Photo-thermal catalyst Ce1-xFexNiO3 and preparation method and application thereof

Abstract

The invention discloses a photo-thermal catalyst Ce1-xFexNiO3 as well as a preparation method and application thereof, and belongs to the technical field of photo-thermal catalysts. In the photo-thermal catalyst Ce < 1-x > FexNiO < 3 >, 0 < lt >; and x is less than or equal to 0.2. The method comprises the following steps: dissolving a nickel salt, an iron salt and a cerium salt in water according to a stoichiometric ratio to obtain a metal precursor solution; adding citric acid, stirring and mixing; heating and reacting the mixed solution to form gel; drying and grinding the gel to obtain precursor powder; and finally, the Ce < 1-x > FexNiO < 3 > photo-thermal catalyst is prepared through segmented calcination. The catalyst takes non-noble metal as an active component, the cost is low, rich oxygen vacancies are formed through the synergistic effect of Fe and Ce, CO2 activation is promoted, lattice oxygen and active oxygen species in a perovskite skeleton are utilized to effectively inhibit carbon deposition, and the stability is improved. The catalyst shows excellent photo-thermal performance and high activity in a methane dry reforming reaction, is suitable for synthesis gas preparation driven by concentrating solar energy, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of photothermal catalyst technology, specifically to a photothermal catalyst Ce. 1-x Fe x NiO3, its preparation methods, and applications. Background Technology

[0002] Dry reforming of methane (DRM) (CH4 + CO2 → 2H2 + 2CO) can simultaneously convert CH4 and CO2 into high-value-added syngas (H2 and CO). This process not only reduces greenhouse gas emissions but also enables the recycling of carbon resources, making it a promising green chemical pathway. However, the DRM reaction is thermodynamically a strongly endothermic process (ΔH°298 = +247 kJ·mol). - ¹) Traditional thermocatalysis requires temperatures above 800°C to achieve a considerable reaction rate, resulting in enormous energy consumption and high operating costs. Furthermore, high-temperature environments readily trigger side reactions, leading to carbon buildup on the catalyst surface and sintering of active components, causing rapid catalyst deactivation. This is a key bottleneck restricting the industrial application of DRM technology.

[0003] Currently, most reported catalysts for photothermal DRM reactions are based on noble metals (such as Pt, Pd, Ru, etc.). Although they exhibit high activity, their high cost and scarcity severely limit their large-scale application. Among non-noble metal catalysts, nickel-based catalysts have attracted much attention due to their excellent CH bond activation ability, but they have a narrow light absorption range and limited photothermal conversion efficiency under photothermal conditions, and still face the problem of easy carbon deposition.

[0004] Therefore, developing a novel, efficient, stable, and low-cost photothermal synergistic catalyst that can achieve efficient conversion of CH4 and CO2 under low-intensity sunlight is of great significance for promoting the practical application of DRM technology and achieving the goal of carbon neutrality. Summary of the Invention

[0005] To address the problems of high cost, easy carbon deposition, and poor photothermal performance of DRM catalysts, which restrict their industrial application, the purpose of this invention is to provide a photothermal catalyst Ce. 1-x Fe x NiO3, the photothermal catalyst Ce 1-x Fe x NiO3 in 0 <x≤0.2。

[0006] Another object of the present invention is to provide a photothermal catalyst Ce 1-x Fe xThe method for preparing NiO3 specifically includes the following steps: (1) Add nickel salt, iron salt and cerium salt to water according to stoichiometric ratio and mix evenly to obtain metal precursor solution.

[0007] (2) Add citric acid to the metal precursor solution and stir to mix to obtain a mixed solution.

[0008] (3) The mixed solution is heated to react and a gel is obtained.

[0009] (4) Dry the gel and grind it to obtain precursor powder.

[0010] (5) The precursor powder was calcined in stages to obtain Ce. 1-x Fe x NiO3.

[0011] Preferably, the nickel salt in step (1) of the present invention is nickel nitrate hexahydrate.

[0012] Preferably, the iron salt in step (1) of the present invention is ferric chloride hexahydrate.

