A method for detecting a catalyst crystal structure

Abstract

The application belongs to the field of catalysis and relates to a detection method for a catalyst crystal structure, which is performed in an X-ray diffractometer, the X-ray diffractometer comprising an in-situ reaction cell and a reaction atmosphere control device, the method comprising loading a catalyst to be detected into the in-situ reaction cell, providing a reaction atmosphere to the in-situ reaction cell by the reaction atmosphere control device, and starting the X-ray diffractometer to detect the catalyst to be detected. The application provides real-time reaction atmosphere by the reaction atmosphere control device to simulate the use environment, realizes online switching and real-time accurate regulation of multiple gases, and realizes accurate detection of in-situ XRD in cooperation with the in-situ reaction cell, can be used for research on the crystal structure change process of the catalyst, reveals the influence of each component in the catalyst, and has important guiding significance for optimization and production of the catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalysis, specifically relating to a method for detecting the crystal structure of a catalyst. Background Technology

[0002] X-ray diffraction (XRD) is a primary method for studying the crystal structure of materials and its evolution. In-situ XRD involves adding different reaction devices to existing equipment to provide external fields such as electric fields, temperatures, atmospheres, and force fields to obtain information about the evolution of the material's structure. Compared to offline testing, in-situ XRD can establish the relationship between external fields (electric / temperature / force fields, etc.) and the material structure, offering real-time and online advantages. It can accurately reflect structural information and has significant guiding significance for further material improvement.

[0003] NH3 / Urea-SCR technology refers to the selective reduction of nitrogen oxides to N2 using NH3 or urea as a reducing agent under oxygen-rich conditions and in the presence of a catalyst. It is one of the most effective and widely used technologies for removing nitrogen oxides from both stationary and mobile sources, and its core research focus is on the catalyst. Currently, the most important commercial denitrification catalyst system is the vanadium-based catalyst, namely V2O5-WO3(MoO3) / TiO2. V2O5 is a highly active denitrification oxide with high denitrification activity, good selectivity, and high sulfur and toxicity resistance. However, the weight of V2O5 in the catalyst is limited because V2O5 can catalytically oxidize SO2 to SO3, leading to sulfur poisoning of the catalyst. Therefore, the V2O5 content in the catalyst is closely related to the SO2 content in the flue gas being treated. For commercial SCR catalysts in high-ash coal-fired power plants, due to the high SO2 content in their flue gas, a lower V2O5 content is required, typically controlled at around 1%. In practical applications, V₂O₅ is often supported on the surface of other metal oxides. Supported catalysts not only reduce catalyst costs and improve the dispersion of V₂O₅, thus increasing contact opportunities with reactant gases and enhancing catalytic activity, but also weaken the oxidation of SO₂ by V₂O₅. This is the structure widely used in commercial catalysts. V₂O₅ exhibits good dispersion on the surface of TiO₂. In commercial catalysts, TiO₂ accounts for 80-90% of the catalyst composition. The highest activity is obtained by supporting vanadium catalysts with anatase TiO₂. Anatase TiO₂ (A phase) itself is a very unstable system, a metastable allotrope of TiO₂. It tends to form rutile (R phase), which has higher thermal stability, under any temperature and pressure conditions. This leads to sintering of anatase and loss of specific surface area. Therefore, other additives are needed to improve the thermal stability of the catalyst. For example, the addition of WO3 and MoO3 improves the electronic interaction between V2O5 and TiO2, enhancing the catalyst's activity, selectivity, and stability. MoO3 also enhances the catalyst's resistance to arsenic poisoning. In commercial denitrification catalysts, the WO3 content is typically 4–10%. Sintering of denitrification catalysts is a significant cause of catalyst deactivation, and this process is irreversible. In vanadium-based catalysts, the TiO2 support is anatase, which transforms into rutile after sintering, drastically reducing the number of micropores and specific surface area, thus significantly decreasing the number of active sites and leading to catalyst deactivation. In the entire SCR system, catalyst costs account for more than a quarter of the total investment, and annual depreciation due to catalyst replacement or renewal accounts for 60–70% of the total system operating cost. Catalytic removal of nitrogen oxides from both stationary and mobile pollution sources is carried out under specific atmospheres and high temperatures. Therefore, providing the appropriate reaction atmosphere is crucial for studying the thermal stability of catalysts and the dynamic phase and microstructure evolution of the catalytic process.

[0004] Currently, temperature-controlled in-situ reaction cells adapted to X-ray diffractometers are commercially available, enabling in-situ high and low temperature testing of samples. However, these cells typically contain only one gas inlet and outlet, allowing connection to only one type of gas. While suitable for pure gas reaction testing, they rely on pre-ordering specific gas mixtures from gas companies for applications requiring a mixture of two or more gases. Customizing these mixtures in varying proportions incurs high operating costs and prevents online switching and real-time precise control of multiple gases. The atmospheres used in X-ray diffractometer studies of catalyst pyrolysis, activation, and crystal structure evolution during reactions include inert gases (Ar, He, N2) and various reactive gases (O2, H2, CO, CO2, CH4, etc.). Therefore, a universal, integrated, and even programmable in-situ reaction atmosphere configuration device is essential. This device should offer multiple gas inlet options, rapid switching between pure and mixed gases, and the ability to adjust the reaction atmosphere and concentration entering the system via control software to meet the requirements of in-situ X-ray diffraction detection. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing X-ray diffractometers where temperature-controlled in-situ reaction cells cannot achieve online switching and real-time precise control of multiple gases. Instead, this invention provides a method for detecting the crystal structure of catalysts. This method uses a reaction atmosphere control device to simulate the operating environment and provide a real-time reaction atmosphere, enabling online switching and real-time precise control of multiple gases. Combined with an in-situ reaction cell, this method achieves in-situ XRD crystal structure detection of catalysts.

