Application of MoS2-supported diatomic catalysts in selective hydrogenation of dimethyl oxalate to ethanol

Abstract

The present invention relates to an application of a molybdenum disulfide-loaded diatomic catalyst in catalyzing the selective hydrogenation of dimethyl oxalate to prepare ethanol, and belongs to the technical field of catalysts. The preparation method of the molybdenum disulfide-loaded diatomic catalyst comprises the following steps: dissolving an acetate of a platinum group metal in water or an alcohol solvent to obtain a metal precursor solution; the concentration of the metal precursor solution is 0.2mmol / L-2mmol / L; then adding the metal precursor solution to a two-dimensional thin layer MoS2 solution, so that the metal precursor is uniformly dispersed on the surface of the two-dimensional thin layer MoS2, to obtain the molybdenum disulfide-loaded diatomic catalyst; the pH of the two-dimensional thin layer MoS2 solution is 3-6. The MoS2-loaded diatomic catalyst of the present invention realizes high activity and high selectivity (>96%) of selective hydrogenation of dimethyl oxalate to produce ethanol.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to application of a molybdenum disulfide-loaded diatomic catalyst in catalyzing the selective hydrogenation of dimethyl oxalate to prepare ethanol. Background Art

[0002] Ethanol (EtOH) is not only an important raw material for chemical production, but also an important clean energy source, widely used as a fuel additive or a potential substitute for gasoline. Its main production method is based on microbial fermentation of agricultural raw materials such as sugarcane, potatoes and cassava or hydration of ethylene, but is limited by the reduction of petroleum and expensive bioprocesses. Therefore, an economical and environmentally friendly non-petroleum route to produce ethanol (producing dimethyl oxalate (DMO) intermediates from synthesis gas and then selectively hydrogenating them to ethanol) has become a promising alternative route. At present, for the hydrogenation reaction of dimethyl oxalate, the conversion of dimethyl oxalate to ethanol usually needs to be carried out under harsh conditions of high temperature (270-300℃) and high pressure (20-40bar H2), which has the problems of low ethanol selectivity, poor stability, and environmental and safety risks. However, the existing catalyst system is difficult to effectively realize the hydrogenation of dimethyl oxalate to ethanol under mild conditions. It is urgent to develop a catalyst and catalytic reaction route that can convert dimethyl oxalate into ethanol products with high activity and high selectivity under low pressure and low temperature conditions. Summary of the invention

[0003] To this end, the technical problem to be solved by the present invention is to overcome the problems in the prior art of catalytic hydrogenation of dimethyl oxalate to produce ethanol, such as harsh conditions, low ethanol selectivity and poor stability.

[0004] In order to solve the above technical problems, the present invention provides an application of a molybdenum disulfide-supported diatomic catalyst in catalyzing the selective hydrogenation of dimethyl oxalate to produce ethanol.

[0005] The purpose of the present invention is to provide an application of a MoS2-supported diatomic catalyst in catalyzing the selective hydrogenation of dimethyl oxalate to prepare ethanol.

[0006] In one embodiment of the present invention, the mass percentage of diatomic atoms in the catalyst is 0.05%-10%.

[0007] In one embodiment of the present invention, the method for preparing the MoS2-supported diatomic catalyst comprises the following steps:

[0008] (1) dissolving an acetate of a platinum group metal in water or an alcohol solvent to obtain a metal precursor solution; the concentration of the metal precursor solution is 0.2 mmol / L-2 mmol / L;

[0009] (2) Adding the metal precursor solution described in step (1) into the two-dimensional thin layer MoS2 solution, so that the metal precursor is evenly dispersed on the surface of the two-dimensional thin layer MoS2, to obtain the MoS2-loaded diatomic catalyst; the pH of the two-dimensional thin layer MoS2 solution is 3-6.

[0010] In one embodiment of the present invention, in step (1), the platinum group metal is one or more of palladium, rhodium, ruthenium, platinum and iridium.

[0011] In one embodiment of the present invention, in step (2), the method for preparing the two-dimensional thin layer MoS2 includes the following steps: dissolving ammonium molybdate and thiourea in water and mixing them, reacting at 200°C-240°C for 12-24h, collecting the product after the reaction, washing it multiple times and drying it at 40°C-60°C for 10h-14h to obtain the two-dimensional thin layer MoS2.

