Supported iso-diatomic catalyst as well as preparation method and application thereof

Abstract

The invention relates to a supported iso-diatomic catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The supported iso-diatomic catalyst comprises a carrier and metal diatoms supported on the carrier, the carrier is selected from a ZSM-5 type molecular sieve, a TS-1 type titanium silicalite molecular sieve or MOR type mordenite; the metal diatoms include iron and zinc. By optimizing and improving factors such as the ratio of iron to zinc, the pH value of a precursor solution, the reaction temperature, the calcination temperature and time and the like in the synthesis process of the supported heterodiatomic catalyst, uniform loading of iron and zinc heterodiatoms on the surface of a carrier is realized, and clustering of metal atoms is prevented. According to the supported iso-diatomic catalyst, a diatomic active center is constructed on the atomic scale, the high activity that the yield of acetic acid prepared by catalytic oxidation of methane by using molecular oxygen as an oxidizing agent under the conditions of room temperature (25 DEG C) and normal pressure (1bar) reaches 3040 [mu] mol.gcat <-1 >. H <-1 > is realized, and meanwhile, the selectivity of a single product of acetic acid reaches 81%.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a supported heterodiatom catalyst and a preparation method and application thereof. Background Art

[0002] The efficient catalytic conversion of methane (the main component of natural gas, etc.) to produce high-value-added chemicals such as acetic acid is an important direction for achieving efficient utilization of fossil resources. In particular, multi-carbon products such as acetic acid, as important raw materials for bulk chemicals, can be used to manufacture a variety of organic products such as acetic anhydride, acetate and cellulose acetate, and are one of the ideal products for direct oxidation of methane. However, due to the extremely high CH bond activation energy (439 kJ / mol) and low polarizability caused by the tetragonal symmetry of the methane molecule, it is difficult to balance low reaction temperature and high activity. Therefore, harsh reaction conditions such as high temperature (≥400°C) are usually required to effectively activate the first CH bond of methane. Under the above harsh reaction conditions, products such as acetic acid tend to be converted into thermodynamically more stable over-oxidation products such as CO2. Therefore, expensive hydrogen peroxide (H2O2) is often used as an oxidant for catalytic oxidation of methane to reduce the reaction temperature and improve the selectivity of reaction products. However, unlike hydrogen peroxide (H2O2), using oxygen (O2) as an oxidant is not only more economically valuable, but also more environmentally friendly and safe in production process. However, how to directly activate methane using oxygen as an oxidant at low temperatures and regulate its reaction performance is extremely challenging. Summary of the invention

[0003] To this end, the technical problem to be solved by the present invention is to overcome the problems of too high reaction temperature, too expensive oxidant, poor activity and selectivity in the prior art of catalytic oxidation of methane to produce high-value oxygen-containing compounds such as acetic acid.

[0004] In order to solve the above technical problems, the present invention provides a supported heterodiatom catalyst and a preparation method and application thereof.

[0005] The first object of the present invention is to provide a method for preparing a supported hetero-diatom catalyst, comprising the following steps:

[0006] S1, dissolving iron salt in water, adjusting the pH to 1-5, to obtain an iron salt solution;

[0007] Dissolving zinc salt in water and adjusting the pH to 2-6 to obtain a zinc salt solution;

[0008] S2. Dispersing the molecular sieve carrier uniformly in water by ultrasonic vibration, adjusting the pH to 2-5, and obtaining a carrier solution;

[0009] S3. Add the iron salt solution and zinc salt solution described in S1 dropwise to the carrier solution described in S2, react at 0°C-15°C under ultraviolet irradiation, and obtain the supported heterodiatom catalyst by centrifugal washing, drying and calcining.

[0010] In one embodiment of the present invention, in S1, the iron salt is selected from ferric chloride and / or ferric nitrate; the zinc salt is selected from zinc chloride and / or zinc nitrate.

[0011] In one embodiment of the present invention, in S1, by adjusting the pH, Fe 3+ and Zn 2+ The ion hydrolysis generates nanoparticles, so that both Fe and Zn species are uniformly loaded onto the molecular sieve support in atomic form.

[0012] In one embodiment of the present invention, in S1, the concentrations of the iron salt solution and the zinc salt solution are independently 0.01 mmol / L-0.1 mmol / L. Separately preparing the metal solutions can, on the one hand, more conveniently control the ratio of the metals; on the other hand, it can also avoid uneven distribution of the two metals loaded on the molecular sieve carrier.

[0013] In one embodiment of the present invention, in S2, the molecular sieve carrier is selected from zeolite molecular sieve, mordenite or titanium silicon molecular sieve; the silicon-aluminum ratio or silicon-titanium ratio of the molecular sieve carrier is 12.5-150.

