The present invention relates to a real-time double-beam in situ infrared spectrum system and a method thereof, which belongs to the technical field of spectrum analysis instruments.
An infrared spectrometer is an instrument for analyzing the molecular structure and chemical composition using absorption characteristics of material to infrared radiation light with different wavelengths. The infrared spectrometer mainly comprises a light source, a monochromator, a detector and a computer processing information system. With the increase of application requirements, a series of changes have been made in an optical splitting system, which experiences prism, raster and interferometer successively, and a corresponding infrared spectrometer experiences prism spectrometer, raster infrared spectrometer and Fourier transform infrared spectrometer finally.
In situ Fourier transform infrared (in situ FT-IR), in situ diffuse reflectance infrared (in situ DRIFT) and attenuated total reflection-infrared (ATR-IR) spectrum techniques are widely applied to in situ characterization of a gas-solid heterogeneous catalytic reaction, so that the catalyst surface information may be obtained in the condition approximating heterogeneous catalytic reaction. So far, each of the above-mentioned characterization technique uses a commercial infrared spectrometer, and the commercial spectrometer uses single-beam infrared light. If the single-beam infrared spectrometer is used to perform characterization of an in situ catalytic reaction, there is a need to collect background information about a catalyst sample in advance as a background spectrum to eliminate influence of the instrument and sample. However, in the process of a real gas-solid heterogeneous catalytic reaction, the background information about the catalyst may change with the extension of the reaction time. More seriously, a gas molecule vibration spectrum in a real-time state and a transmission spectrum generated in a heating condition may significantly affect test results. Due to the above-mentioned defects thereof, the single-beam infrared spectrum technique cannot obtain surface information about the catalyst in a real reaction state in real time, but only can obtain stationary state and static state information about the catalyst.
To obtain the background information about the catalyst in real time, the patent for invention with the application No. “201110456379.3” obtains a false double-beam light source by adjusting a light source of the infrared spectrum. In the method, a stainless steel in situ infrared sample cell is designed, two ports of the cell body are provided with lids, each lid is provided with an infrared window, a sample bracket is fixed in the cell body, and the sample bracket is provided with two sample tanks, wherein when a sample is tested, one sample tank is unoccupied as a background beam, the other sample tank is used for placing a sample as a sample beam, spectra of two positions are respectively collected, and then a signal adsorbed on the catalyst surface is obtained by subtracting the two spectra from each other. The original intention for designing the in situ infrared cell is good; however, because two sample tanks are set in different positions of the sample bracket, there is a need to adjust the position of the light source of the infrared spectrum in the real process of sample detection to collect spectrograms of the two sample tanks. However, it is difficult to adjust the infrared light source, it is irrealizable to collect the background and sample in real time, and it is difficult to catch the real-time change in the sample surface information. Patent for utility models with the application No. “2013206878256” proposes a method of implementing a double-beam infrared spectrum analyzer, in which a light source is adjusted to obtain two infrared beams which pass through a sample cell and a reference cell respectively, the reference beam passes through an attenuator while the sample beam passes through a chopper, and the two beams are combined into one beam in a light ray concentrator to enter the monochromator. Although the method overcomes the noise interference thereof, there is a need to redesign the light source of the infrared instrument in the real operation process, so that the practicality is poor. So far, it has not been reported that a double-beam infrared spectrometer is used for in situ characterization of a heterogeneous catalytic reaction.
Each commercial infrared spectrum test system comprises a single-beam infrared spectrometer and a single-beam infrared cell, in the process of in situ characterization of the gas-solid heterogeneous catalytic reaction, an infrared spectrum of a catalyst in a static state condition is collected as a background first, and then infrared spectra of gases changing with time in the condition of different temperatures and flow velocities are collected by taking the background as a basis. With the extension of the reaction time, the catalyst surface information is constantly changed, but the background file is not updated in real time so that measurement errors are generated. Moreover, both molecule vibration spectra adsorbing gases and heat radiation generated by heating may disturb final test results. Therefore, a single-beam infrared spectrum system cannot be used for characterization of an in situ heterogeneous catalytic reaction in a real-time state.
To solve the above-mentioned problem, the present invention provides a real-time double-beam in situ infrared spectrum system and a method thereof.
