SINGLE-ATOM CATALYST WITH MOLECULAR SIEVE-CONFINED DOMAINS, PREPARATION METHOD AND APPLICATION THEREOF

Abstract

A single-atom catalyst with molecular sieve-confined domains and a preparation method and application thereof are provided in the present disclosure. According to the present disclosure, the physical structure and chemical anchoring action of the molecular sieve are utilized to confine the bimetallic ions, so that the bimetallic ions of the catalyst are dispersed in single atoms, electrons in the bimetallic ions are transferred from transition metals to precious metals to promote d-* orbital hybridization to enhance NO adsorption, and an electron-rich environment and sufficient active sites are provided for NO adsorption and dissociation in the CO-SCR reaction; the transition metals adsorb CO to promote the transformation of N.sub.2O, NO.sub.2 and other intermediates into N.sub.2, and the transition metal serves as a sacrificial site for the poisoning of SO.sub.2 to enhance the sulphur-resistant property of the catalyst.

Claims

1. A single-atom catalyst with molecular sieve-confined domains, wherein the single-atom catalyst takes a molecular sieve as a carrier and bimetallic ions as active components, and the bimetallic ions are confined in the physical structure of the molecular sieve by utilizing a physical structure and a chemical anchoring action of the molecular sieve.

2. The single-atom catalyst with molecular sieve-confined domains according to claim 1, wherein the physical structure of the molecular sieve comprises a cage or a pore structure; the chemical anchoring action is carried out by using aluminum-rich sites of molecular sieves.

3. The single-atom catalyst with molecular sieve-confined domains according to claim 1, wherein the bimetallic ions are a combination of precious metal ions and transition metal ions.

4. The single-atom catalyst with molecular sieve-confined domains according to claim 3, wherein an electronegativity of the precious metal ions is greater than an electronegativity of the transition metal ions.

5. The single-atom catalyst with molecular sieve-confined domains according to claim 3, wherein a loading of the precious metal ions in the single-atom catalyst is 0.1%-1%, and a loading of the transition metal ions in the single-atom catalyst is 0.1%-10%.

6. A preparation method of the single-atom catalyst with molecular sieve-confined domains according to claim 1, wherein the preparation method comprises a post-processing method or an in-situ synthesis method; the post-processing method comprises: mixing precursors of the molecular sieve and the bimetallic ions with a solvent for a reaction, carrying out solid-liquid separation on a reaction product, collecting and drying a solid, and activating the solid after drying to obtain the single-atom catalyst with molecular sieve-confined domains; and the in-situ synthesis method comprises: mixing a template agent, a silicon source, an aluminum source, alkali and water according to a molar ratio of a general formula of a molecular sieve, simultaneously adding precursors of the 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.

7. The preparation method according to claim 6, wherein in the post-processing method and the in-situ synthesis method: the general formula of the molecular sieve is (M2M)O.Math.Al.sub.2O.sub.3.Math.xSiO.sub.2.Math.yH.sub.2O; in the general formula of the molecular sieve, x is a ratio of silicon to aluminum, with a value of 2-500; and a value of y in the general formula of the molecular sieve is 50-250; and the precursors of the bimetallic ions comprise precursors of precious metal ions and precursors of transition metal ions; the precursors of the precious metal ions comprise 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; and the precursors of the transition metal ions comprise ammonium metatungstate and/or ammonium tungstate, ammonium molybdate, cerium nitrate, cobalt nitrate, manganese nitrate and copper nitrate.

8. The preparation method according to claim 6, wherein in the post-processing method: the solvent is water, a temperature of the reaction is 25-100 degrees Celsius, a duration is 2-6 hours, a pH value is 6-8; a method of the solid-liquid separation comprise filtration, rotary steaming and/or centrifugation; a method of the drying comprises one or a combination of vacuum drying or air atmosphere drying; a temperature of the drying is 100-120 degrees Celsius; a method of the activating includes any one or a combination of at least two of vacuum activation, air atmosphere activation, inert atmosphere activation or reducing atmosphere activation; a temperature of the activating is 350-600 degrees Celsius, a heating rate is 2-10 degrees Celsius per minutes, with a duration of 1-8 hours.

