CN117443442A - Preparation method and application of a Pt-K bimetallic molecular sieve catalyst - Google Patents

Abstract

The invention discloses a method for preparing a Pt-K bimetallic molecular sieve catalyst. Specifically, at 25-30°C, tetrapropylammonium hydroxide, deionized water, and ethyl orthosilicate are mixed, and stirred to react to obtain water. gel, add platinum nitrate, potassium nitrate and ethylenediamine solutions to deionized water, mix well to prepare a Pt‑K precursor solution, and slowly drop the Pt‑K precursor solution into the hydrogel under ultrasonic conditions in an ice water bath. In the method, the mixture is subjected to a hydrothermal reaction at 150 to 180°C for 24 to 72 hours, and the reaction product is solid-liquid separated. The solid is washed alternately with ethanol and deionized water with a volume concentration of 45 to 55% until the pH of the washing liquid is <8, and then dried and roasted; The preparation process of the present invention is simple, the catalytic activity is high, and the catalytic performance is stable. Through the method of in-situ synthesis and adding a cocatalyst, the precious metal is stably applied in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction, and has good catalytic activity and stability. sex.

Description

Preparation method and application of a Pt-K bimetallic molecular sieve catalyst

Technical field

The invention belongs to the technical field of bimetallic catalysts, and particularly relates to a preparation method and application of a core-shell structure Pt-K bimetallic molecular sieve catalyst.

Background technique

Methane and carbon dioxide are the two main greenhouse gases that cause global warming. The development of various greenhouse gas utilization technologies that can effectively utilize them as chemical raw materials and reduce greenhouse gas emissions has become the focus of widespread attention. As an effective carbon capture technology, chemical chain technology uses oxygen carriers as oxygen storage media to collect and utilize greenhouse gases in a safe and efficient form. The chemical chain CH _reforming coupled _CO reduction reaction uses methane and carbon dioxide as raw materials to produce synthesis gas and carbon monoxide gas with high industrial utilization value. It is a new and efficient means of utilizing greenhouse gases. The nature of the oxygen carrier that acts as a redox mediator during the reaction is key to chemical chain reactions. However, existing oxygen carriers still have shortcomings in reaction conversion rate and catalytic stability.

The mechanical combination of oxygen carriers and molecular sieves is an effective method to regulate the activity of oxygen carriers. Molecular sieves are widely used in various fields due to their unique large specific surface area and pore volume as well as abundant oxygen vacancies on the surface. Studies have shown that it can effectively improve the performance of oxygen carriers.

In the field of methane catalysis, several types of commonly used catalysts have their shortcomings: Ni-based catalysts are prone to carbon deposition at high temperatures, causing serious environmental pollution; Cu agents have low catalytic activity and are easily poisoned and deactivated; in recent years, Pt-based catalysts have been Excellent catalytic activity and reaction selectivity have attracted much attention. However, noble metals are prone to agglomeration under high temperature conditions, resulting in a reduction in their activity and limiting their application in the field of thermocatalysis.

Contents of the invention

The invention provides a method for preparing a Pt-K bimetallic molecular sieve catalyst, which has high reaction activity, strong anti-sintering performance, low metal loading, high utilization rate, small size and uniform distribution; the method of the invention is through in-situ Synthesis method: During the synthesis of Silicalite-1, the Pt-K metal precursor solution complexed with ethylenediamine is added, and after hydrothermal, washing, drying and calcination, a bimetallic molecular sieve catalyst with small metal particle size and uniform particle size distribution is obtained. , it has open pores, a surface easily accessible to reactant molecules, a large specific surface area and fully exposed metal active sites.

In order to achieve the above objects, the present invention adopts the following technical solutions:

1. Mix tetrapropylammonium hydroxide (TPAOH) and deionized water at 25-30°C at a rate of 400-500 rpm, stir for 8-10 minutes, then slowly add ethyl orthosilicate dropwise, and continue to stir and hydrolyze after the dropwise addition. The hydrogel is obtained in 6 to 8 hours; the molar ratio of ethyl orthosilicate and tetrapropylammonium hydroxide is 1: (0.2 to 0.6);

2. Add the platinum nitrate, potassium nitrate and ethylenediamine solutions to deionized water and use ultrasound to completely dissolve them to obtain a Pt-K precursor solution. Under ultrasonic conditions in an ice-water bath, slowly drop the Pt-K precursor solution into the water. In the gel, the molar ratio of platinum nitrate to potassium nitrate is 1:(0.2~4.0), and the molar ratio of platinum nitrate to ethylenediamine is 1:(0.1~0.2);

