Preparation method of novel catalyst of molecular sieve defect anchored palladium metal for co-production of dimethyl carbonate

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method of a novel catalyst for co-producing dimethyl carbonate and anchoring palladium metal through molecular sieve defects. The molecular sieve supported noble metal Pd catalyst is prepared, the type of the molecular sieve is one or a combination of more of FAU, MOR, FER, LTL, MFI, beta, ZSM-5 and silicalite-1, and the noble metal Pd accounts for 0.1%-2.5% of the mass of the catalyst. The catalyst is applied to a reaction for synthesizing dimethyl carbonate by carbonylation of methyl nitrite in a process of co-producing ethylene glycol from coal and co-producing dimethyl carbonate, solves the problem that a traditional chlorine-free catalyst is easy to inactivate, is a high-stability, high-selectivity, high-conversion-rate, anti-sintering and chlorine-free high-performance catalyst, and has a certain industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and in particular relates to a method for preparing a novel molecular sieve defect-anchored palladium metal catalyst for co-production of dimethyl carbonate. Background Art

[0002] Dimethyl carbonate (DMC) is an important green chemical raw material, listed as a non-toxic chemical by many European countries since the 1990s. As a key organic chemical intermediate, DMC can be used in the synthesis of chemical products such as polycarbonates, pharmaceuticals, and pesticides, and can replace phosgene, methyl halides, and dimethyl sulfate as a carbonylation and methylation reagent. As an excellent solvent, DMC has broad application prospects in lithium battery electrolytes and paint and coatings. As an environmentally friendly fuel additive, DMC can effectively improve the combustion and anti-knock properties of fuel products and is considered an ideal alternative to the toxic methyl tert-butyl ether (MTBE) as a gasoline and diesel additive. With the rapid development of the new energy and polycarbonate industries, DMC production capacity has increased rapidly, showing enormous market potential and development prospects.

[0003] The synthesis methods of dimethyl carbonate mainly include phosgene method, transesterification method, urea alcoholysis method, direct synthesis method of methanol and carbon dioxide, decarbonylation method of dimethyl oxalate and indirect carbonylation method of methanol via methyl nitrite, etc. Phosgene method is a mature production technology with a wide range of applications, but the use of highly toxic phosgene leads to a sharp increase in safety risks in the production process, and the by-product HCl can cause equipment corrosion and deterioration in the quality of the product DMC, and is being gradually eliminated; although the transesterification method has the advantages of simple operation and mild reaction conditions, the separation and purification of the target product is relatively difficult and the cost is high; the process flow of urea alcoholysis is simple, but in actual application it is found that the conversion rate of this process is not ideal, and the catalyst used is expensive and has a short lifespan, which limits its large-scale industrial application; direct synthesis of DMC from methanol and carbon dioxide The MC process is simple and environmentally friendly. However, due to the difficulty in activating the reactants, the catalytic activity of the catalysts currently used in this process is relatively low, which limits the further development of this process. The decarbonylation of dimethyl oxalate avoids the use of toxic substances, reduces environmental pollution and safety risks, and has significant economic benefits. However, the active components of the catalyst used will gradually be lost with the increase in the number of reactions, resulting in a decrease in catalytic activity. In comparison, the indirect carbonylation of methanol with methyl nitrite has the advantages of cheap and readily available raw materials, a pollution-free and environmentally friendly production process, and no subsequent separation problems, and has received widespread attention.

[0004] The indirect carbonylation of methanol with methyl nitrite primarily involves two steps: carbonylation of carbon monoxide with methyl nitrite to form dimethyl carbonate (2CH₃ONO+CO→(CH₃O)₂CO+2NO) and non-catalytic regeneration of methyl nitrite (2NO+2CH₃OH+1 / 2O₂→2CH₃ONO+H₂O). The catalysts used in the carbonylation of carbon monoxide with methyl nitrite to form dimethyl carbonate primarily include a chlorine-containing Pd-Cu / oxide catalyst system and a chlorine-free Pd / molecular sieve catalyst system. Chlorine-containing catalysts require the regular addition of a chlorine replenisher to the reaction feedstock to extend the catalyst's service life. However, the use of chlorine replenishers can lead to equipment corrosion and low product purity. For example, U.S. Patent No. 5,688,984 discloses a spinel-supported catalyst for dimethyl carbonate synthesis. This catalyst requires the addition of a chlorine replenisher, hydrogen chloride or methyl chloroformate, to the feedstock. The use of hydrogen chloride can severely corrode the equipment, while methyl chloroformate is expensive and reduces the purity of the dimethyl carbonate product. Therefore, subsequent research gradually focused on the development of chlorine-free catalysts.

