A universal method for constructing diatomic catalysts and its application in co2 hydrogenation to methanol

Abstract

The application discloses a kind of general method of constructing diatomic catalyst and CO2 hydrogenation methanol application, belong to carbon dioxide conversion application field.The catalyst of the present application is composed of diatomic center and photo-induced semiconductor oxide carrier, specifically by the homonuclear or heteronuclear second metal monatomic atom is directionally loaded to the side of first monatomic center using photo-induced adjacent deposition strategy to form diatomic center.There is strong synergistic catalysis between the adjacent diatomic sites in the catalyst, so it is beneficial to hydrogen transfer and intermediate species adsorption in the catalytic reaction process.The present application can realize the precise synthesis of different diatomic catalysts through photo-induced adjacent deposition strategy, and by adjusting the combination of metal monatomic atom to regulate its synergistic effect, thereby improving the catalytic performance of CO2 hydrogenation methanol, CO2 conversion rate>8.0%, methanol selectivity>80%.

Description

Technical Field

[0001] This invention relates to a universal method for constructing diatomic catalysts and their application in CO2 hydrogenation to methanol, belonging to the fields of carbon dioxide conversion applications and fine catalyst synthesis. Background Technology

[0002] Global warming and environmental degradation caused by massive emissions of the greenhouse gas CO2 have become a global concern. However, as an alternative carbon resource, converting CO2 into fuels and high-value-added chemicals can not only reduce atmospheric CO2 levels and mitigate the greenhouse effect but also alleviate the fossil fuel crisis. The use of renewable "green hydrogen" to catalytically hydrogenate CO2 to produce methanol has attracted widespread attention because methanol can be used directly as a high-quality fuel or further converted into valuable chemicals commonly found in non-renewable fossil resources such as alpha-olefins.

[0003] In recent years, single-atom catalysts have attracted widespread attention in the field of heterogeneous catalysis due to their uniform active center configuration, 100% atom utilization, and tunable coordination structure. In the CO2 hydrogenation reaction, there have been reports on the design and construction of unique single-atom catalysts for the highly selective production of single products such as CO, methanol, formic acid, and ethanol. However, isolated active centers cannot simultaneously adsorb reactants and intermediates, and cannot simultaneously address the adsorption and activation of multiple reactants, thus hindering the overall reaction kinetics. Particularly in the hydrogenation reaction, although single-atom active centers effectively suppress side reactions, they also weaken their ability to dissociate H2, resulting in a significant reduction in hydrogenation activity. Therefore, single-atom catalysts require high reaction temperatures and pressures to exhibit ideal catalytic performance, but harsh catalytic environments lead to the rapid sintering of single-atom active centers and a decrease in selectivity.

[0004] Numerous studies have revealed that current catalysts for CO2 hydrogenation to methanol suffer from drawbacks such as low CO2 conversion efficiency and difficulty in controlling methanol selectivity, leading to increasingly higher demands for high-performance catalysts in synthesis and industrial applications. Therefore, developing catalysts for CO2 hydrogenation to methanol that simultaneously possess high activity and selectivity while maintaining good stability remains a formidable challenge. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a photoinduced deposition strategy to directionally deposit a second type of metal single atom around the center of a first type of single atom, constructing a homonuclear / heteronuclear diatomic catalyst. By utilizing the synergistic effect between specific diatoms, CO2 can be controlled to hydrogenate to methanol, suppressing excessive hydrogenation and the desorption of intermediates to generate byproducts CH4 and CO, effectively improving the CO2 conversion rate and methanol selectivity.

[0006] The first object of the present application is to provide a preparation method of a diatomic catalyst for catalyzing CO2 hydrogenation to produce methanol, comprising the following steps:

[0007] (1) loading a first metal monatomic atom onto the surface of a carrier by an impregnation method, an electrostatic adsorption method, a coprecipitation method or a photo-deposition method to obtain a monatomic material, denoted as M1-MO x ;

[0008] (2) dispersing the obtained monatomic material in deionized water, ultrasonic dispersion to obtain a suspension, then adding a second metal precursor into the suspension, stirring uniformly, then stirring under ultraviolet light irradiation for a certain time, centrifugation, drying, and calcination to obtain a diatomic material, denoted as M1N1-MO x .

