Preparation method of ruthenium monatomic catalyst for efficient photo-thermal catalytic methane dry reforming

Abstract

The application discloses a preparation method of a Ru monatomic catalyst for efficient photo-thermal catalysis of dry reforming of methane, and comprises the following steps: 1) preparing a CeO2 carrier with a Mg-CeO2-NR structure through a hydrothermal synthesis method; and 2) preparing a Ru monatomic catalyst through electrostatic adsorption with the CeO2 carrier. The catalyst obtained through the method has excellent photo-thermal catalysis performance and catalytic stability.

Description

Technical Field

[0001] This invention belongs to the field of energy photothermal chemical conversion technology, and relates to a method for preparing a Ru single-atom catalyst for efficient photothermal catalytic dry reforming of methane. Background Technology

[0002] Converting the major greenhouse gases CH4 and CO2 into syngas is a promising method for mitigating the greenhouse effect. This can be achieved through dry reforming of methane (DRM), simultaneously yielding syngas for downstream industrial applications, such as the production of high-value-added syngas for methanol and alkanes. However, the DRM reaction is considered kinetically and thermodynamically unfavorable. Therefore, it is widely driven at high operating temperatures (>700°C). At these temperatures, catalyst coking and deactivation, along with increased equipment material costs, necessitate the search for milder catalytic conditions to drive the DRM reaction without compromising catalytic performance.

[0003] In recent decades, the concept of photocatalysis, which utilizes the photoelectric effect to excite photoelectrons and holes to promote surface reactions, has been applied to various research fields. In photocatalysis, due to the photoelectric effect, excited photoelectrons are transferred to active sites, accelerating the dissociation of surface reactants or specific microsteps during the reaction. Separated holes can also serve as potential catalytic active sites. However, due to the high bond energies of the reactants in the DRM reaction (CH bond energy approximately 430 kJ·mol⁻¹), the photocatalysis process is challenging. -1 The C=O bond energy is approximately 750 kJ·mol⁻¹ -1 Due to its strong endothermic properties, the driving force of the reaction under photocatalytic conditions remains limited. Currently, it has been reported that the efficiency of the photocatalytic DRM reaction exceeds the maximum thermodynamic allowable value of the thermocatalytic system, but its absolute syngas production rate (μmol·g⁻¹) is still limited. cat -1 ·h -1 (grade) and reactant conversion rate (<10) -3 The levels remain extremely low, making it difficult to apply to actual industrial processes.

[0004] In recent years, high-temperature photothermal catalysis (HT-PTC) DRM reactions have been widely reported. Initial experimental setups feature an additional heating mode, allowing direct light irradiation onto the catalyst surface. This enables the imparting of initial energy to reactant molecules during the reaction, while simultaneously weakening the reaction energy barrier by exciting electron-hole pairs, thus promoting the rate-determining step (RDS), generally considered the first step in activating CH4 and CO2, thereby enhancing the surface reaction. This synergistic catalysis of photocatalysis and thermocatalysis results in photothermal DRM reactions achieving more impressive reaction rates than thermocatalysis. Yang et al. reported that a Rh / CeWO3 catalyst excited photothermal and photoelectric effects, overcoming the thermodynamic limitations under conventional reaction conditions and achieving super-generation rates of H2 and CO between 300-400 °C. Furthermore, researchers have developed a series of catalysts based on photothermal catalysis routes, achieving high catalytic performance. However, it is noteworthy that in the published literature, most reactant / product conversion / generation rates remain below the thermodynamic limit or operate at low equivalence flow rates, and catalytic stability is also unsatisfactory. The technological advantages of photothermal catalysis have not been fully realized.