[0014] In one embodiment of the present invention, in S2, the dripping rate is 0.1 mL / min-0.5 mL / min.

[0015] In one embodiment of the present invention, in S3, the wavelength of the ultraviolet irradiation is 200nm-400nm, and the power is 5W-20W; the drying is performed at 40℃-60℃ for 10h-14h; and the calcination is performed at 300℃-350℃ for 2h-4h under a protective atmosphere.

[0016] In one embodiment of the present invention, in S3, the mass proportion of iron element and zinc element in the supported hetero-diatom catalyst is 0.5%-1.5%, and the mass ratio of iron element to zinc element is 1:3-3:1.

[0017] The second object of the present invention is to provide a supported heterodiatom catalyst prepared by the method described above.

[0018] The third object of the present invention is to provide an application of the supported hetero-diatomic catalyst in the catalytic oxidation of methane to prepare acetic acid, which specifically comprises the following steps: introducing methane and oxygen into a reactor containing a supported hetero-diatomic catalyst solution, reacting under light conditions, and obtaining acetic acid.

[0019] In one embodiment of the present invention, the wavelength of the light is 220nm-1100nm; the concentration of the supported hetero-diatomic catalyst solution is 0.05mg / mL-0.2mg / mL; the flow rate of the oxygen is 5mL / min-30mL / min; the flow rate ratio of the methane and the oxidant is (0.5-5):1.

[0020] In one embodiment of the present invention, the reaction temperature is 20°C-35°C, the reaction time is 1h-24h, and the pressure is 1 bar.

[0021] The principle of the present invention is that the active site Z[Fe-O-Zn] of the supported hetero diatomic catalyst of the present invention 2+ The unique geometric configuration and electronic state enable O* formed by light-assisted activation of oxygen O=O bonds (5.2 eV) to be stably adsorbed on iron sites, ultimately generating Z[O=Fe-(μ-O)2-Zn] 2+ The special active oxygen species α-O (Fe=O) on the active center. The electronic interaction between Fe and Zn makes the O species in Fe=O in a unique O - The free radical electronic state (-0.41|e|) makes it very easy to capture hydrogen protons in methane through hydrogen abstraction reaction to activate CH bonds of methane, which is the key to the high activity of the catalyst. Specifically, the first CH bond activation of CH4 is activated by α-O (Fe=O) adsorbed on the unit site iron through a free radical mechanism to generate a methyl radical CH3·, and this process only needs to overcome a 0.40eV free energy barrier. Then, the generated methyl radical CH3· is further captured by the bridging oxygen μ-O to finally generate CH3O*, and the process releases heat of 2.33eV. Subsequently, it overcomes a 0.67eV free energy barrier to dehydrogenate to the hydroxyl adsorbed on iron to generate methyleneoxy CH2O*, and then the methyleneoxy CH2O* is transferred to zinc. Subsequently, oxygen adsorption and dissociation reactivate the active site on iron, and the first CH bond activation of another CH4 is activated by α-O (Fe=O) adsorbed on the unit site iron through a free radical mechanism to overcome a 0.56eV free energy barrier to generate a methyl radical CH3·. Then, the generated methyl radical CH3· is further captured by the methyleneoxy CH2O* to generate CH3CH2O*, and the process releases heat of 0.61eV. Subsequently, CH3CH2O* overcomes the 0.58eV free energy barrier to dehydrogenate to μ-O to generate CH3CHO*, and then CH3CHO* overcomes the 0.60eV free energy barrier to dehydrogenate to another μ-O to finally generate CH3CO*. At this time, the intermediate state is Z[(HO)Fe(μ-OH)2Zn(CH3CO)] 2+Then, the H of one μ-OH transfers to another μ-OH with a free energy barrier of 0.69 eV and generates H2O which desorbs. The intermediate structure is Z[(OH)-Fe(μ-O)Zn(CH3CO)] 2+ Finally, CH3CO* and OH* couple to overcome the 0.86eV free energy barrier to generate the product acetic acid CH3COOH. Then CH3COOH desorbs and regenerates Z[Fe-(μ-O)-Zn] 2+ Active center. The catalytic principle of this catalyst lies in the strong electronic interaction between Fe-Zn heteroatoms, which enables O* generated by light-assisted activation of oxygen O=O double bonds to be stably adsorbed on the iron site to generate Z[O=Fe-(μ-O)2-Zn] 2+ The special active oxygen species Fe=O on the active center regulates the electronic state structure of the oxygen species to make it in a unique O - Free radical state, then through the active site Z[O=Fe-(μ-O)2-Zn] 2+ The special active oxygen species (Fe=O) on the surface achieves efficient activation of methane.

