CN112403512B - Platinum-based catalyst loaded by nano titanium-silicon molecular sieve, preparation method and application thereof - Google Patents

Abstract

The invention discloses a platinum-based catalyst loaded by a nano titanium-silicon molecular sieve, a preparation method and application thereof, and belongs to the preparation of organic chemical raw materials. The catalyst consists of two phases of a nano titanium-silicon molecular sieve and a platinum metal cluster, wherein strong interaction and tight combination occur between the two phases, and platinum is uniformly dispersed on the surface of the titanium-silicon molecular sieve in an atomic cluster form; wherein the content of platinum is 0.5-1.0wt%, and the size of platinum atom cluster is 1nm-2nm. The invention prepares the platinum-based single-metal catalyst loaded by the nano titanium-silicon molecular sieve by an ethylene glycol pre-reduction method. The catalyst prepared by the method can better disperse pt, and has more concentrated and smaller particle size.

Description

Nano-titanium-silicon molecular sieve-supported platinum-based catalyst, its preparation method and application

technical field

The invention belongs to the technical field of preparation of organic chemical raw materials, in particular to a platinum-based catalyst supported by a nano-titanium-silicon molecular sieve, a preparation method and an application thereof.

Background technique

Butane is an important part of liquefied petroleum gas, and it is cheap and widely available. The huge annual output of liquefied petroleum gas is mainly used as fuel, which is a great waste of energy. Butene is an intermediate product of important chemicals in the chemical industry. It is used to produce rubber, plastics and other polymers. It is an important chemical basic raw material next to ethylene and propylene. With the downstream market, especially the increase in synthetic rubber production, the market demand for butene is increasing year by year. Therefore, converting butane into olefins by catalytic dehydrogenation has important application value. The current process for preparing butene from butane dehydrogenation is mainly divided into direct dehydrogenation and oxidative dehydrogenation. Due to the existence of oxides in the reaction, oxidative dehydrogenation has no thermodynamic limitation, but at the same time, it also has the problem of over-oxidation, which makes the product selectivity of the final target products butene and butadiene low. Compared with oxidative dehydrogenation, the research on direct dehydrogenation is more extensive. Direct dehydrogenation is limited by thermodynamics. It is a strong endothermic reaction and needs to be carried out at a higher temperature. Butane dehydrogenation is carried out at a temperature range of 1 bar and 550-750 °C. The conversion rate of hydrogen to olefins is ≥50%, so the butane dehydrogenation temperature is generally above 500°C. However, high temperature will lead to high energy consumption, cracking and coking, which will reduce the selectivity. Therefore, it is very important to develop catalysts with high productivity and excellent carbon deposition resistance at lower temperatures.

In the catalytic reaction system of direct dehydrogenation of butane, the platinum-based catalyst prepared by the traditional impregnation method is prone to the problem of uneven distribution of active components. However, the pre-reduction method of ethylene glycol can effectively improve this problem. In the catalyst prepared by this method, the size distribution of platinum particles is more concentrated, the size is smaller, and there is a strong interaction with the carrier. This is conducive to improving the catalytic activity and stability of the catalyst, and effectively reducing the occurrence of side reactions (carbon deposition and hydrogenolysis reactions). Although carbon deposits can be removed by catalyst recycling, how to promote the stable use of catalysts has always been the focus of attention.

Contents of the invention

Purpose of the invention: to provide a platinum-based catalyst supported by a nano-titanium-silicon molecular sieve, its preparation method and application, so as to solve the problems involved in the background technology.

Technical solution: a platinum-based catalyst supported by a nano-titanium-silicon molecular sieve, its preparation method and application, including:

The catalyst is composed of two phases of nano-titanium-silicon molecular sieve and platinum metal cluster, and there is a strong interaction between the two phases, and they are tightly combined. Platinum is evenly dispersed on the surface of the titanium-silicon molecular sieve in the form of atomic clusters; wherein, the content of platinum is 0.5 -1.0wt%, the size of platinum atomic clusters is 1nm-2nm.

The present invention also provides a method for preparing a platinum-based catalyst supported by a nano-titanium-silicon molecular sieve, which is characterized in that the method first prepares a nano-titanium-silicon molecular sieve, and then loads platinum clusters on the titanium-silicon molecular sieve carrier by means of ethylene glycol pre-reduction above, the platinum-based single-metal catalyst supported by nano-titanium-silicon molecular sieves can be obtained.

