Method for measuring concentration of active site
By using chemical probe method and intelligent gravimetric analyzer to determine the amount of toxic gas adsorption of the catalyst at the catalyst reaction temperature, the problem of inaccurate measurement of the catalyst active position concentration in the prior art is solved, accurate measurement at the catalyst reaction temperature is achieved, and the efficiency of catalyst design is improved.
Patent Information
- Application Number
- CN202510594023.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-09
- Publication Date
- 2025-08-08
AI Technical Summary
The existing catalyst active site concentration measurement method cannot be performed at the actual reaction temperature of the catalyst, resulting in inaccurate test results.
The chemical probe method was used to change the concentration of the toxic gas, and the catalyst activity evaluation and adsorption measurement were performed at the catalyst reaction temperature. The catalyst adsorption amount of the toxic gas by the catalyst was determined by using an intelligent gravimetric analyzer and the concentration of the active site was calculated.
It provides accurate measurement of active site concentration at catalyst reaction temperature, improves the accuracy and application value of measurement results, and provides guidance for the design of efficient catalysts.
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Abstract
Description
Technical Field
[0001] The invention provides a method for measuring active site concentration, belonging to the technical field of catalyst characterization. Background Art
[0002] Catalyst active site concentration refers to the number of active sites per unit volume or mass of catalyst. Active sites are specific locations on the catalyst surface that can participate in catalytic reactions, adsorbing reactant molecules and reacting chemically in this adsorbed state, thereby accelerating the overall reaction process. The number of active sites directly affects the contact area and adsorption degree between the catalyst and the reactants, which in turn influences the adsorption of reactants and the progress of the catalytic reaction. Generally speaking, a greater number of active sites indicates a greater adsorption capacity on the catalyst surface, enabling the adsorption and activation of more reactant molecules and improving the catalyst's catalytic efficiency.
[0003] Methods for measuring active site concentration include physical adsorption, chemical probe method, and electron microscopy technology.
[0004] The physical adsorption method estimates the number of active sites by measuring the amount of specific gas adsorbed by the catalyst. The adsorption amount measured by this method is the amount of gas adsorbed on all exposed surfaces of the sample, which cannot accurately reflect the number of active sites, and is carried out at low temperatures.
[0005] Chemical probe method uses a specific chemical probe to react with the active sites on the catalyst surface and estimates the number of active sites by measuring the amount of reaction products;
[0006] Electron microscopy technology can directly observe the morphology of the catalyst surface and the distribution of active sites using scanning tunneling microscopy (STM) and atomic force microscopy (AFM).
[0007] Temperature is an important factor affecting catalyst activity. However, none of the above methods for measuring active site concentration can be performed at the actual reaction temperature, resulting in inaccurate test results. Summary of the Invention
[0008] Based on the principle of chemical probe method and from the perspective of catalyst poisoning reaction, this invention proposes a quantitative analysis method for measuring the catalyst active site concentration at the reaction temperature of the catalyst to address the problem that previous active site concentration measurement methods cannot be tested at the reaction temperature and fail to truly reflect the catalyst active site concentration.
[0009] The technical solution of the present invention:
[0010] A method for measuring active site concentration includes two steps: catalyst activity evaluation and catalyst adsorption measurement.
[0011] The first part is to evaluate the catalyst activity by changing the concentration of the poisoning gas to determine the concentration of the poisoning gas when the catalyst is deactivated; the second part is to measure the mass of the poisoning gas adsorbed by the catalyst under the actual conditions of the catalyst reaction based on the poisoning gas concentration determined by the catalyst activity evaluation;
[0012] Finally, based on the "platform" of the two curves, that is, the catalyst adsorption of CO2 reaches saturation, that is, the active sites of the catalyst are all occupied by CO2, the mass of the poisoning gas adsorbed by the catalyst is calculated, and then the concentration of the catalyst active sites is calculated.
[0013] Part I Catalyst Activity Evaluation
[0014] In the first step, an appropriate amount of catalyst was pressed into tablets, sieved, and 0.2 g of sample was selected and mixed with 2 g of quartz sand (the mass ratio of quartz sand to catalyst was 10:1). After mixing, the mixture was placed in a stainless steel tube.
