogen-containing gas as a modifier to modify the carbon carrier of a platinum-carbon catalyst, thereby improving the dispersion of the platinum-carbon catalyst, making it significantly better than an unmodified platinum-carbon catalyst, and in addition, the prepared platinum-carbon catalyst is applied to a propane dehydrogenation reaction, and the catalyst has good stability. The method provided by the present invention has a simple process and mild conditions, and can obtain a platinum-carbon catalyst with high stability and highly dispersed active components without destroying the pore structure and defect degree of the carbon carrier and without changing the graphitization degree of the carbon carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a C1s X-ray photoelectron spectrum of the carbon material selected in Example 1 and the carbon material selected in Comparative Example 2;

[0020] Figure 2 is an O1s X-ray photoelectron spectrum of the carbon material selected in Example 1 and the carbon material selected in Comparative Example 2;

[0021] Figure 3 is an X-ray diffraction (XRD) diagram of the carbon material and the modified carbon material selected in Example 1;

[0022] Figure 4 1 is a Raman spectrum of the carbon material and the modified carbon material selected in Example 1;

[0023] Figure 5 The isothermal adsorption-desorption curves of the carbon material and the modified carbon material selected in Example 1;

[0024] Figure 6 is a scanning transmission electron microscope (Cs-STEM) image of the catalyst prepared in Example 1;

[0025] Figure 7 1 is the propane conversion rate and propylene selectivity curve of Example 1 and Example 6;

[0026] Figure 8 This is a scanning transmission electron microscope (Cs-STEM) image of the catalyst prepared in Example 6. DETAILED DESCRIPTION

[0027] 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.

[0028] In the present invention, the term "sp 2 Carbon refers to the carbon species with a binding energy of ~284.4±0.2 eV in the C1s spectrum measured by X-ray photoelectron spectroscopy, and the “sp 3 “Carbon” refers to carbon species with a binding energy of ~285.2±0.2 eV in the C1s spectrum measured by X-ray photoelectron spectroscopy.

[0029] In the present invention, the term "C-OH / COC" refers to an oxygen-containing group whose binding energy is located at ~533.7±0.2eV in the O1s spectrum measured by X-ray photoelectron spectroscopy. "OC=O" refers to an oxygen-containing group whose binding energy is located at ~532.4±0.2eV in the O1s spectrum measured by X-ray photoelectron spectroscopy. "C=O" refers to an oxygen-containing group whose binding energy is located at ~531.3±0.2eV in the O1s spectrum measured by X-ray photoelectron spectroscopy. "Oxide" refers to an oxygen species whose binding energy is located at ~530.0eV in the O1s spectrum measured by X-ray photoelectron spectroscopy. "Adsorbed water" refers to an oxygen species whose binding energy is located at ~535.0eV in the O1s spectrum measured by X-ray photoelectron spectroscopy.

[0030] The Pt / carbon catalyst in the prior art is used to catalyze the propane dehydrogenation reaction with excellent properties, including rich pore structure, which is conducive to mass transfer and heat transfer, and the acidity of the carbon carrier is adjustable, etc., but it is still a difficult problem to prepare a stable and highly dispersed Pt / carbon catalyst with active components by a simple method. Jiang et al. (Chemical Rection Engineering and Technology, 2007, 23: 375-379.) found that the high-temperature hydrogen treatment of activated carbon and palladium carbon catalyst performance will reduce the active component palladium dispersion when the activated carbon treated with high-temperature hydrogen is used as a carrier. The inventor of the present invention found in the research process that as long as a specific carbon material is treated with a reducing gas at a suitable temperature, and then a platinum precursor is introduced to perform gas phase reduction to prepare a platinum carbon catalyst, a platinum carbon catalyst with high dispersion can be obtained to a certain extent. In the presence of a hydrogen-containing atmosphere, the carbon material is modified, which can not only improve the stability of the platinum carbon catalyst in the propane dehydrogenation reaction and the dispersion of the active component Pt, but also the modification method is simple and easy to implement, green and environmentally friendly, and helps to promote the industrial application of Pt / carbon catalysts.