[0005] Chlorine-free Pd / molecular sieve catalysts circumvent the drawbacks of chlorine loss in chlorine-containing catalysts. However, they face a technical bottleneck of poor stability. This is because in the carbonylation reaction system of carbon monoxide and methyl nitrite to dimethyl carbonate, the precious metal Pd is gradually reduced to zero valence by the reducing reactant carbon monoxide during the catalytic reaction, sintering into larger Pd nanoparticles, reducing the number of Pd active sites in the catalyst and leading to catalyst deactivation. Yamamoto et al. prepared a Pd / NaY catalyst with a selectivity of about 80% for dimethyl carbonate based on methyl nitrite. After 700 hours of operation, the space-time yield of the product DMC gradually decreased from the initial 353g Lcat -1 h -1 Reduced to 180g Lcat -1 h -1About, it can be seen that the stability of the catalyst is poor, (Catalysis and characterization of Pd / NaY fordimethyl carbonate synthesis from methyl nitrite and CO, Yamamoto et al., J.Chem.Soc.Faraday Trans., 1997, Vol. 93, p. 3721). Wang et al. reported that molecular sieve-supported Pd catalysts are used to synthesize dimethyl carbonate, wherein the initial carbon monoxide conversion of Pd / NaY catalysts can reach 89%. However, due to the sintering of Pd species, the catalyst is rapidly deactivated during the catalytic reaction of 12 hours, and the carbon monoxide conversion is significantly reduced to 21% (Highly active Pd containing EMT zeolite catalyst for indirect oxidative carbonylation of methanol to dimethyl carbonate, Wang et al., Journal of Energy Chemistry. 2021, Vol. 52, p. 191). It can be seen that how to suppress the sintering of precious metal Pd and solve the problem of easy deactivation of catalysts is of great significance.

[0006] In summary, the present invention proposes a method for preparing a novel molecular sieve defect-anchored palladium metal catalyst for the co-production of dimethyl carbonate, aiming to prepare a high-performance catalyst with high stability, high selectivity, high conversion rate, sintering resistance, and chlorine-free, thereby improving the reaction performance of methyl nitrite carbonylation to synthesize dimethyl carbonate in the process of coal-to-ethylene glycol co-production of dimethyl carbonate. Summary of the Invention

[0007] In view of the problem of poor stability of Pd species in the prior art, the present invention aims to provide a method for preparing a molecular sieve-supported Pd catalyst with high stability, high selectivity, high conversion rate, sintering resistance, and chlorine-free, thereby providing a high-performance catalyst for the carbonylation of methyl nitrite to synthesize dimethyl carbonate in the process of coal-to-ethylene glycol co-production of dimethyl carbonate.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0009] A method for preparing a catalyst for anchoring palladium metal on molecular sieve defects for the novel co-production of dimethyl carbonate is characterized in that the preparation method combines high-temperature pretreatment and modification methods to construct defect sites on the molecular sieve carrier, and utilizes the interaction between the molecular sieve framework defects and the Pd metal to anchor the Pd metal, thereby preparing a molecular sieve-supported Pd catalyst with high catalytic performance and sintering resistance. The catalyst is applied to the carbonylation reaction of methyl nitrite to synthesize dimethyl carbonate in the process of co-production of dimethyl carbonate from coal to ethylene glycol, with a reaction temperature of 100-140°C, a reaction pressure of 0.1-1.0 MPa, and a gas space velocity of 2000-12000 h / d. -1 The volume ratio of carbon monoxide to methyl nitrite feed is 1:2-7, the catalyst is composed of a Pd active component and a molecular sieve carrier, wherein the mass fraction of the Pd active component in the catalyst is 0.1%-2.5%, and the specific surface area of ​​the molecular sieve carrier is 150-950m 2 / g, the average particle size of the molecular sieve carrier particles is 0.1 to 4 microns, and the catalyst preparation method comprises the following steps:

[0010] 1) dissolving a Pd precursor in one or a combination of water, dilute hydrochloric acid, acetic acid, methanol, ethanol, acetone, petroleum ether, benzene, toluene, dichloromethane, acetonitrile or diethyl ether, and stirring uniformly to form a Pd precursor solution;

[0011] 2) The molecular sieve carrier is mixed with deionized water in a mass ratio of 1:0.5 to 10, and after standing for 0.5 to 10 hours, it is transferred to an oven at 25 to 120 ° C and dried for 0.5 to 12 hours. The dried molecular sieve is placed in a muffle furnace and heated from room temperature to 200 to 1000 ° C at a certain heating rate and maintained for 0.5 to 12 hours. After cooling, it is taken out to obtain a high-temperature pretreated molecular sieve;

[0012] 3) adding the high-temperature pretreated molecular sieve obtained in step 2) to a modification solution having a volume content of 1 to 90%, stirring for 0.5 to 48 hours, filtering, washing until neutral, and drying at 25 to 120° C. for 0.5 to 12 hours to obtain a molecular sieve rich in framework defects;

[0013] 4) mixing the framework defect-rich molecular sieve obtained in step 3) with one or more of water, dilute hydrochloric acid, acetic acid, methanol, ethanol, acetone, petroleum ether, benzene, toluene, dichloromethane, acetonitrile or diethyl ether in a mass ratio of 1:3 to 100, stirring for 0.5 to 6 hours, gradually adding a certain mass of the Pd precursor solution obtained in step 1) so that the mass content of the precious metal Pd in ​​the molecular sieve is 0.1% to 2.5%, stirring at a temperature of 25 to 120° C. for 0.5 to 12 hours, filtering the resulting suspension, washing it to neutrality, and drying it at a temperature of 25 to 120° C. for 0.5 to 12 hours to obtain a molecular sieve loaded with a Pd precursor;

[0014] 5) placing the molecular sieve loaded with Pd precursor obtained in step 4) in a muffle furnace, heating the temperature from room temperature to 100-600° C. at a certain heating rate, and maintaining the temperature for 0.5-12 hours. After cooling, the molecular sieve defect-anchored palladium metal catalyst of the present invention is obtained.

