Preparation method of photo-thermal catalytic methane dry reforming composite material based on ternary Schottky-p-n heterojunction structure

Abstract

The invention provides a preparation method of a Ni-NiO / Sr2Nb2O7 ternary Schottky-p-n heterojunction composite material for photo-thermal catalytic methane dry reforming, and the catalyst can efficiently and selectively convert methane (CH4) and carbon dioxide (CO2) into synthesis gas (CO and H2) under a relatively mild reaction condition (500 DEG C). Therefore, negative emission of greenhouse gas and green upgrading of low-added-value raw materials are realized. The preparation method of the Ni-NiO / Sr2Nb2O7 ternary Schottky-p-n heterojunction composite catalyst material comprises the following steps: (1) preparing the substrate Sr2Nb2O7, and preparing the substrate Sr2Nb2O7; (2) preparation of a ternary Ni-NiO-Sr2Nb2O7 composite material; (3) preparation of the ternary According to the invention, the NiOx (Ni-NiO) nanoparticles with partial reduction characteristics are utilized to modify the Sr2Nb2O7, so that the composite catalyst material with double heterojunctions of a Schottky junction and a p-n junction is successfully constructed. Due to the structure, photo-induced electrons generated by optical excitation can be effectively separated and directionally migrated to Ni and Sr2Nb2O7 active sites which are spatially separated, so that the reverse water gas shift side reaction is obviously inhibited, and the competitive consumption of CO2 is avoided. Due to the characteristic, high selectivity of the synthesis gas is ensured, and the durability of the catalyst is enhanced, so that the economic benefit of the methane dry reforming process is greatly improved.

Description

Technical Field

[0001] The present invention relates to the fields of nanomaterials and photocatalysis technology, and particularly to a ternary Schottky-p-n heterojunction structure Ni-NiO / Sr for photothermal catalytic dry reforming of methane 2 Nb 2 O 7 composite photothermal catalyst material and its preparation method. Background Art

[0002] Dry reforming of methane (DRM) is an effective strategy for co-converting the greenhouse gas methane (CH 4 ) and carbon dioxide (CO 2 ) into syngas (hydrogen (H 2 ) and carbon monoxide (CO)). Although DRM shows great potential in reducing greenhouse gas emissions and efficient resource utilization, developing DRM catalysts with both high activity and long lifespan still faces significant challenges. First, under high-temperature operating conditions (> 700 °C), non-noble metal catalysts such as nickel-based catalysts are prone to deactivation due to sintering. The fundamental reason is that the Tamman temperature (the theoretical starting temperature of sintering) of the active metal is much lower than the operating temperature. Second, under medium and low-temperature conditions (< 600 °C), the reaction kinetics of the DRM process is sluggish, especially the activation rate of methane is low, and side reactions such as the reverse water-gas shift reaction (CO 2 +H 2 → H 2 O + CO) and the Boudouard reaction (2CO → C + CO 2 ) occur. These side reactions not only lead to a decrease in the selectivity of the target product but also further accelerate the deactivation of the catalyst, thus having an adverse impact on the profitability and stability of the DRM process. Among them, the reverse water-gas shift reaction has a particularly significant negative impact on the DRM process. On the one hand, the reverse water-gas shift reaction consumes the H 2 generated in the DRM process, making the H 2 / CO ratio in the target product syngas less than the theoretical value of 1, greatly reducing the economic value of the product; on the other hand, this reaction seriously disrupts the equilibrium of the DRM reaction by competitively consuming the raw material carbon dioxide. Specifically, a stable DRM process requires maintaining the semi-reaction rate of methane cracking to generate carbon species (*C) and CO 2The dynamic equilibrium between the semi-reaction rates of generating reactive oxygen species (*O) for carbon deposition removal. However, excessive reverse water-gas shift reaction will lead to insufficient supply of reactive oxygen species, and further deactivate the catalyst surface due to carbon deposition coverage. At present, the photothermal catalysis technology has been widely proven to significantly reduce the starting temperature of the DRM process. Based on this advantage, effectively suppressing the reverse water-gas shift side reaction while carrying out the photothermal DRM reaction in the temperature range with low sintering risk will provide a key guarantee for the long-term stability and high efficiency of syngas production.

