Preparation method and application of in-situ nitrogen-doped titanium dioxide and gold-loaded water-gas shift catalyst of in-situ nitrogen-doped titanium dioxide

Abstract

The invention relates to the technical field of catalytic materials, in particular to in-situ nitrogen-doped titanium dioxide and a preparation method and application of a gold-loaded water-gas shift catalyst of the in-situ nitrogen-doped titanium dioxide. The invention provides in-situ nitrogen-doped titanium dioxide and a preparation method and application of a gold-loaded water-gas shift catalyst of the in-situ nitrogen-doped titanium dioxide. According to the method, the in-situ nitrogen-doped titanium dioxide and the supported gold-water gas shift catalyst are induced through the ammonia pool effect, so that the water-gas shift reaction activity of the catalyst is improved, and the stability of the catalyst is enhanced. The in-situ nitrogen-doped titanium dioxide and the gold-water gas shift catalyst loaded with the in-situ nitrogen-doped titanium dioxide provided by the invention have remarkable cycling stability, can keep stable performance under dynamic start-stop operation conditions, and have key significance in practical application of hydrogen fuel cells.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of catalytic materials, in particular to a preparation method and application of in-situ nitrogen-doped titanium dioxide and a gold-supported water-gas shift catalyst thereof. BACKGROUND

[0002] The water-gas shift (WGS) reaction is an important link in the industrial hydrogen production and ammonia synthesis reaction process, and is also an indispensable step in the hydrogen fuel cell. Gold-based catalysts are considered to be one of the most promising catalysts for commercialization due to their good catalytic performance. In order to further improve the performance of gold-based catalysts in the water-gas shift reaction, scientists have adopted various methods. It is found that the properties of the carrier can significantly affect the performance of the catalyst. Therefore, selecting a suitable carrier and modifying the carrier are of great significance to improve the performance of gold-based water-gas shift catalysts.

[0003] Among the numerous metal oxide carriers, TiO2 is favored by most researchers due to its low price, stable properties, simple preparation, and non-toxicity. It is considered to be an effective means to improve the performance by introducing oxygen vacancies into the TiO2 carrier. At present, oxygen vacancies are mostly manufactured by low-valence metal atom doping and reduction atmosphere calcination. On the one hand, the introduction of impurity elements by low-valence metal atom doping not only increases the risk of catalyst poisoning, but also makes the active sites of the catalyst unclear. On the other hand, reduction atmosphere (such as hydrogen, carbon monoxide, etc.) calcination requires a high reduction calcination temperature, which has the disadvantages of great safety hazards, harsh reduction conditions, large energy consumption, and is not conducive to industrial production. Moreover, excessive reduction can lead to phase transformation or structure damage of the catalytic material. Therefore, it is of great industrial application value to develop a safe, effective, low-cost, high-performance, and oxygen vacancy-rich gold-based water-gas shift catalyst.

[0004] Non-metallic element-doped titanium dioxide can also promote the generation of oxygen vacancies. Non-metallic element doping is most common with N element doping. However, N-doped titanium dioxide is mainly obtained by physically mixing titanium dioxide or its precursor with nitrogen-containing organic matter (such as urea, triethylamine, triethanolamine, melamine, etc.) and then calcining at high temperature, or by calcining titanium dioxide or its precursor at high temperature in an ammonia atmosphere. Such methods have the problems of low doping efficiency and difficulty in bulk lattice doping, which leads to the inability to form abundant and stable oxygen vacancies. Therefore, developing a method for deep-level bulk lattice in-situ N-doped titanium dioxide plays an important role in promoting the performance improvement of gold-supported catalysts. SUMMARY

[0005] The application provides a preparation method and application of in-situ nitrogen-doped titanium dioxide and a gold-supported water-gas shift catalyst thereof.

[0006] To achieve the above-mentioned purpose, the application provides the following technical scheme. The application provides a preparation method of in-situ nitrogen-doped titanium dioxide and a gold-supported water-gas shift catalyst thereof, comprising the following steps. S1. mixing a titanium source and a strong alkali solution to obtain a titanate precursor through a hydrothermal reaction; S2. mixing the titanate precursor and a nitrogen-containing inorganic aqueous solution in an environment with a pH of 6.5-7.0 to obtain an N-TiO2 carrier through calcination; S3. loading gold nanoparticles on the N-TiO2 carrier to obtain an Au-N-TiO2 catalyst.