The double-beam infrared reaction cell comprises two identical infrared cells (a reference cell and a sample cell) which are in communication with each other and are at the same level, and uses two groups of identical infrared windows to guarantee that the sample beams are identical to the reference beams. The heat distribution and optical path difference of the sample beams are guaranteed to be identical to those of the reference beams through the above-mentioned design.
The present invention has the following technical solution:
A real-time double-beam in situ infrared spectrum system, comprising two identical infrared spectrometers and a double-beam infrared reactor cell,
wherein the two identical infrared spectrometers refer to two infrared spectrometers with identical models, parameters, placing levels and vertical heights, or two infrared spectrometer with different models of which the conditions are identical by debugging; and the two infrared spectrometers are connected to computers respectively, the two computers may automatically collect reference beams and sample beams in real time by controlling the two infrared spectrometers, i.e. the two identical infrared spectrometers are used as a reference infrared spectrometer and a sample infrared spectrometer respectively.
The double-beam infrared reaction cell comprises two identical sample chambers which are in communication with each other and are at the same level, wherein one sample chamber is used as a reference cell, the other sample chamber is used as a sample cell; and uses two groups of identical infrared windows to guarantee that the sample beams are identical to the reference beams; each sample chamber is equipped with a circular sample bracket, and a cell body of the infrared reactor cell is equipped with two pairs of windows which are symmetrical to each other and respectively correspond to the infrared spectrometers collecting the reference beams and the sample beams respectively; circular parts of the two circular sample brackets are wound by two sections of identical heating wires, a thermocouple is inserted in the middle part of the bracket from the top end of the sample bracket to test the real-time temperature of a sample, an inlet and an outlet for condensed water are provided on the periphery of the double-beam infrared reaction cell to control the temperatures of the double-beam infrared reaction cell to be identical, and the sample bracket is connected to the double-beam infrared reaction cell through grinding mouth sealing; and the double-beam infrared reaction cell is connected to a vacuum system through grinding mouth sealing.
Each of the infrared spectrometers is equipped with a mercury cadmium telluride (MCT) detector, an indium stibide (InSb) detector or a DTGS detector with a polythene window, and relevant parameters are adjusted to be consistent.
The cell body of the double-beam infrared reaction cell is made of glass, quartz, polytetrafluoroethylene, stainless steel, aluminum or copper.
A method of using the real-time double-beam in situ infrared spectrum system, comprising the following steps:
while in use, a sample to be tested is prepared into a self-support sheet, the sample sheet is placed on a sample cell bracket of the double-beam infrared reaction cell, and the reference cell is unoccupied; the reference cell is placed on one infrared spectrometer, and the sample cell is placed on the other infrared spectrometer; the double-beam infrared reactor cell is connected to the vacuum system, air, vapor and carbon dioxide in the sample cell are pumped out, the situation of pumping out the gases in the sample cell is detected by a vacuum gauge, and a gas adsorption test is performed according to required conditions; and in the test process, an infrared spectrogram of the reference beams is collected by one infrared spectrometer, and then an infrared spectrogram of the sample beams is collected by the other infrared spectrometer as a final result by taking the infrared spectrogram of the reference beams as a background file. Wherein after the double-beam infrared reactor cell is connected to the vacuum system, cooling water is introduced to control the temperature of the double-beam infrared reactor cell, the temperature of the self-support sheet is increased to 450° C., and the self-support sheet is processed for 4 hours at a system pressure of less than 10−3 Pa; and the double-beam infrared reactor cell is disconnected from the vacuum system, an interface between same and the vacuum system is sealed, a reaction gas is introduced into the sample cell at −150 to 500° C., the reacted gas is discharged by the reference cell, a gas adsorption test is performed in the process of introducing the reaction gas, and a test is performed.
