Under the context of global energy transition and carbon neutrality,controlling nitrogen oxide(NO_(x))emissions from biomass combustion is of great significance,and the development of high-efficiency low-temperature c...Under the context of global energy transition and carbon neutrality,controlling nitrogen oxide(NO_(x))emissions from biomass combustion is of great significance,and the development of high-efficiency low-temperature catalysts has become a current research focus.In this study,Nb was used to dope and modify the Mn_(7)-Cu_(3)/BCN catalyst to construct the Mn_(7)-Cu_(3)-Nb_(x)/BCN system.The doping amount was optimized through selective catalytic reduction(SCR)activity tests.The reaction mechanism was explored by combining in situ DRIFTS and density functional theory(DFT)simulations.Experimental findings revealed that the catalyst doped with 0.05%Nb achieved the optimal performance,sustaining a NO conversion efficiency of≥94%within the temperature window of 150−275℃while demonstrating improved resistance to alkali metal K poisoning.Mechanistic analyses showed that at low temperatures,the catalyst facilitated the SCR reaction via both the Eley-Rideal(E-R)and Langmuir-Hinshelwood(L-H)pathways,with the synergistic interaction between multiple active sites driving the efficient conversion of NH3 and NO.DFT calculations further confirmed that both pathways had the characteristics of low reaction energy barriers and significant exothermicity,ensuring the high activity and feasibility of the low-temperature reaction.The findings provided foundational theoretical support for the design of Nb-doped Mn-Cu-supported catalysts and the exploration of the underlying working mechanisms.展开更多
Nitrogen oxides(NO_(x))present in flue gas are economically renewable N1 resources.Unlike traditional selective catalytic reduction processes that convert NO into N_(2),redirecting NO towards the synthesis of value-ad...Nitrogen oxides(NO_(x))present in flue gas are economically renewable N1 resources.Unlike traditional selective catalytic reduction processes that convert NO into N_(2),redirecting NO towards the synthesis of value-added NH_(3)offers significant practical benefits.In this study,a Ti-based metal-organic framework(Ti-MOF),specifically MIL-125,was utilized as a support for Fe,which was subsequently calcined at 400℃to produce a Fe_(2)O_(3)/TiO_(2)-MOF catalyst.The resulting catalyst demonstrated exceptional performance,achieving 99%NO conversion and 95%NH_(3)selectivity under optimal conditions of 450℃,0.1 MPa,and a gas hourly space velocity of 38000 mL g^(–1)h^(−1).Additionally,the catalyst exhibited excellent stability and resistance to water and sulfur.The high efficiency of Fe_(2)O_(3)/TiO_(2)-MOF is attributed to the abundance of Fe^(2+)sites at the reaction temperature,which enhances NO adsorption and activation.Furthermore,density functional theory calculations suggest that NO undergoes hydrogenation at the N-terminus on the Fe_(2)O_(3)/TiO_(2)-MOF surface,leading directly to NH_(3)synthesis rather than dissociation followed by hydrogenation.This catalyst presents a novel approach for converting NO_(x)into high-value chemical products.展开更多
Selective reduction of N_(2)O by CO under excess O_(2) was effectively catalyzed by Fe(0.9 wt%)-exchangedβzeolite(Fe0.9β)in the temperature range of 250–500°C.Kinetic experiments showed that the apparent activ...Selective reduction of N_(2)O by CO under excess O_(2) was effectively catalyzed by Fe(0.9 wt%)-exchangedβzeolite(Fe0.9β)in the temperature range of 250–500°C.Kinetic experiments showed that the apparent activation energy for N_(2)O reduction with CO was lower than that for the direct N_(2)O decomposition,and the rate of N_(2)O reduction with CO at 300℃ was 16 times higher than that for direct N_(2)O decomposition.Reaction order analyses showed that CO and N_(2)O were involved in the kinetically important step,while O_(2) was not involved in the important step.At 300℃,the rate of CO oxidation with 0.1%N_(2)O was two times higher than that of CO oxidation with 10%O_(2).This quantitatively demonstrates the preferential oxidation of CO by N_(2)O under excess O_(2) over Fe0.9β.Operando/in-situ diffuse reflectance ultraviolet-visible spectroscopy showed a redox-based catalytic cycle;α-Fe-O species are reduced by CO to give CO_(2) and reduced Fe species,which are then re-oxidized by N_(2)O to regenerate theα-Fe-O species.The initial rate for the regeneration ofα-Fe-O species under 0.1%N_(2)O was four times higher than that under 10%O_(2).This result shows quantitative evidence on the higher reactivity of N_(2)O than O_(2) for the regeneration ofα-Fe-O intermediates,providing a fundamental reason why the Fe0.9βcatalyst selectively promotes the CO+N_(2)O reaction under excess O_(2) rather than the undesired side reaction of CO+O_(2).The mechanistic model was verified by the results of in-situ Fe K-edge X-ray absorption spectroscopy.展开更多
The distributions of framework aluminum(Al)in zeolites critically govern the location and speciation of active copper(Cu)centers,thereby influencing their performance in ammonia selective catalytic reduction(NH_(3)-SC...The distributions of framework aluminum(Al)in zeolites critically govern the location and speciation of active copper(Cu)centers,thereby influencing their performance in ammonia selective catalytic reduction(NH_(3)-SCR)of nitrogen oxides(NO_(x)).Conventional Cu-SSZ-39(Cu-SSZ-39-T)exhibits excellent hydrothermal stability but limited low-temperature activity(150–225℃)due to a low concentration of Al in 8-membered rings(8MRs)that inhibits the formation of active[Cu(OH)]^(+)-Z species.Herein,an SSZ-39 zeolite synthesized with potassium ions(SSZ-39-K)achieved a significantly higher 8MR Al fraction(37.6%).Density functional theory calculations and H_(2)-temperature-programmed reduction analyses confirmed that the increased 8MR Al population facilitated the formation of[Cu(OH)]^(+)-Z species.Aged Cu-SSZ-39-K exhibited nearly twice the NO_(x)conversion of aged Cu-SSZ-39-T in the 150–225℃range while maintaining comparable high-temperature activity(250–550℃)under a gas hourly space velocity of 250,000 h^(-1).Enhanced low-temperature performance is particularly beneficial for mitigating NO_(x)emissions during cold-start phase.Moreover,SSZ-39-K was synthesized with a high crystallization yield(~65%),nearly double the highest yield(33%)reported for direct synthesis routes.This work establishes a robust strategy for tailoring Al distributions in SSZ-39 zeolites,offering an effective pathway to improve low-temperature NH_(3)-SCR performance and promote practical implementation.展开更多
Developing a high-efficiency catalyst with both superior low-temperature activity and good N_(2)selectivity is still challenging for the NH_(3)selective catalytic reduction(SCR)of NO_(x)from mobile sources.Herein,we d...Developing a high-efficiency catalyst with both superior low-temperature activity and good N_(2)selectivity is still challenging for the NH_(3)selective catalytic reduction(SCR)of NO_(x)from mobile sources.Herein,we demonstrate the improved low-temperature activity and N_(2)selectivity by regulating the redox and acidic properties of MnCe oxides supported on etched ZSM-5 supports.The etched ZSM-5 enables the highly dispersed state of MnCeOx species and strong interaction between Mn and Ce species,which promotes the reduction of CeO2,facilitates electron transfer from Mn to Ce,and generates more Mn^(4+)and Ce^(3+)species.The strong redox capacity contributes to forming the reactive nitrate species and-NH_(2)species from oxidative dehydrogenation of NH_(3).Moreover,the adsorbed NH_(3)and-NH_(2)species are the reactive intermediates that promote the formation of N_(2).This work demonstrates an effective strategy to enhance the low-temperature activity and N_(2)selectivity of SCR catalysts,contributing to the NO_(x)control for the low-temperature exhaust gas during the cold-start of diesel vehicles.展开更多