[0013] Preferably, the cerium salt in step (1) of the present invention is cerium nitrate hexahydrate.

[0014] Preferably, in step (1) of the present invention, the Ni in the metal precursor solution... 2+ The concentration was 0.03 mol / L.

[0015] Preferably, in step (2) of the present invention, the molar ratio of citric acid to metal ions in the precursor solution is 1.1:1, and the metal ions in the precursor solution include Ce. 3+ Fe 3+ with Ni 2+ sum.

[0016] Preferably, the heating reaction conditions in step (3) of the present invention are: heating and stirring at 80-100°C for 6-10 hours.

[0017] Preferably, the drying conditions in step (4) of the present invention are: drying at 100-120°C for 10-15 hours.

[0018] Preferably, the gradient calcination in step (5) of the present invention specifically involves: keeping the precursor powder at 180-220°C for 1.5-2.5 hours, and then calcining it at 730-780°C for 3-6 hours at a heating rate of 1-3°C / min.

[0019] Another object of the present invention is to provide a photothermal catalyst Ce 1-x Fe xApplication of NiO3 in dry reforming of methane.

[0020] Mechanism of the invention: This invention improves the precipitation of Ni active sites at B sites during H2 reduction pretreatment by replacing part of the Ce at the A sites in perovskite CeNiO3 with Fe, achieving high dispersion and exposure of more Ni sites and enhancing the ability to activate CH4. Furthermore, because Fe has a smaller atomic radius than Ce, the introduction of Fe causes lattice distortion in the perovskite, generating more oxygen vacancies near the precipitated Ni species. The surface lattice oxygen and the active oxygen adsorbed on these oxygen vacancies can continuously vaporize the surface carbon generated during the methane dry reforming process, achieving "dynamic carbon removal." Additionally, Ce... 3+ / Ce 4+ with Fe 2+ / Fe 3+ The redox cycle can maintain the number of oxygen vacancies, ensuring the long-term stability of the catalyst.

[0021] Compared with the prior art, the present invention provides a photothermal catalyst Ce 1-x Fe x NiO3, its preparation methods, and applications have the following beneficial effects: (1) The catalyst of this invention partially replaces part of the Ce at the A site in the perovskite CeNiO3 with Fe, promoting the precipitation of Ni active species at the B site during the H2 reduction pretreatment process, achieving high dispersion and exposure of more Ni sites, and enhancing the ability to activate CH4; at the same time, the introduction of Fe causes lattice distortion of the perovskite, inducing a large number of oxygen vacancies around the precipitated Ni species, enhancing the adsorption and activation of CO2. During the reaction, the surface lattice oxygen and the active oxygen adsorbed by the oxygen vacancies can continuously vaporize the surface carbon generated in the reaction, forming a "dynamic carbon removal" mechanism; Ce 3+ / Ce 4+ with Fe 2+ / Fe 3+ The redox cycle maintains the number of oxygen vacancies, ensuring the long-term stability of the catalyst. This catalyst system utilizes all widely available and low-cost non-precious metal elements (Ce, Fe, Ni), overcoming the cost limitations of traditional precious metal catalysts (such as Ru, Pt, Rh, etc.) and possessing excellent potential for industrial scale-up applications.

[0022] (2) The catalyst of the present invention has good photothermal properties, catalytic activity, stability and performance repeatability. The catalyst described in the present invention can be used continuously for a long time to obtain the same good catalytic effect, so as to solve the problem of low catalyst activity and easy deactivation under high temperature conditions in methane dry reforming reaction.

[0023] (3) The catalyst of the present invention has good reproducibility in preparation. The raw materials of the composite catalyst described in the present invention are inexpensive, the preparation method is simple and easy to control, and it is easy to repeat the preparation to obtain products with the same quality and performance, thereby meeting the needs of large-scale stable industrial production. Attached Figure Description

[0024] Figure 1 The values ​​are the gas conversion rates of the catalysts prepared in Examples 1-3 and Comparative Examples 1-2 of this invention at different temperatures. (a) represents the CH4 conversion rate, and (b) represents the CO2 conversion rate.

