In-situ raman detection device and method for low-temperature plasma catalytic reaction

Abstract

The application provides an in-situ Raman detection device and method for low-temperature plasma catalytic reaction, which comprises a set of in-situ reaction cell matched with a Raman spectrometer, a set of light source system and a set of plasma generator, the set of light source system comprises a light source and a power line, an optical fiber and an optical fiber support, and the plasma generator comprises a plasma generator, a power and frequency regulator, and a power line and an electrode connecting line. Compared with the prior art, the application has the advantages of simple assembly, good sealing, adjustable focal length, easy acquisition of high-quality Raman spectrum information, and connection of the plasma generator, and a characterization method combining low-temperature plasma catalytic reaction and in-situ Raman technology is invented, which has good effects on the mechanism research and application research of practical low-temperature plasma applied to catalytic reaction. The application has the advantages of simple structure, simple and easy-to-obtain accessories, and easy industrial production.

Description

Technical Field

[0001] This invention relates to the field of spectroscopic instrument accessories and instrumental analysis technology, specifically to an in-situ Raman detection device and method for low-temperature plasma catalytic reactions. Background Technology

[0002] In recent years, the massive consumption of fossil fuels has led to a continuous increase in atmospheric carbon dioxide concentration, resulting in increasingly serious energy shortages and environmental problems. Therefore, developing clean chemical conversion processes has become an urgent research and development direction. Among these, low-temperature plasma catalysis processes, due to their simple equipment and ability to be rapidly started and stopped at ambient temperature and pressure, have attracted increasing attention and become a research hotspot in chemical processes such as ammonia synthesis, carbon dioxide conversion, methane conversion, and water-gas transformation.

[0003] However, compared to traditional thermocatalysis, large-scale research on low-temperature plasma catalysis has only been conducted for about 20 years. In-situ characterization techniques for these processes are quite limited, particularly due to the effect of photons emitted by the low-temperature plasma itself, which severely restricts the application of in-situ spectroscopic characterization techniques in low-temperature plasma catalysis. This makes the study and analysis of the microscopic mechanisms of chemical reactions in low-temperature plasma catalysis extremely difficult, significantly impacting the possibility of solving problems and the industrialization of low-temperature plasma catalysis. Therefore, developing in-situ characterization techniques for low-temperature plasma catalysis is crucial and a key focus of research in this area. Hardacre successfully designed and completed in-situ infrared and synchrotron radiation detection devices for low-temperature plasma catalysis in 2015 and 2017, respectively, providing excellent precedents for applying in-situ spectroscopic characterization techniques to low-temperature plasma catalysis. Subsequently, some researchers have also developed in-situ infrared devices for low-temperature plasma catalysis.

[0004] The development of in-situ Raman spectroscopy has driven the research and analysis of the microscopic mechanisms of chemical reactions. It allows for online, real-time analysis of the relationship between the structure and properties of substances; during testing, no additional sample modification is required, and the study of the mechanisms involved in chemical reactions can be achieved, contributing to a deeper understanding of these reactions. However, Raman detection is particularly sensitive to optical signals, and the effect of photons emitted by the low-temperature plasma itself can severely affect the collection of Raman spectral signals. To date, no in-situ Raman apparatus or applications have been reported for low-temperature plasma-catalyzed reaction processes. Summary of the Invention

[0005] In view of the technical problems mentioned in the background section, this invention provides an in-situ Raman detection device and method for low-temperature plasma catalytic reactions. The invention aims to provide an in-situ Raman detection device and method for low-temperature plasma catalytic reactions, which is of great significance for the practical application of in-situ Raman characterization methods in the study and application of low-temperature plasma catalytic reaction mechanisms.

[0006] The technical means employed in this invention are as follows: An in-situ Raman detection device for low-temperature plasma catalytic reactions, comprising: An in-situ reaction cell and light source system matched and connected to a Raman spectrometer, and a plasma generator matched and connected to the in-situ reaction cell; The plasma generator includes: a plasma generator, a power and frequency regulator, a power supply line, and electrode connection lines; the light source system includes a light source and a power supply line, optical fiber, and a light beam support. The in-situ reaction tank includes an in-situ tank cylinder, an inlet, an outlet, a medium cylinder, a fixed threaded sleeve, a gas chamber, a discharge chamber, a high-voltage electrode, a grounding electrode, a quartz window, a top cover, a window cover, sealing screws, a quartz window, a conductive copper strip, a first sealing O-ring, and a second sealing O-ring.

