Co-based alloy coating was prepared on Zr alloy using laser melting and cladding technique to study the difference in the high-temperature oxidation behavior between pure metal Co coatings and Co-T800 alloy coatings,a...Co-based alloy coating was prepared on Zr alloy using laser melting and cladding technique to study the difference in the high-temperature oxidation behavior between pure metal Co coatings and Co-T800 alloy coatings,as well as the wear resistance of the coatings.Besides,the effect of changing the laser melting process on the coatings was also investigated.The oxidation mass gain at 800–1200℃and the high-temperature oxidation behavior during high-temperature treatment for 1 h of two coated Zr alloy samples were studied.Results show that the Co coating and the Co-T800 coating have better resistance against high-temperature oxidation.After oxidizing at 1000℃for 1 h,the thickness of the oxide layer of the uncoated sample was 241.0μm,whereas that of the sample with Co-based coating is only 11.8–35.5μm.The friction wear test shows that the depth of the abrasion mark of the coated sample is only 1/2 of that of the substrate,indicating that the hardness and wear resistance of the Zr substrate are greatly improved.The disadvantage of Co-based coatings is the inferior corrosion resistance in 3.5wt%NaCl solution.展开更多
Propane dehydrogenation(PDH)has emerged as a key on-purpose technology for the production of propylene,but it often depends on toxic chromium and expensive platinum catalysts,highlighting the need for environmentally ...Propane dehydrogenation(PDH)has emerged as a key on-purpose technology for the production of propylene,but it often depends on toxic chromium and expensive platinum catalysts,highlighting the need for environmentally friendly and cost-effective alternatives.In this study,we developed a facile impregnation method to fabricate unsaturated Co single-atoms with a tricoordinated Co_(1)O_(3)H_(x) structure by regulating silanol nests in purely siliceous Beta zeolites.Detailed PDH catalytic tests and characterizations revealed a positive correlation between the presence of silanol nests and enhanced catalytic activity.Additionally,the unsaturated Co single-atoms exhibited a carbon deposition rate more than an order of magnitude slower than that of Co nanoparticles.Notably,the optimized Co_(0.3%)/deAl-meso-Beta catalyst achieved a record-high propylene formation rate of 21.2 mmol_(C3H6) g_(cat)^(-1) h^(-1),with an exceptional propylene selectivity of 99.1%at 550℃.Moreover,the Co_(0.3%)/deAl-meso-Beta catalyst demonstrated excellent stability,with negligible deactivation after 5 consecutive regeneration cycles.This study emphasizes the pivotal role of silanol nests of zeolites in stabilizing and modulating the coordination environment of metallic active sites,providing valuable insights for the design of high-activity,high-stability,and low-cost PDH catalysts.展开更多
Hydrocracking technology represents a crucial position in the conversion of heavy oil and the transformation development from oil refining to the chemical industry.The properties of catalysts are one of the key factor...Hydrocracking technology represents a crucial position in the conversion of heavy oil and the transformation development from oil refining to the chemical industry.The properties of catalysts are one of the key factors in the hydrocracking process.As the main acidic component of hydrocracking catalyst,the influence of zeolite properties on the reaction performance has been the focus of research.In this study,a series of NiMo/Al_(2)O_(3)-Y catalysts were prepared using different Y zeolites as acidic components,and their performances in the hydrocracking of n-C_(10)were also evaluated.The structure-activity relationship between Y zeolite and the cracking performance of n-C_(10)was investigated with machine learning.First,a database of the physical and chemical properties of Y zeolite and their performance was established,and the correlation analysis was also conducted.Parameters such as the cell constant,acid content,acid strength,B/L ratio,mesopore volume,micropore volume of Y zeolite,and the reaction temperature were selected as independent variables.The conversion of n-C_(10)and the ratios of products C_(3)/C_(7)and i-C_(4)/n-C_(4)were selected as dependent variables.A model was established by the random forest algorithm and a new zeolite was predicted based on it.The results of model prediction were in good agreement with the experimental results.The R^(2)of the n-C_(10)conversion,C_(3)/C_(7)ratio,and i-C_(4)/n-C_(4)ratio were 0.9866,0.9845,and 0.9922,and the minimum root mean square error values were 0.0163,0.101,and 0.0211,respectively.These results can provide reference for the development of high performance hydrocracking catalyst and technology.展开更多
Transition metal-based nanomaterials have emerged as promising electrocatalysts for oxygen evolution reaction(OER).Considerable research efforts have shown that self-reconstruction occurs on these nanomaterials under ...Transition metal-based nanomaterials have emerged as promising electrocatalysts for oxygen evolution reaction(OER).Considerable research efforts have shown that self-reconstruction occurs on these nanomaterials under operating conditions of OER process.However,most of them undergo incomplete reconstruction with limited thickness of reconstruction layer,leading to low component utilization and arduous exploration of real catalytic mechanism.Herein,we identify the dynamic behaviors in complete reconstruction of Co-based complexes during OER.The hollow phytic acid(PA)cross-linked CoFe-based complex nanoboxes with porous nanowalls are designed because of their good electrolyte penetration and mass transport ability,in favor of the fast and complete reconstruction.A series of experiment characterizations demonstrate that the reconstruction process includes the fast substitution of PA by OH-to form Co(Fe)(OH)xand subsequent potential-driven oxidation to Co(Fe)OOH.The obtained CoFeOOH delivers a low overpotential of 290 mV at a current density of 10 mA cm^(-2)and a long-term stability.The experiment results together with theory calculations reveal that the Fe incorporation can result in the electron rearrangement of reconstructed CoFeOOH and optimization of their electronic structure,accounting for the enhanced OER activity.The work provides new insights into complete reconstruction of metal-based complexes during OER and offers guidelines for rational design of high-performance electrocatalysts.展开更多
