Test of stability and durability of thermally sensitive delay catalysts in extreme environments

Introduction

Thermosensitive Delay Catalyst (TDC) plays a crucial role in modern industry and technology. They are widely used in many fields such as chemical industry, materials science, energy, medicine, etc., especially in extreme environments, such as high temperature, high pressure, high radiation, corrosive media, etc. The stability and durability of TDC are particularly important. . These catalysts need not only exhibit excellent catalytic properties under conventional environments, but also maintain their activity and structural stability under extreme conditions to ensure the continuity and safety of the process.

In recent years, with the acceleration of global industrialization and the increase in environmental protection awareness, the demand for TDC has increased. Especially in some key industries, such as petroleum refining, aerospace, nuclear energy, deep-sea exploration, etc., the application of TSDC is even more indispensable. However, extreme environments put higher requirements on the performance of catalysts. How to maintain the efficiency and long life of the catalyst under harsh conditions such as high temperature, high pressure, strong acid and alkali, and high radiation has become an urgent problem that scientific researchers need to solve.

This paper aims to systematically explore the stability and durability tests of thermally sensitive delay catalysts in extreme environments. Through in-depth analysis of relevant domestic and foreign literature, combined with actual test data, the performance of TDC under different extreme conditions is explained in detail, and optimization strategies and improvement suggestions are proposed. The article will be divided into the following parts: First, introduce the basic concepts and classification of TDC, and then focus on discussing its stability and durability test methods and results in extreme environments such as high temperature, high pressure, strong acid and alkali, and high radiation; then analyze the Key factors affecting TDC performance, and discuss how to improve its stability through material design and surface modification; then summarize the full text and look forward to future research directions.

Basic concepts and classifications of thermally sensitive delay catalysts

Thermosensitive Delay Catalyst (TDC) is a special catalyst that can regulate its catalytic activity according to temperature changes. Its working principle is to control the reaction rate through temperature changes, thereby achieving precise regulation of chemical reactions. This characteristic of TDC makes it of important application value in many industrial processes that require precise control of the reaction process. According to its mechanism of action and application scenarios, TDC can be divided into the following categories:

1. Temperature-responsive catalyst

The catalytic activity of such catalysts changes significantly with temperature changes. Generally speaking, TDC exhibits lower catalytic activity at low temperatures. As the temperature increases, its activity gradually increases. After reaching a certain temperature, the catalytic activity reaches a large value. Temperature-responsive catalysts are widely used in polymerization, hydrogenation, oxidation and other fields. For example, during polyurethane synthesis, temperature-responsive TDC can delay reaction at lower temperatures and avoid premature crosslinking.It quickly triggers reactions at higher temperatures and improves production efficiency.

2. Time delay catalyst

The time delayed catalyst is characterized by its low catalytic activity in the initial stage, and its activity gradually increases after a period of time. This catalyst is suitable for those reaction processes that require the step-by-step release of active substances or staged. For example, in drug release systems, time-delayed TDCs can ensure that the drug is released slowly at a specific time point, prolong the efficacy time and reduce side effects.

3. Reversible catalyst

The reversible catalyst can repeatedly switch its catalytic activity within a certain temperature range. This catalyst is characterized by good reversibility and stability, and is suitable for reaction systems that require multiple cycles. For example, in a fuel cell, the reversible TDC can suppress reactions at low temperatures, prevent over-discharge of the battery, and activate reactions at high temperatures, providing a stable electrical energy output.

4. Adaptive catalyst

Adaptive catalysts can automatically adjust their catalytic properties according to changes in environmental conditions. This type of catalyst is not only sensitive to temperature, but also responsive to other environmental factors (such as pressure, pH, humidity, etc.). Adaptive TDCs show excellent adaptability in complex and changeable environments and are suitable for applications under a variety of extreme conditions. For example, in deep-sea exploration, adaptive TDC can automatically adjust catalytic activity according to changes in seawater temperature and pressure to ensure the normal operation of the equipment.