[0009] In an embodiment of the present application, the carrier (MO x ) in step (1) is one or more of zinc oxide, indium trioxide, zirconium dioxide, cerium dioxide and titanium dioxide.

[0010] In an embodiment of the present application, the first metal monatomic atom in step (1) is any one of platinum, ruthenium, rhodium, palladium, iridium, copper, silver and gold.

[0011] In an embodiment of the present application, the loading amount of the first metal monatomic atom on the carrier in step (1) is 0.01-0.1 mmol / g.

[0012] In an embodiment of the present application, the ratio of the monatomic material M1-MO x to water in step (2) is 0.1-10 g / L.

[0013] In an embodiment of the present application, the ultrasonic time in step (2) is 10-120 min.

[0014] In an embodiment of the present application, the second metal involved in the second metal precursor in step (2) is any one of platinum, ruthenium, rhodium, palladium, copper, silver and gold.

[0015] In an embodiment of the present application, the second metal precursor in step (2) is any one of chloroplatinic acid, chlororuthenic acid, chlororhodium acid, chloropalladic acid, copper chloride, silver nitrate, chloroauric acid or a hydrate of each of the above substances.

[0016] In an embodiment of the present application, the molar ratio of the metal atom of the second metal precursor in step (2) to the metal atom of the monatomic material in step (1) is 1:1.

[0017] In one embodiment of the present invention, the ultraviolet light irradiation time in step (2) is 0.5-12h.

[0018] In one embodiment of the present invention, the roasting temperature in step (2) is 300-600℃ and the time is 2-12h.

[0019] In one embodiment of the present invention, the above method involves directionally loading a second type of homonuclear or heteronuclear metal single atom next to the center of the first single atom using a photoinduced proximity deposition strategy to form a diatomic center, thereby obtaining a diatomic catalyst. The spacing between the two diatomic sites has a significant impact on catalytic performance, and there is a strong synergistic catalytic effect between adjacent diatomic sites, which is beneficial for hydrogenation transfer and intermediate species adsorption during the catalytic reaction. The present invention can achieve the precise synthesis of different diatomic catalysts through a photoinduced proximity deposition strategy, and can regulate their synergistic effect by adjusting the combination of metal single atoms, thereby improving the catalytic performance of CO2 hydrogenation to methanol.

[0020] Based on the above method, this invention provides a diatomic catalyst for catalytic hydrogenation of CO2 to methanol.

[0021] In one embodiment of the present invention, the above-mentioned diatomic catalyst is composed of a diatomic center (with two atoms, and homonuclear or heteronuclear diatomic atoms adjacent to each other) and a photogenerated semiconductor oxide support.

[0022] In one embodiment of the present invention, the metal active component in the diatomic catalyst is highly dispersed on the support in a diatomic configuration, wherein the two atoms are the same atom or different atoms.

[0023] In one embodiment of the present invention, the content of the metal active component in the catalyst accounts for 0.02% to 2% of the total mass of the catalyst.

[0024] In one embodiment of the present invention, the total metal loading in the diatomic catalyst is 0.04-0.1 mmol / g.

[0025] The present invention also provides a method for producing methanol by hydrogenation of CO2, wherein the above-mentioned catalyst is used as the hydrogenation catalyst in the method.

[0026] In one embodiment of the present invention, the method involves introducing CO2 / H2 syngas into a catalyst for the hydrogenation of CO2 to methanol, and carrying out the reaction of CO2 hydrogenation to methanol in a fixed bed.

[0027] In one embodiment of the present invention, the catalyst does not require activation pretreatment before use.

[0028] In one embodiment of the present application, the reaction conditions for the methanol synthesis from CO2 hydrogenation are as follows: CO2:H2=1:3-4, reaction temperature is 150-400℃, reaction pressure is 0.1-5 MPa, and raw gas flow rate is 5-200 mL / min.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] (1) The present application introduces the concept of diatomic synergistic catalysis to solve the deficiency of single active site in the process of continuous hydrogenation and side reaction inhibition. The catalyst of the present application is composed of a single-atom center with good hydrogenation performance and a single-atom center with strong adsorption performance for CO intermediates, which shows excellent CO2 hydrogenation performance and inhibition of side reactions, with CO2 conversion rate >8% and methanol selectivity >80%.

