Highly active and coking prone pt-based catalyst for dehydrogenation of lower alkane to olefin and method of making same

Abstract

The application discloses a high-activity easy-coking Pt-based catalyst for dehydrogenation of low-carbon alkanes to olefins and a preparation method thereof. The catalyst carrier is gamma-alumina, and the active components include Pt 0.1-1.0 wt%, Sn 0.05-2.0 wt%, La or Eu 0.05-2.0 wt%, Cl 0.5-2.0 wt%, alkali metal and / or alkaline earth metal 0.3-3.0 wt%. The Pt is dispersed in the carrier by being close to the outer surface of the carrier, a Pt-containing shell layer is formed in the carrier, and the volume of the Pt-containing shell layer is 10-90% of the volume of the carrier. The catalyst is suitable for the dehydrogenation of low-carbon alkanes to olefins, and has excellent high conversion rate of alkanes, high selectivity of olefins and high yield.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to a high-activity easy-coking Pt-based catalyst for dehydrogenation of low-carbon alkanes to olefins and a preparation method thereof. BACKGROUND

[0002] At present, the demand for propylene and its derivatives is growing globally, and in order to meet the growing demand for propylene, the propane dehydrogenation to propylene technology is increasingly valued. The propane dehydrogenation technologies that have been industrialized include the Oleflex process of UOP Company and the Catofin process of Rumms Company.

[0003] Propane catalytic dehydrogenation catalysts are divided into platinum-based catalysts and chromium-based catalysts. The Oleflex process adopts platinum-based catalysts, and the Catofin process adopts chromium-based catalysts. Since the catalysts of each process involve confidential information, the information about the catalysts found is not comprehensive, but the service life of the catalysts of each process is about two years, only the operation cycle is different. Platinum-based catalysts have the remarkable characteristics of high activity, high selectivity and low attrition rate, but are expensive, and the preparation method of traditional supported catalysts is difficult to make the performance stable. Chromium-based catalysts have good activity for dehydrogenation of low-carbon alkanes and relatively low requirements for impurities in the raw materials, have strong resistance to poisoning, resistance to olefins and resistance to oxygen-containing compounds, are inexpensive, and have no catalyst loss. However, such catalysts are easy to coke and deactivate, have poor stability, and are limited due to the toxicity and harm of heavy metal Cr.

[0004] The existing disclosed Pt-based catalysts for propane dehydrogenation have Pt atoms dispersed on the catalyst from the inside to the outside and from the core to the surface. When the catalyst is coked, the coke is also dispersed on the catalyst from the inside to the outside and from the core to the surface. When the coked catalyst is regenerated, the coke on the central part or core of the catalyst is not easy to be completely burned off, the catalyst is damaged, and dust is serious, which leads to problems such as reduced strength of the regenerated catalyst, blocked screen, increased pressure drop, decreased reaction performance, shortened operation cycle, and the like, affecting production efficiency and safe operation. At the same time, since the core Pt also has high reactivity, the core part is not conducive to the internal diffusion of the reaction products, which will cause hydrogenolysis, cracking and other side reactions to cause the selectivity of propylene to decrease.

[0005] Patent CN202010348244.4 discloses a yolk-eggshell type SiO2-Al2O3 noble metal propane dehydrogenation catalyst and its preparation method. The catalyst takes solid SiO2-Al2O3 microspheres as the yolk and porous SiO2-Al2O3 hollow spheres as the eggshell. The yolk and the eggshell layer respectively load effective catalytically active components with different functions. The yolk is Cr, Ni, Zn, Fe, Pt, Sn, Ca, Cu, Al hydrogenation active component, and the eggshell is Fe, Co, Ni, Ru, Rh, Pd, Os, Ir dehydrogenation active component.

[0006] Patent CN201710606979.0 discloses a catalyst for catalyzing propane dehydrogenation reaction. The carrier is obtained by crystallization of a template agent, trimethylpentane and tetramethoxysilane. The prepared carrier is composed of countless micron-sized shell-shaped hollow small crystal grains under a microscope. Then the active metal is mixed with the carrier and silica gel and calcined to obtain the final catalyst. The propane dehydrogenation reaction performance of the catalyst is improved compared with that of pure silica gel carrier.