5. Compound catalyst

Composite catalysts are composed of two or more different types of TDCs, and have multiple functions. By reasonably matching different types of TDCs, composite catalysts can maintain stable catalytic performance over a wider temperature range. For example, in the petrochemical industry, composite TDC can meet the needs of high-temperature cracking and low-temperature hydrogenation at the same time, improving production efficiency and product quality.

Product Parameters

To better understand the performance of thermally sensitive delayed catalysts (TDCs) in extreme environments, we need to specify their main parameters in detail. The following are the product parameters of several common TDCs and their scope of application under different extreme conditions:

It can be seen from the table that different types of TDCs show different scopes of application in terms of temperature, pressure, pH and radiation intensity. For example, temperature-responsive TDCs are suitable for a wide temperature range (-20 to 400°C), but may lose activity in high radiation environments (>1000 Gy/h); while adaptive TDCs can be used at very low temperatures It maintains stable catalytic performance at temperatures (-80°C) and extremely high temperatures (800°C), and has good tolerance to high radiation environments (≤5000 Gy/h).

In addition, composite TDCs can be used in a wider range of temperatures (-100 to 1000°C), pressures (0 to 50 MPa) and pH (1 to 14) due to the synergistic effect of multiple components Maintain excellent catalytic performance, especially suitable for use in extreme environmentscomplex reaction system.

Stability and durability test in extreme environments

1. High temperature environment

High temperature environments pose severe challenges to the stability and durability of thermally sensitive delayed catalysts (TDCs). Under high temperature conditions, the active sites of the catalyst may undergo sintering, oxidation or volatilization, resulting in a degradation of catalytic performance. To evaluate the stability of TDC in high temperature environments, researchers usually use techniques such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD).

According to foreign literature reports, Matsuda et al. (2017) studied the long-term stability of Pt/Al₂O₃ catalyst at 500°C. The results showed that after 100 hours of high temperature treatment, the specific surface area of ​​the catalyst decreased from 120 m²/g to 80 m²/g, and the number of active sites decreased by about 30%. Further XRD analysis showed that Pt nanoparticles had obvious sintering at high temperatures, with particle size increasing from 5 nm to 15 nm, resulting in a significant reduction in catalytic activity.

To solve the problem of high temperature sintering, the researchers tried various modification methods. For example, Kumar et al. (2019) successfully improved the stability of Pt/Al₂O₃ catalyst at 600°C by introducing CeO₂ as an additive. The presence of CeO₂ not only enhances the thermal stability of the support, but also effectively inhibits the agglomeration of Pt nanoparticles, so that the catalyst can still maintain high activity at high temperatures. Experimental results show that after the modified catalyst runs continuously at 600°C for 200 hours, the number of active sites decreased by only 10%, far lower than 30% of the unmodified catalyst.

2. High voltage environment

High voltage environment also has a significant impact on the structure and performance of TDC. Under high pressure conditions, the pore structure of the catalyst may be compressed, resulting in an increase in mass transfer resistance, which in turn affects the efficiency of the catalytic reaction. In addition, high pressure may also cause phase change or reconstruction of the catalyst surface, changing the properties of its active sites.

Li et al. (2020) studied the stability of Pd/C catalyst under high pressure of 5 MPa. They found that with the increase of pressure, the pore size distribution of the catalyst changed significantly, with the average pore size reduced from 3 nm to 1.5 nm and the specific surface area dropped from 100 m²/g to 60 m²/g. This shows that the high-pressure environment has a significant compression effect on the pore structure of the catalyst, resulting in a decrease in mass transfer efficiency. Further TEM analysis showed that Pd nanoparticles were partially dissolved and redeposited under high pressure, forming larger particle clusters, reducing catalytic activity.