The implementation of embedded selective catalytic reduction(SCR)denitration in chain grate during iron ore pelletizing process obviates additional flue gas heating.However,the influence of gas components and alkali m...The implementation of embedded selective catalytic reduction(SCR)denitration in chain grate during iron ore pelletizing process obviates additional flue gas heating.However,the influence of gas components and alkali metal on SCR denitration requires attention.The SCR denitration behavior in the preheating section of chain grate was investigated,and the combined influence mechanisms of H_(2)O(g),SO_(2),and potassium were revealed.The results show that the presence of H_(2)O(g)and SO_(2) in the flue gas decreases the NO conversion rate of the catalyst from 96.3%to 79.5%,while potassium adsorbed on the catalyst surface further reduces the NO conversion rate to 74.1%.H_(2)O(g),SO_(2),and potassium in the flue gas form sulfate and potassium salt on the catalyst surface,blocking the pore structure,thereby decreasing the gas adsorption capacity of the catalyst.Moreover,SO_(2) and potassium engage in competitive adsorption and reaction with NH_(3) and NO at the active sites on the catalyst surface,reducing the content and activity of the catalyst effective component.Increasing the flue gas temperature can promote the decomposition of ammonium sulfate and ammonium bisulfate on the catalyst surface,but it has little effect on potassium.Additionally,potassium will exacerbate sulfur poisoning of the catalyst.Hence,the embedded SCR denitration process requires electrostatic precipitation to eliminate the adverse impacts of potassium and thermal regime optimization to raise flue gas temperature to 350℃,thereby increasing NO conversion rate exceeding 85%.展开更多
Ammonia selective catalytic reduction(NH_(3)-SCR)is the most widely used technology in thefield of industrialflue gas denitrification.However,the presence of heavy metals influe gas can seriously affect the performance of...Ammonia selective catalytic reduction(NH_(3)-SCR)is the most widely used technology in thefield of industrialflue gas denitrification.However,the presence of heavy metals influe gas can seriously affect the performance of SCR catalysts,leading to their deactivation or even failure.Therefore,it is of great significance to deeply study the poisoning mechanism of SCR catalysts under the action of heavy metals and how to enhance their resistance to poisoning.This article reviews the reaction mechanism of NH_(3)-SCR technology,compares the impact of heavy metals on the activity of different SCR catalysts,and then discusses in detail the poisoning mechanism of SCR catalysts by heavy metals,including pore blockage,reduction of specific surface area,and destruction of active centers caused by heavy metal deposition,all of which jointly lead to the physical or chemical poisoning of the catalyst.Meanwhile,the mechanism of action when multiple toxicants coexist was analyzed.To effectively address these challenges,the article further summarizes various methods to improve the catalyst's resistance to heavy metal poisoning,such as element doping,structural optimization,and carrier addition,which significantly enhance the heavy metal resistance of the catalyst.Finally,the article provides a prospective analysis of the challenges faced by NH_(3)-SCR catalysts in anti-heavy metal poisoning technology,emphasizing the necessity of in-depth research on the poisoning mechanism,exploration of the mechanism of synergistic action of multiple pollutants,development of comprehensive anti-poisoning strategies,and research on catalyst regeneration technology,in order to promote the development of efficient anti-heavy metal poisoning NH_(3)-SCR catalysts.展开更多
The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) ...The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) and promote the balance of the carbon cycle.Formate is one of the most economical and practical products of all the electrochemical CO_(2) reduction products.Among the many metal-based electrocatalysts that can convert CO_(2) into formate,Sn-based catalysts have received a lot of attention because of their low-cost,non-toxic characteristics and high selectivity for formate.In this article,the most recent development of Sn-based electrocatalysts is comprehensively summarized by giving examples,which are mainly divided into monometallic Sn,alloyed Sn,Sn-based compounds and Sn composite catalysts.Finally,the current performance enhancement strategies and future directions of the field are summarized.展开更多
Silicoaluminophosphate(SAPO)molecular sieves possess diverse architectures and exceptional high-temperature hydrothermal stability,rendering them important acid catalysts.However,enhancing acid concentration of certai...Silicoaluminophosphate(SAPO)molecular sieves possess diverse architectures and exceptional high-temperature hydrothermal stability,rendering them important acid catalysts.However,enhancing acid concentration of certain SAPO materials remains challenging,which limits their catalytic applications.Here,we report the synthesis of a series of SAPO materials using a developed SAPO precursor plus dual template(SPDT)strategy.A variety of SAPO materials characterized by high silica content and enhanced acidity,such as SAPO-34/56 intergrowths,SAPO-56,and SAPO-17,have been synthesized and thoroughly characterized using various techniques including integrated differential phase-contrast scanning transmission electron microscopy,two-dimensional solid-state nuclear magnetic resonance spectroscopy,and continuous rotation electron diffraction.The use of silica-enriched SAPO precursor combined with the flexible selection of the second template enables the crystalline phase regulation and improves the Si atoms incorporation into the framework.Notably,the synthesized SAPO-17 with abundant Si(4Al)species and unprecedentedly high acid density exhibits exceptional DeNO_(x)activity after Cu loading,with NO_(x)conversion exceeding 90%at 175–700℃.This outstanding performance can be attributed to the unique ERI structure and the increased acidity of SAPO-17.This work not only presents an effective method for synthesizing SAPO molecular sieves with enhanced acidity but also offers a new perspective for expanding the active temperature range of the ammonia selective catalytic reduction reaction.展开更多
Transition metal-doped CeO_(2)catalysts exhibit great potentials for the selective catalytic reduction(SCR)of nitrogen oxide(NOx)with NH_(3)(NH_(3)-SCR).However,traditional research mainly relies on a lot of experimen...Transition metal-doped CeO_(2)catalysts exhibit great potentials for the selective catalytic reduction(SCR)of nitrogen oxide(NOx)with NH_(3)(NH_(3)-SCR).However,traditional research mainly relies on a lot of experiments to find out effective catalysts,which wastes a lot of time and resources.Screening out effective CeO_(2)-based catalysts for low-temperature NH_(3)-SCR via density functional theory(DFT)calculations is crucial for the rational design and synthesis of efficient catalysts.Herein,transition metal(M=Co,Cr,Cu,Fe,Mn,Mo,Nb,Ni,Ta,Ti,V,and W)-doped CeO_(2)catalysts were screened out via accelerated DFT calculations for NH_(3)-SCR of nitric-oxide(NO)using three theoretical terms;(i)an adsorption energy of NH_(3),(ii)an adsorption energy of NO,and(iii)the reaction energies between NO with O_(2)and lattice oxygen.The theoretically predicted trend in catalytic performance is as follows:CeO_(2)-Mn,-Cu,-Mo>CeO_(2)-Fe,-Co,-Ni,-V,-Cr>CeO_(2)-W,-Ti>CeO_(2)-Nb,-Ta.The theoretical prediction was well verified via experimental NH_(3)-SCR activity of NO at low temperatures(90–300℃),demonstrating CeO_(2)-Mo as efficient NH_(3)-SCR catalyst across a broad temperature range.Temperature-programmed desorption of NH_(3)and in situ diffuse reflectance infrared Fourier transforms spectroscopy further indicated that metal doping significantly enhanced the NH_(3)adsorption capacity and strength of CeO_(2)in the medium-to low-temperature range.Consequently,accelerated DFT calculations provide a useful tool with great potentials for predicting the catalytic performance.展开更多