[0031] (2) The present application introduces the concept of light-induced deposition strategy. Through the electron guiding property of the pre-prepared single-atom material under light, the second kind of metal single atom can be selectively deposited around the first kind of single-atom center. The two single-atom sites prepared have adjacent atomic spacing, which is conducive to the hydrogen dissociation on one single-atom center and the rapid overflow of the adsorbed intermediate to the other single-atom center during hydrogenation, thus more effectively promoting the directional conversion of CO2 to the target product methanol. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The microstructure image of the catalyst obtained in Example 1 (In2O3 supported Ir-Pd diatomic catalyst), which includes: In2O3 support, and the Ir-Pd diatomic center marked by an oval in the figure. DETAILED DESCRIPTION

[0033] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with specific examples. Those skilled in the art should understand that the specific description below is illustrative rather than limiting, and should not limit the protection scope of the present application.

[0034] The catalyst performance evaluation was carried out in a fixed bed reactor. The specific catalyst performance evaluation method is as follows: the catalyst does not need to be treated, and the catalyst mass is 200 mg. The raw gas of CO2:H2=1:3 is directly introduced into the fixed bed reactor (inner diameter is 8 mm), the reaction pressure is adjusted to 0.1-5 MPa, and the flow rate is adjusted to 5-200 mL / min. The temperature of the fixed bed reactor is increased to the required temperature at a rate of 5℃ / min, and then the reaction is started. The products are introduced into the chromatograph for online analysis after being kept at 120℃.

[0035] CO2 conversion = (moles of CO2 before reaction - moles of CO2 after reaction) / moles of CO2 before reaction x 100%;

[0036] Product selectivity = (moles of product x number of carbon atoms in product molecule) / (moles of CO2 before reaction - moles of CO2 after reaction) x 100%.

[0037] CP refers to co-precipitation deposition of metal atoms; PD refers to photo-induced deposition of metal atoms.

[0038] Catalyst system for hydrogenation of CO2 to methanol and preparation method thereof

[0039] Example 1

[0040] First step, 3.5 g of indium nitrate hydrate was dissolved in 45 mL of deionized water. 10 g of sodium carbonate was dissolved in 100 mL of deionized water, stirred at room temperature, and added dropwise to the indium nitrate solution. Then 5 mL of iridium chloride aqueous solution (0.0259 g of iridium chloride trihydrate was added) was added to the above solution, and the mixed solution was stirred for another 1 h. The precipitate was collected by vacuum filtration, washed with deionized water three times, and dried at 80°C overnight. Then it was calcined at 300°C for 4 h, and the sample was recorded as Ir1-In2O3 (wherein the Ir loading was 0.024 mmol / g);

[0041] Second step, 500 mg of the prepared Ir1-In2O3 sample was dispersed in 200 mL of deionized water, and then 0.0035 g of sodium palladium chloride (0.012 mmol) was added to the solution to ensure that the molar ratio of Ir in the Ir1-In2O3 sample to Pd in the sodium palladium chloride was 1:1. After stirring for 10 min, it was continuously stirred under ultraviolet light (20 W LED, wavelength 365 nm) for 2 h. The sample was centrifuged at 10000 rpm for 5 min and washed with deionized water three times. Finally, the product was dried at 80°C overnight and calcined at 300°C for 2 h. This catalyst was recorded as Ir1Pd1-In2O3 (CP-PD), and the total metal loading in the obtained bimetallic atomic catalyst was 0.048 mmol / g, with an Ir:Pd atomic ratio of 1.

[0042] Example 2

[0043] In the first step of Example 1, replace the iridium chloride trihydrate with palladium nitrate dihydrate, and the rest of the steps and operations remain unchanged, i.e. to obtain a Pd1Pd1-In2O3 (CP-PD) catalyst.