[0025] Figure 2 The values ​​are the gas conversion rates of the catalysts prepared in Examples 1-2 and Comparative Example 1 of this invention under pure heat and photothermal conditions at 700°C. (a) represents the CH4 conversion rate, and (b) represents the CO2 conversion rate.

[0026] Figure 3 The catalysts prepared in Examples 1-2 and Comparative Example 1 of this invention are H2 / CO under photothermal conditions at 700°C.

[0027] Figure 4 These are the XRD patterns of the catalysts prepared in Examples 1-2 and Comparative Example 1 of this invention.

[0028] Figure 5 This is a stability test diagram of the catalysts prepared in Example 1 and Comparative Example 1 of the present invention under photothermal conditions at 700°C.

[0029] Figure 6 These are SEM images of the catalysts prepared in Examples 1-2 and Comparative Example 1 of this invention.

[0030] Figure 7 These are XPS images of the catalysts prepared in Examples 1-2 and Comparative Example 1 of this invention.

[0031] Figure 8 These are SEM and EDS images of the catalyst prepared in Example 1 of this invention. Detailed Implementation

[0032] 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 only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1 Photothermal catalyst Ce 0.9 Fe 0.1 The specific steps for preparing NiO3 are as follows: (1) Nickel nitrate hexahydrate, ferric chloride hexahydrate, and cerium nitrate hexahydrate were added to water according to the stoichiometric ratio and stirred for 1.5 hours to obtain a metal precursor solution. The Ni in the metal precursor solution was... 2+ The concentration was 0.03 mol / L.

[0034] (2) Add citric acid dropwise to the metal precursor solution and stir to mix (the molar ratio of citric acid to metal ions in the precursor solution is 1.1:1, and the metal ions in the precursor solution include Ce). 3+ Fe 3+ with Ni 2+ (The sum of these two solutions yields a mixed solution.)

[0035] (3) Transfer the mixed solution to a 90°C oil bath and stir and heat for 8 hours to obtain a gel.

[0036] (4) The gel was placed in a 120°C forced-air oven for 10 hours to dry (the solution in the gel was evaporated), and then ground thoroughly to obtain the precursor powder.

[0037] (5) The precursor powder was transferred to a muffle furnace and held at 200°C for 2 hours. Then, the temperature was increased to 750°C at a rate of 1°C / min and calcined for 5 hours. After natural cooling, the catalyst Ce was obtained. 0.9 Fe 0.1 NiO3.

[0038] The catalyst Ce prepared in this embodiment 0.9 Fe 0.1 SEM and EDS images of NiO3 are shown below. Figure 8 As shown, the catalyst has a loose and porous structure, and the elements Ce, Fe, Ni and O are evenly distributed.

[0039] Example 2 Photothermal catalyst Ce 0.8 Fe 0.2 The specific steps for preparing NiO3 are as follows: (1) Nickel nitrate hexahydrate, ferric chloride hexahydrate, and cerium nitrate hexahydrate were added to water according to the stoichiometric ratio and stirred for 1.5 hours to obtain a metal precursor solution. The Ni in the metal precursor solution was... 2+ The concentration was 0.03 mol / L.

[0040] (2) Add citric acid dropwise to the metal precursor solution and stir to mix (the molar ratio of citric acid to metal ions in the precursor solution is 1.1:1, and the metal ions in the precursor solution include Ce). 3+ Fe 3+ with Ni 2+ (The sum of these two solutions yields a mixed solution.)

[0041] (3) Transfer the mixed solution to an 80°C oil bath and stir and heat for 10 hours to obtain a gel.

[0042] (4) The gel was placed in a 100°C forced-air oven and dried for 15 hours (the solution in the gel was evaporated). After thorough grinding, the precursor powder was obtained.

[0043] (5) The precursor powder was transferred to a muffle furnace and held at 180°C for 2.5 hours. Then, the temperature was increased to 730°C at a rate of 3°C / min and calcined for 6 hours. After natural cooling, the catalyst Ce was obtained. 0.8 Fe 0.2 NiO3.

