In-situ attenuated total reflection Fourier transform infrared spectrum detection method based on microwave heating

Abstract

The invention discloses an in-situ attenuated total reflection Fourier transform infrared spectrum detection method based on microwave heating, and belongs to the technical field of spectrum detection and analysis. According to the method, a design strategy that microwave heating and an infrared spectrum system are arranged separately is adopted, and a high-refractive-index infrared reflection crystal is used as a unique coupling detection area, so that real-time infrared spectrum monitoring of a reaction system is realized. The detection method disclosed by the invention is particularly suitable for in-situ monitoring of hydrogenation, cracking and conversion reaction of an oxygen-containing or unsaturated substituent compound on a furan ring or a benzene ring, and is compatible with microwave and catalytic reaction mechanism research, material interface reaction analysis and spectroscopic characterization of a biomass derivative conversion process; the method has the advantages of being accurate in temperature control, high in response speed, high in signal stability and good in data repeatability, dynamic spectrum tracking can be conducted on a complex reaction system, a traditional external heating detection mode is compatible, and the space matching degree and the time resolution of microwave field in-situ characterization are remarkably improved.

Description

Technical Field

[0001] This application belongs to the field of spectroscopic analysis and in-situ detection technology of catalytic reaction, specifically involving an in-situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) detection method suitable for microwave field conditions, which can realize real-time, quantitative monitoring and infrared spectral analysis of catalytic and conversion reaction processes in microwave irradiation environment. Background Technology

[0002] Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) offers advantages such as high sensitivity, in-situ monitoring, and minimal disturbance to the reaction system, and has been widely applied in catalysis characterization, reaction kinetics, and interfacial chemical process research. However, existing in-situ infrared detection devices mostly employ conventional heating methods (such as electric heating or isothermal liquid circulation), which are insufficient to meet the instrument design and detection requirements under microwave fields. Under microwave heating conditions, electromagnetic fields can selectively couple with polar molecules and metal surfaces, significantly accelerating reaction rates and altering reaction pathways. Therefore, it is crucial to capture these dynamic processes through in-situ characterization. However, traditional infrared detection cells are prone to problems such as metal shielding, infrared light attenuation, and temperature measurement errors in microwave fields, making it difficult to achieve effective coupling between the reaction system and spectral detection.

[0003] Furthermore, in solid-liquid-gas multiphase systems, uneven temperature and medium distribution can severely affect the stability and quantitative accuracy of infrared signals, placing higher demands on sample preparation precision and the rationality of the detection process. To address these issues, existing research has attempted to employ methods such as microwave transmission windows, external detectors, or fiber optic remote acquisition. However, these methods still suffer from drawbacks such as complex structures and inconsistent reaction and detection environments, making it difficult to achieve a high degree of integration between microwave heating and in-situ infrared detection.

[0004] Therefore, there is an urgent need for an in-situ ATR-FTIR detection device and method that can achieve rapid and uniform heating of the reaction system in a microwave field, real-time acquisition of spectral signals, and temperature compensation control. This device and method would be applicable to homogeneous liquid, liquid-solid two-phase, and gas-liquid-solid multiphase reaction systems, enabling real-time monitoring of the evolution of catalytic surface species and functional groups and reaction kinetics, and providing a precise experimental platform for the study of catalytic mechanisms and reaction kinetics. Summary of the Invention

[0005] To address the problems of signal interference, temperature runaway, and optical path mismatch in existing in-situ infrared detection technologies under microwave heating conditions, this application aims to provide an in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating. By highly integrating the microwave irradiation system with attenuated total internal reflection Fourier transform infrared spectroscopy technology, rapid and controllable heating of the reaction system in a microwave field and real-time acquisition of infrared signals are achieved, creating a high-precision experimental platform. Based on this platform, spectroscopic characterization and in-situ reaction analysis can be performed.

[0006] To solve the above-mentioned technical problems, the technical solution adopted in this application is as follows:

[0007] An in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating is disclosed. The method is performed in a dedicated device and includes: preparing a catalyst film or catalyst-substrate composite film on the surface of a high-refractive-index infrared-reflective crystal using spin coating to form a stable and uniform solid active layer; loading a liquid substrate or substrate solution onto the catalyst film surface in liquid film form, or introducing a reactant gas and trace solvent into a gas-carrying system to construct a solid-liquid-gas three-phase reaction interface; achieving rapid and uniform heating of the reaction system through microwave heating and a thermal compensation system; and simultaneously acquiring infrared spectral signals throughout the reaction process, and monitoring the intensity and shift of functional group absorption peaks in real time to obtain reaction kinetics and species evolution information.

