Phosphorus-modified cerium dioxide catalyst as well as preparation method and application thereof
By introducing phosphorus modification into the cerium dioxide catalyst to form a Ceδ+-OP heterostructure, the problems of low catalyst activity and easy water poisoning were solved, and a highly efficient process for synthesizing dimethyl carbonate from CO2 and methanol was realized.
Patent Information
- Application Number
- CN202511076080.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-01
- Publication Date
- 2025-12-12
AI Technical Summary
Existing catalysts exhibit low catalytic activity and are prone to water poisoning during the synthesis of dimethyl carbonate from CO2 and methanol, making it difficult to effectively control the adsorption and activation state of CO2/CH3OH.
By using a phosphorus-modified cerium dioxide catalyst, a unique charge transfer channel is constructed through the formation of a Ceδ+-OP heterostructure, which enhances the synergistic effect of Lewis acidic and basic sites, forming electrons that can be transferred to the unfilled antibonding π* orbitals of CO2, thereby reducing the activation energy of the reaction.
The catalytic activity and selectivity of the catalyst were improved, and the efficiency of synthesizing dimethyl carbonate from CO2 and CH3OH was increased, thus achieving a highly efficient synthesis of dimethyl carbonate.
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Figure CN121103395A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of catalysts, in particular to a phosphorus modified ceria catalyst and a preparation method and application thereof. BACKGROUND
[0002] Excessive emission of CO2 leads to increasingly serious global warming, and catalytic conversion of CO2 into high value-added products has attracted great attention. Among them, dimethyl carbonate (DMC) is a low-toxicity, environmentally friendly and widely used chemical raw material, with downstream covering pesticide, pharmaceutical and other industries, and it is also an important oxygen-containing carrier (oxygen content 53.3%) that can be used as a gasoline additive. Its main raw material methanol (CH3OH) will further reduce in price with the large-scale industrial production of coal-to-methanol, liquid sunlight green methanol, and biomass-to-green methanol. Therefore, it is of great significance to combine CO2 and CH3OH to directly synthesize DMC in gas phase reaction.
[0003] However, due to the unfavorable reaction thermodynamics of the reaction and the difficulty of CO2 / CH3OH activation, the yield of DMC is low, and the catalyst is easily water-poisoned, so the development of high-efficiency catalyst has become a research focus. Current research mainly includes ionic liquid catalyst, basic carbonate catalyst, supported catalyst, heteropoly acid catalyst, and metal oxide catalyst. Among them, the metal oxide catalyst does not exist oxidation deactivation, and has great industrial application advantage, mainly with CeO2 as the main component. CeO2 can actively participate in the catalytic reaction and promote the activation of reactant molecules, but due to its disordered electronic distribution and active site, it is difficult to accurately control the adsorption and activation state of CO2 / CH3OH by traditional methods of constructing surface / interface electron-deficient defects. SUMMARY
[0004] In view of the above problems, the present application aims to provide a phosphorus modified ceria catalyst and a preparation method and application thereof.
[0005] The technical scheme of the present application is as follows: On the one hand, a phosphorus modified ceria catalyst is provided, which comprises ceria and cerium phosphorus composite oxide, the cerium phosphorus composite oxide is composed of cerium ions and acid radical ions, the acid radical ions are P n O 3n+1 n+2- , n is a positive integer; and the ceria and the cerium phosphorus composite oxide form a Ce δ+ -O-P heterojunction interface connected by Ce-O bond of ceria and P-O bond of cerium phosphorus composite oxide.
[0006] As a preferred, the molar ratio of the ceria and the cerium phosphorus composite oxide is 0.01-100.
[0007] As a preference, the cerium phosphate composite oxide is cerium phosphate, cerium pyrophosphate or cerium polyphosphate.
[0008] In another aspect, a method for preparing the phosphorus-modified ceria catalyst according to any one of the above aspects is also provided, comprising the following steps: S1: preparing a cerium metal salt solution, an organic / inorganic phosphoric acid solution, and a precipitant solution; S2: mixing the cerium metal salt solution with part of the precipitant solution, precipitating, then adding the organic / inorganic phosphoric acid solution and dropping the remaining precipitant solution, and continuing to precipitate to obtain a precipitate product; S3: drying the precipitate product, and then calcining under an atmosphere induction condition to obtain the phosphorus-modified ceria catalyst.
