Preparation method and application of a specific crystal phase Ga2O3 modified Cu-based catalyst

Abstract

The application belongs to the field of catalysts, and discloses a preparation method and application of a specific crystal phase Ga2O3 modified Cu-based catalyst. The steps are as follows: a specific crystal phase Ga2O3 carrier is prepared by a precipitation method; a Cu precursor solution is used, and Cu species is loaded on the Ga2O3 by an impregnation method to obtain a catalyst precursor; the catalyst precursor is dried and calcined to obtain a treated solid powder; and the treated solid powder is reduced by H2 to obtain a Cu / Ga2O3 with different crystal phases. The application is characterized in that the catalyst preparation process is simple, the prepared crystal phase is highly single, and the catalysts with different carrier structures have obvious differences in the field of CO2 hydrogenation to prepare methanol, thereby providing a direction for studying the influence of structure on reaction activity.

Description

Technical Field

[0001] This invention belongs to the field of catalysts and relates to a method for preparing a Cu-based catalyst modified with a specific crystalline phase Ga2O3 and its application. Background Technology

[0002] With excessive CO2 emissions exacerbating the global greenhouse effect and causing a series of environmental problems, CO2 conversion and utilization has become a major research hotspot in the energy and environment fields. Methanol (CH3OH) can serve as a clean fuel, a hydrogen storage carrier, and a basic raw material for a series of chemical synthesis products. Converting CO2 into CH3OH (CO2 + 3H2 = CH3OH + H2O) has significant industrial application prospects for realizing the resource utilization of CO2. However, the reaction of CO2 hydrogenation to methanol requires relatively stringent reaction conditions (typically reaction temperature > 200℃, pressure > 3MPa) and involves a relatively complex reaction mechanism, which places stringent requirements on the selection of suitable catalysts.

[0003] In the CO2 hydrogenation to methanol reaction system, Cu-based catalysts are among the most commonly used catalyst elements due to their low cost, wide availability, and excellent CO2 adsorption and activation capabilities as well as H2 dissociation capabilities. However, existing Cu-based catalysts have significant shortcomings: unstable catalytic activity and easy deactivation, easy sintering, poor selectivity, and insufficient understanding of their reaction mechanisms, leading to significant drawbacks in their industrial applications. Ga2O3, as an important metal oxide, is often used as a catalyst modifier or support. It has various crystal phases (α, β, γ, etc.), and different Ga2O3 crystal phases have significantly different effects on catalyst performance regulation due to differences in crystal structure and surface properties. However, in current technology, most studies only use single-phase Ga2O3 to modify Cu-based catalysts, without systematically comparing the effects of different Ga2O3 crystal phases, and without clarifying the specific influence mechanism of crystal structure on the CO2 hydrogenation reaction. This results in the inability to fully improve the performance of Cu-based catalysts, limiting their industrial applications.

[0004] Therefore, studying the specific effects of catalysts with the same elemental composition but different crystal phase structures on the CO2 hydrogenation to methanol reaction will significantly improve the economy and practicality of catalysts in this field, thus becoming one of the key research directions for breaking through existing technological bottlenecks. Summary of the Invention

[0005] Addressing the research challenges of existing Cu-based catalysts in CO2 hydrogenation reactions, and the lack of clarity in the current technology regarding the specific mechanisms by which different Ga2O3 crystal phases regulate the performance of Cu-based catalysts, this invention provides Cu-based catalysts modified with specific Ga2O3 crystal phases and their preparation methods. By screening for the optimal Ga2O3 crystal phase, the CO2 hydrogenation performance of Cu-based catalysts is improved, and the relevant influencing mechanisms are resolved.

[0006] The technical solution of the present invention: A method for preparing a Cu-based catalyst modified with a specific crystalline phase Ga2O3, comprising the following steps: (1) A Ga2O3 support with a specific crystalline phase was prepared by precipitation method; (2) Using a Cu precursor solution, Cu species are loaded onto a Ga2O3 support by impregnation method to obtain a catalyst precursor; (3) The catalyst precursor is dried and then calcined to obtain the treated solid powder; (4) The treated solid powder was reduced by H2 to obtain Cu / Ga2O3 catalysts with different crystal phases, which are Cu-based catalysts modified with Ga2O3 of specific crystal phases.