[0005] Due to the atomic dispersion of active sites, single-atom catalysts (SACs) exhibit high atomic utilization of active components, significantly facilitating key reaction steps in kinetics compared to catalysts with active sites possessing nanocluster / nanoparticle structures (typically considered metallic). This enables the achievement of syngas yields exceeding thermodynamic limits at high equivalence flow rates. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a Ru single-atom catalyst for efficient photothermal catalytic dry reforming of methane. The catalyst obtained by this method has excellent photothermal catalytic performance and catalytic stability.

[0007] To achieve the above objectives, this invention discloses a method for preparing a Ru single-atom catalyst for efficient photothermal catalytic dry reforming of methane, comprising the following steps:

[0008] 1) CeO2 support with Mg-CeO2-NR structure was prepared by hydrothermal synthesis;

[0009] 2) Prepare Ru single-atom catalysts using electrostatic adsorption on CeO2 support.

[0010] The specific operation of step 1) is as follows:

[0011] Ce(NO3)3·6H2O and Mg(NO3)2·6H2O were added to NaOH solution, stirred, and then a turbid liquid was added. The mixture was stirred at room temperature and then subjected to a hydrothermal reaction. The precipitate was then washed, dried, and calcined to obtain a CeO2 support with a Mg-CeO2-NR structure.

[0012] The ratio of Ce(NO3)3·6H2O, Mg(NO3)2·6H2O and NaOH is 20 mmol: 0.0025 mol: 2.4 mol.

[0013] The temperature during the hydrothermal reaction is 100℃.

[0014] The precipitate obtained from the reaction was washed by centrifugation.

[0015] The specific process of step 2) is as follows:

[0016] Add Ru(NO)(NO3) to ultrapure water x (OH) y After adjusting the pH value, the CeO2 support was added and ultrasonically dispersed. The mixture was then stirred at room temperature, and the resulting precipitate was washed to obtain a catalyst precursor. The catalyst precursor was then calcined to obtain a Ru single-atom catalyst.

[0017] Ru(NO)(NO3) x (OH) y The ratio of CeO2 carrier is 0.0159g:1g by mass.

[0018] The present invention has the following beneficial effects:

[0019] The method for preparing a high-efficiency photothermal catalytic Ru single-atom catalyst for dry reforming methane, as described in this invention, involves the hydrothermal synthesis of CeO2 nanorods. By adjusting the catalyst morphology (nanorods) and the doping of the functional group (Mg element), the physicochemical properties of the catalyst are altered to obtain excellent catalytic performance. The Ru-O-Ce structure CeO2 nanorods constructed in this invention exhibit strong catalytic activity for the DRM reaction. Mg doping promotes CeO2 adsorption, thereby accelerating the DRM reaction and eliminating carbon deposition, extending the catalyst's lifespan. Furthermore, under light irradiation, the recombination rate of laser-induced electrons and holes is suppressed by oxygen vacancies and Mg doping, allowing laser-induced electrons to migrate through the Ru-O-Ce structure to the Ru active sites, thus promoting CH4 dissociation. Under Mg and Ru co-doping conditions, oxygen vacancies are more easily formed, and the increased surface defects generated by further light irradiation also facilitate CeO2 adsorption and CH4 activation, promoting the rate-controlling step of the DRM reaction and consequently increasing the product formation rate in the thermal reaction system under photothermal synergistic catalysis. Attached Figure Description

[0020] Figure 1 This is a TEM image of Ru1 / Mg-CeO2-NR in Example 2;

[0021] Figure 2 The UV-vis-nir spectra of the SAC in Example 1, Example 2, and Comparative Example 1 are shown.