The mechanical performance of flexible catalysts remains a significant challenge for industrial applications.In this study,graphene oxide(GO)functions as both a binder and a redox mediator,serving as a crucial"br...The mechanical performance of flexible catalysts remains a significant challenge for industrial applications.In this study,graphene oxide(GO)functions as both a binder and a redox mediator,serving as a crucial"bridge"between metal species and the organic foam,thereby substantially enhancing NO_(x) conversion efficiency.Catalytic activity tests demonstrate that the GO-modified MnCo-MS@0.05GO catalyst achieves a NO_(x) conversion rate exceeding 95%.The incorporation of GO strengthens the adhesion between the organic foam and metal components,increases the surface roughness of the sponge,and ensures the uniform and stable distribution of metal active sites.Additionally,GO enhances the content of effective catalytic species,improves electron transfer efficiency in the selective catalytic reduction reaction,and reduces diffusion resistance.To elucidate the NO reduction mechanism,in situ diffuse reflectance infrared Fourier transform spectroscopy and transient reaction studies were performed.The results indicate that as the reaction temperature increases,both the Eley-Rideal and Langmuir-Hinshelwood mechanisms contribute to promoting the SCR reaction rate.展开更多
The problem of water and sulfur poisoning in flue gas atmosphere remains a significant obstacle for low-temperature deNO_(x) catalysts.This study investigated the sulfation mechanism of the CoMn_(2)O_(4)/CeTiO_(x)(CMC...The problem of water and sulfur poisoning in flue gas atmosphere remains a significant obstacle for low-temperature deNO_(x) catalysts.This study investigated the sulfation mechanism of the CoMn_(2)O_(4)/CeTiO_(x)(CMCT)catalyst during the selective catalytic reduction of NO_(x) with NH3 under conditions containing H2O and SO_(2) at 150℃.Employing a comprehensive suite of time-resolved analysis and characterization techniques,the evolution of sulfate species was systematically categorized into three stages:initial rapid surface sulfate accumulation,the transformation of surface sulfates to bulk metal sulfates,and partial sulfates decomposition after the removal of H2O and SO_(2).These findings indicate that bulk metal sulfates irreversibly deactivate the catalyst by distorting active component lattices and consuming oxygen vacancies,whereas surface sulfates(including ammonium sulfates and surface-coordinated metal sulfates)cause reversible performance loss through decomposition.Furthermore,the competitive adsorption of H2O and SO_(2) significantly influences the catalytic efficiency,with H2O suppressing SO_(2) adsorption while simultaneously enhancing the formation of Brönsted acid sites.This research underscores the critical role of sulfate dynamics on catalyst performance,revealing the enhanced SO_(2) resistance of the Eley-Rideal mechanism facilitated by the Ce-Ti support relative to the Langmuir-Hinshelwood pathway.Collectively,the study unravels the complex interplay of sulfate dynamics influencing catalyst performance and provides potential approaches to mitigate deactivation in demanding atmospheric conditions.展开更多
In order to utilize slag discarded by nickel plants, the selective recovery of nickel and copper versus iron was investigated by selective reduction, which was achieved by controlling the reduction parameters and magn...In order to utilize slag discarded by nickel plants, the selective recovery of nickel and copper versus iron was investigated by selective reduction, which was achieved by controlling the reduction parameters and magnetic separation process on bench scale. The results show that increasing the basicity （mass ratio of CaO to SIO2） of nickel slag facilitates the enrichment of nickel and copper The process parameters for selective reduction were optimized as follows： basicity of 0.15, reducing at 1200 ~C for 20 min, 5% coal on a dried slag mass base. The grinding-magnetic separation results of reduced briquettes show that concentrate containing 3.25%Ni, 1.20%Cu and 75.26%Fe is obtained and selective enrichment is achieved with a recovery of 82.20%, 80.00% for nickel and copper respectively, while the recovery of iron is only 42.17%. The S and P contents are not reduced obviously and further research may be needed to examine the behaviors of S and P in the process.展开更多
Different transition metals were used to modify V2O5-based catalysts （M-V, M = Cu, Fe, Mn, Co） on TiO2 via impregnation, for the selective reduction of NO with NH3. The introduced metals induced high dispersion in t...Different transition metals were used to modify V2O5-based catalysts （M-V, M = Cu, Fe, Mn, Co） on TiO2 via impregnation, for the selective reduction of NO with NH3. The introduced metals induced high dispersion in the vanadium species and the formation of vanadates on the TiO2 support, and increased the amount of surface acid sites and the strength of these acids. The strong acid sites might be responsible for the high N2 selectivity at higher temperatures. Among these catalysts, Cu-V/TiO2 showed the highest activity and N2 selectivity at 225-375 ~C. The results of X-ray photo- electron spectroscopy, NH3-temperature-programmed desorption, and in-situ diffuse reflectance infrared Fourier transform spectroscopy suggested that the improved performance was probably due to more active surface oxygen species and increased strong surface acid sites. The outstanding activity, stability, and SO2/H2O durability of Cu-V/TiO2 make it a candidate to be a NOx removal catalyst for stationary flue gas.展开更多
V2O5/TiO2-ZrO2 catalysts containing various amounts of WO3 were synthesized.The catalyst morphologies,catalytic performances,and reaction mechanisms in the selective catalytic reduction of NOx by NH3 were investigated...V2O5/TiO2-ZrO2 catalysts containing various amounts of WO3 were synthesized.The catalyst morphologies,catalytic performances,and reaction mechanisms in the selective catalytic reduction of NOx by NH3 were investigated using in situ diffuse-reflectance infrared Fourier-transform spectroscopy,temperature-programmed reduction（TPR）,X-ray diffraction,and the Brunauer-Emmett-Teller（BET） method.The BET surface area of the triple oxides increased with increasing ZrO2 doping but gradually decreased with increasing WO3 loading.Addition of sufficient WO3 helped to stabilize the pore structure and the combination of WO3 and ZrO2 improved dispersion of all the metal oxides.The mechanisms of reactions using V2O5-9%WO3/TiO2-ZrO2 and V2O5-9%WO3/TiO2were compared by using either a single or mixed gas feed and various pretreatments.The results suggest that both reactions followed the Eley-Ridel mechanism;however,the dominant acid sites,which depended on the addition of WO3 or ZrO2,determined the pathways for NOx reduction,and involved[NH4^＋-NO-Bronsted acid site]^＊ and[NH2-NO-Lewis acid site]^＊ intermediates,respectively.NH3-TPR and H2-TPR showed that the metal oxides in the catalysts were not reduced by NH3 and O2did not reoxidize the catalyst surfaces but participated in the formation of H2O and NO2.展开更多