3. Transfer the mixture in step 2 to a stainless steel hydrothermal kettle lined with polytetrafluoroethylene, react at 150 to 180°C for 24 to 72 hours for hydrothermal crystallization, and separate the solid and liquid. The resulting crystallized product has a volume concentration of 45 to Wash with 55% ethanol solution and centrifuge alternately with deionized water. Wash several times until the pH of the supernatant is <8; dry at 80 to 100°C for 12 to 24 hours; raise the temperature to 500 at a heating rate of 5 to 15°C/min. Calcined at ~600°C for 4 to 6 hours to prepare a Pt-K bimetallic molecular sieve catalyst.

The molar ratio of ethyl orthosilicate:potassium nitrate is 1:(0.009～0.018).

Another object of the present invention is to apply the Pt-K bimetallic molecular sieve prepared by the above method in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction, and to use it together with the perovskite oxygen carrier in the reaction, which can significantly increase the yield. , achieves efficient utilization of precious metals, has higher reactivity at lower temperatures, and saves costs.

Compared with the existing technology, the present invention has the following beneficial effects:

(1) The method of the present invention fixes Pt metal in the pores of the molecular sieve through in-situ synthesis. Through the confinement effect of the molecular sieve pores, the catalytic activity of the Pt metal can be effectively maintained, the service life of the catalyst is extended, and the catalytic activity is reduced. Economic cost, the introduction of K ⁺ can improve the stability of Pt metal in the high-temperature calcination process, adjust its particle size, fully expose the active sites, and improve its stability; the prepared Pt-K bimetallic catalyst metal particle size is small , uniform particle size distribution, high reactivity, strong sintering resistance, and efficient utilization of precious metals;

(2) The Pt-K bimetallic catalyst prepared by the present invention is used in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction, and cooperates with the perovskite oxygen carrier to show extremely high reactivity and reaction at lower temperatures. Stability can lower the reaction temperature, improve cycle stability, and keep CH _conversion rate, CO selectivity and synthesis gas yield stable.

Description of the drawings

Figure 1 is a TEM spectrum of the Pt-K bimetallic catalyst synthesized in Example 1 of the present invention;

Figure 2 shows the results of the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction using LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier and LFCC/PKS-1 catalyst in Example 1;

Figure 3 shows the results of the application of LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier and LFCC/PKS-2 catalyst in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction in Example 2;

Figure 4 shows the results of the application of LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier and LFCC/PKS-3 catalyst without molecular sieve in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction in Example 3;

Figure 5 shows the results of the application of LaFe _0.85 Ni _0.15 O ₃ oxygen carrier and Pt-K bimetallic catalyst in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction in Example 4;

Figure 6 shows the results of the application of LaFe _0.8 Co _0.2 O ₃ oxygen carrier and Pt-K bimetallic catalyst in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction in Example 5.

Detailed ways

The present invention will be further described in detail through examples below, but the protection scope of the present invention is not limited to the content described; in Examples 1, 2, and 3, the LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier is prepared by the sol-gel method, refer to the literature ZeolitesBoost the Reactivity of Chemical Looping by It was prepared by the method in Acid Sites.ACS SustainableChem.Eng.2023,11,24,9143-9152; in Example 4, the LaFe _0.85 Ni _0.15 O ₃ oxygen carrier was prepared by the sol-gel method, refer to the literature Increased nickel exsolution from LaFe _0.8 Ni _0.2 O ₃ perovskite-derived CO ₂ methanation catalysts through strontium doping.Applied CA:GeneralVolume 590,25January 2020,117-328 is prepared in the same way; in Example 5, the oxygen carrier is prepared by the sol-gel method, refer to the literature Modification of LaFe1- xCoxO3 oxygen carrier by Silicalite-1forchemical looping coupled with the reduction of CO _2. Prepared by the method in Journal of CO ₂ Utilization, Volume 63, 2022, 102-124;