[0008] The specialized device includes an in-situ flow cell, a microwave irradiation system, an infrared optical system, and a temperature control module. The in-situ flow cell is used to contain the sample and form a closed reaction space. The microwave irradiation system is used to input microwave energy into the region of the in-situ flow cell. The infrared optical system is used to collect real-time infrared spectral signals. The temperature control module is used to realize real-time temperature detection and adjustment during microwave heating, thereby ensuring the temperature stability of the sample region.

[0009] The aforementioned in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating comprises an in-situ flow cell including a flow cell body, a quartz sealing cap, a high refractive index infrared reflective crystal, an inlet / liquid pipe and an outlet / liquid pipe, a thermal compensation medium pipe, a sample cell, a thermal compensation medium cell, and a sealing ring. The high refractive index infrared reflective crystal is located at the bottom of the flow cell body, and the quartz sealing cap is fastened to the upper end of the flow cell body and has a through hole for inserting a temperature-sensing optical fiber. The components are sealed together by the sealing ring. A threaded hole is provided on the outside of the flow cell body and it is fixed to the bottom plate of the microwave resonant cavity with screws. The temperature-sensing optical fiber is led out through an opening in the side wall of the resonant cavity and sealed with an interface, and an impedance tube is provided at the opening. The quartz sealing cap and the thermal compensation medium cell together form a sealed thermal compensation medium cavity. The thermal compensation medium cell is connected to an external circulating heat exchange device to maintain the temperature stability of the reaction and compensation medium. The inlet / liquid pipe is connected to a gas source or a horizontal flow pump, and the outlet / liquid pipe is connected to a back pressure valve to regulate the system pressure and output the reaction products.

[0010] The aforementioned in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating includes an infrared optical system comprising an infrared light source, a spectral detector, and an optical path unit composed of an off-axis parabolic mirror and a reflector. Infrared light is focused by the infrared light source through a plane reflector and the first and second off-axis parabolic mirrors, and then enters a high-refractive-index infrared reflective crystal through an optical path impedance tube. Multiple total internal reflections within the crystal form evanescent waves that interact with the sample to generate absorption signals. After being output from the crystal, the signals are converged to the spectral detector through a third off-axis parabolic mirror, a plane reflector, and a fourth off-axis parabolic mirror.

[0011] The aforementioned in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating includes a microwave irradiation system comprising a microwave source and a microwave resonant cavity, which are connected via a coaxial interface to input microwave energy into the in-situ flow cell region.

[0012] The in-situ attenuated total reflection Fourier transform infrared spectroscopy detection method based on microwave heating includes a temperature control module comprising a temperature-measuring optical fiber and an infrared temperature probe, used to achieve real-time temperature detection and adjustment during microwave heating, thereby ensuring the temperature stability of the sample area.

[0013] The aforementioned in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating comprises a flow cell body and a thermal compensation medium cell made of polyetheretherketone (PEEK), a sealing ring made of polytetrafluoroethylene (PTFE), a high refractive index infrared reflective crystal made of zinc germanide or silicon dioxide, and a microwave resonant cavity made of stainless steel. The surfaces of the off-axis parabolic mirror and the plane mirror are plated with gold to improve reflection efficiency. The temperature-measuring optical fiber is a hollow-core quartz waveguide optical fiber.

[0014] The aforementioned in-situ attenuated total reflection Fourier transform infrared spectroscopy detection method based on microwave heating involves preparing a catalyst film by dispersing catalyst particles in a solvent containing a film-forming agent and then spin-coating it onto the surface of an infrared crystal. The film-forming agent is Nalfon or other fluoropolymer binders.

[0015] The aforementioned in-situ attenuated total reflectance Fourier transform infrared spectroscopy detection method based on microwave heating employs three in-situ reaction modes: homogeneous liquid, liquid-solid two-phase, or gas-liquid-solid three-phase. In the solid-containing system, a liquid film is formed by covering the catalyst film surface with a solvent-substrate solution, while in the homogeneous liquid system, a liquid film can be directly formed on the crystal surface. All of the different in-situ reaction modes can achieve continuous spectrum acquisition within a temperature range of 20℃ to 200℃.