CeTiOx and CeZrTiOx catalysts were prepared by a coprecipitation method and used for selective catalytic reduction of NOx by NH3 （NH3‐SCR）. Various amounts of KNO3 were impregnated on the catalyst surface to invest...CeTiOx and CeZrTiOx catalysts were prepared by a coprecipitation method and used for selective catalytic reduction of NOx by NH3 （NH3‐SCR）. Various amounts of KNO3 were impregnated on the catalyst surface to investigate the effects of Zr addition on the K＋‐poisoning resistance of the CeTiOx catalyst. The NH3‐SCR performance of the catalysts showed that the NOx removal activity of the Zr‐modified catalyst after poisoning was better than that of the CeTiOx catalyst. Brunau‐er‐Emmett‐Teller data indicated that the Zr‐containing catalyst had a larger specific surface area and pore volume both before and after K＋poisoning. X‐ray diffraction, Raman spectroscopy, and transmission electron microscopy showed that Zr doping inhibited anatase TiO2 crystal grain growth, i.e., the molten salt flux effect caused by the loaded KNO3 was inhibited. The Ce 3d X‐ray photoelectron spectra showed that the Ce3＋/Ce4＋ratio of CeZrTiOx decreased more slowly than that of CeTiOx with increasing K＋loading, indicating that Zr addition preserved more crystal defects and oxygen vacancies; this improved the catalytic performance. The acidity was a key factor in the NH3‐SCR performance; the temperature‐programmed desorption of NH3 results showed that Zr doping inhibited the decrease in the surface acidity. The results suggest that Zr improved the K＋‐poisoning resistance of the CeTiOx catalyst.展开更多
A series of CuSO4/TiO2 catalysts were prepared using a wet impregnation method.The activity of each sample in the selective catalytic reduction of NO by NH3（NH3-SCR） was determined.The effects of SO2 and H2O,and the...A series of CuSO4/TiO2 catalysts were prepared using a wet impregnation method.The activity of each sample in the selective catalytic reduction of NO by NH3（NH3-SCR） was determined.The effects of SO2 and H2O,and their combined effect,on the activity were examined at 340 ℃ for 24 h.The catalysts were characterized using N2 adsorption-desorption,X-ray diffraction,X-ray photoelectron spectroscopy,temperature-programmed reduction of H2（H2-TPR）,temperature-programmed desorption of NH3（NH3-TPD）,and in situ diffuse-reflectance infrared Fourier-transform spectroscopy（DRIFTS）.The CuSO4/TiO2 catalysts had good activities,with low production of N2O above 340 ℃.SO2 or a combination of SO2 and H2O had little effect on the activity,and H2O caused only a slight decrease in activity during the experimental period.The NH3-TPD and H2-TPR results showed that CuSO4 increased the amounts of acid sites and adsorbed oxygen on the catalyst.In situ DRIFTS showed that the NH3-SCR reaction on the CuSO4/TiO2 catalysts followed an Eley-Rideal mechanism.The reaction of gaseous NO with NH3 adsorbed on Lewis acid sites to form N2 and H2O could be the main reaction pathway,and oxygen adsorption might favor this process.展开更多
ZSM-5 zeolites were directly synthesized on the surface of honeycomb cordierite substrates by hydrothermal method and certified by XRD and SEM techniques; the adhesion of ZSM-5 coatings was evaluated by ultrasonic vib...ZSM-5 zeolites were directly synthesized on the surface of honeycomb cordierite substrates by hydrothermal method and certified by XRD and SEM techniques; the adhesion of ZSM-5 coatings was evaluated by ultrasonic vibration. Cu-ZSM-5/cordierite monolithic catalyst was prepared by ion-exchange and impregnation method and applied for the selective catalytic reduction （SCR） of NO by NH3 using a simulated diesel exhaust. The results show that the cordierite surface is almost completely covered by ZSM-5 crystals and the crystallization time greatly impacts the loadings and adhesion of ZSM-5 coatings on substrate, the NOx removal rate over Cu-ZSM-5/cordierite is above 90% in a temperature range of 240-480℃. Moreover, Cu-ZSM-5/cordierite prepared by different methods shows a wide temperature window （240-540 ℃） with high NO removal activities.展开更多
A series of Fe‐Mn/Al2O3 catalysts were prepared and studied for low temperature selective catalytic reduction （SCR） of NO with NH3 in a fixed‐bed reactor. The effects of Fe and Mn on NO conversion and the deactiva...A series of Fe‐Mn/Al2O3 catalysts were prepared and studied for low temperature selective catalytic reduction （SCR） of NO with NH3 in a fixed‐bed reactor. The effects of Fe and Mn on NO conversion and the deactivation of the catalysts were studied. N2 adsorption‐desorption, X‐ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, H2 temperature‐programmed reduction, NH3 temperature‐programmed desorption, X‐ray photoelectron spectroscopy （XPS）, thermal gravimetric analysis and Fourier transform infrared spectroscopy were used to character‐ize the catalysts. The 8Fe‐8Mn/Al2O3 catalyst gave 99%of NO conversion at 150？？ and more than 92.6%NO conversion was obtained in a wide low temperature range of 90–210？？. XPS analysis demonstrated that the Fe3＋was the main iron valence state on the catalyst surface and the addition of Mn increased the accumulation of Fe on the surface. The higher specific surface area, enhanced dispersion of amorphous Fe and Mn, improved reduction properties and surface acidity, lower binding energy, higher Mn4＋/Mn3＋ratio and more adsorbed oxygen species resulted in higher NO conversion for the 8Fe‐8Mn/Al2O3 catalyst. In addition, the SCR activity of the 8Fe‐8Mn/Al2O3 cata‐lyst was only slightly decreased in the presence of H2O and SO2, which indicated that the catalyst had better tolerance to H2O and SO2. The reaction temperature was crucial for the SO2 resistance of catalyst and the decrease of catalytic activity caused by SO2 was mainly due to the sulfate salts formed on the catalyst.展开更多
Cu-SAPO-34/cordierite catalysts were prepared via one-step hydrothermal synthesis method and their performances to remove NO x from the diesel vehicle exhaust were evaluated. The morphology, structure, Cu content and ...Cu-SAPO-34/cordierite catalysts were prepared via one-step hydrothermal synthesis method and their performances to remove NO x from the diesel vehicle exhaust were evaluated. The morphology, structure, Cu content and valence state were characterized by SEM, XRD, ICP and XPS, respectively. The experimental results show the active component Cu of the catalysts via in situ synthesis could significantly improve the selective catalytic reduction （SCR） activities of NOx and the optimal Cu content is in the range of 0.30%-0.40%（mass fraction）. No N 2 O is detected by gas chromatograph （GC） during the evaluation process, which implies that NOx is almost entirely converted to N2 over Cu-SAPO-34/cordierite catalyst. The conversion rate of NOx to N2 by NH3 over catalyst could almost be up to 100%in the temperature range of 300-670 ℃with a space velocity of 12000 h-1 and it is still more than 60% at 300-620 ℃ under 36000 h-1. The catalysts also show the good hydrothermal and chemical stability at the atmosphere with H 2 O.展开更多
基金Supported by National Key Research and Development Program of China(2020YFD1100302)。
文摘Under the context of global energy transition and carbon neutrality,controlling nitrogen oxide(NO_(x))emissions from biomass combustion is of great significance,and the development of high-efficiency low-temperature catalysts has become a current research focus.In this study,Nb was used to dope and modify the Mn_(7)-Cu_(3)/BCN catalyst to construct the Mn_(7)-Cu_(3)-Nb_(x)/BCN system.The doping amount was optimized through selective catalytic reduction(SCR)activity tests.The reaction mechanism was explored by combining in situ DRIFTS and density functional theory(DFT)simulations.Experimental findings revealed that the catalyst doped with 0.05%Nb achieved the optimal performance,sustaining a NO conversion efficiency of≥94%within the temperature window of 150−275℃while demonstrating improved resistance to alkali metal K poisoning.Mechanistic analyses showed that at low temperatures,the catalyst facilitated the SCR reaction via both the Eley-Rideal(E-R)and Langmuir-Hinshelwood(L-H)pathways,with the synergistic interaction between multiple active sites driving the efficient conversion of NH3 and NO.DFT calculations further confirmed that both pathways had the characteristics of low reaction energy barriers and significant exothermicity,ensuring the high activity and feasibility of the low-temperature reaction.The findings provided foundational theoretical support for the design of Nb-doped Mn-Cu-supported catalysts and the exploration of the underlying working mechanisms.