[0031] The first aspect of the present invention provides a method for preparing a platinum-carbon catalyst, the method comprising the following steps:

[0032] (1) modifying the carbon material in the presence of a hydrogen-containing atmosphere to obtain a modified carbon support;

[0033] (2) introducing a platinum precursor onto the modified carbon support and then performing gas phase reduction;

[0034] Wherein, the surface sp of the carbon material 2 Carbon and sp 3 The ratio of carbon is 0.2-1.5;

[0035] The surface of the carbon material contains only two oxygen-containing groups, namely C-OH / COC and OC=O.

[0036] In the present invention, the surface sp 2 Carbon and sp 3 The carbon ratio and the amount of surface oxygen-containing functional groups (oxides, C-OH / COC, OC=O, C=O and adsorbed water) were determined by X-ray photoelectron spectroscopy (XPS) analysis, and the peak separation software was Avantage. The X-ray photoelectron spectrometer used was an ESCALab220i-XL type X-ray electron spectrometer equipped with AvantageV5.926 software produced by VG Scientific, and the X-ray photoelectron spectroscopy analysis test conditions were: the excitation source was monochromatized Al Kα X-ray.

[0037] According to the present invention, the carbon material surface sp2 Carbon and sp 3 The carbon ratio is 0.2-1.5, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4 or 1.5. Preferably, the carbon material surface sp 2 Carbon and sp 3 The carbon ratio is 0.5 -1.2.

[0038] According to the present invention, the oxygen-containing groups OC=O on the surface of the carbon material account for 40-60 weight% of the total surface oxygen content, for example, it can be 40 weight%, 41 weight%, 42 weight%, 43 weight%, 44 weight%, 45 weight%, 46 weight%, 47 weight%, 48 weight%, 49 weight%, 50 weight%, 51 weight%, 52 weight%, 53 weight%, 54 weight%, 55 weight%, 56 weight%, 57 weight%, 58 weight%, 59 weight% or 60 weight%, more preferably 45-50 weight%.

[0039] Using the above preferred surface sp 2 Carbon and sp 3 The carbon material with a high carbon ratio and an oxygen-containing group OC=O content combined with the method of the present invention is more conducive to improving the dispersibility of the prepared platinum-carbon catalyst and the stability of the catalyst when applied to propane dehydrogenation reaction.

[0040] The present invention has a wide range of selection for the type of the carbon material, as long as it can meet the above parameter limitations. Preferably, the carbon material is carbon black.

[0041] The present invention has a wide selection range for the source of the carbon material, which can be purchased commercially or prepared by any preparation method in the prior art, and the present invention has no particular limitation on this.

[0042] In the present invention, the "modification treatment" refers to a method of treating a carbon material at a certain temperature in the presence of a hydrogen-containing atmosphere (reducing atmosphere).

[0043] Preferably, the hydrogen-containing atmosphere is provided by a hydrogen-containing gas, and the hydrogen-containing gas includes hydrogen and an optional inert gas. The hydrogen-containing atmosphere may or may not contain an inert gas. Preferably, the hydrogen content in the hydrogen-containing gas is 5-100% by volume, and more preferably 10-30% by volume. The use of such an atmosphere with a more preferred hydrogen content is more conducive to controlling the surface chemical properties of the carbon material within a state range that is conducive to the preparation of a highly stable and highly dispersed Pt / carbon catalyst.

[0044] The present invention has no particular limitation on the inert gas, which has a conventional definition in the art, including but not limited to one or more of nitrogen, argon, neon and helium.

[0045] According to the present invention, preferably, the modification treatment conditions include: a temperature of 450-600°C, preferably 480-520°C, and a time of 30-130 min, preferably 40-90 min. This preferred embodiment is more conducive to controlling the surface chemical properties of the carbon material within a state range that is conducive to the preparation of a highly stable and highly dispersed Pt / carbon catalyst.