[0016] The in-situ attenuated total reflection Fourier transform infrared spectroscopy detection method based on microwave heating analyzes the changes in the absorption peak intensity of the marker functional groups with time and temperature by comparing the catalyst-free reference spectrum with the reaction spectrum, so as to obtain the reaction kinetic parameters and product formation sequence.

[0017] The aforementioned in-situ attenuated total reflection Fourier transform infrared spectroscopy detection method based on microwave heating includes in-situ monitoring of hydrogenation, cracking, and conversion reactions of compounds containing oxygen or unsaturated substituents on furan or benzene rings. It is compatible with microwave and catalytic reaction mechanism studies, material interface reaction analysis, and spectroscopic characterization of biomass derivative conversion processes.

[0018] Beneficial effects: Compared with the prior art, this application has the following advantages:

[0019] 1. The apparatus of this method highly integrates a microwave irradiation system with attenuated total reflectance Fourier transform infrared spectroscopy, enabling rapid and controllable heating of the reaction system in a microwave field and real-time acquisition of infrared signals. This provides a new high-precision experimental platform for catalytic characterization and in-situ reaction analysis. Specifically:

[0020] 1) The microwave heating and optical detection systems are physically separated, with the crystal as the only coupling interface, which effectively isolates the infrared detection and microwave field, avoiding metal shielding and optical signal attenuation;

[0021] 2) Precise temperature control: By forming a closed-loop feedback between the thermal compensation fluid and the real-time temperature measurement fiber, the temperature gradient caused by microwaves can be eliminated, ensuring the quantitative reliability of the results.

[0022] 3) The signal response is fast and stable. The microwave field directly couples the molecular dipoles of the reaction system, enabling second-level heating and synchronous acquisition of spectral signals.

[0023] 4) The device is compatible with multiphase reaction systems and is suitable for liquid-phase, solid-liquid and gas-liquid-solid reaction environments. It can be widely used in catalytic mechanism analysis, material interface research and in-situ monitoring of complex systems.

[0024] 5) By precisely matching the microwave field distribution with the infrared detection area, the reflective crystal generates multiple reflections and enhances the signal acquisition capability, significantly improving spatial and temporal resolution, and enabling dynamic tracking of the reaction process.

[0025] 2. The results of the embodiments of this application confirm that the detection method disclosed in this application is particularly suitable for in-situ monitoring of hydrogenation, cracking and conversion reactions of compounds containing oxygen or unsaturated substituents on furan rings or benzene rings. It is compatible with microwave and catalytic reaction mechanism research, material interface reaction analysis and spectroscopic characterization of biomass derivative conversion processes. It has the advantages of precise temperature control, fast response speed, high signal stability and good data repeatability. It can perform dynamic spectral tracking of complex reaction systems and is compatible with traditional external heating detection methods. It significantly improves the spatial matching degree and temporal resolution of microwave field in-situ characterization and has good practicality. Attached Figure Description

[0026] Figure 1 This is a three-dimensional structural diagram of an in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection device based on microwave heating.

[0027] Figure 2 This is a schematic diagram of the structure of an in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection device based on microwave heating;

[0028] Figure 3 This is a schematic diagram of the in-situ flow cell structure;

[0029] Figure 4 This is a schematic diagram of the assembly and disassembly of the in-situ flow cell;

[0030] Figure 5 This is a cross-sectional schematic diagram of the in-situ flow cell;

[0031] Figure 6 This is a schematic diagram of an infrared optical system;

[0032] Figure 7 These are infrared spectra of 4-allyl guaiacol collected at different temperatures in Example 1;

[0033] Figure 8 These are infrared spectra of lignin dimer model compounds collected at different temperatures in Example 2;

[0034] Figure 9 This is the infrared spectrum of the Pd / C surface lignin model material collected in air atmosphere over time in Example 4;

[0035] In the figure: 1. Flow cell body, 2. Quartz sealing cap, 3. High refractive index infrared reflective crystal, 4. Gas / liquid inlet pipe, 5. Gas / liquid outlet pipe, 6. Thermal compensation medium pipe, 7. Sample cell, 8. Thermal compensation medium cell, 9. Sealing ring, 10. Coaxial interface, 11. Microwave resonant cavity, 12. Probe cone, 13. Short-circuit piston, 14. Optical path impedance tube, 15. Pipeline path impedance tube; 16. Infrared light source, 17. Spectrometer detector, 18. First off-axis parabolic mirror, 19. Second off-axis parabolic mirror, 20. Third off-axis parabolic mirror, 21. Fourth off-axis parabolic mirror, 22. Plane reflector, 23. Temperature measuring fiber, 24. Infrared temperature probe. Detailed Implementation