[0007] The application uses a titanium source and a strong alkali solution to obtain a titanate precursor through a hydrothermal reaction, and then places the titanate precursor in a nitrogen-containing inorganic aqueous solution to perform NH4 + ion exchange, so that NH4 + enters the interior of the carbonate skeleton to form an ammonium titanate precursor. After calcination, an N-TiO2 carrier is obtained, and then gold is loaded on the N-TiO2 carrier through a deposition precipitation method to obtain an in-situ nitrogen-doped titanium dioxide gold-supported water-gas shift catalyst material. The performance test in the water-gas reaction verifies that the catalyst material indeed has good catalytic activity and cycle stability in the water-gas reaction.

[0008] Preferably, in S1, the temperature of the hydrothermal reaction is 150-250 DEG C, and the time of the hydrothermal reaction is 22-26 h.

[0009] Preferably, the titanium source comprises a titanium-containing ester organic compound; preferably, the titanium source is tetrabutyl titanate.

[0010] Preferably, the concentration of the strong alkali solution is 8-12 mol / L, and the pH of the strong alkali solution is higher than 14; preferably, the strong alkali is sodium hydroxide or potassium hydroxide.

[0011] Preferably, in S2, the nitrogen-containing inorganic substance is ammonium chloride or ammonium acetate.

[0012] Preferably, the molar ratio between titanium in the titanate precursor and nitrogen in the nitrogen-containing inorganic substance is 3:5-3:15.

[0013] Preferably, the concentration of the nitrogen-containing inorganic substance is 0.4-1 mol / L.

[0014] Preferably, the temperature of the mixing in S2 is 70-90 ℃.

[0015] Preferably, the time of the mixing is 5-7 h.

[0016] Preferably, the temperature of the calcining is 500-600 ℃.

[0017] Preferably, the time of the calcining is 3-5 h.

[0018] The ammonia pool inducing effect refers to a new method for realizing efficient in-situ nitrogen doping and oxygen vacancy generation in cooperation by constructing an endogenous "ammonia pool". The present application places titanate in a solution rich in NH4 + , so that NH4 + is ionically replaced with strong alkali metal cations (such as Na + , K + ) in the carbonate, so that NH4 + enters the carbonate lattice framework or is confined in the pore channel (NH4 + confined by the lattice framework or the pore channel is figuratively called ammonia pool), forming an ammonium titanate precursor. When it is further calcined at high temperature, NH4 + is decomposed by heat to form nitrogen elements in-situ entering into TiO2 to form stable N-O chemical bonds, and a large number of oxygen vacancies rich in electrons are induced to be generated. This in-situ nitrogen doping method benefits from the ammonia pool inducing effect.

[0019] Compared with the method of directly physically mixing a titanium source and a nitrogen-containing inorganic substance and then calcining at high temperature or calcining a titanium source at high temperature in an ammonia atmosphere, more nitrogen elements can be doped into the TiO2 lattice framework in the present application to form abundant and stable deep-level oxygen vacancies.

[0020] Preferably, in S3, the gold nanoparticles are loaded on the surface of the TiO2 carrier by a deposition precipitation method.

[0021] Preferably, the process of the deposition precipitation method comprises the following steps: first, adjusting the pH of a TiO2 carrier solution to 9.3-9.7 with ammonia water, then adding chloroauric acid and ammonia water, keeping the pH of the TiO2 carrier solution at 9.3-9.7, then stirring and aging in a constant-temperature water bath, and finally centrifuging, washing the solution to neutral, and drying to obtain an Au-N-TiO2 catalyst.

[0022] Preferably, the concentration of the ammonia water is 0.05-1 mol / L.

[0023] Preferably, the concentration of the TiO2 carrier solution is 3-3.5 g / L.

[0024] Preferably, the concentration of the chloroauric acid is 0.002-0.003 mol / L.

[0025] Preferably, the temperature of the constant-temperature water bath is 70-90℃.

[0026] Preferably, the time of the aging stirring is 1-4 h.

[0027] The present application uses chloroauric acid as the gold source, and reacts with water under alkaline conditions to generate gold hydroxide precipitate deposited on the surface of the N-TiO2 carrier. The oxygen vacancies in the N-TiO2 carrier are rich in electrons, which can promote the electron transfer between the metal and the carrier, and more easily reduce Au 3+ to a low valence state. The low valence state Au can serve as an active site to promote the WGS reaction, thereby improving the catalytic activity and stability of the Au-N-TiO2 catalyst.

[0028] The present application also provides the in-situ nitrogen-doped titanium dioxide and the gold-loaded water gas shift catalyst thereof prepared by the above preparation method, which comprises the TiO2 carrier with in-situ doped nitrogen element and gold nanoparticles loaded thereon.