[0015] As a preferred embodiment, in step 1), the Pd precursor is one or a combination of palladium nitrate, palladium acetate, palladium chloride, ammonium chloropalladate, potassium chloropalladate, tetraamminepalladium chloride, tetraamminepalladium nitrate, dichlorotetraamminepalladium, and sodium chloropalladate.

[0016] As a preferred embodiment, the molecular sieve carrier in step 2) is one or a combination of FAU, MOR, FER, LTL, MFI, beta, ZSM-5, and silicalite-1.

[0017] As a preferred embodiment, the solute of the modified solution in step 3) is one or more combinations of sodium hydroxide, sodium chloride, sodium nitrate, sodium carbonate, silicon tetrachloride, ammonium hexafluorosilicate, potassium hydroxide, citric acid, hydrochloric acid, oxalic acid, sulfuric acid, nitric acid, potassium carbonate, acetylacetone, and disodium edetate, and the solvent of the modified solution is one or more combinations of water, ethanol, acetone, toluene, and methanol.

[0018] As a preferred solution, the heating rate during calcination in step 5) is 0.5-10°C / min.

[0019] The molecular sieve defect-anchored palladium metal catalyst of the present invention is applied to the reaction process of synthesizing dimethyl carbonate from methyl nitrite by carbonylation in the process of producing dimethyl carbonate from coal to ethylene glycol.

[0020] Compared with the prior art, the method for preparing a novel molecular sieve defect-anchored palladium metal catalyst for co-production of dimethyl carbonate of the present invention has the following significant features:

[0021] (1) The technical bottleneck that limits the large-scale industrial application of chlorine-free molecular sieve-supported Pd catalysts is that Pd species easily sinter during the catalytic reaction. At present, the research on molecular sieve-supported Pd catalysts is mostly focused on the introduction of metal additives to regulate the physical and chemical properties of the catalyst and the Pd active sites. Various additives (such as Cu, K, etc.) have played a certain role in promoting the improvement of catalyst conversion rate and selectivity. However, the effect of improving catalyst stability is still not obvious or has not been mentioned. The present invention regulates the defects of the molecular sieve carrier and conducts a detailed study on the stability of the catalyst. The prepared molecular sieve defect-anchored palladium metal catalyst shows excellent catalytic performance in the reaction of methyl nitrite carbonylation to synthesize dimethyl carbonate in the process of coal-to-ethylene glycol co-production of dimethyl carbonate. The CO conversion rate is greater than 95%, and it can operate stably for more than 150 hours. In addition, the Pd metal can still remain highly dispersed on the catalyst after 150 hours of reaction, providing a basis for the industrial application of high-activity, high-conversion, and sintering-resistant catalysts.

[0022] (2) The unique pore structure of the molecular sieve provides it with abundant sites for loading active metals. Through reasonable molecular sieve defect control, defect sites can be constructed on the molecular sieve surface. These defect sites include bridged silanol, aluminum hydroxyl, silanol and hydroxyl nests, which can effectively inhibit the sintering of Pd species through the anchoring effect. They show excellent catalytic stability in the carbonylation of methyl nitrite to dimethyl carbonate. Currently, no relevant patents or papers have been found to report the use of molecular sieve defects to anchor Pd metal for this catalytic system.

[0023] (3) Defect control has attracted much attention in the field of molecular sieves. There are many methods for constructing molecular sieve defects, such as synthesizing flaky molecular sieves, controlling mesopores, and using chemical reagents such as acids and alkalis to dealuminate and desiliconize molecular sieves. The current methods each have their own advantages and show good performance under specific application conditions. However, it is worth noting that these defect control methods are not suitable for the catalytic reaction system of carbonylation of methyl nitrite to dimethyl carbonate. In particular, acid treatment will leave strong acid sites on the molecular sieve that are difficult to remove. These strong acid sites will cause the reactant methyl nitrite to be ineffectively decomposed into by-products such as methyl formate and dimethoxymethane, thereby reducing the selectivity of the main product dimethyl carbonate. The advantage of the present invention is that it combines high-temperature pretreatment and modification methods to construct defect sites on the molecular sieve. The defect control method used is simple, efficient, green and environmentally friendly, and will not leave strong acid sites on the molecular sieve, and will not adversely affect the selectivity of the product dimethyl carbonate.

[0024] The Pd / molecular sieve catalyst prepared in the present invention is an environmentally friendly catalyst with high activity and stability, and is particularly suitable for the reaction of carbonylating methyl nitrite to synthesize dimethyl carbonate in the process of producing ethylene glycol from coal and co-producing dimethyl carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the XRD pattern of the molecular sieve framework defect anchored palladium metal catalyst prepared in Example 1;

[0026] Figure 2 TEM image of the molecular sieve framework defect anchored palladium metal catalyst prepared in Example 1;

[0027] Figure 3 This is the XRD pattern of the molecular sieve framework defect anchored palladium metal catalyst prepared in Example 2;

[0028] Figure 4 TEM image of the molecular sieve framework defect anchored palladium metal catalyst prepared in Example 2;

[0029] Figure 5 This is the XRD pattern of the molecular sieve framework defect anchored palladium metal catalyst prepared in Example 3;

[0030] Figure 6 TEM image of the molecular sieve framework defect anchored palladium metal catalyst prepared in Example 3;