[0036] The present application is further illustrated below with reference to specific embodiments. The embodiments are implemented based on the technical solution of the present application. It should be understood that these embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0037] like Figure 1-6 The present application provides an in-situ attenuated total reflectance Fourier transform infrared spectroscopy detection device for microwave catalytic reactions, comprising an in-situ flow cell, a microwave irradiation system, an infrared optical system, and a temperature control module. This device couples and synchronously controls heat, fluid, and microwave fields through the in-situ flow cell, thereby obtaining the real-time spectral response and dynamic infrared spectral information of the reaction system.

[0038] The in-situ flow cell is used to contain the sample and form a sealed reaction space. Its main structure includes the flow cell body 1, a quartz sealing cap 2, a high-refractive-index infrared reflective crystal 3, inlet / outlet gas / liquid pipes 5, a thermal compensation medium pipe 6, a sample cell 7, a thermal compensation medium cell 8, and a sealing ring 9. The microwave irradiation system includes a microwave source and a microwave resonant cavity 11, which are connected via a coaxial interface 10 to input microwave energy into the in-situ flow cell region. The sidewall of the microwave cavity 11 has through holes for connecting external pipes to the flow cell inside the cavity. Impedance tubes 15 are welded to the outside of the through holes to suppress microwave leakage. A light aperture is formed at the bottom of the microwave cavity 11 along the oblique section of the high-refractive-index infrared reflective crystal 3, perpendicular to its cut surface, to provide a transmission path for the infrared light source; an impedance tube 14 is welded to the outside of the aperture, also for suppressing microwave leakage.

[0039] A high-refractive-index infrared reflective crystal 3 is disposed at the bottom of the flow cell body 1. A quartz sealing cap 2 is fastened to the upper end of the flow cell body and has a through hole for inserting a temperature-sensing optical fiber 23. The components are sealed together by a sealing ring 9. A threaded hole is provided on the outside of the flow cell body 1 and it is fixed to the bottom plate of the microwave resonant cavity by screws. The temperature-sensing optical fiber 23 is led out through an opening in the side wall of the resonant cavity and sealed with an interface. An impedance tube is provided at the opening. The quartz sealing cap 2 and the thermal compensation medium cell 8 together form a sealed thermal compensation medium cavity. The thermal compensation medium cell 8 is connected to an external circulating heat exchanger to maintain the temperature stability of the reaction and compensation medium. The gas / liquid inlet pipe 4 is connected to a gas source or a horizontal flow pump, and the gas / liquid outlet pipe 5 is connected to a back pressure valve to regulate the system pressure and output the reaction products. Among them, the high-refractive-index infrared reflective crystal 3 serves as the only coupling interface for the interaction between infrared light and the reaction sample.

[0040] The main body of the flow cell 1 and the thermal compensation medium cell 8 are made of polyetheretherketone (PEEK), the sealing ring 9 is made of polytetrafluoroethylene, the high refractive index infrared reflective crystal 3 is made of zinc germanide or silicon dioxide, and the microwave resonant cavity 11 is made of stainless steel. The temperature measuring optical fiber 23 is a hollow-core quartz waveguide optical fiber.

[0041] The infrared optical system is used to acquire real-time infrared spectral signals. Its main structure includes an infrared light source 16, a spectrometer 17, and an optical path unit composed of several off-axis parabolic mirrors (first off-axis parabolic mirror 18, second off-axis parabolic mirror 19, third off-axis parabolic mirror 20, and fourth off-axis parabolic mirror 21) and multiple reflectors 22. Infrared light emitted from the infrared light source 16 is reflected by the plane reflector 22 and focused by the first off-axis parabolic mirror 18 and the second off-axis parabolic mirror 19. It then enters the high-refractive-index infrared reflective crystal 3 through an optical path impedance tube. Multiple total internal reflections within the crystal generate evanescent waves that interact with the sample, producing an absorption signal. The signal is then output from the crystal and converged to the spectrometer 17 via the third off-axis parabolic mirror 20, another plane reflector 22, and the fourth off-axis parabolic mirror 21, thus acquiring real-time infrared spectral signals. Each off-axis parabolic mirror and plane reflector is coated with a gold film to improve reflection efficiency.