[0015] In the second step, the stainless steel tube was installed in a micro fixed-bed reactor, and the temperature was raised to 550°C at a certain rate in a N2 atmosphere, stabilized for 10 minutes, then switched to air atmosphere for oxidation for 15 minutes, and then switched to N2 for stabilization for 30 minutes;
[0016] The third step is to control the total flow rate of the introduced gas to 100 mL / min, of which the propane flow rate accounts for 5 mL / min, and the total flow rate of carbon dioxide and nitrogen accounts for 95%, of which the concentration of carbon dioxide is 0%, and analyze and detect the reaction products using a gas chromatograph;
[0017] Step 4: After the reaction is completed, the catalyst is oxidized and stabilized according to the experimental operation shown in Step 2, and a mixture of N2 and CO2 with a CO2 volume concentration of 2% to 100% is introduced for reaction. This process is repeated as a cycle until the catalyst is no longer active. The CO2 concentration can be 2%, 5%, 10%, 20%, 30%, 50%, 70% and 100% in sequence.
[0018] The fifth step is to plot the catalyst activity against CO2 concentration based on the test results.
[0019] Part 2 Test of the adsorption capacity of the catalyst for the poisonous gas CO2
[0020] The first step is to weigh an appropriate amount of catalyst and place it in an intelligent gravimetric analyzer. First, evacuate the chamber, then heat it to 550°C and introduce a mixture of CO2 and N2 at a rate of 100 mL / min, with a CO2 concentration of 0%, until the mass stops increasing.
[0021] In the second step, after the adsorption was completed, the catalyst was oxidized with air for 15 min, then reduced with 5% H2 / Ar gas for 15 min, and finally purged with N2 for 30 min;
[0022] The third step is to evacuate the chamber and introduce a mixture of N2 and CO2 with a CO2 volume concentration of 2% to 100% for adsorption; the CO2 concentration can be 2%, 5%, 10%, 20%, 30%, 50%, 70% and 100% in sequence;
[0023] In the fourth step, after each adsorption, the oxidation, reduction, and N2 purge cycles are repeated until the mass of CO2 adsorbed by the catalyst no longer increases with the increase of CO2 concentration.
[0024] The fifth step is to plot the change in catalyst mass during the adsorption of CO2 at different concentrations.
[0025] The first part is to evaluate the catalyst activity by changing the concentration of the poisoning gas to determine the concentration of the poisoning gas when the catalyst is deactivated; the second part is to measure the mass of the poisoning gas adsorbed by the catalyst under the actual conditions of the catalyst reaction based on the poisoning gas concentration determined by the catalyst activity evaluation.
[0026] Finally, based on the "platform" of the two curves, that is, the catalyst adsorption of CO2 reaches saturation, the mass of the poisoning gas adsorbed by the catalyst can be calculated, and then the concentration of the catalyst active sites can be calculated.
[0027] The key technical points of the present invention are:
[0028] (1) Using an intelligent gravimetric analyzer to measure the amount of poisoning gas adsorbed by the catalyst, the active site concentration of the catalyst is calculated based on the specific adsorption of the poisoning gas by the active sites of the catalyst;
[0029] (2) The resolution of the intelligent gravimetric analyzer is the key, which can appropriately improve the sample quality and increase the gas adsorption capacity;
[0030] (3) During the catalyst activity test, the concentration of the reaction gas is the key to reduce the space velocity as much as possible and increase the propane conversion rate;
[0031] (4) During the adsorption of poisoning gas by the catalyst, the H2 / Ar reduction process is added, and the time should be long enough to ensure that the catalyst is completely reduced;
[0032] (5) During the catalyst activity test and the poisoning gas adsorption test, the total gas flow rate and the poisoning gas concentration must be consistent.