[0022] The technical solution of the present invention has the following advantages over the prior art:

[0023] (1) The unique spatial configuration and electronic structure of the supported heterodiatom catalyst of the present invention make the catalytic reaction highly active and highly selective, and can maximize the atomic utilization efficiency and reduce the cost of the catalyst.

[0024] (2) The supported heterodiatom catalyst of the present invention achieves a yield of 3040 μmol·g of acetic acid by catalytic oxidation of methane using molecular oxygen as an oxidant at room temperature (25°C) and atmospheric pressure (1 bar) by constructing diatomic active centers at the atomic scale. cat -1 ·h -1 The single product selectivity of acetic acid reached 81%.

[0025] (3) The supported hetero-diatom catalyst of the present invention has a unique diatomic active site. By introducing light as an energy source in a normal pressure photocatalytic reactor, the O=O double bond of oxygen can be effectively activated to generate active oxygen species (Fe=O), so that methane molecules can be efficiently activated at the diatomic site and migrate to the adjacent Zn atom to promote CC bond coupling, thereby highly selectively generating multi-carbon high-value oxygen-containing compound acetic acid. The directional conversion of methane to high-value-added product acetic acid is achieved, opening up a frontier road for sustainable energy and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a transmission electron microscopy image of Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0028] Figure 2 X-ray photoelectron absorption spectra of the 2p orbital of the iron element in the Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention and the Fe1 / ZSM-5 prepared in Comparative Example 2;

[0029] Figure 3 X-ray photoelectron absorption spectra of the 2p orbital of zinc element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention and Zn1 / ZSM-5 prepared in Comparative Example 3;

[0030] Figure 4 The local coordination environment of the Fe-Zn atomic pair in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0031] Figure 5 The extended X-ray absorption fine structure spectrum of the iron element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0032] Figure 6 The extended X-ray absorption fine structure spectrum of zinc element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0033] Figure 7 Fitting of EXAFS data of iron element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0034] Figure 8 EXAFS data fitting of zinc element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0035] Fig. 9 The extended X-ray absorption near-edge structure spectrum of the iron element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0036] Fig.10 The extended X-ray absorption near-edge structure spectrum of zinc element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0037] Fig.11 The Bader charge analysis spectrum of the iron element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0038] Fig.12 The Bader charge analysis spectrum of the zinc element in Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention;

[0039] Fig.13 Schematic diagram of the 3d orbital energy of the iron element in the Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention and the Fe1 / ZSM-5 prepared in Comparative Example 2;

[0040] Fig.14 This is a test of the cyclic stability of methane catalysis by Fe1-Zn1 / ZSM-5 prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0042] In the present invention, unless otherwise specified, the application tests of supported single-atom catalysts are all carried out in an atmospheric pressure autoclave reactor.

[0043] In the present invention, unless otherwise specified, the mass percentage of metal atoms in the supported single-atom catalyst is abbreviated as wt.%.

[0044] Example 1

[0045] The supported heterodiatom catalyst and the preparation method thereof of the present invention specifically comprise the following steps:

[0046] S1. Preparation of metal precursor solution: at 10°C, dissolve 12.0 mg of ferric chloride hexahydrate in 18.2 MΩ ultrapure water, adjust the pH value to 1.2 with hydrochloric acid, and obtain a ferric chloride solution with a concentration of 0.05 mmol / L; at 10°C, dissolve 5.2 mg of zinc chloride in 18.2 MΩ ultrapure water, adjust the pH value to 4.5 with hydrochloric acid, and obtain a zinc chloride solution with a concentration of 0.05 mmol / L;

[0047] S2. Preparation of carrier solution: 0.5 g of zeolite molecular sieve ZSM-5 (abbreviated as ZSM-5 (25)) with a silicon-aluminum ratio of 25 was dispersed in 18.2 MΩ ultrapure water, the pH value was adjusted to 3.5 with hydrochloric acid, and ultrasonic vibration was performed for 20 minutes to improve the dispersion in the solution to obtain a carrier solution.

[0048] S3. The above two metal precursor solutions are added to the above carrier solution at the same time by the peristaltic pump micro-injection method (rate of 0.25 mL / min), and the carrier solution is irradiated with ultraviolet light (254 nm, 5 W LED), and the temperature of the carrier solution is controlled at 5±2°C using an ice bag, so that the iron and zinc hetero-diatoms are evenly dispersed on the surface of ZSM-5. Then, the mixture is centrifuged and washed three times, vacuum dried at 60°C for 12 h, and calcined at 350°C in an argon atmosphere for 3 h to obtain a loaded hetero-diatom catalyst, i.e., ZSM-5 (25) loaded with Fe-Zn hetero-diatom catalyst (the iron loading is 0.5 wt.%, and the zinc loading is 0.5 wt.%), recorded as Fe1-Zn1 / ZSM-5.