[0046] According to the method provided by the present invention, there is no particular limitation on the device for performing the modification treatment in step (1), and it can be performed in a tubular furnace, for example.

[0047] According to a specific embodiment of the present invention, step (1) comprises: placing the carbon material in a tubular furnace, heating it to the target modification treatment temperature at a constant heating rate (preferably 5-10°C / min) in an inert atmosphere, maintaining the temperature and switching the inert atmosphere to a hydrogen-containing atmosphere, and then cooling the temperature to obtain the modified carbon carrier.

[0048] According to the present invention, preferably, the amount of the carbon carrier and the platinum precursor is such that the platinum metal loading in the prepared platinum-carbon catalyst is 0.20-0.55 wt %, preferably 0.25-0.48 wt %, based on the total amount of the platinum-carbon catalyst. The method provided by the present invention has a high platinum utilization rate, and a catalyst with a lower platinum content can have better catalytic performance.

[0049] In the present invention, the content of Pt in the platinum-carbon catalyst can be determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0050] According to the present invention, preferably, the platinum precursor is selected from at least one of chloroplatinic acid, platinum nitrate, tetraamineplatinum chloride, tetraamineplatinum nitrate and tetraamineplatinum acetate.

[0051] The present invention does not particularly limit the specific method of introducing the platinum precursor into the modified carbon carrier in step (2). Preferably, in step (2), the method of introducing the platinum precursor into the modified carbon carrier includes: impregnating the modified carbon carrier with a solution of the platinum precursor.

[0052] The present invention has no particular limitation on the impregnation method, and may be any conventional impregnation method in the art, such as equal volume impregnation or supersaturated impregnation, which will not be described in detail herein.

[0053] According to a preferred embodiment of the present invention, the modified carbon support is impregnated with an equal volume of a solution of a platinum precursor.

[0054] The present invention has no particular limitation on the type of solvent in the platinum precursor solution. Preferably, the solvent is water and / or alcohol, and the alcohol is, for example, ethanol. The amount of water and alcohol can be selected in a wide range.

[0055] The present invention has no particular limitation on the concentration of the platinum precursor solution, and the concentration can be adaptively selected according to the platinum content in the target catalyst.

[0056] According to the present invention, preferably, the method further comprises sealed standing and / or drying after the impregnation. The sealed standing after impregnation provided by the present invention is conducive to the adsorption of the platinum precursor solution on the carrier surface and diffusion in the pores.

[0057] Preferably, the standing time is 8-72 hours, preferably 12-24 hours.

[0058] Preferably, the drying conditions include: a drying temperature of 5-50° C., preferably 15-30° C.; and a drying time of 8-72 h, preferably 8-15 h.

[0059] According to the present invention, preferably, in step (2), the gas phase reduction conditions include: in the presence of a reducing gas, the reduction temperature is 140-200°C, preferably 140-160°C; the reduction time is 1-3h, preferably 1.5-2.5h. The use of such preferred gas phase reduction conditions is more conducive to the preparation of a platinum-carbon catalyst with high dispersion.

[0060] Preferably, the reducing gas comprises hydrogen and an inert gas (the selection range may be the same as the selection range described above), and further preferably, the content of hydrogen in the reducing gas is 5-20% by volume, preferably 5-10% by volume.

[0061] According to a specific embodiment of the present invention, step (2) gas phase reduction comprises: heating to the target gas phase reduction temperature at a constant heating rate (preferably 5-10°C / min) in an inert atmosphere, maintaining the temperature and switching the inert atmosphere to a reducing gas, and then cooling to obtain the catalyst.

[0062] The preparation method of the platinum-carbon catalyst provided by the present invention has a simple process, does not involve environmentally harmful substances, does not require acid washing, and does not generate wastewater, waste gas and solid waste. Compared with the existing preparation method of the platinum-carbon catalyst, it is green and environmentally friendly and more suitable for large-scale industrial production. In addition, the platinum-carbon catalyst prepared by the preparation method provided by the present invention is highly dispersed and has good stability.