文摘Nitrogen oxides(NO_(x))present in flue gas are economically renewable N1 resources.Unlike traditional selective catalytic reduction processes that convert NO into N_(2),redirecting NO towards the synthesis of value-added NH_(3)offers significant practical benefits.In this study,a Ti-based metal-organic framework(Ti-MOF),specifically MIL-125,was utilized as a support for Fe,which was subsequently calcined at 400℃to produce a Fe_(2)O_(3)/TiO_(2)-MOF catalyst.The resulting catalyst demonstrated exceptional performance,achieving 99%NO conversion and 95%NH_(3)selectivity under optimal conditions of 450℃,0.1 MPa,and a gas hourly space velocity of 38000 mL g^(–1)h^(−1).Additionally,the catalyst exhibited excellent stability and resistance to water and sulfur.The high efficiency of Fe_(2)O_(3)/TiO_(2)-MOF is attributed to the abundance of Fe^(2+)sites at the reaction temperature,which enhances NO adsorption and activation.Furthermore,density functional theory calculations suggest that NO undergoes hydrogenation at the N-terminus on the Fe_(2)O_(3)/TiO_(2)-MOF surface,leading directly to NH_(3)synthesis rather than dissociation followed by hydrogenation.This catalyst presents a novel approach for converting NO_(x)into high-value chemical products.
文摘Selective reduction of N_(2)O by CO under excess O_(2) was effectively catalyzed by Fe(0.9 wt%)-exchangedβzeolite(Fe0.9β)in the temperature range of 250–500°C.Kinetic experiments showed that the apparent activation energy for N_(2)O reduction with CO was lower than that for the direct N_(2)O decomposition,and the rate of N_(2)O reduction with CO at 300℃ was 16 times higher than that for direct N_(2)O decomposition.Reaction order analyses showed that CO and N_(2)O were involved in the kinetically important step,while O_(2) was not involved in the important step.At 300℃,the rate of CO oxidation with 0.1%N_(2)O was two times higher than that of CO oxidation with 10%O_(2).This quantitatively demonstrates the preferential oxidation of CO by N_(2)O under excess O_(2) over Fe0.9β.Operando/in-situ diffuse reflectance ultraviolet-visible spectroscopy showed a redox-based catalytic cycle;α-Fe-O species are reduced by CO to give CO_(2) and reduced Fe species,which are then re-oxidized by N_(2)O to regenerate theα-Fe-O species.The initial rate for the regeneration ofα-Fe-O species under 0.1%N_(2)O was four times higher than that under 10%O_(2).This result shows quantitative evidence on the higher reactivity of N_(2)O than O_(2) for the regeneration ofα-Fe-O intermediates,providing a fundamental reason why the Fe0.9βcatalyst selectively promotes the CO+N_(2)O reaction under excess O_(2) rather than the undesired side reaction of CO+O_(2).The mechanistic model was verified by the results of in-situ Fe K-edge X-ray absorption spectroscopy.
文摘The distributions of framework aluminum(Al)in zeolites critically govern the location and speciation of active copper(Cu)centers,thereby influencing their performance in ammonia selective catalytic reduction(NH_(3)-SCR)of nitrogen oxides(NO_(x)).Conventional Cu-SSZ-39(Cu-SSZ-39-T)exhibits excellent hydrothermal stability but limited low-temperature activity(150–225℃)due to a low concentration of Al in 8-membered rings(8MRs)that inhibits the formation of active[Cu(OH)]^(+)-Z species.Herein,an SSZ-39 zeolite synthesized with potassium ions(SSZ-39-K)achieved a significantly higher 8MR Al fraction(37.6%).Density functional theory calculations and H_(2)-temperature-programmed reduction analyses confirmed that the increased 8MR Al population facilitated the formation of[Cu(OH)]^(+)-Z species.Aged Cu-SSZ-39-K exhibited nearly twice the NO_(x)conversion of aged Cu-SSZ-39-T in the 150–225℃range while maintaining comparable high-temperature activity(250–550℃)under a gas hourly space velocity of 250,000 h^(-1).Enhanced low-temperature performance is particularly beneficial for mitigating NO_(x)emissions during cold-start phase.Moreover,SSZ-39-K was synthesized with a high crystallization yield(~65%),nearly double the highest yield(33%)reported for direct synthesis routes.This work establishes a robust strategy for tailoring Al distributions in SSZ-39 zeolites,offering an effective pathway to improve low-temperature NH_(3)-SCR performance and promote practical implementation.
基金the National Natural Science Foundation of China(Nos.22125604,22106100,21976117,22276119)Shanghai Rising-Star Program(No.22QA1403700).