[0003] Based on the above research background, considering two aspects of promoting methane activation at medium and low temperatures and suppressing the reverse water-gas side reaction, the applicant of the present invention provides a Ni-NiO / Sr with a ternary Schottky-p-n heterojunction structure (abbreviated as TSPN structure) 2 Nb 2 O 7 Composite photothermal catalyst material and its preparation method. At the same time, the material was systematically compared with Ni-NiO supported on silica (SiO 2 ). This TSPN structure has dual-functional advantages: on the one hand, its unique photogenerated carrier separation mechanism directs photogenerated holes to p-type NiO, significantly enhancing the activation efficiency of CH 4 . On the other hand, this structure efficiently guides photogenerated electrons to spatially separated n-type Sr 2 Nb 2 O 7 (SNO) and metal Ni sites, which are used for CO 2 reduction and H 2 generation respectively. This spatial separation mechanism of dual reduction sites effectively suppresses the occurrence of the reverse water-gas shift side reaction. The Ni-NiO / Sr 2 Nb 2 O 7 composite photothermal catalyst material prepared by the present invention realizes an efficient and highly stable photothermal catalytic methane dry reforming process at 500 °C, providing a highly potential technical solution for the industrial production of syngas. Summary of the Invention

[0004] The applicant of the present invention provides a Ni-NiO / Sr with a ternary Schottky-p-n heterojunction structure 2 Nb 2 O 7 Composite photothermal catalyst material and its preparation method. The present invention adopts a grinding method combined with a hydrogen calcination reduction strategy to load NiO x (Ni-NiO) nanoparticles with partial reduction characteristics onto Sr 2 Nb 2 O 7On the substrate material.

[0005] The technical solution of the present invention is as follows:

[0006] The Ni-NiO / Sr with a ternary Schottky-p-n heterojunction structure 2 Nb 2 O 7 The preparation method of the composite photothermal catalyst material includes the following steps:

[0007] (1) Preparation of the substrate Sr 2 Nb 2 O 7 ;

[0008] (2) Preparation of the ternary Ni-NiO-Sr 2 Nb 2 O 7 composite material;

[0009] In step (1), the Sr 2 Nb 2 O 7 is prepared by: adding niobium pentachloride (NbCl 5 ) and strontium nitrate (Sr(NO 3 )) 2 powders into 30 mL of 3 M sodium hydroxide (NaOH) solution, stirring at room temperature for 0.5 hour to obtain a precursor solution. Subsequently, transfer the precursor solution to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene, react at 180 °C for 20 hours. After the autoclave is cooled, collect the precipitate by centrifugation and wash it three times with ultrapure water. Finally, place the obtained precipitate in an oven at 70 °C and dry it for 24 hours to obtain Sr 2 Nb 2 O 7 powder.

[0010] In step (1), the molar ratio of NbCl 5 and Sr(NO 3 ) 2 is 1:2 to 2:1.

[0011] In step (1), the total amount of substance of NbCl 5 and Sr(NO 3 ) 2 is 0.0075 mol to 0.01 mol.

[0012] In step (2), the method for preparing Ni-NiO / Sr 2 Nb 2 O 7 is as follows: Add a certain amount of 0.5 M nickel nitrate hexahydrate (Ni(NO3 ) 2 ·6H 2 O solution was dropped into 250 mg of Sr 2 Nb 2 O 7 powder, and then continuously ground in a mortar for 30 minutes and dried in an oven at 120 °C. The obtained solid sample was calcined in a tubular furnace at a certain temperature and atmosphere for 4 hours to obtain Ni-NiO / Sr 2 Nb 2 O 7 catalyst.

