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

Abstract

The invention discloses a preparation method of a Pt-K bimetallic molecular sieve catalyst. Specifically, tetrapropylammonium hydroxide, deionized water and tetraethyl orthosilicate are mixed at 25-30 DEG C, stirred for reaction to obtain a hydrogel, platinum nitrate, potassium nitrate and ethylenediamine solution are added into the deionized water, mixed to obtain a Pt-K precursor solution, slowly dripped into the hydrogel under ice-water bath ultrasonic conditions, the mixture is hydrothermally reacted at 150-180 DEG C for 24-72 hours, the reaction product is separated into a solid and a liquid, the solid is alternately washed with ethanol and deionized water with a volume concentration of 45-55% until the pH value of the washing solution is less than 8, and dried and roasted to obtain the catalyst. The preparation method of the catalyst is simple in process, high in catalytic activity and stable in catalytic performance, and the noble metal is stably applied in the chemical chain CH4 reforming coupled CO2 reduction reaction by in-situ synthesis and adding a co-catalyst, and the catalyst has good catalytic activity and stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of bimetallic catalysts, and in particular relates to a preparation method and application of a core-shell structured Pt-K bimetallic molecular sieve catalyst. Background Art

[0002] Methane and carbon dioxide are the two main greenhouse gases that cause global warming. The development of various greenhouse gas utilization technologies, which can not only effectively utilize them as chemical raw materials but also reduce greenhouse gas emissions, has become a focus of widespread attention. As an effective carbon capture technology, chemical chaining technology uses oxygen carriers as oxygen storage media to collect and utilize greenhouse gases in a safe and efficient manner. Chemical chaining CH4 reforming coupled with CO2 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 greenhouse gas utilization method. The properties of oxygen carriers as redox media in the reaction process are the key to chemical chain reactions. However, existing oxygen carriers still have defects in reaction conversion rate and catalytic stability.

[0003] The mechanical combination of oxygen carriers and molecular sieves is an effective method to regulate the activity of oxygen carriers. The unique large specific surface area and pore volume of molecular sieves and the abundant oxygen vacancies on the surface make them widely used in various fields. Studies have shown that they can effectively improve the performance of oxygen carriers.

[0004] In the field of methane catalysis, several commonly used catalysts have their defects: Ni-based catalysts are prone to carbon deposition at high temperatures, causing serious environmental pollution; Cu-based catalysts have low catalytic activity and are easily poisoned and deactivated; in recent years, Pt-based catalysts have attracted much attention due to their excellent catalytic activity and reaction selectivity. However, precious metals are prone to agglomeration under high temperature conditions, resulting in a decrease in their activity, which limits their application in the field of thermal catalysis. Summary of the invention

[0005] The invention provides a method for preparing a Pt-K bimetallic molecular sieve catalyst. The catalyst 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 to add a Pt-K metal precursor solution complexed with ethylenediamine during the synthesis of Silicalite-1 through an in-situ synthesis method, and obtain a bimetallic molecular sieve catalyst with small metal particle size and uniform particle size distribution through hydrothermal, washing, drying and calcination. The bimetallic molecular sieve catalyst has open pores, a surface that is easily contacted by reactant molecules, a large specific surface area and fully exposed metal active sites.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] 1. Stir tetrapropylammonium hydroxide (TPAOH) and deionized water at 25-30°C at a rate of 400-500 rpm for 8-10 minutes, then slowly drop ethyl orthosilicate, and continue stirring and hydrolyzing for 6-8 hours after the addition is completed to obtain a hydrogel; the molar ratio of ethyl orthosilicate to tetrapropylammonium hydroxide is 1:(0.2-0.6);

[0008] 2. Add platinum nitrate, potassium nitrate and ethylenediamine solution into deionized water, and completely dissolve them by ultrasonication to obtain a Pt-K precursor solution. Slowly drip the Pt-K precursor solution into the hydrogel under ultrasonication in an ice-water bath, wherein 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);

[0009] 3. Transfer the mixture from step 2 to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner, react at 150-180° C. for 24-72 hours for hydrothermal crystallization, separate the solid and liquid, wash the resulting crystallized product with an ethanol solution having a volume concentration of 45-55%, and alternately centrifuge with deionized water for several times until the pH of the supernatant is less than 8; dry at 80-100° C. for 12-24 hours; heat up to 500-600° C. at a heating rate of 5-15° C. / min and calcine for 4-6 hours to obtain a Pt-K bimetallic molecular sieve catalyst.

