阅读说明：本技术 一种负载型PtZn金属间合金催化剂及其制备方法和应用 (Supported PtZn intermetallic alloy catalyst and preparation method and application thereof ) 是由 巩金龙 陈赛 曾亮 于 2019-01-08 设计创作，主要内容包括：本发明公开了一种负载型PtZn金属间合金催化剂及其制备方法和应用,该催化剂以SiO<Sub>2</Sub>为载体,以Zn为助剂,负载少量活性组分Pt；其中Pt的质量百分含量为0.025％-1％,Zn的质量百分含量为0.025％-1.7％；制备时采用共浸渍方法,将SiO<Sub>2</Sub>载体浸渍于氯铂酸和硝酸锌的水溶液中,经过干燥、高温还原后得到PtZn/SiO<Sub>2</Sub>催化剂,该催化剂具有高活性和高稳定性,且价格低廉,毒性小。本发明的催化剂适用于低链烷烃脱氢制烯烃反应,特别是临氢气氛下的丙烷脱氢制丙烯,在高温条件下脱氢活性很高,丙烯选择性可达到90％以上,稳定性良好,并且Pt用量少,利用率高,相比工业Pt系催化剂更为廉价。(The invention discloses a supported PtZn intermetallic alloy catalyst and a preparation method and application thereof, wherein the catalyst is SiO 2 As a carrier, Zn is used as an auxiliary agent, and a small amount of active component Pt is loaded; wherein the mass percent of Pt is 0.025-1%, and the mass percent of Zn is 0.025-1.7%; the preparation method adopts a co-impregnation method to prepare SiO 2 The carrier is dipped in the water solution of chloroplatinic acid and zinc nitrate, and the PtZn/SiO is obtained after drying and high-temperature reduction 2 The catalyst has high activity and stability, low cost and low toxicity. The catalyst of the invention is suitable for the reaction of preparing olefin by low paraffin hydrocarbon dehydrogenation, especially for preparing propylene by propane dehydrogenation in the hydrogen atmosphere, has high dehydrogenation activity under the high temperature condition, propylene selectivity of more than 90 percent, good stability andand the Pt consumption is less, the utilization rate is high, and the catalyst is cheaper than industrial Pt catalysts.)

1. A supported PtZn intermetallic alloy catalyst is characterized in that Pt is used as an active component, Zn is used as an auxiliary agent and is loaded on a carrier, Pt and Zn form an atomic ordered intermetallic alloy, and the mass percentage of Pt is not more than 1% and the mass percentage of Zn is not more than 1.7% based on the mass of the carrier in the catalyst.

2. A supported PtZn intermetallic alloy catalyst according to claim 1, characterized in that the Pt content is 0.025% to 1% by mass, preferably 0.1% to 0.5% by mass.

3. A supported PtZn intermetallic alloy catalyst according to claim 1, characterized in that the mass percentage of Zn ranges from 0.025% to 1.5%, preferably from 0.17% to 0.85%.

4. A supported PtZn intermetallic alloy catalyst according to claim 1, 2 or 3, characterized in that the support is silica, molecular sieve, zeolite or alumina.

5. A preparation method of a supported PtZn intermetallic alloy catalyst is characterized by comprising the following steps:

step 1, putting a carrier into a solution containing metal platinum and metal zinc for impregnation so as to load the metal platinum and the metal zinc on the carrier;

and 2, placing the carrier loaded with the metal platinum and the metal zinc in the step 1 in a hydrogen atmosphere for reduction at the temperature of 400-700 ℃ to obtain the loaded PtZn intermetallic alloy catalyst.

6. The method for preparing a supported PtZn intermetallic alloy catalyst according to claim 5, wherein in step 1, soluble zinc salt and chloroplatinic acid are selected to provide metallic zinc and metallic platinum, respectively, and are uniformly dispersed in deionized water; the soluble zinc salt is zinc nitrate, zinc chloride or zinc sulfate; the carrier is silicon dioxide, molecular sieve, zeolite or alumina; the using amount of the carrier is 1 part by mass, the using amount of the metal platinum is 0.0025-0.01 part by mass, and the using amount of the metal zinc is 0.0025-0.017 part by mass.