[0013] In step (2), the Ni(NO 3 ) 2 ·6H 2 O dosage is 0.34 - 0.68 mL.

[0014] In step (2), the calcination temperature is 300 - 600 °C.

[0015] In step (2), the calcination atmosphere is a reducing gas containing hydrogen, where the hydrogen volume concentration is 5% (the remaining gas is balanced with Ar). The advantages of the present invention are reflected in

[0016] Using Sr with a layered perovskite structure 2 Nb 2 O 7 as a carrier, the oxygen defect sites in its crystal structure and alkali metal ions can significantly enhance the adsorption strength of carbon dioxide through synergistic effects, realizing the adsorption and activation of CO 2 on the carrier Sr 2 Nb 2 O 7 .

[0017] Loading NiO x (Ni-NiO) nanoparticles with partial reduction characteristics on Sr 2 Nb 2 O 7 carrier, a Schottky junction is formed between Ni and NiO, and at the same time, a p-n junction is constructed between NiO and Sr 2 Nb 2 O 7 . This unique ternary Schottky-p-n heterojunction structure can significantly promote the separation and migration of photo-generated carriers and extend their lifetime, thereby improving the photothermal catalytic performance of the material.

[0018] The ternary Schottky-p-n heterojunction structure constructs spatially separated Sr 2 Nb 2 O7 and the double-electron enrichment sites of metal Ni are used for CO 2 reduction and H 2 formation respectively. This spatial separation mechanism of the double reduction sites effectively inhibits the occurrence of the reverse water-gas shift side reaction and promotes the carbon deposition elimination process, thereby realizing the efficient and stable operation of the catalyst. Description of the Drawings

[0019] Figure 1 a is the TEM image of the unmodified Sr 2 Nb 2 O 7 support, which is a relatively thin amorphous flake structure. Figure 1 b is the mapping image of different elements in Ni-NiO / Sr 2 Nb 2 O 7 in Example 1, visually showing the distribution of Nb, Sr, Ni, and O. Figure 1 c is the N 2 Nb 2 O 7 and Ni-NiO / Sr 2 Nb 2 O 7 in Example 1 2 adsorption-desorption isotherm curve. The specific surface areas of both are in the range of 120 - 140 m 2 g -1 range and have no obvious relationship with the treatment conditions. The flaky morphology of Sr 2 Nb 2 O 7 provides a relatively large specific surface area, which is beneficial to the adsorption of guest molecules and the dispersion of supported nickel particles. Figure 1 d is the X-ray diffraction pattern of Sr 2 Nb 2 O 7 and Ni-NiO / Sr 2 Nb 2 O 7 in Example 1. All samples show an incomplete Sr 2 Nb 2 O 7 crystal form. Due to the high dispersion and small size of NiO x (Ni-NiO) particles, no obvious peaks of NiO x particles can be observed on the SNO substrate material. Figure 1 e is the carbon monoxide pulse chemisorption experiment graph. It can be seen that the size of NiO x (Ni-NiO) is about 3.4 nm. Figure 1 f is Sr 2 Nb2 O 7 and the electrochemical impedance spectroscopy of Ni-NiO / Sr in Example 1 2 Nb 2 O 7 Compared with the unmodified Sr 2 Nb 2 O 7 The Ni-NiO / Sr 2 Nb 2 O 7 sample shows a significantly reduced electrochemical impedance value. This result indicates that the Ni-NiO composite modification effectively promotes the migration and separation efficiency of photo-generated carriers, thus improving the electrochemical performance of the material. Figure 1 g is the X-ray photoelectron spectroscopy of Ni-NiO / Sr in Example 1 2 Nb 2 O 7 and Ni-NiO / SiO in Comparative Example 2 2 In both samples, the characteristic peaks of Ni 0 and Ni 2+ are clearly detected, confirming the successful formation of the Ni-NiO composite structure. In addition, the relative ratios of Ni 0 and Ni 2+ are basically the same in the two carrier materials, indicating that the type of carrier has little effect on the overall reduction degree of NiO x . Figure 1 h is the Ni K-edge X-ray absorption near-edge spectroscopy of Ni-NiO / Sr in Example 1 2 Nb 2 O 7 The white line peak intensity of the sample Ni-NiO / Sr 2 Nb 2 O 7 is between that of the reference sample NiO and Ni foil, further indicating the formation of its Ni-NiO structure.