9. The preparation method according to claim 6, wherein the template agent comprises one of tetramethylammonium hydroxide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide and cetyltrimethylammonium bromide; the silicon source comprises one of water glass, silica sol, silica gel, amorphous SiO.sub.2 powder and Si(OCH.sub.3).sub.4, Si(OC.sub.2H.sub.5).sub.4; the aluminum source comprises one of sodium metaaluminate, boehmite, pseudo-boehmite, amorphous aluminum hydroxide powder and aluminum isopropoxide; the alkali comprises one of sodium hydroxide and potassium hydroxide; the ligands comprise precious metal ligands and transition metal ligands; the precious metal ligand comprises ethylenediamine; the transition metal ligand comprises tetraethylenepentamine; a temperature of the hydrothermal reaction is 80-200 degrees Celsius, with a duration of 4-72 hours; a time of the centrifugal washing is more than two times, solvents of the centrifugal washing are water and ethanol; a method for the drying is oven drying; a temperature of the roasting 400-600 degrees Celsius, with a heating rate of 1 degrees Celsius per minutes-10 degrees Celsius per minutes and a duration of 2-6 hours.

10. An application of the single-atom catalyst with molecular sieve-confined domains according to claim 1 in catalytic reduction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] 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:

[0102] FIG. 1 is a schematic structural diagram of a single-atom catalyst with molecular sieve-confined domains prepared in Embodiment 1.

[0103] FIG. 2 is a schematic structural diagram of the single-atom catalyst with molecular sieve-confined domains prepared in Embodiment 2.

[0104] FIG. 3 is a schematic structural diagram of the single-atom catalyst with molecular sieve-confined domains prepared in Comparative embodiment 1.

[0105] FIG. 4 is a schematic structural diagram of the single-atom catalyst with molecular sieve-confined domains prepared in Comparative embodiment 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0106] 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.

Embodiment 1

Preparation of 0.1% Ir-5% W/ZSM-5 Single-Atom Catalyst With Molecular Sieve-Confined Domains

[0107] 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.

[0108] 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.

Embodiment 2

Preparation of 0.1% Ir-5% W@ZSM-5 Single-Atom Catalyst With Molecular Sieve-Confined Domains

[0109] Compared with Embodiment 1, Ir is introduced in the process of molecular sieve synthesis.

[0110] 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 H.sub.2O, and 0.3274 g of NaAlO.sub.2 is added and stirred for 1 h. 0.6 g of NaOH is weighed and added with 16 g of H.sub.2O, 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.

[0111] 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.

[0112] 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.

[0113] Among them, the structural schematic diagram of the 0.1% Ir-5% W@ZSM-5 catalyst is shown in FIG. 2, and the bimetal is located inside the molecular sieve.

Comparative Embodiment 1

Preparation of 0.1% Ir/ZSM-5 Single-Atom Catalyst With Molecular Sieve-Confined Domains

[0114] 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.

[0115] Among them, the structural schematic diagram of the 0.1% Ir@ZSM-5 catalyst is shown in FIG. 3, and the single metal is located on the surface of molecular sieve.

Comparative Embodiment 2

Preparation of 0.1% Ir@ZSM-5 Single-Atom Catalyst With Molecular Sieve-Confined Domains

[0116] Compared with Comparative embodiment 1, Ir is introduced during the synthesis of molecular sieve.

[0117] 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 H.sub.2O, and 0.3274 g of NaAlO.sub.2 is added and stirred for 1 h. 0.6 g of NaOH is weighed and added with 16 g of H.sub.2O, 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.

[0118] 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.

[0119] 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.

[0120] Among them, the structural schematic diagram of 0.1% Ir@ZSM-5 catalyst is shown in FIG. 4, and the single metal is located inside the molecular sieve.

Comparative Embodiment 3

[0121] Compared with Comparative embodiment 1, the catalyst carrier is changed to Al.sub.2O.sub.3, 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/Al.sub.2O.sub.3.