[0007] Preferably, the preparation method of Ga2O3 support includes the following steps: Dissolve dried Ga(NO3)3 powder in deionized water at a mass ratio of 1g:15-20ml, stir until uniformly mixed, then add ammonia water until the pH is 9-10, continue stirring at room temperature for 1 hour, and then let stand for 2 hours; then filter and wash with deionized water to neutralize, place the obtained white solid in an oven at 60℃-80℃ to dry thoroughly, and then calcine in an air atmosphere at a calcination temperature of 500℃-800℃ for 5 hours to obtain Ga2O3 support.

[0008] Preferably, in step (1), when the calcination temperature is 500... o At C, α-Ga2O3 support is obtained; Preferably, in step (1), when the calcination temperature is 800°C... o At C, a β-Ga2O3 support is obtained; Preferably, in step (1), deionized water is replaced with anhydrous ethanol, and the solvent used to dilute ammonia is also replaced with anhydrous ethanol, and the solution is diluted at 500... o When calcined under C conditions, γ-Ga2O3 support was obtained.

[0009] Preferably, the precursor solution of Cu in step (2) is a copper nitrate solution with a mass concentration of 0.8 g / mL, calculated as Cu(NO3)2·3H2O.

[0010] Preferably, the impregnation method in step (2) is as follows: the ground Ga2O3 support is placed in a container, the volume of the Cu precursor solution required is calculated according to the mass fraction of metal Cu in the final specific crystal phase Ga2O3 modified Cu-based catalyst being 10 wt%, and the Cu is added dropwise, while stirring continuously for 30 min during the addition process to obtain the catalyst precursor.

[0011] Preferably, the drying temperature in step (3) is 80℃-100℃; Preferably, the roasting temperature in step (3) is 300°C and the roasting time is 4 hours.

[0012] Preferably, the flow rate of H2 in step (4) is 20 ml / min and the reduction time is 2 h.

[0013] Application of a Cu-based catalyst modified with a specific Ga2O3 phase in the reaction of CO2 hydrogenation to methanol.

[0014] Preferably, the application of Cu / Ga2O3 catalyst in the CO2 hydrogenation to methanol reaction comprises the following steps: Cu / Ga2O3 catalyst is granulated and placed in a fixed-bed reactor; the feed gas composition is 10%-40% carbon dioxide, 20%-80% hydrogen, and 10%-70% argon; the temperature is 200℃-300℃, and the space velocity is 6000-24000 mL / g. cat / h.

[0015] The beneficial effects of this invention are as follows: This invention uses a simple precipitation method to prepare a high-purity single-phase Ga2O3 catalyst support. After loading an equal amount of Cu species by impregnation, the Cu / γ-Ga2O3 catalyst exhibits significant performance advantages in the CO2 hydrogenation to methanol reaction, with the highest catalytic activity and the largest methanol yield, which are 2.4 times and 5.4 times that of Cu / α-Ga2O3 and Cu / β-Ga2O3 catalysts, respectively. At the same time, the influence of the Ga2O3 structure on the catalytic reaction is elucidated. Attached Figure Description

[0016] Figure 1 The XRD patterns of different Ga2O3 supports and Cu / Ga2O3 catalysts are shown. (a) shows the XRD patterns of the three supports α-Ga2O3, β-Ga2O3 and γ-Ga2O3 and the corresponding standard PDF cards; (b) shows the XRD patterns of Cu / α-Ga2O3, Cu / β-Ga2O3 and Cu / γ-Ga2O3 after Cu loading and the standard PDF card of Cu.

[0017] Figure 2 These are the Raman results for different Ga2O3 support samples.

[0018] Figure 3 These are the activity data of three (α, β, γ) Cu / Ga2O3 catalysts in the CO2 hydrogenation reaction (experimental conditions: 3 MPa, 240℃, GHSV = 21600 mL / g). cat / h); where (a) represents the selectivity and STY data for CH3OH, and (b) represents the conversion rate of CO2.

[0019] Figure 4 These are TEM images of Cu / Ga2O3 catalysts with three (α, β, γ) crystal phases; where (a) is the lattice fringe pattern of Cu and α-Ga2O3 support in Cu / α-Ga2O3 catalyst, (b) is the lattice fringe pattern of Cu and β-Ga2O3 support in Cu / β-Ga2O3 catalyst, and (c) is the lattice fringe pattern of γ-Ga2O3 support in Cu / γ-Ga2O3 catalyst.

