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Catalytic activities of different types of catalysts under the action of plasma atmospheric plasma

Catalytic activities of different types of catalysts under the action of plasma atmospheric plasma

Catalytic activities of different types of catalysts under the action of plasma atmospheric plasma: Atmospheric pressure plasma and catalyst co-activate CO2 to oxidize ethane. The main products are ethylene, acetylene and a small amount of methane. Of course, the by-products of ethane deradon reaction with CO2 as oxidant (CO+H2) and a small amount of water are also detectable. The catalytic activity of different kinds of catalysts under the action of atmospheric plasma is shown. , under pure plasma conditions, the conversion rates of C2H6 and CO2 are 33.8% and 22.7%, respectively, and the sum of the yields of C2H4 and C2H2 is 12.7%. When the supported rare earth oxide catalysts (La2O3/Y-Al2O3 and CeO2/Y-Al2O3) were introduced into the reaction system, the conversion of C2H6, the selectivity and yield of C2H4, the selectivity and yield of C2H2 were improved, but the CO2 Conversion rates are slightly lower. When La2O3/Y-Al2O3 and CeO2/Y-Al2O3 were used as catalysts, the yields of C2H4 and C2H2 were 19.8% and 21.8%, respectively. When the Pd/Y-Al2O3; catalyst was introduced into the plasma, the ethylene selectivity was significantly improved, and the C2H4/C2H2 ratio was as high as 7.4, but the C2H6 conversion rate decreased. This is because Pd reduces C2H2 to C2H4 and also reduces C2H4 Caused by C2H6. The above experimental results show that the rare earth oxide catalyst is beneficial to improve the conversion rate of C2H6 and the yields of C2H4 and C2H2, while Pd/Y-Al2O3 is beneficial to the generation of C2H2. Note: The reaction conditions are catalyst dosage of 0.7ml, discharge power of 20W (peak voltage 28kV: frequency 44Hz), flow rate of 25 ml/min, and feeds of C2H6 (50vol.%) and CO2 (50vol.%).

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The effect of energy density on the ethane conversion reaction under the combined action of plasma plasma and 10CeO2/Y-Al2O3

The effect of energy density on the ethane conversion reaction under the combined action of plasma plasma and 10CeO2/Y-Al2O3

The effect of energy density on the ethane conversion reaction under the combined action of plasma plasma and 10CeO2/Y-Al2O3: Table 3-5 shows the effect of energy density on the ethane conversion reaction under the combined action of plasma plasma and 10CeO2/Y-Al2O3. When the energy density reaches 300 kJ/mol, the plasma reaction is initiated, and the conversion rate of C2H6 and CO6 increases with the increase of the energy density, and the total yield of C2H4 and C2H2 increases accordingly until the energy density reaches 1500 kJ/mol. stability. In a flow plasma reactor, the increase in energy density means that the energy and number of high-energy electrons increase, which will facilitate the reaction of equations (3-26) to (3-29). The relative amount of active species increased. Therefore, the higher the energy density in the plasma reactor, the higher the conversion of C2H6 and CO2. At the same time, the research shows that the increase of energy density is not good for C2H4 or C2H2 selectivity. When the energy density increases from 380 kJ/mol to 1500 kJ/mol, the C2H4 selectivity decreases from 36.0% to 16.2%, and the C2H2 selectivity decreases from 55.4%. fell to 24.2%. Tables 3-5 show the effect of energy density on the gas product C2H4/C2H2 ratio and H2/CO ratio. The C2H4/C2H2 ratio and H2/CO ratio varied in the range of 0.63-0.68 and 2.47-2.91 under different energy densities. Under the action of atmospheric pressure non-equilibrium plasma plasma, C2H6 can undergo oxidative dehydrogenation reaction in CO2 atmosphere to generate C2H2 and C2H4. With CeO2/Y-Al2O3 as the catalyst, CO2 oxidation of CH6 dehydrogenation can occur when the reaction temperature is 973K. The reaction temperature and the ratio of reactant gas have a great influence on the reaction results; when the plasma and the catalyst are jointly activated, CO2 is oxidized to C2H6 conversion. The properties of the catalyst in the reaction have a significant impact on the reaction. The metal oxide catalyst is beneficial to the conversion of ethane to C2H2 and C2H4, and the metal catalyst can increase the percentage of C2H4 in the product.