[0009] As a preference, in step S1, the solute of the cerium metal salt solution is any one or more of carbonates, acetates, nitrates, sulfates, and halides; The solute of the organic / inorganic phosphoric acid solution is any one or more of inorganic compounds, phosphorus oxyacids and salts thereof, and organic phosphorus compounds; The solute of the precipitant solution is any one or more of urea, ammonium carbonate, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, ammonia, sodium hydroxide, and potassium hydroxide.
[0010] As a preference, the solute of the organic / inorganic phosphoric acid solution is any one or more of hypophosphorous acid, phosphorous acid, orthophosphoric acid, phosphorus trichloride, phosphorus pentachloride, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, calcium phosphate, calcium pyrophosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, triphenylphosphine, and triethyl phosphate.
[0011] As a preference, in step S2, the first precipitation is carried out at 20-90 ℃ for 2-24 h, and the second precipitation is carried out at 20-90 ℃ for 5-10 h; in step S3, the drying is carried out at 20-110 ℃ for 4-48 h, and the calcining is carried out at 150-1000 ℃ under nitrogen, oxygen, carbon monoxide or carbon dioxide gas for 2-8 h.
[0012] As a preference, the method further comprises a step of preparing the phosphorus-modified ceria catalyst into a monolithic catalyst.
[0013] As a preference, the substrate of the monolithic catalyst is a cordierite honeycomb ceramic substrate, and the catalyst binder is Al2O3, TiO2, SiO2 or ZrO2.
[0014] In another aspect, the phosphorus-modified ceria catalyst according to any one of the above aspects is also provided for use in the synthesis of dimethyl carbonate.
[0015] The beneficial effects of the present application are: The present application can utilize Ce δ+ The unique charge transfer channel at the -O-P heterojunction realizes the distribution of charge gradient; this new heterojunction can enhance the synergistic effect of Lewis acid sites and basic sites, form electrons that can be transferred to the un-filled anti-bonding π* orbital of CO2, reduce the activation energy of the subsequent reaction steps, and improve the catalytic activity of the catalyst. In addition, the present application has high catalytic activity for the synthesis of dimethyl carbonate from CO2 and CH3OH, and at the same time has high selectivity for dimethyl carbonate, which can provide technical support for the synthesis of dimethyl carbonate. BRIEF DESCRIPTION OF DRAWINGS
[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.
[0017] Figure 1 XRD pattern of the monolithic catalyst of Example 3-Example 5; Figure 2 TEM image of the monolithic catalyst of Example 3; Figure 3 TEM image and spherical aberration-corrected scanning transmission electron microscopy image of the monolithic catalyst of Example 4; Figure 4 TEM image of the monolithic catalyst of Example 5; Figure 5 BET pattern of the monolithic catalyst of Example 4; Figure 6 XPS O1s pattern of the monolithic catalyst of Example 4, Comparative Example 1 and Comparative Example 2. DETAILED DESCRIPTION
[0018] The present application will be further described below in conjunction with the drawings and examples. It should be noted that the examples in the present application and the technical features in the examples can be combined with each other without conflict. It should be noted that unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs. The present application discloses that the "including" or "containing" and similar words mean that the elements or objects before the words cover the elements or objects listed after the words and their equivalents, and do not exclude other elements or objects.
[0019] In one aspect, the present application provides a phosphorus-modified ceria catalyst, comprising ceria and cerium phosphate composite oxide, wherein the cerium phosphate composite oxide is composed of cerium ions and acid radical ions, and the acid radical ions are P n O 3n+1 n+2- , n is a positive integer; and a Ce δ+ -O-P hetero-interface is formed between the ceria and the cerium phosphate composite oxide.
[0020] In the above embodiments, the present application utilizes the cerium atoms stabilized by phosphate framework to form Ce δ+ -O-P hetero-interface with cubic fluorite CeO2, constructs a unique charge transfer channel at the interface, and realizes the charge gradient distribution. This new heterostructure can enhance the synergistic effect of Lewis acid sites and basic sites, form electrons that can be transferred to the empty π* orbital of CO2, and reduce the activation energy of the subsequent reaction steps.
[0021] In one specific embodiment, the molar ratio of the ceria and the cerium phosphate composite oxide is 0.01-100. Alternatively, the molar ratio of the ceria and the cerium phosphate composite oxide is 0.1-5.
[0022] In one specific embodiment, the acid radical ions are PO4 3- , P2O7 4- or P3O 10 5- . Alternatively, the acid radical ions are PO4 3- , P2O7 4- .