[0007] This invention also includes an in-situ Raman detection method for low-temperature plasma catalytic reactions, characterized by comprising the following steps: Step 1: Connect an external plasma generator to the in-situ reaction tank. Press the catalyst into tablets and install them above the discharge section. During the low-temperature plasma catalytic reaction, the plasma is excited and the plasma signal parameters are controlled by the connected plasma generator. Step 2: During the low-temperature plasma catalytic reaction, the reaction gas passes through the gas chamber and discharge chamber via the gas inlet. The catalyst tablet is placed above the discharge section and supported by the high electrode. The in-situ reaction cell is connected to an external plasma generator. The plasma signal mode, frequency, and power are controlled by the plasma generator. Then, the catalyst surface is observed through a quartz window, and the Raman spectral signal in the low-temperature plasma catalytic reaction is collected.

[0008] Compared with the prior art, the present invention has the following advantages: (1) The present invention designs an in-situ Raman detection device and method for low-temperature plasma catalytic reaction, which can realize the low-temperature plasma catalytic reaction and study the reaction process at the same time. It is of great significance for the study of the mechanism of low-temperature plasma applied to catalytic reaction.

[0009] (2) The present invention designs an extendable quartz window for Raman lens, which can reduce the focal length and provide a guarantee for obtaining high-quality Raman spectrum information.

[0010] (3) The present invention is simple to assemble, has good sealing performance, adjustable focal length, and is easy to obtain high-quality Raman spectrum information. The device embeds the reaction cell into the sample stage of the Raman spectrometer and connects it to the plasma generator. It has invented a characterization method that combines low-temperature plasma catalytic reaction with in-situ Raman technology, which has a good effect on the mechanism research and application research of actual low-temperature plasma in catalytic reaction.

[0011] (4) The structure is simple, the parts are easy to obtain, and it is easy to industrialize. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is an exploded view of the in-situ Raman reaction cell of the present invention; Figure 2 This is a cross-sectional view of the in-situ Raman reaction cell of the present invention; Figure 3 This is a schematic diagram of the instrument connection for in-situ Raman testing of the in-situ Raman reaction cell of this invention applied to low-temperature plasma catalytic reactions; Detailed Implementation To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0014] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0015] An in-situ Raman detection device for low-temperature plasma catalytic reaction includes: an in-situ reaction cell and a light source system matched and connected to a Raman spectrometer, and a plasma generator matched and connected to the in-situ reaction cell. The plasma generator includes a plasma generator, power and frequency regulators, power lines, and electrode connection lines; the light source system includes a light source and power lines, optical fibers, and a light support; the in-situ reaction cell includes an in-situ cell body, an inlet, an outlet, a dielectric body, a fixed threaded ferrule, a gas chamber, a discharge chamber, a high-voltage electrode, a grounding electrode, a quartz window, a top cover, a window cover, sealing screws, a quartz window, a conductive copper strip, a first sealing O-ring, and a second sealing O-ring.

[0016] Furthermore, the in-situ pool cylinder material includes at least one of polytetrafluoroethylene (PTFE), fluorinated propylene (FEP), ethylene trifluorochloroethylene (ECTE), ethylene tetrafluoroethylene (ETFE), and fusible polytetrafluoroethylene (PFA).

[0017] Furthermore, the top of the in-situ pool cylinder has a sealing threaded hole and a first O-ring mounting groove, and the upper part of the gas chamber inside the in-situ pool cylinder has a sealing screw hole and a second O-ring mounting groove. The medium cylinder is embedded into the second O-ring mounting groove inside the in-situ pool cylinder by installing the second sealing O-ring, and then fixed and sealed by the installation and fixing threaded sleeve.

[0018] Furthermore, the medium cylinder material includes at least one of polytetrafluoroethylene (PTFE), fluoropropylene (FEP), ethylene trifluorochloroethylene (ECTE), ethylene tetrafluoroethylene (ETFE), fusible polytetrafluoroethylene (PFA), quartz, glass, and ceramics.

[0019] Furthermore, the material for the fixed threaded ferrule includes at least one of polytetrafluoroethylene (PTFE), fluoropropylene (FEP), ethylene trifluorochloroethylene (ECTE), ethylene tetrafluoroethylene (ETFE), and fusible polytetrafluoroethylene (PFA).

[0020] Furthermore, a high-voltage electrode through hole is opened in the center of the in-situ cell cylinder, an air inlet is opened on one side of the in-situ cell connecting to the gas chamber, a ground electrode through hole is opened on the same side, and an air outlet is opened on the opposite side connecting to the center of the in-situ cell cylinder. The gas source pipeline is connected to the air inlet by a screw-in fixed threaded sleeve through the installation of a second sealing O-ring. The gas enters the discharge chamber and the in-situ cell cylinder through the air inlet and then is discharged through the air outlet.

