Introduction
As the acceleration of global industrialization, the emission of volatile organic compounds (VOCs) is attracting increasing attention. VOCs refer to a type of organic compounds with a higher vapor pressure at room temperature. They not only cause pollution to the environment, but also have potential harm to human health. Studies have shown that VOCs react photochemically with pollutants such as nitrogen oxides (NOx) in the atmosphere, forming ozone (O₃), causing deterioration of air quality, and thus causing a series of health problems such as respiratory diseases and cardiovascular diseases. In addition, VOCs are also an important part of greenhouse gases, and their emissions have also had an important impact on global climate change.
To address this challenge, governments and environmental protection agencies have introduced strict emission standards and control measures. For example, the U.S. Environmental Protection Agency (EPA) has formulated the Clean Air Act, which stipulates emission limits for VOCs; the EU has passed the Industrial Emissions Directive (IED) and the Solvent Emissions Directive (SED) Other regulations require enterprises to reduce VOCs emissions. China also clearly stated in the "Action Plan for Air Pollution Prevention and Control" (hereinafter referred to as "Ten Atmospheric Measures") and the "Three-Year Action Plan for Winning the Battle of Blue Sky" that it is necessary to strengthen the governance of VOCs and promote the application of green production and clean technology.
In this context, thermis-sensitive delay catalyst, as a new VOCs emission reduction technology, has gradually attracted widespread attention. Thermal-sensitive delayed catalyst delays the occurrence of catalytic reactions by adjusting the reaction temperature and time, thereby effectively reducing the generation and emission of VOCs. This technology is not only suitable for petrochemicals, coatings, printing and other industries, but can also play an important role in automotive exhaust treatment and indoor air purification. This article will discuss in detail the product parameters, working principles, application effects of the thermally sensitive delay catalyst, and combine with relevant domestic and foreign literature to comprehensively evaluate its effectiveness in reducing VOCs emissions.
The working principle of thermally sensitive delay catalyst
Thermal-sensitive delay catalyst is a catalyst based on temperature sensitivity. Its core lies in the precise control of the reaction temperature and time, and the occurrence of catalytic reactions is delayed, thereby reducing the generation and emission of VOCs. Unlike traditional catalysts, the thermally sensitive delayed catalyst exhibits lower activity under low temperature conditions. As the temperature increases, its activity gradually increases, and finally achieves the best catalytic effect within a specific temperature range. This temperature-dependent catalytic behavior allows the thermally sensitive delayed catalyst to effectively reduce VOCs emissions without affecting production efficiency.
1. Temperature sensitivity
The temperature sensitivity of the thermally sensitive delay catalyst is one of its significant features. Generally, the activity of a catalyst is closely related to the number of reactant molecules adsorbed on its surface, and the adsorption amount depends on the temperature. For a thermosensitive delay catalyst, its surfactant site is partially employed at low temperaturesInhibition makes it difficult for reactant molecules to adsorption, thereby delaying the initiation of catalytic reactions. As the temperature increases, the active sites on the catalyst surface gradually unblock, reactant molecules begin to adsorb in large quantities and participate in the reaction, and the catalytic activity also increases.
Study shows that the temperature sensitivity of the thermally sensitive delayed catalyst can be achieved by adjusting the composition and structure of the catalyst. For example, adding an appropriate amount of transition metal oxide (such as alumina, titanium oxide, etc.) can improve the thermal stability of the catalyst and extend its service life at high temperatures; while introducing rare earth elements (such as lanthanum, cerium, etc.) can adjust the catalyst the electronic structure enhances its selective adsorption and conversion capabilities of VOCs. These modification methods not only improve the performance of the catalyst, but also provide more possibilities for its application under different operating conditions.
2. Delay effect
Another important characteristic of a thermosensitive delay catalyst is its delay effect, that is, the occurrence of a catalytic reaction is suppressed within a certain period of time, and then the reaction is quickly initiated under certain conditions. This delay effect can be achieved by regulating the pore structure and surface properties of the catalyst. Specifically, the pore size and distribution of the catalyst directly affect the diffusion rate of reactant molecules. Smaller pore size can slow down the entry of reactant molecules, thereby delaying the occurrence of reactions; while larger pore sizes are conducive to the rapidity of reactant molecules. diffusion, promote the progress of the reaction. In addition, functional groups (such as hydroxyl groups, carboxyl groups, etc.) on the surface of the catalyst can also have weak interactions with reactant molecules, further delaying the initiation of the reaction.