In a further embodiment, the preparation method comprises the steps of:

Step 1, preparation of nano titanium silicon molecular sieve carrier

Using the hydrothermal synthesis method, tetraethyl silicate is used as the silicon source, tetraethyl titanate is used as the titanium source, and tetrapropyl ammonium hydroxide is used as the template agent, and the catalyst is prepared by hydrothermal reaction; after the hydrothermal reaction is completed, Nano titanium silicon molecular sieves are obtained after washing, drying and roasting; wherein, the ratio of silicon to titanium is adjusted by adjusting the ratio of tetraethyl silicate and tetraethyl titanate;

Step 2, ethylene glycol pre-reduction method

Mix the platinum nitrate aqueous solution with a certain amount of ethylene glycol according to the mass ratio, add a certain amount of PVP polyvinylpyrrolidone and stir to dissolve evenly, add a certain amount of nano-titanium silicon molecular sieve, heat up to a predetermined temperature in the reflux device, and heat Stir for a predetermined hour; after cooling, remove the ethylene glycol solvent and polyvinylpyrrolidone, and obtain a platinum-based single metal catalyst supported by nano-titanium-silicon molecular sieves after roasting.

In a further embodiment, in the step 1, the molar ratio of Si:Ti in the titanium silicon molecular sieve ranges from 10 to 50.

In a further embodiment, in the step 2, the mass ratio of titanium-silicon molecular sieve to ethylene glycol is 1: (20-50), and the mass of platinum in platinum nitrate is 0.1-1.0 wt of the mass of nano-titanium-silicon molecular sieve %, the mass ratio of ethylene glycol to PVP polyvinylpyrrolidone is 1: (0.1-0.15).

In a further embodiment, the predetermined temperature is 160-170° C., and the heating and stirring time is 16-18 hours.

The invention also provides the application of a platinum-based catalyst supported by nano-titanium-silicon molecular sieves in n-butane dehydrogenation.

In a further embodiment, in the reaction process of the direct dehydrogenation of n-butane, the temperature of the catalyst is 400-550°C; the reaction conditions of the catalyst are: space velocity 1500-15000ml/g·h, n-butane The molar concentration is 10-50%, and the molar ratio of n-butane to hydrogen is 1:0.5-5.

In a further embodiment, the catalyst is used for the direct dehydrogenation of n-butane to prepare butenes, wherein the butenes are 1-butene, cis-2-butene, trans-2-butene and butadiene.

Beneficial effects: the present invention relates to a platinum-based catalyst supported by nano-titanium-silicon molecular sieves, its preparation method and application. The present invention uses tetraethyl silicate as the silicon source, tetraethyl titanate as the titanium source, and tetrapropyl hydrogen Ammonium oxide is used as a template, and nano-titanium-silicon molecular sieves are prepared by hydrothermal synthesis, and then platinum-based single metal catalysts supported by nano-titanium-silicon molecular sieves are prepared by ethylene glycol pre-reduction. The catalyst prepared by this method can better disperse pt, and the particle size is more concentrated and smaller. Moreover, platinum is evenly distributed on the surface of nano-titanium-silicon molecular sieves in the form of atomic clusters, and has a strong interaction with the carrier, resulting in better stability and anti-sintering.

The catalyst of the present invention has good catalytic activity at 500°C, and the olefin product selectivity is stable above 96%, the initial conversion rate can reach 21%, and there is no obvious drop in 10 hours. Moreover, the catalyst of the present invention has good stability, has no pollution to the environment, and is environmentally friendly and highly efficient.

Implementation

The present invention will be further described below in conjunction with the embodiments, and the examples of the described embodiments are intended to explain the present invention, but should not be construed as limiting the present invention.

Embodiment 1 to Embodiment 5

The preparation process of catalyst in embodiment 1～embodiment 5 is as follows:

Step 1, preparation of nano titanium silicon molecular sieve carrier

Using a hydrothermal synthesis method, using tetraethyl silicate as a silicon source, tetraethyl titanate as a titanium source, and tetrapropylammonium hydroxide as a template agent, the catalyst is prepared through hydrothermal reaction. The ratio of silicon to titanium is adjusted by adjusting the ratio of tetraethyl silicate and tetraethyl titanate, the ratio of Ti:Si is 1:50. The hydrothermal reaction temperature was controlled at 160° C., and the temperature was maintained for 4 hours. After the hydrothermal reaction is finished, it is washed, dried, and air-baked at 550° C. for 4 hours to obtain nano-titanium-silicon molecular sieves.