Example 1: Preparation and application of PKS-1 molecular sieve catalyst

1. Preparation of PKS-1 molecular sieve catalyst

(1) Under 25°C water bath conditions, stir 15g of deionized water and 30.0g of tetrapropylammonium hydroxide at 400rpm for 8 minutes; after mixing evenly, slowly add 11.3827g of ethyl orthosilicate dropwise, and complete the addition in 60 minutes Then stir and age for 6 hours to prepare the hydrogel;

(2) Add 0.7043g platinum nitrate, 0.0552g potassium nitrate and 0.0163g ethylenediamine solution into 2mL of deionized water, and sonicate for 10mim to completely dissolve them to obtain a Pt-K precursor solution;

(3) Slowly drip the Pt-K precursor solution into the hydrogel under ultrasonic conditions in an ice-water bath, and then the mixture is crystallized at 150°C for 72 hours to generate a solution containing a light gray solid powder precipitate;

(4) Collect the solid by centrifugation. The solid product is centrifuged and washed alternately with ethanol solution with a volume concentration of 45% and deionized water. Centrifuge and wash several times until the supernatant pH is <8;

(5) The solid obtained by centrifugation is dried at 80°C for 24 hours;

(6) The dried product is heated to 500°C and calcined for 6 hours at 5°C/min to prepare the PKS-1 molecular sieve catalyst;

The SEM spectrum of the PKS-1 catalyst is shown in Figure 1. It can be seen from the figure that the S-1 molecular sieve as the skeleton has a typical hexagonal morphology and narrow size distribution, and the Pt metal and K metal nanoparticles are evenly dispersed;

2. Mixing of PKS-1 catalyst and oxygen carrier

The LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier prepared by the sol-gel method was weighed and mechanically mixed with the PKS-1 catalyst (mass ratio 9:1), and then pressed into tablets and sieved (20 to 40 mesh) to obtain Granular molecular sieve mixed oxygen carrier, labeled LFCC/PKS-1;

At the same time, the LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier prepared by the sol-gel method was weighed, pressed into tablets, and sieved (20 to 40 mesh) to obtain the granular LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier, labeled LFCC ;

3. Chemical chain CH _reforming coupled CO _reduction reaction

Load LFCC and LFCC/PKS-1 into fixed-bed reactors respectively, with the filling masses of 1.6g and 1.78g respectively. The CH ₄ -N ₂ mixed gas is introduced, the CH ₄ volume concentration is 50000ppm, and the feed space velocity is 5625mL/g(cat)·h, perform CH ₄ oxidation reaction at normal pressure and 750°C. After the reaction, the catalyst is reduced under CO ₂ /N ₂ mixed gas (CO ₂ :N ₂ volume ratio 1:9). Then three redox cycle experiments are carried out, and the products are detected by a flue gas analyzer;

Figure 2 shows the synthesis gas yield of LFCC and LFCC/PKS-1 in three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-1, the oxygen carrier changes CH in the chemical chain CH ₄ reforming coupling CO ₂ reduction reaction. The synthesis gas yield of the ₄ reforming step has been significantly improved, and the average synthesis gas yield has increased from 5.87mmol/g to 6.82mmol/g.

Table 1 shows the CH ₄ conversion rate of the molecular sieve-free oxygen carrier LFCC and LFCC/PKS-1 in three redox cycle reactions. It can be seen from the table that the oxygen carrier is reformed and coupled in the chemical chain CH ₄ after the introduction of PKS-1. The average CH4 conversion rate in the _CO reduction reaction has been significantly improved.

Table 1

Example 2: Preparation and application of PKS-2 molecular sieve catalyst

1. Preparation of PKS-2 molecular sieve catalyst

(1) Under 30°C water bath conditions, stir 15g deionized water and 30.0g tetrapropylammonium hydroxide at 500rpm for 10 minutes; after mixing evenly, slowly add 17.0740g ethyl orthosilicate dropwise, and complete the dropwise addition in 60 minutes Then stir and age for 8 hours to prepare the hydrogel;

(2) Add 0.4550g platinum nitrate, 0.1242g potassium nitrate and 0.0090g ethylenediamine solution into 2mL of deionized water, and sonicate for 10mim to completely dissolve them to obtain a Pt-K precursor solution;

(3) Slowly drip the Pt-K precursor solution into the hydrogel under ultrasonic conditions in an ice-water bath, and then the mixture is crystallized at 180°C for 24 hours to generate a solution containing a light gray solid powder precipitate;