[0044] Example 3

[0045] In the first step of Example 1, replace the iridium chloride trihydrate with ruthenium chloride, and the rest of the steps and operations remain unchanged, i.e. to obtain a Ru1Pd1-In2O3 (CP-PD) catalyst.

[0046] Example 4

[0047] The hydrated indium nitrate of the first step of Example 1 was replaced by rhodium nitrate, and the remaining steps and operations were unchanged, to obtain the Rh1Pd1-In2O3(CP-PD) catalyst.

[0048] Example 5

[0049] The hydrated indium nitrate of the first step of Example 1 was replaced by dichlorotetraamine platinum, and the remaining steps and operations were unchanged, to obtain the Pt1Pd1-In2O3(CP-PD) catalyst.

[0050] Example 6

[0051] The hydrated indium nitrate of the first step of Example 1 was replaced by cerium nitrate hexahydrate, and the remaining steps and operations were unchanged, to obtain the Ir1Pd1-CeO2(CP-PD) catalyst.

[0052] Example 7

[0053] The hydrated indium nitrate of the first step of Example 1 was replaced by zinc nitrate hexahydrate, and the remaining steps and operations were unchanged, to obtain the Ir1Pd1-ZnO(CP-PD) catalyst.

[0054] Example 8

[0055] The hydrated indium nitrate of the first step of Example 1 was replaced by zirconium nitrate pentahydrate, and the remaining steps and operations were unchanged, to obtain the Ir1Pd1-ZrO2(CP-PD) catalyst.

[0056] Example 9

[0057] The amount of the iridium chloride trihydrate of the first step of Example 1 was changed to 0.0130 g, and the amount of the sodium palladate chloride of the second step of Example 1 was changed to 0.0018 g, and the remaining steps and operations were unchanged, to obtain the 0.5Ir1Pd1-In2O3(CP-PD) catalyst.

[0058] Example 10

[0059] The amount of the iridium chloride trihydrate of the first step of Example 1 was changed to 0.0518 g, and the amount of the sodium palladate chloride of the second step of Example 1 was changed to 0.0070 g, and the remaining steps and operations were unchanged, to obtain the 2Ir1Pd1-In2O3(CP-PD) catalyst.

[0060] Example 11

[0061] The amount of the iridium chloride trihydrate of the first step of Example 1 was changed to 0.1036 g, and the amount of the sodium palladate chloride of the second step of Example 1 was changed to 0.0140 g, and the remaining steps and operations were unchanged, to obtain the 4Ir1Pd1-In2O3(CP-PD) catalyst.

[0062] Application of the catalyst for methanol production by CO2 hydrogenation:

[0063] The catalyst was placed in a fixed bed reactor, the mass of the catalyst was 200 mg, under the reaction conditions of CO2:H2=1:3, temperature 250℃, 3 MPa, the raw gas flow was 30 mL / min, and the reaction was carried out for 10 h. The conversion rate and the selectivity or distribution of each product are shown in Table 1.

[0064] Example 12

[0065] The Ir1Pd1-In2O3(CP-PD) catalyst was placed in a fixed bed reactor, and the reaction temperature was changed to 200℃, and the other parameters were unchanged. The conversion rate and the selectivity or distribution of each product are shown in Table 1.

[0066] Example 13

[0067] The Ir1Pd1-In2O3(CP-PD) catalyst was placed in a fixed bed reactor, and the reaction temperature was changed to 225℃, and the other parameters were unchanged. The conversion rate and the selectivity or distribution of each product are shown in Table 1.

[0068] Example 14

[0069] The Ir1Pd1-In2O3(CP-PD) catalyst was placed in a fixed bed reactor, and the reaction temperature was changed to 275℃, and the other parameters were unchanged. The conversion rate and the selectivity or distribution of each product are shown in Table 1.

[0070] Example 15

[0071] The Ir1Pd1-In2O3(CP-PD) catalyst was placed in a fixed bed reactor, and the reaction temperature was changed to 300℃, and the other parameters were unchanged. The conversion rate and the selectivity or distribution of each product are shown in Table 1.