[0023] In one specific embodiment, the cerium phosphate composite oxide is cerium phosphate, cerium pyrophosphate, or cerium polyphosphate.
[0024] In another aspect, the present application also provides a preparation method of the phosphorus-modified ceria catalyst described in any one of the above embodiments, comprising the following steps: S1: preparing a metal cerium salt solution, an organic / inorganic phosphoric acid solution, and a precipitant solution; S2: mixing the metal cerium salt solution with part of the precipitant solution, precipitating, then adding the organic / inorganic phosphoric acid solution and dropping the remaining precipitant solution, continuing to precipitate, and obtaining a precipitate product; S3: drying the precipitate product, then calcining under the condition of atmosphere induction, and obtaining the phosphorus-modified ceria catalyst.
[0025] In the above embodiments, in step S2, when the second precipitant solution is added, the pH of the whole solution is adjusted to 6-10.
[0026] In the above embodiments, the present application adopts a precipitation-inducing method to prepare the phosphorus-modified ceria catalyst. First, a precursor material of the catalyst is prepared by step-by-step precipitation. Then, the precursor material is restructured by atmosphere induction and different temperature conditions to build Ce δ+ -O-P hetero-interface. The precipitation-inducing method can realize the controllable conversion of cerium phosphate nanowires to microspheres, hexagonal crystals to monoclinic crystals, and effectively control the Ce δ+ -O-P hetero-interface structure, change the local electronic structure and coordination environment, and the coordination mismatch of Ce induces lattice distortion to form a large number of coordination-unsaturated interface Ce δ+ atoms, further increasing the activation sites of CO2 and CH3OH.
[0027] In a specific embodiment, the solute of the metal cerium salt solution is any one or more of carbonates, acetates, nitrates, sulfates, and halides. Alternatively, the solute of the metal cerium salt solution is any one or more of acetates, nitrates, and sulfates.
[0028] In a specific embodiment, the solute of the organic / inorganic phosphoric acid solution is any one or more of inorganic compounds, phosphorus oxoacids and salts thereof, and organic phosphorus compounds. Alternatively, the solute of the organic / inorganic phosphoric acid solution is any one or more of hypophosphorous acid, phosphorous acid, orthophosphoric acid, phosphorus trichloride, phosphorus pentachloride, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, calcium phosphate, calcium pyrophosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, triphenylphosphine, and triethyl phosphate. Alternatively, the solute of the organic / inorganic phosphoric acid solution is any one or more of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, triphenylphosphine, orthophosphoric acid, and phosphorous acid.
[0029] In a specific embodiment, the solute of the precipitant solution is any one or more of urea, ammonium carbonate, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, aqueous ammonia, sodium hydroxide, and potassium hydroxide. Alternatively, the solute of the precipitant solution is any one or more of sodium hydroxide, aqueous ammonia, sodium bicarbonate, and potassium carbonate.
[0030] In a specific embodiment, in step S2, the first precipitation is performed at 20-90 ℃ for 2-24 h, and the second precipitation is performed at 20-90 ℃ for 5-10 h. In step S3, the drying is performed at 20-110 ℃ for 4-48 h, and the calcination is performed at 150-1000 ℃ in nitrogen, oxygen, carbon monoxide, or carbon dioxide for 2-8 h.
[0031] In one specific embodiment, in step S3, the calcination is performed using a gradient temperature or a direct temperature. Alternatively, when a gradient temperature is used, the calcination is first performed at 180-450 ℃ for 2-4 h, followed by calcination at 450-1000 ℃ for 1-3 h, or first performed at 180-280 ℃ for 1-2 h, followed by calcination at 450-550 ℃ for 1-2 h.
[0032] It should be noted that the CeO2-P2O5 catalyst obtained by calcination at 150-1000 ℃ has the following characteristics: δ+ The CeO2-P2O5 catalyst has a CeO2-P hetero-interface, and the activity of the catalyst is better at a moderate temperature (300-600 ℃) and a higher abundance. δ+ The CeO2-P2O5 catalyst has a CeO2-P hetero-interface. Based on the XRD test results, one skilled in the art can adjust the calcination temperature and time to obtain a catalyst with the best performance.