[0020] Figure 2 a is the graph of the change of the photothermal catalytic activity of Ni-NiO / Sr in Example 1 2 Nb 2 O 7 with reaction time at 500 °C. It can be observed from the figure that within the 30-hour test time, with the extension of the reaction time, the decrease in the conversion rate of the raw material and the yield of syngas can be ignored, which proves the excellent stability of the catalyst. Figure 2 b is the product H of the Ni-NiO / Sr 2 Nb 2 O 7 sample in the photothermal catalytic test 2The variations of / CO and carbon balance over time, both approaching the theoretical value of 1, indicate high product selectivity and low carbon deposition levels during the photothermal catalytic process. Figure 2 c is Ni-NiO / Sr in Example 1 2 Nb 2 O 7 The curve of the thermocatalytic activity versus reaction time at 500 °C shows low initial activity and obvious deactivation. Meanwhile, H 2 / CO is low, only 0.41, and the carbon balance is less than 1, indicating low selectivity and the potential presence of carbon deposition ( Figure 2 d). Figure 2 e is the Raman spectrum of the catalyst after reaction of the Ni-NiO / Sr 2 Nb 2 O 7 sample in the photothermal catalytic mode and the thermocatalytic mode. Carbon peaks detected at 1350 cm -1 (D band) and 1580 cm -1 (G band) are attributed to the structural defects of graphitized carbon and the in-plane carbon-carbon stretching vibration of graphite layers, respectively. Graphitized carbon is difficult to evaporate during the DRM reaction and easily leads to rapid deactivation of the catalyst. The higher the intensity ratio of I D / I G , the lower the graphitization degree of the deposited carbon. The intensity ratio of I D / I G Data comparison shows that the Ni-NiO / Sr 2 Nb 2 O 7 sample has lower graphitization in the photothermal catalytic mode, revealing its lower carbon deposition level. Figure 2 f is the variation of the photo-fuel efficiency of the Ni-NiO / Sr 2 Nb 2 O 7 sample with light intensity. When the light intensity reaches 4.06 W / cm 2 , the Ni-NiO / Sr 2 Nb 2 O 7 sample exhibits a photo-fuel efficiency of 28.3%, indicating its good light conversion ability. To further reveal the differences in stability under photothermal catalysis and thermocatalysis, we investigated the photothermal catalytic activity of the Ni-NiO / SiO 2 sample in Comparative Example 2 ( Figure 2 g and Figure 2 h), where SiO 2 is a photo-inert support. The results show that the raw material conversion rate rapidly decreases during the reaction process, and the product has a low H 2 / CO, the carbon balance in the whole process always maintains a level less than 1. The above results show that NiO and Sr 2 Nb 2 O 7 The charge transfer between them plays an important role in maintaining high activity and high stability.