[0049] Example 2

[0050] The method is basically the same as Example 1, except that ZSM-5(25) is replaced by ZSM-5(12.5) to obtain a supported hetero-diatom catalyst, i.e., ZSM-5(12.5) supported Fe-Zn hetero-diatom catalyst, denoted as Fe1-Zn1 / ZSM-5.

[0051] Example 3

[0052] The method is basically the same as Example 1, except that ZSM-5(25) is replaced by ZSM-5(80) to obtain a supported hetero-diatom catalyst, i.e., ZSM-5(80) supported Fe-Zn hetero-diatom catalyst, denoted as Fe1-Zn1 / ZSM-5.

[0053] Example 4

[0054] The method is basically the same as Example 1, except that ZSM-5(25) is replaced by ZSM-5(150) to obtain a supported hetero-diatom catalyst, i.e., ZSM-5(150) supported Fe-Zn hetero-diatom catalyst, denoted as Fe1-Zn1 / ZSM-5.

[0055] Example 5

[0056] The method is basically the same as Example 1, except that the concentration of the ferric chloride solution is replaced by 0.025 mmol / L, the concentration of the zinc chloride solution is replaced by 0.075 mmol / L, and the loaded hetero-diatom catalyst, i.e., ZSM-5 (25) loaded Fe-Zn hetero-diatom catalyst (the iron loading is 0.25 wt.%, and the zinc loading is 0.75 wt.%), is denoted as Fe1-Zn1 / ZSM-5.

[0057] Example 6

[0058] The method is basically the same as Example 1, except that the concentration of the ferric chloride solution is replaced by 0.075 mmol / L, the concentration of the zinc chloride solution is replaced by 0.025 mmol / L, and the loaded hetero-diatomic catalyst, i.e., ZSM-5 (25) loaded Fe-Zn hetero-diatomic catalyst (the iron loading is 0.75 wt.%, and the zinc loading is 0.25 wt.%), is denoted as Fe1-Zn1 / ZSM-5.

[0059] Example 7

[0060] The method is basically the same as Example 1, except that ZSM-5(25) is replaced by mordenite MOR (abbreviated as MOR(30)) with a silicon-aluminum ratio of 30 to obtain a supported hetero-diatom catalyst, i.e., MOR(30) supported Fe-Zn hetero-diatom catalyst, denoted as Fe1-Zn1 / MOR.

[0061] Example 8

[0062] The method is basically the same as Example 1, except that ZSM-5(25) is replaced by titanium silicon molecular sieve TS-1 (abbreviated as TS-1(30)) with a silicon-titanium ratio of 30 to obtain a supported hetero-diatom catalyst, i.e., TS-1(30) supported Fe-Zn hetero-diatom catalyst, recorded as Fe1-Zn1 / TS-1.

[0063] Comparative Example 1

[0064] Pure ZSM-5 (25) was used as the catalyst.

[0065] Comparative Example 2

[0066] The method is basically the same as Example 1, except that no zinc chloride solution is added, and a supported single-atom catalyst is obtained, namely, ZSM-5 (25) supported Fe single-atom catalyst (the iron loading is 0.5 wt.%), which is recorded as Fe1 / ZSM-5.

[0067] Comparative Example 3

[0068] The method is basically the same as Example 1, except that no ferric chloride solution is added, and a supported single-atom catalyst is obtained, namely, ZSM-5 (25) supported Zn single-atom catalyst (the zinc loading is 0.5 wt.%), recorded as Zn1 / ZSM-5.

[0069] Comparative Example 4

[0070] The method is basically the same as Example 1, except that ferric chloride hexahydrate is replaced by cupric chloride dihydrate to obtain a supported hetero-diatom catalyst, i.e., ZSM-5 (25) supported Cu-Zn hetero-diatom catalyst (copper loading is 0.5 wt.%, zinc loading is 0.5 wt.%), recorded as Cu1-Zn1 / ZSM-5.

[0071] Comparative Example 5

[0072] The method is basically the same as Example 1, except that ZSM-5 (25) is replaced by nano-silicon dioxide to obtain a supported hetero-diatom catalyst, namely, SiO2-supported Fe-Zn hetero-diatom catalyst, denoted as Fe1-Zn1 / SiO2.

[0073] Comparative Example 6

[0074] The method is basically the same as Example 1, except that ZSM-5 (25) is replaced by nano-alumina to obtain a supported hetero-diatom catalyst, namely, Al2O3-supported Fe-Zn hetero-diatom catalyst, denoted as Fe1-Zn1 / Al2O3.

[0075] Comparative Example 7

[0076] The method is basically the same as Example 1, except that ZSM-5 (25) is replaced by nano-titanium oxide to obtain a supported hetero-diatom catalyst, namely, TiO2-supported Fe-Zn hetero-diatom catalyst, denoted as Fe1-Zn1 / TiO2.

