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Calcium sulfate whiskers are fibrous single crystals of calcium sulfate synthesized from gypsum or industrial by-products by a specific process and formula.It is a kind of inorganic material with many excellent characteristics,such as complete shape,stable size and uniform cross-section.However,due to the influence of preparation methods and equipment,the yield of calcium sulfate whiskers is not high and the quality is poor,which limits the application of calcium sulfate whiskers to a certain extent.The preparation methods of calcium sulfate whiskers at home and abroad and their advantages and disadvantages were introduced.The methods of calcium sulfate whisker crystal shape control and calcium sulfate whisker modification and its mechanism,the application of calcium sulfate whisker in modification and environmental protection were reviewed.Finally,some constructive ideas for the related research were provided.
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Platinum-based catalyst is one of the key materials of proton exchange membrane fuel cell (PEMFC),and the catalytic materials should have high activity,high conductivity,high stability,corrosion resistance and other properties.At present,platinum-based catalysts have some problems such as poor durability,low utilization rate and high price.These problems have seriously restricted the commercialization of PEMFC.The preparation of catalysts with high stability,high activity and low cost has become the research focus of scholars at present.In this paper,two directions for improving the catalytic activity of platinum-based catalysts are summarized.One is to modify the carbon carrier to improve the electrocatalytic performance,and the other is to load single metals,bi-metals and metal compounds to improve the electrocatalytic performance.According to the above two aspects,this paper expounds the research and application of platinum-based catalysts to improve catalytic activity in the catalytic process.It is proposed that the catalytic activity of the catalyst can be improved from two aspects at the same time,by changing the catalyst components and carrier characteristics to achieve better catalytic effect,while improving the catalytic activity,reducing the platinum content,and forming an economical and stable fuel cell catalyst.
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Heavy metal pollution is still a global environmental problem,which poses a serious threat to human life.Various methods have been explored to eliminate heavy metal pollutants in the environment.However,most methods are limited by high cost,processing time,geological problems,etc.Metal immobilization and microbial methods have been proved to be feasible in the treatment of heavy metal pollutants in soil.This paper summarizes the general situation of soil heavy metal pollution,and expounds the shortcomings and advantages of various remediation methods.Remediation of contaminated soil needs to consider remediation methods,soil pollution degree,site conditions,wide adoption and various possibilities at different remediation stages.
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Methods for preparing porous alumina were primarily introduced,including the solid-phase method,the liquid-phase method and the gas-phase method.Physical and chemical properties of alumina prepared by different methods were compared,such as particle size,specific surface area,dispersity.Alumina shows good application prospects in the fields of infrastructure,adsorption,catalysis,optics and medicine due to excellent physical-chemical property.
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Due to higher corrosion temperature and 100% concentration,the corrosion rate of molten KOH was 100 to 1000 times that of KOH solution.Fe-based catalyst substrate steel tube for Fischer-Tropsch synthesis prepared with the optimal parameters of corrosion at 500 ℃ for 3 h with carbon 20 material and 20 g KOH·(5 tubes)-1,showed the highest corrosion rate of 10.28%.A small amount of KOH remained on the surface of tube,many irregular rough micro-pits and a large number of pores appeared.Carbon 20 material was more easily corroded than 316L and 304 due to its carbon content.Higher dosage of KOH and higher corrosion temperature led to higher corrosion rate.Serious passivation film formed after corrosion of 5 h reduced the corrosion rate.
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V-Mo/Ti and V-W/Ti De-NOx catalysts were prepared and treated at 650 ℃ subsequently.XRD,N2 adsorption-desorption,H2-TPR,UV-vis,NH3-TPD,and O2-TPD analyses were carried out to investigated the change in the physiochemical properties of the different catalysts.De-NOx performances of catalysts before and after heat treatment were studied.It was found that the thermal treatment at 650 ℃ did not change the crystal structure of the vanadium-titanium based catalysts,but could lead to the decrease of their BET surface area and pore volume.Besides,the thermal treatment resulted in the decline of reducibility,acidity,and chemical adsorbed oxygen of the catalysts,which led to the decrease of the catalytic performance of the catalysts.V-Mo/Ti catalyst was more affected by thermal treatment than V-W/Ti catalyst.As a result,V-W/Ti-T catalyst exhibited better catalytic performance than that of the V-Mo/Ti-T catalyst.In other words,V-W/Ti catalyst possessed stronger thermal stability than that of the V-Mo/Ti catalyst.
