Patent Application
20240399346
This application claims priority to Chinese Patent Application No. 202310642788.5, filed on Jun. 1, 2023, the contents of which are hereby incorporated by reference.
The present application belongs to the technical fields of environmental catalysis, air pollution control and flue gas denitrification catalysis, and in particular to a single-atom catalyst with molecular sieve-confined domains, and a preparation method and application thereof.
NO is a major air pollutant produced by fuel combustion in stationary and mobile sources. In recent years, NO emissions have caused various environmental problems such as acid rain, photochemical smog, ozone depletion and haze, as well as greenhouse gas emissions. Currently, Selective catalytic reduction with NH3 (NH3-SCR) is widely used for NO removal, but problems exist such as the high toxicity and corrosiveness of NH3, the reaction of NH3 with H2O and SO3 to develop ammonium sulphate, and the consumption of large amounts of fossil fuels for the synthesis of NH3.
In many catalytic reactions, it has been found that when the particle size of the active component is reduced to dispersed loading in the form of single atoms, the unique electronic structure and homogeneous active sites may substantially improve the reaction activity and product selectivity. The catalytic materials of metal with molecular sieve-confined domains give full play to the synergistic effect of metal and molecular sieve carriers to achieve the flexible regulation of the reaction microenvironment, and exhibit a wide range of applicability and excellent catalytic performance in several reactions. The synthesis of catalysts designed on the atomic scale enables a green and economical synthesis process by improving metal utilization and effectively reduces the use of metal resources, especially the cost of precious metal catalysts. However, under conventional impregnation conditions, single atoms and nanoparticles usually coexist, with nanoparticles usually having poor catalytic activity, moreover, although CO in the flue gas is used for CO-SCR and simultaneous removal of CO and NO is possible, yet CO-SCR usually has problems of low oxygen resistance, and although precious metals are the active components suitable for higher oxygen content, they usually have the problems of poor stability, low catalytic activity and poor sulphur resistance.
Therefore, it is an urgent problem for the skilled person of the art to provide a molecular sieve domain-limited single-atom catalyst and a preparation method and application thereof, so as to enhance the oxygen resistance, catalytic activity, sulphur resistance and stability of the single-atom catalyst.
In order to solve the above technical problems, the present disclosure provides a single-atom catalyst with molecular sieve-confined domains, and a preparation method and application thereof, whereby bimetallic ions are confined in a physical structure of a molecular sieve by a post-processing method or an in-situ synthesis method, the bimetallic ions are uniformly dispersed in the physical structure of the molecular sieve, and oxygen vacancies on surfaces of the precious metals and transition metals are jointly used as adsorption sites for NO, so that the catalysts show excellent catalytic activity and stability under low precious metal loading, and thus the CO-SCR reaction in oxygen-containing atmospheres achieves high denitrification efficiency and high N2 selectivity.
In order to achieve the above objectives, the present disclosure adopts the following technical scheme.
An aspect of the present disclosure provides a single-atom catalyst with molecular sieve-confined domains, where the single-atom catalyst takes a molecular sieve as a carrier and bimetallic ions as active components, and the bimetallic ions are confined in a physical structure of the molecular sieve by utilizing the physical structure and a chemical anchoring action of the molecular sieve.
The above scheme has the beneficial effects that the bimetallic ions are confined into monatomic states by using the cage or pore structure of the molecular sieve carrier, so that an electron-rich interface environment and sufficient active sites may be provided for the adsorption and dissociation of NO; meanwhile, there is a synergistic effect among the bimetallic ions, the molecular sieve carrier and bimetallic ions, so that the catalytic reaction activity and ideal product selectivity of the catalyst may be improved; and the obtained catalyst has excellent sulfur resistance, water resistance and stability, boasting a broad application prospect.
Optionally, the physical structure of the molecular sieve includes a cage or a pore structure; and the chemical anchoring action is carried out by using aluminum-rich sites of molecular sieves; and
Optionally, the molecular sieve includes one or more of type A molecular sieve with SOD and/or LTA cage structure, type X molecular sieve with super cage and/or SOD cage structure, type Y molecular sieve with super cage and/or SOD cage structure, MCM molecular sieve with super cage and cross pore structure, SAPO molecular sieve with CHA cage and cross pore structure, and ZSM molecular sieve with cross pore structure.