[0077] Application Example 1

[0078] 0.020 g of the catalyst prepared in Example 1 was dispersed in 100 mL of ultrapure water solution, and then the reactor was sealed. After purging the reactor with argon for 30 min, methane (flow rate of 20 mL / min) and oxygen (flow rate of 10 mL / min) were directly introduced into the catalyst solution. At the same time, a mercury vapor lamp with a wavelength of 220 nm-1100 nm was turned on to irradiate the reactor, and the reactor temperature was controlled at 25 ° C with circulating condensed water to start the reaction. The reaction time was 1 h.

[0079] The gas phase products (CH4, CO, CO2) were analyzed by gas chromatograph (Agilent GC-2060) with a methane reformer, and the liquid phase products (CH3OH, HCOOH, CH3COOH, CH3COCH3) were analyzed by nuclear magnetic resonance (NMR) spectrometer (BRUKER 400MHz). The acetic acid yield was 2039 μmol·g cat -1 ·h -1 , with a selectivity of 77%.

[0080] Application Example 2

[0081] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 2 was used to carry out the reaction, and the acetic acid yield was 1889 μmol·g cat -1 ·h -1 , with a selectivity of 70%.

[0082] Application Example 3

[0083] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 3 was used to carry out the reaction, and the yield of acetic acid was 1608 μmol·g cat -1 ·h -1 , with a selectivity of 75%.

[0084] Application Example 4

[0085] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 4 was used to carry out the reaction, and the yield of acetic acid was 1447 μmol·g cat -1 ·h -1 , with a selectivity of 74%.

[0086] Application Example 5

[0087] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 5 was used to carry out the reaction, and the yield of acetic acid was 1086 μmol·g cat -1 ·h -1 , with a selectivity of 73%.

[0088] Application Example 6

[0089] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 6 was used to carry out the reaction, and the yield of acetic acid was 882 μmol·g cat -1 ·h -1 , with a selectivity of 70%.

[0090] Application Example 7

[0091] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 7 was used to carry out the reaction, and the yield of acetic acid was 734 μmol·g cat -1 ·h -1 , with a selectivity of 72%.

[0092] Application Example 8

[0093] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 8 was used to carry out the reaction, and the yield of acetic acid was 1355 μmol·g cat -1 ·h -1 , with a selectivity of 74%.

[0094] Application Example 9

[0095] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 1 was used for the reaction, the reactor temperature was adjusted to 20°C, and the yield of acetic acid was 1783 μmol·g cat -1 ·h -1 , with a selectivity of 79%.

[0096] Application Example 10

[0097] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 1 was used for the reaction, and the reactor temperature was adjusted to 30°C. The yield of acetic acid was 2282 μmol·g cat -1 ·h -1 , with a selectivity of 72%.

[0098] Application Example 11

[0099] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 1 was used for the reaction, the reactor temperature was adjusted to 35°C, and the yield of acetic acid was 2473 μmol·g cat -1 ·h -1 , with a selectivity of 71%.

[0100] Application Example 12

[0101] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 1 was used for the reaction, the methane flow rate was adjusted to 13.4 mL / min, and the oxygen flow rate was adjusted to 26.6 mL / min. The yield of acetic acid was 1673 μmol·g cat -1 ·h -1 , with a selectivity of 71%.

[0102] Application Example 13

[0103] The reaction was basically the same as in Application Example 1, except that the catalyst prepared in Example 1 was used for the reaction, the methane flow rate was adjusted to 26.6 mL / min, and the oxygen flow rate was adjusted to 13.4 mL / min. The yield of acetic acid was 2367 μmol·g cat -1 ·h -1 , with a selectivity of 78%.

[0104] Application Example 14

[0105] The reaction was basically the same as in Application Example 1, except that the catalyst prepared in Example 1 was used for the reaction, the methane flow rate was adjusted to 30 mL / min, and the oxygen flow rate was adjusted to 10 mL / min. The yield of acetic acid was 2011 μmol·g cat -1 ·h-1 , with a selectivity of 79%.

[0106] Application Example 15

[0107] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 1 was used for the reaction, the methane flow rate was adjusted to 33.3 mL / min, and the oxygen flow rate was adjusted to 16.7 mL / min. The yield of acetic acid was 1267 μmol·g cat -1 ·h -1 , with a selectivity of 76%.

[0108] Application Example 16

[0109] The reaction was basically the same as in Application Example 1, except that the catalyst prepared in Example 1 was used for the reaction, the methane flow rate was adjusted to 10 mL / min, and the oxygen flow rate was adjusted to 5 mL / min. The yield of acetic acid was 1491 μmol·g cat -1 ·h -1 , with a selectivity of 76%.