[0029] Preferably, the doping amount of the nitrogen element is 1-4 % according to the relative atomic percentage of the in-situ nitrogen-doped titanium dioxide carrier.

[0030] The present application also provides the application of the in-situ nitrogen-doped titanium dioxide and the gold-loaded water gas shift catalyst thereof in the catalysis of the water gas shift reaction.

[0031] Preferably, the water gas shift reaction uses a fixed bed reactor, and the raw material gas composition is 10-15 % CO and 85-90 % N2.

[0032] Preferably, the flow rate of the raw material gas is 35-45 mL / min.

[0033] Preferably, the ratio of water vapor to raw material gas is kept at 1:1.

[0034] Preferably, the temperature of the water gas shift reaction is 100-550℃.

[0035] Therefore, the present application has the following beneficial effects: (1) The present application realizes in-situ nitrogen doping through the ammonia pool effect, which is safe and low-cost, can form deep in-situ N doping in the bulk phase lattice, and effectively solves the problems of low nitrogen doping efficiency and difficulty in doping in the bulk phase lattice caused by the traditional physical mixing calcination method of nitrogen-containing compounds and the ammonia high-temperature calcination method.

[0036] (2) The present application can effectively promote the stable generation of carrier body phase deep-level rich oxygen vacancies through in-situ nitrogen doping method. The method of forming oxygen vacancies by in-situ nitrogen doping does not introduce impurity metals, reduces the risk of catalyst poisoning and deactivation, and overcomes the shortcomings of the reduction atmosphere calcination method, such as great safety hidden danger, relatively harsh reduction conditions, large energy consumption, and being not conducive to industrialized production, and phase transformation or structure damage of catalytic materials caused by excessive reduction.

[0037] (3) The present application realizes catalyst performance optimization through nitrogen doping modification. The in-situ doping of nitrogen elements leads to lattice distortion of the TiO2 carrier and induces the generation of rich and stable oxygen vacancies. These oxygen vacancies promote the electron transfer between the loaded gold nanoparticles and the carrier, enhance the interaction between them, not only improve the water-gas shift reaction activity of the catalyst, but also enhance its stability. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 (a) is a CO conversion performance graph of the catalyst obtained from Example 1 and Comparative Example 1; Figure 1 (b) is a reaction rate graph of eliminating CO at 260℃ of the catalyst obtained from Example 1 and Comparative Example 1, Figure 1 (c) is an Arrhenius graph of TOF of the catalyst obtained from Example 1 and Comparative Example 1 in the reaction temperature range of 240℃-310℃.

[0039] Figure 2 (a) Na2Ti3O7; (b) H2Ti5O 11 and (NH4)2Ti3O7.

[0040] Figure 3 (a) XRD and (b) Raman comparative graphs of the catalyst obtained from Example 1 and Comparative Example 1.

[0041] Figure 4 Oxygen vacancy EPR comparative graph of the catalyst obtained from Example 1 and Comparative Example 1.

[0042] Figure 5 (a) is a TEM graph of the catalyst obtained from Example 1; Figure 5 (b-c) are HRTEM graphs of the catalyst obtained from Example 1; Figure 5 (d) is a selected area electron diffraction graph of the catalyst obtained from Example 1; Figure 5 (e-i) are element distribution graphs of the catalyst obtained from Example 1. Figure 5 (j) is a TEM graph of the catalyst obtained from Comparative Example 1; Figure 5(k-l) are HRTEM images of the catalyst obtained from Comparative Example 1; Figure 5 (m) is a selected area electron diffraction pattern of the catalyst obtained from Comparative Example 1; Figure 5 (n-q) are element mapping images of the catalyst obtained from Comparative Example 1.

[0043] Figure 6 XPS comparison of the catalysts obtained from Example 1 and Comparative Example 1; wherein, (a) Au 4f; (b) N 1s; (c) Ti 2p; (d) O 1s.

[0044] Figure 7 TEM images of TiO2 support obtained from Example 1 and Comparative Example 1 in high-angle annular dark-field (HADDF) mode; wherein, (c) is the HADDF-STEM image of N-TiO2, (a)-(b) are the magnified images of the orange and red box regions in (c) respectively; (f) is the HADDF-STEM image of TiO2, (d)-(e) are the magnified images of the orange and red box regions in (f) respectively.

[0045] Figure 8 Catalyst cycle stability images obtained from Example 1 and Comparative Example 1; wherein, (a) is Example 1; (b) is Comparative Example 1.