Experimental results show that the retardation effect of the thermally sensitive delay catalyst is closely related to its pore structure and surface properties. For example, Li et al. (2018) found that the thermosensitive delay catalyst using mesoporous silica as a support showed a significant delay effect under low temperature conditions, while the reaction was quickly initiated under high temperature conditions, showing excellent results. catalytic properties. This shows that by rationally designing the pore structure and surface properties of the catalyst, its delay effect can be effectively regulated, thereby achieving precise control of VOCs emissions.
3. Selective Catalysis
In addition to temperature sensitivity and delay effects, the thermally sensitive delay catalyst also has good selective catalytic properties. Selective catalysis refers to the ability of a catalyst to preferentially promote the occurrence of a certain type of reaction and inhibit other side reactions. Selective catalysis is particularly important for the reduction of VOCs, because it can avoid unnecessary by-product generation and improve the conversion rate and removal efficiency of VOCs.
Study shows that the selective catalytic properties of thermally sensitive delayed catalysts are closely related to the geometric configuration and electronic structure of their active sites. For example, Zhang et al. (2019) found through density functional theory (DFT) calculations that thermally sensitive delay catalysts containing copper-zinc bimetallic active sites have high selectivity for VOCs-like and can be used at lower temperatures Convert it completely into carbon dioxide and water without producingHarmful intermediates. In addition, Liu et al. (2020)'s research also shows that the electronic structure of the catalyst can be effectively regulated by introducing nitrogen doping, enhancing its selective catalytic performance for aromatic VOCs.
To sum up, thermally sensitive delay catalysts can effectively reduce the generation and emission of VOCs without affecting production efficiency through mechanisms such as temperature sensitivity, delay effect and selective catalysis. Its unique catalytic behavior not only provides new ideas for VOCs emission reduction, but also brings new opportunities for green production and technological upgrading in the industrial field.
Product parameters of thermally sensitive delay catalyst
To better understand and evaluate the application effect of thermally sensitive delay catalysts in reducing VOCs emissions, it is crucial to understand their specific product parameters. The following are the main parameters and performance characteristics of several common thermally sensitive delay catalysts for reference.
1. Catalyst Type
Depending on different application scenarios and needs, thermally sensitive delay catalysts can be divided into many types, mainly including the following categories:
| Catalytic Type | Main Ingredients | Application Fields | Features |
|---|---|---|---|
| Metal oxide catalyst | Alumina, titanium oxide, cerium oxide, etc. | Petrochemical, coatings, printing | High thermal stability, long life, suitable for high temperature environments |
| Naught Metal Catalyst | Platinum, palladium, rhodium, etc. | Auto exhaust treatment, indoor air purification | High activity, high selectivity, suitable for low temperature environments |
| Bimetal Catalyst | Copper-zinc, iron-manganese, etc. | Chemical waste gas treatment, industrial waste gas purification | High activity, low cost, suitable for complex exhaust gas environments |
| Nitrogen doped catalyst | Natural doped carbon materials, nitrogen doped metal oxides | Indoor air purification, electronics industry | High specific surface area, good conductivity, suitable for low concentration VOCs |
2. Temperature range
The temperature sensitivity of the thermally sensitive delayed catalyst determines its catalytic performance under different temperature conditions. Generally, the temperature range of the thermally sensitive delay catalyst can be adjusted according to the specific application scenario to meet different process requirements. The following are the temperature ranges of several common thermally sensitive delay catalystsSurrounding and applicable scenarios:
| Catalytic Type | Temperature range (℃) | Applicable scenarios |
|---|---|---|
| Metal oxide catalyst | 250-450 | High temperature processes such as petrochemicals, coatings, printing and other products |
| Naught Metal Catalyst | 150-300 | Low-temperature processes such as automobile exhaust treatment and indoor air purification |
| Bimetal Catalyst | 200-400 | Medium temperature processes such as chemical waste gas treatment, industrial waste gas purification |
| Nitrogen doped catalyst | 100-250 | Low-temperature processes such as indoor air purification, electronics industry |
3. Hole structure
The pore structure of the catalyst has an important influence on its catalytic performance. The pore structures of thermally sensitive delay catalysts usually include three types: micropores, mesopores and macropores. Different types of pore structures play different roles in the adsorption and diffusion process. The following are the pore structure parameters and performance characteristics of several common thermally sensitive delay catalysts:
| Catalytic Type | Pore size (nm) | Specific surface area (m²/g) | Hole capacity (cm³/g) | Performance Features |
|---|---|---|---|---|
| Metal oxide catalyst | 2-50 | 50-200 | 0.1-0.5 | Suitable for high temperature environments, with good thermal stability and mechanical strength |
| Naught Metal Catalyst | 1-10 | 100-300 | 0.2-0.6 | Suitable for low temperature environments, with high activity and high selectivity |
| Bimetal Catalyst | 5-100 | 150-400 | 0.3-0.8 | Suitable for medium temperature environments, high activity and low cost |
| Nitrogen doped catalyst | 1-50 | 200-500 | 0.4-0.9 | Suitable for low temperature environments, with high specific surface area and good conductivity |
4. Surface properties
The surface properties of the catalyst directly affect its adsorption and catalytic properties on reactant molecules. The surface properties of the thermally sensitive retardant catalyst usually include functional groups, acid and alkalinity, surface roughness, etc. The following are the surface properties parameters and their performance characteristics of several common thermally sensitive delay catalysts:
| Catalytic Type | Featured Group | Acidality | Surface Roughness (nm) | Performance Features |
|---|---|---|---|---|
| Metal oxide catalyst | Hydroxy, carboxy | Neutral or weakly acidic | 10-50 | Suitable for high temperature environments, with good adsorption performance and thermal stability |
| Naught Metal Catalyst | Hydroxy, carbonyl | Weak alkaline | 5-20 | Suitable for low temperature environments, with high activity and high selectivity |
| Bimetal Catalyst | Hydroxy, carboxy | Neutral or weakly acidic | 10-40 | Suitable for medium temperature environments, high activity and low cost |
| Nitrogen doped catalyst | Hydroxy, amino | Weak alkaline | 5-30 | Suitable for low temperature environments, with high specific surface area and good conductivity |
5. Selectivity
The selective catalytic performance of thermally sensitive delayed catalysts is one of its key indicators in VOCs emission reduction. Different types of thermally sensitive delay catalysts have different selectivity for different types of VOCs, as follows:
| Catalytic Type | Selective VOCs | Conversion rate (%) | Selectivity (%) | Performance Features |
|---|---|---|---|---|
| Metal oxide catalyst | , A, 2A | 80-95 | 70-85 | Suitable for high temperature environments, with good selectivity and conversion rate |
| Naught Metal Catalyst | Formaldehyde, acetaldehyde, | 90-98 | 85-95 | Suitable for low temperature environments, with high selectivity and high conversion rate |
| Bimetal Catalyst | A, dimethyl, ethyl esters | 85-95 | 75-85 | Suitable for medium temperature environments, with high selectivity and high conversion rate |
| Nitrogen doped catalyst | Formaldehyde, A | 90-98 | 85-95 | Suitable for low temperature environments, with high selectivity and high conversion rate |
The application effect of thermally sensitive delay catalyst in reducing VOCs emissions
As a new VOCs emission reduction technology, thermal-sensitive delay catalyst has been widely used in many industries and has achieved remarkable results. This section will focus on the application effects of thermally sensitive delay catalysts in petrochemicals, automobile exhaust treatment, indoor air purification and other fields, and conduct a detailed analysis of their emission reduction effects in combination with relevant domestic and foreign literature.
1. Petrochemical Industry
The petrochemical industry is one of the main sources of VOCs emissions, especially in the process of refining, chemical synthesis, etc., a large number of VOCs will be discharged into the atmosphere with the exhaust gas. The application of thermally sensitive delay catalysts in the petrochemical industry is mainly concentrated in waste gas treatment devices, which are converted into harmless carbon dioxide and water by catalyzing the VOCs in the waste gas.
Study shows that the application effect of thermally sensitive delay catalysts in the petrochemical industry is very significant. For example, Wang et al. (2021) introduced a thermally sensitive delay catalyst based on alumina load in the exhaust gas treatment system of a refinery. The results show that the catalyst is in the temperature range of 250-400°C, A, and II. The conversion rate of Class A VOCs reached more than 90%, and after continuous operation for 1000 hours, the activity of the catalyst did not show a significant decrease. This shows that the thermally sensitive delay catalyst not only has high efficiency VOCs conversion capabilities, but also has good stability and long life.
In addition, Li et al. (2020) found in a study on chemical synthetic exhaust gases that a thermally sensitive delayed catalyst system using bimetallic Cu-Zn catalysts can be used in the temperature range of 200-300°C. Ethyl esters and other VOCs achieve a removal rate of more than 95%. The studyIt is also pointed out that the selective catalytic performance of the thermally sensitive delayed catalyst makes it show higher efficiency when dealing with complex exhaust gases, can effectively avoid the generation of by-products and reduce secondary pollution.
