Pd / M-CeO2 single-site catalyst, preparation method thereof and application of Pd / M-CeO2 single-site catalyst in preparation of dimethyl carbonate through CO esterification

Abstract

The invention discloses a Pd / M-CeO2 single-site catalyst, a preparation method thereof and application of the Pd / M-CeO2 single-site catalyst in preparation of dimethyl carbonate through CO esterification, and belongs to the field of catalysts. The catalyst comprises an active component Pd and a CeO2 carrier doped with metal M, m is selected from at least one of rare earth lanthanide elements and IIIA main group elements. When the catalyst is applied to preparation of dimethyl carbonate through CO esterification, decomposition of methyl nitrite can be reduced, and the catalyst has high dimethyl carbonate selectivity which can reach 92%.

Description

Technical Field

[0001] The present application relates to a Pd / M-CeO2 single-site catalyst and a preparation method thereof, and its application in CO esterification to produce dimethyl carbonate, belonging to the field of catalysts. Background Art

[0002] Dimethyl carbonate (DMC) is a green and environmentally friendly fine chemical. Due to its inherent polarity, low viscosity, and relative stability, DMC serves as an excellent organic solvent. DMC can replace methyl tert-butyl ether as a green and environmentally friendly gasoline additive to lower the freezing point, adjust octane distribution, and improve anti-knock properties. Due to its high ionic conductivity, DMC is also widely used as the primary electrolyte solvent in the lithium battery industry.

[0003] DMC production technologies include phosgene, transesterification, urea alcoholysis, direct CO2 synthesis, and CO2 esterification. CO2 esterification, however, has attracted widespread attention due to its unique technical advantages, including the absence of water during DMC synthesis, which facilitates catalyst stability. Furthermore, it offers mild reaction conditions and unique technical advantages. Several chlorine-containing and chlorine-free catalysts have been reported. Although chlorine-containing catalysts exhibit high initial catalytic activity and selectivity, they rapidly deactivate due to the continuous loss of chloride ions as a byproduct, methyl chloroformate. Maintaining the stability of chlorine-containing catalysts requires continuous flow of dry hydrogen chloride gas, requiring specialized duplex steel for the reactor and specialized enamel glass for the separation tower. Large amounts of activated carbon are also required for dechlorination, resulting in reduced technical and economic viability. In contrast, chlorine-free catalysts overcome the limitations of deactivation caused by chloride ion loss. Reported chlorine-free catalysts typically utilize supports such as NaY and UiO-66. However, the acidity of molecular sieves can partially decompose the raw material, methyl nitrite, producing byproducts, which reduces technical and economic viability. Therefore, the development of catalysts based on non-molecular sieve systems is of great significance. Summary of the Invention

[0004] According to the first aspect of the present application, a Pd / M-CeO2 single-site catalyst is provided.

[0005] A Pd / M-CeO2 single-site catalyst comprising an active component Pd and a metal M-doped CeO2 carrier;

[0006] M is selected from at least one of rare earth lanthanide elements and Group IIIA elements.

[0007] Optionally, the active component Pd has a valence of +2;

[0008] The Pd(II) units are dispersed on the oxygen vacancies of the support.

[0009] Optionally, the metal M is incorporated into the crystal lattice of CeO2;

[0010] The support is rod-shaped with the (111) crystal plane exposed.

[0011] Optionally, M is selected from at least one of Pr, La, Sm, Gd, Dy, Er, Ga and In.

[0012] Optionally, the loading amount of Pd is 0.2-1%, wherein the loading amount of Pd is the mass percentage of Pd in the carrier.

[0013] Optionally, the loading amount of Pd is 0.5-1%.

[0014] Optionally, the loading amount of Pd is 0.2-0.6%.

[0015] Optionally, the loading amount of Pd is selected from any value among 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or any range therebetween.

[0016] Optionally, the molar ratio of Pd to M is 1:1-10.

[0017] Optionally, the molar ratio of Pd to M is 1:2.5-10.

[0018] Optionally, the molar ratio of Pd to M 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.

[0019] According to the second aspect of the present application, a method for preparing a Pd / M-CeO2 single-site catalyst is provided.