[0063] The second aspect of the present invention provides a platinum-carbon catalyst prepared by the preparation method provided in the first aspect.

[0064] The platinum metal in the platinum-carbon catalyst provided by the present invention mainly exists in the form of single atoms and / or atomic clusters (referring to the fact that the platinum metal particles in the catalyst do not have regular lattice stripes. The presence of lattice stripes indicates that the Pt particles exist in the form of nanocrystals). Preferably, according to scanning transmission electron microscopy analysis, in the platinum-carbon catalyst, the number of nanocrystals with a size less than or equal to 2 nm is less than or equal to 2, and more preferably, there are no nanocrystals larger than 2 nm in the platinum-carbon catalyst.

[0065] In the present invention, the morphology of the catalyst is characterized by a JEOL TEM-ARM 200F scanning transmission electron microscope (Cs-STEM) with spherical aberration (Cs) correction.

[0066] The third aspect of the present invention provides the use of the platinum-carbon catalyst described in the second aspect in a propane dehydrogenation reaction. According to the present invention, preferably, the platinum-carbon catalyst is used in a direct propane dehydrogenation reaction. The catalyst provided by the present invention is applied to a propane dehydrogenation reaction with good stability.

[0067] The conditions of the propane dehydrogenation reaction are not particularly limited in the present invention and can be carried out according to conventional technical means in the art. Preferably, the conditions of the propane dehydrogenation reaction include: a reaction temperature of 450-600°C, a reaction pressure of normal pressure, a space velocity of the feed gas of 4500-22500 mL feed gas / (h·g cat ). The feed gas may include propylene, an inert gas and optionally hydrogen. Preferably, the volume content of propylene in the feed gas is 2-10%, and the volume content of hydrogen is 0-10%.

[0068] The present invention will be described in detail below through examples.

[0069] In the following embodiments, the surface sp of the carbon material 2 Carbon and sp 3 The carbon ratio and the amount of surface oxygen-containing groups (oxides, C-OH / COC, OC=O, C=O and adsorbed water) were determined by X-ray photoelectron spectroscopy (XPS) as described above.

[0070] The morphology of the catalyst was characterized by a JEOL TEM-ARM 200F scanning transmission electron microscope (Cs-STEM) with spherical aberration (Cs) correction.

[0071] The content of Pt in the Pt-carbon catalyst was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0072] The crystal structure of the carbon material can be determined by X-ray diffraction (XRD) characterization. The model of the XRD diffractometer used is XRD-6000 X-ray powder diffractometer (Shimadzu, Japan). The XRD test conditions are: Cu target, Kα ray (wavelength λ = 0.154nm), tube voltage of 40kV, tube current of 200mA, and scanning speed of 5° / min.

[0073] The defect degree of the carbon material is tested by Raman spectroscopy, and a 532 nm light source is selected to characterize the carbon material to obtain a characteristic spectrum.

[0074] Example 1

[0075] (1) Place 0.5 g of carbon material (C-0, carbon black) in a tubular furnace and heat the temperature from room temperature to 500 °C at a heating rate of 5 °C / min in a nitrogen atmosphere of 200 mL / min. Switch the gas to a mixture of 100 mL / min nitrogen and 25 mL / min hydrogen and keep the temperature constant for 60 min. After natural cooling, take out the carbon material and record it as C-1.

[0076] (2) An equal volume of chloroplatinic acid solution was impregnated on 0.3 g of C-1, stirred evenly, sealed and allowed to stand for 24 h, and then dried at room temperature for 12 h.

[0077] (3) The dried catalyst precursor was placed in a tubular furnace, and the temperature was raised from room temperature to 150°C at a heating rate of 5°C / min in a nitrogen atmosphere of 200 mL / min. The gas was switched to a mixture of nitrogen at 180 mL / min and hydrogen at 20 mL / min, and the heating was stopped after the temperature was kept constant for 120 min. The catalyst was cooled to room temperature in a nitrogen atmosphere to obtain a CAT-1 catalyst.