[0021] Furthermore, the high-voltage electrode is inserted into the gas chamber of the reaction tank cylinder through the high-voltage electrode through hole in the center of the in-situ tank cylinder to the upper discharge section. Then, the high-voltage electrode is fixed and sealed by fitting a second sealing O-ring and installing a fixing threaded sleeve. The grounding electrode is wrapped around the dielectric cylinder and protrudes from the fixing threaded sleeve. It is fixed by attaching conductive copper tape and extends out of the in-situ tank cavity through the grounding electrode through hole. The high-voltage electrode is then fixed and sealed by fitting an O-ring and installing a fixing threaded sleeve. The space between the high-voltage electrode and the dielectric cylinder covered by the grounding electrode is the discharge chamber. The catalyst is pressed and installed above the discharge chamber and supported by the high-voltage electrode.

[0022] Furthermore, the materials of the high-voltage electrode and the grounding electrode may be the same or different, including at least one of Al, Cu, stainless steel, and graphite.

[0023] Furthermore, the top cover has a sealing threaded through hole corresponding to the top of the in-situ cell cylinder, and the bottom of the top cover has a first O-ring mounting groove corresponding to the top of the in-situ cell cylinder. The in-situ cell cylinder is sealed by installing the first sealing O-ring and screwing in the sealing screw. The top cover has a quartz window and a quartz window mounting groove in the center, which are coaxial with the position of the discharge chamber. The quartz window mounting groove is stepped and connects to the inner cavity of the in-situ cell. The first sealing O-ring is inserted into the step of the quartz window mounting groove, and the quartz window is installed on the first sealing O-ring. Finally, the window cover is screwed into the quartz window mounting groove by a fixing tool to achieve the installation and sealing of the quartz window. The window cover is annular with an inner diameter of 20 mm, which is larger than the diameter of the Raman lens. The quartz window is circular with a diameter of 20 mm. The quartz window is a circular groove with an inner diameter of 16 mm, which is larger than the diameter of the Raman lens.

[0024] Furthermore, the materials for the top cover and window cover include at least one of polytetrafluoroethylene (PTFE), fluoropropylene (FEP), ethylene trifluorochloroethylene (ECTE), ethylene tetrafluoroethylene (ETFE), and fusible polytetrafluoroethylene (PFA).

[0025] Furthermore, the high-voltage electrode extending out of the in-situ cell cylinder is directly connected to the high-voltage line of the plasma generator, and the grounding electrode extending out of the in-situ cell cylinder is connected to the neutral line of the plasma generator. The plasma signal is controlled by the plasma generator.

[0026] An in-situ Raman detection method for low-temperature plasma catalytic reactions includes the following steps: Step 1: The in-situ reaction tank is connected to an external plasma generator. The catalyst is pressed into tablets and installed above the discharge chamber, supported by high-voltage electrodes. During the low-temperature plasma catalytic reaction, the plasma is excited and the plasma signal parameters are controlled by the connected plasma generator. Step 2: During the low-temperature plasma catalytic reaction, the reaction gas (such as CO2, CH4, N2, etc.) passes through the gas chamber to the discharge chamber via the gas inlet. The gas flow rate is controllable at 20-200 mL / min. The catalyst is pressed into a tablet (8 mm) and installed above the discharge section, supported by a high electrode. An external plasma generator is connected to the in-situ reaction cell. The plasma signal mode, frequency, and power are controlled by the plasma generator. The signal mode includes at least one of sinusoidal signal, pulse signal, square wave signal, etc. The signal frequency is 5-200 kHz, and the plasma power is 0-200 W. Then, the catalyst surface is observed through a quartz window, and the Raman spectral signal in the low-temperature plasma catalytic reaction is collected.