[0031] Figure 7 This is the XRD pattern of the molecular sieve-supported palladium metal catalyst prepared in Comparative Example 1;

[0032] Figure 8 TEM image of the molecular sieve-supported palladium metal catalyst prepared in Comparative Example 1;

[0033] Figure 9 This is a stability test diagram of the molecular sieve framework defect anchored palladium metal catalyst prepared in Example 3;

[0034] Figure 10 This is a stability test chart of the molecular sieve-supported palladium metal catalyst prepared in Comparative Example 1. DETAILED DESCRIPTION

[0035] To facilitate understanding of the present invention, the present invention is provided below with examples. These examples are provided solely to aid understanding of the present invention and should not be construed as limiting the present invention. Since the present invention may be described and explained using other alternatives that do not depart from the technical features of the present invention, all modifications within the scope of the present invention or equivalents thereof are intended to fall within the scope of protection of the present invention.

[0036] The present invention is further described below with reference to embodiments, comparative examples and application examples.

[0037] Example 1

[0038] 1) Dissolve 0.026 g of dichlorotetraammine palladium in 4 g of water to form a clear Pd precursor solution;

[0039] 2) 2 g of NaY molecular sieve was mixed with 1 g of deionized water and allowed to stand for 0.5 h. The mixture was then transferred to a 25 °C oven and dried for 1 h. The dried molecular sieve was placed in a muffle furnace and calcined at a heating rate of 0.5 °C / min from room temperature to 200 °C for 12 h. The mixture was cooled and taken out to obtain a high-temperature pretreated molecular sieve.

[0040] 3) adding the high-temperature pretreated molecular sieve obtained in step 2) to a modification solution containing 5% acetylacetone in ethanol, stirring at 25° C. for 0.5 hour, filtering, washing until neutral, and drying in an oven at 25° C. for 12 hours to obtain a molecular sieve rich in framework defects;

[0041] 4) 1 g of the framework defect-rich molecular sieve obtained in step 3) was mixed with 99.6 g of deionized water, and after stirring for 0.5 hour, 0.4 g of the Pd precursor solution obtained in step 1) was added dropwise, and stirring was continued at 25° C. for 12 hours. The resulting suspension was filtered, washed until neutral, and dried in an oven at 25° C. for 12 hours to obtain a molecular sieve loaded with a Pd precursor;

[0042] 5) The molecular sieve loaded with framework defects of the Pd precursor obtained in step 4) is placed in a muffle furnace, and the temperature is raised from room temperature to 100° C. at a heating rate of 0.5° C. / min for 1 hour. After cooling, the molecular sieve defect-anchored palladium metal catalyst of the present invention is obtained.

[0043] Figure 1 This is the XRD pattern of the molecular sieve framework defect-anchored palladium metal catalyst prepared in Example 1 after 150 hours of reaction. The figure shows the absence of characteristic diffraction peaks for palladium metal, indicating that the palladium metal is highly dispersed on the catalyst surface. Measurement by inductively coupled plasma optical emission spectrometry revealed a palladium metal mass fraction of 0.1%. Figure 2 This is a TEM image of the catalyst of molecular sieve framework defect-anchored palladium metal prepared in Example 1 after 150 hours of reaction. No obvious palladium clusters or palladium nanoparticles were observed in the image, indicating that the palladium metal was highly dispersed on the catalyst.

[0044] Example 2

[0045] 1) Dissolve 0.065 g of dichlorotetraammine palladium in 10 g of water to form a clear Pd precursor solution;

[0046] 2) 1 g of NaY molecular sieve was mixed with 10 g of deionized water and allowed to stand for 10 hours. The mixture was then transferred to a 120°C oven and dried for 12 hours. The dried molecular sieve was placed in a muffle furnace and calcined from room temperature to 1000°C at a heating rate of 10°C / min for 0.5 hours. The mixture was cooled and taken out to obtain a high-temperature pretreated molecular sieve.

[0047] 3) adding the high-temperature pretreated molecular sieve obtained in step 2) to a modified solution of water containing 90% acetylacetone, stirring at 120° C. for 48 hours, filtering, washing to neutrality, and drying in an oven at 25° C. for 12 hours to obtain a molecular sieve rich in framework defects;

[0048] 4) 1 g of the framework defect-rich molecular sieve obtained in step 3) was mixed with 100 g of deionized water, and after stirring for 6 hours, 10 g of the Pd precursor solution obtained in step 1) was added dropwise, and stirring was continued at 120° C. for 12 hours. The resulting suspension was filtered, washed to neutrality, and dried in an oven at 120° C. for 12 hours to obtain a molecular sieve loaded with a Pd precursor;

[0049] 5) The molecular sieve loaded with palladium precursor obtained in step 4) is placed in a muffle furnace, and the temperature is raised from room temperature to 600° C. at a heating rate of 0.5° C. / min for 0.5 hours. After cooling, the molecular sieve defect-anchored palladium metal catalyst of the present invention is obtained.

[0050] Figure 3 This is the XRD pattern of the molecular sieve framework defect-anchored palladium metal catalyst prepared in Example 2 after 150 hours of reaction. As can be seen, the figure lacks characteristic diffraction peaks of palladium metal, indicating that the palladium metal is highly dispersed on the catalyst surface. Measurement by inductively coupled plasma optical emission spectrometry reveals a palladium metal mass fraction of 2.5%. Figure 4 This is a TEM image of the molecular sieve framework defect-anchored palladium metal catalyst prepared in Example 2 after 150 hours of reaction. No obvious palladium clusters or palladium nanoparticles were observed in the image, indicating that the palladium metal is highly dispersed on the catalyst.

