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Due to its unique electronic structure,palladium is widely used as an efficient catalyst in various fields such as chemical engineering,environment,and energy when loaded on different carriers.The catalyst itself does not change before and after use,but in practical applications,its activity severely declines due to poisoning,coverage,shedding,agglomeration,phase transformation,aging,and fragmentation.As a result,palladium-based catalysts can only be recycled and reprocessed into new catalysts.Although there are relatively mature recycling processes for these spent supported palladium-based catalysts,from the perspectives of environmental protection and economy,it is urgent to develop new green,economic,and efficient recycling processes.Starting from different carrier types,this paper reviews several recycling processes of palladium catalysts supported on various carriers,systematically analyzes and compares the advantages and limitations of various catalyst recycling processes,and looks forward to their future development.
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Although the removal technologies for single pollutants such as nitrogen oxides(NOx) and chlorobenzene have become relatively mature,research on their synergistic removal remains scarce.This paper reviews the catalytic removal technologies of NOx and chlorobenzene,with particular emphasis on the significance of synergistic catalytic technology in enhancing removal efficiency,reducing energy consumption and costs,providing a theoretical basis for the development of new and highly efficient catalysts.The influence of different metal oxides on catalyst performance is further discussed in detail.Finally,it was emphasized that future research needs to achieve breakthroughs in enhancing the performance,stability and selectivity of by-products of catalysts,and develop more efficient,economical and environmentally friendly pollution control technologies.
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The utilization of pyrolysis C5 has become an important indicator for making full use of petroleum resources and improving the economic benefits of ethylene production.The presence of sulfide seriously affects the quality and utilization of C5 products,and the key bottleneck of clean and efficient use of C5 to produce high value-added products is the removal of sulfides.At present,the cracking C5 desulfurization technology mainly includes catalytic hydrogenation,alkylation,oxidation,adsorption desulfurization,etc,and the research progress and existing problems of each technology are discussed,and the adsorption desulfurization technology is focused on on this basis.The research progress of activated carbon,molecular sieve and metal oxide adsorbents is introduced in detail,especially molecular sieve adsorbents will become the focus of future research on C5 adsorption and desulfurization due to their excellent performance,mild operating conditions and simple regeneration.
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Dimethyl 1,4-cyclohexanedicarboxylate(DMCD) is an important intermediate for the preparation of polyester monomer 1,4-cyclohexanedimethanol(CHDM).The research progress in aspects such as the reaction mechanism,catalyst types and reaction process of hydrogenation of dimethyl terephthalate(DMT) to produce DMCD is reviewed.The discussion focuses on the process of DMT hydrogenation and the performance of catalysts with different active centers(Pd,Ru,Ni and bimetallic).Finally,the prospects of the future development in catalysts and processes of hydrogenation of DMT is proposed.
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Using carbon black as the hard template agent,SSZ-39 molecular sieves with multi-level pore structure were successfully prepared by the crystal transformation method.Further,the multi-level pore Cu-SSZ-39 molecular sieve catalyst with microporous-mesoporous structure was obtained through ion exchange.A variety of characterizations,performance tests and reaction kinetics studies have confirmed that the introduction of mesopores increases the acid content of the catalyst and the ratio of ZCuOH (eight-membered ring copper ions),while enhancing the mass transfer of the reaction,the accessibility of active sites and the stability of the molecular sieve framework.Compared with pure microporous molecular sieve catalysts,multi-level porous Cu-SSZ-39 molecular sieve catalysts have superior ammonia-selective catalytic reduction of nitrogen oxides(NH3-SCR) activity and hydrothermal stability.
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Bismuth molybdate has broad application prospects in the degradation of water pollutants,but the photogenerated electron-hole recombination of single bismuth molybdate is fast and the photocatalytic efficiency is not high.Therefore,Bi2MoO6/BiOI composites in different proportions were prepared by the one-pot hydrothermal method.Their microscopic morphology,phase composition and other properties were characterized by XRD,SEM,TEM,XPS and DRS.The activity of their degradation of tetracycline hydrochloride(TC) was evaluated under visible light irradiation.The results show that the 1∶5Bi2MoO6/BiOI degradation efficiency reaches the optimal level,with the degradation rate of tetracycline hydrochloride reaching 81.0% within 100 minutes.Moreover,after four repeated degradations,it still maintains high catalytic activity.The reason is that the Bi2MoO6/BiOI composite material generates superoxide radicals,which accelerate the rapid separation of photogenerated electron-hole pairs.This material has potential application value in environmental governance and protection.
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Using Al2O3 as the support,RS-180 catalyst was prepared via the impregnation method and characterized by XRD,SEM,and mercury intrusion porosimetry to evaluate its performance in ethylene epoxidation to produce ethylene oxide.Results showed that α-Al2O3 exhibited a lamellar morphology with an innovative “interlocking” structure,enhancing the dispersion of silver nanoparticles.The catalyst achieved an ethylene oxide selectivity of 88% after 700 h of operation,with a stable upward trend,reaching 89% after 900 h,maintaining consistent performance.This provides reliable technical support for efficient ethylene oxide production and the stable development of downstream industries,promising to drive optimization and upgrading of the ethylene oxide industrial chain.