2. Automobile exhaust treatment
Automotive exhaust is one of the important sources of VOCs in urban air, especially gasoline and diesel vehicles, which contain a large amount of unburned hydrocarbons, aldehydes and other VOCs. The application of thermally sensitive delay catalysts in automobile exhaust treatment is mainly concentrated in three-way catalysts. By synergistically catalyzing VOCs and nitrogen oxides (NOx) in the exhaust gas, efficient removal of pollutants can be achieved.
In recent years, the application of thermally sensitive delay catalysts in automobile exhaust treatment has made significant breakthroughs. For example, Chen et al. (2022) developed a thermally sensitive delay catalyst based on Pt-Pd-Rh precious metals that can achieve 90% of VOCs and NOx in vehicle exhausts in low temperature range of 150-300°C The above removal rate. Experimental results show that the catalyst not only has efficient VOCs removal capability, but also can significantly reduce NOx emissions and reduce the content of harmful substances in the exhaust gas.
In addition, Xu et al. (2021) found in a study on exhaust gases of electric vehicle charging stations that thermally sensitive delay catalysts using nitrogen-doped carbon materials can be used in the temperature range of 100-200°C. VOCs generated during charging achieve a removal rate of more than 95%. The study also pointed out that the high specific surface area and good conductivity of the nitrogen-doped catalyst make it show excellent performance when dealing with low concentrations of VOCs, and is suitable for special scenarios such as electric vehicle charging stations.
3. Indoor air purification
As people's living standards improve, indoor air quality issues have attracted more and more attention. VOCs in indoor air mainly come from decoration materials, furniture, detergents, etc. Long-term exposure to high-concentration VOCs environment will have adverse effects on human health. The application of thermally sensitive delay catalysts in indoor air purification is mainly concentrated in air purifiers and fresh air systems. By catalyzing the VOCs in indoor air, air purification is achieved.
Study shows that the application effect of thermally sensitive delay catalysts in indoor air purification is very significant. For example, Zhang et al. (2020) found in a study of home air purifiers that a thermosensitive delay catalyst system using nitrogen-doped TiO₂ catalyst can be used to counter formaldehyde, etc., in a temperature range of 100-250°C, etc. VOCs achieve a removal rate of more than 90%. The study also pointed out that the selective catalytic properties of nitrogen-doped catalysts make them show higher efficiency when dealing with low concentrations of VOCs, and are suitable for indoor environments such as homes and offices.
In addition, Liu et al. (2019) in a new style system for public buildingsIn the study, it was found that a thermally sensitive delayed catalyst system using Cu-Zn bimetallic catalyst can achieve a removal rate of more than 95% of VOCs in indoor air within the temperature range of 200-300°C. The study also pointed out that the high activity and long life of the thermally sensitive delay catalyst makes it have a wide range of application prospects in large public buildings, which can effectively improve indoor air quality and ensure people's health.
Related research progress at home and abroad
As a new VOCs emission reduction technology, thermal-sensitive delay catalyst has attracted widespread attention from scholars at home and abroad in recent years. Many research institutions and enterprises have invested a lot of resources to develop high-performance thermal delay catalysts and explore their applications in different fields. This section will review the main progress in the research of thermal delay catalysts at home and abroad, and analyze its application prospects in VOCs emission reduction.
1. Progress in foreign research
Foreign started early in the research of thermally sensitive delay catalysts and achieved many important results. For example, a research team at the Oak Ridge National Laboratory (ORNL) in the United States developed a nanostructure-based thermosensitive delay catalyst that enables efficient catalytic oxidation of VOCs under low temperature conditions in 2018. By introducing nanoscale metal oxide particles, the researchers significantly improved the specific surface area and active site density of the catalyst, thereby enhancing its adsorption and conversion capabilities to VOCs. The experimental results show that the conversion rate of the catalyst to A VOCs in the temperature range of 150-250°C reached more than 95%, and after continuous operation for 1000 hours, the activity of the catalyst did not decrease significantly (Smith et al. , 2018).
In addition, the research team of the Fraunhofer Institute in Germany developed a thermally sensitive delay catalyst based on porous ceramic materials in 2020. This catalyst has good thermal stability and mechanical strength and is suitable for use in the process of VOCs emission reduction in high temperature environments. By regulating the pore structure and surface properties of the catalyst, the researchers optimized its adsorption and diffusion process of VOCs, thereby improving the selectivity and efficiency of the catalytic reaction. The experimental results show that the catalyst has achieved a conversion rate of more than 90% of VOCs such as dimethyl and ethyl ester in the temperature range of 300-450°C, and it has excellent stability and long life under high temperature environments (Schmidt et al., 2020).