[0110] Application Example 17

[0111] The reaction was basically the same as in Example 1, except that the catalyst prepared in Example 1 was used for the reaction, the methane flow rate was adjusted to 50 mL / min, and the oxygen flow rate was adjusted to 25 mL / min. The yield of acetic acid was 3040 μmol·g cat -1 ·h -1 , with a selectivity of 81%.

[0112] Application Example 18

[0113] The reaction was basically the same as in Example 17, except that the catalyst prepared in Example 1 was used for the reaction, and the reaction time was adjusted to 2 h. The yield of acetic acid was 3921 μmol·g cat -1 , with a selectivity of 82%.

[0114] Application Example 19

[0115] The reaction was basically the same as in Application Example 17, except that the catalyst prepared in Example 1 was used for the reaction, the reaction time was adjusted to 4 h, and the yield of acetic acid was 6948 μmol·g cat -1 , with a selectivity of 79%.

[0116] Application Example 20

[0117] The reaction was basically the same as in Application Example 17, except that the catalyst prepared in Example 1 was used for the reaction, the reaction time was adjusted to 8 h, and the yield of acetic acid was 11471 μmol·g cat -1 , with a selectivity of 76%.

[0118] Application Example 21

[0119] The reaction was basically the same as in Application Example 17, except that the catalyst prepared in Example 1 was used for the reaction, and the reaction time was adjusted to 24 h. The yield of acetic acid was 20182 μmol·g cat -1 , with a selectivity of 70%.

[0120] Comparative application example 1

[0121] The same as Example 1, except that the catalyst prepared in Comparative Example 1 was used to carry out the reaction, and the yield of acetic acid was 18 μmol·g cat -1 , with a selectivity of 10%.

[0122] Comparative Application Example 2

[0123] The reaction was basically the same as in Example 1, except that the catalyst prepared in Comparative Example 2 was used to carry out the reaction, and the yield of acetic acid was 188 μmol·g cat -1 , with a selectivity of 25%.

[0124] Comparative Application Example 3

[0125] The reaction was basically the same as in Example 1, except that the catalyst prepared in Comparative Example 3 was used to carry out the reaction, and the yield of acetic acid was 359 μmol·g cat -1 , with a selectivity of 49%.

[0126] Comparative Application Example 4

[0127] The reaction was basically the same as in Example 1, except that the catalyst prepared in Comparative Example 4 was used to carry out the reaction, and the yield of acetic acid was 388 μmol·g cat -1 , with a selectivity of 42%.

[0128] Comparative Application Example 5

[0129] The reaction was basically the same as in Example 1, except that the catalyst prepared in Comparative Example 5 was used to carry out the reaction, and the yield of acetic acid was 238 μmol·g cat -1 , with a selectivity of 45%.

[0130] Comparative Application Example 6

[0131] The reaction was basically the same as in Example 1, except that the catalyst prepared in Comparative Example 6 was used to carry out the reaction, and the yield of acetic acid was 178 μmol·g cat -1 , with a selectivity of 40%.

[0132] Comparative Application Example 7

[0133] The reaction was basically the same as in Example 1, except that the catalyst prepared in Comparative Example 7 was used to carry out the reaction, and the yield of acetic acid was 168 μmol·g cat -1 , with a selectivity of 27%.

[0134] Test Example 1

[0135] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was photographed by transmission electron microscopy, and the results are as follows: Figure 1 As shown. Figure 1 It can be seen that no clusters of Fe or Zn nanoparticles were found in Fe1-Zn1 / ZSM-5, demonstrating the atomic-level dispersion of Fe-Zn species.

[0136] Test Example 2

[0137] The Fe1-Zn1 / ZSM-5 prepared in Example 1 and the Fe1 / ZSM-5 prepared in Comparative Example 2 were tested by X-ray photoelectron spectroscopy of the iron element 2p orbital. The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the Fe species 2p in Fe1-Zn1 / ZSM-5 3 / 2 The binding energy at is 709.8 eV, which is attributed to Fe δ+ (2<δ<3), indicating that the Fe species has a unique electronic structure. At the same time, compared with Fe1 / ZSM-5, the 2p 3 / 2 The binding energy at 200 μm decreased by 0.4 eV, further proving that the introduction of Zn can adjust the electronic structure of Fe species.

[0138] Test Example 3

[0139] The Fe1-Zn1 / ZSM-5 prepared in Example 1 and the Zn1 / ZSM-5 prepared in Comparative Example 3 were tested by X-ray photoelectron spectroscopy of the zinc element 2p orbital. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the 2p of Zn species in Fe1-Zn1 / ZSM-5 3 / 2 The binding energy at is 1022.0 eV, which is attributed to Zn σ+(1<σ<2), indicating that Zn species have a unique electronic structure. At the same time, compared with Zn1 / ZSM-5, the 2p 3 / 2 The binding energy at 240 nm increased by 0.2 eV, which further proves that the introduction of Fe can adjust the electronic structure of Zn species.