7. The method according to claim 5, wherein in step 2, the reduction temperature is 500 to 600 ℃; the reduction time is from 0.5 to 3 hours, preferably from 0.5 to 1 hour.

8. The method for preparing a supported PtZn intermetallic alloy catalyst according to claim 5, wherein in step 2, the temperature is raised from room temperature 20-25 ℃ to a reduction temperature at a rate of 5-10 ℃ per minute, the temperature is maintained, the temperature is naturally cooled to room temperature 20-25 ℃, the carrier supporting the metal platinum and the metal zinc is always in a hydrogen atmosphere in the whole process, and the hydrogen is pumped away after the carrier is cooled to room temperature.

9. Use of a supported PtZn intermetallic alloy catalyst according to any one of claims 1 to 4 in the dehydrogenation of low alkanes to produce low alkenes.

10. The use according to claim 9, wherein the use of the supported PtZn intermetallic alloy catalyst for the dehydrogenation of propane to propylene is carried out according to the following steps: tabletting a supported PtZn intermetallic alloy catalyst into a granular catalyst, selecting the mesh size of 20-40 meshes, loading the obtained granular catalyst into a fixed bed reactor, introducing nitrogen, and heating to the pretreatment temperature of 500-; introducing hydrogen for pretreatment, maintaining the pretreatment temperature for 0.5h-1h, and cooling to the reaction temperature of 500-650 ℃; reaction gas is introduced for reaction, wherein the molar ratio of hydrogen to propane is (0-2):1, nitrogen is used as equilibrium gas, the total gas number is kept unchanged, and the reaction space velocity based on propane is 1-5h^-1(ii) a Preferably, the temperature for pretreatment by using hydrogen is 600-700 ℃; the reaction temperature is 600-650 ℃; the molar ratio of the hydrogen to the propane is 1:1, and the space velocity of the reaction based on the propane is 3-4h^-1。

Technical Field

The invention relates to a supported catalyst, in particular to SiO₂A supported PtZn intermetallic alloy catalyst, a preparation method thereof and application of the catalyst in olefin preparation through dehydrogenation of low-carbon alkane (taking propane dehydrogenation as an example).

Technical Field

Low olefins (such as ethylene, propylene, butylene, butadiene, etc.) are basic raw materials for chemical industry, particularly propylene, and the demand for them has been increasing in recent years. Propylene is a basic raw material of three synthetic materials and is mainly used for producing acrylonitrile, acetone, propylene oxide and other products. Currently, propylene supply is mainly from the by-products of naphtha cracking to ethylene and petroleum catalytic cracking processes. However, as shale gas technology has developed and ethane has become more and more inexpensive and readily available, ethylene production processes have also begun to shift from naphtha cracking to ethane steam cracking, and thus propylene supply has been limited and prices have increased. In addition to the high energy consumption, low selectivity and shortage of petroleum resources of the traditional process, people are prompted to find more economical and efficient production modes of low-alkene hydrocarbons such as propylene. Propane Dehydrogenation (PDH) processes have received increasing attention in recent years due to the large price difference between propane and propylene. The production of the propane dehydrogenation device with the production capacity of 60 ten thousand tons in 2013 and 10 months in Tianjin Bohai chemical year is formally pulled out in China. During the year 2014-2016, the propane dehydrogenation (mixed-alkane containing) production capacity has increased at least three units per year. By 2017, the total yield of propane dehydrogenation (containing mixed alkane) in China reaches 513.5 ten thousand tons, and the total yield accounts for 15 percent.

The reaction formula for propane dehydrogenation is:△H_298Kat present, the propane dehydrogenation mainly comprises five processes including Catofin (L ummus), Oleflex (UOP), STAR (UHDE), FBD (Snamprogetti and Yarsintez) and L index-BASF PDH, wherein the Catofin (L Umus) and Oleflex (UOP) are two sets of processes which are most widely applied, the Catofin process adopts a Cr-series catalyst, a fixed bed reactor is used, the catalyst is regenerated once in 12 minutes on average, the one-way conversion rate is 55-60%, the selectivity is 90%, the Oleflex process adopts a Pt-series catalyst, a moving bed reactor is used, and the complete continuous operation and the one-way conversion rate are completely continuousAbout 35% -40% and selectivity of 84%. The two catalysts are seriously inactivated due to carbon deposition, the catalysts need to be regenerated, cadmium is highly toxic and is unfavorable for the environment, and platinum is expensive, so that the development of a propane dehydrogenation process is seriously limited. Therefore, the method has great practical significance for finding a PDH catalyst which is low in cost and toxicity, high in activity and stability and capable of reducing the consumption of Pt.