[0044] Example 3 Photothermal catalyst Ce 0.85 Fe 0.15 The specific steps for preparing NiO3 are as follows: (1) Nickel nitrate hexahydrate, ferric chloride hexahydrate, and cerium nitrate hexahydrate were added to water according to the stoichiometric ratio and stirred for 1.5 hours to obtain a metal precursor solution. The Ni in the metal precursor solution was... 2+ The concentration was 0.03 mol / L.

[0045] (2) Add citric acid dropwise to the metal precursor solution and stir to mix (the molar ratio of citric acid to metal ions in the precursor solution is 1.1:1, and the metal ions in the precursor solution include Ce). 3+ Fe 3+ with Ni 2+ (The sum of these two solutions yields a mixed solution.)

[0046] (3) Transfer the mixed solution to a 100°C oil bath and stir and heat for 6 hours to obtain a gel.

[0047] (4) The gel was placed in a 110°C forced-air oven for 12 hours to dry (the solution in the gel was evaporated), and then ground thoroughly to obtain the precursor powder.

[0048] (5) The precursor powder was transferred to a muffle furnace and held at 220°C for 1.5 hours. Then, the temperature was increased to 780°C at a rate of 2°C / min and calcined for 3 hours. After natural cooling, the catalyst Ce was obtained. 0.85 Fe 0.15 NiO3.

[0049] Comparative Example 1 The preparation method of the photothermal catalyst CeNiO3, the specific steps are as follows: (1) Nickel nitrate hexahydrate and cerium nitrate hexahydrate were added to water according to the stoichiometric ratio and stirred for 1.5 hours to obtain a metal precursor solution. The Ni in the metal precursor solution was... 2+The concentration was 0.03 mol / L.

[0050] (2) Add citric acid dropwise to the metal precursor solution and stir to mix (the molar ratio of citric acid to metal ions in the precursor solution is 1.1:1, and the metal ions in the precursor solution include Ce). 3+ Fe 3+ with Ni 2+ (The sum of these two solutions yields a mixed solution.)

[0051] (3) Transfer the mixed solution to a 90°C oil bath and stir and heat for 8 hours to obtain a gel.

[0052] (4) The gel was placed in a 120°C forced-air oven for 10 hours to dry (the solution in the gel was evaporated), and then ground thoroughly to obtain the precursor powder.

[0053] (5) The precursor powder was transferred to a muffle furnace and kept at 200°C for 2 hours. Then, the temperature was increased to 780°C at a rate of 3°C / min and calcined for 3 hours. After natural cooling, the catalyst CeNiO3 was obtained.

[0054] The catalysts prepared in Examples 1-2 and Comparative Example 1 of this invention were subjected to dry recombination of methane into gas (H2 and CO) under photothermal coupling. The specific steps are as follows: 0.1g of catalyst was weighed and placed in a quartz tube with an inner diameter of 8mm. The catalyst was reduced at 700℃ with an H2 flow rate of 2ml / min for 2h. The catalyst was placed in a reactor (the light source was provided by a 300W full-spectrum xenon lamp; the heat source was obtained by focusing light through a convex lens combination). A mixed gas consisting of CH4 / CO2 / N2 (the volume ratio of CH4, CO2, and N2 in the mixed gas was 1:1:2) was introduced at a flow rate of 50ml / min under normal pressure for 30,000h. -1 The reaction was carried out at a space velocity and a temperature of 700℃. The gaseous products after the reaction were analyzed by online gas chromatography. The analysis of the gaseous products is as follows: Figure 2 As shown.