[0022] Figure 3 The distribution diagrams show the H2 generation rate and H2 / CO ratio of the catalysts in Examples 1, 2, and 1 under the DRM photothermal reaction conditions. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0024] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0025] The principle of this invention is as follows: CeO2 nanorod structures are obtained through hydrothermal synthesis, and atomically dispersed catalysts with low Ru loading (<0.5 wt%) are prepared by electrostatic adsorption. The constructed Ru-O-Ce structure exhibits strong catalytic activity for the DRM reaction. Mg doping promotes CO2 adsorption, thereby accelerating the DRM reaction, while simultaneously eliminating carbon deposition and extending the catalyst's lifespan. Furthermore, under light irradiation, the recombination rate of laser-induced electrons and holes is suppressed by oxygen vacancies and Mg doping, allowing laser-induced electrons to migrate through the Ru-O-Ce structure to the active sites, promoting the rate-controlling step of the DRM reaction, thus breaking the limitation on product formation rate in the thermal reaction system under photothermal synergistic catalysis.

[0026] Specifically, the method for preparing a high-efficiency photothermal catalytic methane dry reforming Ru single-atom catalyst (SAC) according to the present invention includes the following steps:

[0027] 1) CeO2 support was prepared by hydrothermal synthesis;

[0028] Step 1) is as follows:

[0029] 20 mmol of Ce(NO3)3·6H2O and Mg(NO3)2·6H2O were added to a 6 mol·L⁻¹ solution. -1 In a NaOH solution, after stirring, a turbid liquid was added and stirred at room temperature for 30 minutes. Then, a hydrothermal reaction was carried out at 100°C for 24 hours. Subsequently, the precipitate was washed by centrifugation until the pH of the supernatant was 7. The precipitate was then dried at 80°C overnight and calcined at 400°C for 4 hours to obtain a CeO2 support with a Mg-CeO2-NR structure.

[0030] 2) Preparation of Ru1 / Mg-CeO2-NR single-atom photothermal catalyst (SAC);

[0031] The operation process for step 2) is as follows:

[0032] Add Ru(NO)(NO3) to 100 mL of ultrapure water. x (OH) y(x+y=3, Shyuanye, Ru content ≥31.3%), add ammonia to adjust the pH to 9.8-10.2, then add the CeO2 support and ultrasonically disperse for 10 min, then stir at room temperature for 24 hours, wash the precipitate to obtain the catalyst precursor, then calcine the catalyst precursor at 400℃ for 3 hours to obtain a Ru single-atom catalyst with a metal loading content of 0.5wt%, and test the catalytic performance of the Ru single-atom catalyst in a self-made photothermal chemical fixed-bed reactor.

[0033] The dry reforming reaction of methane was catalyzed under photothermal catalysis at 500℃ under light irradiation (2.9 W·cm). -2 The production rates of H2 and CO were 559 and 846 mmol·g, respectively. cat -1 ·h -1 Furthermore, under photothermal conditions (300–500 °C), the molar fractions of H2 and CO exceeded the limits of thermocatalysis over a wide temperature range, and this trend can be extended to even higher temperatures. Notably, this was achieved at 160,000 mL·g cat -1 ·h -1 This was achieved at an equivalent gas rate, which means that the high performance of this catalyst is worth considering in actual production processes.

[0034] Example 1

[0035] The method for preparing a high-efficiency photothermal catalytic methane dry reforming Ru single-atom catalyst (SAC) described in this embodiment includes the following steps:

[0036] 1) CeO2 support was prepared by hydrothermal synthesis;

[0037] Specifically, 20 mmol of Ce(NO3)3·6H2O was slowly added to 6 mol·L⁻¹ -1 The mixture was stirred vigorously in a NaOH solution, then a turbid liquid was added and stirred at room temperature for 30 minutes. The mixture was then subjected to hydrothermal reaction at 100°C for 24 hours. The precipitate was then washed by centrifugation until the pH of the supernatant was 7. The precipitate was then dried at 80°C overnight and calcined at 400°C for 4 hours to obtain CeO2-NR nanorods.