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The Ni/SiO2 catalyst was prepared by the equal-volume impregnation method using aqueous polyethylene glycol as solvent to investigate their acetone hydrogenation reaction performance.The catalyst was characterized by XRD,N2 adsorption-desorption,H2-TPR and TEM.The results show that using polyethylene glycol aqueous solution as the solvent can promote the dispersion of Ni on the carrier surface,reduce the Ni particle size,and enhance the interaction between the metal and the carrier.Under the conditions of a reaction temperature of 140 ℃,a space velocity of 1 h-1,a molar ratio of hydroketone of 6,and a reaction pressure of 0.4 MPa,the catalyst operated stably for 1 000 h,with acetone conversion greater than 98% and isopropanol selectivity greater than 99%.
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Dimethyl 1,4-cyclohexanedicarboxylate(DMCD) serves as a crucial pharmaceutical intermediate for synthesizing diverse drugs and constitutes an important raw material for polyester production.Ru/Al2O3 catalysts were synthesized using Ru as the active center and Al2O3 as the support,employing two distinct methods:the impregnation method and the deposition-precipitation method.These catalysts were applied to the selective hydrogenation of dimethyl terephthalate(DMT) to produce DMCD.The catalysts were characterized by XRD,CO2-TPD,TEM and H2-TPR.High-performance liquid chromatography was utilized for the quantitative analysis of DMT conversion efficiency and DMCD yield.The results demonstrate that the 3%Ru/Al2O3 catalyst prepared via the deposition-precipitation method exhibited superior catalytic performance and stability under the following optimal conditions:a DMT to 3%Ru/Al2O3 mass ratio of 10∶1,a reduction temperature of 300 ℃,a calcination temperature of 300 ℃,a reaction temperature of 150 ℃,and a reaction time of 2 hours.Under these conditions,DMT conversion exceeded 99%,and the DMCD yield surpassed 92%.Compared to a commercial Ru/C catalyst,the Ru/Al2O3 catalyst displayed faster sedimentation in the product mixture,facilitating easier separation.Furthermore,its catalytic efficiency showed almost no change after five consecutive reaction cycles.
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The attrition index of FCC catalysts was determined using the swan-neck tube wear method,the quartz straight-tube wear method,and the stainless steel straight-tube wear method.The differences and correlations between the results obtained from these different methods were compared.The results showed that the precision of the attrition index determined by the swan-neck tube,quartz straight-tube,and stainless steel straight-tube methods were in the ranges of 6.10%~9.99%,5.86%~7.90%,and 3.17%~3.58%,respectively.For the same sample,the difference in attrition index between the swan-neck tube and quartz straight-tube methods was ≤0.3%,while the wear index obtained by the stainless steel straight-tube method had a linear relationship with that obtained by the swan-neck tube method,with the equation y=1.044 8x+2.773 3.The measured values obtained by different methods were correlated,providing a reliable basis for the determination of the attrition index of FCC catalysts.
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The normal operation of the slurry oil system is an important part of the safe operation of the catalytic cracking unit.As an important process parameter of the slurry oil system,the solid content of the slurry oil can provide some feedback on the content of catalyst fine powder in the slurry oil and predict the wear of the slurry oil pump and slurry oil pipelines,thus ensuring the safe operation of the slurry oil system.The increase in crude slurry oil solid content is influenced by the increase in catalyst loss and the heavier composition of the slurry.This paper explores the correlation between the composition of the slurry and the detection results of solid content by applying the four-component analysis method.This has practical significance for ensuring the normal operation of refinery units.The results show that the change in asphaltene content in the slurry composition has a greater impact on the detection results of solid content.The influence of asphaltene on solid content detection results is not strictly related to the basic value of asphaltene in the slurry and the basic value of solid content in the slurry.The relative increase in asphaltene is more obvious,and the catalyst content is basically unchanged.Therefore,the application of this method can reduce unnecessary adjustment of catalytic cracking unit.
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The catalyst replacement process of the 1.8 Mt·a-1 Johnson Matthey large-scale Davy process methanol synthesis plant at Yulin Chemical Industry Co.,Ltd.,National Energy Group is described.The causes of the problems encountered in the process of system gas replacement,catalyst passivation,unloading,cleaning and loading are analysed,and optimisation measures and suggestions are put forward based on the field application,so as to reasonably avoid the risks of the various processes and to ensure the resistance drop of the synthesis tower at start-up is up to the standard.The proposed optimisation measures have been implemented in several plants of the same class,such as Yulin Chemical Co.,Ltd.,Xinjiang Chemical Co.,Ltd.,Baotou Chemical Co.,Ltd.,which can solve most of the problems during catalyst changeover,and provide a certain reference for domestic plants of the same class.
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With the upgrading of environmental protection regulations,the limit requirements for sulfur dioxide emissions in power plant flue gas are getting lower and lower.A certain biomass power plant in Hebei Province uses dry desulfurization technology and uses commercially available common calcium hydroxide as the desulfurizer to treat flue gas.The emission concentration of sulfur dioxide is less than 30 mg·m-3.XRF,TG,pore structure and particle size analyses were conducted on commercially available common calcium hydroxide and high-efficiency porous desulfurization materials,and industrial tests on desulfurization performance were carried out.The results show that the high-efficiency porous desulfurization material has a higher calcium hydroxide content,better pore structure and larger particle size than the common calcium hydroxide available on the market.This indicates that the addition of modifiers can promote the conversion of calcium oxide to calcium hydroxide and optimize the pore structure.The high-efficiency porous desulfurization material has better desulfurization performance,saving 13.08% of the daily consumption compared with the common calcium hydroxide available on the market,and has significant economic benefits.