[0006] Specifically, this invention provides a method for detecting the crystal structure of a catalyst. This method is performed in an X-ray diffractometer, which includes an in-situ reaction cell and a reaction atmosphere control device. The reaction atmosphere control device includes a gas distribution box, which contains a mixing tank, a four-way valve, an in-situ reaction cell inlet, an in-situ reaction cell outlet, a mixed gas source interface, a pure gas source interface, and a tail gas outlet. The mixing gas source interface has at least two interfaces, and different mixing gas source interfaces are connected to the inlet of the mixing tank to mix different gases in the mixing tank to obtain a mixed gas. The outlet of the mixing tank and the pure gas source interface are both connected to the inlet of the four-way valve. The switching between mixed gas and pure gas is achieved through a four-way valve. Two-way ball valves are installed on the pipeline connecting the mixed gas source interface to the mixing tank and on the pipeline connecting the pure gas source interface to the four-way valve. One outlet of the four-way valve is connected to the exhaust gas outlet, and a first back pressure valve is installed on the connecting pipeline. The other outlet of the four-way valve is connected to the inlet of the in-situ reaction tank. The outlet of the in-situ reaction tank is connected to the exhaust gas outlet, and a two-way ball valve and a second back pressure valve are installed on the connecting pipeline. The method includes loading the catalyst to be tested into the in-situ reaction tank, providing a reaction atmosphere to the in-situ reaction tank through a reaction atmosphere control device, and starting an X-ray diffractometer to detect the catalyst.

[0007] After in-depth and extensive research, the inventors of this invention discovered that the reason existing X-ray diffractometers do not employ online mixing of the gas inlet is primarily because online mixing and switching of different gases easily leads to fluctuations in system pressure, making perfect online switching and real-time precise control impossible. However, the reaction atmosphere control device involved in the catalyst crystal structure detection method provided by this invention perfectly solves this problem through the rational formulation of its components. Specifically, the reaction atmosphere control device provided by the present invention includes a mixed gas source interface, a pure gas source interface, a mixing tank, a four-way valve, and two back pressure valves. The first back pressure valve is located on a pipeline connecting one outlet of the four-way valve to the exhaust gas outlet, and the second back pressure valve is located on a pipeline connecting the outlet of the in-situ reaction tank to the exhaust gas outlet. When pure gas is required, the switch connecting the pure gas source interface and the four-way valve is opened, and pure gas is introduced into the in-situ reaction tank through the four-way valve. When mixed gas is required, the switch connecting the mixing tank and the four-way valve is opened, and different gases are introduced from different mixed gas source interfaces, mixed in the mixing tank, and then introduced into the in-situ reaction tank through the four-way valve. The two back pressure valves can effectively stabilize the system pressure. This reaction atmosphere control device can achieve precise mixing of various reaction atmospheres with a mixing accuracy of ±0.5%. Pure gas and mixed gas can be quickly switched using a four-way valve, providing a stable range of gas intake options. It accurately simulates the operating environment to provide a real-time reaction atmosphere, enabling online switching and precise real-time control of multiple gases. Combined with an in-situ reaction tank, it enables precise in-situ XRD detection, which can be used to study the crystal structure change process of catalysts and reveal the influence of each component in the catalyst. This has important guiding significance for catalyst optimization and production. Attached Figure Description

[0008] Figure 1 A schematic diagram of the reaction atmosphere control device provided by the present invention;

[0009] Figure 2 A schematic diagram showing the connections of the components in the reaction atmosphere control device provided by the present invention;

[0010] Figure 3 XRD pattern and scanning electron microscope image of the titanium dioxide support used in the preparation example;

[0011] Figure 4 XRD pattern of the vanadium-based catalyst prepared in the example;

[0012] Figure 5 The in-situ XRD pattern of pure TiO2 obtained from sample #1 in the preparation example;

[0013] Figure 6 The in-situ XRD pattern of V2O5 (1.0%) / TiO2 of sample #2 prepared for the preparation example;

[0014] Figure 7 The in-situ XRD pattern of sample #3, V2O5(1.0%)-WO3(4.0%) / TiO2, prepared as an example;

[0015] Figure 8 The in-situ XRD pattern of sample #4, V2O5(1.0%)-WO3(10%) / TiO2, prepared as an example;

[0016] Figure 9 The in-situ XRD pattern of sample 5#, V2O5(1.0%)-MoO3(4.0%) / TiO2, prepared as an example.

[0017] Explanation of reference numerals in the attached figures

[0018] 1-Mixing tank; 2-Four-way valve; 3-First back pressure valve; 4-Second back pressure valve; 5-Filter; 1#-In-situ reaction tank inlet; 2#-In-situ reaction tank outlet; 3#-Mixed gas source interface; 4#-Pure gas source interface; 5#-Tail gas outlet; 6#-Tail gas sampling port; 7#-Vacuum port; 3-1#-A gas source interface; 3-2#-B gas source interface; 3-3#-C gas source interface; 3-4#-D gas source interface; W1-Micro-regulating valve; J1-Stop valve; F1-Check valve; L1-Mass flow meter; K1-Control display panel; T1-Two-way ball valve; P1-First electronic pressure gauge; P2-Second electronic pressure gauge; P3-Third electronic pressure gauge. Detailed Implementation

[0019] Specifically, the method for detecting the crystal structure of a catalyst provided by the present invention includes loading the catalyst to be tested into an in-situ reaction cell, supplying a reaction atmosphere to the in-situ reaction cell through a reaction atmosphere control device, and starting an X-ray diffractometer to detect the catalyst to be tested.