Through real test analysis, the constructed double-beam in situ infrared spectrum system can conduct real-time in situ characterization on the gas-solid heterogeneous catalytic reaction in a real reaction condition, to obtain surface phase information in the changing process of the gas phase composition. The double-beam in situ infrared spectrum system has the following advantages of: (1) detecting a two-dimensional spectrogram and a three-dimensional spectrogram in a stationary state of the reaction, and eliminating the interference of a gas molecule vibration spectrum in a real-time state to obtain real information about an adsorbed species on the catalyst surface especially when the gas-solid heterogeneous catalytic reaction is evaluated; (2) collecting spectrograms of sample beams and background beams synchronously in real time through correlation between applications, to obtain information about a species on the catalyst surface changing with the reaction time; (3) synchronously controlling the temperatures of the sample cell and the reference cell to obtain information about different species on the catalyst surface changing with temperature, and eliminating the heat radiation spectrum interference generated in a heating condition, to obtain real-time information about an active center of the catalyst surface, an active phase and an intermediate species at different temperatures; (4) inspecting the change in species on the catalyst surface at different gas partial pressures and flow velocities and thus exploring a reaction mechanism; (5) studying a dimolecular or polymolecular gas-solid reaction mechanism through means such as preadsorption, coadsorption and the like; (6) conducting an isotope labelling experiment research; and (7) conducting the research at different temperatures (−150 to 550° C.).
The test method of the double-beam in situ infrared sample is as follows: a sample is prepared into a self-support sheet, the sample sheet is placed on one sample cell bracket of the double-beam infrared reaction cell, the other sample cell is used as a reference cell, the double-beam infrared sample cell is placed on two infrared spectrometers and is connected to a home-made vacuum system, air, vapor and carbon dioxide in the sample cell are pumped out, the situation of pumping out the gases in the sample cell is detected by a vacuum gauge, a gas adsorption test is performed at a required temperature, and an infrared spectrogram is collected.
By taking adsorption of isobutene on the HZSM-5 catalyst as an example, the double-beam in situ infrared spectrometer is compared with the single-beam in situ infrared spectrometer. It can be seen from
The process of a gas-solid heterogeneous catalytic reaction is characterized in real time in a real reaction condition using the double-beam in situ infrared spectrometer. The interference of the vibration spectrum of gas-phase molecules in a real-time state and heat radiation is eliminated, to obtain situation of change in the species on the catalyst surface at differential reaction time and reaction temperatures. The specific method is as follows: a sample is prepared into a self-support sheet, the sample sheet is placed on one sample cell bracket of the double-beam infrared reaction cell, the other sample cell is used as a reference cell, the double-beam infrared sample cell is placed on two infrared spectrometers and is connected to a home-made vacuum system, air, vapor and carbon dioxide in the sample cell are pumped out at a certain temperature, and the situation of pumping out the gases in the sample cell is detected by a vacuum gauge. Then, a continuous flowing gas absorption test is conducted at an atmospheric pressure and a certain temperature, to collect an infrared spectrogram in real time, wherein the time interval for collecting the spectrogram is 1.27 minutes.
By taking the in situ reaction of isobutene on the HZSM-5 catalyst as an example, flowing isobutene adsorption is conducted on the sample purified in high vacuum at an atmospheric pressure, wherein the reaction temperature is 150° C., the gas flow velocity of isobutene is 3 ml/min, and the change in the species on the catalyst surface in the reaction process is monitored in real time. See
The reaction temperature is increased to 300° C. It can be seen from
The test method of the double-beam in situ infrared sample is as follows: a sample is prepared into a self-support sheet, the sample sheet is placed on one sample cell bracket of the double-beam infrared reaction cell, the other sample cell is used as a reference cell, the double-beam infrared sample cell is placed on two infrared spectrometers and is connected to a home-made vacuum system, air, vapor and carbon dioxide in the sample cell are pumped out at a certain temperature, the situation of pumping out the gases in the sample cell is detected by a vacuum gauge, a gas adsorption test is performed at a required temperature, and an infrared spectrogram is collected.
By taking adsorption of isobutane on HZSM-5 and Zn/HZSM-5 catalysts as an example, the change in the active center of the catalyst in situ characterized by the double-beam in situ infrared spectrometer is inspected. It can be seen from
The double-beam in situ infrared spectrometer may complete a double-probe molecule adsorption experiment. Pyridine adsorption is an important means for characterizing a Brønsted acid center and a Lewis acid center of the solid catalyst surface. Pyridine and water molecule coadsorption may characterize the changing process of the active center of the catalyst surface in the water-containing reaction process. As shown in
The double-beam in situ infrared sample cell may be used within the temperature range of −150 to 550° C., and may be used for studying active centers and reaction mechanisms of different catalysts. CO low-temperature infrared adsorption is an important means for characterizing active centers of metal oxide. As shown in
Number | Date | Country | Kind |
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201610846387.1 | Sep 2016 | CN | national |