[0033] In one specific embodiment, the method further comprises a step of preparing the phosphorus-modified ceria catalyst into a monolithic catalyst. Alternatively, the substrate of the monolithic catalyst is a cordierite honeycomb ceramic substrate, and the catalyst binder is Al2O3, TiO2, SiO2, or ZrO2.
[0034] In the above embodiment, the phosphorus-modified ceria catalyst is prepared into a monolithic catalyst, which can be used in a fixed bed reactor to directly synthesize dimethyl carbonate from carbon dioxide and methanol. The phosphorus-modified ceria catalyst in the monolithic catalyst is coated on the surface of the cordierite honeycomb ceramic pores to form a catalytic coating. The coating structure allows the reactants and products to quickly react and quickly escape from the reaction system to avoid poisoning the catalyst and further promote the forward reaction. The presence of phosphate can also strengthen the adhesion on the cordierite honeycomb ceramic pores and improve the mechanical stability.
[0035] It should be noted that the monolithic catalyst structure is a prior art, and the improvement of the monolithic catalyst according to the present application is mainly that the active component is the phosphorus-modified ceria catalyst according to the present application. In addition to the substrate and catalyst binder described in the above embodiment, other substrates and catalyst binders in the prior art can also be used in the monolithic catalyst according to the present application.
[0036] In another aspect, the present application also provides the use of the phosphorus-modified ceria catalyst according to any one of the above embodiments in the synthesis of dimethyl carbonate.
[0037] In one specific embodiment, the reaction of carbon dioxide plus methanol to synthesize dimethyl carbonate is carried out in a pressurized fixed-bed flow reactor, and the reaction conditions of carbon dioxide plus methanol to synthesize dimethyl carbonate are as follows: the reaction pressure is 0.5-5 MPa, the reaction temperature is 60-200 ℃, the space velocity is 800-20000 h -1 -1, and n(CO2):n(CH3OH)=0.5-30; the dehydrating agent is 2,2-dimethoxypropane, denoted as DMP. Alternatively, the dehydrating agent is fed by a high-pressure constant-flow pump with methanol, and n(CH3OH):n(DMP)=30-1.
[0038] Example 1 A CeO2-0.5CePO4-Al2O3 monolithic catalyst, which is a N2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and the molar ratio of CeO2 to CeM (M=PO4 3- ) is 1:1, is prepared by the following steps: (1) 10 mL of a 2.5 mol / L Ce(NO3)2 solution, 0.86 mL of orthophosphoric acid, and 4.2 mL of an ammonia water solution (23%) are prepared. At a constant temperature of 50 ℃, the above-mentioned Ce(NO3)2 solution is poured into a three-necked flask and diluted to 80 mL, 2 mL of an ammonia water solution is gradually added dropwise, a light yellow flocculent precipitate appears, and the stirring is continued for 8 h, the precipitate changes from light yellow to purple and then to a milky white precipitate. Further, the second step of precipitation is started, 0.86 mL of orthophosphoric acid is added to the three-necked flask at one time, and 2.2 mL of an ammonia water solution is added dropwise at the same time, and the stirring is continued for 4 h to obtain a precipitate product. The obtained precipitate product is dried at 90 ℃ for 24 h, and calcined at 400 ℃ for 4 h under N2 to obtain a blocky CeO2-0.5CePO4 catalyst. Further, the obtained blocky material is transferred to a mortar and ground into a powder to prepare a CeO2-0.5CePO4 composite material.
[0039] (2) 5 g of the CeO2-0.5CePO4 composite material prepared in step (1) is added to a ball mill tank together with 0.05 g of Al2O3 and 3 mL of deionized water to prepare a slurry by a ball mill; a cordierite honeycomb ceramic substrate is immersed in the slurry, and the excess slurry is blown off by compressed air, and finally a cordierite honeycomb ceramic with a CeO2-0.5CePO4-Al2O3 composite material coating is obtained, which is then dried at 100 ℃ for 12 h and calcined at 400 ℃ for 8 h under air to obtain a monolithic catalyst, which is named as CeO2-0.5CePO4-Al2O3, denoted as Cat 1.