[0078] The C1s X-ray photoelectron high-resolution scanning spectrum of C-0 is as follows Figure 1 As shown, sp in C-0 2 Carbon / sp 3 The carbon ratio is 1.10. The O1s X-ray photoelectron high-resolution scanning spectrum of C-0 is shown in Figure 2 As shown in Figure 2, OC=O in C-0 accounts for 50% of the total surface oxygen content by weight. The XRD patterns of C-0 and C-1 are shown in Figure 2. Figure 3 The Raman images of C-0 and C-1 are shown in Figure 4 The isothermal adsorption and desorption curves of C-0 and C-1 are shown in Figure 5 As shown. Figure 3 , Figure 4 and Figure 5 It can be seen that the graphitization degree, defect degree and pore structure of C-1 and C-0 are similar, indicating that the reducing gas treatment of carbon materials has little effect on their structure.

[0079] The Pt content in the CAT-1 catalyst was determined by ICP-AES to be 0.46 wt %. Figure 6 This is the Cs-STEM image of the CAT-1 catalyst. It can be clearly seen from the figure that the active component Pt of the modified Pt / carbon catalyst has a high degree of dispersion and exists entirely in the form of single atoms and nanoclusters, without nanocrystalline particles with clear lattice fringes.

[0080] Comparative Example 1

[0081] The method of Example 1 was followed, except that the C-0 material was directly used as a catalyst carrier without being treated with a reducing gas. The prepared catalyst was denoted as CAT-1-pair.

[0082] The Pt content in the catalyst CAT-1 was determined by ICP-AES to be 0.37 wt%.

[0083] Comparative Example 2

[0084] The method of Example 1 was followed, except that the C-0 material was replaced with a carbon material C-0-pair (activated carbon), to obtain a catalyst CAT-2-pair. The Pt content in the catalyst CAT-2-pair was 0.30 wt % as measured by ICP-AES.

[0085] The C1s X-ray photoelectron high-resolution scanning spectrum of the C-0 pair is as follows Figure 1 As shown, C-0-centering sp 2 Carbon / sp 3 The carbon ratio is 3.01. The O1s X-ray photoelectron high-resolution scanning energy spectrum of the C-0- pair is as follows Figure 2 As shown, the C-0- pair contains five kinds of surface oxygen-containing groups, namely oxide (~530.0 eV), C=O (~531.2 eV), OC=O (~532.4 eV), C-OH / COC (~533.7 eV) and adsorbed water (~535.0 eV), among which OC=O group accounts for 31.01 weight % of the total surface oxygen-containing groups.

[0086] Example 2

[0087] The method of Example 1 is followed, except that in step (1), the reducing gas treatment time is 40 minutes to obtain C-2, and the remaining steps and conditions are the same as in Example 1 to obtain CAT-2 catalyst.

[0088] The Pt content in the CAT-2 catalyst was determined by ICP-AES to be 0.30 wt%.

[0089] Example 3

[0090] The method of Example 1 is followed, except that in step (1), the reducing gas treatment time is 120 min to obtain C-3, and the remaining steps and conditions are the same as those of Example 1 to obtain CAT-3 catalyst.

[0091] The Pt content in the CAT-3 catalyst was measured by ICP-AES and was 0.34 wt%.

[0092] Example 4

[0093] The CAT-4 catalyst was prepared according to the method of Example 1, except that the amount of chloroplatinic acid solution impregnated was changed to obtain a CAT-4 catalyst having a Pt content of 0.35 wt %, and the Pt content was detected by ICP-AES. The remaining steps and conditions were the same as those of Example 1.

[0094] Example 5

[0095] (1) 0.5 g of carbon material (C-01, carbon black) was placed in a tubular furnace and heated from room temperature to 520 °C at a heating rate of 5 °C / min in a nitrogen atmosphere of 200 mL / min. The gas was switched to a mixture of nitrogen at 70 mL / min and hydrogen at 30 mL / min and kept at a constant temperature for 45 min. After natural cooling, the carbon material was taken out and recorded as C-4.