Optionally, the type A molecular sieve includes a 3A molecular sieve, a 4A molecular sieve and a 5A molecular sieve; the X-type molecular sieve includes a 10× molecular sieve and a 13× molecular sieve; the type Y molecular sieve includes a HY molecular sieve, a NaY molecular sieve and a USY molecular sieve; the MCM molecular sieve includes an MCM-22 molecular sieve, an MCM-41 molecular sieve and an MCM-48 molecular sieve; the SAPO molecular sieve includes an SAPO-5 molecular sieve, an SAPO-11 molecular sieve, an SAPO-34 molecular sieve, an SAPO-44 molecular sieve and an SAPO-47 molecular sieve; the ZSM molecular sieve includes a ZSM-5 molecular sieve, a ZSM-11 molecular sieve, a ZSM-12 molecular sieve, a ZSM-35 molecular sieve and a ZSM-48 molecular sieve.
Optionally, a diameter of the cage or pore structure is larger than a diameter of a reaction gas.
Optionally, the diameter of the cage or pore structure is ≥4 Å, and specifically, it is 4 Å-13 Å.
More optionally, the diameter of the cage or pore structure includes 4 Å, 5 Å, 6 Å, 7 Å, 8 Å, 9 Å, 10 Å, 11 Å, 12 Å or 13 Å.
Optionally, the reaction gas includes NO, CO, O2 and N2.
Optionally, the bimetallic ions are a combination of precious metal ions and transition metal ions.
Optionally, a loading of the precious metal ions in the single-atom catalyst is 0.1%-1%.
Optionally, a loading of the transition metal ions in the single-atom catalyst is 0.1%-10%.
Optionally, the loading is a mass fraction.
Optionally, an electronegativity of the precious metal ions is greater than that of the transition metal ions.
Optionally, an electronegativity value of the precious metal ions is 1-15.6; and an electronegativity value of the transition metal ion is 1-15.3.
Optionally, an electronegativity difference between the precious metal ions and the transition metal ions is 0.1-3, more specifically, 0.5-0.95.
Optionally, the precious metal ions include one of Ir ions, Ag ions, Pt ions, Rh ions, Pd ions, Ru ions or Au ions.
Optionally, the transition metal ions include one of W ions, Mo ions, Ce ions, Co ions, Mn ions or Cu ions.
The beneficial effects of the above preferred and optional schemes are: according to the present disclosure, the single-atom catalyst enhances NO adsorption through electron transfer between bimetallic ions and promotes d-π* orbital hybridization to improve the competitive adsorption of O2 and NO, thereby improving the catalyst's oxygen resistance and increasing the catalyst's NO conversion in CO-SCR; the adsorption of CO by transition metals promotes the transformation of N2O, NO2 and other intermediates into N2, which improves the N2 selectivity of the catalyst. At the same time, transition metals as sacrificial sites improve the sulfur resistance of the catalyst.
It is to be noted that the surface of the single-atom catalyst with molecular sieve-confined domains designed in this disclosure has rich acid sites, in which the bridging hydroxyl group (Si—OH—Al) acts as the Brønsted (B) acid site. Metal ions coordinate with O of the B acid site to achieve anchoring on the molecular sieve carrier. Meanwhile, the acidic sites are tightly coupled with metal ions with a synergistic effect, capable of increasing the selectivity (up to 90%) of the desired products for the catalytic reduction of NO by CO, in which the content of B acid sites in the acidic sites is higher than 50%.
In another aspect, the present disclosure provides a preparation method of the single-atom catalyst with molecular sieve-confined domains, and the preparation method includes a post-processing method or an in-situ synthesis method; and
The in-situ synthesis method includes the following steps: mixing a template agent, a silicon source, an aluminum source, an alkali and water according to a molar ratio of the general formula of the molecular sieve, simultaneously adding precursors of bimetallic ions and ligands, and heating in a hydrothermal kettle for a hydrothermal reaction, performing centrifugal washing and drying on precipitated molecular sieve crystals loaded with bimetallic metals, and then roasting to obtain the single-atom catalyst with molecular sieve-confined domains.