Zeolites are crystalline microporous materials widely used in catalysis,adsorption,and ion exchange owing to their tunable pore structures and acid centers[1].Traditional zeolites,however,often suffer from limitations...Zeolites are crystalline microporous materials widely used in catalysis,adsorption,and ion exchange owing to their tunable pore structures and acid centers[1].Traditional zeolites,however,often suffer from limitations such as restricted molecular diffusion and rapid coking,which hinder their efficiency in processing large molecules.展开更多
To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope...To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that the needle-likeχphase is mainly composed ofD0_(19)-Co_(3)(Ti,Mo),which is transformed from L1_(2-γ′)phase,and a specific orientation relationship exists between them.χphase is nucleated through the shearing ofγ′phase due to the influence of stacking fault.The crystal orientation relationship between L1_(2) andD0_(19)can be confirmed as{111}L1_(2)//{0001}_(D0_(19)),and<112>_(L1_(2))//<1100>_(D0_(19)).The growth ofD0_(19-χ)phase depends on the diffusions of Ti and Mo,and consumes a large number of elements.This progress leads to the appearance ofγ′precipitation depletion zone(PDZ)aroundD0_(19-χ)phase.The addition of Ni improves the stability of L1_(2-γ′)phase and the mechanical properties of Co-based superalloys.展开更多
In this study,we investigated Mo-impregnated H-MCM-22 catalysts(denoted Mo/M)for methanedehydroaromatization(MDA)to produce aromatics such as benzene and toluene(BT).We attemptedto improve the performance of the MDA c...In this study,we investigated Mo-impregnated H-MCM-22 catalysts(denoted Mo/M)for methanedehydroaromatization(MDA)to produce aromatics such as benzene and toluene(BT).We attemptedto improve the performance of the MDA catalysts by reducing the amount of Brönsted acidsites(BAS)of the H-MCM-22 supports via hydrothermal dealumination.Among the prepared catalysts,an optimal hydrothermal treatment(HT)of H-MCM-22 supports at 400℃,followed by Moimpregnation(denoted Mo/M_400),resulted in a reduced and optimal amount of BAS,along with acomparable Mo distribution to Mo/M.Further,Mo/M_400 enhanced BT formation rates(maximumBT formation rate of 5.23 vs.4.73 mmolBT·g^(−1)·h^(−1) for Mo/M);it appears that dealumination-inducedreduction in the quantity of BAS altered their spatial interaction with active Mo species,promotingBT and naphthalene formation.Interestingly,the lifetime of intermediate C_(2)(ethane and ethylene)formation was also improved for Mo/M_400.Rigorous coke analyses revealed that the decreasedcoke content in the aromatic-selective 10-membered-ring(10-MR)pores,as well as the ability ofthe 12-MR pores to accommodate coke deposits over a longer reaction time,improved the stabilityof Mo/M_400.Nonetheless,for all catalysts,the deactivations of BAS,and subsequently,the activeMo sites were mainly ascribed to coke deposition.The overall enhancement in MDA performance byMo/M_400 was attributed to the advantages of the optimally reduced BAS,allowing such performanceto surpass those of previously reported Mo-based catalysts.展开更多
Transition metal cobalt exhibits strong activation capabilities for alkanes,however,the instability of Co sites leads to sintering and coke deposition,resulting in rapid deactivation.Hierarchical zeolites,with their d...Transition metal cobalt exhibits strong activation capabilities for alkanes,however,the instability of Co sites leads to sintering and coke deposition,resulting in rapid deactivation.Hierarchical zeolites,with their diverse pore structures and high surface areas,are used to effectively anchor metals and enhance coke tolerance.Herein,a post-treatment method using an alkaline solution was employed to synthesize meso-microporous zeolite supports,which were subsequently loaded with Co species for propane dehydrogenation catalyst.The results indicate that the application of NaOH,an inorganic base,produces supports with a larger mesopore volume and more abundant hydroxyl nests compared to TPAOH,an organic base.UV-vis,Raman,and XPS analyses reveal that Co in the 0.5Co/SN-1-0.05 catalyst is mainly in the form of tetrahedral Co^(2+),which effectively activates C-H bonds.In contrast,the 0.5Co/S-1 catalyst contains mainly Co_(3)O_(4)species.Co^(2+)supported on hierarchical zeolites shows better propane conversion(58.6%)and propylene selectivity(>96%)compared to pure silica zeolites.Coke characterization indicates that hierarchical zeolites accumulate more coke,but it is mostly in the form of easily removable disordered carbon.The mesopores in the microporous zeolite support help disperse the active Co metal and facilitate coke removal during dehydrogenation,effectively preventing deactivation from sintering and coke coverage.展开更多