The dehydrogenation reaction of the light alkane is a structure insensitive reaction, which means that the monoatomic Pt can catalyze the dehydrogenation reaction. While these side reactions are structure-sensitive reactions associated with dehydrogenation of lower alkanes, such as hydrogenolysis, isomerization and carbon deposition, the larger the size of the Pt particles, the more favorable these side reactions occur [ Molecular understatings on the catalysis of light hydrocarbons over catalysts 2015,6(8),4403-4425 ]. Therefore, the single-site Pt is expected to be used as the active site for dehydrogenation of the low-carbon alkane to realize high-selectivity production of the low-carbon alkene. The intermetallic alloy is a bimetallic alloy, wherein the metal with catalytic activity is separated by inert metal atoms in the form of single atoms, and is mostly applied to low-temperature electrocatalytic reaction, but the application of the intermetallic alloy in high-temperature low-carbon alkane dehydrogenation reaction is rarely reported.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, and aims to solve the technical problems of easy carbon deposition inactivation and large consumption of noble metals of the conventional Pt-based catalyst, and provides a supported PtZn intermetallic alloy catalyst, a preparation method thereof and application thereof in propane dehydrogenation.

The technical scheme of the invention is realized by the following technical scheme.

A supported PtZn intermetallic alloy catalyst takes Pt as an active component and Zn as an auxiliary agent to be supported on a carrier, wherein Pt and Zn form an intermetallic alloy with atomic order, and the mass percentage of Pt is not more than 1% (mass of metal Pt/mass of carrier × 100 wt%), and the mass percentage of Zn is not more than 1.7% (mass of metal Zn/mass of carrier × 100 wt%).

The carrier is silicon dioxide, molecular sieve, zeolite or alumina.

The mass percentage content of Pt is 0.025% -1%, preferably 0.1% -0.5%.

The mass percentage of Zn is 0.025-1.5%, preferably 0.17-0.85%.

Pt and Zn atoms are orderly arranged at intervals and form an intermetallic alloy with ordered atoms.

The preparation method of the catalyst comprises the following steps:

step 1, putting a carrier into a solution containing metal platinum and metal zinc for impregnation so as to load the metal platinum and the metal zinc on the carrier;

in the step 1, soluble zinc salt and chloroplatinic acid are selected to respectively provide metal zinc and metal platinum, and are uniformly dispersed in deionized water; the soluble zinc salt is zinc nitrate, zinc chloride or zinc sulfate.

In step 1, the support is silica, molecular sieve, zeolite or alumina.

In the step 1, the dosage of the carrier is 1 part by mass, the dosage of the metal platinum is 0.0025-0.01 part by mass, the dosage of the metal zinc is 0.0025-0.017 part by mass, each part by mass is 1g, and equal volume impregnation can be selected.

In the step 1, ultrasonic wave is selected for dispersing when dipping is carried out, the ultrasonic time is 0.5h-1h, the dipping is carried out, natural drying is carried out for 10-12 h at the room temperature of 20-25 ℃, and then the dipping is completely dried at the temperature of 80-120 DEG C

And 2, placing the carrier loaded with the metal platinum and the metal zinc in the step 1 in a hydrogen atmosphere for reduction, wherein the reduction (heat preservation) temperature is 400-700 ℃, and obtaining the supported PtZn intermetallic alloy catalyst.

In step 2, the reduction temperature is 500-600 ℃.

In step 2, the reduction time is 0.5 to 3 hours, preferably 0.5 to 1 hour.

In the step 2, the temperature is raised to the reduction temperature from the room temperature of 20-25 ℃ at the speed of 5-10 ℃ per minute for heat preservation, then the temperature is naturally cooled to the room temperature of 20-25 ℃, the carrier loaded with the metal platinum and the metal zinc is always in the hydrogen atmosphere in the whole process, and the hydrogen is pumped away after the carrier is cooled to the room temperature.