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Difficulties in the controllable preparation of monolithic coatings by atmospheric plasma spraying process

Difficulties in the controllable preparation of monolithic coatings by atmospheric plasma spraying process

Difficulties in the controllable preparation of monolithic coatings by atmospheric plasma spraying process: Atmospheric plasma spraying technology is a commonly used coating preparation process. As the structural unit of the prepared coating, the morphology and stacking behavior of the monolithic layer determine the microstructure of the coating, which has a significant impact on the performance of the coating. The main factors related to the physical and chemical state of the droplet itself, the guest factors related to the substrate on which the coating is deposited, and the environmental factors affect the formation process of the monolithic layer. A variety of different influences and the correlation between them, and through the comparison of their characteristics, the future development direction that is closer to the real production conditions is proposed. With the continuous development of industrial technology, the requirements for the comprehensive performance of components are getting higher and higher, and the importance of surface engineering has become increasingly prominent. Preparing functional thin layers with a thickness of several micrometers to several millimeters on the surface of parts can change the surface properties of parts, greatly improve their performance, and effectively prolong their service life, which is in line with the requirements of green, circular economy and sustainable development. Thermal spraying is an important part of surface engineering. The spraying process is constantly evolving, the online monitoring and control technology of the spraying process is also developing rapidly, and the types of spraying materials are also expanding, forming a complete industrial system including equipment, raw materials, processes and applications. Atmospheric isomonic spraying (APS) is a kind of thermal spraying technology, which is characterized by high-temperature and high-speed plasma jet as the heat source, and has unique advantages in the preparation of ceramic coatings. In the atmospheric plasma spraying process, the powder particles are sent by the carrier gas into the high-temperature and high-speed plasma flame, heated and accelerated, hit the substrate in a molten or semi-molten state at high speed, spread rapidly, cool and solidify, and finally form a flat A large number of monolithic layers are continuously stacked to form a macro-scale coating. The characteristic unit of the atmospheric plasma sprayed coating, the morphology of the monolithic layer and the stacking behavior between the monolithic layers determine the microstructure of the coating. The monolithic layer is the structural unit of the coating prepared by thermal spraying, and its characteristics are closely related to the macroscopic properties of the coating. The difficulty in the controllable preparation of coatings by the atmospheric plasma spraying process is that there are many factors that need to be controlled in the process, and they often affect each other. The characteristics of high temperature, high speed, and wide distribution of physical and chemical states of droplets also bring great challenges to real-time observation and process control. The formation of the monolayer in the atmospheric plasma spraying process is mainly controlled by the cooling ability of the droplet. When the droplet cooling rate is fast, the fluidity of the liquid material decreases rapidly, and tends to form a disc-shaped monolithic layer; otherwise, it has a strong tendency to sputter. A closely related difference in coating performance brought about by the change in the monolithic profile is that the bond between the disc-shaped monolithic layer and the substrate is stronger, while the bond between the sputtered monolithic layer and the substrate is relatively strong. lower. More reliable in-situ temperature and velocity monitoring, especially temperature and velocity measurement that can track individual droplets, is undoubtedly a direct and effective method to study the effect of process parameters on the characteristics of monolithic layers. It is also an important direction for future development to digitize the morphology characteristics of the monolithic layer and establish a (semi-)quantitative relationship between it and the overall performance of the coating.