Direct converting carbon dioxide(CO_(2))and propane(C_(3)H_(8))into aromatics with high carbon utilization offers a desirable opportunity to simultaneously mitigate CO_(2)emission and adequately utilize C_(3)H_(8) in ...Direct converting carbon dioxide(CO_(2))and propane(C_(3)H_(8))into aromatics with high carbon utilization offers a desirable opportunity to simultaneously mitigate CO_(2)emission and adequately utilize C_(3)H_(8) in shale gas.Owing to their thermodynamic resistance,converting CO_(2)and C_(3)H_(8) respectively remains difficult.Here,we achieve 60.2%aromatics selectivity and 48.8%propane conversion over H-ZSM-5-25 via a zeolite-catalyzing the coupling of CO_(2)and C_(3)H_(8).Operando dual-beam FTIR spectroscopy combined with ^(13)C-labeled CO_(2)tracing experiments revealed that CO_(2)is directly involved in the generation of aromatics,with its carbon atoms selectively embedded into the aromatic ring,bypassing the reverse water-gas shift pathway.Accordingly,a cooperative aromatization mechanism is proposed.Thereinto,lactones,produced from CO_(2)and olefins,are proven to be the key intermediate.This work not only provides an opportunity for simultaneous conversion of CO_(2)and C_(3)H_(8),but also expends coupling strategy designing of CO_(2)and alkanes over acidic zeolites.展开更多
Current ever-accumulating plastic waste can be considered a significant carbon resource for energy conversion and chemical production.The development of new approaches for upcycling plastic waste through chemical degr...Current ever-accumulating plastic waste can be considered a significant carbon resource for energy conversion and chemical production.The development of new approaches for upcycling plastic waste through chemical degradation may enable circularity and promote closed-loop recycling of carbon sources compared to traditional recycling methods.Zeolite,a widely used solid acid catalyst with high industrial potential in petroleum and biomass refining,has been extensively studied for its role in transforming plastics.In this review,we present an overview of zeolite-based catalytic systems for the chemical recycling of plastic waste and discuss how zeolites could potentially contribute to the future development of a circular economy.To provide a comprehensive understanding,we begin with a brief introduction to zeolites,analyzing their key features and exploring their opportunities as well as challenges in processing plastic waste.Subsequently,we delve into the chemistry of catalytic cracking and tandem catalysis using zeolite-based catalysts on plastics.Overall,we emphasize the importance of intelligent catalyst design and lower-energy pathways to incentivize plastic upcycling while alleviating the burden caused by waste plastics.展开更多
Selective catalytic reduction with NH3(NH3-SCR)is an important means of NO_(x) abatement from stationary and mobile sources,and the key element is efficient and stable NH3-SCR catalysts.In this study,we propose a meth...Selective catalytic reduction with NH3(NH3-SCR)is an important means of NO_(x) abatement from stationary and mobile sources,and the key element is efficient and stable NH3-SCR catalysts.In this study,we propose a method to construct superior Fe-Beta catalysts based on Al-rich zeolites.This strategy successfully promotes the formation of NH3-SCR-active isolated Fe^(3+)species,thus effectively improving the low-temperature activity of the Fe-Beta catalysts.Thanks to the abundant Brønsted acid sites of the Al-rich zeolite,the Fe_(2)O_(3) particles are redispersed and anchored as isolated Fe^(3+)during hydrothermal aging.This dynamic evolution of Fe species makes up for the adverse effect of dealumination of the Al-rich zeolite framework and achieves high stability for the Al-rich Fe-Beta catalyst.This study may promote the understanding of highly efficient and stable catalyst design using Al-rich zeolites.展开更多
Rare earth(RE)Y-type zeolite was synthesized in situ by acidic co-hydrolysis route and hydrothermal method.The key process parameters were optimized based on the RE utilization rate.The effect of inducing a rotating p...Rare earth(RE)Y-type zeolite was synthesized in situ by acidic co-hydrolysis route and hydrothermal method.The key process parameters were optimized based on the RE utilization rate.The effect of inducing a rotating packed bed(RPB)in premixing and crystallization on crystallinity and RE utilization rate was further investigated.The results indicate that lanthanide(La)cations are successfully introduced into the sodalite cage of Y-type zeolite.The optimized conditions are that the molar ratio of Si/La is 150,premixing for 5 h,crystallization at 90℃ for 18 h,and calcination at 550℃ for 3.5 h.At this stage,the RE utilization rate reaches 74.5%.Compared with the conventional stirred tank reactor(STR),RPB can effectively shorten the premixing time and crystallization time by 4.3 h and 6 h,improve the crystallinity by 23%and RE utilization rate by 7.5%.The RE utilization rate is more than 80%by RPB,surpassing the effectiveness of using the one-exchange one-calcination process in the traditional liquid ion exchange process.It is expected to provide a reference for the in-situ efficient and green synthesis of RE zeolite.展开更多
Various ZSM-5 zeolites modified with alkali metals （Li, Na, K, Rb, and Cs） were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid （LA） to acrylic acid （AA）....Various ZSM-5 zeolites modified with alkali metals （Li, Na, K, Rb, and Cs） were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid （LA） to acrylic acid （AA）. The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, tempera- ture-programmed desorptions of NH3 and CO2, pyridine adsorption spectroscopy, and N2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities （LHSVs） to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions （40 wt% LA aqueous solution, 365 ℃, and LHSV 2 h-1）.展开更多