[0042] The temperature control module includes a temperature-measuring fiber optic cable 23 and an infrared temperature probe 24, which are used to detect and adjust the temperature in real time during microwave heating, thereby ensuring the temperature stability of the sample area.

[0043] The thermal compensation medium pool is connected to an external circulating heat exchange system to regulate the temperature of the reaction zone and the reference zone. The entire device is fixed to the metal resonant cavity base plate with screws to ensure precise spatial alignment between the optical path and the microwave field, avoiding signal interference and energy loss.

[0044] Under microwave irradiation, the reaction system achieves rapid and uniform heating, with a thermal compensation system simultaneously monitoring and controlling the temperature. Throughout the reaction process, ATR-FTIR continuously acquires infrared spectra, analyzing the intensity, position, and trends of functional group absorption peaks in real time. By comparing the reference spectrum with the reaction spectrum, the transformation laws of reactants and intermediates are revealed, thereby obtaining reaction kinetic parameters and product formation pathways.

[0045] The aforementioned device performs in-situ attenuated total reflectance Fourier transform infrared spectroscopy (ATIR). A catalyst film or catalyst-substrate composite film is prepared on the surface of a high-refractive-index infrared-reflective crystal using spin-coating, forming a stable and uniform solid active layer. A liquid substrate or substrate solution is loaded onto the catalyst film surface in liquid film form, or a reactant gas and trace solvent are introduced into a gas-carrying system to construct a solid-liquid-gas three-phase reaction interface. Rapid and uniform heating of the reaction system is achieved through microwave heating and a thermal compensation system. Infrared spectral signals are simultaneously acquired throughout the reaction process, and the intensity and shift of functional group absorption peaks are monitored in real time to obtain reaction kinetics and species evolution information. This in-situ detection method is applicable to homogeneous liquid, liquid-solid two-phase, and gas-liquid-solid multiphase systems. In the presence of a solid catalyst, a solid catalytic film or catalyst-substrate composite film containing catalytically active components can be prepared on the surface of a high-refractive-index reflective crystal by spin-coating to form a stable reaction layer. A liquid substrate or substrate solution is coated on the surface of a catalytic membrane in the form of a liquid film, and a reactive or inert gas is introduced into the gas flow system to construct a controllable solid-liquid-gas three-phase interface.

[0046] The catalyst film is prepared by dispersing catalyst particles in a solvent containing a film-forming agent and then spin-coating them onto the surface of an infrared crystal. The film-forming agent is Nalfon or other fluoropolymer binders.

[0047] The reaction system can employ three in-situ reaction modes: homogeneous liquid, liquid-solid two-phase, or gas-liquid-solid three-phase. In the solid-containing system, a liquid film is formed by covering the catalyst film surface with a solvent-substrate solution, while in the homogeneous liquid system, a liquid film can be formed directly on the crystal surface. Continuous spectrum acquisition can be achieved in all in-situ reaction modes within a temperature range of 20℃ to 200℃.

[0048] This method is applicable to in-situ monitoring of hydrogenation, cracking, and conversion reactions of compounds containing oxygen or unsaturated substituents on furan or benzene rings. It is compatible with microwave and conventional catalytic reaction mechanism studies, material interface reaction analysis, and spectroscopic characterization of biomass derivative conversion processes. By comparing catalyst-free reference spectra with reaction spectra, the changes in absorption peak intensity of marker functional groups with time and temperature are analyzed to obtain reaction kinetic parameters and product formation sequences.

[0049] The following embodiments all use the above-described apparatus and method.

[0050] Example 1

[0051] Using 4-allylguaiacol as the analyte, microwave heating-in-situ infrared spectroscopy was performed on a single substrate (liquid) in an in-situ test cell.

[0052] The in-situ testing cell adopts a double-layer structure design, divided into a sample cell and a thermal compensation medium cell by a high-temperature resistant quartz window to achieve effective temperature control. After assembling the flow cell body 1 and the high-refractive-index infrared reflective crystal 3, an appropriate amount of 4-allyl guaiacol is dropped onto the crystal surface and evenly spread. The sealing assembly is then completed, and the tubing is connected before placing it into the microwave cavity. Nitrogen gas is introduced and back pressure is applied, while heat-conducting oil is injected into the thermal compensation medium cell.