Optionally, the general formula of the molecular sieve in the post-processing method and the in-situ synthesis method is (M′2M)O·Al2O3·xSiO2·yH2O.
Optionally, in the general formula of the molecular sieve, x is a ratio of silicon to aluminum, with a value of 2-500.
Optionally, a value of y in the general formula of the molecular sieve is 50-250.
Optionally, in the post-processing method and the in-situ synthesis method:
Optionally, a pH of the template, silicon source, aluminum source, alkali and water after mixing is 10-14, optionally including but not limited to pH 10, pH 11, pH 12, pH 13 or pH 14.
Optionally, the precursors of the precious metal ions include iridium acetate and/or chloroiridium acid, silver nitrate and/or silver chloride, chloroplatinic acid and/or platinum tetraamine dinitrate, rhodium acetate and/or rhodium trichloride, palladium nitrate and/or chloroplatinic acid, ruthenium acetate and/or ruthenium chloride, gold acetate and/or chloroauric acid.
Optionally, the precursors of the transition metal ions include ammonium metatungstate and/or ammonium tungstate, ammonium molybdate, cerium nitrate, cobalt nitrate, manganese nitrate and copper nitrate.
Optionally, the precursors of the precious metal ion are configured as a solution for use with a solution concentration of 1-10 grams per liter (g/L), optionally including but not limited to 1 g/L, 2 g/L, 3 g/L, 4 g/L, 5 g/L, 6 g/L, 7 g/L, 8 g/L, 9 g/L or 10 g/L; and
Optionally, in step S1 of the post-processing method:
Optionally, in step S2 of the post-processing method:
Optionally, a rotational speed of the rotary steaming is 60-80 revolutions per minute (rpm), optionally including but not limited to 60 rpm, 65 rpm, 70 rpm, 75 rpm or 80 rpm, and more specifically the rotational speed of the rotary steaming is 80 rpm; a heating temperature is 50-60° C., optionally including but not limited to 50° C., 51° C., 52° C., 53° C., 54° C., 58° C., 59° C. or 60° C., and more specifically the heating temperature is 60° C.
Optionally, the filtration and/or centrifugation involves solvent washing, and the solvent includes ethanol.
Optionally, the method of the drying is air atmosphere drying, and the temperature of the drying is 110° C.
Optionally, the method of the activating is air atmosphere activation, and the heating rate is 5° C./min.
Optionally, the inert atmosphere activation includes a combination of one or more of N2 activation, Ar activation or He activation.
Optionally, the reducing atmosphere activation includes a combination of one or more of H2 activation, CO activation or NO activation.
The optional and preferred scheme has the beneficial effects that the molecular sieve carrier and the bimetallic ion precursors are dissolved in the solvent, so that the metal ion precursors interact with hydroxyl groups on the surface of the molecular sieve carrier to realize chemical confinement; by using the special cage or pore structure of molecular sieve, the metal ion precursors are confined, so that the metal ions are dispersed into each cage or pore structure of molecular sieve; the single atom breaks the coordination bond between metal ion precursors through the activation step, so that the metal ions coordinate with hydroxyl groups on the surface of the molecular sieve carrier, and the molecular sieve confined single atom is realized.
Optionally, in the in-situ synthesis method:
Optionally, a molar ratio of precious metal ligands to the precious metal ions is 3:1, and a molar ratio of the transition metal ligands to the transition metal ions is 2:1.
Optionally, the precious metal ligands include ethylenediamine.
Optionally, the transition metal ligands include tetraethylenepentamine.
The optional and preferred schemes have the beneficial effects that in the process of molecular sieve synthesis, an active metal precursor protected by ligand amine is introduced, and the lone pair of the N atom in the ligand amine is transferred to the active metal species to complete the interaction, so that the ligand amine separates the active metal precursor and increases the metal dispersion; as the molecular sieve synthesis solution is alkaline, the ligand amine is capable of preventing precipitation by stabilizing the metal precursor through strong interactions with the active metal, which ultimately leads to the loading of bimetallic ions on the molecular sieve.