[0033] The technical effects of the present invention are as follows:
[0034] The adsorption method involved in the background knowledge for measuring the concentration of active sites of catalysts is the amount of gas adsorbed by the entire surface area of the catalyst, including both gas adsorbed at the active sites and gas adsorbed at the inactive sites. The test results are inaccurate. In the present invention, the catalyst-specific poisoning gas is used as a molecular probe, and only the active sites are adsorbed, so the measurement results are more accurate. The adsorption method, molecular probe method and electron microscopy technology mentioned in the background knowledge for measuring the concentration of active sites of catalysts are not carried out at the actual reaction temperature of the catalyst, while the present invention is carried out at the reaction temperature of the catalyst. The test results can truly reflect the performance of the catalyst, and have higher accuracy and application value, providing guidance for the design and preparation of high-performance catalysts with high active site utilization. BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Figure 1 is a flow chart of the present invention;
[0036] Figure 2 This is a graph showing the mass change of the catalyst GaZrO-0.4 during the adsorption process of the embodiment;
[0037] Figure 3 The relationship between the CO2 adsorption capacity and catalytic activity of the catalyst GaZrO-0.4 in the embodiment and the CO2 concentration;
[0038] Figure 4 This is a graph showing the mass change of the catalyst GaZrO-0.2 during the adsorption process of the embodiment;
[0039] Figure 5 The relationship between the CO2 adsorption capacity and catalytic activity of the catalyst GaZrO-0.2 in the embodiment and the CO2 concentration;
[0040] Figure 6 This is a graph showing the mass change of the catalyst ZrO2 during the adsorption process of the embodiment;
[0041] Figure 7 The relationship between the CO2 adsorption capacity and catalytic activity of the catalyst ZrO2 in the example and the CO2 concentration. DETAILED DESCRIPTION
[0042] The efficient and clean process of propane dehydrogenation to propylene (PDH) has gradually developed and become the main force in the expansion of propylene production capacity. Currently, commercial PDH catalysts are mainly Pt- and Cr-based catalysts. However, Pt is expensive and Cr is highly toxic, leading to a surge in research on catalysts based on other metals and their oxides. Among metal oxides, ZrOx-based catalysts have been shown to have high PDH activity, and Ga-doped ZrOx-based catalysts also exhibit high PDH activity. The method described in this invention was used to determine the active site concentration of these catalysts during the PDH process, achieving good results.
[0043] Example 1
[0044] Specific experimental plans include Figure 1 As shown, first, a GaZrO-0.4 catalyst was tested for activity. The catalyst was tableted and sieved, and 0.2g of 40-60 mesh was selected. This was then mixed with 2g of 40-60 mesh quartz sand (the quartz sand to catalyst mass ratio was 10:1). After mixing, the mixture was placed into a stainless steel tube. Next, the temperature was raised, and the catalyst was oxidized, stabilized, and reacted. In a micro-fixed-bed reactor, the temperature was raised to 550°C at a rate of 10°C / min under a nitrogen atmosphere. The temperature was stabilized for 10 minutes, then switched to air oxidation for 15 minutes, and then switched to nitrogen for stabilization for 30 minutes. The total flow rate of the introduced gas was controlled to be 100 mL / min, of which the propane flow rate was 5% (5 ml / min), the carbon dioxide and nitrogen flow rates were 95 mL / min, the carbon dioxide concentration was 0%, and the composition of the reaction product was analyzed by gas chromatography; after the reaction was completed, the catalyst was oxidized and stabilized, and mixed gases of different concentrations of CO2 (2%, 5%, 10%, 20%, 30%, 50%, 70% and 100%) were introduced for reaction, and this process was repeated as a cycle until the catalyst was no longer active.
[0045] Secondly, the catalyst's adsorption capacity for the poisoning gas CO2 was tested. 120mg of GaZrO-0.4 catalyst was weighed and placed in an intelligent gravimetric analyzer. The catalyst was first vacuumed, then heated to 550°C and fed with a mixed gas of CO2 and N2 at a total flow rate of 100mL / min, where the CO2 concentration was 0%, until the mass no longer increased. After adsorption was complete, the catalyst was first oxidized with air for 15 minutes, then reduced with 5% H2 / Ar gas for 15 minutes, and finally purged with N2 for 30 minutes. Subsequently, the catalyst was vacuumed, and a mixed gas of CO2 and N2 with different CO2 concentrations (2%, 5%, 10%, 20%, 30%, 50%, 70% and 100%) was introduced for adsorption. The catalyst was then subjected to cycles of oxidation, reduction, and N2 purge until the mass of CO2 adsorbed by the catalyst no longer increased with increasing CO2 concentrations. By plotting the change in catalyst mass during the adsorption of CO2 at different concentrations, it can be clearly observed that as the CO2 concentration increases, the amount of CO2 adsorbed by the catalyst increases until it no longer changes. Figure 2 shown.
[0046] Finally, the relationship between the CO2 adsorption amount per unit catalyst and the activity change under different CO2 concentrations is plotted. From the figure, it can be seen that both curves will eventually reach a "platform", that is, the catalyst adsorption of CO2 reaches saturation, and at the same time, the catalytic activity also drops to the lowest, see Figure 3The CO2 adsorption amount corresponding to the platform is the active site concentration per unit catalyst mass.