[0072] Table 1 Catalytic performance of different catalysts

[0073]

[0074] As can be seen from the results in Table 1, the diatomic catalyst prepared by the catalyst preparation method of the present application has good CO2 conversion rate (>8.0%) and methanol selectivity (>80%) for methanol production by CO2 hydrogenation under mild reaction conditions. The conversion rate and selectivity are mainly related to the properties of the bimetallic catalyst, and there will be certain differences in different combinations. Considering that Pd is a good hydrogenation catalyst, and Ir is good for CO2 hydrogenation, the combination of the two can achieve good results. xThe intermediate species has strong adsorption, so the two atoms can improve the hydrogenation performance and inhibit the generation of CO byproduct. Secondly, compared with the optimal ratio, the conversion rate and selectivity decrease in the case of reducing and increasing the loading amount, which shows that the active center configuration has a great influence on the catalytic performance. In the case of low loading amount, the performance decreases due to the insufficient number of active sites, while in the case of high loading amount, it may be because the active center configuration has changed. Finally, changing the reaction temperature will also cause certain differences in the hydrogenation ability of the catalyst and the desorption of CO byproduct, thereby changing the catalytic activity and selectivity.

[0075] Comparative Example 1

[0076] The amount of iridium chloride trihydrate added in the first step of Example 1 was changed to 0.0518 g, and the second step was not performed, to obtain an Ir1-In2O3(CP) catalyst, and the total metal loading of the obtained catalyst was 0.048 mmol / g. The CO2 hydrogenation performance evaluation was carried out in a fixed bed reactor, and the evaluation conditions were 250°C, 3 MPa, the raw gas flow rate was 30 mL / min, and the reaction time was 10 h. The conversion rate and the selectivity or distribution of each product are shown in Table 2.

[0077] Comparative Example 2

[0078] The iridium chloride trihydrate in the first step of Example 1 was changed to palladium nitrate dihydrate, and the amount added was changed to 0.0518 g, and the second step was not performed, to obtain a Pd1-In2O3(CP) catalyst, and the total metal loading of the obtained catalyst was 0.048 mmol / g. The CO2 hydrogenation performance evaluation was carried out in a fixed bed reactor, and the evaluation conditions were 250°C, 3 MPa, the raw gas flow rate was 30 mL / min, and the reaction time was 10 h. The conversion rate and the selectivity or distribution of each product are shown in Table 2.

[0079] Comparative Example 3

[0080] The iridium chloride trihydrate in the first step of Example 1 was changed to simultaneously adding iridium chloride trihydrate and palladium nitrate dihydrate, and the amount added was changed to 0.0259 g, and the other catalyst preparation steps were the same as Example 1, to obtain an Ir1Pd1-In2O3(CP-CP) catalyst, and the total metal loading of the obtained catalyst was 0.048 mmol / g. The CO2 hydrogenation performance evaluation was carried out in a fixed bed reactor, and the evaluation conditions were 250°C, 3 MPa, the raw gas flow rate was 30 mL / min, and the reaction time was 10 h. The conversion rate and the selectivity or distribution of each product are shown in Table 2.

[0081] Comparative Example 4

[0082] The UV irradiation treatment in step 2 of Example 1 was removed, and the pH of the solution was adjusted to 3. Other catalyst preparation steps were the same as in Example 1, yielding an Ir1Pd1-In2O3 (CP-AP) catalyst with a total metal loading of 0.048 mmol / g. The CO2 hydrogenation performance was evaluated in a fixed-bed reactor under the following conditions: 240℃, 3 MPa, feed gas flow rate of 30 mL / min, and reaction time of 10 h. The conversion rate and the selectivity or distribution of each product are shown in Table 2.

[0083] Comparative Example 5

[0084] Compared to Example 1, the palladium precursor in the second step is replaced with an iridium precursor, while everything else remains the same:

[0085] The first step is the same as in Example 1.