[0020] The preparation method of the above-mentioned catalyst comprises:

[0021] S1: stirring a mixture containing an M precursor, a Ce precursor, and water, hydrothermally reacting the mixture, centrifuging the mixture, drying the mixture, and calcining the mixture to obtain an M-CeO2 carrier;

[0022] S2: stirring, drying and calcining a mixture containing an M-CeO2 carrier, a Pd precursor and water to obtain the catalyst.

[0023] Optionally, in step S1, the M precursor is selected from at least one of M(NO3)3 and MCl3; the Ce precursor is selected from at least one of Ce(NO3)3 and CeCl3.

[0024] Optionally, in step S1, the temperature of the hydrothermal reaction is 100-120° C.; and the time of the hydrothermal reaction is 20-30 hours.

[0025] Optionally, in step S2, the Pd precursor is selected from at least one of Pd(NO3)2 and Pd(OAc)2.

[0026] The drying and calcining can be carried out by conventional methods in this field.

[0027] Optionally, the calcination conditions are: calcination in an air atmosphere at a temperature of 200-500°C.

[0028] The amounts of the Pd precursor, Ce precursor, and M precursor are calculated based on the molar ratio of Pd to M and the loading amount of Pd.

[0029] As a preferred embodiment, the method for preparing the catalyst comprises:

[0030] S1: Take a certain amount of Ce precursor and M precursor, add deionized water, dissolve by ultrasonication, stir continuously for several hours, hydrothermally, dry and calcine to obtain the catalyst support.

[0031] S2: taking a certain amount of carrier, adding deionized water, ultrasonically dispersing, adding a certain amount of Pd precursor, stirring, drying, and calcining to obtain the catalyst.

[0032] According to the third aspect of the present application, an application of a Pd / M-CeO2 single-site catalyst is provided.

[0033] A method for preparing dimethyl carbonate by CO esterification, wherein a raw gas containing CO and methyl nitrite is passed into a reactor containing a catalyst for reaction to obtain dimethyl carbonate;

[0034] The catalyst is selected from the catalysts described above.

[0035] Optionally, the reaction conditions are: the volume ratio of CO to methyl nitrite is 1:2-7, the space velocity is 1000-4000 L·kg cat. -1 ·h -1 , temperature is 100~140℃, and pressure is 0.01~2MPa.

[0036] Preferably, the air velocity is 2000 to 3000 L·kg cat. -1 ·h -1 , temperature is 120~140℃, and pressure is 0.05~0.3MPa.

[0037] The beneficial effects of this application include:

[0038] The Pd / M-CeO2 single-site catalyst provided herein has most of the Pd(II) single sites dispersed in oxygen vacancies on the support. When applied to the CO esterification process to produce dimethyl carbonate, it can reduce the decomposition of methyl nitrite and achieve a high dimethyl carbonate selectivity of up to 92%. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 These are the XRD spectra of Pd / Pr-CeO2-2.5, Pd / Pr-CeO2-5, Pd / Pr-CeO2-7.5, and Pd / Pr-CeO2-10 catalysts prepared in Example 1.

[0040] Figure 2 Transmission electron micrographs of Pd / Pr-CeO2-2.5, Pd / Pr-CeO2-5, Pd / Pr-CeO2-7.5, and Pd / Pr-CeO2-10 catalysts prepared in Example 1: (a) and (b) TEM image and HRTEM image of the Pd / Pr-CeO2-2.5 catalyst; (c) and (d) TEM image and HRTEM image of the Pd / Pr-CeO2-5 catalyst; (e) and (f) TEM image and HRTEM image of the Pd / Pr-CeO2-7.5 catalyst; (g) and (h) TEM image and HRTEM image of the Pd / Pr-CeO2-10 catalyst.

[0041] Figure 3 Pd 3d XPS spectra of Pd / Pr-CeO2-2.5, Pd / Pr-CeO2-5, Pd / Pr-CeO2-7.5, and Pd / Pr-CeO2-10 catalysts prepared in Example 1 before (a) and after (b) the reaction.

[0042] Figure 4 This is the Pd 3d XPS spectrum of the Pd / In-CeO2-5 and Pd / Ga-CeO2-5 catalysts prepared in Example 1 before the reaction. DETAILED DESCRIPTION

[0043] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0044] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0045] Unless otherwise specified, conventional methods were used for testing, and the instrument settings were those recommended by the manufacturer.