[0020] Figure 5 These are the Arrhenius activation energy data for CO in Cu / Ga2O3 catalysts with three (α, β, γ) crystal phases.

[0021] Figure 6 These are the Arrhenius activation energy data for the Cu / Ga2O3 catalyst CH3OH with three (α, β, γ) crystal phases. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0023] Example 1: Weigh 5g of gallium nitrate (Ga(NO3)3) and dissolve it in 100mL of deionized water to form a solution. Stir for 30min until fully dissolved and mixed. Then, add diluted ammonia solution (concentrated ammonia to deionized water ratio 1:2) to adjust the pH to 9-10. Continue stirring at room temperature (25℃) for 1h, then let stand for 2h. Filter with deionized water and wash 6 times until neutral. Place the resulting white solid in an 80℃ oven and dry thoroughly for 12h. Calcine in air at 500℃ for 5h at a heating rate of 2℃ / min to obtain α-Ga2O3 support powder.

[0024] Weigh 0.9 g of the prepared α-Ga₂O₃ support using an electronic balance and place it in a beaker. Add 475 μL of Cu(NO₃)₂ solution (0.8 g / mL) dropwise onto the α-Ga₂O₃ support and grind thoroughly until all the Cu precursor solution is added. Continue stirring for 30 min to obtain the catalyst precursor. Dry the precursor at 80 °C overnight, then calcine it in air at a rate of 2 °C / min to 400 °C for 4 hours. Finally, reduce the catalyst in a hydrogen atmosphere at 300 °C for 2 hours (flow rate 20 mL / min) to obtain the 10Cu / α-Ga₂O₃ catalyst.

[0025] Example 2: Based on Example 1, the preparation method remains unchanged, except that the "calcination in air at 500°C for 5 hours" step is replaced with "calcination in air at 800°C for 5 hours". Other steps remain unchanged, thus obtaining β-Ga2O3 support powder and 10Cu / β-Ga2O3 catalyst.

[0026] Example 3: Based on Example 1, the preparation method remains unchanged, except that "5g gallium nitrate Ga(NO3)3 is dissolved in 100 mL of deionized water to form a solution" is replaced with "5g gallium nitrate Ga(NO3)3 is dissolved in 100 mL of anhydrous ethanol", and "adding diluted ammonia solution (concentrated ammonia water to deionized water ratio 1:2)" is replaced with "adding diluted ammonia water to anhydrous ethanol solution (concentrated ammonia water to anhydrous ethanol ratio 1:2)". All other steps remain unchanged, thus obtaining γ-Ga2O3 support powder and 10Cu / γ-Ga2O3 catalyst.

[0027] Example 4: Based on Example 1, the mass of the α-Ga2O3 support in "weighing 0.9g of the prepared α-Ga2O3 support and placing it in a beaker, and transferring 475uL of Cu(NO3)2 solution (mass fraction of 0.8g / mL)" was changed to 0.99g, and the amount of Cu(NO3)2 solution (mass fraction of 0.8g / mL) transferred was 47.5uL, thus obtaining the 1Cu / α-Ga2O3 catalyst.

[0028] Example 5: Based on Example 4, the “α-Ga2O3 support” was changed to β-Ga2O3, while other steps remained unchanged, thus obtaining the 1Cu / β-Ga2O3 catalyst.

[0029] Example 6: Based on Example 4, the “α-Ga2O3 support” was changed to γ-Ga2O3, while other steps remained unchanged, thus obtaining the 1Cu / γ-Ga2O3 catalyst.

[0030] Example 7: The catalyst prepared above was sieved to 40-60 mesh. 0.1 g of the catalyst was weighed and its performance was tested in a fixed-bed reactor with a feed gas space velocity of 21600 mL / g. cat. The feed gas composition was CO2:H2:Ar = 1:3:1. The reaction temperature was 240℃, and testing was performed after 1 hour of reaction. Online analysis was performed using a Tianmei GC-7980 gas chromatograph equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). The chromatographic columns included a 13X+5A molecular sieve column and a PN column.