Syngas to ethanol, consisting of dimethyl ether(DME) carbonylation to methyl acetate(MA) over zeolites and MA hydrogenation to ethanol on copper catalyst, has been developed in recent years.DME carbonylation over zeol...Syngas to ethanol, consisting of dimethyl ether(DME) carbonylation to methyl acetate(MA) over zeolites and MA hydrogenation to ethanol on copper catalyst, has been developed in recent years.DME carbonylation over zeolites, a key step in this new process, has attracted increasing attention due to the high reaction efficiency and promising industrial application.In recent years, continuous efforts have been made on improving the activity and stability of the zeolites.From a mechanistic point of view, DME carbonylation to MA, involving the formation of C–C bond, is achieved via the Koch-type CO insertion into DME within the 8-member ring(8-MR) pores of zeolites, typically HMOR and HZSM-35.The unique geometric configuration of the 8-MR pore endowed the formation of the key intermediate(acetyl, CH3CO^*), possibly by a spatial confinement of the transition state during CO insertion into the surface O–CH3 group.This review article summarizes the main progress on zeolite-catalyzed DME carbonylation, including reaction kinetics and mechanism, theoretical calculations, and experimental strategies developed for populating acid sites and engineering pore structure of the zeolites in order to enhance the overall performance.展开更多
Zeolites are crystalline aluminosilicates with three‐dimensional microporous structures. They have been used as ion‐exchangers, catalysts, and adsorbents in various fields such as oil refining, petro‐chemistry, agr...Zeolites are crystalline aluminosilicates with three‐dimensional microporous structures. They have been used as ion‐exchangers, catalysts, and adsorbents in various fields such as oil refining, petro‐chemistry, agriculture, and water and wastewater treatment. Their wide use is because of their many beneficial properties, such as framework and compositional flexibilities, physical and hydro‐thermal stabilities, non‐toxicity, high surface areas, exchangeable cations, and good cost‐benefit ratios. Although many zeolite applications depend on their microporous structures, this can cause diffusional constraints for bulky reactant and product molecules. There have been many efforts to overcome the intrinsic limitations of conventional zeolites by preparing nanosized and hierarchi‐cally structured zeolites. As a result of these efforts, several strategies have been established and the use of new zeolitic materials in various catalytic and adsorptive reactions has been investigated. Longer lifetimes, high catalytic performances, and postponed coking and catalyst deactivation can be achieved using hierarchical and nanosized zeolites. The aim of this review is to provide an over‐view of the enhanced properties of hierarchical and nanosized zeolites, and recent development methods for their synthesis. The advantages and disadvantages of each route are discussed, and the catalytic applications of nanozeolites and zeolites with secondary porosity, and a comparison with conventional zeolites, are briefly presented.展开更多
Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of...Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of 1-hexene was investigated. The results indicate that isomorphous substitution promotes the incorporation of Ga heteroatoms into the framework along with the formation of extra-framework GaO;species（[GaO;]a） that have stronger interactions with the negative potential of the framework. In addition, based on the Py-IR results and catalytic performance, the [GaO;]aspecies with stronger Lewis acid sites produced a better synergism with moderate Br?nsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga;O;phase and small amounts of GaO;species that are mainly located on the external surface（[GaO;];）, which contribute to weaker Lewis acid sites due to weaker interactions with the zeolite framework. During 1-hexene aromatization, the nanosized Ga isomorphously substituted ZSM-5 zeolite samples（Gax-NZ5） exhibited better catalytic performance compared to the impregnated samples, and the highest aromatic yield（i.e.,65.4 wt%） was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content.展开更多
HZSM-5 zeolites with the micro-mesopore hierarchical porosity have been prepared by the post-synthesis of alkali-treatment, and their thermal and hydrothermal stabilities were studied using DTA, XRD, and NH3-TPD chara...HZSM-5 zeolites with the micro-mesopore hierarchical porosity have been prepared by the post-synthesis of alkali-treatment, and their thermal and hydrothermal stabilities were studied using DTA, XRD, and NH3-TPD characterization techniques. Compared to the unmodified zeolite, the thermal and hydrothermal stabilities of the alkali-treated ZSM-5 zeolites were slightly deteriorated because of the introduction of mesopores caused by the desilication. Nevertheless, the alkali-treated zeolite framework could be maintained until the temperature increased to 1175 ℃.展开更多
The exhaust gases, including SO_2,NH_3, H_2S, NO_2, NO, and CO, are principal air pollutants due to their severe harms to the ecological environment.Zeolites have been considered as good absorbent candidates to captur...The exhaust gases, including SO_2,NH_3, H_2S, NO_2, NO, and CO, are principal air pollutants due to their severe harms to the ecological environment.Zeolites have been considered as good absorbent candidates to capture the six exhaust gases.In this work, we performed grand canonical ensemble Monte Carlo(GCMC) simulations to examine the capability of 95 kinds of all-silica zeolites in the removal of the six toxic gases, and to predict the adsorption isotherms of the six gases on all the zeolites.The simulation results showed that, H_2S, NO, NO_2, CO and NH_3 are well-captured by zeolite structures with accessible surface area of 1600–1800 m^2·g^(-1) and pore diameter of 0.6–0.7 nm, such as AFY and PAU, while SO_2 is well-adsorbed by zeolites containing larger accessible surface area(1700–2700 m^2·g^(-1)) and pore diameter(0.7–1.4 nm) at room temperature and an atmospheric pressure.However, at saturated adsorption, zeolites RWY, IRR, JSR, TSC, and ITT are found to exhibit better abilities to capture these gases.Our study provides useful computational insights in choosing and designing zeolite structures with high performance to remove toxic gases for air purification, thereby facilitating the development and application of exhaust gas-processing technology in green industry.展开更多
Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins(MTO)conversion.It has been experimentally established that the topology of zeolite catalysts influenced the distribution of...Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins(MTO)conversion.It has been experimentally established that the topology of zeolite catalysts influenced the distribution of products.Besides the topology effect on reaction kinetics,the topology influences the diffusion of reactants and products in catalysts as well.In this work,by using COMPASS force-field molecular dynamics method,we investigated the intracrystalline diffusion of ethene and propene in four different zeolites,CHA,MFI,BEA and FAU,at different temperatures.The self-diffusion coefficients and diffusion activation barriers were calculated.A strong restriction on the diffusion of propene in CHA was observed because the self-diffusion coefficient ratio of ethene to propene is larger than 18 and the diffusion activation barrier of propene is more than 20 kJ/mol in CHA.This ratio decreases with the increase of temperature in the four investigated zeolites.The shape selectivity on products from diffusion perspective can provide some implications on the understanding of the selectivity difference between HSAPO-34 and HZSM-5 catalysts for the MTO conversion.展开更多
The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics（MD） and grand canonical Monte Carlo（GCMC） simulations. The diffusion coefficient...The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics（MD） and grand canonical Monte Carlo（GCMC） simulations. The diffusion coefficients of benzene and propylene in MFI, MWW and BEA zeolites were calculated by simulating the mean-square displacements（MSD） at 298 and 600 K. Benzene and propylene showed the different adsorption rules in the channels of the three zeolites. For propylene, the molecular loadings decreased in the order： BEA（linear channel）〉BEA （tortuous channel）〉MFI（linear channel）〉MWW（12-membered rings, 12MR channel）〉MFI（tortuous channel）〉MWW （10-membered rings, 10MR channel）; for benzene, the molecular loadings decreased in the order： BEA（linear chan-nel）〉BEA（tortuous channel）〉MWW（12MR channel）〉MFI（linear channel）〉MFI（tortuous channel）〉MWW（10MR channel）. Besides, the adsorption isotherms of benzene and propylene in the three zeolites at 298 and 443 K were simulated. The results show that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the different rules for the adsorption of benzene and propylene molecules in the zeolites. At a low pressure, the unfavorable energy would make the loadings of propylene lower than those of benzene. When pressure was higher than 0.25 kPa, the adsorption of benzene in MFI would nearly reach saturation.展开更多
基金National Natural Science Foundation of China(52071126)Natural Science Foundation of Tianjin City,China(22JCQNJC01240)+2 种基金Central Guidance on Local Science and Technology Development Fund of Hebei Province(226Z1009G)Special Funds for Science and Technology Innovation in Hebei(2022X19)Anhui Provincial Natural Science Foundation(2308085ME135)。
文摘Co-based alloy coating was prepared on Zr alloy using laser melting and cladding technique to study the difference in the high-temperature oxidation behavior between pure metal Co coatings and Co-T800 alloy coatings,as well as the wear resistance of the coatings.Besides,the effect of changing the laser melting process on the coatings was also investigated.The oxidation mass gain at 800–1200℃and the high-temperature oxidation behavior during high-temperature treatment for 1 h of two coated Zr alloy samples were studied.Results show that the Co coating and the Co-T800 coating have better resistance against high-temperature oxidation.After oxidizing at 1000℃for 1 h,the thickness of the oxide layer of the uncoated sample was 241.0μm,whereas that of the sample with Co-based coating is only 11.8–35.5μm.The friction wear test shows that the depth of the abrasion mark of the coated sample is only 1/2 of that of the substrate,indicating that the hardness and wear resistance of the Zr substrate are greatly improved.The disadvantage of Co-based coatings is the inferior corrosion resistance in 3.5wt%NaCl solution.
文摘Propane dehydrogenation(PDH)has emerged as a key on-purpose technology for the production of propylene,but it often depends on toxic chromium and expensive platinum catalysts,highlighting the need for environmentally friendly and cost-effective alternatives.In this study,we developed a facile impregnation method to fabricate unsaturated Co single-atoms with a tricoordinated Co_(1)O_(3)H_(x) structure by regulating silanol nests in purely siliceous Beta zeolites.Detailed PDH catalytic tests and characterizations revealed a positive correlation between the presence of silanol nests and enhanced catalytic activity.Additionally,the unsaturated Co single-atoms exhibited a carbon deposition rate more than an order of magnitude slower than that of Co nanoparticles.Notably,the optimized Co_(0.3%)/deAl-meso-Beta catalyst achieved a record-high propylene formation rate of 21.2 mmol_(C3H6) g_(cat)^(-1) h^(-1),with an exceptional propylene selectivity of 99.1%at 550℃.Moreover,the Co_(0.3%)/deAl-meso-Beta catalyst demonstrated excellent stability,with negligible deactivation after 5 consecutive regeneration cycles.This study emphasizes the pivotal role of silanol nests of zeolites in stabilizing and modulating the coordination environment of metallic active sites,providing valuable insights for the design of high-activity,high-stability,and low-cost PDH catalysts.