[0021] Figure 3 a and Figure 3 b is Ni-NiO / Sr in Example 1 2 Nb 2 O 7 In situ diffuse reflectance infrared spectra under light irradiation after heating the adsorbed gas in dark conditions. The results show that within the first 10 minutes at 500 °C, Ni-NiO / Sr 2 Nb 2 O 7 Only a trace amount of reactive gas adsorption was observed on the surface, and the adsorption increased significantly after illumination. As the illumination time increased, the infrared spectrum showed a trend of 4 (3016 and 1303 cm -1 ) and gaseous CO 2 (2340 and 2358 cm -1 ) characteristic peak. It is worth noting that after 10 minutes of illumination, due to CH 4 and CO 2 The rapid transformation of these characteristic peaks shows a significant decreasing trend. 1341 and 1351 cm -1 The absorption peaks at 3 The asymmetric and symmetric deformation vibrations of the groups confirm that methane is activated to -CH 3 and *H species. In addition, 1492 and 1455 cm -1 The absorption peaks at -CH and -CH 2 The deformation vibration of the group shows that the methyl group is 2 Nb 2 O 7 The surface has undergone CH 3 →CH 2 →CH→*C deep activation process. Figure 3 c and Figure 3 d is Ni-NiO / Sr in Example 1 2 Nb 2 O 7 In situ infrared spectra of samples under dark conditions. The results show that Ni-NiO / Sr 2 Nb 2 O 7 The samples were kept in dark conditions. 3 and -CH2 The content of intermediates such as -1 is relatively low, and the active intermediate of bicarbonate located at 1645 cm

[0022] Figure 4 a is the in-situ Raman spectrum of Ni-NiO / Sr with carbon deposition 2 Nb 2 O 7 under a carbon dioxide atmosphere. Compared with the spectrum under 532 nm laser irradiation ( Figure 4 b), the carbon deposit content of the sample under 325 nm laser irradiation is greatly reduced. Figure 4 c is the in-situ Raman spectrum carried out in an inert argon atmosphere. The results show that as the laser irradiation time prolongs, not only does the Raman peak intensity attributed to carbon deposition gradually weaken, but an additional decrease in the Raman peak intensity attributed to the O displacement in the NbO 6 octahedron is also observed synchronously, which confirms the consumption of lattice oxygen (O L ). The above results verify that photoexcitation can effectively activate Sr 2 Nb 2 O 7 to generate surface reactive oxygen species to promote carbon elimination; meanwhile, CO 2 supplements the oxygen vacancies, thus realizing continuous carbon elimination.

[0023] Figure 5 a shows the Mott-Schottky test results of the NiO / Sr 2 Nb 2 O 7 sample in Comparative Example 1. Its curve shows a typical inverted "V" shape, indicating that a p-n heterojunction structure is successfully constructed between the p-type NiO semiconductor and the n-type Sr 2 Nb 2 O 7 semiconductor. Figure 5 b is the steady-state surface photovoltage spectra of the Ni-NiO / Sr 2 Nb 2 O 7 , NiO / Sr 2 Nb 2 O 7 and Sr 2 Nb 2 O 7 samples. The results show that the photovoltage intensities of the three present as Ni-NiO / Sr 2 Nb 2 O 7 > NiO / Sr 2 Nb 2 O7 > Sr 2 Nb 2 O 7 The trend indicates that the construction of the ternary composite effectively promotes the separation and transport of photo-generated carriers. Figure 5 c is the transient photocurrent spectrum of the sample, which is calculated by integrating the spectrum area. Ni-NiO / Sr 2 Nb 2 O 7 The charge extraction amounts of the materials are 1.32 times and 3.75 times that of NiO / Sr 2 Nb 2 O 7 materials and Sr 2 Nb 2 O 7 materials, respectively. Combining the results of steady-state surface photocurrent and transient photocurrent further confirms that the ternary composite significantly enhances the separation and transport efficiency of photo-generated carriers, providing strong support for the improvement of photocatalytic reactions. Figure 5 d shows the in-situ XPS test results of Ni-NiO / Sr 2 Nb 2 O 7 , NiO / Sr 2 Nb 2 O 7 and Sr 2 Nb 2 O 7 samples under in-situ light irradiation. Under dark conditions, compared with pure Sr 2 Nb 2 O 7 or NiO, the binding energies of Nb and Sr in NiO / Sr 2 Nb 2 O 7 increase significantly, while the binding energy of Ni 2+ decreases. Further analysis reveals that the binding energy of Ni in the Ni-NiO / Sr 2 Nb 2 O 7 sample decreases further compared with that in NiO / Sr 2+ Nb 2 O 2 O 7 The increase and decrease of the binding energy reflect the loss and gain of electrons, respectively. These changes in binding energy indicate that at the interface between p-type NiO and n-type Sr 2 Nb 2 O 7A p-n heterojunction was successfully constructed, and a Schottky junction was formed between Ni and NiO, finally constituting a ternary Schottky-p-n heterojunction structure. Under light illumination, the dual internal electric fields (IEF) generated by the p-n junction and the Schottky junction drive the photo-generated electrons in the conduction band (CB) of NiO to preferentially migrate to the conduction bands of metals Ni and Sr 2 Nb 2 O 7 This process was further confirmed by the increase in the binding energy of Ni 2+ after light irradiation and the decrease in the binding energies of Sr, Nb, and Ni 0 providing direct evidence for elucidating the charge transfer mechanism in the ternary heterojunction. The directional migration of photo-generated electrons to the spatially separated active sites of Ni and Sr 2 Nb 2 O 7 effectively inhibits the occurrence of the reverse water gas shift side reaction. This process ensures that sufficient CO 2 molecules participate in the continuous generation of active oxygen, thus providing an important guarantee for the high efficiency and long-term stability of the reaction system.