Step 2, ethylene glycol pre-reduction method

Put the aqueous solution of platinum nitrate in the flask according to the proportion, add a certain amount of ethylene glycol, add a certain amount of PVP polyvinylpyrrolidone and stir to dissolve evenly, then add a certain amount of nano-titanium silicon molecular sieve, and heat up to 160°C in the reflux device , heated and stirred for 18 hours; after cooling, the ethylene glycol solvent and polyvinyl pyrrolidone were removed, and the platinum-based single metal catalyst supported by nano-titanium silicon molecular sieves was obtained after roasting treatment. Among them, the mass ratio of ethylene glycol to PVP polyvinylpyrrolidone is 1:0.05, 1:0.10, 1:0.12, 1:0.15, 1:0.5, and the molar ratio of Si:Ti in titanium silicon molecular sieve is 49:1, titanium silicon The mass ratio of molecular sieve to ethylene glycol is 1:50; the mass of platinum in platinum nitrate is 1.0 wt% of the mass of nano-titanium silicon molecular sieve.

The catalyst reaction conditions and structural properties (transmission electron microscope images) characterization parameters obtained in Examples 1 to 5 are as follows in Table 1:

Table 1

Table 1 is a statistics of the transmission electron microscope images of the catalyst, specifically by counting the abundance of Pt metal clusters at a specific position in the catalyst and the size and particle size of 200 random Pt metal clusters. It can be seen from the above table that as the mass ratio increases, the abundance of Pt metal clusters on the nano-titanium-silicon molecular sieve gradually increases. The mass ratio of ethylene glycol to PVP polyvinylpyrrolidone is 1:0.12, and the size of the Pt metal clusters The distribution presents a more excellent distribution of Pt nanoparticles. Moreover, it was found that the average size of the Pt metal clusters of each catalyst gradually increased with the increase of the mass ratio. Under the above mass ratio conditions, the Pt metal clusters are effectively reduced and supported on the carrier, but as the mass ratio increases, the Pt nanoparticles gradually become larger, and even a more obvious agglomeration phenomenon occurs.

Example

On the basis of Example 3, before the pre-reduction of ethylene glycol, adjust the pH to 10.5 by adding ammonia water, then add a certain amount of nano-titanium silicon molecular sieve, heat up to 160 ° C in the reflux device, and heat and stir for 18 hours; the rest of the process And parameter with embodiment 3.

Example

On the basis of Example 3, before the pre-reduction of ethylene glycol, adjust the pH to 10.5 by adding sodium hydroxide solution, then add a certain amount of nano-titanium silicon molecular sieve, heat up to 160°C in the reflux device, and heat and stir for 18 hours ; All the other processes and parameters are the same as in Example 3.

Example

On the basis of Example 3, before the pre-reduction of ethylene glycol, adjust the pH to 10.5 by adding an aqueous solution of ethylenediamine, and then add a certain amount of nano-titanium silicon molecular sieve, heat up to 160°C in the reflux device, and heat and stir for 18 hours ; All the other processes and parameters are the same as in Example 3.

The catalyst reaction conditions and structural properties (transmission electron microscope images) characterization parameters obtained in Examples 6-8 are as follows in Table 2:

It can be seen from the above table that by adding the aqueous solution of lye, the abundance of Pt metal clusters can be effectively increased and the average size of Pt can be reduced. However, due to the introduction of new metal impurities during the synthesis of inorganic bases, it will lead to The Pt atoms agglomerate, and the size of the Pt metal clusters becomes larger.

First of all, compared with the hydrogen calcination reduction method, the silica will not be reduced, which will affect the force between the Pt metal cluster and the nano-titanium-silicon molecular sieve to a certain extent, resulting in a decrease in the stability of the catalyst. However, the pre-reduction with ethylene glycol has less impact on the structure of the carrier, and even has a positive synergistic effect.

Specifically, the reduction of platinum nitrate to platinum in ethylene glycol solution generally includes two steps. In the first reaction, it combines with hydroxide ions in the solvent to form platinum hydroxide; in the second reaction, the Under the action of ethylene glycol, it is reduced to metallic platinum. Among them, since water is an oxidizing agent, when the reaction system contains water molecules, it will interfere with the normal reduction process of ethylene glycol. When the reaction solution reaches the predetermined temperature, it is considered that the water is completely removed, and then the condensation cycle system of the reflux device is opened to collect the refluxed polyol. The polyhydric alcohol can not only dissolve the platinum nitrate, but also act as a reducing agent for reducing the platinum nitrate in the reaction. In the initial state, since the organic base can provide more hydroxide ions in the water solvent, platinum nitrate and organic lye can produce a large amount of platinum hydroxide, and then as the water is completely evaporated, the reduction of ethylene glycol Under the action, platinum hydroxide is reduced to metal platinum, avoiding the interference of water molecules.