[0007] Patent CN200710047872.3 discloses a catalyst for selective oxidation of hydrogen, which comprises a layered composite carrier composed of an inert carrier core and a porous coating material outer layer combined on the core. The thickness of the porous coating is a micron-scale thin layer. The catalyst is suitable for the selective oxidation of hydrogen (hydrocarbons do not undergo selective oxidation) to remove hydrogen.

[0008] Patent CN201210150480.0 discloses a thin-shell type catalyst for preparing low-carbon olefins by dehydrogenation of low-carbon alkanes. A slurry of coating porous material is coated on the core of an inert carrier, dried, and then calcined at 700-1000°C for 1-9 hours to obtain a layered composite carrier. The porous material coated on the outside is macroscopically shell-shaped. The catalyst composition includes noble metals, group II B elements, rare earth elements, and alkali / alkaline earth metals. The thin shell of the catalyst is defined as another carrier coated on the outside different from the core carrier. The catalyst is Sn-free and Cl-free, and the noble metals on the catalyst do not form a shell. The propane dehydrogenation conversion rate of the catalyst is 33-38%.

[0009] Patent CN202010427158.2 discloses a core-shell structure alumina carrier. The carrier takes alumina or silica as the core material seed, and first grows an alumina precursor on the surface of the core material seed, and then obtains active alumina as the shell after calcination.

[0010] The above technical solutions disclose shell-shaped catalysts, which are all improved carriers that become multi-layer composite materials or micro-particle shell-shaped hollow small crystal grains. The catalyst preparation process is complicated and costly, and Pt shell distribution is not considered in the catalyst preparation process.

[0011] Patent CN202010621436.8 discloses a supported core-shell structure ZnO catalyst, which takes Al2O3 as the carrier and loads NiZn@ZnO core-shell active components, wherein the NiZn alloy is the inner core and ZnO is the outer shell.

[0012] Patent CN201810400639.7 discloses a supported nano Pt catalyst, which takes metal Pt as the active component, and the metal Pt exists in the form of Pt@CeO2 core-shell structure wrapped with CeO2. The active site Pt is the shell structure and CeO2 is the inner core. The catalyst needs to prepare Pt sol first, then prepare core-shell sol, and then impregnate on the carrier. The process is long, and the catalyst only contains Pt and does not contain Sn and other auxiliary metals, resulting in insufficient comprehensive performance of the catalyst.

[0013] Patent CN202110420296.2 discloses a platinum-based catalyst with a core-shell structure as the carrier. First, the metal is coated in SiO2 by stober method, then it is coated again by glucose hydrothermal method, and then it is calcined at high temperature under inert gas to solidify carbon material. The SiO2 is etched by strong alkali to form a core-shell structure carrier with inner metal and outer carbon layer, and then a platinum-containing precursor solution is used for platinum loading. The core-shell structure of this patent refers to that the inner core is metal and the outer shell is carbon under microscope. The preparation process of this method is complicated.

[0014] Patent US201816604559 discloses a core-shell structure propane dehydrogenation catalyst with SBA-15 as the carrier, which contains two element components, one of which is Pt and the other is Fe, Co or Ni as active additive. Under the microscale, Pt and Fe, Co, Ni form an alloy in the form of core-shell structure. The catalyst has a propylene selectivity of 85%, which is relatively low.

[0015] Patent US4608360 discloses a dehydrogenation catalyst, which contains a Group VIII noble metal component supported on an alumina carrier, a co-formed Group IVA metal component and an alkali metal or alkaline earth metal. The noble metal is uniformly distributed inside and outside the carrier. The raw material in this patent is a large molecular weight liquid normal alkane with C9 and above.

[0016] Patent CN201910784608.0 discloses a core-shell type propane dehydrogenation catalyst for preparing propylene. The shell layer of the catalyst is Fe component, and other components are buried in the core layer of the catalyst, which can block the contact opportunity of the inner layer catalyst active component with the reactor wall. This patent does not show the advantage of catalyst coking.

[0017] Patent CN201210150480.0 discloses a kind of for low carbon alkane dehydrogenation preparation low carbon olefin thin shell type catalyst, slurry of coating porous material is coated on the inner core of inert carrier, after drying, it is calcined at 700-1000 DEG C for 1~9 hours to obtain layered composite carrier, coating is macroscopically shell-shaped in porous material outside;The catalyst composition prepared includes noble metal, group II B element, rare earth element, alkali metal / alkaline earth metal.