[0086] In the second step, 500 mg of the prepared Ir1-In2O3 sample was dispersed in 200 mL of deionized water. Then, 0.012 mmol of chloroiridium acid was added to the solution to ensure that the molar ratio of Ir in the Ir1-In2O3 sample to Ir in the chloroiridium acid was 1:1. After stirring for 10 min, the mixture was continuously stirred for 2 h under ultraviolet light (20 W LED, wavelength 365 nm). The sample was centrifuged at 10,000 rpm for 5 min and washed three times with deionized water. Finally, the product was dried at 80 °C overnight and calcined at 300 °C for 2 h. This catalyst is designated Ir1Ir1-In2O3 (CP-PD), and the total metal loading in the obtained bimetallic catalyst is 0.048 mmol / g, with an Ir:Ir atomic ratio of 1.

[0087] Table 2 Catalytic performance of different catalysts for CO2 hydrogenation

[0088]

[0089] As can be seen from the results in Table 2, for single-atom catalysts, whether supported with Ir or Pd, they all exhibit lower catalytic performance. Among them, the conversion rate of Ir is lower, but the selectivity is higher; and Pd has stronger hydrogenation performance, but the selectivity for byproduct CO is higher, which also shows that the two kinds of metal single atoms have different functions in the process of CO2 hydrogenation to methanol, and after the two are synergized, the conversion rate and selectivity are obviously improved, which shows that there is a synergistic catalytic effect between the two kinds of single atoms. At the same time, the distance between the two kinds of metal single atoms also has a significant influence on the catalytic performance, the dual-atom catalyst prepared by the light-induced deposition method has Ir and Pd single atoms close to each other, the *H transfer and electron reconstruction between the two are conducive to improving the hydrogenation performance and inhibiting the generation of byproduct CO, and the IrPd catalysts prepared by the coprecipitation method or the adsorption method have the same loading amount, the distribution of the two kinds of single atoms is random (cannot become dual-atom catalysts), so they do not have strong synergistic effect between the two, so they do not exhibit good performance of CO2 hydrogenation to methanol.

[0090] The above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the present application. Various changes or modifications can be made on the basis of the above description for those skilled in the art. It is impossible to enumerate all the embodiments here. Therefore, the protection scope of the present application should be defined by the claims.

Claims

1. A diatomic catalyst for the catalytic hydrogenation of CO2 to methanol, characterized in that, The active metal component in the diatomic catalyst for catalytic CO2 hydrogenation to methanol is highly dispersed in a diatomic configuration on the support; the total metal loading in the diatomic catalyst for catalytic CO2 hydrogenation to methanol is 0.04-0.1 mmol / g. The preparation method of the diatomic catalyst for catalytic CO2 hydrogenation to methanol includes the following steps: (1) The first metal single atom is loaded onto the surface of the support by impregnation, electrostatic adsorption, co-precipitation or photodeposition to obtain a single-atom material, denoted as M1-MO. x ; (2) The obtained single-atom material was dispersed in deionized water and ultrasonically dispersed to obtain a suspension. Then, a second metal precursor was added to the suspension and stirred evenly. The mixture was then stirred for a certain time under ultraviolet light irradiation, centrifuged, dried, and calcined to obtain a diatomic material, denoted as M1N1-MO. x ; The carrier is indium trioxide; the first metal single atom is either rhodium or iridium; the second metal involved in the second metal precursor is palladium.

2. The diatomic catalyst for catalytic CO2 hydrogenation to methanol according to claim 1, characterized in that, Step (2) The molar ratio of the second metal atom in the second metal precursor to the first metal atom in the single-atom material is 1:

1.

3. A diatomic catalyst for catalytic CO2 hydrogenation to methanol according to claim 1, characterized in that, The roasting temperature in step (2) is 400-600℃ and the time is 4-12 h.

4. A method for producing methanol by CO2 hydrogenation, characterized in that, In the method, CO2 / H2 syngas is introduced into the diatomic catalyst for catalytic CO2 hydrogenation to methanol as described in any one of claims 1-3, and the reaction for CO2 hydrogenation to methanol is carried out in a fixed bed.

5. The method according to claim 4, characterized in that, The diatomic catalyst used for catalytic CO2 hydrogenation to methanol does not require activation pretreatment before use; the reaction conditions for CO2 hydrogenation to methanol are: CO2:H2=1:3-4, reaction temperature is 150~400 °C, reaction pressure is 0.1~5 MPa, and feed gas flow rate is 5~200 mL / min.

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