The supported PtZn intermetallic alloy catalyst is applied to the preparation of low-alkene hydrocarbon by low-alkane dehydrogenation, in particular to the preparation of propylene by propane dehydrogenation. When in use, the method comprises the following steps:

tabletting a supported PtZn intermetallic alloy catalyst into a granular catalyst, selecting the mesh size of 20-40 meshes, loading the obtained granular catalyst into a fixed bed reactor, introducing nitrogen, and heating to the pretreatment temperature of 500-; introducing hydrogen for pretreatment, maintaining the pretreatment temperature for 0.5h-1h, and cooling to the reaction temperature of 500-650 ℃; reaction gas is introduced for reaction, wherein the molar ratio of hydrogen to propane is (0-2):1, nitrogen is used as equilibrium gas, the total gas number is kept unchanged, and the reaction space velocity based on propane is 1-5h^-1。

The temperature for pretreatment by using hydrogen is 600-700 ℃; the reaction temperature is 600-650 ℃; the molar ratio of the hydrogen to the propane is 1:1, and the space velocity of the reaction based on the propane is 3-4h^-1。

The PtZn intermetallic alloy loaded on the carrier by the catalyst has high specific surface area and mesoporous pore channels, and is beneficial to uniform distribution of active components and diffusion of gas molecules; a small amount of Pt is used as an active component (0.025% -1%, and the Pt content of the industrial Pt catalyst is more than 0.5%), so that the Pt content in the catalyst is reduced, and the cost of the catalyst is reduced; pt and Zn form an intermetallic alloy with ordered atoms, and the Pt and Zn are spaced in order, so that the atom utilization rate of Pt is greatly improved; on the other hand, the desorption of the product propylene is promoted, and side reactions such as C-C bond breakage, deep dehydrogenation and the like are inhibited, so that the activity, selectivity and stability of the catalyst are well improved. The catalyst is prepared by a co-impregnation method, the raw materials are easy to obtain, the process is simple, the repeatability is high, and the catalyst has certain industrial significance. The catalyst of the invention is suitable for the hydrogen atmosphere, has good effect on the propylene preparation by propane dehydrogenation, has high dehydrogenation activity under the high temperature condition, has propylene selectivity of more than 90 percent, and has good stability.

Drawings

FIG. 1 shows SiO produced in example 1 of the present invention₂And (3) ac-HAADF-TEM image of the PtZn-loaded intermetallic alloy catalyst.

FIG. 2 shows SiO produced in example 1 of the present invention₂XRD test pattern of supported PtZn intermetallic alloy catalyst.

FIG. 3 shows the use of SiO in example 1 of the present invention₂And Al₂O₃The activity test chart of the supported PtZn intermetallic alloy catalyst shows that the curve above the chemical formula corresponds to propylene selectivity and the curve below the chemical formula corresponds to propane conversion.

FIG. 4 is a graph showing the test results of the influence of different Zn contents on the catalytic activity in the examples of the present invention, wherein the upper curve corresponds to the propylene selectivity and the lower curve corresponds to the propane conversion.

FIG. 5 is a graph showing the effect of different Pt contents on catalytic activity in examples of the present invention, wherein the upper curve corresponds to propylene selectivity and the lower curve corresponds to propane conversion.

FIG. 6 is a graph showing the effect of different pre-reduction temperatures on catalytic activity in the examples of the present invention, wherein the upper curve corresponds to propylene selectivity and the lower curve corresponds to propane conversion.

FIG. 7 is a graph showing the effect of different reaction temperatures on catalytic activity in examples of the present invention, wherein the upper curve corresponds to propylene selectivity and the lower curve corresponds to propane conversion.

FIG. 8 is a graph of a test of the effect of different propane space velocities on catalytic activity for examples of the present invention, where the upper curve corresponds to propylene selectivity and the lower curve corresponds to propane conversion.

FIG. 9 is a graph showing the test results of the effect of different propane/hydrogen ratios on the catalytic activity in the examples of the present invention, wherein the upper curve corresponds to the propylene selectivity and the lower curve corresponds to the propane conversion.

Detailed Description

The present invention is further described in detail below by way of specific examples, which will enable one skilled in the art to more fully understand the present invention, but which are not intended to limit the invention in any way.