[0040] Example 2 A CeO2-0.25CePO4-Al2O3 monolithic catalyst, which is a N2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and the molar ratio of CeO2 to CeM (M = PO4 3- ) is 3:1, is prepared by the following steps: (1) A 20 mL 3.5 mol / L Ce(NO3)2 solution, 0.96 mL of orthophosphoric acid, and 4.5 mL of an ammonia water solution (23%) are prepared. At a constant temperature of 50°C, the above-mentioned Ce(NO3)2 solution is poured into a three-necked flask and diluted to 200 mL, 2.5 mL of an ammonia water solution is gradually added dropwise, a light yellow flocculent precipitate appears, and the stirring is continued for 6 h, the precipitate changes from light yellow to purple and then to a milky white precipitate. Further, the second step of precipitation is started, 0.96 mL of orthophosphoric acid is added to the three-necked flask at one time, and 2.0 mL of an ammonia water solution is added dropwise at the same time, and the stirring is continued for 5 h to obtain a precipitate product. The obtained precipitate product is dried at 100°C for 24 h, and calcined at 500°C for 3 h under N2 to obtain a blocky CeO2-0.25CePO4 catalyst. Further, the obtained blocky material is transferred to a mortar and ground into a powder to prepare a CeO2-0.25CePO4 composite material.
[0041] (2) 4 g of the CeO2-0.25CePO4 composite material prepared in step (1) is taken and mixed with 0.04 g of Al2O3 and 3 mL of deionized water in a ball mill tank to prepare a slurry by a ball mill; a cordierite honeycomb ceramic substrate is immersed in the slurry, and the excess slurry is blown off by compressed air, and finally a cordierite honeycomb ceramic with a CeO2-0.25CePO4-Al2O3 composite material coating is obtained, which is then dried at 100°C for 12 h and calcined at 400°C for 8 h under air to obtain a monolithic catalyst, which is named as CeO2-0.25CePO4-Al2O3 and is denoted as Cat 2.
[0042] Example 3 A CeO2-0.25CePO4-Al2O3 monolithic catalyst, which is a N2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and the molar ratio of CeO2 to CeM (M = PO4 3- ) is 3:1, is prepared by the following steps: (1) Preparation of 20 mL of 3.5 mol / L Ce(NO3)2 solution, 0.61 g of ammonium dihydrogen phosphate and 4.5 mL of ammonia solution (23%). At a constant temperature of 50 ℃, pour the above-mentioned Ce(NO3)2 solution into a three-necked flask and dilute to 150 mL, gradually add 2.5 mL of ammonia solution dropwise, a light yellow flocculent precipitate appears, continue to stir vigorously for 6 h, the precipitate changes from light yellow to purple and then to a milky white precipitate. Further, start the second step of precipitation, add 0.61 g of ammonium dihydrogen phosphate to the three-necked flask at one time, and synchronously add 2.0 mL of ammonia solution dropwise, keep stirring vigorously for 5 h to obtain the precipitate product. Dry the obtained precipitate product at 100 ℃ for 24 h, calcine at 200 ℃ under O2 for 3 h to obtain a blocky CeO2-0.25CePO4 catalyst. Further, transfer the obtained blocky material to a mortar and grind to a powder to prepare a CeO2-0.25CePO4 composite material.
[0043] (2) Take 4 g of the CeO2-0.25CePO4 composite material prepared in step (1) and 0.04 g of Al2O3 and 3 mL of deionized water into a ball mill tank to prepare a slurry by a ball mill; immerse the cordierite honeycomb ceramic substrate in the slurry, blow off the excess slurry by compressed air, and finally obtain a cordierite honeycomb ceramic with a CeO2-0.25CePO4-Al2O3 composite material coating, then dry at 100 ℃ for 12 h and calcine at 200 ℃ under air (in order to ensure the same structure, the calcination temperature in this step should not exceed the calcination temperature in step (1)) for 8 h to obtain a monolithic catalyst, which is named as CeO2-0.25CePO4-Al2O3 and recorded as Cat3.
[0044] Example 4 A CeO2-0.25CePO4-Al2O3 monolithic catalyst is an O2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and the molar ratio of CeO2 to CeM (M = PO4 3- ) is 3:1. The preparation process is similar to that of Example 3, except that the types and amounts of the precursors and precipitants are different, and the calcination conditions of the precipitate product are different. The specific parameters are shown in Table 1. The monolithic catalyst obtained in this example is named as CeO2-0.25CePO4-Al2O3 and recorded as Cat4.
