A Pt / MnOx catalyst for reverse water gas shift reaction x Catalyst and methods of making and using same

Abstract

The application discloses a Pt / MnO x catalyst for reverse water gas shift reaction and a preparation and use method thereof. x The catalyst is prepared by a one-step method, Pt is loaded on a manganese oxide (MnO x ) carrier to prepare a series of Pt / MnO x catalysts. The obtained catalysts can still have monatomic Pt at a high Pt loading (2 wt%), have atomic-level dispersion, and have high stability. In addition, the catalysts significantly improve the activity and selectivity of the reverse water gas shift reaction, the CO2 conversion rate approaches the thermodynamic equilibrium, and the CO selectivity reaches 100%; and the preparation method is simple in operation, controllable in reaction process, and has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide conversion technology, specifically relating to a Pt / MnO2 for counter-current gasification reaction. x Catalysts and their preparation and application methods. Background Technology

[0002] As the energy cornerstone of modern industry, the massive combustion of fossil fuels induces large-scale CO2 emissions, causing a severe greenhouse effect and seriously threatening the ecological environment. CO2 emission reduction and resource utilization are of great significance for solving energy and environmental problems and achieving "carbon neutrality." The reverse-flow gasification reaction can directly convert CO2 into CO using hydrogen produced from renewable energy sources, and then further obtain various high-value-added chemicals through processes such as Fischer-Tropsch synthesis, thus possessing good economic benefits. However, the occurrence of methanation side reactions reduces the efficiency of the reverse-flow gasification reaction.

[0003] Single-atom catalysts, due to their 100% atomic utilization, unique surface structure and electronic properties, and uniform active sites, exhibit high reactivity and excellent selectivity in many selective hydrogenation reactions. Currently, single-atom catalysts used in reverse water-gas reactions primarily employ noble metal-based catalysts (Pt, Ru, Ir) as the active component, and are mainly prepared through methods such as impregnation, precipitation, and ball milling. However, these preparation processes are complex, resulting in poor catalyst homogeneity and failing to ensure that all active components are atomically dispersed. Furthermore, they impose stringent requirements on the loading of active components; at higher loadings (>1%), the active components are prone to agglomeration, undergoing a structural transformation from single atoms to clusters. In contrast, single-atom catalysts prepared by one-step doping with active metals are not only simple to operate and have a controllable process, but also exhibit uniform composition and maintain atomic dispersion even at higher loadings.

[0004] Manganese oxide (MnO) x It exhibits excellent redox properties; after hydrogen reduction treatment, its surface readily generates abundant oxygen vacancies, which combine with MnO. x The moderately alkaline sites on MnO can promote CO2 adsorption. However, due to the lack of further transformation sites, the adsorbed CO2 is difficult to further activate and transform, so pure MnO... x The activity is poor, resulting in a lower CO2 conversion rate.

[0005] To address the above issues, MnO x MnO was prepared in a one-step process by loading active metal Pt onto a support. x Supported single-atom Pt catalyst. Wherein, Pt and MnO... xThe synergistic effect of Pt and Mn (especially the formation of Pt-O-Mn bonds and the electron transfer between them) significantly improves the activation and conversion of CO2, promotes the transformation of the intermediate species HCOO* to CO, and inhibits the methanation reaction pathway, thus resulting in high reactivity of the reverse-flow gas reaction. Furthermore, the Pt single atoms obtained through the one-step method can effectively crack hydrogen gas and accelerate the reaction of MnO through hydrogen overflow. x The reduction of the support promotes the formation of oxygen vacancies and the adsorption and activation of CO2 on the support. Simultaneously, the resulting MnO... x The support can interact strongly with Pt, effectively inhibiting the aggregation and growth of Pt single atoms during the reaction process, maintaining the stability of the active center, and improving the stability of the reaction.

[0006] Therefore, the technical problem to be solved by the present invention is to address the shortcomings of existing MnO... x To address the issues of low activity and poor stability of catalysts in countercurrent gas reactions, as well as the complex preparation processes, poor uniformity, and stringent loading requirements of existing supported single-atom catalysts in countercurrent gas reactions, a Pt / MnO catalyst with a unique single-atom structure was designed. x The catalyst exhibits high activity, high selectivity, and high stability in the counter-current water-gas reaction. A one-step method is used to load Pt onto MnO. x Atomic-scale dispersed Pt / MnO was obtained on the support. x The catalyst has a simple preparation process, mild conditions, is easy to promote and use, and can effectively suppress the occurrence of methanation side reactions. Summary of the Invention

[0007] The main objective of this invention is to address the shortcomings of existing MnO... x To address the issues of low activity and poor stability of catalysts in low-temperature countercurrent water gas reactions, a Pt / MnO catalyst with a unique single-atom structure is proposed. x The catalyst exhibits high activity and stability in low-temperature countercurrent water-gas shift reactions. Addressing the challenges of complex preparation processes, poor uniformity, and stringent loading requirements for supported single-atom catalysts in countercurrent water-gas shift reactions, a one-step method is employed to load Pt onto MnO. x Atomic-scale dispersed Pt / MnO was obtained on the support. x Catalysts are simple to prepare, require mild conditions, and are easy to promote and use.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A Pt / MnO catalyst for catalytic reverse water gas reaction x The catalyst consists of a support and an active component; the support is MnO. xIt exists in one or more of the following forms: MnO, MnO2, Mn2O3, and Mn3O4; the active component Pt is dispersed on the support in the form of single atoms.