[0024] The above experimental results prove that the synthesized ternary Schottky-p-n heterojunction structured Ni-NiO / Sr 2 Nb 2 O 7 composite photothermal catalyst material has excellent photothermal catalytic DRM performance and stability. Specific implementation examples

[0025] The present invention will be described in more detail below through specific examples, but the protection scope of the present invention is not limited to these examples.

[0026] Example 1

[0027] A preparation method of a Ni-NiO / Sr 2 Nb 2 O 7 composite photocatalyst material is as follows:

[0028] (1) Synthesis of the substrate Sr 2 Nb 2 O 7 : Mix 0.0025 mol of NbCl 5 and 0.005 mol of Sr(NO 3 ) 2Mix thoroughly with 30 mL of NaOH (3 M) solution. At room temperature, magnetically stir the mixture for 30 minutes. Subsequently, transfer the mixture to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 180 °C for 20 hours. After the autoclave has cooled, collect the precipitate by centrifugation and wash it three times with ultrapure water. Place the obtained precipitate in an oven at 70 °C to dry and obtain Sr 2 Nb 2 O 7 powder.

[0029] (2) Synthesis of ternary Ni-NiO / Sr 2 Nb 2 O 7 composite material: Gradually add 0.34 mL of 0.5 M Ni(NO 3 ) 2 ·6H 2 O solution to 250 mg of Sr 2 Nb 2 O 7 powder, and grind it thoroughly in a mortar for 30 minutes to homogenize the mixture system. Subsequently, place the mixture in an oven at 120 °C to dry and ensure that the solvent has completely evaporated. The dried solid sample is calcined at 450 °C for 4 hours in a 5% H 2 / Ar atmosphere to obtain the finished product Ni-NiO / Sr 2 Nb 2 O 7 .

[0030] Example 2

[0031] A preparation method of a Ni-NiO / Sr 2 Nb 2 O 7 composite photocatalyst material is as follows:

[0032] (1) Synthesis of substrate Sr 2 Nb 2 O 7 : Mix 0.005 mol of NbCl 5 and 0.005 mol of Sr(NO 3 ) 2 thoroughly with 30 mL of NaOH (3 M) solution. At room temperature, magnetically stir the mixture for 30 minutes. Subsequently, transfer the mixture to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 180 °C for 20 hours. After the autoclave has cooled, collect the precipitate by centrifugation and wash it three times with ultrapure water. Place the obtained precipitate in an oven at 70 °C to dry and obtain Sr 2 Nb 2 O 7 powder.