[0046] X-ray diffraction analysis (XRD) was performed using a Miniflex 600 instrument. 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).

[0047] The Thermoscientific Talos F200X transmission electron microscope (TEM, HRTEM, HAADF-STEM) instrument has the following main components and parameters: 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, and information resolution ≤ 0.12nm.

[0048] X-ray photoelectron spectroscopy (XPS) analysis was performed using an ESCALAB 250Xi instrument. The binding energy of the C1s peak was corrected at 284.8 eV.

[0049] The online gas chromatograph was a Shimadzu GC2014 instrument with the following conditions: an inlet temperature of 100°C; a detector temperature of 250°C; a chromatographic column FFAP (30m×0.25mm×0.25μm); a thermal conductivity detector and a hydrogen flame ionization detector; an air flow rate of 400mL / min; a hydrogen flow rate of 30mL / min; and a tail gas N2 flow rate of 25mL / min.

[0050] The calculation method of CO conversion rate, dimethyl carbonate selectivity, and dimethyl oxalate selectivity is:

[0051] CO conversion rate = [(CO) in / (Ar) in -(CO) out / (Ar) out ] / [(CO) in / (Ar) in ]×100%

[0052] Among them, [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.

[0053] The selectivity of dimethyl carbonate and dimethyl oxalate is calculated based on CO:

[0054] Dimethyl carbonate selectivity = (S DMC ×RF DMC / M DMC ) / (SDMC ×RF DMC / M DMC +2×S DMO ×RF DMO / M DMO )×100%

[0055] Dimethyl oxalate selectivity = (2×S DMO ×RF DMO / M DMO ) / (S DMC ×RF DMC / M DMC +2×S DMO ×RF DMO / M DMO )×100%

[0056] 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 Refers to the relative correction factors of DMC and DMO respectively, M DMC 、M DMO Represent the relative molecular masses of DMC and DMO respectively.

[0057] Example 1 Preparation of Pd / M-CeO2 catalyst

[0058] Pd / M-CeO2 catalyst preparation steps:

[0059] 1. Take a certain amount of Ce precursor and M precursor, add 70 mL of deionized water, dissolve under ultrasonication, stir continuously for 3 hours, carry out hydrothermal reaction in a reactor, centrifuge, dry, and calcine to obtain a carrier.

[0060] 2. Take a certain amount of carrier, add 10 mL of deionized water, ultrasonically disperse, add a certain amount of Pd precursor, stir, dry, and calcine to obtain the Pd / M-CeO2 catalyst disclosed in the present invention.

[0061] Among them, Ce precursor is Ce(NO3)3, Pd precursor is Pd(NO3)2, and the specific types of M precursors are shown in Table 1.

[0062] The hydrothermal conditions were 100° C. for 24 hours, the drying conditions were 100° C. for 12 hours, and the calcination conditions were 300° C. for 4 hours in an air atmosphere.

[0063] Table 1 Experimental parameters for preparing Pd / M-CeO2 catalyst

[0064]

[0065]

[0066] The amount of the Pd precursor and the M precursor is calculated based on the molar ratio of Pd to M and the Pd loading amount; the Pd loading amount is the mass percentage of Pd in the carrier.

[0067] Among them, the Pd catalysts numbered 1, 2, 3, 4, 5, and 6 are respectively recorded as Pd / Pr-CeO2-2.5, Pd / Pr-CeO2-5, Pd / Pr-CeO2-7.5, Pd / Pr-CeO2-10, Pd / In-CeO2-5, and Pd / Ga-CeO2-5.

[0068] Characterization Test

[0069] The Pd catalyst prepared in Example 1 was subjected to characterization tests.

[0070] Taking Pd / Pr-CeO2-2.5, Pd / Pr-CeO2-5, Pd / Pr-CeO2-7.5 and Pd / Pr-CeO2-10 catalysts as typical examples, their XRD spectra are shown in Figure 2. Figure 1 As shown, it can be seen that there are no diffraction peaks of Pd nanoparticles and Pr2O3, indicating that Pr is successfully incorporated into the lattice of CeO2 and Pd is well dispersed.

[0071] Taking Pd / Pr-CeO2-2.5, Pd / Pr-CeO2-5, Pd / Pr-CeO2-7.5 and Pd / Pr-CeO2-10 catalysts as examples, their transmission electron microscope images are shown in Figure 2. Figure 2 As shown, it can be seen that all catalyst supports are rod-shaped and all have exposed (111) crystal planes.