[0053] Microwave heating is initiated with a power range of 100-500W, the specific power being set according to the substrate's dielectric constant and dielectric loss parameters. Linear incremental control is implemented based on the temperature curve within the tank, while preheated heat-conducting oil circulates within the medium cavity. An embedded fiber optic temperature probe and a reflective infrared temperature measurement component provide real-time correction signals to correct temperature drift caused by microwave coupling.

[0054] The experimental temperature range was set from room temperature to 200℃, and spectral acquisition was conducted in stages: In the initial stage (≤50℃), the basic absorption spectrum was recorded to correct the background signal; in the heating stage (>50℃), the position and relative intensity changes of the characteristic absorption peaks of each functional group were monitored by gradually increasing the temperature; in the isothermal stage (200℃), the target temperature was maintained for a certain period of time, and spectral signals at different time points were collected. Figure 7 As can be seen, the peaks of each characteristic functional group are clear and still have good distinguishability under high temperature conditions. After the experiment, the microwave power was turned off, the heat compensation medium cavity was emptied, and the system was allowed to cool naturally to room temperature before the device was disassembled and the in-situ cell and crystal were cleaned.

[0055] Example 2

[0056] Using 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethyl ketone as the analyte, the substrate was placed in an in-situ test cell for microwave heating-in-situ infrared spectroscopy of a single substrate (solid).

[0057] After assembling the flow cell body 1 with the high-refractive-index infrared reflective crystal 3, an appropriate amount of substrate solid is added to the crystal surface to complete the sealed assembly. After connecting the pipeline, it is placed into the microwave cavity. Nitrogen gas is introduced and back pressure is applied, while heat-conducting oil is injected into the thermal compensation medium cavity.

[0058] Microwave heating is initiated with a power range of 100-500W, the specific power being set according to the substrate's dielectric constant and dielectric loss parameters. Linear incremental control is implemented based on the temperature curve within the tank. The heat transfer oil circulates within the medium cavity, and correction signals are provided through a fiber optic temperature probe and a reflective infrared temperature measurement unit to achieve temperature drift compensation.

[0059] The experimental temperature range was from room temperature to 200°C, and segmented spectral acquisition was performed following the steps in Example 1. Baseline spectra were recorded in the initial stage; changes in characteristic absorption peaks were monitored during the heating stage; and the temperature was maintained at 200°C for a certain period during the isothermal stage, with spectra acquired at different time points. Figure 8 As can be seen, the peaks of each characteristic functional group are clear and still have good distinguishability under high temperature conditions. After the test, the components were cooled, drained of oil, and cleaned.

[0060] Example 3

[0061] Using the substrate 4-allylguaiacol as the analyte, microwave heating-in-situ infrared spectroscopy was performed on crystals loaded with a Pd / C catalyst film.

[0062] Take 50 mg of Pd / C catalyst, disperse it in a mixed solution of isopropanol-water (volume ratio 2:1), add 0.1 mL of Nafion film-forming agent, disperse it by ultrasonication, and then spin-coat the resulting dispersion evenly onto the crystal surface. Dry it to remove the volatile solvent and form a dense and uniform catalytic film.

[0063] After assembling the flow cell body 1 with the high-refractive-index infrared reflective crystal 3 modified with a catalytic membrane, a mixed solution of ethanol and substrate at a volume ratio of 1:1 is prepared and uniformly dropped onto the crystal surface in the form of a liquid film, ensuring full contact between the substrate liquid film and the catalytic membrane. After assembly and sealing, the pipeline is connected and placed into the microwave cavity. Nitrogen gas is introduced and back pressure is applied, while heat transfer oil is injected into the thermal compensation medium cavity.

[0064] Start microwave heating (100-500W), set the power according to the dielectric properties of the substrate, control the circulation of heat transfer oil, and correct temperature drift through fiber optic temperature probe and infrared temperature measurement components.

[0065] During testing, the temperature was gradually increased to 50℃, 100℃, 150℃, and 200℃, with in-situ infrared spectra acquired in real time. The experimental temperature range was from room temperature to 200℃, and the spectra were recorded in stages to analyze the changes in the morphology and intensity of functional group absorption peaks at different temperatures. After the test, the microwave source was turned off, the dielectric cavity was emptied, and the device was disassembled and cleaned after natural cooling.

[0066] Example 4

[0067] Microwave heating-in-situ infrared spectroscopy was performed on the solid-liquid interface using 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethyl ketone and Pd / C catalyst as the analytical objects.