[0031] The XRD patterns of the catalysts and their supports obtained in Examples 1-3 are shown in the attached figures. Figure 1 As shown in Figure a, for the catalyst support, the characteristic diffraction peaks of α-Ga₂O₃ appear at 24.5°, 33.8°, 36.0°, 41.4°, 50.3°, 55.1°, 59.0°, 63.4°, 64.8°, 73.9°, and 76.4° (PDF#43-1013). The characteristic diffraction peaks of β-Ga₂O₃ are identified at 19.0°, 30.5°, 31.7°, 33.5°, 35.2°, 37.4°, 38.4°, 45.8°, 48.6°, 57.6°, 59.0°, 60.9°, and 64.6° (PDF#41-1103). The characteristic diffraction peaks of γ-Ga₂O₃ are located at 36.2° and 64.2° (PDF#20-0426). These supports correspond perfectly to the PDF cards, indicating that the crystal phases of these supports are highly homogeneous. Subsequently... Figure 1 Figure b shows the XRD pattern of the Cu-supported catalyst. An additional signal can be observed at 43.3°, corresponding to the (111) crystal plane of Cu (PDF#04-0836). It is worth noting that the shapes of the Cu signals are different in the three catalysts; the Cu diffraction peak of 10Cu / γ-Ga2O3 is significantly wider than that of the other two catalysts, indicating that the state of Cu species is different on different supports.

[0032] The Raman spectra of the catalyst supports obtained in Examples 1-3 are shown in the attached figures. Figure 2 As shown, only the Raman characteristic peak of the corresponding crystal phase was detected for each support, indicating that the surface of the support is highly consistent with the bulk phase, and all of them are Ga2O3 supports of the corresponding single crystal phase.

[0033] The 10Cu / α-Ga₂O₃, 10Cu / β-Ga₂O₃ and 10Cu / γ-Ga₂O₃ catalysts prepared in Examples 1-3 were tested at a pressure of 3 MPa and a space velocity of 21600 mL·g⁻¹. cat. -1 ·h-1 Performance was evaluated under a mixed atmosphere of 1CO2 / 3H2 / 1Ar, and the results are attached. Figure 3 As shown, catalysts with different crystal phases exhibit significant differences at 240℃. It can be observed that the methanol space-time yield of the 10Cu / γ-Ga₂O₃ catalyst is 136 g. MeOH kg cat -1 h -1 The efficiency was 2.4 times and 5.4 times that of 10Cu / α-Ga₂O₃ and 10Cu / β-Ga₂O₃, respectively. The conversion rate was 4.3%, far exceeding that of the 10Cu / α-Ga₂O₃ and 10Cu / β-Ga₂O₃ catalysts, indicating that the crystallinity significantly affects the catalytic activity of the catalyst. The 1Cu / α-Ga₂O₃, 1Cu / β-Ga₂O₃, and 1Cu / γ-Ga₂O₃ catalysts prepared in Examples 4-6 also showed that the 1Cu / γ-Ga₂O₃ catalyst exhibited the highest catalytic activity. This excluded the influence of differences in optimal loading, further demonstrating that γ-Ga₂O₃ has a significant impact on improving the catalytic activity of Cu-based catalysts.

[0034] TEM images of the 10Cu / α-Ga₂O₃, 10Cu / β-Ga₂O₃, and 10Cu / γ-Ga₂O₃ catalysts prepared in Examples 1-3 are attached. Figure 4 As shown, on the 10Cu / α-Ga2O3 catalyst, the lattice fringes of the α-Ga2O3 support with d(104)=0.265nm and the lattice fringes of Cu with d(111)=0.208nm can be clearly observed. On the 10Cu / β-Ga2O3 catalyst, the lattice fringes of the β-Ga2O3 support with d(111)=0.254nm and the lattice fringes of Cu with d(111)=0.208nm can be clearly observed. However, on the 10Cu / γ-Ga2O3 catalyst, only the lattice fringes of the γ-Ga2O3 support with d(311)=0.248nm are observed, and no lattice fringes of Cu are observed. This indicates that Cu has the highest dispersion on the γ-Ga2O3 support, which is consistent with XRD.