[0055] The catalysts prepared in Examples 1-2 and Comparative Example 1 of this invention were subjected to dry recombination of methane into gas (H2 and CO). The specific steps are as follows: 0.1 g of catalyst was weighed and placed in a quartz tube with an inner diameter of 8 mm. The sample was reduced at 700 °C (heat source was only external electric furnace) at a flow rate of 2 ml / min for 2 h. A mixed gas composed of CH4 / CO2 / N2 (the volume ratio of CH4, CO2 and N2 in the mixed gas was 1:1:2) was introduced at a flow rate of 50 ml / min under normal pressure for 30,000 h. -1 The reaction was carried out at a space velocity and a temperature of 700℃. The gaseous products after the reaction were analyzed by online gas chromatography. The analysis of the gaseous products is as follows: Figure 2 As shown.

[0056] like Figure 2 As shown, the gas conversion rate under photothermal conditions is higher than that under pure thermal conditions. Although undoped CeNiO3 can suppress electron-hole recombination through the CeO2-NiO heterostructure, the lattice distortion induced by iron doping generates more oxygen vacancies. These oxygen vacancies not only provide abundant active sites for the reaction but also optimize the electron transport path, making the Fe-doped catalyst (CeNiO3) more efficient. 0.9 Fe 0.1 NiO3, Ce 0.8 Fe 0.2 The conversion rates of CH4 and CO2 of NiO3 under photothermal conditions are significantly higher than those of undoped CeNiO3. On the other hand, the absorption range of light and thermal activation efficiency of the catalyst are further enhanced by iron doping. Compared with the undoped sample, it can convert light energy into chemical energy more efficiently, and the reaction kinetics under thermal effect are accelerated due to the increase of active sites. Finally, under photothermal coupling, it exhibits gas conversion performance far exceeding that of the undoped sample.

[0057] Figure 3 The H2 / CO ratio of the catalysts prepared in Examples 1-2 and Comparative Example 1 at 700°C under photothermal conditions is shown. The H2 / CO ratio of the catalysts prepared in Examples 1-2 is higher than that of Comparative Example 1. This is because the introduction of Fe causes lattice distortion in the perovskite lattice, which reduces the oxygen vacancy formation energy, making it easier to form oxygen vacancies under reaction conditions. At the same time, the LSPR effect of Fe further improves the photothermal conversion efficiency, resulting in better selectivity and stability of the catalyst.

[0058] Combination Figure 4 , Figure 7 and Figure 8 This proves that the Fe doping was successful, as shown by the XRD pattern ( Figure 4 The catalyst, after Fe doping, still retains the perovskite main phase, and its diffraction peak positions do not show a significant shift compared to the undoped sample. This may be because Fe... 3+ / Fe 2+ Partially replaces A position Ce 3+ / Ce 4+ The resulting lattice contraction is offset by effects such as doping-induced oxygen vacancies (which typically lead to lattice expansion); meanwhile, Fe 3+ / Fe 2+ With B site Ni 2+ / Ni 3+ The ionic radii are similar, and the impact on the overall lattice parameters is small, so the diffraction peak positions do not shift significantly; combined with XPS analysis, the XPS spectra ( Figure 7In Comparative Example 1, Ce, Ni, and O corresponding Ce3d, Ni2p, and O1s peaks were detected. In Examples 1 and 2, Fe2p peaks were added, and the intensities of Ce3d and O1s peaks also changed slightly, corresponding to the adjustment of the element ratio in the crystal lattice. This proves that Fe doping was successful, and Fe doping produces defect structures that improve catalytic performance.

[0059] like Figure 5 As shown, the catalysts of Comparative Example 1 and Example 1 were subjected to a stability test at 700°C under photothermal conditions for nearly 13 hours. The gas conversion rate of Fe-doped Example 1 was higher than that of Comparative Example 1. After Fe doping, due to the variable valence state (Fe... 3+ / Fe 2 + This can further enhance oxygen storage capacity and oxygen mobility, while perturbing the CeO2 lattice to generate more defects, thereby improving performance.

[0060] Figure 6 The images shown are scanning electron microscope images of Comparative Example 1, Example 1, and Example 2. After Fe doping, the catalyst becomes a loose and porous structure, which is more conducive to the exposure of active sites and mass transfer.