[0051] Example 3

[0052] 1) Dissolve 0.026 g of dichlorotetraammine palladium in 4 g of water to form a clear Pd precursor solution;

[0053] 2) 1 g of NaY molecular sieve was mixed with 5 g of deionized water and allowed to stand for 5 hours. The mixture was then transferred to an 80°C oven and dried for 6 hours. The dried molecular sieve was placed in a muffle furnace and calcined at a heating rate of 10°C / min from room temperature to 700°C for 4 hours. The mixture was cooled and taken out to obtain a high-temperature pretreated molecular sieve.

[0054] 3) adding the high-temperature pretreated molecular sieve obtained in step 2) to a modified solution of water containing 50% potassium hydroxide, stirring at 80° C. for 24 hours, filtering, washing to neutrality, and drying in an oven at 80° C. for 6 hours to obtain a molecular sieve rich in framework defects;

[0055] 4) 1 g of the framework defect-rich molecular sieve obtained in step 3) was mixed with 90 g of deionized water, and after stirring for 2 hours, 4 g of the Pd precursor solution obtained in step 1) was added dropwise, and stirring was continued at 80° C. for 6 hours. The resulting suspension was filtered, washed until neutral, and dried in an oven at 80° C. for 10 hours to obtain a molecular sieve loaded with a Pd precursor;

[0056] 5) The molecular sieve loaded with Pd precursor obtained in step 4) is placed in a muffle furnace and calcined from room temperature to 200° C. at a heating rate of 0.5° C. / min for 2 hours. After cooling, the molecular sieve defect-anchored palladium metal catalyst of the present invention is obtained.

[0057] Figure 5 This is the XRD pattern of the molecular sieve framework defect-anchored palladium metal catalyst prepared in Example 3 after 150 hours of reaction. The figure shows the absence of characteristic diffraction peaks for palladium metal, indicating that the palladium metal is highly dispersed on the catalyst surface. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements revealed a Pd mass fraction of 0.9%. Figure 6 This is a TEM image of the molecular sieve framework defect anchored palladium metal catalyst prepared in Example 3 after 150 hours of reaction. No obvious palladium clusters or palladium nanoparticles were observed in the image, indicating that the palladium metal is highly dispersed on the catalyst.

[0058] Example 4

[0059] 1) Dissolve 0.034 g of palladium chloride in 2 g of dilute hydrochloric acid to form a clear Pd precursor solution;

[0060] 2) 1 g of Na-ZSM-5 molecular sieve was mixed with 8 g of deionized water and allowed to stand for 3 hours. The mixture was then transferred to a 40°C oven and dried for 10 hours. The dried molecular sieve was placed in a muffle furnace and calcined at a heating rate of 5°C / min from room temperature to 500°C for 6 hours. The mixture was cooled and taken out to obtain a high-temperature pretreated molecular sieve.

[0061] 3) adding the high-temperature pretreated molecular sieve obtained in step 2) to a modified solution containing 30% disodium ethylenediaminetetraacetic acid in water, stirring at 40° C. for 36 hours, filtering, washing to neutrality, and drying in a 40° C. oven for 6 hours to obtain a molecular sieve rich in framework defects;

[0062] 4) 1 g of the framework defect-rich molecular sieve obtained in step 3) was mixed with 60 g of deionized water, and after stirring for 3 hours, 2 g of the Pd precursor solution obtained in step 1) was added dropwise, and stirring was continued at 40° C. for 8 hours. The resulting suspension was filtered, washed until neutral, and dried in an oven at 40° C. for 10 hours to obtain a molecular sieve loaded with a Pd precursor;

[0063] 5) The molecular sieve loaded with framework defects and palladium precursor obtained in step 4) is placed in a muffle furnace, and the temperature is raised from room temperature to 500° C. at a heating rate of 5° C. / min for 2 hours. After cooling, the molecular sieve defect-anchored palladium metal catalyst of the present invention is obtained.

[0064] The mass fraction of Pd was measured by inductively coupled plasma optical emission spectrometry and was 1.9%.

[0065] Example 5

[0066] 1) Dissolve 0.034 g of palladium chloride in 2 g of dilute hydrochloric acid to form a clear Pd precursor solution;

[0067] 2) 1 g of beta molecular sieve was mixed with 5 g of deionized water and allowed to stand for 8 hours. The mixture was then transferred to a 90°C oven and dried for 10 hours. The dried molecular sieve was placed in a muffle furnace and calcined at a heating rate of 5°C / min from room temperature to 900°C for 5 hours. The mixture was cooled and removed to obtain a high-temperature pretreated molecular sieve.