[0038] 2) Preparation of Ru1 / CeO2-NR single-atom photothermal catalyst (SAC);

[0039] Specifically, add Ru(NO)(NO3) to 100 mL of ultrapure water. x (OH) y(x+y=3, Shyuanye, Ru content ≥31.3%), ammonia was added to adjust the pH to 10, then CeO2-NR nanorods were added and ultrasonically dispersed for 10 minutes. After ultrasonic dispersion, the mixture was stirred at room temperature for 24 hours, and then the precipitate was washed to obtain the catalyst precursor. The catalyst precursor was calcined at 400℃ for 3 hours to obtain a Ru-based catalyst with a metal loading content of 0.5wt%. The catalytic performance of the obtained Ru-based catalyst was tested in a self-made photothermal chemical fixed-bed reactor, and the results are shown in Table 1:

[0040] Table 1

[0041] Reaction temperature / ℃ 300 350 400 450 500 <![CDATA[H2 generation rate / mmol·g cat -1 ·h -1 > 3.3 17.8 74.2 209.8 449.2 <![CDATA[H2 / CO]]> 0.194 0.297 0.428 0.543 0.627

[0042] During the test, the reaction conditions were: light intensity: 2.9 W / cm². 2 Catalyst loading: 30 mg; CHSV: 160,000 mL·g cat -1 ·h -1 .

[0043] Example 2

[0044] The method for preparing a high-efficiency photothermal catalytic methane dry reforming Ru single-atom catalyst (SAC) described in this embodiment includes the following steps:

[0045] 1) CeO2 support was prepared by hydrothermal synthesis;

[0046] Specifically, 20 mmol of Ce(NO3)3·6H2O was dissolved in 40 ml of ultrapure water, Mg(NO3)3·6H2O was added, and the resulting mixed solution was slowly added to 6 mol·L⁻¹ water. -1 The mixture was stirred vigorously in NaOH solution, and then the turbid liquid was added and stirred at room temperature for 30 minutes. Then, the mixture was hydrothermally reacted at 100℃ for 24 hours. The precipitate was then washed by centrifugation until the pH of the supernatant was 7. The precipitate was then dried at 80℃ overnight and calcined at 400℃ for 4 hours to obtain Mg-CeO2-NR nanorods.

[0047] 2) Preparation of Ru1 / Mg-CeO2-NR single-atom photothermal catalyst (SAC);

[0048] Specifically, add Ru(NO)(NO3) to 100mL of ultrapure water. x (OH) y(x+y=3, Shyuanye, Ru content ≥31.3%), add ammonia to adjust the pH to 10.2, then add the Mg-CeO2-NR support obtained in step 1), and then ultrasonically disperse for 10 minutes. Stir at room temperature for 24 hours, wash the resulting precipitate to obtain the catalyst precursor, and then calcine the catalyst precursor at 400℃ for 3 hours to obtain a Ru-based catalyst with a metal loading content of 0.5wt%. The Ru-based catalyst obtained in this example was tested for catalytic performance in a self-made photothermal chemical fixed-bed reactor. The results are shown in Table 2.

[0049] Table 2

[0050] Reaction temperature / ℃ 300 350 400 450 500 <![CDATA[H2 generation rate / mmol·g cat -1 ·h -1 > 7.4 34.8 117 287.8 559.4 <![CDATA[H2 / CO]]> 0.256 0.367 0.487 0.586 0.662

[0051] During the catalytic performance test, the reaction conditions were: light intensity: 2.9 W / cm². 2 Catalyst loading: 30 mg; CHSV: 160,000 mL·g cat -1 ·h -1 .

[0052] Comparative Example 1

[0053] Preparation of Ru1 / CeO2-NP single-atom photothermal catalyst (SAC): Add Ru(NO)(NO3) to 100 mL of ultrapure water. x (OH) y (x+y=3, Shyuanye, Ru content ≥31.3%), ammonia was added to adjust the pH to 10, then commercial cerium oxide nanoparticles CeO2-NP support were added and ultrasonically dispersed for 10 minutes. The mixture was stirred at room temperature for 24 hours, and the precipitate was washed to obtain the catalyst precursor. The catalyst precursor was then calcined at 400℃ for 3 hours to obtain a Ru-based catalyst with a metal loading of 0.5wt%. The catalytic performance of the 0.5wt% Ru-based catalyst obtained in this comparative example was tested in a self-made photothermal chemical fixed-bed reactor. The results are shown in Table 3.