文摘Developing a high-efficiency catalyst with both superior low-temperature activity and good N_(2)selectivity is still challenging for the NH_(3)selective catalytic reduction(SCR)of NO_(x)from mobile sources.Herein,we demonstrate the improved low-temperature activity and N_(2)selectivity by regulating the redox and acidic properties of MnCe oxides supported on etched ZSM-5 supports.The etched ZSM-5 enables the highly dispersed state of MnCeOx species and strong interaction between Mn and Ce species,which promotes the reduction of CeO2,facilitates electron transfer from Mn to Ce,and generates more Mn^(4+)and Ce^(3+)species.The strong redox capacity contributes to forming the reactive nitrate species and-NH_(2)species from oxidative dehydrogenation of NH_(3).Moreover,the adsorbed NH_(3)and-NH_(2)species are the reactive intermediates that promote the formation of N_(2).This work demonstrates an effective strategy to enhance the low-temperature activity and N_(2)selectivity of SCR catalysts,contributing to the NO_(x)control for the low-temperature exhaust gas during the cold-start of diesel vehicles.
基金financially supported by the National Key Research and Development Program of China(No.2023YFC3707002)Hunan Provincial Innovation Foundation for Postgraduate(No.QL20220069)Postgraduate Innovative Project of Central South University(No.1053320214756).
文摘The implementation of embedded selective catalytic reduction(SCR)denitration in chain grate during iron ore pelletizing process obviates additional flue gas heating.However,the influence of gas components and alkali metal on SCR denitration requires attention.The SCR denitration behavior in the preheating section of chain grate was investigated,and the combined influence mechanisms of H_(2)O(g),SO_(2),and potassium were revealed.The results show that the presence of H_(2)O(g)and SO_(2) in the flue gas decreases the NO conversion rate of the catalyst from 96.3%to 79.5%,while potassium adsorbed on the catalyst surface further reduces the NO conversion rate to 74.1%.H_(2)O(g),SO_(2),and potassium in the flue gas form sulfate and potassium salt on the catalyst surface,blocking the pore structure,thereby decreasing the gas adsorption capacity of the catalyst.Moreover,SO_(2) and potassium engage in competitive adsorption and reaction with NH_(3) and NO at the active sites on the catalyst surface,reducing the content and activity of the catalyst effective component.Increasing the flue gas temperature can promote the decomposition of ammonium sulfate and ammonium bisulfate on the catalyst surface,but it has little effect on potassium.Additionally,potassium will exacerbate sulfur poisoning of the catalyst.Hence,the embedded SCR denitration process requires electrostatic precipitation to eliminate the adverse impacts of potassium and thermal regime optimization to raise flue gas temperature to 350℃,thereby increasing NO conversion rate exceeding 85%.
基金supported by National Natural Science Foundation of China(U20A20130)Fundamental Research Funds for the Central Universities(FRF-EYIT-23-07).
文摘Ammonia selective catalytic reduction(NH_(3)-SCR)is the most widely used technology in thefield of industrialflue gas denitrification.However,the presence of heavy metals influe gas can seriously affect the performance of SCR catalysts,leading to their deactivation or even failure.Therefore,it is of great significance to deeply study the poisoning mechanism of SCR catalysts under the action of heavy metals and how to enhance their resistance to poisoning.This article reviews the reaction mechanism of NH_(3)-SCR technology,compares the impact of heavy metals on the activity of different SCR catalysts,and then discusses in detail the poisoning mechanism of SCR catalysts by heavy metals,including pore blockage,reduction of specific surface area,and destruction of active centers caused by heavy metal deposition,all of which jointly lead to the physical or chemical poisoning of the catalyst.Meanwhile,the mechanism of action when multiple toxicants coexist was analyzed.To effectively address these challenges,the article further summarizes various methods to improve the catalyst's resistance to heavy metal poisoning,such as element doping,structural optimization,and carrier addition,which significantly enhance the heavy metal resistance of the catalyst.Finally,the article provides a prospective analysis of the challenges faced by NH_(3)-SCR catalysts in anti-heavy metal poisoning technology,emphasizing the necessity of in-depth research on the poisoning mechanism,exploration of the mechanism of synergistic action of multiple pollutants,development of comprehensive anti-poisoning strategies,and research on catalyst regeneration technology,in order to promote the development of efficient anti-heavy metal poisoning NH_(3)-SCR catalysts.
基金Project(52204378)supported by the National Natural Science Foundation of China。
文摘The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) and promote the balance of the carbon cycle.Formate is one of the most economical and practical products of all the electrochemical CO_(2) reduction products.Among the many metal-based electrocatalysts that can convert CO_(2) into formate,Sn-based catalysts have received a lot of attention because of their low-cost,non-toxic characteristics and high selectivity for formate.In this article,the most recent development of Sn-based electrocatalysts is comprehensively summarized by giving examples,which are mainly divided into monometallic Sn,alloyed Sn,Sn-based compounds and Sn composite catalysts.Finally,the current performance enhancement strategies and future directions of the field are summarized.
文摘Silicoaluminophosphate(SAPO)molecular sieves possess diverse architectures and exceptional high-temperature hydrothermal stability,rendering them important acid catalysts.However,enhancing acid concentration of certain SAPO materials remains challenging,which limits their catalytic applications.Here,we report the synthesis of a series of SAPO materials using a developed SAPO precursor plus dual template(SPDT)strategy.A variety of SAPO materials characterized by high silica content and enhanced acidity,such as SAPO-34/56 intergrowths,SAPO-56,and SAPO-17,have been synthesized and thoroughly characterized using various techniques including integrated differential phase-contrast scanning transmission electron microscopy,two-dimensional solid-state nuclear magnetic resonance spectroscopy,and continuous rotation electron diffraction.The use of silica-enriched SAPO precursor combined with the flexible selection of the second template enables the crystalline phase regulation and improves the Si atoms incorporation into the framework.Notably,the synthesized SAPO-17 with abundant Si(4Al)species and unprecedentedly high acid density exhibits exceptional DeNO_(x)activity after Cu loading,with NO_(x)conversion exceeding 90%at 175–700℃.This outstanding performance can be attributed to the unique ERI structure and the increased acidity of SAPO-17.This work not only presents an effective method for synthesizing SAPO molecular sieves with enhanced acidity but also offers a new perspective for expanding the active temperature range of the ammonia selective catalytic reduction reaction.
基金financially supported by the National Key R&D Program of China(Nos.2021YFC1910504 and 2024YFC3907701)the National Energy-Saving and Low-Carbon Materials Production and Application Demonstration Platform Program(No.TC220H06N)+2 种基金the Fundamental Research Funds for the Central Universities(No.FRF-EYIT-23-07)the National Natural Science Foundation of China(No.52204412)Beijing Natural Science Foundation(No.2242046)
文摘Transition metal-doped CeO_(2)catalysts exhibit great potentials for the selective catalytic reduction(SCR)of nitrogen oxide(NOx)with NH_(3)(NH_(3)-SCR).However,traditional research mainly relies on a lot of experiments to find out effective catalysts,which wastes a lot of time and resources.Screening out effective CeO_(2)-based catalysts for low-temperature NH_(3)-SCR via density functional theory(DFT)calculations is crucial for the rational design and synthesis of efficient catalysts.Herein,transition metal(M=Co,Cr,Cu,Fe,Mn,Mo,Nb,Ni,Ta,Ti,V,and W)-doped CeO_(2)catalysts were screened out via accelerated DFT calculations for NH_(3)-SCR of nitric-oxide(NO)using three theoretical terms;(i)an adsorption energy of NH_(3),(ii)an adsorption energy of NO,and(iii)the reaction energies between NO with O_(2)and lattice oxygen.The theoretically predicted trend in catalytic performance is as follows:CeO_(2)-Mn,-Cu,-Mo>CeO_(2)-Fe,-Co,-Ni,-V,-Cr>CeO_(2)-W,-Ti>CeO_(2)-Nb,-Ta.The theoretical prediction was well verified via experimental NH_(3)-SCR activity of NO at low temperatures(90–300℃),demonstrating CeO_(2)-Mo as efficient NH_(3)-SCR catalyst across a broad temperature range.Temperature-programmed desorption of NH_(3)and in situ diffuse reflectance infrared Fourier transforms spectroscopy further indicated that metal doping significantly enhanced the NH_(3)adsorption capacity and strength of CeO_(2)in the medium-to low-temperature range.Consequently,accelerated DFT calculations provide a useful tool with great potentials for predicting the catalytic performance.