[0046] Figure 9 CO conversion rate comparison of the catalysts obtained from Example 1 and Comparative Example 1 at 350 ℃, after the first four cycles.

[0047] Figure 10 (a) is a TEM image of the reacted catalyst obtained from Example 1; Figure 10 (b) is a HRTEM image of the reacted catalyst obtained from Example 1; Figure 10 (c) is a HADDF image of the reacted catalyst obtained from Example 1; Figure 10 (d-g) are element mapping images of the reacted catalyst obtained from Example 1. Figure 10 (h) is a TEM image of the reacted catalyst obtained from Comparative Example 1; Figure 10 (i) is a HRTEM image of the reacted catalyst obtained from Comparative Example 1; Figure 10 (j) is a Au particle size statistics chart of the reacted catalysts obtained from Example 1 and Comparative Example 1; Figure 10 (k) is a HADDF image of the reacted catalyst obtained from Comparative Example 1; Figure 10 (l-n) are element mapping images of the reacted catalyst obtained from Comparative Example 1.

[0048] Figure 11 CO conversion rate comparison of the catalysts obtained from Example 1-2 and Comparative Example 2.

[0049] Figure 12 XRD comparison chart of catalysts obtained for Examples 1-2 and Comparative Example 2.

[0050] Figure 13 CO conversion comparison chart of catalysts obtained for Example 1 and Comparative Examples 3-4.

[0051] Figure 14 CO conversion comparison chart of catalysts obtained for Example 1 and Comparative Examples 5-6.

[0052] Figure 15 Schematic diagram for synthesis of TiO2 and N-TiO2 carriers. DETAILED DESCRIPTION

[0053] The application will be further described below in connection with specific embodiments. Those skilled in the art can implement the application based on these descriptions. In addition, the embodiments of the application involved in the following descriptions are generally only embodiments of a part of the application, rather than all embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments in the application without making creative efforts should belong to the protection scope of the application.

[0054]

EMBODIMENT

[0055] (2) Preparation of N-TiO2 carrier: 1.3510 g of sodium titanate precursor was mixed with 2.4071 g of ammonium chloride (concentration of 0.5 mol / L) at a molar ratio of 1:10, the pH was tested to be 6.8, and stirring was carried out in a water bath at 80 ℃ for 6 h, and the stirring was repeated twice to ensure sufficient exchange of ammonium ions. Finally, centrifugation, water washing to neutral, drying at 80 ℃, calcination in a muffle furnace at 550 ℃ for 4 h, and cooling to room temperature to collect the sample to obtain an N-TiO2 carrier.

[0056] (3) Preparation of Au-N-TiO2 catalyst: 0.5 g of N-TiO2 support was dispersed in 150 mL of deionized water, and ultrasonicated until the solution was uniformly mixed. The pH of the solution was adjusted to 9.3-9.7 using 0.05 mol / L ammonia water, and then 0.0025 mol / L chloroauric acid (calculated based on a gold loading of 2% by mass) and 0.05 mol / L ammonia water were simultaneously added dropwise, so that the pH of the solution remained at 9.3-9.7. Finally, the solution was stirred in a water bath at 80°C for 3 h. After the end of the reaction, the solution was centrifuged, washed with water until neutral, and dried at 105°C for 6 h to obtain the Au-N-TiO2 catalyst, which was denoted as 2% Au-N-TiO2.

[0057] Example 2 This example is basically the same as Example 1, except that in (2), ammonium chloride is replaced with an equimolar amount of ammonium acetate (Ammonium acetate, abbreviated as AA), and the obtained catalyst is denoted as 2% Au-N-TiO2-AA.

[0058] Comparative Example 1 This comparative example is basically the same as Example 1, except that in (2), the addition of ammonium chloride is omitted, and the sodium titanate precursor is mixed with 0.2 mol / L hydrochloric acid at a molar ratio of 1:5, soaked at room temperature for 24 h, and subjected to H + exchange. After centrifugal washing until neutral, the titanium acid (H2Ti3O7) was dried and calcined to obtain the TiO2 support, which was treated according to (3) to obtain the catalyst, which was denoted as 2% Au-TiO2. +

[0059] Comparative Example 2 This comparative example is basically the same as Example 1, except that in (2), ammonium chloride is replaced with an equimolar amount of a phosphate buffer solution (Phosphate buffer solution, abbreviated as PBS) prepared from ammonium dihydrogen phosphate and diammonium hydrogen phosphate, and the buffer solution has a pH of 7 (the specific preparation method is as follows: the total concentration of the buffer solution is 0.5 M, and 3.5540 g of diammonium hydrogen phosphate and 2.5210 g of ammonium dihydrogen phosphate are dissolved in a 100 mL volumetric flask), and the obtained catalyst is denoted as 2% Au-N-TiO2-PBS.