[0012] In one embodiment of the present invention, the process of catalytically selectively hydrogenating dimethyl oxalate to prepare ethanol is: adding dimethyl oxalate and a MoS2-loaded diatomic catalyst into a reaction vessel filled with a solvent, then introducing H2 into the reaction vessel until a predetermined H2 pressure is reached, and heating the reaction under stirring to obtain the ethanol.

[0013] In one embodiment of the present invention, the solvent is methanol, 1,4-dioxane or tetrahydrofuran solvent.

[0014] In one embodiment of the present invention, the predetermined H2 pressure is 0.6MPa-1.5MPa.

[0015] In one embodiment of the present invention, the stirring speed is 750rpm-850rpm.

[0016] In one embodiment of the present invention, the heating reaction temperature is 200°C-240°C and the time is 4h-8h.

[0017] In one embodiment of the present invention, the reaction vessel is a batch-type high-temperature and high-pressure reactor.

[0018] In one embodiment of the present invention, the concentration of dimethyl oxalate is 0.25 mol / L-0.42 mol / L; the mass ratio of dimethyl oxalate to the MoS2-loaded diatomic catalyst is 30-50:18-21.

[0019] In one embodiment of the present invention, when the MoS2-supported diatomic catalyst catalyzes the selective hydrogenation of dimethyl oxalate, the conversion rate of dimethyl oxalate reaches 100% and the selectivity of ethanol reaches 96.5%.

[0020] The principle of the present invention is: in view of the uneven active sites of traditional nanoparticle systems and the diversity of adsorption states of key intermediate species, the selective hydrogenation of DMO to produce ethanol has harsh reaction conditions and inevitably produces a large amount of C3-C4OH by-products, resulting in the problem of low selectivity for ethanol. The present invention develops a platinum group metal (Ir, Rh, Ru, Pt, Pd) diatomic active site catalyst system anchored on the edge sites of two-dimensional MoS2. On the one hand, the synergistic effect between the diatoms is utilized to reduce the reaction energy barrier required for the DMO hydrogenation reaction process. On the other hand, the precise diatomic reaction sites are utilized to normalize the adsorption states of key surface species, so that C=O and CO can be easily hydrogenated with the introduction of H species to produce intermediate products methyl glycolate (MG) and ethylene glycol (EG), and then further catalyze the dehydration of ethylene glycol (EG) to ethanol (EtOH). In addition, the constructed diatomic active sites not only enhance the dissociation ability of H2 due to the unique electronic structure, but also restrict the adsorption configuration of reactants and reaction intermediates due to the steric effect, thereby greatly improving the catalytic activity and selectivity for the selective hydrogenation of DMO to produce ethanol.

[0021] The technical solution of the present invention has the following advantages over the prior art:

[0022] (1) The synergistic effect between the two metal atoms in the MoS2-loaded diatomic catalyst described in the present invention improves the H2 activation ability on the one hand, and enhances the catalytic performance of the activation of dimethyl oxalate to generate key intermediates (ethylene glycol) and its further dehydration to ethanol on the other hand, so that dimethyl oxalate can be efficiently converted into ethanol under relatively mild reaction conditions.

[0023] (2) The MoS2-supported diatomic catalyst of the present invention achieves high activity (100%) and high selectivity (>96%) in the selective hydrogenation of dimethyl oxalate to ethanol. Taking the Rh2 / MoS2 diatomic catalyst as an example, under relatively mild reaction conditions (240°C, 1MPaH2), the conversion rate of dimethyl oxalate is 100%, and the selectivity of ethanol is as high as 96.5%, showing an extremely simple and efficient reaction process, and has good application prospects.

[0024] (3) The MoS2-loaded diatomic catalyst described in the present invention has a unique edge confinement structure, which can limit the adsorption configuration of reactants and reaction intermediates, thereby obtaining a highly selective ethanol product. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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:

[0026] Figure 1Schematic diagrams of the structures of different MoS2 catalysts of the present invention; among them, (a) is a Rh2 / MoS2 diatomic catalyst; (b) is a Rh1 / MoS2 single-atom catalyst.