[0045] Example 5 A CeO2-0.25CePO4-Al2O3 monolithic catalyst is an O2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and the molar ratio of CeO2 to CeM (M = PO4 3-CeO2-0.25CeP2O7-Al2O3 monolithic catalyst, which is an O2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and CeO2 and CeM (M = P2O7
[0046] Example 6 CeO2-0.25CeP2O7-Al2O3 monolithic catalyst, which is an O2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and CeO2 and CeM (M = P2O7 4- CeO2-0.25CeP2O7-Al2O3 monolithic catalyst, which is an O2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and CeO2 and CeM (M = P2O7
[0047] Example 7 CeO2-0.5CePO4-Al2O3 monolithic catalyst, which is a CO-induced CeO2-xCeM-Al2O3 monolithic catalyst, and CeO2 and CeM (M = PO4 3- CeO2-0.5CePO4-Al2O3 monolithic catalyst, which is a CO-induced CeO2-xCeM-Al2O3 monolithic catalyst, and CeO2 and CeM (M = PO4
[0048] Example 8 CeO2-0.25CePO4-Al2O3 monolithic catalyst, which is a CO2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and CeO2 and CeM (M = PO4 3- CeO2-0.25CePO4-Al2O3 monolithic catalyst, which is a CO2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and CeO2 and CeM (M = PO4
[0049] Example 9 CeO2-0.3CePO4-Al2O3 monolithic catalyst, which is a CO2-induced CeO2-xCeM-Al2O3 monolithic catalyst, and CeO2 and CeM (M = PO4 3-A CeO2-0.3CePO4-Al2O3 monolithic catalyst was prepared according to the method similar to that of Example 3, except that the types and amounts of the precursors and the precipitant were different, and the calcination conditions of the precipitated product were different. The specific parameters are shown in Table 1. The monolithic catalyst obtained in this example was named CeO2-0.3CePO4-Al2O3, and was denoted as Cat 9.
[0050] Example 10 A CeO2-0.3CeP2O7-Al2O3 monolithic catalyst was prepared according to the method similar to that of Example 3, except that the types and amounts of the precursors and the precipitant were different, and the calcination conditions of the precipitated product were different. The specific parameters are shown in Table 1. The monolithic catalyst obtained in this example was named CeO2-0.3CePO4-Al2O3, and was denoted as Cat 9. 4-- A CeO2-0.3CePO4-Al2O3 monolithic catalyst was prepared according to the method similar to that of Example 3, except that the types and amounts of the precursors and the precipitant were different, and the calcination conditions of the precipitated product were different. The specific parameters are shown in Table 1. The monolithic catalyst obtained in this example was named CeO2-0.3CePO4-Al2O3, and was denoted as Cat 9.
[0051] It should be noted that the above examples are only part of the examples of the present application. The solute of the cerium salt solution, the solute of the organic / inorganic phosphoric acid solution, the solute of the precipitant solution, the precipitation temperature, the precipitation time, the drying temperature, the drying time, the calcination temperature, the calcination time, and the like can be changed, as long as the CeO2-0.3CePO4-Al2O3 monolithic catalyst can be obtained. δ+ The phosphorus modified ceria catalysts described in the present application can be prepared by the method of changing the solute of the cerium salt solution, the solute of the organic / inorganic phosphoric acid solution, the solute of the precipitant solution, the precipitation temperature, the precipitation time, the drying temperature, the drying time, the calcination temperature, the calcination time, and the like.
[0052] Comparative Example 1 An O2-induced CeO2-Al2O3 monolithic catalyst was prepared according to the method similar to that of Example 1, except that the types and amounts of the precursors and the precipitant were different. The specific amounts are shown in Table 1. The monolithic catalyst obtained in this comparative example was named CeO2-Al2O3, and was denoted as Cat 11.
[0053] Comparative Example 2 An O2-induced CePO4-Al2O3 monolithic catalyst was prepared according to the method similar to that of Example 1, except that the types and amounts of the precursors and the precipitant were different. The specific amounts are shown in Table 1. The monolithic catalyst obtained in this comparative example was named CePO4-Al2O3, and was denoted as Cat 12.
[0054] Table 1. Amounts of raw material components of the catalysts of each example and each comparative example and induction conditions
[0055] It should be noted that although the components in the preparation method of Comparative Example 2 are similar to those in Example 1 of this invention, the content of cerium ions in Comparative Example 2 is insufficient to support the formation of CeO2. During the calcination process, cerium ions preferentially react with PO4. 3- CePO4 is formed. Therefore, the catalyst prepared in this comparative example does not contain CeO2. In the preparation method described in this invention, those skilled in the art can determine the amount of each reagent based on the molar ratio of each ion to ensure that CeO2 can be generated in the product, thereby forming Ce. δ+ -OP heterogeneous interface.