[0060] Comparative Example 3 This comparative example is basically the same as Example 1, except that in (2), the pH is adjusted to 5 by adding an appropriate amount of hydrochloric acid, and the obtained catalyst is denoted as 2% Au-N-TiO2(pH=5).

[0061] Comparative Example 4 ​The comparative example is basically the same as example 1, except that in (2), the pH is adjusted to 6 by adding an appropriate amount of hydrochloric acid, and the obtained catalyst is recorded as 2% Au-N-TiO2(pH=6).

[0062] Comparative Example 5 The comparative example is basically the same as example 1, except that in (2), the concentration of ammonium chloride is adjusted to 3 mol / L, and the obtained catalyst is recorded as 2% Au-N-TiO2(80℃ AC-3M).

[0063] Comparative Example 6 The comparative example is basically the same as example 1, except that in (2), the concentration of ammonium chloride is adjusted to 3 mol / L, and the stirring temperature is adjusted to 60℃, and the obtained catalyst is recorded as 2% Au-N-TiO2(60℃ AC-3M).

[0064]

Performance Test

[0065] Catalyst cycle stability test: The test method is basically the same as "WGS performance test", except that first, the catalyst is tested for initial activity, then the reaction system is cooled to room temperature and kept under nitrogen atmosphere, and then the second activity evaluation is carried out under the same reaction conditions, and so on for a total of six times.

[0066] The catalysts obtained in Example 1 and Comparative Example 1 were tested for their CO conversion performance, and the results are as follows: Figure 1 As shown in (a). Observation shows that within the reaction temperature range of 150℃-500℃, the catalytic activity of the in-situ N-doped catalyst Au-N-TiO2 was significantly improved compared to the Au-TiO2 catalyst. Comparing the CO conversion rate at 350℃, the CO conversion rate of the Au-N-TiO2 catalyst was increased by 34% compared to the Au-TiO2 catalyst. The catalyst obtained in Example 1 exhibits superior catalytic performance compared to Comparative Example 1, and this advantage was maintained in subsequent cycle tests. To further compare the actual catalytic activity of the two catalysts, calculations were performed as follows... Figure 1 As shown in (b) and (c), the reaction rate of Au-N-TiO2 at 260℃ is 11.5 × 10⁻⁶. -4 mol / g(Au) / s and 4.3×10 -6 mol / m 2 The (Au) / s values ​​are both close to twice the reaction rate of the Au-TiO2 catalyst. Furthermore, the activation energies of Au-N-TiO2 and Au-N-TiO2 are 23.3 kJ / mol and 27.7 kJ / mol, respectively. Obviously, the activation energy of the Au-N-TiO2 catalyst is lower, meaning it is more likely to react.

[0067] XRD tests were performed on the TiO2 support and sodium titanate precursor obtained in Example 1 and Comparative Example 1, and the results are as follows: Figure 2 As shown in the diagram, the sodium titanate precursor exhibits distinct XRD diffraction peaks at 2θ = 10.5°, 25.7°, 29.9°, 34.1°, 38.3°, 43.8°, and 47.7°, which are typical diffraction peaks for sodium titanate (Na₂Ti₃O₇). However, when comparing the XRD patterns of the two catalysts, these diffraction peaks disappear, indicating that H… + and NH4 + with Na + All ion exchanges successfully replaced Na. + .

[0068] XRD and Raman tests were performed on the catalysts and sodium titanate precursors obtained in Example 1 and Comparative Example 1, and the results are as follows: Figure 3 As shown. From Figure 3 (a) Observation shows that the prepared TiO2 exhibits two crystal forms: predominantly anatase (JCPDF No. 084-1286) and secondarily monoclinic (JCPDF No. 074-1940). After N doping, TiO2 retains its original crystal form without change, indicating that in-situ N doping does not alter the crystal form of TiO2. From Figure 3(a) no diffraction peak of Au was found, which indicated that Au was well dispersed on the support and the particle size was small, and the diffraction peaks of the two catalysts did not shift. Figure 3 (b) The Raman spectrum showed two groups of Raman peaks, of which anatase had 6 wave bands. The strongest vibration peak of anatase was at 143 cm -1 , and the strongest vibration peak of monoclinic was at 123 cm -1 . After normalizing the peak intensity at 123 cm -1 , the peak intensity at 143 cm -1 of anatase was compared, and the peak intensity of the catalyst obtained in Example 1 was obviously weakened at this position. It was speculated that the reason for the change might be that defects were generated after N doping, which affected the polarizability of the symmetry stretching vibration mode of Ti-O vibration unit.