[0018] Patent CN200910209534.4 discloses a kind of propane dehydrogenation preparation propylene catalyst, including alumina carrier and active component with carrier as the basis of content as follows: platinum group metal 0.1~2.0 mass%, IVA group metal 0.1~2.0 mass%, potassium 0.5~5.0 mass%, cerium or samarium 0.2~5.0 mass%, halogen 0.3~10 mass%, the catalyst is used for propane dehydrogenation preparation propylene reaction, propane conversion rate is about 30%.

[0019] Document "the influence of solvent and competitive adsorbent on PtSnK / γ-Al2O3 isobutane dehydrogenation catalyst performance", industrial catalysis, 2014 February, PtSnK / γ-Al2O3 isobutane dehydrogenation catalyst is prepared by equal volume co-impregnation method, and it is considered that the catalyst prepared by using ethanol as solvent of active component impregnation solution and oxalic acid as competitive adsorbent has better performance.

[0020] Document "preparation and TPT characterization of Pt-Sn / Al2O3 catalysts with different Pt distribution", Qilu petrochemical, 2010 No.1, for the catalytic reforming reaction of which the raw material is liquid naphtha and the product is aromatic hydrocarbon, Pt-Sn / Al2O3 catalysts with different morphologies are prepared, and it is considered in conclusion 3 that the Pt dispersion value of eggshell type catalyst is lower than that of uniform distribution type catalyst. SUMMARY

[0021] The purpose of the present application is to provide a kind of for low carbon alkane dehydrogenation preparation olefin high activity easy burn Pt-based catalyst and its preparation method, to solve the defects of existing catalyst, such as low olefin selectivity, more catalyst components, complex preparation process and carbon deposition on the inner core not easy to completely burn when catalyst is regenerated.

[0022] To achieve the above purpose, the present application provides a kind of for low carbon alkane dehydrogenation preparation olefin high activity easy burn Pt-based catalyst, carrier is γ-alumina, active component includes Pt 0.1~1.0wt%, Sn 0.05~2.0wt%, La or Eu 0.05~2.0wt%, Cl 0.5~2.0wt%, alkali metal and / or alkaline earth metal 0.3~3.0wt%;The Pt is all dispersed in the carrier near the outer surface of the carrier, and forms a Pt-containing shell layer in the carrier, and the volume of the Pt-containing shell layer is 10~90% of the volume of the carrier.

[0023] The high-activity easy-coking Pt-based catalyst for preparing olefins by dehydrogenation of low-carbon alkanes has a Pt dispersion greater than or equal to 85%, preferably greater than or equal to 95%.

[0024] The high-activity easy-coking Pt-based catalyst for preparing olefins by dehydrogenation of low-carbon alkanes has a Pt content of 0.2-0.6 wt%, a Sn content of 0.2-0.6 wt%, a La or Eu content of 0.2-0.6 wt%, a Cl content of 1-1.2 wt%, and an alkali metal and / or alkaline earth metal content of 1.2-1.5 wt%.

[0025] The high-activity easy-coking Pt-based catalyst for preparing olefins by dehydrogenation of low-carbon alkanes has a Pt shell layer volume of 30-70% of the volume of the carrier.

[0026] The high-activity easy-coking Pt-based catalyst for preparing olefins by dehydrogenation of low-carbon alkanes has a carrier of γ-spherical alumina.

[0027] The high-activity easy-coking Pt-based catalyst for preparing olefins by dehydrogenation of low-carbon alkanes has Pt atoms or atom clusters in the catalyst, and the diameter of the Pt atoms or atom clusters is less than 2 nm.

[0028] The nanoscale highly-dispersed atoms are beneficial to exposing each atom to the outer surface of the cluster and exerting catalytic activity, thereby producing higher reaction efficiency.

[0029] The high-activity easy-coking Pt-based catalyst for preparing olefins by dehydrogenation of low-carbon alkanes has a low-carbon alkane of C3-C5 alkanes.

[0030] To achieve the above-mentioned purpose, the application further provides a preparation method of the high-activity easy-coking Pt-based catalyst for preparing olefins by dehydrogenation of low-carbon alkanes, which comprises the following steps:

[0031] The Pt-containing impregnation solution is prepared, the pH of the impregnation solution is adjusted to 1-2, the carrier is immersed in the impregnation solution for 0.2-0.8 h, and then the catalyst is obtained by drying and calcining, and Sn, Cl, La or Eu, alkali metal and / or alkaline earth metal are added during the preparation of the carrier or by impregnation.