[0010] The molar ratio of tetraethyl orthosilicate to potassium nitrate is 1:(0.009-0.018).

[0011] Another object of the present invention is to apply the Pt-K bimetallic molecular sieve prepared by the above method to the chemical chain CH4 reforming coupled CO2 reduction reaction, and use it together with the perovskite oxygen carrier in the reaction, which can significantly improve the yield, realize the efficient utilization of precious metals, have higher reaction activity at lower temperature, and save costs.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] (1) The method of the present invention fixes Pt metal in the pores of the molecular sieve by an in-situ synthesis method. Through the confinement effect of the pores of the molecular sieve, the catalytic activity of the Pt metal can be effectively maintained, the service life of the catalyst can be extended, and the economic cost of the catalysis can be reduced. + The introduction of can improve the stability of Pt metal during high-temperature calcination, adjust its particle size, fully expose the active sites, and enhance its stability; the prepared Pt-K bimetallic catalyst has small metal particle size, uniform particle size distribution, high reaction activity, strong anti-sintering performance, and realizes efficient utilization of precious metals;

[0014] (2) The Pt-K bimetallic catalyst prepared in the present invention is used in the chemical chaining CH4 reforming coupled with CO2 reduction reaction, and cooperates with the perovskite oxygen carrier to show extremely high reaction activity and reaction stability at a relatively low temperature, which can reduce the reaction temperature, improve the cycle stability, and keep the CH4 conversion rate, CO selectivity and synthesis gas yield stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 TEM spectrum of the Pt-K bimetallic catalyst synthesized in Example 1 of the present invention;

[0016] Figure 2 is LaFe in Example 1 0.8 Co 0.15 Cu 0.05 Results of O3 oxygen carrier and LFCC / PKS-1 catalyst in chemical looping CH4 reforming coupled with CO2 reduction reaction;

[0017] Figure 3 is LaFe in Example 2 0.8 Co 0.15 Cu 0.05 Results of the application of O3 oxygen carrier and LFCC / PKS-2 catalyst in chemical looping CH4 reforming coupled with CO2 reduction reaction;

[0018] Figure 4 The LaFe2O3 without molecular sieve in Example 3 0.8 Co 0.15 Cu 0.05 Results of the application of O3 oxygen carrier and LFCC / PKS-3 catalyst in chemical looping CH4 reforming coupled with CO2 reduction reaction;

[0019] Figure 5 is LaFe in Example 4 0.85 Ni 0.15 Results of the application of O3 oxygen carrier and Pt-K bimetallic catalyst in chemical looping CH4 reforming coupled with CO2 reduction reaction;

[0020] Figure 6 is LaFe in Example 5 0.8 Co 0.2 The results of applying O3 oxygen carrier and Pt-K bimetallic catalyst in chemical looping CH4 reforming coupled with CO2 reduction reaction. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below through examples, but the protection scope of the present invention is not limited to the above contents; in Examples 1, 2, and 3, LaFe 0.8 Co 0.15 Cu 0.05O3 oxygen carrier is prepared by sol-gel method, refer to the literature ZeolitesBoost the Reactivity of Chemical Looping by Acid Sites.ACS SustainableChem.Eng.2023,11,24,9143-9152; LaFe in Example 4 0.85 Ni 0.15 The O3 oxygen carrier was prepared by sol-gel method, referring to the literature Increased nickel exsolution from LaFe 0.8 Ni 0.2 O3perovskite-derived CO2 methanation catalysts through strontium doping.Applied CA:GeneralVolume 590,25January 2020,117-328; The oxygen carrier in Example 5 was prepared by a sol-gel method, referring to the method in the literature Modification of LaFe1-xCoxO3 oxygen carrier by Silicalite-1forchemical looping coupled with the reduction of CO2.Journal of CO2Utilization,Volume 63,2022,102-124;

[0022] Example 1: Preparation and application of PKS-1 molecular sieve catalyst

[0023] 1. Preparation of PKS-1 molecular sieve catalyst

[0024] (1) In a water bath at 25°C, 15 g of deionized water and 30.0 g of tetrapropylammonium hydroxide were stirred at 400 rpm for 8 min; after being uniformly mixed, 11.3827 g of ethyl orthosilicate was slowly added dropwise, and after 60 min of addition, the mixture was stirred and aged for 6 h to obtain a hydrogel;