[0068] 3) adding the high-temperature pretreated molecular sieve obtained in step 2) to a modified solution of water containing 80% ammonium hexafluorosilicate, stirring at 90° C. for 10 hours, filtering, washing to neutrality, and drying in an oven at 90° C. for 6 hours to obtain a molecular sieve rich in framework defects;

[0069] 4) 1 g of the framework defect-rich molecular sieve obtained in step 3) was mixed with 30 g of deionized water, and after stirring for 4 hours, 1 g of the Pd precursor solution obtained in step 1) was added dropwise, and stirring was continued at 90° C. for 10 hours. The resulting suspension was filtered, washed to neutrality, and dried in an oven at 90° C. for 10 hours to obtain a molecular sieve loaded with a Pd precursor;

[0070] 5) The molecular sieve loaded with Pd precursor obtained in step 4) is placed in a muffle furnace, and calcined from room temperature to 300° C. at a heating rate of 6° C. / min for 3 hours. After cooling, the molecular sieve defect-anchored palladium metal catalyst of the present invention is obtained.

[0071] The mass fraction of Pd was measured by inductively coupled plasma optical emission spectrometry and was 1.0%.

[0072] Example 6

[0073] 1) Dissolve 0.026 g of dichlorotetraammine palladium in 4 g of water to form a clear Pd precursor solution;

[0074] 2) 1 g of beta molecular sieve was mixed with 4 g of deionized water and allowed to stand for 4 hours. The mixture was then transferred to a 50°C oven and dried for 10 hours. The dried molecular sieve was placed in a muffle furnace and calcined at a heating rate of 10°C / min from room temperature to 400°C for 10 hours. The mixture was cooled and taken out to obtain a high-temperature pretreated molecular sieve.

[0075] 3) adding the high-temperature pretreated molecular sieve obtained in step 2) to a modification solution containing 20% ​​disodium ethylenediaminetetraacetic acid in methanol, stirring at 50° C. for 6 hours, filtering, washing to neutrality, and drying in an oven at 50° C. for 10 hours to obtain a molecular sieve rich in framework defects;

[0076] 4) 1 g of the framework defect-rich molecular sieve obtained in step 3) was mixed with 3 g of deionized water, and after stirring for 5 hours, 4 g of the Pd precursor solution obtained in step 1) was added dropwise, and stirring was continued at 50° C. for 12 hours. The resulting suspension was filtered, washed until neutral, and dried in an oven at 50° C. for 12 hours to obtain a molecular sieve loaded with a Pd precursor;

[0077] 5) The molecular sieve loaded with Pd precursor obtained in step 4) is placed in a muffle furnace and calcined from room temperature to 200° C. at a heating rate of 10° C. / min for 3 hours. After cooling, the molecular sieve defect-anchored palladium metal catalyst of the present invention is obtained.

[0078] The mass fraction of Pd was measured by inductively coupled plasma optical emission spectrometry and was 1.1%.

[0079] Comparative Example 1

[0080] 1) Dissolve 0.026 g of dichlorotetraammine palladium in 4 g of water to form a clear Pd precursor solution;

[0081] 2) washing 1 g of NaY molecular sieve with deionized water until neutral, and then transferring it to an oven at 80° C. and drying it for 10 hours to obtain a pretreated molecular sieve;

[0082] 3) The pretreated molecular sieve obtained in step 2) was mixed with 96 g of deionized water, stirred for 2 hours, and then 4 g of Pd precursor solution was added dropwise. The mixture was stirred at 60° C. for 6 hours. The resulting suspension was filtered, washed until neutral, and dried in an oven at 80° C. for 10 hours to obtain a molecular sieve loaded with Pd precursor;

[0083] 4) The molecular sieve loaded with Pd precursor obtained in step 3) was placed in a muffle furnace, and calcined from room temperature to 400° C. at a heating rate of 10° C. / min for 5 hours. After cooling, a molecular sieve loaded with palladium metal catalyst was obtained.

[0084] Figure 7 This is the XRD pattern of the molecular sieve-supported palladium metal catalyst prepared in Comparative Example 1 after 12 hours of reaction. As can be seen, a characteristic diffraction peak attributed to the Pd(111) crystal plane was detected at 2Theta = 40°, indicating that the palladium species sintered on the catalyst after the reaction. Measurement by inductively coupled plasma optical emission spectrometry revealed a palladium metal mass fraction of 0.9%. Figure 8 This is a TEM image of the molecular sieve-supported palladium metal catalyst prepared in Comparative Example 1 after 12 hours of reaction. In the image, the average size of the palladium nanoparticles is 13.6 nm, indicating that the palladium species has undergone severe sintering.

[0085] Comparative Example 2

[0086] 1) Dissolve 0.034 g of palladium chloride in 2 g of dilute hydrochloric acid to form a clear Pd precursor solution;

[0087] 2) washing 1 g of Na-ZSM-5 molecular sieve with deionized water until neutral, and then transferring it to an oven at 80° C. and drying it for 10 hours to obtain a pretreated molecular sieve;

[0088] 3) The pretreated molecular sieve obtained in step 2) was mixed with 60 g of deionized water, stirred for 3 hours, and then 0.5 g of Pd precursor solution was added dropwise. The mixture was stirred at 80° C. for 6 hours. The resulting suspension was filtered, washed until neutral, and dried in an oven at 80° C. for 6 hours to obtain a molecular sieve loaded with Pd precursor;

[0089] 4) The molecular sieve loaded with Pd precursor obtained in step 3) was placed in a muffle furnace, and calcined from room temperature to 200° C. at a heating rate of 5° C. / min for 3 hours. After cooling to room temperature, the molecular sieve was taken out to obtain a molecular sieve loaded with palladium metal catalyst.

[0090] The mass fraction of palladium metal was measured by inductively coupled plasma optical emission spectrometry and was 0.5%.