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Under the action of plasma plasma, CH4 and CO2 are the raw material gas to synthesize C2 hydrocarbon reforming reaction

Under the action of plasma plasma, CH4 and CO2 are the raw material gas to synthesize C2 hydrocarbon reforming reaction

Under the action of plasma plasma, CH4 and CO2 are the raw material gas to synthesize C2 hydrocarbon reforming reaction: Synthesis of C2 hydrocarbons with CH4 and CO2 as feed gas is a very interesting reaction. The first complete reduction product of CO2 hydrogenation is CH4, and the partial reduction product is C2 hydrocarbon; secondly, the complete oxidation product of CH4 is CO2, the partial oxidation product is C2 hydrocarbon, and the intermediate product is CHx. Obviously, these two reactions are mutually reversible. , such as co-activation of CH4 and CO2, that is, the presence of CO2 will be beneficial to the partial oxidation of CH4, and the presence of CH4 will inhibit the deep reduction of CO2, the result of the joint action will be conducive to the formation of C2 hydrocarbons. The significance of studying the CH4 coupling reaction with CO2 as the oxidant is that: first, a method to solve the difficult activation of CH4 is proposed, which provides an effective way to make full use of natural gas: Secondly, the conversion and utilization of CO2 can reduce greenhouse gases to a certain extent. emission. Therefore, this research has important academic value and broad application prospects. The synthesis route of CO2 oxidation of CH4 to C2 hydrocarbons has been reported. Under the action of plasma plasma, CO2 oxidation of CH4 to C2 hydrocarbons can be divided into indirect method and direct method. Synthetic system of C2 hydrocarbons. Zhou et al. used the dielectric barrier discharge method to realize the CO2 reforming CH4 reaction. When the injection energy was 87kW.h/(N∙m3), the conversion rate of methane was 64%, and the conversion rate of carbon dioxide was 54%. Gallon et al. and Pinhao et al. respectively investigated the reforming reaction of CH4 and CO2 under the action of DBD discharge plasma, and the results showed that the main product of the reforming reaction was syngas, and only a small amount of hydrocarbons (mainly C2H6) were generated. However, under the action of DBD discharge plasma, the reactant conversion of CH4 and CO2 reforming reaction is relatively low and the reaction energy consumption is high. Li et al. investigated the reforming reaction of CH4 and CO2 under the action of DC and AC corona discharge respectively. The experimental results show that the reformation reaction of CH4 and CO2 under the action of corona discharge plasma can obtain higher conversion rate of reactants, H2 selectivity and CO selectivity, compared with that obtained by DC positive corona discharge. , followed by AC corona, low DC negative corona. Malik et al. and Gesser et al. realized CO2 reforming CH4 reaction under pulsed corona plasma and silent discharge plasma conditions, respectively. The direct method is to prepare C2 hydrocarbons from CH4 and CO2 in one step, and the reaction can be realized under the action of microwave, flow column discharge and radio frequency plasma. Liu uses the flow column discharge method, with He as the balance gas (accounting for 60%~80% of the total gas flow), under a certain discharge power, according to the different molar ratios of CO2 and CH4, the methane conversion rate is between 20%~80% , the conversion rate of carbon dioxide is between 8% and 49%, and the yield of C2 hydrocarbons is between 20% and 45%. Chen Dongliang et al. directly converted CH4 and CO2 under the action of microwave plasma, and produced C2 hydrocarbons in one step. The main C hydrocarbon products in the reaction were C2H2 and C2H6. The increase of plasma power is conducive to the generation of C2H2. Yao et al. used radio frequency plasma to realize the reaction of CO2 oxidation of CH to C2 hydrocarbons, the methane conversion rate was 31%, the carbon dioxide conversion rate was 24%, and the C2 hydrocarbon selectivity was 64%.