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Metal-organic framework compound Cu-BTC was synthesized by ultrasonic-assisted hydrothermal method and characterized by XRD,SEM,BET,FT-IR and EDS.The characterization results showed that Cu-BTC was a microporous material with octahedral structure and high crystallinity.The desulfurization performance of the synthesized catalyst was evaluated by adsorption removal of sulfide-dibenzothiophene in simulated oil (n-octane-dibenzothiophene).The desulfurization efficiency of regenerated adsorption material using solvent elution remained 85.46% after being repeatedly used for three times,indicating that the metal-organic framework compound Cu-BTC synthesized by ultrasonic assisted hydrothermal synthesis has a good application prospect in adsorption desulfurization.
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α-Al2O3 support (Al2O3-B) was prepared by ball-milling method using γ-AlOOH as raw material.Compared with the α-Al2O3 prepared by calcination,the surface area of Al2O3-B was larger,reaching 70.7 m2·g-1.Pd/α-Al2O3 catalyst (Pd/Al2O3-B) was synthesized by impregnation.The catalyst was characterized by X-ray diffraction (XRD),N2 adsorption-desorption,NH3-temperature-programmed desorption (TPD) and transmission electron microscopy (TEM) and tested in the CO oxidative coupling to dimethyl oxalate reaction.Pd/Al2O3-B showed wonderful catalytic activity in the CO oxidative coupling reaction,space-time yield of dimethyl oxalate reaching 2 175 g·(L·h)-1.
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Aiming at the spray drying process of catalytic cracking catalyst,a 100 kg·h-1 single spray gun pressure spray drying tower model was established to simulate the distribution of hot air in the drying tower under different tower structures,and the influence of hot air outlet position on temperature distribution,velocity distribution and air flow trajectory in the drying tower was investigated.The results show that when there is no hot air distribution plate in the drying tower,the hot air is in a swirling downward state,there is an obvious low temperature zone downstream of the spray gun,and the uniformity of flow field distribution is relatively poor;When two layers of hot air distribution plates with uniform holes are set,the hot air moves vertically downward,the temperature is gradient distribution,and the flow field distribution is uniform;When two layers of hot air distribution plates with central holes are set,the hot air flow is in a centralized distribution state,and the distribution of air velocity and temperature near the spray gun tends to be high in the middle and low around.Changing the position of the hot air outlet in the outlet flue has a significant effect on the flow field distribution in the drying tower.
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In this paper,the thermal efficiency model of the electric heating furnace is established,and the effects of the air volume,operating pressure and sealing structure on the thermal efficiency are analyzed.The furnace heat loss is reduced by coating nano-materials on the outer surface of the furnace hearth.The operation results showed that the deviation between the simulation results and the operation results is within 2.5%.The thermal efficiency of the furnace is increased from 81.7% to 85.7% by optimizing the operation parameters and equipment structure,and 210 500 CNY annual operation cost is saved.It has created good economic benefits for enterprises.
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With graphene oxide as the structure directing agent,resorcinol-formaldehyde-melamine as the precursor,and melamine as the nitrogen source,three-dimensional stacked graphene based nitrogen doped hierarchical porous carbon nanosheets (NCNS) with uniform thickness and adjustable nitrogen content were prepared by sol-gel and carbonization.After loaded with Pd,Pd/NCNS catalyst was applied in PTA hydrofining.Compared with commercial Pd/C catalyst,Pd/NCNS catalyst shows higher activity,which can be attributed to its shorter diffusion channel,nitrogen doping and its high Pd dispersion.