[0032] The preparation method of the high-activity easy-coking Pt-based catalyst for preparing olefins by dehydrogenation of low-carbon alkanes uses a platinum-containing reagent to impregnate Pt elements, and the platinum-containing reagent is one or more of chloroplatinic acid, chloroplatinic acid salt and tetraammine platinum nitrate.

[0033] The preparation method of the high-activity easy-coking Pt-based catalyst for dehydrogenation of low-carbon alkanes to olefins in the application has a Pt impregnation temperature of 20-95 DEG C, and the catalyst calcination conditions are as follows: calcination at 500-600 DEG C for 2-5 h.

[0034] In the preparation of the catalyst, the Pt content cannot be too high, and too high Pt content is prone to form large clusters and is not easy to be highly dispersed; and the pH value and time during impregnation need to be controlled, which is the key to ensuring high dispersion and shell distribution of Pt. If the pH value is too small or the impregnation time is too long, Pt is prone to be generated in the center of the core and cannot form a shell morphology; if the pH value is too large or the impregnation time is too small, the shell thickness becomes very small and the dispersion degree is low. During preparation, increasing the temperature can shorten the formation time of the target effect.

[0035] The application has the following beneficial effects:

[0036] The catalyst is suitable for the dehydrogenation of low-carbon alkanes to olefins, has excellent high conversion rate of alkanes, high selectivity and high yield of olefins. The catalyst carrier is simple, the active component is less, the cost is low, and the catalyst is easy to prepare. Since Pt is enriched on the outer layer of the carrier, the catalyst is easy to coke and regenerate, has the advantages of low coking regeneration temperature and low catalyst breakage rate, and can alleviate the phenomena of reduced strength of the regenerated catalyst, clogging of the screen, increased pressure drop, and decreased reaction performance, thereby enhancing safe operation, prolonging the operation cycle, and increasing production efficiency.

[0037] For a hydrocarbon hydrogenation and dehydrogenation reaction system, the catalytic activation efficiency of active metal Pt is the highest. The catalyst has a shell structure, Pt elements are dispersed in the shell and are in a highly dispersed state, can fully exert the effect of Pt atoms, and can achieve high catalyst effect with fewer components. In the catalyst, the additive Sn can ensure the high-temperature stability of the catalyst, the Pt grains highly dispersed at high temperature are not prone to agglomeration, and the decrease in dispersion degree caused by agglomeration is avoided, thereby avoiding the decrease in catalytic performance. The additive alkali metal or alkaline earth metal can inhibit the generation of by-products such as methane and ethane, thereby increasing the selectivity of olefins. The acidity of Cl element can increase the conversion rate, and can also promote the high dispersion of Pt during preparation or regeneration. The addition of La or Eu makes the catalyst have better selectivity for the generation of olefins, especially in the process of dehydrogenation of propane to propylene, which is beneficial to the selectivity of propylene generation. The above several elements and the appropriate acidity of γ-alumina jointly act to achieve excellent reaction activity.

[0038] Meanwhile, the shell distribution of active element Pt ensures the easy-coking regeneration characteristics of the catalyst, and a lower coking temperature can reduce the catalyst breakage rate. The shell distribution of Pt also reduces the intensification of side reactions caused by internal diffusion factors. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1STEM electron micrograph of the catalyst prepared in Example 1. DETAILED DESCRIPTION

[0040] The application will be described in detail below by way of examples. It is necessary to point out here that the following examples are only used to further illustrate the application and cannot be understood as limiting the scope of protection of the application, and those skilled in the art can make some non-essential improvements and adjustments to the application according to the above content of the application.