[0010] The present invention also provides a Pt / MnO for counter-current gas reaction. x The catalyst preparation method includes the following steps:

[0011] First, according to the elemental mass percentage, chloroplatinic acid (H₂PtCl₆·6H₂O) solution was added dropwise to potassium permanganate (KMnO₄) powder. The mixture was stirred thoroughly at room temperature and then placed in an oven at 60-100℃ to completely evaporate the moisture. After the dried sample cooled to room temperature, anhydrous citric acid (C₆H₈O₇) powder was added and ground thoroughly until the two mixtures were uniformly dispersed, free of particles, and of uniform color. The mixture was then spread evenly on a quartz glass plate and ignited with an open flame. After complete combustion, a black solid was obtained and washed several times with deionized water. Finally, the resulting filter cake was dried overnight in an oven at 60-100℃. The dried filter cake was mixed with an ammonium salt solution and subjected to ion exchange at 70-90℃ for 6-12 hours. After centrifugation with deionized water until pH=7, the sample was then dried overnight in an oven at 60℃. After repeating the ion exchange step three times, the sample was calcined at 300-500℃ for 2-10 h in an oxygen atmosphere to obtain a one-step Pt-supported catalyst, denoted as Pt(y) / MnO. x -SDC(y=Pt wt%).

[0012] In the aforementioned step, the molar ratio of KMnO4 to anhydrous C6H8O7 powder is 13:1.

[0013] In the aforementioned steps, the loading of Pt, expressed as an elemental mass percentage, is 0.1-5 wt%.

[0014] In the aforementioned steps, the ammonium salt solution is either ammonium chloride (NH4Cl) solution or ammonium nitrate (NH4NO3) solution, with a concentration of 0.1-1 mol / L.

[0015] This invention relates to Pt / MnO for catalyzing counter-current water gas reactions. x How to use the catalyst:

[0016] The catalyst was loaded into a fixed-bed reactor and reduced at 300-500℃ for 1 hour under a H2 atmosphere with an H2 flow rate of 30 mL / min. -1 Then, H2 / CO2 mixed gases with volume ratios of 1:1, 2:1, 3:1, and 4:1 are introduced, and the mixture is kept at a temperature of 300-500℃ and a gas weight space-time velocity of... The reaction takes place under specific conditions.

[0017] Compared with the prior art, the superior effects of the present invention are:

[0018] Compared with existing single-atom catalyst preparation processes, the preparation method provided by this invention is simple and convenient to operate, operates under mild conditions, and is easy to scale up and promote.

[0019] Compared with existing MnO x Compared with other catalysts, this invention has better low-temperature catalytic activity and can achieve high CO2 conversion rates at lower temperatures, such as reaching thermodynamic equilibrium conversion rates at 440°C.

[0020] Compared with existing single-atom catalysts, the present invention has 100% CO selectivity and no byproducts such as CH4. Attached Figure Description

[0021] Figure 1 X-ray diffraction pattern of the catalyst of this invention

[0022] Figure 2 X-ray photoelectron spectroscopy of the catalyst of this invention

[0023] Figure 3 a: The Pt(0.2) / MnO used in this invention x -High-angle annular dark-field scanning transmission electron microscopy image of SDC catalyst

[0024] Figure 3 b: The Pt(2) / MnO used in this invention x -High-angle annular dark-field scanning transmission electron microscopy image of SDC catalyst

[0025] Figure 3 c: The Pt(0.2) / MnO used in this invention x High-angle annular dark-field scanning transmission electron microscopy image of IMP catalyst

[0026] Figure 3 d: Pt(2) / MnO used in this invention x High-angle annular dark-field scanning transmission electron microscopy image of IMP catalyst

[0027] Figure 4 : Catalytic performance diagram of the catalyst of this invention in the CO2 hydrogenation reaction Detailed Implementation

[0028] The main purpose of this invention is to obtain atomically dispersed Pt(y) / MnO with a unique structure. x The catalyst is applied to the countercurrent water gas reaction to improve its activity and selectivity. To achieve the above objectives, embodiments of the present invention are described in detail below with reference to examples.