[0047] Example 2
[0048] First, the GaZrO-0.2 catalyst was tested for activity. The catalyst was tableted and sieved, and 0.2g of 40-60 mesh was selected. It was then mixed with 2g of 40-60 mesh quartz sand (the quartz sand to catalyst mass ratio was 10:1). After mixing, it was placed into a stainless steel tube. Next, the temperature was raised and the catalyst was oxidized, stabilized, and reacted. In a micro-fixed-bed reactor, the temperature was raised to 550°C at a rate of 10°C / min under a nitrogen atmosphere. The temperature was stabilized for 10 minutes, then switched to air oxidation for 15 minutes, and then switched to nitrogen for stabilization for 30 minutes. The total flow rate of the introduced gas was controlled to be 100 mL / min, of which the propane flow rate was 5% (5 ml / min), and the flow rates of carbon dioxide and nitrogen were 95 mL / min, of which the concentration of carbon dioxide was 0%. The composition of the reaction product was analyzed by gas chromatography. After the reaction was completed, the catalyst was oxidized and stabilized, and mixed gases of different concentrations of CO2 (2%, 5%, 10%, 20%, 30%, 50%, 70% and 100%) were introduced for reaction. This process was repeated as a cycle until the catalyst was no longer active.
[0049] Secondly, the catalyst's adsorption capacity for the poisoning gas CO2 was tested. 120mg of GaZrO-0.2 catalyst was weighed and placed in an intelligent gravimetric analyzer. The catalyst was first vacuumed, then heated to 550°C and fed with a mixed gas of CO2 and N2 at a total flow rate of 100mL / min, where the CO2 concentration was 0%, until the mass no longer increased. After adsorption was complete, the catalyst was first oxidized with air for 15 minutes, then reduced with 5% H2 / Ar gas for 15 minutes, and finally purged with N2 for 30 minutes. Subsequently, the catalyst was vacuumed, and a mixed gas of CO2 and N2 with different CO2 concentrations (2%, 5%, 10%, 20%, 30%, 50%, 70% and 100%) was introduced for adsorption. The catalyst was then subjected to cycles of oxidation, reduction, and N2 purge until the mass of the catalyst adsorbed CO2 did not increase as the CO2 concentration increased. By plotting the change in catalyst mass during the adsorption of CO2 at different concentrations, it can be clearly observed that as the CO2 concentration increases, the amount of CO2 adsorbed by the catalyst increases until it no longer changes. Figure 4 shown.
[0050] Finally, the relationship between the CO2 adsorption amount per unit catalyst and the activity change under different CO2 concentrations is plotted. From the figure, it can be seen that both curves will eventually reach a "plateau", that is, the catalyst will no longer adsorb CO2, and at the same time, the catalytic activity will also reach the lowest level, as shown in Figure 2. Figure 5The CO2 adsorption amount corresponding to the platform is the active site concentration per unit catalyst mass.
[0051] Example 3
[0052] First, a ZrO2 catalyst was tested for activity. The catalyst was tableted and sieved, and 0.2g of 40-60 mesh was selected. This was then mixed with 2g of 40-60 mesh quartz sand (with a quartz sand to catalyst mass ratio of 10:1). After mixing, the mixture was placed into a stainless steel tube. The temperature was then raised, and the catalyst was oxidized, stabilized, and reacted. In a micro-fixed-bed reactor, the temperature was raised to 550°C at a rate of 10°C / min under a nitrogen atmosphere. The temperature was stabilized for 10 minutes, then switched to air oxidation for 15 minutes, and then switched to nitrogen for stabilization for 30 minutes. The total flow rate of the introduced gas was controlled to be 100 mL / min, of which the propane flow rate was 5% (5 ml / min), and the flow rates of carbon dioxide and nitrogen were 95 mL / min, of which the concentration of carbon dioxide was 0%. The composition of the reaction product was analyzed by gas chromatography. After the reaction was completed, the catalyst was oxidized and stabilized, and a mixed gas with different CO2 concentrations (2%, 5%, 10%, 20%, 30%, 50%, 70% and 100%) was introduced for reaction. This process was repeated as a cycle until the catalyst was no longer active.