[0041] Example 1

[0042] A commercially available pseudoboehmite sol was drop-sphere formed, and after dehydration and calcination at 650°C for 2h, a spherical carrier with a crystal phase of γ-alumina and a radius of 0.5mm was finally prepared. Pt was uniformly loaded on the outer layer of the catalyst, and the process control was as follows: the solvent was deionized water, and the solute was tetraammine platinum nitrate (0.1wt% of Pt content of the carrier), lanthanum chloride (0.05wt% of La content of the carrier), stannous chloride (0.05wt% of Sn content of the carrier), and sodium chloride (0.3wt% of Na content of the carrier). Nitric acid was added to adjust the pH value of the solution to 2, the above-mentioned spherical carrier was added, and the impregnation was carried out at 20°C for 0.2h under stirring conditions, followed by drying at 80°C and calcination at 500°C for 5h. It was determined that the Pt content of the catalyst was 0.1%, the La content was 0.05%, the Sn content was 0.05%, the Cl content was 0.5%, and the Na content was 0.3%. At this time, the Pt of the catalyst was in the oxidation state, and if necessary, it can be further reduced to the reduced state by reduction in hydrogen at 500°C for 2h. The Pt dispersion value was determined by the hydrogen-oxygen titration method to be 90%. After the catalyst was cut from the center, it was found that the core was white or light-colored (no Pt distribution at the center), and the Pt-loaded outer layer was gray or dark. The thickness of the gray or dark Pt shell layer accounted for 10% of the radius. The catalyst was characterized by STEM electron microscopy, as shown in FIG. 1, the white bright spots were Pt atoms, and it can be seen that the micro-morphology of Pt presented single atoms, double atoms or atomic clusters, and was in a highly dispersed state of nanoscale. Figure 1

[0043] Example 2

[0044] ​Commercially available γ-alumina spherical support with 0.2% Sn and 0.8 mm radius. Pt is uniformly loaded on the outer layer of the catalyst by the following procedure: deionized water as solvent, chloroplatinic acid ammonia (0.2% Pt loading on the support) as solute, lanthanum chloride (0.2% La loading on the support), lithium chloride (1.2% Li loading on the support), adjust the pH of the solution to 1.5 by adding hydrochloric acid, add the above-mentioned spherical support, impregnate at 50°C for 0.4 h under stirring, then dry at 100°C and calcine at 550°C for 3 h. The Pt loading on the catalyst is 0.2%, La loading is 0.2%, Sn loading is 0.2%, Cl loading is 1.0%, and Li loading is 1.2%. At this time, the Pt is in the oxidized state, and if necessary, it can be further reduced to the reduced state by reduction in hydrogen at 500°C for 2 h. The Pt dispersion is 98% as determined by the hydrogen-oxygen titration method. After cutting the catalyst from the center, the core is found to be white or light-colored (no Pt distribution at the center), and the Pt-loaded outer layer is gray or dark, with the gray or dark Pt shell layer accounting for 45% of the radius.

[0045] Example 3

[0046] An aluminum solution containing 0.6% Sn is prepared and drop-sphere formed by the sol-gel method. After calcination at 550°C for 5 h, a spherical support with a radius of 1.0 mm and a final crystal phase of γ-alumina is obtained. Pt is uniformly loaded on the outer layer of the catalyst by the following procedure: deionized water as solvent, chloroplatinic acid (0.6% Pt loading on the support) as solute, europium chloride (0.6% Eu loading on the support), calcium chloride (1.5% Ca loading on the support), adjust the pH of the solution to 1.2 by adding hydrochloric acid, add the above-mentioned spherical support, impregnate at 20°C for 0.6 h under stirring, then dry at 90°C and calcine at 600°C for 2 h. The Pt loading on the catalyst is 0.6%, Eu loading is 0.6%, Sn loading is 0.6%, Cl loading is 1.2%, and Ca loading is 1.2%. At this time, the Pt is in the oxidized state, and if necessary, it can be further reduced to the reduced state by reduction in hydrogen at 500°C for 2 h. The Pt dispersion is 92% as determined by the hydrogen-oxygen titration method. After cutting the catalyst from the center, the core is found to be white or light-colored (no Pt distribution at the center), and the Pt-loaded outer layer is gray or dark, with the gray or dark Pt shell layer accounting for 65% of the radius.