[0020] In this invention, the catalyst to be tested can be, for example, a vanadium-based catalyst. The vanadium-based catalyst generally includes a support and active components and additives supported on the support. Currently, the most important catalyst system for commercial denitrification catalysts is the vanadium-based catalyst, namely V2O5-WO3(MoO3) / TiO2. V2O5 is a good denitrification catalytically active oxide with high denitrification activity, good selectivity, and high sulfur resistance and anti-toxicity. However, the weight of V2O5 in the catalyst is limited because V2O5 can catalyze the oxidation of SO2 to SO3, leading to sulfur poisoning of the catalyst. Therefore, the V2O5 content in the catalyst is closely related to the SO2 content in the flue gas being treated. For commercial SCR catalysts for high-ash coal-fired power plants, due to the high SO2 content in their flue gas, a low V2O5 content is required, typically controlled at around 1%. In practical applications, V₂O₅ is often supported on the surface of other metal oxides. Supported catalysts not only reduce catalytic costs and improve the dispersion of V₂O₅, thus increasing contact opportunities with reactant gases and enhancing catalytic activity, but also weaken the oxidation of SO₂ by V₂O₅. This structure is currently widely used in commercial catalysis. V₂O₅ exhibits good dispersion on the surface of TiO₂. In commercial catalysts, TiO₂ accounts for 80-90% of the catalyst composition. The highest activity is obtained by supporting vanadium catalysts with anatase TiO₂. Anatase TiO₂ (A phase) itself is a very unstable system, a metastable allotrope of TiO₂. It tends to form rutile (R phase), which has higher thermal stability, under any temperature and pressure conditions. This leads to sintering of anatase and loss of specific surface area. Therefore, other additives are needed to improve the thermal stability of the catalyst. For example, the addition of WO3 and MoO3 improves the electronic interaction between V2O5 and TiO2, enhancing the catalyst's activity, selectivity, and stability. MoO3 also enhances the catalyst's resistance to arsenic poisoning. In commercial denitration catalysts, the WO3 content is typically 4–10%. Sintering of denitration catalysts is a significant cause of catalyst deactivation, and this process is irreversible. In vanadium-based catalysts, the TiO2 support is anatase, which transforms into rutile after sintering, drastically reducing the number of micropores and the specific surface area, thus significantly decreasing the number of active sites and leading to catalyst deactivation. In the entire SCR system, catalyst costs account for more than a quarter of the total investment, and annual depreciation losses due to catalyst replacement or renewal account for 60–70% of the total system operating cost.

[0021] In one specific embodiment, the vanadium-based catalyst includes a support and an active component and an additive supported on the support. The support is TiO2, the active component is V2O5, and the additive is WO3 or MoO3. Based on a support content of 100 wt% in the vanadium-based catalyst, the content of the active component is preferably 0.5–4 wt%, and the content of the additive is 3–10 wt%.

[0022] This invention takes the catalyst to be tested, such as the vanadium-based catalyst [V2O5-WO3(MoO3) / TiO2], as the research object, to explore the change law of the crystal structure of the supported TiO2 with temperature in the reaction atmosphere of practical application. The effects of the active component V2O5, the auxiliary agent WO3 or MoO3 on the phase transformation of the supported TiO2 and the evolution law of its phase structure are studied by in-situ XRD technology.

[0023] like Figure 1 and Figure 2 As shown, the reaction atmosphere control device includes a gas distribution box, which contains a mixing tank 1, a four-way valve 2, an in-situ reaction tank inlet 1#, an in-situ reaction tank outlet 2#, a mixed gas source interface 3#, a pure gas source interface 4#, and a tail gas outlet 5#. The mixing gas source interface 3# has at least two locations, and different mixing gas source interfaces 3# are connected to the inlet of the mixing tank 1 to mix different gases in the mixing tank 1 to obtain a mixed gas. The outlet of the mixing tank 1 and the pure gas source interface 4# are both connected to the inlet of the four-way valve 2. The switching between mixed gas and pure gas is achieved through the four-way valve 2. Two-way ball valves T1 are installed on the pipeline connecting the mixed gas source interface 3# to the mixed gas tank 1 and the pipeline connecting the pure gas source interface 4# to the four-way valve 2. One outlet of the four-way valve 2 is connected to the tail gas outlet 5# and a first back pressure valve 3 is installed on the connecting pipeline. The other outlet of the four-way valve 2 is connected to the in-situ reaction tank inlet 1#. The in-situ reaction tank outlet 2# is connected to the tail gas outlet 5# and a two-way ball valve and a second back pressure valve 4 are installed on the connecting pipeline.