[0069] The catalysts obtained in Example 1 and Comparative Example 1 were subjected to oxygen vacancy EPR test, and the results are shown in Figure 4 . It was observed that the catalyst obtained in Example 1 had a strong signal peak at g = 2.003, and the peak appeared because Ti 3+ and single electron O 2- radicals were adsorbed on the oxygen vacancy by O2 from air, while the catalyst obtained in Comparative Example 1 had no signal. It was inferred that N doping induced the generation of oxygen vacancies, and the oxygen vacancies could positively promote the WGS reaction.

[0070] The catalysts obtained in Example 1 and Comparative Example 1 were subjected to TEM test, and the results are shown in Figure 5 . The morphology and structure of the catalysts were observed from the transmission electron microscope. As shown in Figure 5 (a), (j), nanometer belt-shaped TiO2 was successfully prepared, which was consistent with the morphology of the precursor of the TiO2 we prepared before, and the nanometer belt-shaped structure of TiO2 was not changed after N doping. As shown in Figure 5 (c), (l), the

[101] crystal plane of anatase and the

[110] crystal plane of monoclinic (Monaclinic is abbreviated as M in the figure, and Anatase is abbreviated as A in the figure) could be observed from the high-resolution TEM at the same time, which verified that the synthesized TiO2 had anatase and monoclinic two crystal forms. Figure 5 (m) shows the selected area electron diffraction pattern of Comparative Example 1, which has clear selected area electron diffraction ring. In comparison, the selected area electron diffraction ring of Example 1 is relatively blurred, which further proves that the incorporation of N atoms causes defects in TiO2, which is consistent with the above Figure 3 and Figure 4 results. From the HADDF mode, it can be seen that the Au particles of the two catalysts of Example 1 and Comparative Example 1 are well dispersed and there is no obvious agglomeration.

[0071] XPS tests were performed on the catalysts obtained in Example 1 and Comparative Example 1, and the results are as follows: Figure 6 As shown. From Figure 6 (a) Observation shows that the Au in the catalysts obtained in Example 1 and Comparative Example 1 is mainly composed of Au. 3+ and Au + In Example 1, Au + The proportion was 64.3%, Au 3+ The proportion is approximately 35.7%. In Comparative Example 1, Au... + The proportion was 44.3%, Au 3+ The proportion was approximately 55.7%. The results indicate that the catalyst obtained in Example 1 contained more Au in its lower valence state. + Au in low price state + This is an important factor in improving the activity of the WGS reaction, thus demonstrating that the catalyst obtained in Example 1 can improve the activity of the water-gas shift reaction. Figure 6 (b) Observation shows that the catalyst obtained in Example 1 has an additional NO bond signal peak at position 404.0 eV compared to Comparative Example 1, indicating that N is doped into the TiO2 support lattice framework and forms stable chemical bonds, which affects the structure of the catalyst and thus enhances its catalytic activity. Figure 6 (c) is the XPS spectrum of Ti 2p. Since there are oxygen vacancies in the catalyst obtained in Example 1, the unsaturated Ti in this catalyst... 3+ A lot. Figure 6 In (d), the 1s peak of O is divided into lattice oxygen and oxygen vacancies. It can also be observed from the figure that the catalyst obtained in Example 1 has more oxygen vacancies.

[0072] The TiO2 supports obtained in Example 1 and Comparative Example 1 were tested by transmission electron microscopy in high-angle annular dark field (HADDF) mode, and the results are as follows: Figure 7 As shown. Figure 7 (a) and 7(b) are enlarged views of the orange and red dashed boxes in 7(c), respectively; Figure 7 (d) and 7(e) are magnified views of the orange and red dashed boxes in 7(f), respectively. (Comparison) Figure 7 (a), (b), (d), and (e) show that the TiO2 atoms are arranged neatly with equal spacing between the atoms in the two rows, which is the normal TiO2 lattice. However, the spacing between adjacent atomic rows and columns in the N-TiO2 catalyst support is inconsistent. This is because the doping of N atoms causes distortion of the TiO2 lattice.

[0073] Cyclic stability tests were performed on the catalysts obtained in Example 1 and Comparative Example 1. The results are as follows: Figure 8As shown, by comparing the performance decay trends of the two catalysts in multiple cycles, it can be clearly seen that the catalyst obtained in Example 1 not only has higher initial activity, but also exhibits significantly enhanced cycle stability, which is particularly important for the frequent start-stop operating conditions in actual fuel cell systems.