文摘The mechanical performance of flexible catalysts remains a significant challenge for industrial applications.In this study,graphene oxide(GO)functions as both a binder and a redox mediator,serving as a crucial"bridge"between metal species and the organic foam,thereby substantially enhancing NO_(x) conversion efficiency.Catalytic activity tests demonstrate that the GO-modified MnCo-MS@0.05GO catalyst achieves a NO_(x) conversion rate exceeding 95%.The incorporation of GO strengthens the adhesion between the organic foam and metal components,increases the surface roughness of the sponge,and ensures the uniform and stable distribution of metal active sites.Additionally,GO enhances the content of effective catalytic species,improves electron transfer efficiency in the selective catalytic reduction reaction,and reduces diffusion resistance.To elucidate the NO reduction mechanism,in situ diffuse reflectance infrared Fourier transform spectroscopy and transient reaction studies were performed.The results indicate that as the reaction temperature increases,both the Eley-Rideal and Langmuir-Hinshelwood mechanisms contribute to promoting the SCR reaction rate.
文摘The problem of water and sulfur poisoning in flue gas atmosphere remains a significant obstacle for low-temperature deNO_(x) catalysts.This study investigated the sulfation mechanism of the CoMn_(2)O_(4)/CeTiO_(x)(CMCT)catalyst during the selective catalytic reduction of NO_(x) with NH3 under conditions containing H2O and SO_(2) at 150℃.Employing a comprehensive suite of time-resolved analysis and characterization techniques,the evolution of sulfate species was systematically categorized into three stages:initial rapid surface sulfate accumulation,the transformation of surface sulfates to bulk metal sulfates,and partial sulfates decomposition after the removal of H2O and SO_(2).These findings indicate that bulk metal sulfates irreversibly deactivate the catalyst by distorting active component lattices and consuming oxygen vacancies,whereas surface sulfates(including ammonium sulfates and surface-coordinated metal sulfates)cause reversible performance loss through decomposition.Furthermore,the competitive adsorption of H2O and SO_(2) significantly influences the catalytic efficiency,with H2O suppressing SO_(2) adsorption while simultaneously enhancing the formation of Brönsted acid sites.This research underscores the critical role of sulfate dynamics on catalyst performance,revealing the enhanced SO_(2) resistance of the Eley-Rideal mechanism facilitated by the Ce-Ti support relative to the Langmuir-Hinshelwood pathway.Collectively,the study unravels the complex interplay of sulfate dynamics influencing catalyst performance and provides potential approaches to mitigate deactivation in demanding atmospheric conditions.
基金Project([2009]606)supported by the National Development and Reform Commission of ChinaProject(50974135)supported by the National Natural Science Foundation of China
文摘In order to utilize slag discarded by nickel plants, the selective recovery of nickel and copper versus iron was investigated by selective reduction, which was achieved by controlling the reduction parameters and magnetic separation process on bench scale. The results show that increasing the basicity （mass ratio of CaO to SIO2） of nickel slag facilitates the enrichment of nickel and copper The process parameters for selective reduction were optimized as follows： basicity of 0.15, reducing at 1200 ~C for 20 min, 5% coal on a dried slag mass base. The grinding-magnetic separation results of reduced briquettes show that concentrate containing 3.25%Ni, 1.20%Cu and 75.26%Fe is obtained and selective enrichment is achieved with a recovery of 82.20%, 80.00% for nickel and copper respectively, while the recovery of iron is only 42.17%. The S and P contents are not reduced obviously and further research may be needed to examine the behaviors of S and P in the process.
基金supported by the National Natural Science Foundation of China (21303099)the National Basic Research Program of China(973 Program,2014CB660803)+1 种基金the Shanghai Municipal Education Commission(14ZZ097, B.3704713001)the Research Fund for Innovation Program of Shanghai University (K.10040713003)~~
文摘Different transition metals were used to modify V2O5-based catalysts （M-V, M = Cu, Fe, Mn, Co） on TiO2 via impregnation, for the selective reduction of NO with NH3. The introduced metals induced high dispersion in the vanadium species and the formation of vanadates on the TiO2 support, and increased the amount of surface acid sites and the strength of these acids. The strong acid sites might be responsible for the high N2 selectivity at higher temperatures. Among these catalysts, Cu-V/TiO2 showed the highest activity and N2 selectivity at 225-375 ~C. The results of X-ray photo- electron spectroscopy, NH3-temperature-programmed desorption, and in-situ diffuse reflectance infrared Fourier transform spectroscopy suggested that the improved performance was probably due to more active surface oxygen species and increased strong surface acid sites. The outstanding activity, stability, and SO2/H2O durability of Cu-V/TiO2 make it a candidate to be a NOx removal catalyst for stationary flue gas.
基金supported by the National Natural Science Foundation of China(51306034)Key Research&Development Projects of Jiangsu Province(BE2015677)the National Basic Research Program of China(2013CB228505)~~
文摘V2O5/TiO2-ZrO2 catalysts containing various amounts of WO3 were synthesized.The catalyst morphologies,catalytic performances,and reaction mechanisms in the selective catalytic reduction of NOx by NH3 were investigated using in situ diffuse-reflectance infrared Fourier-transform spectroscopy,temperature-programmed reduction（TPR）,X-ray diffraction,and the Brunauer-Emmett-Teller（BET） method.The BET surface area of the triple oxides increased with increasing ZrO2 doping but gradually decreased with increasing WO3 loading.Addition of sufficient WO3 helped to stabilize the pore structure and the combination of WO3 and ZrO2 improved dispersion of all the metal oxides.The mechanisms of reactions using V2O5-9%WO3/TiO2-ZrO2 and V2O5-9%WO3/TiO2were compared by using either a single or mixed gas feed and various pretreatments.The results suggest that both reactions followed the Eley-Ridel mechanism;however,the dominant acid sites,which depended on the addition of WO3 or ZrO2,determined the pathways for NOx reduction,and involved[NH4^＋-NO-Bronsted acid site]^＊ and[NH2-NO-Lewis acid site]^＊ intermediates,respectively.NH3-TPR and H2-TPR showed that the metal oxides in the catalysts were not reduced by NH3 and O2did not reoxidize the catalyst surfaces but participated in the formation of H2O and NO2.