[0140] Test Example 4

[0141] The local coordination environment of Fe1-Zn1 / ZSM-5 prepared in Example 1 was simulated according to density functional theory. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that the Fe atom coordinates with three oxygen atoms, one bridging oxygen atom and two skeleton oxygen atoms; the Zn atom coordinates with three oxygen atoms, one bridging oxygen atom and two skeleton oxygen atoms. This indicates that the special local coordination environment around the Fe-Zn heteroatom leads to its unique electronic state, which can efficiently catalyze the directional conversion of methane into multi-carbon high-value oxygen-containing compounds.

[0142] Test Example 5

[0143] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was subjected to an extended X-ray absorption fine structure (EXAFS) test of iron element, and the results are as follows: Figure 5 As shown. Figure 5 It can be seen that compared with iron foil (Fe foil), iron oxide (Fe2O3) and ferrous oxide (FeO), the first shell of Fe1-Zn1 / ZSM-5 is There is a Fe-O scattering at There is no Fe-Fe scattering in the , indicating that the Fe species are dispersed at the atomic level rather than nanoparticles or clusters. The peak at is higher than the Fe-Fe scattering peak in Fe foil. But it is lower than the Fe-Fe scattering peak in FeO and Fe-Fe scattering peaks in Fe2O3 This can be attributed to the Fe-Zn scattering peak in the second shell. This data further confirms that there are Zn species dispersed around the highly dispersed Fe species.

[0144] Test Example 6

[0145] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was subjected to zinc element extended X-ray absorption fine structure (EXAFS) test, and the results are as follows: Figure 6 As shown. Figure 6 It can be seen that compared with zinc foil (Zn foil) and zinc oxide (ZnO), the first shell of Fe1-Zn1 / ZSM-5 is There is a Zn-O scattering at There is no Zn-Zn scattering in the Zn foil, which indicates that the Zn species are atomically dispersed rather than nanoparticles or clusters. In addition, the Zn-Zn scattering in the Zn foil is higher than that in the Zn foil. But it is lower than Zn-Zn scattering in ZnO of The peak at can be attributed to Fe-Zn scattering in the second shell. This data further confirms that there are Fe species scattered around the highly dispersed Zn species.

[0146] Test Example 7

[0147] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was fitted with the iron element EXAFS data. The results are as follows: Figure 7 As shown. Figure 7 It can be seen that the Fe atom is connected to a bridging oxygen atom (O BG ) and two framework oxygen atoms (O FM Specifically, for Fe atoms, the Fe atoms and the bridging oxygen (Fe-O BG ) has a bond length of With framework oxygen (Fe-O FM ) has an average bond length of In addition, the fitting data of Fe element in the second shell show that the distance between Fe and Zn atoms is

[0148] Test Case 8

[0149] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was fitted with the zinc element EXAFS data. The results are as follows: Figure 8 As shown. Figure 8 It can be seen that the Zn atom is connected to a bridging oxygen atom (O BG ) and two framework oxygen atoms (O FM ) coordination. Zn atoms and bridging oxygen (Zn-O BG ) With framework oxygen (Zn-O FM ) has an average bond length of In addition, the fitting data of the Zn element on the second shell show that the distance between Fe and Zn atoms is

[0150] Test Example 9

[0151] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was subjected to Fe element X-ray absorption near edge structure (XANES) test, and the results are as follows: Fig. 9 As shown. Fig. 9It can be seen that the absorption edge of Fe1-Zn1 / ZSM-5 is higher than that of FeO, but lower than that of Fe2O3, indicating that the valence state of Fe atoms is between Fe 2+ and Fe 3+ This further proves that the introduction of Zn can adjust the electronic structure of Fe species and put it in a unique intermediate valence state.

[0152] Test Example 10

[0153] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was subjected to a Zn element X-ray absorption near edge structure (XANES) test, and the results are as follows: Fig.10 As shown. Fig.10 It can be seen that the absorption edge of Fe1-Zn1 / ZSM-5 is higher than that of Zn foil, but lower than that of ZnO foil, indicating that the valence state of Zn atoms is between Zn 0 and Zn 2+ This further proves that the introduction of Fe can adjust the electronic structure of Zn species and put it in a unique intermediate valence state.

[0154] Test Example 11

[0155] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was subjected to a Bader charge analysis of the Fe element based on first principle (DFT) computational chemistry simulation. Fig.11 As shown. Fig.11 It can be seen that the Bader charge of Fe in the Fe-Zn heteroatom (1.17|e|) is higher than that of FeO (1.01|e|) and lower than that of Fe2O3 (1.42|e|), indicating that the valence state of Fe atoms is between Fe 2+ and Fe 3+ This further proves that the Fe atom is in a unique intermediate valence state.