[0027] Figure 2 The graphs show the reaction performance of the selective hydrogenation of dimethyl oxalate to ethanol catalyzed by different MoS2 catalysts of the present invention; wherein (a) is the selectivity graph; and (b) is the intrinsic activity graph. DETAILED DESCRIPTION

[0028] 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.

[0029] Example 1

[0030] The MoS2-supported diatomic catalyst and the preparation method thereof specifically comprise the following steps:

[0031] (1) Preparation of two-dimensional thin layer MoS2: Use 0.6 mmol ammonium molybdate as a precursor and 18 mmol thiourea as a reducing agent. Add 21 mL of deionized water and stir vigorously to dissolve it into a transparent solution. React at 220°C for 18 h. After cooling to room temperature, wash with deionized water several times and vacuum dry at 60°C for 12 h to obtain a two-dimensional thin layer MoS2 (2DMoS2) carrier.

[0032] (2) Preparation of MoS2-supported diatomic catalyst: The two-dimensional thin layer MoS2 carrier is dispersed in deionized water, and the pH value of the solution is adjusted to 4.7 by ultrasonic dispersion for 10 minutes. Dimeric rhodium acetate is dispersed in deionized water to form a metal precursor solution with a concentration of 0.54mmol / L, and ultrasonic dispersion is performed for 30 minutes by heating. Then, the metal precursor solution is added to the solution of the carrier by microinjection of a peristaltic pump, and aged for 4 hours to make it uniformly dispersed on the surface of the two-dimensional thin layer MoS2. The mixed solution is centrifuged to obtain a product precipitate, which is vacuum dried at 60°C for 12 hours to obtain a Rh2 / MoS2 diatomic catalyst with a mass percentage of Rh diatoms of 0.24wt.%, abbreviated as 0.24wt.%Rh2 / MoS2.

[0033] Example 2

[0034] Basically the same as Example 1, the precursor is changed to palladium acetate, and the obtained catalyst is 0.35wt.% Pd2 / MoS2.

[0035] Example 3

[0036] Basically the same as Example 1, the precursor is changed to platinum acetate, and the obtained catalyst is 0.42wt.% Pt2 / MoS2.

[0037] Comparative Example 1

[0038] Basically the same as Example 1, the precursor is changed to rhodium nitrate, and the obtained catalyst is 0.28wt.% Rh1 / MoS2.

[0039] Comparative Example 2

[0040] Basically the same as Example 1, the metal precursor was changed to a rhodium particle solution reduced with ethylene glycol under argon protection, and the obtained catalyst was 0.27wt.% nano-Rh / MoS2.

[0041] Comparative Example 3

[0042] Two-dimensional thin layer MoS2 prepared in Example 1.

[0043] Application Example 1

[0044] All test experiments were carried out in a 50mL high-pressure high-temperature reactor, in which 10mL methanol solvent, 500mg dimethyl oxalate substrate and 210mg Rh2 / MoS2 diatomic catalyst prepared in Example 1 were added. H2 was then introduced 5 times to rinse the reactor to exhaust the air in the reactor. 1MPaH2 was introduced afterwards, and the reaction temperature was gradually increased to 240°C of setting. After reaching the temperature, the timing was started for 8h, and 800rpm was kept stirring during the reaction. After the reaction, the product was analyzed by a gas chromatograph (GC-2060) with an automatic sampler, and the dimethyl oxalate conversion rate was 100%, and the ethanol selectivity was up to 96.5%.

[0045] Application Example 2

[0046] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 10 mL of methanol solvent, 500 mg of dimethyl oxalate and 210 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 6 h under the conditions of H2 pressure of 1.0 MPa and temperature of 240°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 91.3%.

[0047] Application Example 3

[0048] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 10 mL of methanol solvent, 400 mg of dimethyl oxalate and 210 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 5 h under the conditions of H2 pressure of 1.0 MPa and temperature of 240°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 90.5%.

[0049] Application Example 4

[0050] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 10 mL of methanol solvent, 400 mg of dimethyl oxalate and 190 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 6 h under the conditions of H2 pressure of 1.5 MPa and temperature of 230°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 94.9%.

[0051] Application Example 5

[0052] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 8 mL of methanol solvent, 300 mg of dimethyl oxalate and 180 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 8 h under the conditions of H2 pressure of 1.5 MPa and temperature of 220°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 92.6%.