[0056] Test Example 1 The microstructure of the monolithic catalysts in each embodiment was observed using X-ray diffraction. The XRD patterns of the O2-induced CeO2-0.25CePO4-Al2O3 monolithic catalysts in Examples 3-5 at different temperatures (200 ℃, 550 ℃, 750 ℃) are shown below. Figure 1 As shown. From Figure 1 It can be seen that as the calcination temperature increases, the cubic fluorite phase of cerium dioxide remains unchanged, while cerium phosphate changes from a hexagonal phase to a monoclinic phase. This indicates that the electron configuration of the heterostructure interface of the catalyst is controllably modulated, and cerium dioxide and the weakly crystalline monoclinic cerium phosphate form a heterostructure interface Ce. δ+ -OP bond, which is most conducive to the activation of CO2 and CH3OH, thus having the best activity.
[0057] Transmission electron microscopy (TEM) was used to identify the contact state between cerium dioxide and cerium phosphate in the monolithic catalysts of each embodiment. The TEM results of Examples 3-5 are shown below. Figure 2 As shown. From Figure 2 It can be seen that O2 induction at 200 ℃ is conducive to the formation of hexagonal cerium phosphate in the shape of cerium dioxide nanospheres and nanowires, with highly uniform dispersion between the two phases, forming abundant heterogeneous interfaces. From Figure 3 It can be seen that O2 induction at 550 ℃ is conducive to the formation of spherical cerium dioxide and weakly crystalline monoclinic cerium phosphate. Aberration-corrected scanning transmission electron microscopy results show that the heterostructure is formed by the connection of the (110) crystal plane of cerium dioxide and the (120) crystal plane of cerium phosphate. Figure 4 It can be seen that O2 induction at 750 ℃ is conducive to the formation of spherical cerium dioxide and cerium phosphate with strong crystallinity monoclinic phase. The size of the spherical particles grows from 5.9 nm (O2 induction at 200 ℃) to 24.9 nm. The increase in particle size makes it difficult for the active sites of the catalyst to be exposed on the surface, thus reducing the activity.
[0058] Test Example 2 BET tests were performed on the monolithic catalysts of each embodiment, with the test results of Example 4 as follows: Figure 5 As shown. FromFigure 5 It can be seen that the O2-induced CeO2-0.25CePO4-Al2O3 monolithic catalyst at 550 ℃ exhibits a large specific surface area (59 m²). 2 ( / g), which helps to provide more activation sites for reactant molecules and promotes the reaction.
[0059] Test Example 3 The catalysts of each embodiment and comparative example were tested using X-ray photoelectron spectroscopy. The test results of Example 4 and Comparative Examples 1-2 are as follows: Figure 6 As shown. From Figure 6 It can be seen that the CeO2-Al2O3 monolithic catalyst mainly contains Ce-O bonds, the CePO4-Al2O3 monolithic catalyst mainly contains PO bonds, while the CeO2-0.25CePO4-Al2O3 monolithic catalyst of Example 4 contains a novel Ce-O bond. δ+ -OP heterogeneous interface structure.
[0060] Test Example 4 The catalysts from the above examples and comparative examples were used to directly synthesize dimethyl carbonate (DMC) from CH3OH and CO2 in a fixed-bed reactor, and the activity of each catalyst was tested. Specifically, the monolithic catalysts prepared in Examples 1-10 and Comparative Examples 11 and 12 were respectively loaded into steel tube reactors and tested at a temperature of 140 °C, a pressure of 2.4 MPa, and a space velocity of 2880 h⁻¹. -1 Under the conditions of a CO2 to CH3OH feed ratio of 20 and a CH3OH to DMP molar ratio of 30, the composition of the product was analyzed and detected online using an Agilent GC7890B gas chromatograph. The test results are shown in Table 2. Table 2 Catalyst activity test results
[0061] Note: C CH3OH S represents the methanol conversion rate. DMC For dimethyl carbonate selectivity, Y DMC The yield of dimethyl carbonate is given.