[0047] Example 4

[0048] Commercially available γ-alumina spherical support with 2.0% Sn and 1.2 mm radius. Pt was loaded on the outer layer of the catalyst by impregnation with deionized water as solvent and chloroplatinic acid (1.0 wt% Pt on support), lanthanum chloride (1.0 wt% La on support), europium chloride (1.0 wt% Eu on support), potassium chloride (2.0 wt% K on support), magnesium chloride (1.0 wt% Mg on support) as solutes. The pH of the solution was adjusted to 1.0 by adding hydrochloric acid, and the above-mentioned spherical support was added. The impregnation was carried out at 5°C for 0.8 h under stirring, followed by drying at 80°C and calcination at 500°C for 4 h. The Pt content on the catalyst was determined to be 1.0%, the La content 1.0%, the Eu content 1.0%, the Sn content 2.0%, the Cl content 2.0%, the K content 2.0%, and the Mg content 1.0%. At this time, the Pt on the catalyst was in the oxidized state, and if necessary, it can be further reduced to the reduced state by reduction in hydrogen at 500°C for 2 h. The Pt dispersion was determined by the hydrogen-oxygen titration method to be 92%. After the catalyst was cut from the center, it was found that the core was white or light-colored (no Pt distribution at the center), and the Pt-loaded outer layer was gray or dark-colored. The thickness of the gray or dark-colored Pt shell layer accounted for 90% of the radius.

[0049] Comparative Example 1

[0050] The catalyst was prepared according to the method of Example 1 in patent CN200910209534.4.

[0051] First, γ-Al2O3spheres containing 0.3 wt% Sn were prepared by oil-ammonia column drop ball forming. Cerium nitrate solution was used as the impregnating solution, which contained 0.5 wt% cerium, and the liquid / solid ratio was 0.8 ml / g. The γ-Al2O3spheres were impregnated at 25°C for 4 hours, dried at 120°C for 12 hours, and calcined at 500°C for 4 hours. The calcined solid was then impregnated with an impregnating solution containing chloroplatinic acid and hydrochloric acid at 25°C for 4 hours, which contained 0.29 wt% platinum and 2.5 wt% chlorine. The liquid / solid ratio was 1.8 ml / g. After impregnation, the solid was dried at 120°C for 12 hours and calcined at 500°C for 4 hours. The calcined solid was then impregnated with potassium nitrate solution at 25°C for 4 hours, which contained 2.0 wt% potassium, and the liquid / solid ratio was 0.8 ml / g. After impregnation, the solid was dried at 120°C for 4 hours and calcined at 500°C for 4 hours. The calcined catalyst was reduced with hydrogen at 600°C for 2 hours to obtain a catalyst with uniform Pt distribution inside and outside, and no Pt shell layer was formed. The platinum content of the catalyst was 0.29%, the tin content was 0.3%, the cerium content was 0.5%, the potassium content was 2.0%, and the chlorine content was 1.2%.

[0052] Comparative Example 2

[0053] The preparation method was the same as Example 2, except that no La element was added.

[0054] Comparative Example 3

[0055] The preparation method is the same as that of Example 2, except that hydrochloric acid is added during the preparation to adjust the pH value of the solution to 0.5, and the impregnation time is 2 h. The catalyst with uniform Pt distribution inside and outside is prepared, and Pt shell layer is not formed.

[0056] Comparative Example 4

[0057] The preparation method is the same as that of Example 2, except that no hydrochloric acid is added during the preparation, the pH value of the impregnation solution is 6, and the impregnation time is 0.1 h. The catalyst with very thin Pt shell layer is prepared.

[0058] The Pt dispersion and shell thickness of the catalysts prepared in the test examples and comparative examples are detected, and the detection method is as follows:

[0059] The specific determination principle and method of Pt dispersion are as follows: the metal active site of the propane dehydrogenation catalyst is provided by noble metal Pt. The platinum dispersion refers to the ratio of the number of platinum atoms exposed on the surface of platinum grains to the total number of platinum atoms in the catalyst. The higher the platinum dispersion, the higher the catalyst activity. The value of 1.00 or 100% indicates that all platinum atoms in the catalyst can effectively act on the reaction. If the adsorbate is chemisorbed in the form of a monolayer, there is a simple relationship between the number of saturated adsorbed gas molecules and the number of metal atoms on the surface of the catalyst, so that the number of surface atoms can be directly calculated from the amount of chemisorbed adsorbate molecules, and then the dispersion of the surface metal is obtained. The determination method is hydrogen-oxygen titration method. Hydrogen-oxygen titration method is adopted because on the one hand it can reduce hydrogen overflow, and on the other hand the correlation coefficient of platinum oxide and hydrogen reaction is 3 / 2, which can improve the sensitivity of the equipment. Pulse mode is adopted to obtain more accurate hydrogen consumption.