[0068] 50 mg of Pd / C catalyst was dispersed in an isopropanol-water solution (volume ratio 2:1), Nafion film-forming agent was added, and the mixture was sonicated and then uniformly spin-coated onto the crystal surface, and dried to form a dense film. After assembling the flow cell body 1 and the high-refractive-index infrared reflective crystal 3, a mixed solution of ethanol and 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethyl ketone at a volume ratio of 1:1 was prepared and uniformly dropped onto the surface of the catalyst-loaded crystal. After assembly, the tubing was connected, the chamber was placed in a microwave cavity, pressurized with nitrogen, and filled with heat transfer oil.

[0069] Microwave heating (100-500W) is initiated, and the temperature is increased linearly according to the temperature curve within the tank. The heat transfer oil circulation and online temperature measurement are calibrated simultaneously. The temperature is gradually increased in stages at setpoints of 50℃, 100℃, 150℃, and 200℃, and infrared spectra are collected in real time to observe the changes in functional group signals with temperature. Figure 9 It is evident that the peaks of each characteristic functional group are clear, and the functional groups of the substrate on the surface of the Pd / C catalyst still have good identifiability under high temperature conditions.

[0070] After the experiment, the microwave was turned off, the heat transfer oil was drained, and the system was cooled to room temperature before being disassembled and cleaned.

[0071] Example 5

[0072] In this embodiment, gas-solid in-situ reaction testing was further conducted. Using the substrate 4-allylguaiacol as the target, microwave heating-in-situ infrared spectroscopy was performed using a Pd / C catalyst system.

[0073] 50 mg of Pd / C catalyst was dispersed in isopropanol-water (volume ratio 2:1), 0.1 mL of Nafion film-forming agent was added, and after sonication, it was uniformly spin-coated onto the surface of crystal 3 and dried to form a catalytic film.

[0074] After assembling the flow cell body 1 with the high-refractive-index infrared reflective crystal 3, a mixed solution of ethanol and substrate (volume ratio 1:1) is prepared and dropped onto the surface of the catalytic membrane to form a liquid film. After assembly, sealing, and connection of pipelines, the membrane is placed into a microwave cavity, nitrogen gas is introduced and back pressure is applied, and heat transfer oil is injected into the thermal compensation medium cavity.

[0075] Simultaneously, weigh 50 mL of Pd / C and an appropriate amount of 4-allyl guaiacol, disperse them in an isopropanol-water solution (volume ratio 2:1), add Nafion film-forming agent, mix and spin-coat the mixture onto the crystal surface to form a catalyst-substrate composite film, and allow it to air dry to remove the solvent.

[0076] After drying, the crystals are placed in an in-situ reaction tank and purged with nitrogen for 30 minutes at room temperature to remove air. Then, reaction gas is introduced and a trace amount of solvent is introduced into the carrier gas through an ethanol vaporizer or a gas washing bottle to maintain the activity of the membrane.

[0077] After sealing the system, the background spectrum was collected before heating and subtracted, and the initial spectrum of the sample was recorded as the reaction starting point. The temperature was increased stepwise according to the set program, and in-situ infrared spectra were collected at each temperature. The spectra of samples with different heating times were recorded at 200℃, and the evolution of absorption peaks of typical functional groups with temperature and time was analyzed.

[0078] After the test, turn off the microwave source and drain the heat transfer oil. After the system has cooled down, disassemble the device and clean it.

Claims

1. A method for in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection based on microwave heating, characterized in that, The method is carried out in a dedicated device and includes: preparing a catalyst film or catalyst-substrate composite film on the surface of a high-refractive-index infrared-reflective crystal using spin coating to form a stable and uniform solid active layer; loading a liquid substrate or substrate solution onto the surface of the catalyst film in the form of a liquid film, or introducing a reactant gas and trace solvent into a gas-carrying system to construct a solid-liquid-gas three-phase reaction interface; achieving rapid and uniform heating of the reaction system through microwave heating and a thermal compensation system; and simultaneously acquiring infrared spectral signals throughout the reaction process and monitoring the intensity and shift of functional group absorption peaks in real time to obtain reaction kinetics and species evolution information. The specialized device includes an in-situ flow cell, a microwave irradiation system, an infrared optical system, and a temperature control module. The in-situ flow cell is used to contain the sample and form a closed reaction space. The microwave irradiation system is used to input microwave energy into the region of the in-situ flow cell. The infrared optical system is used to collect real-time infrared spectral signals. The temperature control module is used to realize real-time temperature detection and adjustment during microwave heating, thereby ensuring the temperature stability of the sample region.

2. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, The in-situ flow cell includes a flow cell body (1), a quartz sealing cap (2), a high refractive index infrared reflective crystal (3), an inlet / liquid pipe (4) and an outlet / liquid pipe (5), a thermal compensation medium pipe (6), a sample cell (7), a thermal compensation medium cell (8), and a sealing ring (9); the high refractive index infrared reflective crystal (3) is located at the bottom of the flow cell body (1), and the quartz sealing cap (2) is fastened to the upper end of the flow cell body and has a through hole for inserting a temperature measuring optical fiber (23); the components are sealed together by the sealing ring (9); The main body of the resonant chamber (1) has a threaded hole on the outside and is fixed to the bottom plate of the microwave resonant cavity with screws; the temperature measuring fiber (23) is led out through the opening of the resonant cavity side wall and the interface is sealed, and an impedance tube is provided at the opening; the quartz sealing cover (2) and the heat compensation medium pool (8) together form a sealed heat compensation medium cavity; the heat compensation medium pool is connected to an external circulating heat exchange device to maintain the temperature stability of the reaction and compensation medium; the gas / liquid inlet pipe (4) is connected to a gas source or a horizontal flow pump, and the gas / liquid outlet pipe (5) is connected to a back pressure valve to adjust the system pressure and output the reaction products.

3. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, The infrared optical system includes an infrared light source (16), a spectrometer (17), and an optical path unit composed of an off-axis parabolic mirror and a reflector (22). The infrared light is focused by the infrared light source (16) through the plane reflector (22), the first off-axis parabolic mirror (18), and the second off-axis parabolic mirror (19), and then enters the high refractive index infrared reflective crystal (3) through the optical path impedance tube. Multiple total internal reflections inside the crystal form an evanescent wave that interacts with the sample to generate an absorption signal. After being output from the crystal, the signal is converged to the spectrometer through the third off-axis parabolic mirror (20), the plane reflector (22), and the fourth off-axis parabolic mirror (21).

4. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, The microwave irradiation system includes a microwave source and a microwave resonant cavity (11), which are connected by a coaxial interface (10) for inputting microwave energy into the in-situ flow cell region.

5. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, The temperature control module includes a temperature measuring fiber (23) and an infrared temperature probe (24), which are used to realize real-time temperature detection and adjustment during microwave heating, thereby ensuring the temperature stability of the sample area.

6. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, The main body of the flow cell (1) and the thermal compensation medium cell (8) are made of polyetheretherketone, the sealing ring (9) is made of polytetrafluoroethylene, the high refractive index infrared reflective crystal (3) is made of zinc germanide or silicon dioxide, the microwave resonant cavity (11) is made of stainless steel, the surface of the off-axis parabolic mirror and the plane mirror (22) is plated with gold film to improve the reflection efficiency, and the temperature measuring fiber (23) is a hollow quartz waveguide fiber.

7. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, The catalyst film is prepared by dispersing catalyst particles in a solvent containing a film-forming agent and then spin-coating them onto the surface of an infrared crystal. The film-forming agent is Nalfon or other fluoropolymer binders.

8. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, The reaction system employs three in-situ reaction modes: homogeneous liquid, liquid-solid two-phase, or gas-liquid-solid three-phase. In the solid-containing system, a liquid film is formed by covering the catalyst film surface with a solvent-substrate solution, while in the homogeneous liquid system, a liquid film can be formed directly on the crystal surface. All of the different in-situ reaction modes can achieve continuous spectrum acquisition within a temperature range of 20℃ to 200℃.

9. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, By comparing the reference spectrum without a catalyst with the reaction spectrum, the variation of the absorption peak intensity of the marker functional group with time and temperature was analyzed to obtain the reaction kinetic parameters and the product formation sequence.

10. The in-situ attenuated total internal reflection Fourier transform infrared spectroscopy detection method based on microwave heating according to claim 1, characterized in that, Spectroscopic detection includes in-situ monitoring of hydrogenation, cracking, and conversion reactions of compounds with oxygen- or unsaturated substituents on the furan or benzene rings, compatible with microwave and catalytic reaction mechanism studies, material interface reaction analysis, and spectroscopic characterization of biomass derivative conversion processes.

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