[0096] The subsequent steps and conditions were the same as those in Example 1 to obtain a CAT-5 catalyst. The Pt content in the CAT-5 catalyst was 0.26 wt % as measured by ICP-AES.

[0097] Among them, C-01 sp 2 Carbon / sp 3 The carbon ratio is 0.52, and the O1s X-ray photoelectron high-resolution scanning spectrum of the C-0-pair shows that C-01 contains two types of surface oxygen-containing groups, namely OC=O and C-OH / COC, among which OC=O groups account for 46.37 wt% of the total surface oxygen-containing groups.

[0098] Example 6

[0099] The method of Example 1 is followed, except that in step (1), the reducing gas treatment time is 20 minutes to obtain a CAT-6 catalyst. The Pt content in the CAT-6 catalyst is 0.30 wt % as measured by ICP-AES.

[0100] Figure 8 This is the Cs-STEM image of the CAT-6 catalyst. As can be seen from the figure, Pt nanocrystals with lattice fringes appear in the CAT-6 catalyst, and the Pt dispersion is lower than that of CAT-1.

[0101] Example 7

[0102] The method of Example 1 is followed, except that in step (1), the reducing gas treatment time is 240 minutes to obtain a CAT-7 catalyst. The Pt content in the CAT-7 catalyst is 0.34% by weight as measured by ICP-AES.

[0103] Test Example 1

[0104] The catalysts prepared in the above examples and comparative examples were placed in fixed bed reactors for propane dehydrogenation evaluation. The catalyst loading was 200 mg, the reaction temperature was 500°C, the reaction pressure was normal pressure, the volume ratio of each component in the reaction gas was propane: hydrogen: nitrogen = 1:1:48, and the reaction gas space velocity was 4500 ml / (h·gCat). The evaluation results are shown in Table 1. Among them,

[0105] Propane conversion rate:

[0106]

[0107] Propylene selectivity:

[0108]

[0109] In the formula, F in (C3H8), F out (C3H8) and F out (C3H6) represent the inlet propane flow rate, outlet propane flow rate and outlet propylene flow rate respectively.

[0110] Catalyst stability is measured by the deactivation rate constant. The smaller the deactivation rate constant, the higher the catalyst stability. Deactivation rate constant:

[0111]

[0112] X jinal and X max represent the conversion rate at the end of the reaction and the maximum conversion rate during the reaction, respectively, and t is the reaction time (h).

[0113] Table 1

[0114] catalyst Reaction time (h) <![CDATA[Inactivation rate constant (h -1 )]]> Example 1 CAT-1 17.5 0.009 Comparative Example 1 CAT-1-Pair 17.5 0.065 Comparative Example 2 CAT-2-Pair 3 0.042 Example 2 CAT-2 17.5 0.027 Example 3 CAT-3 17.5 0.042 Example 4 CAT-4 12 0.024 Example 5 CAT-5 17.5 0.027 Example 6 CAT-6 17.5 0.080 Example 7 CAT-7 1 0.103

[0115] By comparing Example 1 with Comparative Example 1, it can be seen that the deactivation rate constant of the catalyst in Comparative Example 1 is 0.065h -1 , that is, the stability is lower than that of CAT-1, CAT-2, CAT-3 and CAT-4. Example 1 and Comparative Example 1 together illustrate that the reducing gas treatment of the carbon material described in the present invention is the key to preparing a Pt / carbon catalyst with high stability for propane dehydrogenation reaction.