[0024] The atmosphere required for the catalytic system includes inert gases (Ar, He, N2, etc.) and various reactive gases (NOx, NH3, O2, H2, CO, CO2, CH4, etc.), specifically pure gases or mixtures of two or more gases (e.g., mixtures of two, three, four, five, or more gases). Therefore, the reaction atmosphere control device is equipped with one pure gas supply path and one mixed gas supply path to meet the needs of sample characterization. The pure gas supply path and the mixed gas supply path use mass flow meters to precisely control the flow rate and component ratio, and are switched into the in-situ reaction cell via a four-way valve to achieve multiple gas inlet selections. Pure gas is introduced from pure gas source interface 4#, and mixed gas supply is introduced from mixed gas source interface 3#, with the pure gas supply and mixed gas supply switched via the four-way valve. The four ports of the four-way valve are connected in pairs to switch between pure gas and mixed gas entering the in-situ reaction tank. When pure gas is connected to the in-situ reaction tank, mixed gas is connected to the first back pressure valve; when mixed gas is connected to the in-situ reaction tank, pure gas is connected to the first back pressure valve, so as to ensure the stability of system pressure when switching between different reaction gases.

[0025] The number of the mixing gas source interfaces 3# is at least two, specifically two, three, four, or more, depending on actual needs. In one specific embodiment, such as... Figure 1 As shown, there are four gas source interfaces: NOx (3-1#), NH3 (3-2#), O2 (3-3#), and N2 (3-4#). These four interfaces connect to four different gas cylinders, allowing for two, three, or four-way mixing as needed, and enabling switching between pure gas and different mixtures. For example, when pure gas is required, the two-way ball valve on the pipeline connecting the gas source and the mixing tank is closed, and the two-way ball valve on the pipeline connecting the pure gas source and the four-way valve is opened. When a mixture of NOx and NH3 is required, the two-way ball valves on the pipelines connecting the NOx and NH3 gas sources to the mixing tank are opened, while the other two-way ball valves are closed. The intake of other mixtures is controlled using the same method, which will not be elaborated further here.

[0026] Both the in-situ reaction tank inlet and outlet are connected to the in-situ reaction tank. Gas exiting from the in-situ reaction tank inlet enters the in-situ reaction tank. After reaction, the gas in the in-situ reaction tank is introduced into the gas distribution box through the in-situ reaction tank outlet, the pressure is adjusted, and then the exhaust gas is discharged through the tail gas outlet. The reaction atmosphere control device preferably has a tail gas sampling port 6#, which is connected to the in-situ reaction tank outlet and a micro-adjustment valve W1 is installed on the connecting pipeline. At this time, while detecting the in-situ reaction, a sample can be taken from the tail gas sampling port for tail gas analysis. In addition, the reaction atmosphere control device preferably has a vacuum port 7# to provide vacuum. Vacuuming can be carried out according to the reaction conditions. Only a small vacuum pump needs to be connected to complete the process, which is versatile and does not require a separate vacuum port at the in-situ reaction tank end. The vacuum port is connected to the in-situ reaction tank outlet and a shut-off valve J1 is installed on the connecting pipeline for shut-off, adjustment, and throttling. The vacuum port serves two purposes: firstly, it allows the gas in the in-situ reaction cell to be extracted before the reaction begins, preventing interference from other gases and allowing the necessary reaction atmosphere to be introduced before testing; secondly, it allows for vacuuming, maintaining the in-situ reaction cell under a certain pressure to complete the vacuum state detection.

[0027] In one specific embodiment, a mass flow meter L1 and a one-way valve F1 are installed on the pipeline connecting the mixed gas source interface to the mixing tank, and a mass flow meter L1 and a one-way valve F1 are installed on the pipeline connecting the pure gas source interface to the four-way valve. The flow rate can be controlled by the mass flow meter L1, and the one-way valve F1 is used to prevent gas backflow. Furthermore, as mentioned above, a two-way ball valve is installed on both the pipeline connecting the mixed gas source interface to the mixing tank and the pipeline connecting the pure gas source interface to the four-way valve. Different gas path switches can be controlled by the two-way ball valve T1.

[0028] In one specific embodiment, a first electronic pressure gauge P1 is installed on the pipeline connecting the four-way valve to the exhaust gas outlet, and a second electronic pressure gauge P2 is installed on the pipeline connecting the outlet of the in-situ reaction tank to the exhaust gas outlet. The first electronic pressure gauge P1 is used to set and display the pressure of the first back pressure valve 3, and the second electronic pressure gauge P2 is used to set and display the pressure of the second back pressure valve 4. To maintain system pressure stability, the first electronic pressure gauge P1 and the second electronic pressure gauge P2 are preferably set to the same pressure conditions when in use.

[0029] In one specific embodiment, a third electronic pressure gauge P3 is also installed on the connecting pipeline between the four-way valve 2 and the in-situ reaction tank inlet 1#, for displaying the pressure of the pure gas or mixed gas entering the in-situ reaction tank. The pressure range of the in-situ reaction tank is generally 0.1–1.0 MPa. Furthermore, a shut-off valve J1 is also installed on the connecting pipeline between the four-way valve 2 and the in-situ reaction tank inlet 1#, for controlling the flow rate of the pure gas or mixed gas entering the in-situ reaction tank.

[0030] In one specific embodiment, the reaction atmosphere control device further includes a filter installed at the outlet 2# of the in-situ reaction tank, which is used to filter the gas originating from the in-situ reaction tank before exhaust and sampling, so as to avoid large particles from adversely affecting the atmosphere and sampling results.

[0031] In one specific embodiment, the flow rate of each reactant gas in the reaction atmosphere control device is controlled by software. This software is commercially available, for example, Multi-Digital MFC software V1.0.

[0032] In one specific embodiment, the reaction atmosphere control device further includes a control display panel K1 for setting and displaying the flow rate of each reaction gas. In this case, it does not rely on additional computer software operation, which is beneficial for use in other devices and has promotional value.