Another aspect of the present disclosure provides an application of the single-atom catalyst with molecular sieve-confined domains prepared by the method in catalytic reduction.
Optionally, the application includes using the single-atom catalyst with molecular sieve-confined domains in a catalytic reduction of NO by CO.
Optionally, the catalytic reduction of NO by CO by using the single-atom catalyst with molecular sieve-confined domains also includes O2.
Optionally, a concentration of the O2 in the catalytic reduction of NO by CO by using the single-atom catalyst with molecular sieve-confined domains is 0%-5%.
Optionally, a temperature of the catalytic reduction of NO by CO by using the single-atom catalyst with molecular sieve-confined domains is 150-400° C., optionally including but not limited to 150° C., 175° C., 200° C., 225° C., 250° C., 275° C., 300° C., 325° C., 350° C., 375° C. or 400° C.
Optionally, a concentration of the NO in the catalytic reduction of NO by CO by using the single-atom catalyst with molecular sieve-confined domains is 100-600 parts per million (ppm), optionally including but not limited to 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm or 600 ppm, and more preferably 400 ppm.
Optionally, the application in the catalytic reduction includes an application in stationary source flue gas and/or mobile source tail gas.
Optionally, the stationary source flue gas and/or the mobile source tail gas include NO, CO and O2.
Optionally, the stationary source flue gas or the mobile source tail gas also includes one or two of SO2 or H2O.
Optionally, the single-atom catalyst with molecular sieve-confined domains is used for a selective CO catalytic reduction of NO, where a concentration of NO is 0-400 ppm, optionally including but not limited to 0 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm or 400 ppm.
Optionally, the single-atom catalyst with molecular sieve-confined domains is used for the selective CO catalytic reduction of NO, where a concentration of CO is 0-8000 ppm, optionally including but not limited to 0 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000ppm, 6000 ppm, 7000 ppm or 8000 ppm.
Optionally, the single-atom catalyst with molecular sieve-confined domains is used for the NO catalytic reduction by CO, where the concentration of the O2 is 0%-5%, optionally including but not limited to 0%, 1%, 2%, 3%, 4% or 5%.
Optionally, the single-atom catalyst with molecular sieve-confined domains is used for the selective CO catalytic reduction of NO, where a SO2 concentration is 0-20 ppm, optionally including but not limited to 0 ppm, 1 ppm, 2 ppm, 8 ppm, 10 ppm, 12 ppm, 14 ppm, 18 ppm or 20 ppm.
Optionally, the single-atom catalyst with molecular sieve-confined domains is used for the selective CO catalytic reduction of NO, where a concentration of H2O is 0-10%, optionally including but not limited to 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.
Compared with the prior art, the present disclosure has the following advantages and technical effects.
The single-atom catalyst with molecular sieve-confined domains of this disclosure enables the catalyst bimetallic ions to be dispersed as single atoms, so that the oxygen vacancies on the surfaces of the precious metal and the transition metal provide sufficient active sites for the adsorption and dissociation of NO, and the transition metal serves as a sacrificial site for the poisoning of SO2 to enhance the sulphur-resistant property of the catalyst, and at the same time, promotes the conversion of intermediates, such as N2O, NO2 and so forth, to N2. The efficient adsorption and catalytic reduction of NO by the catalyst is achieved through the synergistic effect of molecular sieves and active components.
The single-atom catalyst with molecular sieve-confined domains provided in the present disclosure makes use of the cage or pore structure of the molecular sieve, thus avoiding the weakening of the NO adsorption capacity of the B acid sites on the surface of the molecular sieve when used as the single-atom anchoring sites, and retaining the surface acidity of the molecular sieve while improving the stability of the single-atom catalyst.
In the single-atom catalyst with molecular sieve-confined domains disclosed by the present disclosure, the ZSM-5 single-atom catalyst with molecular sieve-confined domains with 0.1 wt % Ir and 5 wt % W has a catalytic reduction of NO conversion rate of 98% and N2 selectivity of 91% at 250° C. under the condition of 3% O2, suggesting a broad application prospects.
