Pd1Zn monatomic alloy catalyst, preparation method thereof and application of Pd1Zn monatomic alloy catalyst in preparation of dimethyl carbonate through CO esterification

Abstract

The invention discloses a Pd1Zn monatomic alloy catalyst, a preparation method thereof and application of the Pd1Zn monatomic alloy catalyst in preparation of dimethyl carbonate through CO esterification, and belongs to the field of catalysts. The alloy catalyst comprises a Pd1Zn monatomic alloy and a carrier, part of Pd atoms are dispersed on the carrier in the form of single atoms; wherein the molar ratio of Pd to Zn is 1: (1-10). According to the Pd1Zn monatomic alloy catalyst provided by the invention, CO esterification product selectivity can be regulated and controlled, dimethyl oxalate is changed into dimethyl carbonate, the selectivity of the dimethyl oxalate is remarkably reduced, the selectivity of the dimethyl carbonate is remarkably improved and can reach 91.5%, and therefore the purpose that a coal-to-ethylene glycol device and a dimethyl oxalate device are converted into the dimethyl carbonate can be achieved.

Description

Technical Field

[0001] This application relates to a Pd 1 The invention relates to a Zn single-atom alloy catalyst and a preparation method thereof, and application thereof in CO esterification to prepare dimethyl carbonate, belonging to the field of catalysts. Background Art

[0002] In 2022, China's coal-to-ethylene glycol production capacity has reached 13.278 million tons. The key step of coal-to-ethylene glycol, CO esterification reaction, can produce dimethyl oxalate or dimethyl carbonate. It is a new carbon-one technology route with advantages such as low cost and high reaction efficiency. It has attracted widespread research interest in recent years. Dimethyl oxalate and dimethyl carbonate are important chemical raw materials, among which dimethyl carbonate is a green chemical widely used in chemical products such as lithium-ion battery solvents and polycarbonate, with higher economic value.

[0003] With the large-scale construction and commissioning of coal-to-ethylene glycol production facilities, ethylene glycol production capacity has become excessive, resulting in the shutdown of many production facilities, which urgently need transformation. In order to obtain higher economic benefits, converting the product dimethyl oxalate into dimethyl carbonate with higher added value is a transformation idea. Decarbonylation of dimethyl oxalate to prepare dimethyl carbonate is an industrially feasible route, but it requires the addition of additional decarbonylation reactors and catalysts, which increases production costs. If the old coal-to-ethylene glycol equipment is used, it is more economical and more challenging to directly produce dimethyl carbonate by replacing the new catalyst in the CO esterification reactor. Pd-based supported catalysts are widely used in CO esterification reactions, and different catalysts can be used to catalyze the production of different products. Common dimethyl oxalate catalysts are Pd(0) nanoparticles supported on alkaline or neutral carriers, such as Pd / MgO, and Pd / α-Al 2 O 3 The selectivity of dimethyl carbonate of this type of catalyst is low. If a dimethyl carbonate catalyst containing Pd(II) supported by a porous molecular sieve is used, the preparation cost of the catalyst is high. Summary of the invention

[0004] In view of the difficulty that traditional dimethyl oxalate catalysts are difficult to achieve high selectivity in preparing dimethyl carbonate, the present invention discloses a Pd 1 Zn single-atom alloy catalyst can regulate the selectivity of CO esterification products from dimethyl oxalate to dimethyl carbonate.

[0005] According to the first aspect of the present application, there is provided a Pd 1 Zn single atom alloy catalyst. The active component is Pd 1 Zn single atom alloy.

[0006] A Pd 1Zn single atom alloy catalyst, the alloy catalyst includes Pd 1 Zn single atom alloy and support;

[0007] Some Pd atoms are dispersed on the support in the form of single atoms;

[0008] Wherein, the molar ratio of Pd to Zn is 1:1-10.

[0009] Optionally, the molar ratio of Pd to Zn is 1:4-10.

[0010] Optionally, the molar ratio of Pd to Zn is selected from any value of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any range therebetween.

[0011] Optionally, the loading amount of Pd is 0.2-1.5%;

[0012] The Pd loading is the mass percentage of Pd in ​​the carrier.

[0013] Optionally, the loading amount of Pd is 0.5-1.2%.

[0014] Optionally, the loading amount of Pd is 0.2-1%.

[0015] Optionally, the carrier is selected from α-Al 2 O 3 ,γ-Al 2 O 3 , ZnO, MgO and at least one of the above.

[0016] According to a second aspect of the present application, there is provided a Pd 1 A method for preparing Zn single atom alloy catalyst.