基金supported by the Major Research Program of Sichuan Province Science and Technology Department (2012FZ0008)the National Natural Science Foundation of China (21173153)+1 种基金the National High Technology Research and Development Program of China (863 Program,2013AA065304)the Sichuan University Research Foundation for Young Teachers (2015SCU11056)~~
文摘CeTiOx and CeZrTiOx catalysts were prepared by a coprecipitation method and used for selective catalytic reduction of NOx by NH3 （NH3‐SCR）. Various amounts of KNO3 were impregnated on the catalyst surface to investigate the effects of Zr addition on the K＋‐poisoning resistance of the CeTiOx catalyst. The NH3‐SCR performance of the catalysts showed that the NOx removal activity of the Zr‐modified catalyst after poisoning was better than that of the CeTiOx catalyst. Brunau‐er‐Emmett‐Teller data indicated that the Zr‐containing catalyst had a larger specific surface area and pore volume both before and after K＋poisoning. X‐ray diffraction, Raman spectroscopy, and transmission electron microscopy showed that Zr doping inhibited anatase TiO2 crystal grain growth, i.e., the molten salt flux effect caused by the loaded KNO3 was inhibited. The Ce 3d X‐ray photoelectron spectra showed that the Ce3＋/Ce4＋ratio of CeZrTiOx decreased more slowly than that of CeTiOx with increasing K＋loading, indicating that Zr addition preserved more crystal defects and oxygen vacancies; this improved the catalytic performance. The acidity was a key factor in the NH3‐SCR performance; the temperature‐programmed desorption of NH3 results showed that Zr doping inhibited the decrease in the surface acidity. The results suggest that Zr improved the K＋‐poisoning resistance of the CeTiOx catalyst.
基金supported by the Bureau of Science and Technology,Fujian Province,China(2015H0043)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB05050500)the National Natural Science Foundation of China(21403210)~~
文摘A series of CuSO4/TiO2 catalysts were prepared using a wet impregnation method.The activity of each sample in the selective catalytic reduction of NO by NH3（NH3-SCR） was determined.The effects of SO2 and H2O,and their combined effect,on the activity were examined at 340 ℃ for 24 h.The catalysts were characterized using N2 adsorption-desorption,X-ray diffraction,X-ray photoelectron spectroscopy,temperature-programmed reduction of H2（H2-TPR）,temperature-programmed desorption of NH3（NH3-TPD）,and in situ diffuse-reflectance infrared Fourier-transform spectroscopy（DRIFTS）.The CuSO4/TiO2 catalysts had good activities,with low production of N2O above 340 ℃.SO2 or a combination of SO2 and H2O had little effect on the activity,and H2O caused only a slight decrease in activity during the experimental period.The NH3-TPD and H2-TPR results showed that CuSO4 increased the amounts of acid sites and adsorbed oxygen on the catalyst.In situ DRIFTS showed that the NH3-SCR reaction on the CuSO4/TiO2 catalysts followed an Eley-Rideal mechanism.The reaction of gaseous NO with NH3 adsorbed on Lewis acid sites to form N2 and H2O could be the main reaction pathway,and oxygen adsorption might favor this process.
基金Project (20906067) supported by the National Natural Science Foundation of China
文摘ZSM-5 zeolites were directly synthesized on the surface of honeycomb cordierite substrates by hydrothermal method and certified by XRD and SEM techniques; the adhesion of ZSM-5 coatings was evaluated by ultrasonic vibration. Cu-ZSM-5/cordierite monolithic catalyst was prepared by ion-exchange and impregnation method and applied for the selective catalytic reduction （SCR） of NO by NH3 using a simulated diesel exhaust. The results show that the cordierite surface is almost completely covered by ZSM-5 crystals and the crystallization time greatly impacts the loadings and adhesion of ZSM-5 coatings on substrate, the NOx removal rate over Cu-ZSM-5/cordierite is above 90% in a temperature range of 240-480℃. Moreover, Cu-ZSM-5/cordierite prepared by different methods shows a wide temperature window （240-540 ℃） with high NO removal activities.
基金supported by the National High Technology Research and Development Program of China (863 Program,2015AA03A401)the National Natural Science Foundation of China (51276039)+1 种基金the Fundamental Research Funds for the Central Universities (020514380020,020514380030)the Postdoctoral Science Foundation of Jiangsu Province,China (1501033A)~~
文摘A series of Fe‐Mn/Al2O3 catalysts were prepared and studied for low temperature selective catalytic reduction （SCR） of NO with NH3 in a fixed‐bed reactor. The effects of Fe and Mn on NO conversion and the deactivation of the catalysts were studied. N2 adsorption‐desorption, X‐ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, H2 temperature‐programmed reduction, NH3 temperature‐programmed desorption, X‐ray photoelectron spectroscopy （XPS）, thermal gravimetric analysis and Fourier transform infrared spectroscopy were used to character‐ize the catalysts. The 8Fe‐8Mn/Al2O3 catalyst gave 99%of NO conversion at 150？？ and more than 92.6%NO conversion was obtained in a wide low temperature range of 90–210？？. XPS analysis demonstrated that the Fe3＋was the main iron valence state on the catalyst surface and the addition of Mn increased the accumulation of Fe on the surface. The higher specific surface area, enhanced dispersion of amorphous Fe and Mn, improved reduction properties and surface acidity, lower binding energy, higher Mn4＋/Mn3＋ratio and more adsorbed oxygen species resulted in higher NO conversion for the 8Fe‐8Mn/Al2O3 catalyst. In addition, the SCR activity of the 8Fe‐8Mn/Al2O3 cata‐lyst was only slightly decreased in the presence of H2O and SO2, which indicated that the catalyst had better tolerance to H2O and SO2. The reaction temperature was crucial for the SO2 resistance of catalyst and the decrease of catalytic activity caused by SO2 was mainly due to the sulfate salts formed on the catalyst.
基金Project(20906067)supported by the National Natural Science Foundation of ChinaProject(2011M500543)supported by the Postdoctoral Science Foundation of ChinaProject supported by the Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi
文摘Cu-SAPO-34/cordierite catalysts were prepared via one-step hydrothermal synthesis method and their performances to remove NO x from the diesel vehicle exhaust were evaluated. The morphology, structure, Cu content and valence state were characterized by SEM, XRD, ICP and XPS, respectively. The experimental results show the active component Cu of the catalysts via in situ synthesis could significantly improve the selective catalytic reduction （SCR） activities of NOx and the optimal Cu content is in the range of 0.30%-0.40%（mass fraction）. No N 2 O is detected by gas chromatograph （GC） during the evaluation process, which implies that NOx is almost entirely converted to N2 over Cu-SAPO-34/cordierite catalyst. The conversion rate of NOx to N2 by NH3 over catalyst could almost be up to 100%in the temperature range of 300-670 ℃with a space velocity of 12000 h-1 and it is still more than 60% at 300-620 ℃ under 36000 h-1. The catalysts also show the good hydrothermal and chemical stability at the atmosphere with H 2 O.