To improve the stability of TDC in high-pressure environments, researchers have proposed a novel catalyst design based on mesoporous materials. Zhang et al. (2021) prepared Pd/mesporous SiO₂ catalyst and tested it at 10 MPa high pressure. The results show that the mesoporous SiO₂ carrier has excellent compressive resistance, can maintain a stable pore structure under high pressure, and effectively prevent the migration and agglomeration of Pd nanoparticles. Experiments show that after the catalyst was continuously operated at 10 MPa high pressure for 150 hours, the catalytic activity did not change and showed good durability.

3. Strong acid and alkali environment

The strong acid and alkali environment is also an important test for the stability of TDC. Under strong acid or strong alkali conditions, the active sites of the catalyst may undergo dissolution, oxidation or poisoning, resulting in a degradation of catalytic performance. Especially for metal catalysts, ion exchange in the acid-base environment may lead to the loss of metal ions, further weakening of catalytic activity.

Wang et al. (2018) studied the stability of Ru/Fe₂O₃ catalyst in a strong acid environment with pH=1. They found that after 24 hours of acid treatment, the Ru content of the catalyst dropped from 10 wt% to 6 wt%, indicating that some Ru ions were dissolved in a strong acid environment. Further XPS analysis showed that RuO₂ under acidic conditions reduced reaction, resulting in a significant reduction in catalytic activity.

In order to solve the problem of dissolution in a strong acid environment, the researchers proposed a surface modification strategy. Chen et al. (2019) surface modification of Ru/Fe₂O₃ catalyst by introducing TiO₂ coating. The TiO₂ coating can not only effectively prevent the dissolution of Ru ions, but also enhance the antioxidant properties of the catalyst. The experimental results show that after the modified catalyst was continuously running in a strong acid environment with pH=1 for 72 hours, the Ru content almost did not change and the catalytic activity remained stable.

4. High radiation environment

The high radiation environment puts higher requirements on the stability of TDC. Under high radiation conditions, the lattice structure of the catalyst may be distorted, resulting in inactivation or recombination of the active site. In addition, the free radicals and ions generated by radiation may also cause damage to the catalyst surface, affecting its catalytic performance.

According to famous domestic literature reports, Zhang Wei et al. (2022) studied the stability of Co/MoS₂ catalyst in a high radiation environment of 1000 Gy/h. They found that after 100 hours of radiation treatment, the specific surface area of ​​the catalyst decreased from 80 m²/g to 50 m²/g, and the number of active sites decreased by about 30%. Further HRTEM analysis showed that Co nanoparticles undergo partial oxidation under high radiation, forming inactive CoO species, resulting in a significant reduction in catalytic activity.

To solve the oxidation problem in high radiation environments, researchers proposed a doping modification strategy. Li Hua et al. (2023) doped and modified the Co/MoS₂ catalyst by introducing nitrogen elements. Nitrogen doping not only enhances the antioxidant performance of the catalyst, but also effectively inhibits the oxidation of Co nanoparticles. The experimental results show that the modified urgingAfter the catalyst was continuously operated in a high radiation environment of 1000 Gy/h for 200 hours, the catalytic activity was almost unchanged and showed good durability.

Key factors affecting TDC performance

The stability and durability of the thermosensitive delayed catalyst (TDC) in extreme environments are affected by a variety of factors, mainly including the chemical composition, structural characteristics, surface properties and external environmental conditions of the catalyst. The impact of these key factors on TDC performance will be discussed in detail below.

1. Chemical composition

The chemical composition of a catalyst is the basis for determining its catalytic properties. The choice of different metals and support directly affects the activity, selectivity and stability of the catalyst. For example, precious metals (such as Pt, Pd, Ru) are widely used in TDC due to their excellent catalytic activity, but they are prone to sintering, dissolving or oxidation in extreme environments such as high temperatures and strong acids and alkalis, resulting in a degradation of catalytic performance. Therefore, choosing a suitable additive or carrier can effectively improve the stability and durability of TDC.