[0061] Comparative Example 2 Photothermal catalyst Ce 0.7 Fe 0.3 The specific steps for preparing NiO3 are as follows: (1) Add nickel nitrate hexahydrate, ferric chloride hexahydrate and cerium nitrate hexahydrate to water according to the stoichiometric ratio and stir for 1.5 hours to mix evenly to obtain a metal precursor solution.

[0062] (2) Add citric acid dropwise to the metal precursor solution and stir to mix to obtain a mixed solution.

[0063] (3) Transfer the mixed solution to a 90°C oil bath and stir and heat for 8 hours to obtain a gel.

[0064] (4) The gel was placed in a 120°C forced-air oven for 10 hours to dry (the solution in the gel was evaporated), and then ground thoroughly to obtain the precursor powder.

[0065] (5) The precursor powder was transferred to a muffle furnace and held at 200°C for 2 hours. Then, the temperature was increased to 750°C at a rate of 1°C / min and calcined for 5 hours. After natural cooling, the catalyst Ce was obtained. 0.7 Fe 0.3 NiO3.

[0066] The CO2 and CH4 conversion rates of the photothermal catalysts prepared in Examples 1-3 and Comparative Examples 1-2 of this invention at 650℃ and 700℃ are as follows: Figure 1As shown, the catalysts prepared in Examples 1-3 enhanced CO2 adsorption and activation through the introduction of Fe, and the CO2 and CH4 conversion rates were higher than those of the catalysts without Fe doping (Comparative Example 1). However, excessive Fe doping led to a decrease in catalytic activity, which may be due to the destruction of the perovskite structure caused by excessive Fe doping, resulting in insufficient exposure of Ni active sites.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A photothermal catalyst Ce 1-x Fe x NiO3, characterized in that... The photothermal catalyst Ce 1-x Fe x 0 in NiO3 <x≤0.2。 2. The photothermal catalyst Ce as described in claim 1 1-x Fe x The method for preparing NiO3 is characterized by, Specifically, the following steps are included: (1) Add nickel salt, iron salt and cerium salt to water according to the stoichiometric ratio and mix evenly to obtain a metal precursor solution; (2) Add citric acid to the metal precursor solution and stir to mix, to obtain a mixed solution; (3) The mixed solution is heated to react and a gel is obtained; (4) The gel is dried and ground to obtain precursor powder; (5) The precursor powder was calcined in stages to obtain Ce. 1-x Fe x NiO3.

3. The photothermal catalyst Ce according to claim 2 1-x Fe x The method for preparing NiO3 is characterized by, The nickel salt mentioned in step (1) is nickel nitrate hexahydrate; the iron salt is ferric chloride hexahydrate; and the cerium salt is cerium nitrate hexahydrate.

4. The photothermal catalyst Ce according to claim 2 1-x Fe x The method for preparing NiO3 is characterized by, Ni in the metal precursor solution described in step (1) 2+ The concentration was 0.03 mol / L.

5. The photothermal catalyst Ce according to claim 2 1-x Fe x The method for preparing NiO3 is characterized by, In step (2), the molar ratio of citric acid to metal ions in the precursor solution is 1.1:1, and the metal ions in the precursor solution include Ce. 3+ Fe 3+ with Ni 2+ sum.

6. The photothermal catalyst Ce according to claim 2 1-x Fe x The method for preparing NiO3 is characterized by, The heating reaction conditions described in step (3) are: heating and stirring at 80-100℃ for 6-10 hours.

7. The photothermal catalyst Ce according to claim 2 1-x Fe x The method for preparing NiO3 is characterized by, The drying conditions described in step (4) are: drying at 100-120℃ for 10-15 hours.

8. The photothermal catalyst Ce according to claim 2 1-x Fe x The method for preparing NiO3 is characterized by, The segmented calcination in step (5) specifically involves: keeping the precursor powder at 180-220℃ for 1.5-2.5 hours, and then calcining it at 730-780℃ for 3-6 hours at a heating rate of 1-3℃ / min.

9. The photothermal catalyst Ce as described in claim 1 1-x Fe x Application of NiO3 in dry reforming of methane.

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