(4) Collect the solid by centrifugation. The solid product is washed by alternating centrifugation with ethanol solution with a volume concentration of 55% and ionized water. Centrifuge and wash several times until the pH of the supernatant is <8;

(5) The solid obtained by centrifugation is dried at 100°C for 12 hours;

(6) The dried product is heated to 600°C and calcined for 4 hours at 15°C/min to prepare the PKS-2 molecular sieve catalyst;

2. PKS-2 molecular sieve catalyst combined with oxygen carrier

Weigh the LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier and PKS-2 molecular sieve (LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier: molecular sieve mass ratio is 9:1) prepared by the sol-gel method, mechanically mix, and press Slice and sieve (20-40 mesh) to obtain granular molecular sieve mixed oxygen carrier, labeled LFCC/PKS-2;

3. Chemical chain CH _reforming coupled CO _reduction reaction

LFCC (same as Example 1) and LFCC/PKS-2 were loaded into fixed bed reactors respectively to perform CH ₄ reforming coupled with CO ₂ reduction reaction, and the experimental conditions were the same as Example 1;

Figure 3 shows the synthesis gas yield of LFCC and LFCC/PKS-2 in three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-2, the oxygen carrier changes CH in the chemical chain CH ₄ reforming coupling CO ₂ reduction reaction. The synthesis gas yield in the ₄ reforming step has been significantly improved, and the average synthesis gas yield has increased from 5.87mmol/g to 6.65mmol/g.

Table 2 shows the CH ₄ conversion rates of LFCC and LFCC/PKS-2 in the three redox cycle reactions. From the table, it can be seen that the oxygen carrier after the introduction of PKS-2 in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction The average conversion rate of CH ₄ has been significantly improved.

Table 2:

Example 3: Preparation and application of PKS-3 molecular sieve

1. Preparation of PKS-3 molecular sieve

(1) Stir 15g deionized water and 30.0g tetrapropylammonium hydroxide at 430rpm for 9 minutes in a water bath at 28°C; after mixing evenly, slowly add 13.6592g ethyl orthosilicate dropwise, and after 60 minutes, the addition is completed Stir and age for 8 hours to prepare hydrogel;

(2) Add 0.6527g platinum nitrate, 0.0795g potassium nitrate and 0.0139g ethylenediamine solution into 1.5mL of deionized water, and sonicate for 10mim to completely dissolve them to obtain a Pt-K precursor solution;

(3) Slowly drip the Pt-K precursor solution into the hydrogel under ultrasonic conditions in an ice-water bath, and then the hydrogel is crystallized at 170°C for 48 hours to generate a solution containing a light gray solid powder precipitate;

(4) Collect the solid by centrifugation. The solid product is centrifuged and washed alternately with an ethanol solution with a volume concentration of 50% and ionized water. The solid product is centrifuged and washed several times until the pH of the supernatant is <8;

(5) The solid obtained by centrifugation is dried at 90°C for 18 hours;

(6) The dried product is calcined at a heating rate of 10°C/min and a final temperature of 550°C, and is maintained at constant temperature for 5.5 hours to prepare PKS-3 molecular sieve;

2. Combine with oxygen carrier

The LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier and PKS-3 molecular sieve prepared by the sol-gel method were weighed respectively (the mass ratio of LaFe _0.8 Co _0.15 Cu _0.05 O ₃ oxygen carrier: molecular sieve is 9:1), mechanically mixed, and Press into tablets and sieve (20-40 mesh) to obtain granular molecular sieve mixed oxygen carrier, labeled LFCC/PKS-3.

3. Chemical chain CH _reforming coupled CO _reduction reaction

LFCC (same as Example 1) and LFCC/PKS-3 were loaded into fixed bed reactors respectively to perform CH ₄ reforming coupled with CO ₂ reduction reaction, and the experimental conditions were the same as Example 1;

Figure 4 shows the synthesis gas yield of LFCC and LFCC/PKS-3 in three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-3, the oxygen carrier changes CH in the chemical chain CH ₄ reforming coupling CO ₂ reduction reaction. The synthesis gas yield of the ₄ reforming step has been significantly improved, and the average synthesis gas yield has increased from 5.87mmol/g to 8.46mmol/g.