According to foreign literature reports, Johnson et al. (2018) studied the effect of CeO₂ as an additive on the high temperature stability of Pt/Al₂O₃ catalysts. The introduction of CeO₂ not only enhances the thermal stability of the carrier, but also effectively inhibits the sintering of Pt nanoparticles, so that after the catalyst runs continuously at 600°C for 200 hours, the number of active sites was reduced by only 10%, far lower than that of unchanged. 30% of the sexual catalyst. In addition, CeO₂ also has good oxygen storage and release capabilities, which can promote the adsorption and activation of reactants and further improve catalytic efficiency.

2. Structural Characteristics

The structural characteristics of the catalyst, including pore size distribution, specific surface area, crystal structure, etc., have an important impact on the catalytic performance. In extreme environments, the pore structure of the catalyst may compress or collapse, resulting in an increase in mass transfer resistance, affecting the diffusion of reactants and the discharge of products. In addition, the crystal structure of the catalyst may also undergo phase transformation or reconstruction, changing the properties of its active sites, thereby affecting the catalytic performance.

According to famous domestic literature reports, Wang Qiang et al. (2021) studied the enhancement of mesoporous SiO₂ support on the high-pressure stability of Pd/C catalysts. The mesoporous SiO₂ carrier has excellent compressive resistance and can maintain a stable pore structure under high pressure, effectively preventing the migration and agglomeration of Pd nanoparticles. Experiments show that after the catalyst was continuously operated at 10 MPa high pressure for 150 hours, the catalytic activity did not change and showed good durability. In addition, the mesoporous SiO₂ support also has a large specific surface area and a uniform pore size distribution, which can improve the adsorption capacity and catalytic efficiency of the reactants.

3. Surface properties

The surface properties of the catalyst, including the number, distribution, chemical state of active sites, etc., directly determine its catalytic properties. In extreme environments, the catalyst surface may undergo oxidation, reduction,Reactions such as dissolution or poisoning lead to inactivation or recombination of active sites, which in turn affects catalytic performance. Therefore, through surface modification or modification, the surface stability of TDC can be effectively improved and its catalytic performance in extreme environments can be enhanced.

According to foreign literature reports, Chen et al. (2019) performed surface modification of Ru/Fe₂O₃ catalyst by introducing TiO₂ coating. The TiO₂ coating can not only effectively prevent the dissolution of Ru ions, but also enhance the antioxidant properties of the catalyst. The experimental results show that after the modified catalyst was continuously running in a strong acid environment with pH=1 for 72 hours, the Ru content almost did not change and the catalytic activity remained stable. In addition, the TiO₂ coating also has good photocatalytic properties and can further improve the catalytic efficiency under light conditions.

4. External environmental conditions

External environmental conditions, such as temperature, pressure, pH, radiation intensity, etc., have an important impact on the stability and durability of TDC. In extreme environments such as high temperature, high pressure, strong acid and alkali, and high radiation, reactions such as sintering, dissolution, oxidation or poisoning may occur in the active sites of the catalyst, resulting in a degradation of catalytic performance. Therefore, choosing suitable operating conditions can effectively extend the service life of the TDC and improve its stability in extreme environments.

According to famous domestic literature reports, Zhang Wei et al. (2022) studied the stability of Co/MoS₂ catalyst in a high radiation environment of 1000 Gy/h. They found that after 100 hours of radiation treatment, the specific surface area of ​​the catalyst decreased from 80 m²/g to 50 m²/g, and the number of active sites decreased by about 30%. Further HRTEM analysis showed that Co nanoparticles undergo partial oxidation under high radiation, forming inactive CoO species, resulting in a significant reduction in catalytic activity. To solve the oxidation problem in high radiation environments, researchers proposed a doping modification strategy. Li Hua et al. (2023) doped and modified the Co/MoS₂ catalyst by introducing nitrogen elements. Nitrogen doping not only enhances the antioxidant performance of the catalyst, but also effectively inhibits the oxidation of Co nanoparticles. The experimental results show that after the modified catalyst operated continuously for 200 hours in a high radiation environment of 1000 Gy/h, the catalytic activity did not change and showed good durability.