[0156] Test Example 12

[0157] The Bader charge analysis of Zn element based on the computational chemistry simulation of the Fe1-Zn1 / ZSM-5 prepared in Example 1 was performed. The results are as follows: Fig.12 As shown. Fig.12 It can be seen that the Bader charge of Zn in the Fe-Zn heteroatom (1.11|e|) is slightly lower than that of ZnO (1.21|e|), indicating that the valence state of Zn atom is between that of Zn + and Zn 2+ This further proves that the Zn atom is in a unique intermediate valence state.

[0158] Test Example 13

[0159] The Fe1-Zn1 / ZSM-5 prepared in Example 1 and the Fe1 / ZSM-5 prepared in Comparative Example 2 were subjected to DFT calculation simulation of the 3d orbital energy analysis of the Fe element. The results are as follows: Fig.13 As shown. Fig.13 It can be seen that compared with Fe1 / ZSM-5, the Fe 3d orbital in Fe1-Zn1 / ZSM-5 is at the Fermi level (E f ), which further proves that the introduction of Zn significantly regulates the electronic structure of Fe species.

[0160] Test Case 14

[0161] The Fe1-Zn1 / ZSM-5 prepared in Example 1 was subjected to a room temperature and pressure methane selective oxidation cycle test. The results are as follows: Fig.14 As shown. Fig.14 It can be seen that the catalytic yield of acetic acid (3071 ± 127 μmol·g cat -1 ·h -1 ) and selectivity (~81%) without obvious loss, indicating that Fe1-Zn1 / ZSM-5 possesses high stability during the selective oxidation of methane at room temperature and atmospheric pressure.

[0162] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing a supported heterodiatom catalyst, characterized in that: The following steps are involved: S1, dissolving iron salt in water, adjusting the pH to 1-5, to obtain an iron salt solution; Dissolving zinc salt in water and adjusting the pH to 2-6 to obtain a zinc salt solution; S2. Dispersing the molecular sieve carrier uniformly in water by ultrasonic vibration, adjusting the pH to 2-5, and obtaining a carrier solution; S3. Add the iron salt solution and zinc salt solution described in S1 dropwise to the carrier solution described in S2, react at 0°C-15°C under ultraviolet irradiation, and obtain the supported heterodiatom catalyst by centrifugal washing, drying and calcining.

2. The method for preparing a supported hetero-diatom catalyst according to claim 1, characterized in that: In S1, the iron salt is selected from ferric chloride and / or ferric nitrate; the zinc salt is selected from zinc chloride and / or zinc nitrate.

3. The method for preparing a supported hetero-diatom catalyst according to claim 1, characterized in that: In S1, the concentrations of the iron salt solution and the zinc salt solution are independently 0.01 mmol / L-0.1 mmol / L.

4. The method for preparing a supported heterodiatom catalyst according to claim 1, characterized in that: In S2, the molecular sieve carrier is selected from zeolite molecular sieve, mordenite or titanium silicon molecular sieve; the silicon-aluminum ratio or silicon-titanium ratio of the molecular sieve carrier is 12.5-150.

5. The method for preparing a supported heterodiatom catalyst according to claim 1, characterized in that: In S3, the wavelength of the ultraviolet irradiation is 200nm-400nm, and the power is 5W-20W; the drying is carried out at 40℃-60℃ for 10h-14h; and the calcination is carried out at 300℃-350℃ for 2h-4h under a protective atmosphere.

6. The method for preparing a supported heterodiatom catalyst according to claim 1, characterized in that: In S3, the mass proportion of iron element and zinc element in the supported heterodiatom catalyst is 0.5%-1.5%, and the mass ratio of iron element to zinc element is 1:3-3:

1.

7. A supported heterodiatom catalyst prepared by the method according to any one of claims 1 to 6.

8. Use of the supported heterodiatom catalyst according to claim 7 in catalytic oxidation of methane to prepare acetic acid, characterized in that: The specific steps include: Methane and oxygen are introduced into a reactor containing a supported heterodiatomic catalyst solution, and reacted under light conditions to obtain acetic acid.

9. The use according to claim 8, characterized in that: The concentration of the supported hetero-diatomic catalyst solution is 0.05 mg / mL-0.2 mg / mL; the flow rate of the oxygen is 5 mL / min-30 mL / min; and the flow rate ratio of the methane and the oxidant is (0.5-5):

1.

10. The use according to claim 8, characterized in that: The wavelength of the light is 220nm-1100nm; the temperature of the reaction is 20°C-35°C, the time is 1h-24h, and the pressure is 1 bar.

Images