The accompanying drawings, which constitute a part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application, and do not constitute an improper limitation of this application. In the attached drawings:
The following is a clear and complete description of the technical schemes in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, but not the whole embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without creative labor belong to the scope of protection of the present disclosure.
Chloroiridic acid solution of 0.56 mL (Ir concentration of 10 g/L) and 0.134 g of ammonium metatungstate are taken and added with 100 mL of deionized water and 1.898 g of ZSM-5 molecular sieve carrier, stirred at room temperature for 2 h under the action of magnetic stirrer, and then dried under vacuum on a rotary evaporator at 60° C. and 80 rpm, and dried for 4 h in a blower dryer at 120° C. The solid blocks obtained are ground into powder and placed in a muffle furnace in an air atmosphere of 400° C. for activation for 3 h, with a heating rate of 10° C./min, and cooled to room temperature naturally to obtain the single-atom catalyst with molecular sieve-confined domain, noted as 0.1% Ir-5% W/ZSM-5 catalyst.
Among them, the structural schematic diagram of 0.1% Ir-5% W/ZSM-5 catalyst is shown in FIG. 1, where the bimetal is located on the surface of molecular sieve.
Compared with Embodiment 1, Ir is introduced in the process of molecular sieve synthesis.
The silicon and aluminum sources are prepared into two aqueous solutions, whereby 0.286 g of NaOH is weighed and added with 20 g of H2O, and 0.3274 g of NaAlO2 is added and stirred for 1 h. 0.6 g of NaOH is weighed and added with 16 g of H2O, and 5.3 g of TPABr is added, and after stirring for 15 min, 20 g of silica sol is added and stirred for 1 h.
The silicon and aluminum sources are mixed, and a mixed solution of 9.6 mL of chloroiridic acid and 10 mL of ethylenediamine ligand is added with a mixed solution of 0.4644 g of ammonium metatungstate and 2.1 mL of tetraethylenepentamine ligand, and co-stirring is carried out for 3 h. The mixed solution is transferred into a 100 mL reactor, and is hydrothermally heated at 170° C. for 32 h.
After centrifugal washing for several times, it is completely dried at 100° C. The dried solid is moved into a muffle furnace and roasted at 550° C. for 6 h at a heating rate of 1° C./min, followed by tabletting and sieving with 40-60 meshes to obtain the single-atom catalyst with molecular sieve-confined domains, which is designated as 0.1% Ir-5% W@ZSM-5 catalyst.
Among them, the structural schematic diagram of the 0.1% Ir-5% W@ZSM-5 catalyst is shown in
Chloroiridic acid solution (Ir concentration of 10 g/L) of 0.56 mL is taken, and 100 mL of deionized water and 1.998 g of ZSM-5 molecular sieve carrier are added, stirred for 2 h at room temperature under the action of magnetic stirrer, and then dried under vacuum on a rotary evaporator at 60° C. and 80 rpm, and dried for 4 h in a blower dryer at 120° C. The solid blocks obtained are ground into powder and placed in a muffle furnace in an air atmosphere of 400° C. for activation for 3 h, with a heating rate of 10° C./min, and cooled to room temperature naturally to obtain the single-atom catalyst with molecular sieve-confined domain, noted as 0.1% Ir/ZSM-5 catalyst.
Among them, the structural schematic diagram of the 0.1% Ir@ZSM-5 catalyst is shown in
Compared with Comparative embodiment 1, Ir is introduced during the synthesis of molecular sieve.
The silicon and aluminum sources are prepared into two aqueous solutions, whereby 0.286 g of NaOH is weighed and added with 20 g of H2O, and 0.3274 g of NaAlO2 is added and stirred for 1 h. 0.6 g of NaOH is weighed and added with 16 g of H2O, and 5.3 g of TPABr is added, and after stirring for 15 min, 20 g of silica sol is added and stirred for 1 h.
The silicon and aluminum sources are mixed, and a mixed solution of 8.6 mL of chloroiridic acid and 10 mL of ethylenediamine ligand is added with a mixed solution of 0.4644 g of ammonium metatungstate and 2.1 mL of tetraethylenepentamine ligand, and co-stirring is carried out for 3 h. The mixed solution is transferred into a 100 mL reactor, and is hydrothermally heated at 170° C. for 32 h.