[0091] As can be seen from Table 1, the compositions of the molecular sieve-supported palladium catalysts prepared in Examples 1 to 6 and Comparative Examples 1 to 2 do not contain chlorine, indicating that the prepared catalysts are all chlorine-free catalysts. The relative crystallinity represents the content of framework defects in the molecular sieve. A relative crystallinity of 100% indicates that the molecular sieve does not contain defects. TEM characterization revealed that the palladium species of the catalysts prepared in Examples 1 to 6 and Comparative Examples 1 to 2 all had a high degree of dispersion on the catalyst surface before the reaction, and the palladium particle sizes were 1.8, 0.9, 1.3, 1.6, 1.2, 1.7, 1.5 and 1.9 nm, respectively.

[0092] Table 1 Physicochemical properties of molecular sieve supported palladium metal catalysts prepared in Examples 1 to 6 and Comparative Examples 1 to 2

[0093]

[0094] Application Example 1

[0095] The catalysts prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were evaluated for catalytic activity in a reactor. The catalyst loading was 0.1 g. Carbon monoxide and methyl nitrite were used as raw materials. The volume ratio of carbon monoxide to methyl nitrite was 1 / 6. The reaction temperature was 110° C., the reaction pressure was 0.1 MPa, and the gas space velocity was 8000 h -1 The obtained products were analyzed by gas chromatography online. The main product was dimethyl carbonate (DMC), and the by-products included dimethoxymethane (DMM) and methyl formate (MF). The conversion rate of carbon monoxide X was calculated from this. CO , dimethyl carbonate based on the selective S of methyl nitrite DMC And the selectivity of each by-product based on methyl nitrite DME and S ME .

[0096] Table 2 Catalytic performance of catalysts in Examples 1 to 6 and Comparative Examples 1 to 2

[0097] catalyst <![CDATA[X CO / %]]> <![CDATA[S DMC / %]]> <![CDATA[S DMM / %]]> <![CDATA[S MF / %]]> Example 1 94.9 64.5 20.3 15.2 Example 2 97.5 70.8 13.4 15.8 Example 3 98.5 73.1 11.9 15.0 Example 4 96.7 70.9 15.5 13.6 Example 5 99.8 67.5 18.6 13.9 Example 6 95.9 69.8 14.9 15.3 Comparative Example 1 92.9 60.2 17.9 21.9 Comparative Example 2 90.7 59.8 24.9 15.3

[0098] As can be seen from Table 2, the carbon monoxide conversion rate and DMC selectivity of the molecular sieve defect-anchored palladium metal catalysts prepared in Examples 1 to 6 are significantly higher than those in Comparative Examples 1 to 2, which indicates that the molecular sieve framework defect-anchored palladium metal catalysts prepared in the present invention have higher catalytic performance.

[0099] All catalysts were tested for stability. The results showed that the catalysts prepared in Examples 1 to 6 with molecular sieve defects anchoring palladium metal could all operate stably for more than 150 hours, with the CO conversion rate remaining essentially unchanged. However, the molecular sieve-supported palladium catalysts prepared in Comparative Examples 1 and 2 were unable to effectively anchor palladium metal due to the small number of molecular sieve defect sites or the lack of defects, and all showed gradual deactivation. Figure 9 This is a stability test diagram of the molecular sieve defect-anchored palladium metal catalyst prepared in Example 3. Figure 10 Figure 1 is a stability test diagram of the molecular sieve supported palladium catalyst prepared in Comparative Example 1. It was found through TEM characterization that after 150 hours of reaction, the palladium particle sizes of Example 2, Example 3 and Example 5 were 1.1nm, 1.5nm and 1.4nm respectively, which was basically unchanged compared with the palladium particle size before the reaction counted in Table 1, indicating that the molecular sieve skeleton defect anchored palladium metal catalyst prepared by Example 2, Example 3 and Example 5 has excellent anti-sintering performance. However, the molecular sieve supported palladium catalyst prepared by Comparative Examples 1 and 2 gradually decreased in activity during the 100-hour reaction process. It was found through TEM characterization that the palladium particle size on the catalyst surface reached 41.4nm and 35.7nm respectively after 100 hours of reaction, which was severely sintered compared with the palladium particle size before the reaction counted in Table 1. This indicates that the molecular sieve supported palladium catalyst prepared by Comparative Examples 1 to 2 cannot effectively anchor Pd metal to inhibit Pd sintering, thereby resulting in poor catalytic stability.

[0100] The following conclusions can be drawn from Tables 1 and 2: the molecular sieve framework defect-anchored palladium metal catalyst prepared in the present invention is a highly stable, high conversion, highly selective, chlorine-free, and sintering-resistant catalyst.