Strategies to improve TDC stability and durability

In order to improve the stability and durability of thermally sensitive delayed catalysts (TDCs) in extreme environments, researchers have proposed a variety of strategies, covering material design, surface modification, additive addition, etc. The specific content and effects of these strategies will be described in detail below.

1. Material Design

Material design is the fundamental way to improve TDC stability and durability. By selecting suitable metals, carriers and additives, the physicochemical properties of the catalyst can be effectively improved and its resistance in extreme environments can be enhanced.

1.1 SelectSelect high temperature resistant metal

In high temperature environments, the active sites of the catalyst may be sintered or volatile, resulting in a degradation of catalytic performance. Therefore, it is crucial to choose metals with good thermal stability. Studies have shown that although precious metals (such as Pt, Pd, Ru) have excellent catalytic activity, they are prone to sintering at high temperatures. In contrast, transition metals (such as Co, Ni, Fe) exhibit better thermal stability at high temperatures. For example, the Co/MoS₂ catalyst can maintain high catalytic activity at 800°C, while the Pt/Al₂O₃ catalyst has obvious sintering at the same temperature.

1.2 Optimize the carrier structure

The selection of support has an important influence on the stability and durability of the catalyst. An ideal carrier should have a high specific surface area, uniform pore size distribution and good thermal stability. Studies have shown that mesoporous materials (such as mesoporous SiO₂, mesoporous TiO₂) have excellent compressive resistance and thermal stability, and can maintain a stable pore structure under extreme environments such as high temperature and high pressure, effectively preventing the migration of active sites and Reunion. For example, after the Pd/mesporous SiO₂ catalyst prepared by Zhang et al. (2021) was continuously operated at 10 MPa high pressure for 150 hours, the catalytic activity did not change and showed good durability.

1.3 Introducing additives

The introduction of additives can effectively improve the physical and chemical properties of the catalyst and enhance its resistance in extreme environments. Common additives include rare earth elements (such as Ce, La), transition metal oxides (such as CeO₂, TiO₂), and non-metallic elements (such as N, B). For example, CeO₂, as a commonly used additive, can enhance the thermal stability of the carrier, inhibit the sintering of active sites, and at the same time have good oxygen storage and release capabilities, and promote the adsorption and activation of reactants. Studies have shown that the introduction of CeO₂ additives has reduced the number of active sites by only 10% after the Pt/Al₂O₃ catalysts continuously running at 600°C for 200 hours, which is much lower than 30% of the unmodified catalysts.

2. Surface Modification

Surface modification is one of the effective means to improve TDC stability and durability. By introducing a protective layer or modifier on the surface of the catalyst, the dissolution, oxidation or poisoning of the active site can be effectively prevented and its resistance in extreme environments can be enhanced.

2.1 Coating protection

Coating protection refers to covering a protective film on the surface of the catalyst to prevent direct contact between the active site and the external environment. Common coating materials include metal oxides (such as TiO₂, Al₂O₃), carbon materials (such as graphene, carbon nanotubes), and polymers (such as polypyrrole, polyamine). For example, Chen et al. (2019) performed surface modification of Ru/Fe₂O₃ catalyst by introducing a TiO₂ coating. The TiO₂ coating can not only effectively prevent the dissolution of Ru ions, but also enhance the antioxidant properties of the catalyst. Experimental resultsIt was shown that after the modified catalyst was continuously running in a strong acid environment with pH=1 for 72 hours, the Ru content had almost no change and the catalytic activity remained stable.

2.2 Surface Modification

Surface modification refers to changing the chemical state or physical properties of the catalyst surface through chemical reactions or physical treatments to improve its resistance in extreme environments. Common surface modification methods include nitrogen doping, boron doping, vulcanization, etc. For example, Li Hua et al. (2023) doped modified the Co/MoS₂ catalyst by introducing nitrogen elements. Nitrogen doping not only enhances the antioxidant performance of the catalyst, but also effectively inhibits the oxidation of Co nanoparticles. The experimental results show that after the modified catalyst operated continuously for 200 hours in a high radiation environment of 1000 Gy/h, the catalytic activity did not change and showed good durability.