[0027] Example 1 In-situ Raman Detection Method and Apparatus for Ni / Al2O3 in Low-Temperature Plasma Catalytic Ammonia Synthesis Reactions Detection device such as Figure 1 , Figure 2As shown, the system includes an in-situ reaction cell and a light source system matched with a Raman spectrometer, as well as a plasma generator matched with the in-situ reaction cell. The plasma generator includes a plasma generator, power and frequency regulators, power lines, and electrode connection lines. The light source system includes a light source and power lines, optical fibers, and a light beam support. The in-situ reaction cell includes an in-situ cell body 1, an inlet 15, an outlet 16, a dielectric body 4, fixed threaded sleeves 3, 10, 11, 12, and 13, a gas chamber 17, a discharge chamber 18, a high-voltage electrode 5, a grounding electrode 7, a quartz window 8, a top cover 2, a window cover 9, 14×6 sealing screws, a quartz window 21, a conductive copper strip, a first sealing O-ring, and a second sealing O-ring. The in-situ cell cylinder 1 is made of PTFE, with six sealing threaded holes 19 and a first O-ring mounting groove 20 on its top. Above the gas chamber 17 within the in-situ cell cylinder, there are sealing screw holes 19 and a second O-ring mounting groove 22. The medium cylinder 4 is made of quartz, and is secured and sealed by a PTFE-made first sealing O-ring embedded in the second O-ring mounting groove 22 within the in-situ cell cylinder, and then fixed and sealed by a PTFE-made fixing threaded sleeve 3. A high-voltage electrode through-hole 23 is located at the center of the in-situ cell cylinder's inner cavity. An air inlet 15 is located on one side of the in-situ cell, connecting to the gas chamber 17. A grounding electrode through-hole 24 is located on the same side, and an air outlet 16 is located on the opposite side, connecting to the center of the in-situ cell cylinder's inner cavity. The gas supply pipe is screwed into a PTFE-made fixing threaded sleeve and connected to the air inlet 15. Gas enters the discharge chamber 18 and the in-situ cell cylinder's inner cavity through the air inlet 15, passing through the gas chamber 17, and then exits through the air outlet 16. The high-voltage electrode 5 is made of copper. It is inserted into the gas chamber 17 of the reaction tank cylinder through the high-voltage electrode through-hole 23 in the center of the in-situ tank cylinder to the upper discharge section. It is then fixed and sealed by a second sealing O-ring made of PTFE and a fixed threaded sleeve 10 made of PTFE. The grounding electrode is made of aluminum. It is wrapped around the dielectric cylinder 4, with the portion of the fixed threaded sleeve protruding. It is fixed by pasting conductive copper tape and extends out of the in-situ tank cavity through the grounding electrode through-hole 24. It is then fixed and sealed by a second sealing O-ring made of PTFE and a fixed threaded sleeve 12 made of PTFE. The space between the high-voltage electrode and the dielectric cylinder covered by the grounding electrode is the discharge chamber 18.The top cover, made of PTFE, has a sealing threaded through hole corresponding to the top of the in-situ cell cylinder 1. The bottom of the top cover has a first O-ring mounting groove corresponding to the top of the in-situ cell cylinder. The in-situ cell cylinder is sealed by installing the first sealing O-ring and screwing in six sealing screws 14. The top cover has a circular groove-shaped quartz window 21 with an inner diameter of 16 mm and a quartz window mounting groove 25, coaxial with the discharge chamber. The quartz window mounting groove 25 is stepped and connects to the inner cavity of the in-situ cell. The first sealing O-ring is inserted into the step of the quartz window mounting groove 25, and a circular quartz window 8 with a diameter of 20 mm is installed on the PTFE-made first sealing O-ring. Finally, a 20 mm inner diameter annular window cover 9 is screwed into the quartz window mounting groove 25 using a fixing tool to install and seal the quartz window 8. The window cover is made of PTFE. The diameter of the Raman lens is smaller than the inner diameter of the quartz window. The high-voltage electrode of the in-situ cell extends out of the in-situ cell cylinder and is directly connected to the high-voltage line of the plasma generator. The grounding electrode extends out of the in-situ cell cylinder and is connected to the neutral line of the plasma generator. The plasma signal is controlled by the plasma generator.

[0028] Detection methods such as Figure 3 As shown, the Ni / Al₂O₃ catalyst was pressed into a thin sheet with a diameter of 8 mm and a thickness of approximately 0.5 mm, and mounted above the discharge section, supported by a high-voltage electrode. The assembled in-situ reaction cell was placed in the sample measurement area of ​​the Raman spectrometer. The high-voltage electrode and grounding electrode of the in-situ reaction cell were connected to the high-voltage line and neutral line of the plasma generator, respectively. During the low-temperature plasma catalytic reaction, a pre-mixed N₂ / H₂ at a ratio of 1:3 was introduced through the gas inlet at a flow rate of 30 mL / min. The plasma signal mode was controlled to input a sinusoidal signal, with a control signal frequency of 10 kHz and a discharge power of 5 W. The catalyst surface was then observed through a quartz window, and the Raman spectral signal during the low-temperature plasma catalytic reaction was collected. The relevant parameters of the Raman light source system were: Raman laser wavelength of 785 nm and laser power of 3 mW.