[0062] As can be seen from Table 2, the catalyst of the present invention has higher methanol conversion rate, dimethyl carbonate selectivity, and dimethyl carbonate yield than the catalyst of the comparative example. This is because the catalyst of the present invention has a unique Ce content. δ+The -O-P hetero-interface can enhance the synergistic effect of Lewis acid sites and basic sites, form electrons that can be transferred to the un-filled anti-bonding π* orbital of CO2, and reduce the activation energy of the reaction steps. The performance of the embodiment 4 is the best, because the embodiment 4 has the largest specific surface area, can provide more active sites for the reaction, and promote the reaction to proceed.
[0063] In conclusion, the present application can provide a phosphorus modified ceria catalyst with better catalytic activity. Compared with the prior art, there is a significant progress.
[0064] The above is only a representative embodiment of the present application, and does not limit the present application in any form. Any skilled person in the art can make some minor changes or modifications to the above disclosed technical content without departing from the technical solution of the present application, and the equivalent embodiments are still within the scope of the present application. Any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application are still within the scope of the present application.
Claims
1. A phosphorus-modified cerium dioxide catalyst, characterized in that, It includes cerium dioxide and cerium-phosphorus composite oxide, wherein the cerium-phosphorus composite oxide is composed of cerium ions and acid radical ions, wherein the acid radical ion is P. n O 3n+1 n+2- n is a positive integer; and the cerium dioxide and the cerium-phosphorus composite oxide form a Ce bond consisting of Ce-O bonds in the cerium dioxide and PO bonds in the cerium-phosphorus composite oxide. δ+ -OP heterogeneous interface.
2. The phosphorus-modified cerium dioxide catalyst according to claim 1, characterized in that, The molar ratio of cerium dioxide to the cerium-phosphorus composite oxide is 0.01 to 100.
3. The phosphorus-modified cerium dioxide catalyst according to claim 1, characterized in that, The cerium-phosphorus composite oxide is cerium phosphate, cerium pyrophosphate, or cerium polyphosphate.
4. The method for preparing the phosphorus-modified cerium dioxide catalyst according to any one of claims 1-3, characterized in that, Includes the following steps: S1: Prepare cerium salt solution, organic / inorganic phosphoric acid solution, and precipitant solution; S2: Mix the cerium salt solution with a portion of the precipitant solution, precipitate, then add the organic / inorganic phosphoric acid solution and dropwise add the remaining precipitant solution, continue precipitation, and obtain the precipitate product; S3: The precipitated product is dried and then calcined under atmosphere-induced conditions to obtain the phosphorus-modified cerium dioxide catalyst.
5. The method for preparing the phosphorus-modified cerium dioxide catalyst according to claim 4, characterized in that, In step S1, the solute in the cerium salt solution is any one or more of carbonates, acetates, nitrates, sulfates, and halides; The solute in the organic / inorganic phosphoric acid solution is any one or more of inorganic compounds, phosphoric acid and its salts, and organic phosphorus compounds; The solute in the precipitant solution is any one or more of urea, ammonium carbonate, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, ammonia, sodium hydroxide, and potassium hydroxide.
6. The method for preparing the phosphorus-modified cerium dioxide catalyst according to claim 5, characterized in that, The solute in the organic / inorganic phosphoric acid solution is any one or more of hypophosphoric acid, phosphorous acid, orthophosphoric acid, phosphorus trichloride, phosphorus pentachloride, diammonium hydrogen phosphate, diammonium dihydrogen phosphate, calcium phosphate, calcium pyrophosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, triphenylphosphine, and triethyl phosphate.
7. The method for preparing the phosphorus-modified cerium dioxide catalyst according to claim 4, characterized in that, In step S2, the first precipitation is carried out at 20~90 ℃ for 2~24 h; the second precipitation is carried out at 20~90 ℃ for 5~10 h; in step S3, the drying is carried out at 20~110 ℃ for 4~48 h, and the calcination is carried out under nitrogen, oxygen, carbon monoxide or carbon dioxide gas at 150~1000 ℃ for 2~8 h.
8. The method for preparing the phosphorus-modified cerium dioxide catalyst according to any one of claims 4-7, characterized in that, It also includes the step of preparing the phosphorus-modified cerium dioxide catalyst into a monolithic catalyst.
9. The method for preparing the phosphorus-modified cerium dioxide catalyst according to claim 8, characterized in that, The substrate of the monolithic catalyst is a cordierite honeycomb ceramic substrate, and the catalyst binder is Al2O3, TiO2, SiO2 or ZrO2.
10. The application of the phosphorus-modified cerium dioxide catalyst as described in any one of claims 1-3 in the synthesis of dimethyl carbonate.