[0025] (2) 0.7043 g of platinum nitrate, 0.0552 g of potassium nitrate and 0.0163 g of ethylenediamine solution were added to 2 mL of deionized water and ultrasonicated for 10 min to completely dissolve them to obtain a Pt-K precursor solution;

[0026] (3) The Pt-K precursor solution was slowly dripped into the hydrogel under ice-water bath ultrasonic conditions, and then the mixture was crystallized at 150 °C for 72 h to generate a solution containing a light gray solid powder precipitate;

[0027] (4) Collecting the solid by centrifugation, washing the solid product by alternating centrifugation with 45% ethanol solution and deionized water for several times until the pH of the supernatant is less than 8;

[0028] (5) drying the solid obtained by centrifugation at 80°C for 24 h;

[0029] (6) The dried product was heated to 500° C. at a rate of 5° C. / min and calcined for 6 h to obtain a PKS-1 molecular sieve catalyst;

[0030] The SEM spectrum of PKS-1 catalyst is shown in Figure 1 , it can be seen from the figure that the S-1 molecular sieve as a skeleton has a typical hexagonal morphology and a narrow size distribution, and the Pt metal and K metal nanoparticles therein are uniformly dispersed;

[0031] 2. Mixing of PKS-1 catalyst and oxygen carrier

[0032] Weigh the LaFe prepared by the sol-gel method 0.8 Co 0.15 Cu 0.05 The O3 oxygen carrier and the PKS-1 catalyst (mass ratio of 9:1) were mechanically mixed, tableted, and sieved (20-40 mesh) to obtain a granular molecular sieve mixed oxygen carrier, which was labeled as LFCC / PKS-1;

[0033] At the same time, weigh the LaFe prepared by the sol-gel method 0.8 Co 0.15 Cu 0.05 O3 oxygen carrier, after tableting and sieving (20-40 mesh) to obtain granular LaFe 0.8 Co 0.15 Cu 0.05 O3 oxygen carrier, labeled LFCC;

[0034] 3. Chemical looping CH4 reforming coupled with CO2 reduction reaction

[0035] LFCC and LFCC / PKS-1 were loaded into a fixed bed reactor with a loading mass of 1.6 g and 1.78 g, respectively. A CH4-N2 mixed gas was introduced with a CH4 volume concentration of 50000 ppm and a feed space velocity of 5625 mL / g(cat)·h. CH4 oxidation reaction was carried out at normal pressure and 750°C. After the reaction, the catalyst was reduced under a CO2 / N2 mixed gas (CO2:N2 volume ratio of 1:9). Three redox cycle experiments were then carried out, and the product was detected by a flue gas analyzer.

[0036] Figure 2is the syngas yield of LFCC and LFCC / PKS-1 in the three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-1, the syngas yield of the oxygen carrier in the CH4 reforming step in the chemical chain CH4 reforming coupled CO2 reduction reaction is significantly improved, and the average syngas yield is increased from 5.87mmol / g to 6.82mmol / g.

[0037] Table 1 shows the CH4 conversion rates of oxygen carriers LFCC without molecular sieves and LFCC / PKS-1 in three redox cycle reactions. It can be seen from the table that after the introduction of PKS-1, the average CH4 conversion rate of the oxygen carrier in the chemical chain CH4 reforming coupled CO2 reduction reaction is significantly improved.

[0038] Table 1

[0039]

[0040] Example 2: Preparation and application of PKS-2 molecular sieve catalyst

[0041] 1. Preparation of PKS-2 molecular sieve catalyst

[0042] (1) In a water bath at 30°C, 15 g of deionized water and 30.0 g of tetrapropylammonium hydroxide were stirred at 500 rpm for 10 min; after being uniformly mixed, 17.0740 g of ethyl orthosilicate was slowly added dropwise, and after 60 min of addition, the mixture was stirred and aged for 8 h to obtain a hydrogel;

[0043] (2) 0.4550 g of platinum nitrate, 0.1242 g of potassium nitrate and 0.0090 g of ethylenediamine solution were added to 2 mL of deionized water and ultrasonicated for 10 min to completely dissolve them to obtain a Pt-K precursor solution;