Table 3 shows the CH ₄ conversion rates of LFCC and LFCC/PKS-3 in the three redox cycle reactions. From the table, it can be seen that the oxygen carrier in the chemical chain CH reforming coupled _{CO 2 reduction} reaction after the introduction of PKS-3 The average conversion rate of CH4 has been significantly improved;

table 3:

Example 4: The preparation of the Pt-K bimetallic catalyst in this example is the same as in Example 3. The Pt-K bimetallic catalyst is used in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction. The experimental conditions are the same as in Example 1, with different The perovskite oxygen carrier is LaFe _0.85 Ni _0.15 O ₃ and is labeled as LFN. The mixture of LFN and PKS-3 (9:1) is labeled as LFN/PKS-3.

Figure 5 shows the synthesis gas yield of LFN and LFN/PKS-3 in three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-3, the oxygen carrier changes CH in the chemical chain CH ₄ reforming coupling CO ₂ reduction reaction. The synthesis gas yield in the ₄ reforming step has been significantly improved, and the average synthesis gas yield has increased from 7.02mmol/g to 8.80mmol/g.

Table 4 shows the CH ₄ conversion rates of LFN and LFN/PKS-3 in the three redox cycle reactions. From the table, it can be seen that the oxygen carrier after the introduction of PKS-3 in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction The average conversion rate of CH4 has been significantly improved;

Table 4:

Example 5: The preparation of the Pt-K bimetallic catalyst in this example is the same as in Example 3. The Pt-K bimetallic catalyst is applied in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction. The experimental conditions are the same as in Example 1, with different The perovskite oxygen carrier is LaFe _0.8 Co _0.2 O ₃ , labeled LFC, and mixed with PKS-3 (9:1) labeled LFC/PKS-3.

Figure 6 shows the synthesis gas yield of LFC and LFC/PKS-3 in three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-3, the oxygen carrier changes CH in the chemical chain CH ₄ reforming coupling CO ₂ reduction reaction. The synthesis gas yield in the ₄ reforming step has been significantly improved, and the average synthesis gas yield has increased from 6.78mmol/g to 8.00mmol/g.

Table 5 shows the CH ₄ conversion rates of LFC and LFC/PKS-3 in the three redox cycle reactions. It can be seen from the table that after the introduction of PKS-3, the oxygen carrier in the chemical chain CH ₄ reforming coupled CO ₂ reduction reaction The average conversion rate of CH4 has been significantly improved;

table 5:

Claims (6)

1. A method for preparing a Pt-K bimetallic molecular sieve catalyst, which is characterized by: mixing tetrapropylammonium hydroxide, deionized water, and ethyl orthosilicate at 25 to 30°C, and stirring to react to obtain water. gel, add platinum nitrate, potassium nitrate and ethylenediamine solutions to deionized water, mix well to prepare a Pt-K precursor solution, and slowly drip the Pt-K precursor solution into the hydrogel under ultrasonic conditions in an ice-water bath. In the process, the mixture undergoes a hydrothermal reaction at 150 to 180°C for 24 to 72 hours, and the reaction product is solid-liquid separated. The solid is washed alternately with ethanol and deionized water with a volume concentration of 45 to 55% until the pH of the washing liquid is <8, and the Pt is obtained by drying and roasting. -K bimetallic molecular sieve catalyst. 2. The preparation method of the Pt-K bimetallic molecular sieve catalyst according to claim 1, characterized in that: the molar ratio of ethyl orthosilicate and tetrapropylammonium hydroxide is 1: (0.2~0.6). 3. The preparation method of Pt-K bimetallic molecular sieve catalyst according to claim 1, characterized in that: the molar ratio of platinum nitrate and potassium nitrate is 1: (0.2~4.0), and the molar ratio of platinum nitrate and ethylenediamine It is 1: (0.1～0.2). 4. The preparation method of Pt-K bimetallic molecular sieve catalyst according to claim 1, characterized in that: roasting is performed at 500-600°C for 2-4 hours. 5. The preparation method of Pt-K bimetallic molecular sieve catalyst according to claim 1, characterized in that: the molar ratio of ethyl orthosilicate: potassium nitrate is 1: (0.009-0.018). 6. The application of the Pt-K bimetallic molecular sieve catalyst prepared by the preparation method of the Pt-K bimetallic molecular sieve catalyst according to any one of claims 1 to 5 in the chemical chain CH reforming _coupled CO _reduction reaction, wherein The characteristic is that the Pt-K bimetallic molecular sieve catalyst and the perovskite oxygen carrier synergistically catalyze the reaction.