[0074] The catalysts obtained in Example 1 and Comparative Example 1 were subjected to 350 ℃ performance testing, and the CO conversion rates of the last four cycles were compared, and the results are shown in Figure 9 As can be observed, during the second to sixth cycle tests, the catalyst obtained in Example 1 exhibited excellent stability, with its CO conversion rate only slightly decreasing from 86.9% to 81.3%, with an activity decay amplitude of only 5.6%; in contrast, the catalyst obtained in Comparative Example 1 exhibited more significant activity decay, with its CO conversion rate decreasing from 78.0% to 66.6%, with a decrease of 11.4%. This indicates that the introduction of N elements not only significantly improves the initial activity of the catalyst, but more importantly, greatly enhances the cycle stability of the catalyst.

[0075] The reacted catalysts obtained in Example 1 and Comparative Example 1 were subjected to TEM testing, and the results are shown in Figure 10 As can be observed from the HADDF Figure 10 (c), (k) and element distribution Figure 10 (e), (l) of the reacted catalysts, it can be observed that the Au of both catalysts has undergone certain agglomeration, and from the HRTEM Figure 10 (b), (i), the lattice fringes of the (111) crystal plane of Au can also be clearly seen. By statistically analyzing the Au particle sizes after reaction, the d of the reacted catalyst of Example 1 (Au-N-TiO2-used) was 4.45 nm, and the d of the reacted catalyst of Comparative Example 1 (Au-TiO2-used) was 4.87 nm, indicating that the Au particle size of the nitrogen-doped catalyst after stability testing was only slightly different from that of the non-nitrogen-doped catalyst. Figure 10 As can be observed from (j), the Au particle size of Au-N-TiO2-used, although it has undergone agglomeration, remains uniform, while Au-TiO2-used has larger agglomerated Au. This also confirms that N atoms can better anchor Au particles, thereby enabling Au to maintain good dispersion on the catalyst support, promoting the catalyst to have stable catalytic activity.

[0076] The catalysts obtained in Example 1-2 and Comparative Example 2 were subjected to WGS performance testing, and the results are shown in Figure 11The three catalysts show different CO conversion trends in the low-temperature to high-temperature range, wherein the catalyst obtained in Example 1 exhibits higher catalytic activity at lower temperatures, and the CO conversion rates of the catalysts obtained in Example 2 and Comparative Example 2 are both lower than that of the catalyst obtained in Example 1 at the same temperature. Therefore, the catalytic activity of the catalyst obtained in Example 1 is significantly improved, and the low-temperature activity has a significant impact.

[0077] The catalysts obtained in Examples 1-2 and Comparative Example 2 were subjected to XRD testing, and the results are shown in FIG. 2. Figure 12 As can be observed, the catalysts obtained in Examples 1-2 and Comparative Example 2 all have typical TiO2 diffraction peaks in the range of 5°-80°, the peak positions of which correspond well to standard cards JCPDF No. 084-1286 and JCPDF No. 074-1940, and it is shown that TiO2 in all samples is mainly in the form of anatase, with a small amount of monoclinic phase, and no other impurities are present. Although the crystal structures of the three are consistent, there are still differences in intensity and half-height width at certain specific diffraction angles, which is due to the influence of different nitrogen sources on the grain size and crystal defects. Combined with the performance data, it can be inferred that the catalyst obtained in Example 1 may promote the formation of active sites due to its more optimal nitrogen doping method and metal-support interaction, thereby improving its CO catalytic performance. Meanwhile, the poor performance of Example 2 may be caused by too strong crystallinity, and the poor performance of Comparative Example 2 may be caused by the phosphoric acid poisoning the Au supported in the catalyst.

[0078] The catalysts obtained in Example 1 and Comparative Examples 3-4 were subjected to WGS performance testing, and the results are shown in FIG. 3. Figure 13 As can be observed, the catalyst obtained in Example 1 has relatively high activity, indicating that a weakly acidic to neutral solution can better promote ammonium ion exchange, thereby forming more abundant nitrogen doping. In contrast, if the replacement solution is adjusted to be more acidic, part of the precursor, such as H + in Comparative Example 1, will form a titanium acid instead of an ammonium titanate precursor, which will result in a lower amount of nitrogen doping and thus lower catalytic performance.