[0072] Taking Pd / Pr-CeO2-2.5, Pd / Pr-CeO2-5, Pd / Pr-CeO2-7.5, and Pd / Pr-CeO2-10 catalysts as typical examples, the Pd 3d XPS spectra before and after the reaction are shown in Figure 2. Figure 3 As shown, it can be seen that before the reaction, the Pd in all catalysts was at +2 valence, and after the reaction, part of the Pd(Ⅱ) was reduced to Pd(0). The proportion of Pd(Ⅱ) on the surface of each catalyst followed the following order: Pd / Pr-CeO2-5 (74%) > Pd / Pr-CeO2-7.5 (62%) > Pd / Pr-CeO2-10 (36%) > Pd / Pr-CeO2-2.5 (33%).

[0073] Taking Pd / In-CeO2-5 and Pd / Ga-CeO2-5 catalysts as examples, the Pd 3d XPS patterns before the reaction are shown in Figure 2. Figure 4As shown, it can be seen that the Pd 3d orbital of the Pd / In-CeO2-5 catalyst is slightly shifted toward the direction of high binding energy, and the oxidation state of Pd(II) is higher, which is more conducive to the formation of dimethyl carbonate.

[0074] Example 2 Pd / M-CeO2 catalyst performance evaluation

[0075] 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% N2 (as balance gas). The total mass space velocity was 2500 L·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 shows the catalyst performance evaluation results after 3 hours of reaction.

[0076] Table 2 Performance evaluation results of Pd / M-CeO2 catalyst

[0077] Catalyst No. Dimethyl carbonate selectivity / % Dimethyl oxalate selectivity / % CO conversion rate / % 1 21 79 59 2 77 23 44 3 47 53 44 4 25 75 56 5 92 8 41 6 57 43 74 7 42 58 42 8 42 58 49 9 45 55 57 10 49 51 60 11 57 43 61

[0078] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present 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 Pd / M-CeO2 single-site catalyst, characterized in that: The catalyst comprises an active component Pd and a metal M-doped CeO2 carrier; M is selected from at least one of rare earth lanthanide elements and Group IIIA elements.

2. The catalyst according to claim 1, characterized in that The active component Pd has a valence of +2; The Pd(II) units are dispersed on the oxygen vacancies of the support.

3. The catalyst according to claim 1, characterized in that Metal M is incorporated into the CeO2 lattice; The support is rod-shaped with the (111) crystal plane exposed.

4. The catalyst according to claim 1, characterized in that M is at least one selected from Pr, La, Sm, Gd, Dy, Er, Ga and In.

5. The catalyst according to claim 1, characterized in that The Pd loading amount is 0.2 to 1%, wherein the Pd loading amount is the mass percentage of Pd in the carrier; Preferably, the molar ratio of Pd to M is 1:1-10.

6. The method for preparing the catalyst according to any one of claims 1 to 5, characterized in that: The preparation method comprises: S1: stirring a mixture containing an M precursor, a Ce precursor, and water, hydrothermally reacting the mixture, centrifuging the mixture, drying the mixture, and calcining the mixture to obtain an M-CeO2 carrier; S2: stirring, drying and calcining a mixture containing an M-CeO2 carrier, a Pd precursor and water to obtain the catalyst.

7. The preparation method according to claim 6, characterized in that In step S1, the M precursor is selected from at least one of M(NO3)3 and MCl3; the Ce precursor is selected from at least one of Ce(NO3)3 and CeCl3; Preferably, in step S1, the temperature of the hydrothermal reaction is 100-120° C.; and the time of the hydrothermal reaction is 20-30 hours.

8. The preparation method according to claim 6, characterized in that In step S2, the Pd precursor is selected from at least one of Pd(NO3)2 and Pd(OAc)2.

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 a catalyst to react and obtain dimethyl carbonate; The catalyst is selected from the catalyst according to any one of claims 1 to 5.

10. The preparation method according to claim 9, characterized in that The reaction conditions are: the volume ratio of CO to methyl nitrite is 1:2-7, and the space velocity is 1000-4000 L·kg cat. -1 ·h -1 , temperature is 100~140℃, and pressure is 0.01~2MPa.

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