[0033] In one specific embodiment, the reaction atmosphere control device is equipped with two back pressure valves. The first back pressure valve is located on the pipeline connecting one outlet of the four-way valve to the tail gas outlet, and the second back pressure valve is located on the pipeline connecting the outlet of the in-situ reaction tank to the tail gas outlet. Preferably, each back pressure valve has a display screen to read the current pressure in real time. During use, the pressures of the two back pressure valves are set to be consistent to maintain stable system pressure. Back pressure valves are installed at these two specific locations in the gas distribution box, and corresponding electronic pressure gauges are preferably installed. Pure gas and mixed gas are switched into the in-situ reaction tank through the four-way valve. When switching reaction gases under a certain system pressure, the back pressure valves can effectively stabilize the system pressure. First, the same pressure is set on the electronic pressure panels of both back pressure valves. When switching between pure gas and mixed gas, a pressure difference will occur. This pressure difference may cause the sample in the in-situ reaction cell to be flushed away or backflowed. The function of the back pressure valve is to stabilize the pressure. When the system pressure is lower than the set pressure, the diaphragm of the back pressure valve blocks the pipeline under the action of the spring force; when the system pressure is higher than the set pressure, the diaphragm compresses the spring, the pipeline is opened, and gas passes through the back pressure valve to maintain a stable pipeline pressure. In the case of unstable pipeline or equipment container pressure, the back pressure valve can maintain the required pipeline pressure, allowing the pump to output flow normally. In addition, siphoning often occurs at the pump outlet due to gravity or other factors. In this case, the back pressure valve can reduce the flow and pressure fluctuations caused by siphoning. The terms "first" and "second" are only used to distinguish and describe back pressure valves in different locations and are not specifically limited.

[0034] In the in-situ reaction chamber, the pressure of the reaction atmosphere changes with increasing temperature. A back pressure valve effectively balances the pressure difference during the reaction. The in-situ reaction chamber containing the sample is programmed to heat up under a temperature control system. The reaction atmosphere enters the chamber at a certain flow rate. As the temperature rises, the pressure in the in-situ reaction chamber may change (according to the ideal gas law pV = nRT, with a constant volume and a constant amount of gas, increasing temperature leads to increased pressure). Therefore, a pressure sensor and a back pressure valve are installed at the exhaust port (according to Bernoulli's principle, increased flow rate leads to decreased pressure). The back pressure valve maintains a stable pressure in the in-situ reaction chamber by real-time regulation of the exhaust flow rate.

[0035] In one specific embodiment, the four-way valve is manually switched on the gas distribution box, and the control of gas flow rate and mass flow meter is completed through software settings, which is convenient to operate. The concentration of each component of the reaction gas is controlled by controlling the flow rate of each gas.

[0036] In this invention, the reaction atmosphere control device can achieve precise mixing of various reaction atmospheres and rapid, stable switching between different reaction atmospheres. Preferably, five mass flow meters are provided to control the gas flow rate and ratio, and different range mass flow meters can be replaced as needed. A four-way valve is configured to switch between pure gas and mixed gas entering the in-situ reaction tank. Two sets of back pressure valves are used to maintain stable system pressure. Simultaneously, a vacuum port and a tail gas sampling port are preferably provided. All components are integrated into a 57cm*46cm*56cm housing, connected to external gas cylinders, the in-situ reaction tank, the tail gas exhaust port, a vacuum pump, and a tail gas collector via multiple interfaces and corresponding pipelines. After use, the device can be quickly separated from the main unit by disconnecting the inlet and outlet ports connected to the in-situ reaction tank. Furthermore, it is easily expandable for use in detecting the reaction atmosphere provided by other instruments.

[0037] The reaction atmosphere control device provided by this invention can integrate all components such as gas pipelines, mass flow meters, pressure gauges, and switching valves between devices into a single gas distribution box, forming an integrated unit. A display screen is installed on the box panel to set and read system flow rate, pressure, and other information. Furthermore, gas flow rate can be set and read using software. It is also portable and convenient for use with other instruments, facilitating the expansion of its applications, such as in-situ infrared detection and in-situ XPS detection, and thus has significant potential for widespread adoption.

[0038] The present invention will be described in detail below through embodiments.

[0039] Example 1 illustrates that the reaction atmosphere control device provided by the present invention can achieve online switching and real-time precise control of multiple gases.

[0040] The reaction atmosphere control device provided in this embodiment includes a gas distribution box, which is equipped with a mixing tank 1, a four-way valve 2, an in-situ reaction tank inlet 1#, an in-situ reaction tank outlet 2#, a mixed gas source interface 3#, a pure gas source interface 4#, and a tail gas outlet 5#. The number of mixed gas source interfaces 3# is at least four, denoted as A gas source interface (3-1#), B gas source interface (3-2#), C gas source interface (3-3#), and D gas source interface (3-4#). These four different gas source interfaces are connected to different gas sources, and the different mixed gas source interfaces 3# are connected to the inlet of the mixing tank 1 to mix different gases in the mixing tank 1. The mixture is mixed to obtain a mixed gas. The outlet of the mixing tank 1 and the pure gas source interface 4# are both connected to the inlet of the four-way valve 2. The four-way valve 2 is used to switch between mixed gas and pure gas. Two-way ball valves T1 are installed on the pipeline connecting the mixed gas source interface 3# to the mixing tank 1 and the pipeline connecting the pure gas source interface 4# to the four-way valve 2. One outlet of the four-way valve 2 is connected to the tail gas outlet 5# and a first back pressure valve 3 is installed on the connecting pipeline, while the other outlet is connected to the in-situ reaction tank inlet 1#. The in-situ reaction tank outlet 2# is connected to the tail gas outlet 5# and a two-way ball valve and a second back pressure valve 4 are installed on the connecting pipeline.