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Plasmon-enhanced InAs Single Quantum Dot Fluorescence Radiation Changes Nanoscale Size Tuning Wavelength Research

Plasmon-enhanced InAs Single Quantum Dot Fluorescence Radiation Changes Nanoscale Size Tuning Wavelength Research

Plasmon-enhanced InAs Single Quantum Dot Fluorescence Radiation Changes Nanoscale Size Tuning Wavelength Research: Semiconductor quantum dots are quantum structures with limited three-dimensional dimensions, which restrict the spatial distribution and motion of carriers, and thus have some unique physical properties, such as discrete energy levels, density of states similar to functions, etc. Quantum dots have good application prospects in single-photon emitting devices. After the surface plasmon treatment of metal nanostructures, it has rich and unique physical properties, which makes the optical field localized in the sub-wavelength size range, and has a strong localized electromagnetic field enhancement effect. Changing the nanometer size of metals can tune the resonant wavelength of surface plasmons. At the same time, metal nanostructures will also reduce the lifetime of fluorescence, reduce the intensity of fluorescence, or cause fluorescence quenching. When the nanostructures only resonate with the excitation light field, the fluorescence lifetime of the quantum dots remains unchanged; when the nanostructures resonate with the fluorescence of the quantum dots, the quantum yield can be improved, while the fluorescence lifetime of the quantum dots is reduced. The luminescence lifetime, luminescence intensity and saturation excitation power of the obtained quantum dots are all modulated by the gold island film. This is mainly manifested in the following three aspects: One is the enhancement of the localized laser field. The nanostructure of the gold island film allows the optical field to be localized in the sub-wavelength size, especially at some sharp corners or slits, which increases the localized strength of the electric field, which will lead to saturated excitation power. reduce; 2. The coupling between the quantum dot dipole transition and the gold island film leads to a decrease in the fluorescence lifetime, which belongs to the non-radiative recombination process of excitons. At the same time, the luminous energy is absorbed by the gold island film and lost, resulting in a decrease in the luminous intensity and an increase in the saturation excitation power; 3. The gold island film structure is used as a directional coupling-out antenna for quantum dot light emission, which increases the PL collection efficiency, resulting in a higher spectral collection efficiency, but has little effect on the saturated excitation power and fluorescence lifetime. The coupling between the gold island film and the quantum dot emission is related to the emission wavelength of the quantum dot and the specific nanostructure of the gold island film in the quantum dot sample. The metal nanostructure can change the radiation direction of the light field to form the directional emission of the light field. Therefore, metal nanostructures are widely used to study excitation light field enhancement, fluorescence emission coupling and their interaction with dipole luminescence, such as using Tam plasmon modes, nanoparticles, nanoantennas, metal films, nanostructures And plasmon resonance, etc., improve the fluorescence radiation intensity of quantum dots, form fluorescence directional emission, improve fluorescence collection efficiency, etc. Plasma enhances the fluorescence radiation of single quantum dots and improves the quality of the luminous effect of the product. The main physical mechanism of the fluorescence enhancement effect is that the gold island film structure acts as an effective directional coupling output of quantum dots, and the antenna increases the PL collection efficiency of the quantum dots, thereby obtaining a higher spectral collection efficiency. The gold island film structure mainly enhances the collection efficiency of quantum dot spectra, providing an efficient method for preparing bright single-photon sources. At the same time, it is also observed that a small number of quantum dots like QD2 have the phenomenon that the luminescence lifetime is shortened (about 270ps), the saturation excitation power is increased (about 1nW), and the total fluorescence intensity is weakened. This is because the luminescence energy is reduced by gold. The island film is absorbed and lost, and no radiation recombination plays a major role. The gold island film has a certain modulation effect on the luminescence lifetime, luminescence intensity and saturation excitation power of quantum dots. The gold island film nanostructure is beneficial to improve the collection efficiency of PL spectra of quantum dots, which provides an efficient method for fabricating bright single-photon sources.