[0017] The preparation method of the alloy catalyst described above comprises:

[0018] S1: stirring, drying, and calcining a mixture containing a Pd precursor, a carrier, and water to obtain an intermediate product;

[0019] S2: stirring, drying, calcining, and reducing the mixture containing the intermediate product, the Zn precursor, and water under a reducing atmosphere to obtain the alloy catalyst.

[0020] Optionally, in step S1, the Pd precursor is selected from Pd(NO 3 ) 2 、Pd(OAc) 2 , K 2 PdCl 4 , PdCl 2At least one of .

[0021] Optionally, in step S2, the Zn precursor is selected from Zn(NO 3 ) 2 、Zn(OAc) 2 At least one of .

[0022] The amounts of the Pd precursor and the Zn precursor are calculated based on the molar ratio of Pd to Zn and the loading amount of Pd.

[0023] Optionally, in step S2, the reducing atmosphere includes hydrogen and an inactive gas.

[0024] Optionally, the volume proportion of hydrogen is 5 to 100 vol%.

[0025] Optionally, the inert gas is argon or nitrogen.

[0026] As a preferred embodiment, Pd 1 A method for preparing a Zn single-atom alloy catalyst comprises:

[0027] S1 Take a certain amount of Pd precursor, add deionized water, ultrasonically dissolve, and add a certain amount of carrier α-Al 2 O 3 , stir quickly to mix, stir continuously for several hours, wash with deionized water two to three times, dry and calcine to obtain the sample.

[0028] S2 takes a certain amount of sample, adds deionized water, disperses by ultrasonic, adds a certain amount of Zn precursor, stirs, dries, calcines, and reduces with hydrogen to obtain the catalyst disclosed in the present invention.

[0029] According to the third aspect of the present application, there is provided a Pd 1 Application of Zn single atom alloy catalysts.

[0030] A method for preparing dimethyl carbonate by CO esterification, wherein a raw gas containing CO and methyl nitrite is introduced into a reactor equipped with an alloy catalyst for reaction to obtain dimethyl carbonate;

[0031] The alloy catalyst is selected from the alloy catalysts described above.

[0032] Optionally, the reaction conditions are: the volume ratio of CO to methyl nitrite is 1:2-6, and the air velocity is 500-5000 L·kg cat. -1 ·h -1 , temperature is 80~160℃, and pressure is 0.01~2MPa.

[0033] Preferably, the air velocity is 1000 to 3000 L·kgcat. -1 ·h -1 , temperature is 100~140℃, and pressure is 0.05~0.3MPa.

[0034] The beneficial effects of this application include:

[0035] Pd provided by this application 1 Zn single-atom alloy catalyst can regulate the selectivity of CO esterification products from dimethyl oxalate to dimethyl carbonate. The selectivity of dimethyl oxalate decreases significantly, while the selectivity of dimethyl carbonate increases significantly, reaching 91.5%, thereby realizing the conversion of the dimethyl oxalate unit of the coal-to-ethylene glycol unit to the production of dimethyl carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The PdZn (1:1), PdZn (1:2), and PdZn (1:4) alloy catalysts prepared in Example 1, and the Pd / α-Al 2 O 3 XRD spectra of the catalysts, (a) is the XRD spectra of different catalysts; (b) is the partially enlarged XRD spectra of different catalysts (2θ=39-43°);

[0037] Figure 2 Transmission electron microscopy images and elemental analysis images of the PdZn (1:4) alloy catalyst prepared in Example 1, (a), (b), and (c) are TEM, HRTEM, and HAADF-STEM images of the PdZn (1:4) alloy catalyst, respectively; (d), (e), (f), (g), and (h) are EDX mapping images of Al, O, Pd, Zn, and a mixture of Pd and Zn elements, respectively;

[0038] Figure 3 The PdZn (1:1), PdZn (1:2), and PdZn (1:4) alloy catalysts prepared in Example 1, and the Pd / α-Al 2 O 3 XPS spectrum of the catalyst;

[0039] Figure 4 The PdZn (1:1), PdZn (1:2), and PdZn (1:4) alloy catalysts prepared in Example 1, and the Pd / α-Al 2 O 3 Product selectivity of catalysts in CO esterification. DETAILED DESCRIPTION

[0040] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0041] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0042] Unless otherwise specified, conventional methods were used for testing and instrument settings were those recommended by the manufacturer.

[0043] X-ray diffraction analysis (XRD) was performed using Miniflex 600, and the analysis conditions were Cu-Kα radiation (hν = 8047.8 eV, ), working voltage 40KV and working current 30mA, the scanning range of the measured sample is 5°-60° (scanning speed is 5° / min).