[0116] The propane conversion and propylene selectivity of the catalysts in Example 1 and Example 6 are shown in Table 1. Figure 7 As shown, it can be seen that the propylene selectivity of the catalysts of Example 1 and Example 6 is similar. Although the maximum propane conversion rate of the catalyst of Example 6 is higher than that of the catalyst of Example 1 in the initial stage of the reaction, the propane conversion rate of the catalyst of Example 1 changes less and after 5.5 hours of reaction evaluation, the propane conversion rate of the catalyst of Example 1 is higher than that of the catalyst of Example 6. It is found through calculation that the deactivation rate constant of the catalyst of Example 6 is 0.080h -1 , that is, the stability is lower than CAT-1, CAT-2, and CAT-3. Similarly, the stability of the catalyst in Example 7 is lower than that of CAT-1, CAT-2, and CAT-3. Examples 1-3 and Examples 6 and 7 together illustrate that the present invention provides a Pt / carbon catalyst for propane dehydrogenation reaction with higher stability and highly dispersed active components by treating the carbon material with a reducing gas for an appropriate period of time.

[0117] By comparing Example 1 with Comparative Example 2, it can be seen that the type of the pre-modified carbon material used in the present invention is crucial to the preparation of a Pt / carbon catalyst with high stability for propane dehydrogenation reaction.

[0118] 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 method for preparing a platinum-carbon catalyst, characterized in that: The method comprises the following steps: (1) modifying the carbon material in the presence of a hydrogen-containing atmosphere to obtain a modified carbon support; (2) introducing a platinum precursor onto the modified carbon support and then performing gas phase reduction; Wherein, the surface sp of the carbon material 2 Carbon and sp 3 The ratio of carbon is 0.2-1.5; The surface of the carbon material contains only two oxygen-containing groups, namely C-OH / COC and OC=O.

2. The method according to claim 1, wherein: The carbon material surface sp 2 Carbon and sp 3 The ratio of carbon is 0.5-1.2; And / or, the oxygen-containing groups OC=O on the surface of the carbon material account for 40-60 wt % of the total surface oxygen content.

3. The method according to claim 1 or 2, wherein: The hydrogen-containing atmosphere is provided by a hydrogen-containing gas, wherein the hydrogen-containing gas comprises hydrogen and an optional inert gas; Preferably, the hydrogen content in the hydrogen-containing gas is 5-100% by volume, more preferably 10-30% by volume.

4. The method according to any one of claims 1 to 3, wherein: The modification treatment conditions include: temperature of 450-600° C., preferably 480-520° C., and time of 30-130 min, preferably 40-90 min.

5. The method according to any one of claims 1 to 4, wherein: The carbon carrier and the platinum precursor are used in an amount such that the platinum metal loading in the prepared platinum-carbon catalyst is 0.2-0.55 wt %, preferably 0.25-0.48 wt %, based on the total amount of the platinum-carbon catalyst; Preferably, the platinum precursor is selected from at least one of chloroplatinic acid, platinum nitrate, tetraamineplatinum chloride, tetraamineplatinum nitrate and tetraamineplatinum acetate; Preferably, the carbon material is carbon black.

6. The method according to any one of claims 1 to 5, wherein: In step (2), the method of introducing the platinum precursor into the modified carbon support includes: impregnating the modified carbon support with a solution of the platinum precursor; Preferably, the method further comprises closed standing and / or drying after the impregnation; Preferably, the standing time is 8-72h, preferably 12-24h; Preferably, the drying conditions include: a drying temperature of 5-40° C., preferably 15-30° C.; and a drying time of 8-72 h, preferably 8-15 h.

7. The method according to any one of claims 1 to 6, wherein: In step (2), the gas phase reduction conditions include: in the presence of a reducing gas, the reduction temperature is 140-200° C., preferably 140-160° C.; the reduction time is 1-3 h, preferably 1.5-2.5 h; Preferably, the reducing gas comprises hydrogen and an inert gas. Further preferably, the content of hydrogen in the reducing gas is 5-20% by volume, preferably 5-10% by volume.

8. A platinum-carbon catalyst prepared by the method described in any one of claims 1 to 7.

9. The catalyst according to claim 8, wherein According to the analysis of scanning transmission electron microscope, there are no nanocrystals larger than 2 nm in the platinum-carbon catalyst.

10. Use of the platinum-carbon catalyst according to claim 8 or 9 in propane dehydrogenation reaction.

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