[0060] The thickness measurement method of the Pt shell layer of the catalyst is as follows: the catalyst is fully reduced in flowing hydrogen at 500℃ for 2 h, the catalyst is cut in half from the center, and the cross section is observed by visual observation or magnifying glass. The core is white or light color, indicating that there is no Pt distribution in the center, and the shell layer is gray or dark color, indicating the position of Pt distribution. The thickness of the gray or dark color is measured as the thickness of the Pt shell layer.

[0061] The results are shown in Table 1.

[0062] Table 1

[0063]

[0064]

[0065] The reaction performance evaluation of propane dehydrogenation to propylene of each catalyst is carried out. The raw material is pure propane, the reaction evaluation device is a 20 mL fixed bed evaluation device, the average reaction temperature is 580℃, the pressure is atmospheric pressure, and the space velocity is 3 h-1 The results of the reaction of each catalyst after 4 hours are shown in Table 2 below.

[0066] Table 2

[0067]

[0068] The regeneration performance of each catalyst was evaluated. The atmosphere was normal pressure, nitrogen gas with 1 mol% oxygen content, and the temperature was 500°C, with ablation for 0.5 hours. The coking performance of each catalyst was investigated, and the state after coking is shown in Table 3.

[0069] Table 3

[0070]

[0071]

[0072] Of course, the present application can have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims of the present application.

Claims

1. A highly active and coking prone Pt-based catalyst for the dehydrogenation of lower alkanes to olefins, characterized in that, The carrier is γ-alumina, the active components include Pt 0.1-1.0 wt%, Sn 0.05-2.0 wt%, La or Eu 0.05-2.0 wt%, Cl 0.5-2.0 wt%, alkali metal and / or alkaline earth metal 0.3-3.0 wt%; the Pt is dispersed in the carrier close to the outer surface of the carrier, forming a Pt-containing shell layer in the carrier, the volume of the Pt-containing shell layer is 10-90% of the volume of the carrier; the Pt in the catalyst is nano-sized Pt atom or atom cluster, the diameter of the Pt atom or atom cluster is less than 2 nm; The preparation method of the catalyst comprises the following steps: Preparation of Pt-containing impregnation solution, and adjusting the pH of the impregnation solution to 1-2, impregnating the carrier in the impregnation solution for 0.2-0.8 h, and then drying and calcining to obtain the catalyst, Sn, Cl, La or Eu, alkali metal and / or alkaline earth metal are added during the preparation of the carrier or by impregnation method.

2. The high activity and easy to coke Pt-based catalyst for dehydrogenation of lower alkane to olefin according to claim 1, characterized in that, The dispersion degree of Pt in the catalyst is greater than or equal to 85%.

3. The high activity and easy to coke Pt-based catalyst for dehydrogenation of lower alkane to olefin according to claim 1, characterized in that, The dispersion degree of Pt in the catalyst is greater than or equal to 95%.

4. The high activity and easy to coke Pt-based catalyst for dehydrogenation of lower alkane to olefin according to claim 1, characterized in that, The content of Pt is 0.2-0.6 wt%, the content of Sn is 0.2-0.6 wt%, the content of La or Eu is 0.2-0.6%, the content of Cl is 1-1.2 wt%, and the content of alkali metal and / or alkaline earth metal is 1.2-1.5 wt%.

5. The high activity and easy to coke Pt-based catalyst for dehydrogenation of lower alkane to olefin according to claim 1, characterized in that, The volume of the Pt-containing shell layer is 30-70% of the volume of the carrier.

6. The high activity and easy to coke Pt-based catalyst for dehydrogenation of lower alkane to olefin according to claim 1, characterized in that, The carrier is spherical γ-alumina.

7. The high activity and easy to coke Pt-based catalyst for dehydrogenation of lower alkane to olefin according to claim 1, characterized in that, Pt element is impregnated by using a platinum-containing reagent, the platinum-containing reagent is one or more of chloroplatinic acid, chloroplatinic acid salt and tetraammine platinum nitrate.

8. The high activity and easy to coke Pt-based catalyst for dehydrogenation of lower alkane to olefin according to claim 1, characterized in that, The impregnation temperature of Pt is 20-95℃, and the calcination conditions of the catalyst are: calcination at 500-600℃ for 2-5 h.

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