[0054] Table 3

[0055] Reaction temperature / ℃ 300 350 400 450 500 <![CDATA[H2 generation rate / mmol·g cat -1 ·h -1 > 2.3 14 59.2 178.1 403.2 <![CDATA[H2 / CO]]> 0.193 0.287 0.404 0.521 0.616

[0056] During the catalytic performance test, the reaction conditions were: light intensity: 2.9 W / cm². 2 Catalyst loading: 30 mg; CHSV: 160,000 mL·g cat -1 ·h -1 .

[0057] It should be noted that the present invention has the following characteristics:

[0058] This invention enables the construction of a Ru1 / Mg-CeO2-NR SAC photothermal catalyst. Specifically, CeO2 nanorods are synthesized via a hydrothermal synthesis method. By adjusting the morphology (nanororods) and group metal (Mg element) doping of the catalyst, the physicochemical properties of the catalyst are altered, and the optical properties and valence band structure of the catalyst are further modified, making the Ru1 / Mg-CeO2-NR catalyst more active under photothermal conditions, thereby significantly promoting the dry reforming reaction of methane.

[0059] The raw materials used in this invention are widely available, highly active, and have a simple preparation process, making them suitable for further mass production of photothermal catalysts. Specifically, the main raw materials used in this invention, such as NaOH, magnesium nitrate hexahydrate, cerium nitrate hexahydrate, and ammonia, are inexpensive and readily available. The content of metallic Ru used in this invention is approximately 0.5 wt%, which is low and the cost is controllable.

[0060] The catalyst obtained by this invention can stably and efficiently produce syngas by photothermal catalysis of methane and carbon dioxide at high temperatures. Specifically, under photothermal catalysis conditions, the mole fraction of syngas can exceed the thermodynamic equilibrium limit at the same temperature even at high equivalent flow rates, and can achieve a molar-level syngas generation rate at only 500°C, which is several times or an order of magnitude higher than the prior art, and remains stable during a 20-hour test.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. The application of a Ru single-atom catalyst in photothermal catalytic dry reforming of methane, characterized in that, The preparation method of the Ru single-atom catalyst includes the following steps: 1) CeO2 support with Mg-CeO2-NR structure was prepared by hydrothermal synthesis; 2) Preparation of Ru single-atom catalysts via electrostatic adsorption using CeO2 support; The specific operation of step 1) is as follows: Ce(NO3)3·6H2O and Mg(NO3)2·6H2O were added to NaOH solution and stirred to obtain a turbid liquid. The mixture was stirred at room temperature and then subjected to a hydrothermal reaction. The precipitate was washed and dried before calcination to obtain a CeO2 support with a Mg-CeO2-NR structure. The ratio of Ce(NO3)3·6H2O, Mg(NO3)2·6H2O and NaOH is 20 mmol: 0.0025 mol: 2.4 mol; The temperature during the hydrothermal reaction is 100℃; The specific process of step 2) is as follows: Add Ru(NO)(NO3) to ultrapure water x (OH) y x+y=3, after adjusting the pH value, the CeO2 support is added and ultrasonically dispersed. Then, the mixture is stirred at room temperature, the resulting precipitate is washed to obtain the catalyst precursor, and then the catalyst precursor is calcined to obtain the Ru single-atom catalyst. Ru(NO)(NO3) x (OH) y The mass ratio of CeO2 carrier to CeO2 carrier is 0.0159 g: 1 g.

2. The application of the Ru single-atom catalyst according to claim 1 in photothermal catalytic dry reforming of methane, characterized in that, The precipitate obtained from the reaction was washed by centrifugation.

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