文摘Hydrocracking technology represents a crucial position in the conversion of heavy oil and the transformation development from oil refining to the chemical industry.The properties of catalysts are one of the key factors in the hydrocracking process.As the main acidic component of hydrocracking catalyst,the influence of zeolite properties on the reaction performance has been the focus of research.In this study,a series of NiMo/Al_(2)O_(3)-Y catalysts were prepared using different Y zeolites as acidic components,and their performances in the hydrocracking of n-C_(10)were also evaluated.The structure-activity relationship between Y zeolite and the cracking performance of n-C_(10)was investigated with machine learning.First,a database of the physical and chemical properties of Y zeolite and their performance was established,and the correlation analysis was also conducted.Parameters such as the cell constant,acid content,acid strength,B/L ratio,mesopore volume,micropore volume of Y zeolite,and the reaction temperature were selected as independent variables.The conversion of n-C_(10)and the ratios of products C_(3)/C_(7)and i-C_(4)/n-C_(4)were selected as dependent variables.A model was established by the random forest algorithm and a new zeolite was predicted based on it.The results of model prediction were in good agreement with the experimental results.The R^(2)of the n-C_(10)conversion,C_(3)/C_(7)ratio,and i-C_(4)/n-C_(4)ratio were 0.9866,0.9845,and 0.9922,and the minimum root mean square error values were 0.0163,0.101,and 0.0211,respectively.These results can provide reference for the development of high performance hydrocracking catalyst and technology.
基金National Natural Science Foundation of China(22478310,U21A20286 and 22206054)。
文摘Transition metal-based nanomaterials have emerged as promising electrocatalysts for oxygen evolution reaction(OER).Considerable research efforts have shown that self-reconstruction occurs on these nanomaterials under operating conditions of OER process.However,most of them undergo incomplete reconstruction with limited thickness of reconstruction layer,leading to low component utilization and arduous exploration of real catalytic mechanism.Herein,we identify the dynamic behaviors in complete reconstruction of Co-based complexes during OER.The hollow phytic acid(PA)cross-linked CoFe-based complex nanoboxes with porous nanowalls are designed because of their good electrolyte penetration and mass transport ability,in favor of the fast and complete reconstruction.A series of experiment characterizations demonstrate that the reconstruction process includes the fast substitution of PA by OH-to form Co(Fe)(OH)xand subsequent potential-driven oxidation to Co(Fe)OOH.The obtained CoFeOOH delivers a low overpotential of 290 mV at a current density of 10 mA cm^(-2)and a long-term stability.The experiment results together with theory calculations reveal that the Fe incorporation can result in the electron rearrangement of reconstructed CoFeOOH and optimization of their electronic structure,accounting for the enhanced OER activity.The work provides new insights into complete reconstruction of metal-based complexes during OER and offers guidelines for rational design of high-performance electrocatalysts.
基金the support of the National Natural Science Foundation of China(Nos.22205207 and 22378369).
文摘Zeolites are crystalline microporous materials widely used in catalysis,adsorption,and ion exchange owing to their tunable pore structures and acid centers[1].Traditional zeolites,however,often suffer from limitations such as restricted molecular diffusion and rapid coking,which hinder their efficiency in processing large molecules.
基金The financial supports from the National Natural Science Foundation of China(Nos.52171107,52201203)the National Natural Science Foundation of China-Joint Fund of Iron and Steel Research(No.U1960204)the“333”Talent Project of Hebei Province,China(No.B20221001)are gratefully acknowledged.
文摘To explain the precipitation mechanism ofχphase in Co-based superalloys,the microstructural evolution of Co−Ti−Mo superalloys subjected to aging was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that the needle-likeχphase is mainly composed ofD0_(19)-Co_(3)(Ti,Mo),which is transformed from L1_(2-γ′)phase,and a specific orientation relationship exists between them.χphase is nucleated through the shearing ofγ′phase due to the influence of stacking fault.The crystal orientation relationship between L1_(2) andD0_(19)can be confirmed as{111}L1_(2)//{0001}_(D0_(19)),and<112>_(L1_(2))//<1100>_(D0_(19)).The growth ofD0_(19-χ)phase depends on the diffusions of Ti and Mo,and consumes a large number of elements.This progress leads to the appearance ofγ′precipitation depletion zone(PDZ)aroundD0_(19-χ)phase.The addition of Ni improves the stability of L1_(2-γ′)phase and the mechanical properties of Co-based superalloys.
文摘In this study,we investigated Mo-impregnated H-MCM-22 catalysts(denoted Mo/M)for methanedehydroaromatization(MDA)to produce aromatics such as benzene and toluene(BT).We attemptedto improve the performance of the MDA catalysts by reducing the amount of Brönsted acidsites(BAS)of the H-MCM-22 supports via hydrothermal dealumination.Among the prepared catalysts,an optimal hydrothermal treatment(HT)of H-MCM-22 supports at 400℃,followed by Moimpregnation(denoted Mo/M_400),resulted in a reduced and optimal amount of BAS,along with acomparable Mo distribution to Mo/M.Further,Mo/M_400 enhanced BT formation rates(maximumBT formation rate of 5.23 vs.4.73 mmolBT·g^(−1)·h^(−1) for Mo/M);it appears that dealumination-inducedreduction in the quantity of BAS altered their spatial interaction with active Mo species,promotingBT and naphthalene formation.Interestingly,the lifetime of intermediate C_(2)(ethane and ethylene)formation was also improved for Mo/M_400.Rigorous coke analyses revealed that the decreasedcoke content in the aromatic-selective 10-membered-ring(10-MR)pores,as well as the ability ofthe 12-MR pores to accommodate coke deposits over a longer reaction time,improved the stabilityof Mo/M_400.Nonetheless,for all catalysts,the deactivations of BAS,and subsequently,the activeMo sites were mainly ascribed to coke deposition.The overall enhancement in MDA performance byMo/M_400 was attributed to the advantages of the optimally reduced BAS,allowing such performanceto surpass those of previously reported Mo-based catalysts.