[0044] (3) The Pt-K precursor solution was slowly dripped into the hydrogel under ice-water bath ultrasonic conditions, and then the mixture was crystallized at 180 °C for 24 h to generate a solution containing a light gray solid powder precipitate;

[0045] (4) Collecting the solid by centrifugation, and washing the solid product by alternating centrifugation with 55% ethanol solution and deionized water for several times until the pH of the supernatant is less than 8;

[0046] (5) The solid obtained by centrifugation was dried at 100°C for 12 h;

[0047] (6) The dried product was heated to 600° C. at a rate of 15° C. / min and calcined for 4 h to obtain a PKS-2 molecular sieve catalyst;

[0048] 2. PKS-2 molecular sieve catalyst combined with oxygen carrier

[0049] Weigh the LaFe prepared by the sol-gel method 0.8 Co 0.15 Cu 0.05 O3 oxygen carrier and PKS-2 molecular sieve (LaFe 0.8 Co 0.15 Cu 0.05 O3 oxygen carrier: molecular sieve mass ratio is 9:1), mechanically mixed, tableted, sieved (20-40 mesh) to obtain a granular molecular sieve mixed oxygen carrier, marked as LFCC / PKS-2;

[0050] 3. Chemical looping CH4 reforming coupled with CO2 reduction reaction

[0051] LFCC (same as in Example 1) and LFCC / PKS-2 were respectively loaded into fixed bed reactors to carry out CH4 reforming coupled with CO2 reduction reaction, and the experimental conditions were the same as in Example 1;

[0052] Figure 3 is the syngas yield of LFCC and LFCC / PKS-2 in the three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-2, the syngas yield of the oxygen carrier in the CH4 reforming step in the chemical chain CH4 reforming coupled CO2 reduction reaction is significantly improved, and the average syngas yield is increased from 5.87mmol / g to 6.65mmol / g.

[0053] Table 2 shows the CH4 conversion rates of LFCC and LFCC / PKS-2 in the three redox cycle reactions. It can be seen from the table that after the introduction of PKS-2, the average CH4 conversion rate of oxygen carriers in the chemical chain CH4 reforming coupled CO2 reduction reaction is significantly improved.

[0054] Table 2:

[0055]

[0056] Example 3: Preparation and application of PKS-3 molecular sieve

[0057] 1. Preparation of PKS-3 molecular sieve

[0058] (1) In a water bath at 28°C, 15 g of deionized water and 30.0 g of tetrapropylammonium hydroxide were stirred at 430 rpm for 9 min; after being uniformly mixed, 13.6592 g of ethyl orthosilicate was slowly added dropwise, and after 60 min of addition, the mixture was stirred and aged for 8 h to obtain a hydrogel;

[0059] (2) 0.6527 g of platinum nitrate, 0.0795 g of potassium nitrate and 0.0139 g of ethylenediamine solution were added to 1.5 mL of deionized water and ultrasonicated for 10 min to completely dissolve them to obtain a Pt-K precursor solution;

[0060] (3) The Pt-K precursor solution was slowly dripped into the hydrogel under ice-water bath ultrasonic conditions, and then the hydrogel was crystallized at 170 °C for 48 h to generate a solution containing light gray solid powder precipitation;

[0061] (4) collecting the solid by centrifugation, and washing the solid product by alternating centrifugation with 50% by volume ethanol solution and deionized water for several times until the pH of the supernatant is less than 8;

[0062] (5) drying the solid obtained by centrifugation at 90°C for 18 h;

[0063] (6) The dried product was calcined at a heating rate of 10°C / min to a final temperature of 550°C and kept at the constant temperature for 5.5 h to obtain PKS-3 molecular sieve;

[0064] 2. Combined with oxygen carriers

[0065] Weigh the LaFe prepared by the sol-gel method 0.8 Co 0.15 Cu 0.05 O3 oxygen carrier and PKS-3 molecular sieve (LaFe 0.8 Co 0.15 Cu 0.05 The O3 oxygen carrier: molecular sieve mass ratio is 9:1), mechanically mixed, tableted, and sieved (20-40 mesh) to obtain a granular molecular sieve mixed oxygen carrier, which is marked as LFCC / PKS-3.