After centrifugal washing for many times, it is completely dried at 100° C. The dried solid is moved into a muffle furnace and roasted at 550° C. for 6 h at a heating rate of 1° C./min, followed by tabletting and sieving with 40-60 meshes to obtain the single-atom catalyst with molecular sieve-confined domains, which is designated as 0.1% Ir@ZSM-5 catalyst.
Among them, the structural schematic diagram of 0.1% Ir@ZSM-5 catalyst is shown in
Compared with Comparative embodiment 1, the catalyst carrier is changed to Al2O3, and other conditions are completely the same as those of Comparative embodiment 1 to obtain the single-atom catalyst with molecular sieve-confined domains, recorded as 0.1% Ir/Al2O3.
The catalysts prepared in Embodiments 1-2 and Comparative embodiments 1-3 are tested for catalytic reduction of NO by CO, and the test method is as follows.
The composition of the simulated flue gas is as follows: the volume concentration of NO is 400 ppm, the volume concentration of CO is 8000 ppm, the volume fraction of O2 is 3%, the volume concentration of SO2 is 20 ppm, N2 is the equilibrium gas, the catalyst loading in the fixed bed reactor is 0.2 g, the airspeed in the test process is GHSV≈16,000 h−1, and the test temperatures are 225° C., 250° C. and 275° C. respectively, and each temperature is held for 1 h; the above test results are shown in Table 1, and the calculation methods of NO conversion rate (XNO) and N2 selectivity (SN2) are shown in formulas 1-1 and 1-2.
In the formulas, in represents the inflow and out represents the discharge.
The catalysts prepared in Embodiments 1-2 and Comparative embodiments 1-3 are tested for catalytic reduction of NO by CO, and the test method is as follows.
The composition of simulated flue gas is as follows: the volume concentration of NO is 400 ppm, the volume concentration of CO is 8000 ppm, the volume fraction of O2 is 3%, the volume concentration of SO2 is 20 ppm, N2 is the equilibrium gas, the catalyst loading in the fixed bed reactor is 0.2 g, the airspeed in the test process is GHSV≈16,000 h−1, and the test temperature is 250° C. The above test results are shown in Table 1. The calculation methods of NO conversion (XNO) and N2 selectivity (SN2) are the same as those in the formulas 1-1 and 1-2.
It can be seen from Table 1 that the single-atom catalyst with molecular sieve-confined domains prepared by the present disclosure is capable of significantly improving the NO conversion rate and N2 selectivity, with the NO conversion rate as high as 99.8% and N2 selectivity as high as 98.4%, indicating that the single-atom catalyst with molecular sieve-confined domains provided by the present disclosure has excellent catalytic activity and may significantly improve the ideal product selectivity of the catalyst.
From Table 2, it is observed that the single-atom catalyst with molecular sieve-confined domains provided by the present disclosure is capable of significantly improving the stability of the catalyst, enabling a maintenance of more than 94% NO conversion rate and more than 94% N2 selectivity within 24 hours of reaction, indicating that the single-atom catalyst with molecular sieve-confined domains provided by the present disclosure has excellent catalytic stability and may significantly improve the service life of the catalyst.
By comparing the data of Embodiment 1 and Embodiment 2 in the Table 1, the catalytic activity of the single-atom catalyst with molecular sieve-confined domains prepared by the post-processing method (Embodiment 1) is higher than that of the single-atom catalyst with molecular sieve-confined domains prepared by the in-situ synthesis method (Embodiment 2).
The stability of the single-atom catalyst with molecular sieve-confined domains prepared by the in-situ synthesis method (Embodiment 2) is higher than that of the single-atom catalyst with molecular sieve-confined domains prepared by the post-processing method (Embodiment 1), as may be seen from the comparison of the data of Embodiment 1 and Embodiment 2 in Table 2.
The above describes only the preferred embodiments of this application, but the protection scope of this application is not limited to this. Any change or replacement that may be easily thought of by a person familiar with this technical field within the technical scope disclosed in this application should be included in the protection scope of this application. Therefore, the protection scope of this application should be based on the protection scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202310642788.5 | Jun 2023 | CN | national |