[0035] The CO activation energy data of the 10Cu / α-Ga₂O₃, 10Cu / β-Ga₂O₃ and 10Cu / γ-Ga₂O₃ catalysts prepared in Examples 1-3 are attached. Figure 5 As shown, the CO formation energies of the three catalysts are 102.2, 112.8, and 110.1 kJ / mol, respectively, indicating that CO formation by the three catalysts is highly dependent on temperature. (See attached image.) Figure 6As shown, the CH3OH formation energies of the three catalysts are 57.9, 65.9, and 35.5 kJ / mol, respectively. It can be observed that the methanol formation energy of 10Cu / γ-Ga2O3 is significantly lower than that of 10Cu / α-Ga2O3 and 10Cu / β-Ga2O3. This directly indicates that the γ-Ga2O3 support can reduce the methanol formation energy of Cu-based catalysts without changing the CO formation energy, thereby improving the methanol yield.

[0036] This invention reveals the influence of different Ga2O3 phases on Cu-based catalysts during the CO2 hydrogenation reaction. We found that γ-Ga2O3 can improve the dispersion of Cu and reduce the formation energy of CH3OH while keeping the CO formation energy constant, thus giving it higher methanol catalytic activity.

Claims

1. A method for preparing a Cu-based catalyst modified with a specific crystalline phase Ga2O3, characterized in that, The steps are as follows: (1) A Ga2O3 support with a specific crystalline phase was prepared by precipitation method; (2) Using a Cu precursor solution, Cu species are loaded onto a Ga2O3 support by impregnation method to obtain a catalyst precursor; (3) The catalyst precursor is dried and then calcined to obtain the treated solid powder; (4) The treated solid powder was reduced by H2 to obtain Cu / Ga2O3 catalysts with different crystal phases, which are Cu-based catalysts modified with Ga2O3 of specific crystal phases.

2. The preparation method according to claim 1, characterized in that, The preparation method of Ga2O3 support includes the following steps: Dissolve dried Ga(NO3)3 powder in deionized water at a mass ratio of 1g:15-20ml, stir until uniformly mixed, then add ammonia water until the pH is 9-10, continue stirring at room temperature for 1 hour, and then let stand for 2 hours; then filter and wash with deionized water to neutralize, place the obtained white solid in an oven at 60℃-80℃ to dry thoroughly, and then calcine in an air atmosphere at a calcination temperature of 500℃-800℃ for 5 hours to obtain Ga2O3 support.

3. The preparation method according to claim 2, characterized in that, When the roasting temperature is 500 o At C, α-Ga2O3 support is obtained; When the roasting temperature is 800 o At C, a β-Ga2O3 support is obtained; Replace deionized water with anhydrous ethanol, and also replace the solvent used to dilute ammonia with anhydrous ethanol, and at 500... o When calcined under C conditions, γ-Ga2O3 support was obtained.

4. The preparation method according to claim 1, characterized in that, The precursor solution for Cu is a copper nitrate solution with a mass concentration of 0.8 g / mL, calculated as Cu(NO3)2·3H2O.

5. The preparation method according to claim 1, characterized in that, In step (2), the impregnation method is as follows: the ground Ga2O3 support is placed in a container, and the volume of the Cu precursor solution required is calculated according to the mass fraction of metal Cu in the final specific crystal phase Ga2O3 modified Cu-based catalyst being 10 wt%. The Cu precursor solution is added dropwise and stirred continuously for 30 min during the addition process to obtain the catalyst precursor.

6. The preparation method according to claim 1, characterized in that, In step (3), the drying temperature is 80℃-100℃; The roasting temperature was 300℃ and the roasting time was 4 hours.

7. The preparation method according to claim 1, characterized in that, In step (4), the flow rate of H2 is 20 ml / min and the reduction time is 2 h.

8. Application of a Cu-based catalyst modified with a specific Ga2O3 phase in the reaction of CO2 hydrogenation to methanol.

9. The application according to claim 8, characterized in that, The steps are as follows: The Cu-based catalyst modified with a specific Ga2O3 phase is pressed into tablets and granulated, then placed in a fixed-bed reactor; the feed gas integral composition is 10%-40% carbon dioxide, 20%-80% hydrogen, and 10%-70% argon; the temperature is 200℃-300℃, and the space velocity is 6000-24000 mL / g. cat / h.

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