基金supported by the National Natural Science Foundation of China(Nos.22035009,22178381)the National Key R&D Program of China(Nos.2021YFA1501301,2021YFC2901100)the State Key Laboratory of Heavy Oil Processing(No.2021-03).
文摘Transition metal cobalt exhibits strong activation capabilities for alkanes,however,the instability of Co sites leads to sintering and coke deposition,resulting in rapid deactivation.Hierarchical zeolites,with their diverse pore structures and high surface areas,are used to effectively anchor metals and enhance coke tolerance.Herein,a post-treatment method using an alkaline solution was employed to synthesize meso-microporous zeolite supports,which were subsequently loaded with Co species for propane dehydrogenation catalyst.The results indicate that the application of NaOH,an inorganic base,produces supports with a larger mesopore volume and more abundant hydroxyl nests compared to TPAOH,an organic base.UV-vis,Raman,and XPS analyses reveal that Co in the 0.5Co/SN-1-0.05 catalyst is mainly in the form of tetrahedral Co^(2+),which effectively activates C-H bonds.In contrast,the 0.5Co/S-1 catalyst contains mainly Co_(3)O_(4)species.Co^(2+)supported on hierarchical zeolites shows better propane conversion(58.6%)and propylene selectivity(>96%)compared to pure silica zeolites.Coke characterization indicates that hierarchical zeolites accumulate more coke,but it is mostly in the form of easily removable disordered carbon.The mesopores in the microporous zeolite support help disperse the active Co metal and facilitate coke removal during dehydrogenation,effectively preventing deactivation from sintering and coke coverage.
文摘Direct converting carbon dioxide(CO_(2))and propane(C_(3)H_(8))into aromatics with high carbon utilization offers a desirable opportunity to simultaneously mitigate CO_(2)emission and adequately utilize C_(3)H_(8) in shale gas.Owing to their thermodynamic resistance,converting CO_(2)and C_(3)H_(8) respectively remains difficult.Here,we achieve 60.2%aromatics selectivity and 48.8%propane conversion over H-ZSM-5-25 via a zeolite-catalyzing the coupling of CO_(2)and C_(3)H_(8).Operando dual-beam FTIR spectroscopy combined with ^(13)C-labeled CO_(2)tracing experiments revealed that CO_(2)is directly involved in the generation of aromatics,with its carbon atoms selectively embedded into the aromatic ring,bypassing the reverse water-gas shift pathway.Accordingly,a cooperative aromatization mechanism is proposed.Thereinto,lactones,produced from CO_(2)and olefins,are proven to be the key intermediate.This work not only provides an opportunity for simultaneous conversion of CO_(2)and C_(3)H_(8),but also expends coupling strategy designing of CO_(2)and alkanes over acidic zeolites.
文摘Current ever-accumulating plastic waste can be considered a significant carbon resource for energy conversion and chemical production.The development of new approaches for upcycling plastic waste through chemical degradation may enable circularity and promote closed-loop recycling of carbon sources compared to traditional recycling methods.Zeolite,a widely used solid acid catalyst with high industrial potential in petroleum and biomass refining,has been extensively studied for its role in transforming plastics.In this review,we present an overview of zeolite-based catalytic systems for the chemical recycling of plastic waste and discuss how zeolites could potentially contribute to the future development of a circular economy.To provide a comprehensive understanding,we begin with a brief introduction to zeolites,analyzing their key features and exploring their opportunities as well as challenges in processing plastic waste.Subsequently,we delve into the chemistry of catalytic cracking and tandem catalysis using zeolite-based catalysts on plastics.Overall,we emphasize the importance of intelligent catalyst design and lower-energy pathways to incentivize plastic upcycling while alleviating the burden caused by waste plastics.
基金supported by the National Key R&D Program of China(No.2023YFC3707200)the National Natural Science Foundation of China(Nos.22306191 and 52270112).
文摘Selective catalytic reduction with NH3(NH3-SCR)is an important means of NO_(x) abatement from stationary and mobile sources,and the key element is efficient and stable NH3-SCR catalysts.In this study,we propose a method to construct superior Fe-Beta catalysts based on Al-rich zeolites.This strategy successfully promotes the formation of NH3-SCR-active isolated Fe^(3+)species,thus effectively improving the low-temperature activity of the Fe-Beta catalysts.Thanks to the abundant Brønsted acid sites of the Al-rich zeolite,the Fe_(2)O_(3) particles are redispersed and anchored as isolated Fe^(3+)during hydrothermal aging.This dynamic evolution of Fe species makes up for the adverse effect of dealumination of the Al-rich zeolite framework and achieves high stability for the Al-rich Fe-Beta catalyst.This study may promote the understanding of highly efficient and stable catalyst design using Al-rich zeolites.
基金supported by the NationalKey Research and Development Program of China(2023YFA1507701)National Natural Science Foundation of China(U22B6011,22288102)“Announcement and Challenge”Science and Technology Project of Xinjiang Uygur Autonomous Region(XJKJTJBGS-2023).