[0029] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

[0030] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An in-situ Raman detection device for low-temperature plasma catalytic reactions, characterized in that, include: An in-situ reaction cell and light source system matched with a Raman spectrometer, and a plasma generator matched with the in-situ reaction cell; The plasma generator includes: a plasma generator, a power and frequency regulator, a power supply line, and electrode connection lines; the light source system includes a light source and a power supply line, optical fiber, and a light beam support. The in-situ reaction tank includes an in-situ tank cylinder, an air inlet, an air outlet, a medium cylinder, a fixed threaded sleeve, a gas chamber, a discharge chamber, a high-voltage electrode, a grounding electrode, a quartz window, a top cover, a window cover, sealing screws, a quartz window, a conductive copper strip, a first sealing O-ring, and a second sealing O-ring. The top of the in-situ pool cylinder has a sealing threaded hole and a first O-ring mounting groove; the upper part of the gas chamber inside the in-situ pool cylinder has a sealing screw hole and a second O-ring mounting groove; the medium cylinder is embedded into the second O-ring mounting groove inside the in-situ pool cylinder by installing the second sealing O-ring, and then fixed and sealed by the installation and fixing threaded sleeve. A high-voltage electrode through hole is opened in the center of the inner cavity of the in-situ cell cylinder. An air inlet is opened on one side of the in-situ cell cylinder, which is connected to the gas chamber. A ground electrode through hole is opened on the same side. An air outlet is opened on the opposite side, which is connected to the center of the inner cavity of the in-situ cell cylinder. The gas source pipeline is connected to the air inlet by screwing in a fixed threaded sleeve. The gas enters the discharge chamber and the inner cavity of the in-situ cell cylinder through the air inlet and then is discharged through the air outlet. The high-voltage electrode is inserted into the gas chamber of the reaction tank cylinder through the high-voltage electrode through hole in the center of the in-situ tank cylinder to the upper discharge section. Then, the high-voltage electrode is fixed and sealed by fitting a second sealing O-ring and installing a fixed threaded sleeve. The grounding electrode is wrapped around the dielectric cylinder and protrudes from the fixed threaded sleeve. It is fixed by pasting conductive copper tape and extends out of the in-situ tank cavity through the grounding electrode through hole. The high-voltage electrode is fixed and sealed by fitting a second sealing O-ring and installing a fixed threaded sleeve. The space between the high-voltage electrode and the dielectric cylinder covered by the grounding electrode is the discharge chamber. The top cover has a sealing threaded through hole corresponding to the top of the in-situ cell cylinder, and the bottom of the top cover has a first O-ring mounting groove corresponding to the top of the in-situ cell cylinder. The in-situ cell cylinder is sealed by installing the first sealing O-ring and screwing in the sealing screw. The top cover has a quartz window and a quartz window mounting groove in the center, which are coaxial with the position of the discharge chamber. The quartz window mounting groove is stepped and connects to the inner cavity of the in-situ cell. The first sealing O-ring is inserted into the step of the quartz window mounting groove, and the quartz window is installed on the first sealing O-ring. Finally, the window cover is screwed into the quartz window mounting groove by a fixing tool to achieve the installation and sealing of the quartz window. The window cover is annular, with an inner diameter larger than the diameter of the Raman lens. The quartz window is circular, and the quartz window is a circular groove, with an inner diameter larger than the diameter of the Raman lens.

2. The in-situ Raman detection device for low-temperature plasma catalytic reactions according to claim 1, characterized in that, The high-voltage electrode extends out of the in-situ cell cylinder and is directly connected to the high-voltage line of the plasma generator. The grounding electrode extends out of the in-situ cell cylinder and is connected to the neutral line of the plasma generator. The plasma signal is controlled by the plasma generator.

3. An in-situ Raman detection method for low-temperature plasma catalytic reactions, employing the apparatus described in any one of claims 1-2, characterized in that, Includes the following steps: Step 1: Connect an external plasma generator to the in-situ reaction tank. Install the catalyst tablet above the discharge section. During the low-temperature plasma catalytic reaction, the plasma is excited and the plasma signal parameters are controlled through the connected plasma generator. Step 2: During the low-temperature plasma catalytic reaction, the reaction gas passes through the gas chamber and discharge chamber via the gas inlet. The catalyst tablet is placed above the discharge section and supported by the high electrode. The in-situ reaction cell is connected to an external plasma generator. The plasma signal mode, frequency, and power are controlled by the plasma generator. Then, the catalyst surface is observed through a quartz window, and the Raman spectral signal in the low-temperature plasma catalytic reaction is collected.

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