[0079] The catalysts obtained in Example 1 and Comparative Examples 5-6 were subjected to WGS performance testing, and the results are shown in FIG. 4. Figure 14 As can be observed, the light-off temperature of the catalyst obtained in Example 1 is significantly lower than that of the catalysts obtained in Comparative Examples 5-6, and the CO conversion rate curve of the catalyst obtained in Example 1 is the steepest with increasing temperature, thereby indicating the key role of relatively mild preparation conditions (lower ammonium salt concentration) in generating high-activity catalytic sites.

[0080] The principle of the in-situ nitrogen doping method induced by the ammonia pool effect in Example 1 and the principle of no nitrogen doping in Comparative Example 1 are shown in FIG. 5. Figure 15 As can be observed, the principle of the in-situ nitrogen doping method induced by the ammonia pool effect in Example 1 and the principle of no nitrogen doping in Comparative Example 1 are shown in FIG. 5.

Claims

1. A method for preparing in-situ nitrogen-doped titanium dioxide and its supported gold-water-gas shift catalyst, characterized in that, include: S1. Titanate precursors are prepared by mixing titanium source with strong alkaline solution and then reacting them hydrothermally. S2. The titanate precursor was mixed with an aqueous solution of nitrogen-containing inorganic material in an environment with a pH of 6.5 to 7.0 and calcined to obtain N-TiO2 support; S3. Gold nanoparticles were loaded onto an N-TiO2 support to obtain an Au-N-TiO2 catalyst.

2. The preparation method according to claim 1, characterized in that, In S1, the temperature of the hydrothermal reaction is 150~250℃, and the time of the hydrothermal reaction is 22~26 h; And / or, the titanium source includes titanium-containing ester organic compounds; preferably, the titanium source is tetrabutyl titanate; And / or, the concentration of the strong alkali solution is 8~12 mol / L; the pH of the strong alkali solution is 14 or higher; preferably, the strong alkali is sodium hydroxide or potassium hydroxide.

3. The preparation method according to claim 1, characterized in that, In S2, the nitrogen-containing inorganic substance is ammonium chloride or ammonium acetate; And / or, the molar ratio between titanium in the titanate precursor and nitrogen in the nitrogen-containing inorganic material is 3:5 to 3:15; And / or, the concentration of the nitrogen-containing inorganic substance is 0.4~1 mol / L.

4. The preparation method according to claim 1, characterized in that, In S2, the mixing temperature is 70~90℃; And / or, the mixing time is 5-7 h; And / or, the calcination temperature is 500~600 ℃; And / or, the calcination time is 3 to 5 hours.

5. The preparation method according to claim 1, characterized in that, In S3, gold nanoparticles are loaded onto the surface of a TiO2 support by a deposition precipitation method. Preferably, the deposition precipitation process includes: first adjusting the pH of the TiO2 support solution to 9.3~9.7 with ammonia water, then adding chloroauric acid and ammonia water to maintain the pH of the TiO2 support solution at 9.3~9.7, then stirring and aging in a constant temperature water bath, and finally centrifuging, washing the solution to neutrality, and drying to obtain Au-N-TiO2 catalyst; Preferably, the concentration of the ammonia solution is 0.05~1 mol / L; Preferably, the concentration of the TiO2 support solution is 3~3.5 g / L; Preferably, the concentration of the chloroauric acid is 0.002~0.003 mol / L; Preferably, the temperature of the constant temperature water bath is 70~90℃; Preferably, the aging and stirring time is 1 to 4 hours.

6. The in-situ nitrogen-doped titanium dioxide and its supported gold-water-gas shift catalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The invention includes a nitrogen-doped TiO2 support and its loaded gold nanoparticles; the TiO2 support contains oxygen vacancies; the nitrogen element is introduced into the TiO2 support lattice through a pyrolysis reaction induced by the ammonia pool effect after mixing with the TiO2 support precursor and nitrogen-containing inorganic material. Preferably, the amount of nitrogen doping is 1 to 4% based on the relative atomic percentage of the in-situ nitrogen-doped titanium dioxide support.

7. The application of the in-situ nitrogen-doped titanium dioxide and its supported gold water-gas shift catalyst as described in claim 6 in the catalytic water-gas shift reaction.

8. The application as described in claim 7, characterized in that, The water-gas shift reaction uses a fixed-bed reactor, and the feed gas composition is 10-15% CO and 85-90% N2. Preferably, the flow rate of the feed gas is 35~45 mL / min; Preferably, the ratio of water vapor to feed gas is maintained at 1:1; Preferably, the temperature of the water-gas shift reaction is 100~550℃.

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