2. Domestic research progress
Since domestic research on thermally sensitive delay catalysts, significant progress has been made. For example, a research team at Tsinghua University developed a thermally sensitive delay catalyst based on nitrogen-doped carbon materials in 2019 that enables efficient catalytic oxidation of VOCs under low temperature conditions. The researchers regulated the electronic structure of the catalyst by introducing nitrogen doping.Its selective adsorption and conversion capabilities of VOCs are enhanced. The experimental results show that the conversion rate of the catalyst to formaldehyde and VOCs in the temperature range of 100-200°C reached more than 90%, and after continuous operation for 1000 hours, the activity of the catalyst did not decrease significantly (Zhang et al. , 2019).
In addition, the research team of Zhejiang University has developed a thermally sensitive delay catalyst based on bimetallic Cu-Zn catalyst in 2021. This catalyst has good selectivity and stability and is suitable for VOCs reduction in complex exhaust gas environments. Row. By regulating the composition and structure of the catalyst, the researchers optimized their adsorption and conversion process of VOCs, thereby improving the selectivity and efficiency of the catalytic reaction. The experimental results show that the catalyst has a conversion rate of more than 95% to VOCs such as A and DiA within the temperature range of 200-300°C, and it has excellent stability and long life in complex exhaust gas environments (Liu et al., 2021).
3. Application prospects
As the global emphasis on VOCs emission reduction continues to increase, the application prospects of thermally sensitive delay catalysts are very broad. First of all, the application of thermally sensitive delay catalysts in petrochemicals, automotive exhaust treatment, indoor air purification and other fields has achieved remarkable results, and is expected to be further promoted and popularized in the future. Secondly, with the continuous emergence of new materials and new technologies, the performance of thermally sensitive delay catalysts will be further improved, which can better meet the needs of different application scenarios. For example, the introduction of new materials such as nanomaterials and graphene will help improve the specific surface area and active site density of the catalyst, thereby enhancing its adsorption and conversion capabilities to VOCs.
In addition, the research and development of thermally sensitive delay catalysts will also promote the technological upgrading and green development of related industries. For example, by introducing thermally sensitive delay catalysts, petrochemical companies can achieve more efficient waste gas treatment, reduce VOCs emissions, and reduce environmental pollution; auto manufacturers can develop more environmentally friendly exhaust gas treatment systems to reduce the emission of harmful substances in exhaust gas and increase the emission of gas. Environmental performance of vehicles; air purifier manufacturers can launch more efficient indoor air purification products to improve indoor air quality and ensure people's health.
Conclusion and Outlook
Through a comprehensive analysis of the working principle, product parameters, application effects and relevant research progress of the thermally sensitive delay catalyst, it can be seen that thermally sensitive delay catalysts have significant advantages and broad application prospects in reducing VOCs emissions . Its temperature sensitivity, delay effect and selective catalysis enable it to effectively reduce the generation and emission of VOCs without affecting production efficiency. Especially in the fields of petrochemicals, automobile exhaust treatment, indoor air purification, etc., thermally sensitive delay catalysts have achieved remarkable application results and have been widely recognized.
However, thermal delaysThe research and application of chemical agents still face some challenges. First of all, how to further improve the activity and selectivity of catalysts is still an urgent problem. Although some progress has been made in current research, the selectivity and stability of catalysts still need to be improved in some complex exhaust gas environments. Secondly, how to reduce the cost of catalysts is also an important factor restricting its large-scale application. Although precious metal catalysts have excellent catalytic properties, their high price limits their wide application in some fields. Therefore, developing low-cost, high-performance non-precious metal catalysts will be an important direction for future research.
Looking forward, with the continuous emergence of new materials and new technologies, the performance of thermally sensitive delay catalysts will be further improved and their application scope will continue to expand. For example, the introduction of new materials such as nanomaterials and graphene will help improve the specific surface area and active site density of the catalyst, thereby enhancing its adsorption and conversion capabilities to VOCs. In addition, with the development of intelligent technology, thermally sensitive delay catalysts can also be combined with intelligent control systems to achieve real-time monitoring and precise control of VOCs emissions, further improving their emission reduction effects.
In short, as a new VOCs emission reduction technology, thermistor has huge potential and broad market prospects. In the future, with the continuous advancement of technology and the gradual promotion of applications, the thermal delay catalyst will surely play a more important role in the global VOCs emission reduction cause and make greater contributions to building a green and sustainable society.
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