[0029] Example 1

[0030] First, take 2.00 g of KMnO4 ground into powder and add 10 mL of 0.02 mol / L H2PtCl6·6H2O solution. After mixing, place the mixture in a 100℃ oven to evaporate the moisture. After cooling to room temperature, add 0.19 g of anhydrous C6H8O7 powder and grind thoroughly for 30 min until it is uniformly dispersed, free of particles, and has a uniform color. Then, spread the mixture in a long strip onto a quartz glass plate and ignite it with an open flame. After complete combustion, a black solid is obtained and washed with 500 mL of deionized water. Finally, dry the obtained sample in a 60℃ oven overnight. Weigh 1.00 g of the dried sample and mix it with 30 mL of 0.50 mol / L NH4NO3 solution. Perform ion exchange at a constant temperature of 75℃ for 8 h, then centrifuge and wash with deionized water until pH = 7. Subsequently, place the sample in a 60℃ oven to dry overnight. The ion exchange step was repeated three times, and finally the sample was calcined at 500℃ for 4 h in an oxygen atmosphere to obtain a one-step Pt-supported catalyst, which was named Pt(2) / MnO. x -SDC. The obtained catalyst was characterized by XRD crystal structure, such as... Figure 1 As shown, the manganese oxide in this catalyst was found to be α-Mn₂O₃. When the Pt loading was 2 wt%, no diffraction peaks of Pt species were observed, indicating that Pt was highly dispersed in the support. According to... Figure 1 The corresponding magnified XRD pattern shows that Pt(2) / MnO x The diffraction peak of -SDC shifted to the left, indicating that Pt species can be stably doped into MnO after ion exchange treatment. x In the crystal lattice of Pt(2) / MnO. x -SDC is used for XPS surface structure characterization, such as Figure 2 As shown, in Pt(2) / MnO x The presence of Pt species on the surface of the SDC catalyst indicates that not all Pt species are incorporated into the support lattice; some Pt ​​is dispersed on the support surface. To verify the size of the Pt, we prepared Pt(0.2) / MnO using the method described above. x -SDC catalyst, and for Pt(0.2) / MnO x -SDC and Pt(2) / MnO x The SDC catalyst was imaged using a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), and the results are as follows: Figure 3 a and Figure 3 As shown in b, it was found that in both samples, the Pt species existed in single-atom form, and even at a high Pt loading of 2 wt%, Pt remained dispersed in the support in single-atom form.

[0031] Comparative Example 1

[0032] Weigh 2.00 g of KMnO4 ground into powder, add 0.19 g of anhydrous C6H8O7 powder and grind until uniformly dispersed, free of particles, and uniform in color. Spread the mixture in a long strip onto a quartz glass plate, then ignite it with an open flame. After complete combustion, a black solid is obtained. Wash with 500 mL of deionized water and dry the sample overnight in an oven at 60 °C to obtain MnO4. x Solid. Then weigh 1.00g MnO x The solid was mixed with 30 mL of 0.50 mol / L NH4NO3 solution. Ion exchange was performed at 75 °C for 8 h. The sample was then washed with deionized water by centrifugation until pH = 7, and subsequently dried overnight in a 60 °C oven. The ion exchange step was repeated three times. Finally, the sample was calcined at 500 °C for 4 h under an oxygen atmosphere to obtain MnO. x Carrier. Finally, based on the elemental mass percentage, weigh 1.00 g of MnO. x The carrier was mixed with 10 mL of 0.02 mol / L H2PtCl6·6H2O solution, stirred at room temperature for 6 h, heated to 60 °C to evaporate the water, and then dried overnight in an oven at 60 °C. The dried sample was then calcined at 300 °C for 3 h under an oxygen atmosphere to obtain Pt(2) / MnO prepared by the impregnation method. x -IMP catalyst. Pt(2) / MnO x XRD crystal structure characterization was performed using an IMP catalyst, such as... Figure 1 As shown, MnO x The support has the crystal form of α-Mn₂O₃. After impregnation with Pt, no diffraction peaks of Pt species were observed (2wt%), indicating that Pt is highly dispersed in the support. For Pt(2) / MnO₃... x -IMP is used for XPS surface structure characterization, such as Figure 2 As shown, the peak intensity of Pt4f is significantly higher than that of Pt(2) / MnO. x -SDC indicates that Pt(2) / MnO prepared by the impregnation method... x In the -IMP catalyst, Pt species are mainly dispersed on the surface of the support. To investigate the size of Pt in the catalyst prepared by conventional impregnation method, we prepared Pt(0.2) / MnO using the same method described above. x -IMP catalyst, and for Pt(0.2) / MnO x -IMP and Pt(2) / MnO x -IMP catalyst was imaged using HAADF-STEM, such as Figure 3 c and Figure 3As shown in Figure d, it was found that when the Pt loading was 0.2 wt%, Pt species were dispersed on the support as small nanoclusters. When the Pt loading reached 2 wt%, the size of the Pt clusters increased significantly. Combined with the results of Example 1, this strongly demonstrates that one-step Pt loading is more beneficial for Pt species in MnO. x Anchoring and dispersion on the carrier.