Application example 1

Based on the catalyst of Example 3, a fixed-bed microreactor was used to carry out the catalytic performance test of the catalyst. Quartz wool was placed in the quartz reactor, and 50 mg of catalyst was weighed and placed in the middle of the reactor, which was in a constant temperature zone in the fixed bed. Before the test, the catalyst was reduced at 500 °C in 40% hydrogen gas mixture with argon as the balance gas for 1 hour, and then cooled with argon purge. During the direct dehydrogenation reaction of n-butane, the temperature of the catalyst is 550°C; the reaction conditions of the catalyst are: the space velocity is 15000ml/g h, the molar concentration of n-butane is 5%, the molar ratio of n-butane to hydrogen 1:0.5, ventilated for 1 hour.

According to above-mentioned catalyst consumption and operating conditions and catalyst consumption, continue reaction, be 10 hours to reaction time, all the other conditions remain unchanged.

Application example 2

Based on the catalyst of Example 8, according to the catalyst consumption, operating conditions and catalyst consumption of Application Example 1, the reaction was continued until the reaction time was 1 or 10 hours, and all the other conditions remained unchanged.

comparative example

Catalyst preparation: Using the same nano-titanium silicate molecular sieve, a platinum-based single metal catalyst was prepared by a traditional impregnation method. Catalytic performance test: according to the catalyst consumption and operating conditions and catalyst consumption of embodiment 2, the reaction time is changed into 10 hours, and all the other conditions remain unchanged, conversion rate and product selectivity are as shown in the table.

During the process, gas chromatography was used to analyze the composition of the reaction product on-line, and the butenes were 1-butene, cis, trans-2-butene and butadiene. The results of conversion and product selectivity are shown in Table 3 below.

table 3:

From Table 3, it can be seen that the catalyst obtained in Example 3 and Example 8 has high activity and good stability during use, and when the reaction time reaches 10 hours, it still has excellent activity and stability .

In addition, it should be noted that the various specific technical features described in the above specific implementation manners may be combined in any suitable manner if there is no contradiction. In order to avoid unnecessary repetition, various possible combinations are not further described in the present invention.

Claims (3)

1. The application of a platinum-based catalyst based on nano titanium silicon molecular sieve loading in n-butane dehydrogenation is characterized in that the platinum-based catalyst loaded by the nano titanium silicon molecular sieve consists of two phases of nano titanium silicon molecular sieve and platinum metal clusters, strong interaction and tight combination occur between the two phases, and platinum is uniformly dispersed on the surface of the titanium silicon molecular sieve in an atomic cluster form; wherein, the content of platinum is 0.5-1.0wt%, and the size of platinum atom clusters is 1nm-2nm; the preparation method of the platinum-based catalyst loaded by the nano titanium-silicon molecular sieve comprises the following steps:

step 1, preparation of nano titanium silicon molecular sieve carrier

Using a hydrothermal synthesis method, using tetraethyl silicate as a silicon source, using tetraethyl titanate as a titanium source, using tetrapropylammonium hydroxide as a template agent, and preparing a catalyst through a hydrothermal reaction; after the hydrothermal reaction is finished, washing, drying and roasting to obtain the nano titanium-silicon molecular sieve; wherein the proportion of silicon to titanium is adjusted by adjusting the proportion of tetraethyl silicate and tetraethyl titanate; si in the nano titanium silicon molecular sieve: the molar ratio of Ti is 10-50;

step 2, glycol prereduction method

Mixing a platinum nitrate aqueous solution with a certain amount of glycol according to a mass ratio, adding a certain amount of PVP polyvinylpyrrolidone, stirring to dissolve uniformly, adding a certain amount of nano titanium silicon molecular sieve, heating to a preset temperature in a reflux device, and heating and stirring for a preset hour; after cooling, removing the glycol solvent and polyvinylpyrrolidone, and roasting to obtain the platinum-based single-metal catalyst loaded by the nano titanium silicon molecular sieve; wherein the preset temperature is 160-170 ℃, the heating and stirring time is 16-18 hours, and after the reaction solution reaches the preset temperature, a condensation circulation system of the reflux device is started; the mass ratio of the glycol to PVP polyvinylpyrrolidone is 1 (0.1-0.12).

2. The application of the platinum-based catalyst based on nano titanium silicalite molecular sieve loading in n-butane dehydrogenation according to claim 1, wherein in the step 2, the mass ratio of the nano titanium silicalite molecular sieve to the ethylene glycol is 1: (20-50), the mass of platinum in the aqueous solution of platinum nitrate is 0.1-1.0 wt% of the mass of the nano titanium silicon molecular sieve.

3. The use of a platinum-based catalyst based on nano titanium silicalite molecular sieve according to claim 1, wherein in step 2, the pH is adjusted to 10-11 by adding an aqueous solution of an organic base before the pre-reduction of ethylene glycol.