[0066] 3. Chemical looping CH4 reforming coupled with CO2 reduction reaction

[0067] LFCC (same as in Example 1) and LFCC / PKS-3 were respectively loaded into a fixed bed reactor to carry out CH4 reforming coupled with CO2 reduction reaction, and the experimental conditions were the same as in Example 1;

[0068] Figure 4 is the syngas yield of LFCC and LFCC / PKS-3 in the three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-3, the syngas yield of the oxygen carrier in the CH4 reforming step in the chemical chain CH4 reforming coupled CO2 reduction reaction is significantly improved, and the average syngas yield is increased from 5.87mmol / g to 8.46mmol / g.

[0069] Table 3 shows the CH4 conversion rate of LFCC and LFCC / PKS-3 in the three redox cycle reactions. It can be seen from the table that after the introduction of PKS-3, the average CH4 conversion rate of oxygen carriers in the chemical chain CH4 reforming coupled CO2 reduction reaction has been significantly improved;

[0070] Table 3:

[0071]

[0072] 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 applied to the chemical chaining CH4 reforming coupled CO2 reduction reaction. The experimental conditions are the same as in Example 1, except that the perovskite oxygen carrier is LaFe 0.85 Ni 0.15 O3, labeled as LFN, and a mixture of LFN and PKS-3 (9:1) labeled as LFN / PKS-3.

[0073] Figure 5 is the syngas yield of LFN and LFN / PKS-3 in the three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-3, the syngas yield of the oxygen carrier in the CH4 reforming step in the chemical chain CH4 reforming coupled CO2 reduction reaction is significantly improved, and the average syngas yield is increased from 7.02 mmol / g to 8.80 mmol / g.

[0074] Table 4 shows the CH4 conversion rates of LFN and LFN / PKS-3 in the three redox cycle reactions. It can be seen from the table that after the introduction of PKS-3, the average CH4 conversion rate of oxygen carriers in the chemical chain CH4 reforming coupled CO2 reduction reaction has been significantly improved;

[0075] Table 4:

[0076]

[0077] 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 chaining CH4 reforming coupled CO2 reduction reaction. The experimental conditions are the same as in Example 1, except that the perovskite oxygen carrier is LaFe 0.8 Co 0.2 O3, labeled as LFC, was mixed with PKS-3 (9:1) and labeled as LFC / PKS-3.

[0078] Figure 6 is the syngas yield of LFC and LFC / PKS-3 in the three redox cycle reactions. It can be seen from the figure that after the introduction of PKS-3, the syngas yield of the oxygen carrier in the CH4 reforming step in the chemical chain CH4 reforming coupled CO2 reduction reaction is significantly improved, and the average syngas yield is increased from 6.78mmol / g to 8.00mmol / g.

[0079] Table 5 shows the CH4 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 average CH4 conversion rate of oxygen carriers in the chemical chain CH4 reforming coupled CO2 reduction reaction has been significantly improved;

[0080] Table 5:

[0081]

Claims

1. Application of a Pt-K bimetallic molecular sieve catalyst in chemical looping CH4 reforming coupled with CO2 reduction reaction, characterized in that: The Pt-K bimetallic molecular sieve catalyst and the perovskite oxygen carrier synergistically catalyze the reaction; The Pt-K bimetallic molecular sieve catalyst is prepared by mixing tetrapropylammonium hydroxide, deionized water and tetraethyl orthosilicate at 25-30°C, stirring and reacting to obtain a hydrogel, adding platinum nitrate, potassium nitrate and ethylenediamine solution into deionized water, mixing to obtain a Pt-K precursor solution, slowly dripping the Pt-K precursor solution into the hydrogel under ultrasonic conditions in an ice-water bath, hydrothermally reacting the mixture at 150-180°C for 24-72h, separating the reaction product into a solid and liquid, washing the solid alternately with ethanol and deionized water with a volume concentration of 45-55% until the pH of the washing solution is less than 8, and drying and calcining to obtain the catalyst.

2. The use according to claim 1, characterized in that: The molar ratio of ethyl orthosilicate to tetrapropylammonium hydroxide is 1:(0.2~0.6).

3. The use according to claim 1, characterized in that: 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).

4. The use according to claim 1, characterized in that: Calcination is carried out at 500~600℃ for 2~4 h.

5. The use according to claim 1, characterized in that: The molar ratio of tetraethyl orthosilicate:potassium nitrate is 1:(0.009-0.018).

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