[0041] Connect gas source interface A (3-1#) to the N2O gas source, gas source interface B (3-2#) to the CO2 gas source, gas source interface C (3-3#) to the CH4 gas source, and gas source interface D (3-4#) to the N2 gas source. Switch the four-way valve to connect to the outlet of mixing tank 1.

[0042] Open the two-way ball valves on the pipelines connecting gas source interfaces A (3-1#) and B (3-2#) to the mixing tank, while closing the other two ball valves to allow the introduction and mixing of N2O and CO2. The N2O flow rate is 12 mL / min, and the CO2 flow rate is 18 mL / min, meaning the theoretical concentrations of N2O and CO2 are 40% and 60%, respectively. After the flow rates stabilize for 10 minutes, the resulting mixture is introduced into the vacuum tank. After 117 minutes of aeration, a sample is taken from the tank, diluted, and analyzed by gas chromatography-mass spectrometry. The results show that the N2O concentration in the tank is 39.84%, and the CO2 concentration is 59.70%.

[0043] Open the two-way ball valves on the pipelines connecting gas source interfaces B (3-2#) and C (3-3#) to the mixing tank, while closing the other two ball valves to allow the introduction and mixing of CO2 and CH4. The CO2 flow rate is 6 mL / min, and the CH4 flow rate is 44 mL / min, meaning the theoretical concentrations of CO2 and CH4 are 12% and 88%, respectively. After the flow rates stabilize for 10 minutes, the resulting mixture is introduced into a vacuum tank. After 50 minutes of aeration, a sample is taken from the tank, diluted, and analyzed by gas chromatography-mass spectrometry. The results show that the CO2 concentration in the tank is 12.05%, and the CH4 concentration is 87.61%.

[0044] Open the two-way ball valves on the gas source interfaces A (3-1#), B (3-2#), and D (3-4#) connecting to the mixing tank, and close the other two-way ball valves to allow the introduction and mixing of N2O, CO2, and N2. The flow rate of N2O is 1 mL / min, CO2 is 15 mL / min, and N2 is 484 mL / min. This corresponds to a theoretical concentration of 0.2% for N2O, 3% for CO2, and 96.8% for N2 (N2 is the equilibrium gas). After the flow rates stabilize for 10 minutes, the resulting mixed gas is introduced into the vacuum tank. After 7 minutes of aeration, a sample is taken from the tank and analyzed using gas chromatography-mass spectrometry (GC-MS). The results show that the concentration of N2O in the tank is 0.19%, and the concentration of CO2 is 2.98%. N2 is used as a carrier gas in GC-MS detection and its precise content cannot be detected; the same applies below.

[0045] Open the two-way ball valves on the pipelines connecting gas source interfaces A (3-1#), B (3-2#), C (3-3#), and D (3-4#) to the mixing tank, and close the other two-way ball valves to allow the introduction and mixing of N2O, CO2, CH4, and N2. The flow rates are: N2O 0.4 mL / min, CO2 0.4 mL / min, CH4 25 mL / min, and N2 474.2 mL / min. This corresponds to theoretical concentrations of 0.08% for N2O, 0.08% for CO2, 5% for CH4, and 94.84% for N2 (N2 is the equilibrium gas). After the flow rate stabilized for 10 minutes, the resulting mixed gas was introduced into a vacuum tank. After 7 minutes of gas introduction, a sample was taken from the tank and analyzed by gas chromatography-mass spectrometry. The results showed that the concentration of N2O in the tank was 0.08%, the concentration of CO2 was 0.079%, and the concentration of CH4 was 5.02%.

[0046] The results above show that the reaction atmosphere control device provided by the present invention can realize online switching and real-time precise control of multiple gases.

[0047] Synthesis of vanadium-based catalysts

[0048] (1) Reagents:

[0049] Ammonium metavanadate (analytical grade) was purchased from Aladdin Biochemical Technology Co., Ltd.; ammonium tungstate (analytical grade), ammonium molybdate (analytical grade), and oxalic acid (analytical grade) were purchased from Sinopharm Chemical Reagent Co., Ltd.; the experimental water was ultrapure water.

[0050] The titanium dioxide used is commercial titanium dioxide with a specific surface area of ​​79 m². 2 / g, XRD analysis identified it as pure anatase (A phase), and its XRD pattern and scanning electron microscope image are shown below. Figure 3 As shown. From Figure 3 It can be seen that the titanium dioxide has a flat, round, disc-like shape with a lateral dimension of approximately 40 nm.

[0051] (2) Synthesis steps of vanadium-based catalysts:

[0052] Samples 2# V2O5(1.0%) / TiO2, 3# V2O5(1.0%)-WO3(4.0%) / TiO2, 4# V2O5(1.0%)-WO3(10%) / TiO2, and 5# V2O5(1.0%)-MoO3(4.0%) / TiO2 were synthesized by impregnation method according to the following steps.