[0053] Application Example 6

[0054] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 8 mL of methanol solvent, 300 mg of dimethyl oxalate and 210 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 4 h under the conditions of H2 pressure of 1.5 MPa and temperature of 240°C, and the conversion rate of dimethyl oxalate was 98.7%, and the selectivity of ethanol was 90.7%.

[0055] Application Example 7

[0056] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 10 mL of 1,4-dioxane solvent, 338 mg of dimethyl oxalate and 210 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 8 hours under the conditions of H2 pressure of 0.6 MPa and temperature of 240°C, and the conversion rate of dimethyl oxalate was 97.2%, and the selectivity of ethanol was 92.1%.

[0057] Application Example 8

[0058] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 8 mL of methanol solvent, 300 mg of dimethyl oxalate and 210 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 8 h under the conditions of H2 pressure of 1.5 MPa and temperature of 200°C, and the conversion rate of dimethyl oxalate was 96.9%, and the selectivity of ethanol was 91.8%.

[0059] Application Example 9

[0060] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzed the selective hydrogenation reaction of dimethyl oxalate, 8 mL of methanol solvent, 435 mg of dimethyl oxalate and 190 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 8 h under the conditions of H2 pressure of 1.0 MPa and temperature of 240°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 95.2%.

[0061] Application Example 10

[0062] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 10 mL of 1,4-dioxane solvent, 325 mg of dimethyl oxalate and 180 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 8 hours under the conditions of H2 pressure of 1.5 MPa and temperature of 240°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 90.5%.

[0063] Application Example 11

[0064] Basically the same as in Application Example 1, the Rh2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 8 mL of tetrahydrofuran solvent, 300 mg of dimethyl oxalate and 210 mg of the Rh2 / MoS2 diatomic catalyst prepared in Example 1. The reaction was carried out for 6 h under the conditions of H2 pressure of 1.0 MPa and temperature of 240°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 91.9%.

[0065] Application Example 12

[0066] Basically the same as in Application Example 1, the Pd2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 10 mL of tetrahydrofuran solvent, 340 mg of dimethyl oxalate and 180 mg of the Pd2 / MoS2 diatomic catalyst prepared in Example 2. The reaction was carried out for 6 hours under the conditions of H2 pressure of 1.5 MPa and temperature of 230°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 93.4%.

[0067] Application Example 13

[0068] Basically the same as in Application Example 1, the Pt2 / MoS2 diatomic catalyst catalyzes the selective hydrogenation reaction of dimethyl oxalate, 8 mL of tetrahydrofuran solvent, 420 mg of dimethyl oxalate and 200 mg of the Pt2 / MoS2 diatomic catalyst prepared in Example 3. The reaction was carried out for 8 h under the conditions of H2 pressure of 1.5 MPa and temperature of 230°C, and the conversion rate of dimethyl oxalate was 99.6%, and the selectivity of ethanol was 92.9%.

[0069] Comparative application example 1

[0070] Basically the same as Application Example 1, the selective hydrogenation reaction of dimethyl oxalate was catalyzed by the Rh1 / MoS2 single atom catalyst of Comparative Example 1, 10 mL of methanol solvent, 500 mg of dimethyl oxalate and 210 mg of Rh1 / MoS2 single atom catalyst. The reaction was carried out for 8 hours under the conditions of H2 pressure of 1.0 MPa and temperature of 240°C, the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 80.9%.

[0071] Comparative Application Example 2

[0072] Basically the same as Application Example 1, the nano-Rh / MoS2 catalyst of Comparative Example 2 was used to catalyze the selective hydrogenation reaction of dimethyl oxalate, 10 mL of methanol solvent, 500 mg of dimethyl oxalate and 210 mg of nano-Rh / MoS2 diatomic catalyst. The reaction was carried out for 8 hours under the conditions of H2 pressure of 1.0 MPa and temperature of 240°C, and the conversion rate of dimethyl oxalate was 100%, and the selectivity of ethanol was 83.2%.