[0053] Secondly, the adsorption capacity of the catalyst to the poisoning gas CO2 was tested. 120mg of ZrO2 catalyst was weighed and placed in an intelligent gravimetric analyzer. The catalyst was first vacuumized, then heated to 550°C and fed with a mixed gas of CO2 and N2 at a total flow rate of 100mL / min, wherein the CO2 concentration was 0%, until the mass no longer increased. After adsorption was complete, the catalyst was first oxidized with air for 15 minutes, then reduced with 5% H2 / Ar gas for 15 minutes, and finally purged with N2 for 30 minutes. Subsequently, the catalyst was vacuumized and fed with mixed gases of CO2 and N2 of different CO2 concentrations (2%, 5%, 10%, 20%, 30%, 50%, 70% and 100%) for adsorption, followed by cycles of oxidation, reduction, and N2 purging, until the mass of the catalyst adsorbed CO2 did not increase with the increase in CO2 concentration. By plotting the change in catalyst mass during the adsorption of CO2 at different concentrations, it can be clearly observed that as the CO2 concentration increases, the amount of CO2 adsorbed by the catalyst increases until it no longer changes. Figure 6 shown.
[0054] Finally, the relationship between the CO2 adsorption amount per unit catalyst and the activity change under different CO2 concentrations is plotted. From the figure, it can be seen that both curves will eventually reach a "plateau", that is, the catalyst will no longer adsorb CO2, and at the same time, the catalytic activity will also reach the lowest level, as shown in Figure 2. Figure 7The CO2 adsorption amount corresponding to the platform is the active site concentration per unit catalyst mass.
Claims
1. A method for measuring active site concentration, characterized in that: It includes two parts: catalyst activity evaluation and catalyst adsorption measurement. The first part is to evaluate the catalyst activity by changing the concentration of the poisoning gas to determine the concentration of the poisoning gas when the catalyst is deactivated. The second part is to determine the concentration of poisoning gas based on the evaluation of catalyst activity and measure the mass of poisoning gas adsorbed by the catalyst under the real conditions of the catalyst reaction; Finally, based on the "platform" of the two curves, that is, the catalyst adsorption of CO2 reaches saturation, the mass of the poisoning gas adsorbed by the catalyst is calculated, and then the concentration of the catalyst active sites is calculated.
2. The method for measuring active site concentration according to claim 1, wherein: The first part of the catalyst activity evaluation specifically includes the following steps: In the first step, an appropriate amount of catalyst is pressed into tablets, sieved, and the catalyst sample is mixed with quartz sand at a mass ratio of quartz sand to catalyst of 10:
1. After mixing, the mixture is placed in a stainless steel tube. In the second step, the stainless steel tube was installed in a micro fixed-bed reactor, and the temperature was raised to 550°C at a certain rate in a N2 atmosphere, stabilized for 10 minutes, then switched to air atmosphere for oxidation for 15 minutes, and then switched to N2 for stabilization for 30 minutes; The third step is to control the total flow rate of the introduced gas to 100 mL / min, of which the propane flow rate accounts for 5%, the total flow rate of the nitrogen and CO2 mixed gas accounts for 95%, and the CO2 concentration is 0%. The reaction products are analyzed and detected by gas chromatography; In the fourth step, after the reaction is completed, the catalyst is oxidized and stabilized according to the experimental operation shown in the second step, and a mixture of N2 and CO2 with a CO2 volume concentration of 2% to 100% is introduced to react, and this process is repeated for the experiment until the catalyst is no longer active. The fifth step is to plot the catalyst activity against the CO2 gas concentration based on the test data.
3. The method for measuring active site concentration according to claim 1, wherein: The second part is the test of the adsorption capacity of the catalyst on the poisoning gas CO2, which specifically includes the following steps: In the first step, an appropriate amount of catalyst was weighed and placed in an intelligent gravimetric analyzer. The system was first vacuumed, then heated to 550°C and nitrogen was introduced at a rate of 100 mL / min until the mass stopped increasing. In the second step, after the adsorption was completed, the catalyst was oxidized with air for 15 min, then reduced with 5% H2 / Ar gas for 15 min, and finally purged with N2 for 30 min; The third step is to evacuate the chamber and introduce a mixture of N2 and CO2 with a CO2 volume concentration of 2% to 100% for adsorption. In the fourth step, after each adsorption, the oxidation, reduction, and N2 purge cycles are repeated until the mass of CO2 adsorbed by the catalyst no longer increases with the increase of CO2 concentration; The fifth step is to plot the change in catalyst mass during the adsorption of CO2 at different concentrations.