[0053] First, weigh out oxalic acid, ammonium metavanadate, ammonium tungstate, ammonium molybdate, and TiO2 according to the raw material ratios for each catalyst in Table 1. Add 150 mL of ultrapure water to a 250 mL beaker, and add oxalic acid while stirring. After the oxalic acid dissolves, add ammonium metavanadate. After the ammonium metavanadate dissolves, add ammonium tungstate or ammonium molybdate. After the ammonium tungstate or ammonium molybdate is completely dissolved, add the TiO2 support. Then cover with plastic wrap and stir for 2 hours. After stopping stirring, pour the suspension into a 500 mL pear-shaped flask and place the pear-shaped flask in a rotary evaporator. Set the water bath temperature to 60℃ and the rotation speed to 90 rpm. Rotary evaporation was carried out at rpm until no obvious water marks were visible on the sample surface. The evaporated eggplant-shaped flask was then placed in an oven to dry at 105℃ for 12 hours. The dried sample was then transferred to a crucible and placed in a muffle furnace for calcination at an end temperature of 450℃ for 3 hours at a heating rate of 5℃ / min. After calcination in the muffle furnace, the precursors of each oxide were converted into their corresponding oxides. The vanadium-based catalysts obtained were sample numbers 2# to 5#. Sample 1#, which was a TiO2 support, was treated with the same steps as a control sample.

[0054] Table 1

[0055]

[0056] Example 2: Method for Determining the Crystal Structure of Vanadium-Based Catalysts

[0057] XRD testing conditions: An X'Pert Pro X-ray diffractometer from Panaco (Netherlands) was used, with an operating voltage of 40kV, a current of 40mA, a Cu target X-ray tube with λKα1 = 0.15406nm, a PIXcel detector, a scanning speed of 0.164° / s, and an X-ray diffraction angle scanning range of 10° to 90°, using continuous scanning mode.

[0058] The vanadium-based catalyst obtained in the preparation example was subjected to XRD analysis in air at room temperature using the method described above. The results are as follows: Figure 4 As shown. From Figure 4 It can be seen that sample #1, as a control, remained pure anatase TiO2 after calcination at 450℃. XRD analysis of samples #2 through #5 only detected diffraction peaks of pure anatase TiO2. The crystal phase of the TiO2 supported on the active ingredient V2O5 and the additives WO3 or MoO3 did not change after calcination at 450℃, indicating that the calcination temperature of 450℃ did not cause a transformation from anatase to rutile crystal phase in the supported TiO2. The near-undetectable presence of V2O5, WO3, or MoO3 crystal phases by XRD demonstrates that the metal oxides were well dispersed on the TiO2 support.

[0059] Example 3: Method for Determining the Crystal Structure of Vanadium-Based Catalysts

[0060] (1) In-situ XRD experimental conditions

[0061] In-situ XRD testing conditions: XRD tests were performed using an X'Pert Pro X-ray diffractometer from Panaco (Netherlands), with an operating voltage of 40 kV and a current of 40 mA. The X-ray tube used a Cu target with λKα1 = 0.15406 nm, a PIXcel detector, a scanning speed of 0.164° / s, and an X-ray diffraction angle scanning range of 10°–90°, employing continuous scanning mode. In grain size calculations, to eliminate the influence of instrument broadening of the XRD spectrum on the calculation results, the broadening results of the X-ray diffractometer were calibrated using the standard sample LaB6 with the same parameters. In-situ heating experiments were conducted in an in-situ reactor from Anton Pear (Austria). The in-situ X-ray diffraction heating range was 25–1050℃, with a heating rate of 5℃ / min. The temperature sampling points for samples 1 to 4 were set at 400℃, 500℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, and 1050℃, totaling 12 temperature points. For sample 5, two additional temperature points, 1100℃ and 1150℃, were added based on experimental conditions. XRD patterns were acquired after holding each point at a constant temperature for 15 minutes. The temperature stability was ±1℃.

[0062] Reaction atmosphere conditions: The reaction gases consisted of NO, NH3, O2, and N2. Since NO accounts for approximately 95% of typical flue gas NOx, with the remainder being NO2, NO was used as the primary component in the gas mixing system to simulate the reaction atmosphere used for the catalyst. The experiment employed a reaction atmosphere control device to provide the required reaction atmosphere, precisely supplying four online gas streams. The flow rate was controlled by a mass flow meter to achieve the appropriate proportions. The concentrations of each component in the reaction atmosphere were: [NO] = [NH3] = 800 ppm, [O2] = 5%, with N2 as the balance gas. The total gas flow rate was 500 mL / min. In-situ XRD testing was performed after the flow rate stabilized for 10 minutes.

[0063] (2) Effect of loading V2O5, WO3 or MoO3 on TiO2 phase transition

[0064] Samples #1 through #5 were subjected to in-situ high-temperature XRD tests under a reaction atmosphere. The obtained variable-temperature XRD spectra are shown below. Figures 5-9 As shown in Table 2, the phase transition temperatures of TiO2 with different catalysts are shown in Table 2.

[0065] Table 2

[0066] Rutile type (R phase) appears 800℃ 850℃ 900℃ 900℃ 850℃ Anatase type (A phase) disappears 900℃ 1050℃ 1050℃ 1050℃ 1150℃ <![CDATA[Peak appearance of WO3]]> - - 900℃ 850℃ -

[0067] from Figure 5 It can be seen that pure TiO2 supported on anatase (A phase) exists from 400℃ to 750℃. With increasing temperature, the diffraction peaks of the A phase narrow, gradually growing from a single broad peak at 2θ of 37°, 55°, and 72° to multiple A phase peaks. After 800℃, typical rutile (R phase) peaks begin to appear at 2θ of 27.29° and 35.74°. With increasing temperature, the diffraction peaks of the A phase weaken and eventually disappear, while the diffraction peaks of the R phase continuously strengthen and narrow, indicating that the R phase is growing. The temperature range from 800℃ to 900℃ is when pure TiO2 completely transforms from the A phase to the R phase. The phase change characteristics of TiO2 supported on V2O5, WO3, or MoO3 are similar to those of pure TiO2, undergoing a process of R phase appearance and A phase disappearance, but the appearance temperature, peak shape, and relative intensity of each phase are different.