[0044] Thermoscientific Talos F200X is an instrument for transmission electron microscopy (TEM, HRTEM, HAADF-STEM) and elemental analysis (EDX mapping). The main components and parameters of the instrument include high-angle annular dark field probe (HAADF), annular dark field probe (ADF), bright field probe (BF), integrated differential phase detector (iDPC), Super-X spectrometer, GATAN Oneview camera, point resolution ≤ 0.25nm, line resolution ≤ 0.14nm, STEM resolution ≤ 0.16nm, information resolution ≤ 0.12nm.

[0045] X-ray photoelectron spectroscopy (XPS) was performed using an ESCALAB 250Xi instrument, and the binding energy of the C1s peak was corrected at 284.8 eV.

[0046] The analytical instrument for the online gas chromatograph was Shimadzu GC2014, and the conditions were as follows: inlet temperature 100°C; detector temperature 250°C; chromatographic column FFAP (30m×0.25mm×0.25μm); thermal conductivity detector and hydrogen flame ionization detector; air flow rate 400mL / min; hydrogen flow rate 30mL / min; tail gas N 2 Flow rate: 25mL / min.

[0047] The calculation method of CO conversion rate, dimethyl carbonate selectivity and dimethyl oxalate selectivity is:

[0048] CO conversion = [(CO) in / (Ar) in -(CO) out / (Ar) out ] / [(CO) in / (Ar) in ]×100%

[0049] Where, [Ar] in and [Ar]out represent the peak area before and after the reaction of argon respectively; [CO] in and [CO] out represent the peak area before and after the reaction of CO, respectively.

[0050] The selectivity of dimethyl carbonate and dimethyl oxalate is calculated based on CO:

[0051] Dimethyl carbonate selectivity = (S DMC ×RF DMC / M DMC ) / (S DMC ×RF DMC / M DMC +2×S DMO ×RF DMO / M DMO )×100%

[0052] Dimethyl oxalate selectivity = (2×S DMO ×RF DMO / M DMO ) / (S DMC ×RF DMC / M DMC +2×S DMO ×RF DMO / M DMO )×100%

[0053] Among them, S DMC , S DMO Respectively refer to the peak areas of dimethyl carbonate DMC and dimethyl oxalate DM O after the reaction, RF DMC ,RF DMO Respectively refer to the relative correction factors of DMC and DMO, M DMC 、M DMO Represent the relative molecular masses of DMC and DMO respectively.

[0054] Example 1 Preparation of PdZn alloy catalyst

[0055] PdZn alloy catalyst preparation steps:

[0056] 1. Take a certain amount of Pd precursor, add 20 mL of deionized water, dissolve by ultrasonic, and add 1 g of carrier α-Al 2 O 3 , stir quickly to mix, stir continuously for 3 hours, wash three times with deionized water, dry and calcine to obtain the intermediate product.

[0057] 2. Take a certain amount of the intermediate product, add 1 mL of deionized water, disperse by ultrasonic, add a certain amount of Zn precursor, stir, dry, calcine, and reduce with hydrogen to obtain the PdZn alloy catalyst disclosed in the present invention.

[0058] The drying conditions were 120°C for 12 h, and the calcination conditions were 300°C for 3 h. The reduction conditions were 10 vol% H 2 / Ar reducing atmosphere, 500℃ for 2h.

[0059] Table 1 Experimental parameters for preparing PdZn alloy catalysts

[0060]

[0061]

[0062] The amount of the Pd precursor and the Zn precursor is calculated based on the molar ratio of Pd to Zn and the loading amount of Pd; the loading amount of Pd is the mass percentage of Pd in ​​the carrier.

[0063] Among them, the PdZn alloy catalysts numbered 1, 2, and 3 are denoted as PdZn (1:1), PdZn (1:2), and PdZn (1:4), respectively.

[0064] Comparative Example 1

[0065] The operation is the same as the preparation method of the PdZn (1:1) alloy catalyst numbered 1, except that there is no operation of adding the Zn precursor in the second step to obtain the Pd / α-Al 2 O 3 Catalyst, code D1.

[0066] Characterization Test

[0067] The PdZn alloy catalyst prepared in Example 1 above was subjected to characterization tests.

[0068] Taking PdZn (1:1), PdZn (1:2), and PdZn (1:4) alloy catalysts as typical examples, their XRD spectra are as follows: Figure 1 As shown, (a) is the XRD spectrum of different catalysts; (b) is the partially enlarged XRD spectrum of different catalysts (2θ=39-43°). It can be seen that the diffraction peak corresponding to the PdZn (111) crystal plane at 2θ of 41.2°, all PdZn alloys were obtained.