Claims

1. A method for preparing a novel catalyst for co-production of dimethyl carbonate using molecular sieve defects anchored with palladium metal, characterized in that: This preparation method combines high-temperature pretreatment and modification methods to construct framework defect sites on the molecular sieve support, and uses the interaction between the molecular sieve framework defects and Pd metal to anchor the Pd metal, thereby preparing a molecular sieve-supported Pd catalyst with high catalytic performance and sintering resistance. This catalyst is used in the carbonylation reaction of methyl nitrite to synthesize dimethyl carbonate in the process of coal-to-ethylene glycol co-production of dimethyl carbonate. The reaction temperature is 100-140°C, the reaction pressure is 0.1-1.0 MPa, and the gas space velocity is 2000-12000 h-1. -1 The volume ratio of carbon monoxide to methyl nitrite feed is 1:2-7, the catalyst is composed of a Pd active component and a molecular sieve carrier, wherein the mass fraction of the Pd active component in the catalyst is 0.1%-2.5%, and the specific surface area of ​​the molecular sieve carrier is 150-950m 2 / g, the average particle size of the molecular sieve carrier particles is 0.1 to 4 microns, and the catalyst preparation method comprises the following steps: 1) dissolving a Pd precursor in one or a combination of water, dilute hydrochloric acid, acetic acid, methanol, ethanol, acetone, petroleum ether, benzene, toluene, dichloromethane, acetonitrile or diethyl ether, and stirring uniformly to form a Pd precursor solution; 2) The molecular sieve carrier is mixed with deionized water in a mass ratio of 1:0.5 to 10, and after standing for 0.5 to 10 hours, it is transferred to an oven at 25 to 120 ° C and dried for 0.5 to 12 hours. The dried molecular sieve is placed in a muffle furnace and heated from room temperature to 200 to 1000 ° C at a certain heating rate and maintained for 0.5 to 12 hours. After cooling, it is taken out to obtain a high-temperature pretreated molecular sieve; 3) adding the high-temperature pretreated molecular sieve obtained in step 2) to a modification solution having a volume content of 1.0 to 90%, stirring for 0.5 to 48 hours, filtering, washing until neutral, and drying at a temperature of 25 to 120° C. for 0.5 to 12 hours to obtain a molecular sieve rich in framework defects; 4) mixing the framework defect-rich molecular sieve obtained in step 3) with one or more of water, dilute hydrochloric acid, acetic acid, methanol, ethanol, acetone, petroleum ether, benzene, toluene, dichloromethane, acetonitrile or diethyl ether in a mass ratio of 1:3 to 100, stirring for 0.5 to 6 hours, gradually adding a certain mass of the Pd precursor solution obtained in step 1) so that the mass content of the precious metal Pd in ​​the molecular sieve is 0.1% to 2.5%, stirring at a temperature of 25 to 120° C. for 0.5 to 12 hours, filtering the resulting suspension, washing it to neutrality, and drying it at a temperature of 25 to 120° C. for 0.5 to 12 hours to obtain a molecular sieve loaded with a Pd precursor; 5) placing the molecular sieve loaded with Pd precursor obtained in step 4) in a muffle furnace, heating the temperature from room temperature to 100-600° C. at a certain heating rate, and maintaining the temperature for 0.5-12 hours. After cooling, the molecular sieve defect-anchored palladium metal catalyst of the present invention is obtained.

2. The method for preparing a novel catalyst for co-production of dimethyl carbonate using molecular sieve defects anchored with palladium metal as claimed in claim 1, wherein: The Pd precursor in step 1) is one or a combination of palladium nitrate, palladium acetate, palladium chloride, ammonium chloropalladate, potassium chloropalladate, tetraamminepalladium chloride, tetraamminepalladium nitrate, dichlorotetraamminepalladium, and sodium chloropalladate.

3. The method for preparing a catalyst for novel molecular sieve defect-anchored palladium metal for co-production of dimethyl carbonate according to claim 1, characterized in that: The molecular sieve carrier in step 2) is one or a combination of FAU, MOR, FER, LTL, MFI, beta, ZSM-5, and silicalite-1.

4. The method for preparing a novel catalyst for co-production of dimethyl carbonate using molecular sieve defects anchored with palladium metal as claimed in claim 1, wherein: The solute of the modified solution in step 3) is one or a combination of sodium hydroxide, sodium chloride, sodium nitrate, sodium carbonate, silicon tetrachloride, ammonium hexafluorosilicate, potassium hydroxide, citric acid, hydrochloric acid, oxalic acid, sulfuric acid, nitric acid, potassium carbonate, acetylacetone, and disodium edetate, and the solvent of the modified solution is one or a combination of water, ethanol, acetone, toluene, and methanol.

5. The method for preparing a novel catalyst for co-production of dimethyl carbonate using molecular sieve defects anchored with palladium metal as claimed in claim 1, wherein: The stirring in step 1), step 3) and step 4) is magnetic stirring or mechanical stirring, and the stirring speed is 10 to 800 revolutions per minute.

6. The method for preparing a novel catalyst for co-production of dimethyl carbonate using molecular sieve defects anchored with palladium metal as claimed in claim 1, wherein: The heating rate in step 5) is 0.5-10.0°C / min.

7. The method for preparing a novel catalyst for co-production of dimethyl carbonate using molecular sieve defects anchored with palladium metal as claimed in claim 1, wherein: The molecular sieve framework defects mainly include silanol, aluminum hydroxyl, silanol and hydroxyl nests.

8. The method for preparing a novel catalyst for co-production of dimethyl carbonate using molecular sieve defects anchored with palladium metal as claimed in claim 1, wherein: The molecular sieve defect-anchored palladium metal catalyst is used in the carbonylation reaction of methyl nitrite to synthesize dimethyl carbonate in the process of coal-to-ethylene glycol co-production of dimethyl carbonate. The reaction equation is as follows: 2CH3ONO+CO→(CH3O)2CO+2NO.

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