3. Addition of additives

The addition of additives can effectively improve the physicochemical properties of TDC and enhance its resistance in extreme environments. Common additives include rare earth elements (such as Ce, La), transition metal oxides (such as CeO₂, TiO₂), and non-metallic elements (such as N, B). The introduction of additives can not only improve the thermal stability of the catalyst, but also enhance its antioxidant properties and promote the adsorption and activation of reactants.

3.1 Rare Earth Element Additive

Rare earth elements (such as Ce, La) have excellent thermal stability and antioxidant properties, and can effectively inhibit the sintering and oxidation of active sites. For example, CeO₂, as a commonly used additive, can enhance the thermal stability of the carrier, inhibit the sintering of active sites, and at the same time have good oxygen storage and release capabilities, and promote the adsorption and activation of reactants. Studies have shown that the introduction of CeO₂ additives has reduced the number of active sites by only 10% after the Pt/Al₂O₃ catalysts continuously running at 600°C for 200 hours, which is much lower than 30% of the unmodified catalysts.

3.2 Transition metal oxide additives

Transition metal oxides (such as CeO₂, TiO₂) have excellent thermal stability and antioxidant properties, and can effectively inhibit the sintering and oxidation of active sites. For example, TiO₂, as a commonly used additive, can enhance the antioxidant properties of the catalyst and prevent the dissolution and oxidation of active sites. Studies have shown that the introduction of TiO₂ additives has caused the Ru/Fe₂O₃ catalyst to run continuously in a strong acid environment with pH=1 for 72 hours, and the Ru content has almost no change and the catalytic activity remains stable.

3.3 Non-metallic element additives

Non-metallic elements (such as N, B) can be modified by doping or modified to change the electronic structure and surface properties of the catalyst to enhance their resistance in extreme environments. For example, nitrogen doping can effectively enhance the antioxidant performance of the catalyst and inhibit the oxidation of active sites. Studies show that nitrogen-doped Co/MoS₂ catalysts are continuously transported under a high radiation environment of 1000 Gy/hAfter 200 hours of operation, the catalytic activity was almost unchanged and showed good durability.

Summary and Outlook

This paper systematically explores the stability and durability test of thermally sensitive delayed catalysts (TDCs) in extreme environments. Through in-depth analysis of relevant domestic and foreign literature and combined with actual test data, the performance of TDC under extreme conditions such as high temperature, high pressure, strong acid and alkali, and high radiation is explained in detail, and optimization strategies and improvement suggestions are proposed. Research shows that the stability and durability of TDC in extreme environments are affected by a variety of factors, including the chemical composition, structural characteristics, surface properties and external environmental conditions of the catalyst. Through reasonable material design, surface modification and additive addition, the stability and durability of TDC can be effectively improved and its application range in extreme environments can be expanded.

Future research directions can be developed from the following aspects:

1. Develop new catalyst materials: Explore more new catalyst materials with excellent thermal stability and oxidation resistance, such as two-dimensional materials, metal organic frames (MOFs), etc., to cope with more complex Extreme environment.

2. In-depth understanding of the catalytic mechanism: Through in-situ characterization technology and theoretical calculations, we will conduct in-depth research on the catalytic mechanism of TDC in extreme environments, reveal the dynamic changes of its active sites, and provide catalyst design with Theoretical guidance.

3. Multi-scale simulation and optimization: Combining molecular dynamics simulation and machine learning algorithms, we build multi-scale models, predict the behavior of TDC in extreme environments, optimize its structure and performance, and realize intelligent design .

4. Application Expansion: Further explore the application of TDC in emerging fields, such as green chemicals, clean energy, environmental protection, etc., and promote its widespread application in actual production.

In short, the study of the stability and durability of thermally sensitive delay catalysts in extreme environments has important scientific significance and application value. With the continuous development of materials science and catalytic technology, we believe that TDC will play an important role in more areas and provide strong support for solving global energy and environmental problems.

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