[0033] Example 2

[0034] First, Pt(y) / MnO with different loading amounts x -SDC (y = 0.2, 0.5, 1, 2, 3) catalysts were sieved to 40-60 mesh. Then, 0.10 g of catalyst and 0.40 g of 40-60 mesh quartz sand were mixed evenly and loaded into a quartz reaction tube, which was then placed in a fixed-bed reactor. Reduction was carried out at 500℃ for 1 h under a H2 atmosphere with a flow rate of 30 mL / min. -1 After reduction, a 1:1 volume ratio of H2 / CO2 reaction gas is introduced, and the reaction temperature is 300-500℃ with a gas weight space-time velocity of [missing value]. Under these conditions, a countercurrent water-gas reaction was carried out. The reaction results are as follows: Figure 4 As shown in the left figure, the most active catalyst among those prepared by the one-step method is Pt(2) / MnO. x -SDC achieves thermodynamic equilibrium conversion at 440℃, and all catalysts exhibit 100% CO selectivity.

[0035] Comparative Example 2

[0036] First, Pt(y) / MnO with different loading amounts x -IMP (y = 0.2, 0.5, 1, 2, 3) catalysts were sieved to 40-60 mesh. Then, 0.10 g of catalyst and 0.40 g of 40-60 mesh quartz sand were mixed evenly and loaded into a quartz reaction tube, which was then placed in a fixed-bed reactor. Reduction was carried out at 500℃ for 1 h under a H2 atmosphere with a flow rate of 30 mL / min. -1 After reduction, a 1:1 volume ratio of H2 / CO2 reaction gas is introduced, and the reaction temperature is 300-500℃ with a gas weight space-time velocity of [missing value]. Under these conditions, a countercurrent water-gas reaction was carried out. The reaction results are as follows: Figure 4 As shown in the right figure, the most active catalyst prepared by the impregnation method is Pt(2) / MnO. x -IMP. Combined with Example 2, it was found that even Pt(2) / MnO x The CO selectivity of the -IMP catalyst is 100%, but its conversion rate is much lower than that of Pt(2) / MnO. x-SDC demonstrates that the one-step prepared single-atom Pt catalyst has better anti-water gas reaction activity.

Claims

1. A Pt / MnO for counter-current gas reaction x A method for preparing a catalyst, wherein the catalyst comprises a support and an active component, and the support is MnO. x It exists in one or more of the following forms: MnO, MnO2, Mn2O3, and Mn3O4, with the active component Pt anchored on the support in monatomic form; characterized in that... Includes the following steps: First, according to the elemental mass percentage, chloroplatinic acid solution is added dropwise to potassium permanganate powder and stirred evenly at room temperature. The mixture is then placed in an oven at 60-100℃ to completely evaporate the moisture. After the dried potassium permanganate powder cools to room temperature, anhydrous citric acid powder is added and ground thoroughly until the mixture is uniformly dispersed, free of particles, and has a uniform color. The mixture is then spread evenly on a quartz glass plate. The molar ratio of potassium permanganate to anhydrous citric acid powder is 13:

1. Subsequently, it is ignited with an open flame, and after complete combustion, a black solid is obtained. This solid is washed several times with deionized water. Finally, the resulting filter cake is dried overnight in an oven at 60-100℃. The dried filter cake is then mixed with an ammonium salt solution and subjected to ion exchange at 70-90℃ for 6-12 hours. Afterward, it is washed with deionized water by centrifugation until pH=7. The sample is then dried overnight in an oven at 60℃. This ion exchange step is repeated three times. Finally, the sample is calcined at 300-500℃ for 2-10 minutes under an oxygen atmosphere. h, a one-step Pt-supported catalyst was obtained, denoted as Pt(y) / MnO. x -SDC, where y = Pt wt%; the loading of Pt is 0.1-5 wt% by mass of the element.

2. The method according to claim 1, characterized in that, The ammonium salt solution is either an NH4Cl solution or an NH4NO3 solution, with a concentration of 0.1-1 mol / L.

3. The Pt / MnO prepared by the method of claim 1 for use in countercurrent water-gas reaction. x The application of catalysts is characterized by, The catalyst was loaded into a fixed-bed reactor and reduced at 300-500℃ for 1 h under a H2 atmosphere with an H2 flow rate of 30 mL / min. -1 Then, a mixture of H2 / CO2 gas with a volume ratio of 1:1 to 4:1 is introduced at a temperature of 200-500℃ and a gas weight space velocity of 10,000-300,000. The reaction takes place under specific conditions.

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