[0033] (2)Ternary Ni-NiO / Sr 2 Nb 2 O 7 Composite material synthesis: Gradually add 0.34 mL of 0.5 M Ni(NO 3 ) 2 ·6H 2 O solution to 250 mg of Sr 2 Nb 2 O 7 powder, and grind it thoroughly in a mortar for 30 minutes to homogenize the mixture system. Subsequently, place the mixture in an oven at 120 °C to dry, ensuring complete volatilization of the solvent. The dried solid sample is calcined at 450 °C for 4 hours under a 5% H 2 / Ar atmosphere to obtain the finished product Ni-NiO / Sr 2 Nb 2 O 7 .

[0034] Example 3

[0035] A preparation method of a Ni-NiO / Sr 2 Nb 2 O 7 composite photocatalyst material is as follows:

[0036] (1)Synthesis of the substrate Sr 2 Nb 2 O 7 : Mix 0.0025 mol of NbCl 5 and 0.005 mol of Sr(NO 3 ) 2 thoroughly with 30 mL of NaOH (3 M) solution. Stir the mixture magnetically at room temperature for 30 minutes. Subsequently, transfer the mixture to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 180 °C for 20 hours. After the autoclave cools, collect the precipitate by centrifugation and wash it three times with ultrapure water. Place the obtained precipitate in an oven at 70 °C to dry to obtain Sr 2 Nb 2 O 7 powder.

[0037] (2)Synthesis of the unit Ni-NiO / Sr 2 Nb 2 O 7 composite material: Gradually add 0.34 mL of 0.5 M Ni(NO 3 ) 2 ·6H 2 O solution to 250 mg of Sr 2Nb 2 O 7 In the powder, it was ground thoroughly in a mortar for 30 minutes to homogenize the mixed system. Subsequently, the mixture was placed in an oven at 120 °C for drying to ensure complete volatilization of the solvent. The dried solid sample was calcined at 600 °C for 4 hours under a 5% H 2 atmosphere to obtain the finished product Ni-NiO / Sr 2 Nb 2 O 7 .

[0038] Comparative Example 1

[0039] A preparation method of a NiO / Sr 2 Nb 2 O 7 composite photocatalyst material is as follows:

[0040] (1) Synthesis of the substrate Sr 2 Nb 2 O 7 : 0.0025 mol of NbCl 5 and 0.005 mol of Sr(NO 3 ) 2 were thoroughly mixed with 30 mL of NaOH (3 M) solution. At room temperature, the mixture was magnetically stirred for 30 minutes. Subsequently, the mixed solution was transferred to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 180 °C for 20 hours. After the autoclave cooled, the precipitate was collected by centrifugation and washed three times with ultrapure water. The obtained precipitate was placed in an oven at 70 °C for drying to obtain Sr 2 Nb 2 O 7 powder.

[0041] (2) Synthesis of the ternary NiO / Sr 2 Nb 2 O 7 composite material: 0.34 mL of 0.5 M Ni(NO 3 ) 2 ·6H 2 O solution was gradually added to 250 mg of Sr 2 Nb 2 O 7 powder, and it was ground thoroughly in a mortar for 30 minutes to homogenize the mixed system. Subsequently, the mixture was placed in an oven at 120 °C for drying to ensure complete volatilization of the solvent. The dried solid sample was calcined at 600 °C for 4 hours under an air atmosphere to obtain the finished product NiO / Sr 2 Nb 2 O 7 .

[0042] Comparative Example 2

[0043] A Ni-NiO / SiO 2 The preparation method of the composite photocatalyst material is as follows:

[0044] 0.34 mL of 0.5 M Ni(NO 3 ) 2 ·6H 2 O solution was gradually added to 250 mg of commercial SiO 2 powder, and thoroughly ground in a mortar for 30 minutes to homogenize the mixed system. Subsequently, the mixture was placed in an oven at 120 °C for drying to ensure complete volatilization of the solvent. The dried solid sample was calcined at 450 °C for 4 hours under a 5% H 2 atmosphere to obtain the finished product Ni-NiO / SiO 2 . The method for evaluating the activity of the photothermal catalytic dry reforming of methane provided by the present invention is as follows:

[0045] 5.0 mg of the catalyst was uniformly dispersed in 1.0 mL of ultrapure water and spread on a heat-resistant quartz filter membrane with a fixed coating area (3.14 cm 2 ). The dried filter membrane was placed on the fixed bed surface at the center of the quartz flow photoreactor, and a feed gas of 50% CH 4 +50% CO 2 was continuously passed through the photoreactor at a flow rate of 50 mL / min for 30 minutes in the dark to fully discharge the air. After that, the feed gas flow rate was adjusted to 20 mL / min to evaluate the catalyst activity. The photocatalytic reaction was carried out at atmospheric pressure without additional heating, and the light source was provided by a PE300BUV type 300 W xenon lamp (Beijing Zhongjiao Jinyuan). The outlet of the reaction device was connected to a gas chromatograph, and the reaction products were detected in the automatic injection mode. The detection of CO was carried out using a flame ionization detector (FID), and the detection of H 2 was carried out using a thermal conductivity detector (TCD).

Claims

1. A photothermal catalytic methane dry reforming composite material based on a ternary Schottky-pn heterojunction structure, characterized in that: The preparation method of the Ni-NiO / Sr2Nb2O7 ternary Schottky-pn heterojunction composite catalyst material comprises the following steps: (1) Preparation of substrate Sr2Nb2O7; (2) Preparation of ternary Ni-NiO-Sr2Nb2O7 composite materials; In step (1), the preparation method of the substrate Sr2Nb2O7 is as follows: niobium pentachloride (NbCl5) and strontium nitrate (Sr(NO3)2) powders are added to 30 mL of 3M sodium hydroxide (NaOH) solution, and stirred at room temperature for 0.5 hours to obtain a precursor solution; then, the precursor solution is transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave, and reacted at 180°C for 20 hours; after the autoclave is cooled, the precipitate is collected by centrifugation and washed three times with ultrapure water; finally, the obtained precipitate is placed in a 70°C oven and dried for 24 hours to obtain Sr2Nb2O7 powder.

2. The Ni-NiO / Sr2Nb2O7 ternary Schottky-pn heterojunction composite catalyst material according to claim 1, characterized in that: In step (1), the molar ratio of NbCl5 and Sr(NO3)2 is 1:2~2:

1.

3. The Ni-NiO / Sr2Nb2O7 ternary Schottky-pn heterojunction composite catalyst material according to claim 1, characterized in that: In step (1), the total amount of NbCl5 and Sr(NO3)2 is 0.0075 mol~0.01 mol.

4. The Ni-NiO / Sr2Nb2O7 ternary Schottky-pn heterojunction composite catalyst material according to claim 1, characterized in that: The synthesis method of step (2) is as follows: a certain amount of 0.5M nickel nitrate hexahydrate (Ni(NO3)2·6H2O) solution is added dropwise to 250mg of Sr2Nb2O7 powder, followed by continuous grinding in a mortar for 30 minutes and drying in an oven at 120°C; the obtained solid sample is calcined in a tube furnace at a certain temperature and atmosphere for 4 hours to obtain a Ni-NiO / Sr2Nb2O7 catalyst.

5. The Ni-NiO / Sr2Nb2O7 ternary Schottky-pn heterojunction composite catalyst material according to claim 1, characterized in that: In step (2), the concentration of Ni(NO3)2·6H2O is 0.5M, and the amount used is 0.34~0.68mL.

6. The Ni-NiO / Sr2Nb2O7 ternary Schottky-pn heterojunction composite catalyst material according to claim 1, characterized in that: In step (2), the calcination temperature is 300-600° C. and the calcination time is 4 hours.

7. The Ni-NiO / Sr2Nb2O7 ternary Schottky-pn heterojunction composite catalyst material according to claim 1, characterized in that: In step (2), the calcination atmosphere is a reducing gas containing hydrogen, wherein the volume concentration of hydrogen is 5% (the remaining gas is balanced by Ar).

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