[0069] Taking PdZn (1:4) alloy catalyst as an example, its transmission electron microscope image and elemental analysis diagram are shown in Figure 2As shown, (a), (b), and (c) are TEM, HRTEM, and HAADF-STEM images of the PdZn (1:4) alloy catalyst, respectively; (d), (e), (f), (g), and (h) are EDX mapping images of Al, O, Pd, Zn, and Pd, Zn element mixtures, respectively. It can be seen that the PdZn alloy particles are usually hemispherically dispersed at the interface of the carrier, and the Pd and Zn elements of the alloy nanoparticles are evenly distributed.

[0070] Taking PdZn (1:1), PdZn (1:2), and PdZn (1:4) alloy catalysts as typical examples, their XPS spectra are as follows: Figure 3 As shown in the figure, it can be seen that as the ratio of Zn to Pd in ​​the alloy catalyst increases, δ+ / Pd 0 From 0.33 to 1.64, it shows that Pd δ+ The components increased and Pd 0 As the components decrease, the electron density of Pd decreases, and some single atomic Pd appears.

[0071] Case 2: Performance Evaluation of PdZn Alloy Catalyst

[0072] 200 mg of the catalyst prepared in Example 1 was loaded, and the reaction raw gas was introduced: 19% CO, 45% methyl nitrite, 3% Ar (as internal standard gas) and 33% N 2 (As a balance gas). Total mass space velocity is 2500L·kg cat. -1 ·h -1 , the reaction pressure was 0.1 MPa, the reaction temperature was 120°C, and the reaction raw materials and products were analyzed in real time by online gas chromatography. Table 2 is the catalyst performance evaluation results after 3 hours of reaction.

[0073] Table 2 Performance evaluation results of PdZn alloy catalyst

[0074]

[0075] As can be seen from the table above, the PdZn (1:1), PdZn (1:2), PdZn (1:4) alloy catalysts prepared in Example 1, and the Pd / α-Al 2 O 3 The performance evaluation results of the catalyst are plotted, such as Figure 4 As shown, it can be seen that the selectivity of dimethyl carbonate increased significantly, especially when the molar ratio of Pd to Zn was 1:4, a leap forward was achieved, reaching 83.2%.

[0076] Therefore, the Pd provided in this application 1Zn single-atom alloy catalyst can regulate the selectivity of CO esterification products from dimethyl oxalate to dimethyl carbonate. The selectivity of dimethyl oxalate decreases significantly, while the selectivity of dimethyl carbonate increases significantly, reaching a maximum of 91.5%.

[0077] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A Pd1Zn single atom alloy catalyst, characterized in that: The alloy catalyst comprises a Pd1Zn single atom alloy and a carrier; Some Pd atoms are dispersed on the support in the form of single atoms; Wherein, the molar ratio of Pd to Zn is 1:1-10.

2. The alloy catalyst according to claim 1, characterized in that The molar ratio of Pd to Zn is 1:4-10.

3. The alloy catalyst according to claim 1, characterized in that The loading amount of Pd is 0.2-1.5%; The Pd loading is the mass percentage of Pd in ​​the carrier.

4. The alloy catalyst according to claim 1, characterized in that The carrier is selected from at least one of α-Al2O3, γ-Al2O3, ZnO and MgO.

5. The method for preparing the alloy catalyst according to any one of claims 1 to 4, characterized in that: The preparation method comprises: S1: stirring, drying, and calcining a mixture containing a Pd precursor, a carrier, and water to obtain an intermediate product; S2: stirring, drying, calcining, and reducing the mixture containing the intermediate product, the Zn precursor, and water under a reducing atmosphere to obtain the alloy catalyst.

6. The preparation method according to claim 5, characterized in that: In the step S1, the Pd precursor is selected from at least one of Pd(NO3)2, Pd(OAc)2, K2PdCl4, and PdCl2.

7. The preparation method according to claim 5, characterized in that: In the step S2, the Zn precursor is selected from at least one of Zn(NO3)2 and Zn(OAc)2.

8. The preparation method according to claim 5, characterized in that: In the step S2, the reducing atmosphere includes hydrogen and inactive gas; Preferably, the volume proportion of hydrogen is 5 to 100 vol%.

9. A method for preparing dimethyl carbonate by CO esterification, characterized in that: The raw gas containing CO and methyl nitrite is passed into a reactor equipped with an alloy catalyst to react and obtain dimethyl carbonate; The alloy catalyst is selected from the alloy catalyst according to any one of claims 1 to 4.

10. The preparation method according to claim 9, characterized in that: The reaction conditions are: the volume ratio of CO to methyl nitrite is 1:2-6, and the air velocity is 500-5000 L·kg cat. -1 ·h -1 , temperature is 80~160℃, and pressure is 0.01~2MPa.

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