[0073] Comparative Application Example 3

[0074] Basically the same as Application Example 1, the two-dimensional thin layer MoS2 catalyst of Comparative Example 3 was used to catalyze the selective hydrogenation reaction of dimethyl oxalate, 10 mL of methanol solvent, 500 mg of dimethyl oxalate and 210 mg of two-dimensional thin layer MoS2 catalyst. The reaction was carried out for 8 hours under the conditions of H2 pressure of 1.0 MPa and temperature of 240°C, and the conversion rate of dimethyl oxalate was 73.5%, and the selectivity of ethanol was 47.3%.

[0075] Test Example 1

[0076] The Rh2 / MoS2 diatomic catalyst of Example 1 and the Rh1 / MoS2 single atom catalyst of Comparative Example 1 were structurally characterized. The HAADF-STEM results are as follows: Figure 1 As shown. Figure 1 As can be seen in (a), Rh is mainly anchored at the edge of 2DMoS2 nanosheets in the form of diatomic Rh2; Figure 1 As can be seen in (b), the Rh single atom is anchored on the edge of the 2DMoS2 nanosheet in the form of a single atom.

[0077] Test Example 2

[0078] Catalytic performance of different MoS2 catalysts for hydrogenation of dimethyl oxalate, such as Figure 2 As shown. Figure 2 (a) It can be seen that the selectivity of Rh1 / MoS2 single-atom catalyst, nano-Rh / MoS2 and 2DMoS2 for ethanol is 80.9%, 83.2% and 47.3%, respectively, while the Rh2 / MoS2 diatomic catalyst shows a high selectivity of 96.5%. Figure 2(b) It can be seen that the intrinsic activity of Rh2 / MoS2 diatomic catalyst for catalytic hydrogenation of dimethyl oxalate (TOF = 6879.2 / h) is much higher than that of Rh1 / MoS2 single atom catalyst (TOF = 796.9 / h) and nano-Rh / MoS2 (TOF = 108.7 / h), indicating that the hydrogenation reaction of dimethyl oxalate is more favorable at the diatomic site.

[0079] 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. Application of a MoS2-supported diatomic catalyst in catalyzing the selective hydrogenation of dimethyl oxalate to produce ethanol; the mass percentage of diatomic atoms in the catalyst is 0.05%-10%; The method for preparing the MoS2-supported diatomic catalyst comprises the following steps: (1) dissolving an acetate of a platinum group metal in water or an alcohol solvent to obtain a metal precursor solution; The concentration of the metal precursor solution is 0.2mmol / L-2mmol / L; (2) Adding the metal precursor solution described in step (1) into the two-dimensional thin layer MoS2 solution, so that the metal precursor is evenly dispersed on the surface of the two-dimensional thin layer MoS2, to obtain the MoS2-loaded diatomic catalyst; the pH of the two-dimensional thin layer MoS2 solution is 3-6.

2. The use according to claim 1, characterized in that: In step (1), the platinum group metal is one or more of palladium, rhodium, ruthenium, platinum and iridium.

3. The use according to claim 1, characterized in that: In step (2), the preparation method of the two-dimensional thin layer MoS2 includes the following steps: dissolving ammonium molybdate and thiourea in water and mixing them, reacting at 200°C-240°C for 12-24 hours, collecting the product after the reaction, washing it multiple times and drying it at 40°C-60°C for 10 hours-14 hours to obtain the two-dimensional thin layer MoS2.

4. The use according to claim 1, characterized in that: The process of catalyzing the selective hydrogenation of dimethyl oxalate to prepare ethanol is as follows: dimethyl oxalate and a MoS2-loaded diatomic catalyst are added into a reaction vessel filled with a solvent, H2 is then introduced into the reaction vessel until a predetermined H2 pressure is reached, and a heating reaction is performed under stirring to obtain the ethanol.

5. The use according to claim 4, characterized in that: The solvent is methanol, 1,4-dioxane or tetrahydrofuran.

6. The use according to claim 4, characterized in that: The predetermined H2 pressure is 0.6MPa-1.5MPa.

7. The use according to claim 4, characterized in that: The temperature of the heating reaction is 200°C-240°C; and the time is 4h-8h.

8. The use according to claim 4, characterized in that: The concentration of dimethyl oxalate is 0.25 mol / L-0.42 mol / L; the mass ratio of dimethyl oxalate to the MoS2-loaded diatomic catalyst is 30-50:18-21.

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