[0122] FIG. 1 and FIG. 3 schematically show that the single-metal/bimetal is located on the surface of molecular sieve in the catalyst synthesized by post-processing; while FIG. 2 and FIG. 4 schematically show that the single-metal/bimetal of the catalyst synthesized by in-situ synthesis is located inside the molecular sieve.

Performance Test

Activity Test of Catalytic Reduction of NO by CO

[0123] 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.

[0124] 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 O.sub.2 is 3%, the volume concentration of SO.sub.2 is 20 ppm, N.sub.2 is the equilibrium gas, the catalyst loading in the fixed bed reactor is 0.2 g, the airspeed in the test process is GHSV16,000 h.sup.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 (X.sub.NO) and N.sub.2 selectivity (S.sub.N2) are shown in formulas 1-1 and 1-2.

[00001]$\begin{array}{cc}{X}_{\mathrm{NO}}=\left[1-\frac{\mathrm{NO}\left(\mathrm{out}\right)}{\mathrm{NO}\left(\mathrm{in}\right)}\right]100\%& \left(1-1\right)\end{array}$$\begin{array}{cc}{S}_{N_2}=\frac{\left[\mathrm{NO}\left(\mathrm{in}\right)-\mathrm{NO}\left(\mathrm{out}\right)\right]-2N_{2}O\left(\mathrm{out}\right)-{\mathrm{NO}}_2\left(\mathrm{out}\right)}{\mathrm{NO}\left(\mathrm{in}\right)-\mathrm{NO}\left(\mathrm{out}\right)}100\%& \left(1-2\right)\end{array}$

[0125] In the formulas, in represents the inflow and out represents the discharge.

TABLE-US-00001 TABLE 1 Embodiment Embodiment Comparative Comparative Comparative 1 2 embodiment 1 embodiment 2 embodiment 3 225 C. NO 68.3 64.8 48.9 43.8 1.5 conversion rate (%) N.sub.2 62.4 61.2 61.7 56.5 4.6 selectivity (%) 250 C. NO 98.3 93.4 92.8 90.5 91.3 conversion rate (%) N.sub.2 96.1 91.2 80.6 73.3 10.1 selectivity (%) 275 C. NO 99.8 95.9 94.4 92.4 12.4 conversion rate (%) N.sub.2 98.4 96.7 96.7 95.2 12.3 selectivity (%) 300 C. NO 98.8 96.5 95.6 93.9 12.4 conversion rate (%) N.sub.2 97.1 95.3 93.4 92.5 12.3 selectivity (%)

Stability Test of Catalytic Reduction of NO by CO

[0126] 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.

[0127] 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 O.sub.2 is 3%, the volume concentration of SO.sub.2 is 20 ppm, N.sub.2 is the equilibrium gas, the catalyst loading in the fixed bed reactor is 0.2 g, the airspeed in the test process is GHSV16,000 h.sup.1, and the test temperature is 250 C. The above test results are shown in Table 1. The calculation methods of NO conversion (X.sub.NO) and N.sub.2 selectivity (S.sub.N2) are the same as those in the formulas 1-1 and 1-2.

TABLE-US-00002 TABLE 2 Embodiment Embodiment Comparative Comparative Comparative 1 2 embodiment 1 embodiment 2 embodiment 3 6 h NO 95.7 94.7 92.6 91.2 12.3 conversion rate (%) N.sub.2 selectivity 98.8 95.6 80.1 94.3 11.2 (%) 12 NO 95.3 94.5 92.5 90.9 10.3 h conversion rate (%) N.sub.2 selectivity 97.9 95.2 79.8 93.8 10.6 (%) 18 NO 80.3 93.9 71.5 90.1 9.5 h conversion rate (%) N.sub.2 selectivity 85.6 95.3 65.2 91.5 8.4 (%) 24 NO 76.8 94.0 70.3 90.2 8.2 h conversion rate (%) N.sub.2 selectivity 81.0 95.1 63.1 89.9 6.5 (%)

Experimental Results:

[0128] 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 N.sub.2 selectivity, with the NO conversion rate as high as 99.8% and N.sub.2 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.

[0129] 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% N.sub.2 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.

[0130] 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).

[0131] 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.

[0132] 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.