[0068] Figures 5-9As shown in Table 2, the R phase transition initiation temperature of sample #1 (TiO2 support) is 800℃; the 1% V2O5 loading of sample #2 increased the R phase appearance temperature of TiO2 by 50℃ compared to pure TiO2 in sample #1, and also increased the phase transition completion temperature by 150℃. This proves that 1% highly dispersed V2O5 has a certain inhibitory effect on the phase transition of TiO2 support, slowing down its rate; the addition of WO3 to samples #3 and #4 on the basis of 1% V2O5 loading increased the R phase appearance temperature of TiO2 by 100℃, that is, the R phase transition initiation temperature was 900℃, and the phase transition completion temperature was the same as that of sample #2; Sample 4% WO3 loading and sample 4# 10% WO3 loading had the same R phase transition start and end temperatures. It is worth mentioning that the diffraction peaks of WO3 crystals began to appear after 850℃ and the diffraction peaks intensified with increasing temperature, proving that the gradual sintering of WO3 from 850℃ onwards led to a decrease in its dispersibility on the TiO2 support, and the sintering process also weakened its effect on inhibiting the TiO2 R phase transition. Sample 5#, with 4% MoO3 added to a 1% V2O5 loading, had the same R phase transition start temperature as samples 1# and 2#, but the phase transition process was significantly delayed, and the temperature at which the A phase completely disappeared was 100℃ higher than that of sample 2#.

[0069] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for detecting the crystal structure of a catalyst, characterized in that, The method is performed in an X-ray diffractometer, which includes an in-situ reaction cell and a reaction atmosphere control device. The reaction atmosphere control device includes a gas distribution box, which contains a mixing tank, a four-way valve, an in-situ reaction cell inlet, an in-situ reaction cell outlet, a mixed gas source interface, a pure gas source interface, and a tail gas outlet. The mixing gas source interface has at least two ports, and each port is connected to the inlet of the mixing tank to mix different gases in the mixing tank to obtain a mixed gas. The outlet of the mixing tank... Both the inlet and the pure gas source interface are connected to the inlet of the four-way valve, and the four-way valve is used to switch between mixed gas and pure gas. Two-way ball valves are installed on the pipeline connecting the mixed gas source interface to the mixing tank and the pipeline connecting the pure gas source interface to the four-way valve. One outlet of the four-way valve is connected to the tail gas outlet and a first back pressure valve is installed on the connecting pipeline. The other outlet of the four-way valve is connected to the inlet of the in-situ reaction tank. The outlet of the in-situ reaction tank is connected to the tail gas outlet and a two-way ball valve and a second back pressure valve are installed on the connecting pipeline. A first electronic pressure gauge is installed on the pipeline connecting the four-way valve to the exhaust gas outlet, a second electronic pressure gauge is installed on the pipeline connecting the outlet of the in-situ reaction tank to the exhaust gas outlet, and a third electronic pressure gauge is installed on the connecting pipeline between the four-way valve and the in-situ reaction tank inlet. The method includes loading the catalyst to be tested into an in-situ reaction cell, supplying a reaction atmosphere to the in-situ reaction cell through a reaction atmosphere control device, and starting an X-ray diffractometer to detect the catalyst to be tested.

2. The method for detecting the crystal structure of a catalyst according to claim 1, characterized in that, The catalyst to be tested is a vanadium-based catalyst.

3. The method for detecting the crystal structure of a catalyst according to claim 2, characterized in that, The vanadium-based catalyst includes a support and an active component and an additive supported on the support. The support is TiO2, the active component is V2O5, and the additive is WO3 or MoO3. Based on a support content of 100wt% in the vanadium-based catalyst, the content of the active component is 0.5~4wt%, and the content of the additive is 3~10wt%.

4. The method for detecting the crystal structure of a catalyst according to claim 1, characterized in that, The mixed gas source interface includes a NOx gas source interface, an NH3 gas source interface, an O2 gas source interface, and an N2 gas source interface.

5. The method for detecting the crystal structure of a catalyst according to any one of claims 1 to 4, characterized in that, The reaction atmosphere control device also includes an exhaust gas sampling port, which is connected to the outlet of the in-situ reaction tank and a micro-regulating valve is installed on the connecting pipeline.

6. The method for detecting the crystal structure of a catalyst according to any one of claims 1 to 4, characterized in that, The reaction atmosphere control device also includes a vacuum port, which is connected to the outlet of the in-situ reaction tank and a shut-off valve is installed on the connecting pipeline.

7. The method for detecting the crystal structure of a catalyst according to any one of claims 1 to 4, characterized in that, Mass flow meters and one-way valves are installed on the pipelines connecting the mixed gas source interface to the mixed gas tank, and mass flow meters and one-way valves are installed on the pipelines connecting the pure gas source interface to the four-way valve.

8. The method for detecting the crystal structure of a catalyst according to any one of claims 1 to 4, characterized in that, A shut-off valve is installed on the connecting pipeline between the four-way valve and the air inlet of the in-situ reaction tank.

9. The method for detecting the crystal structure of a catalyst according to any one of claims 1 to 4, characterized in that, The reaction atmosphere control device also includes a control display panel for setting and displaying the flow rate of each gas.

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