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The effect of plasma plasma energy density on the conversion of reactants CH4 and CO2, C2 hydrocarbons, and CO yields

The effect of plasma plasma energy density on the conversion of reactants CH4 and CO2, C2 hydrocarbons, and CO yields

The effect of plasma plasma energy density on the conversion of reactants CH4 and CO2, C2 hydrocarbons, and CO yields: The effect of plasma energy density on the conversion rates of CH4 and CO2, the yields of C2 hydrocarbons and CO. It can be seen that the conversion rates of CH4 and CO2 both increase with the increase of energy density, which means increasing plasma plasma power and decreasing feed gas flow. That is, increasing the energy density is beneficial to improve the conversion rate of CH and CO2. When the energy density is 2200kJ/mol, the conversion rates of CH4 and CO2 are 43.6% and 58.4%, respectively. Although increasing the energy density is beneficial to improve the conversion rate of CH4 and CO2, it is beneficial to the cleavage of the C-H bond of methane (4.5eV) and the cleavage of the C-O bond of carbon dioxide (5.45eV), but the effects on the two are not the same. When the energy density is lower than 1500KJ/mol, the CH4 conversion rate is higher than the CO2 conversion rate under the same experimental conditions, which means that at a lower energy density, the average energy of the high-energy electrons in the system is lower, and the average energy of most electrons and the CH bond of methane is The bond energy is similar but lower than the cracking energy of carbon dioxide CO bond, so the CH4 conversion rate is higher than the CO2 conversion rate. When the energy density is higher than 1500 kJ/mol, the average energy of electrons in the system increases, and the energy of most electrons gradually approaches the cracking energy of carbon dioxide C-O bond, and the CO2 conversion rate increases rapidly. At the same time, the conversion rate of CH4 showed a logarithmic upward trend with the increase of energy density, and the conversion rate of CO2 showed a linear upward trend with the increase of energy density. This may be related to the cracking characteristics of methane and carbon dioxide under plasma plasma. Methane is cracked successively, that is, the conversion of one methane molecule often consumes multiple high-energy electrons. Methane. A lower energy density should be chosen for methane conversion. The influence of energy density on the yields of C2 hydrocarbons and CO both showed a linear upward trend with the increase of energy density, and the linear slope of CO yield was significantly higher than that of C2 hydrocarbon yield. For the C2 hydrocarbon yield, when the energy density was increased from 350 kJ/mol to 2200 k.J/mol, the C2 hydrocarbon yield increased from 5.7% to 20.6%, an increase of nearly 15 percentage points. For the CO yield, when the energy density increased from 350 kJ/mol to 2200 kJ/mol, the CO yield increased from 11.6% to 76.4%, an increase of nearly 65 percentage points. This shows that in the energy range investigated in the experiment, increasing the energy density is beneficial to improve the yield of C2 hydrocarbons and CO, but from the perspective of energy consumption, it is not comprehensive to measure the reaction efficiency only by the product yield, so it is necessary to introduce energy Efficiency This physical quantity evaluates the CO2 oxidation CH4 conversion reaction under the action of plasma plasma. Since no direct evidence for the conversion of CO2 to C2 hydrocarbons can be obtained under the experimental conditions, it can be considered that the C2 hydrocarbons originate from the coupling reaction of methane: CH4 → 0.5C2H6+0.5H2 ∆H11 =32.55kJ/mol (4-2) CH4 → 0.5C2H4+1H2 ∆H12=101.15kJ/mol (4-3) CH4 → 0.5C2H2+1.5H2 ∆H13=188.25kJ/mol (4-4) Coupling the above three reaction equations and considering the distribution of C2 hydrocarbon products, the overall reaction equation of methane coupling to form C2 hydrocarbons can be expressed as CH4 → 0.5n11C2H6+0.5n12C2H4+0.5n13C2H2+(2-1.5n11-n12-0.5n13)H2 ∆H1=(32.55n11+101.15n12+188.25n13)kJ/mol (4-5) n11, n2, n3 in formula (4-5) represent respectively: n11 is the mole fraction of C2H6 in the C2 hydrocarbon product, mol/%; n12 is the C2 hydrocarbon

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