文摘Rare earth(RE)Y-type zeolite was synthesized in situ by acidic co-hydrolysis route and hydrothermal method.The key process parameters were optimized based on the RE utilization rate.The effect of inducing a rotating packed bed(RPB)in premixing and crystallization on crystallinity and RE utilization rate was further investigated.The results indicate that lanthanide(La)cations are successfully introduced into the sodalite cage of Y-type zeolite.The optimized conditions are that the molar ratio of Si/La is 150,premixing for 5 h,crystallization at 90℃ for 18 h,and calcination at 550℃ for 3.5 h.At this stage,the RE utilization rate reaches 74.5%.Compared with the conventional stirred tank reactor(STR),RPB can effectively shorten the premixing time and crystallization time by 4.3 h and 6 h,improve the crystallinity by 23%and RE utilization rate by 7.5%.The RE utilization rate is more than 80%by RPB,surpassing the effectiveness of using the one-exchange one-calcination process in the traditional liquid ion exchange process.It is expected to provide a reference for the in-situ efficient and green synthesis of RE zeolite.
文摘Various ZSM-5 zeolites modified with alkali metals （Li, Na, K, Rb, and Cs） were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid （LA） to acrylic acid （AA）. The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, tempera- ture-programmed desorptions of NH3 and CO2, pyridine adsorption spectroscopy, and N2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities （LHSVs） to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions （40 wt% LA aqueous solution, 365 ℃, and LHSV 2 h-1）.
基金supported by the National Natural Science Foundation of China(Grant no.20973166)
文摘Syngas to ethanol, consisting of dimethyl ether(DME) carbonylation to methyl acetate(MA) over zeolites and MA hydrogenation to ethanol on copper catalyst, has been developed in recent years.DME carbonylation over zeolites, a key step in this new process, has attracted increasing attention due to the high reaction efficiency and promising industrial application.In recent years, continuous efforts have been made on improving the activity and stability of the zeolites.From a mechanistic point of view, DME carbonylation to MA, involving the formation of C–C bond, is achieved via the Koch-type CO insertion into DME within the 8-member ring(8-MR) pores of zeolites, typically HMOR and HZSM-35.The unique geometric configuration of the 8-MR pore endowed the formation of the key intermediate(acetyl, CH3CO^*), possibly by a spatial confinement of the transition state during CO insertion into the surface O–CH3 group.This review article summarizes the main progress on zeolite-catalyzed DME carbonylation, including reaction kinetics and mechanism, theoretical calculations, and experimental strategies developed for populating acid sites and engineering pore structure of the zeolites in order to enhance the overall performance.
文摘Zeolites are crystalline aluminosilicates with three‐dimensional microporous structures. They have been used as ion‐exchangers, catalysts, and adsorbents in various fields such as oil refining, petro‐chemistry, agriculture, and water and wastewater treatment. Their wide use is because of their many beneficial properties, such as framework and compositional flexibilities, physical and hydro‐thermal stabilities, non‐toxicity, high surface areas, exchangeable cations, and good cost‐benefit ratios. Although many zeolite applications depend on their microporous structures, this can cause diffusional constraints for bulky reactant and product molecules. There have been many efforts to overcome the intrinsic limitations of conventional zeolites by preparing nanosized and hierarchi‐cally structured zeolites. As a result of these efforts, several strategies have been established and the use of new zeolitic materials in various catalytic and adsorptive reactions has been investigated. Longer lifetimes, high catalytic performances, and postponed coking and catalyst deactivation can be achieved using hierarchical and nanosized zeolites. The aim of this review is to provide an over‐view of the enhanced properties of hierarchical and nanosized zeolites, and recent development methods for their synthesis. The advantages and disadvantages of each route are discussed, and the catalytic applications of nanozeolites and zeolites with secondary porosity, and a comparison with conventional zeolites, are briefly presented.
基金supported by the National Natural Science Foundation of China(Nos.21276067 and 21676074)Programs of International S&T cooperation(No.2014DFR41110)
文摘Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of 1-hexene was investigated. The results indicate that isomorphous substitution promotes the incorporation of Ga heteroatoms into the framework along with the formation of extra-framework GaO;species（[GaO;]a） that have stronger interactions with the negative potential of the framework. In addition, based on the Py-IR results and catalytic performance, the [GaO;]aspecies with stronger Lewis acid sites produced a better synergism with moderate Br?nsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga;O;phase and small amounts of GaO;species that are mainly located on the external surface（[GaO;];）, which contribute to weaker Lewis acid sites due to weaker interactions with the zeolite framework. During 1-hexene aromatization, the nanosized Ga isomorphously substituted ZSM-5 zeolite samples（Gax-NZ5） exhibited better catalytic performance compared to the impregnated samples, and the highest aromatic yield（i.e.,65.4 wt%） was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content.
基金the National Key Project for Basic Research of China(973 Project)(No.2005CB221403)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant:DICP K2007D3)
文摘HZSM-5 zeolites with the micro-mesopore hierarchical porosity have been prepared by the post-synthesis of alkali-treatment, and their thermal and hydrothermal stabilities were studied using DTA, XRD, and NH3-TPD characterization techniques. Compared to the unmodified zeolite, the thermal and hydrothermal stabilities of the alkali-treated ZSM-5 zeolites were slightly deteriorated because of the introduction of mesopores caused by the desilication. Nevertheless, the alkali-treated zeolite framework could be maintained until the temperature increased to 1175 ℃.
基金Supported by the National Natural Science Foundation of China(21406172)the Natural Science Foundation of Hubei Province,China(2016CFB388 and 2013CFA091)
文摘The exhaust gases, including SO_2,NH_3, H_2S, NO_2, NO, and CO, are principal air pollutants due to their severe harms to the ecological environment.Zeolites have been considered as good absorbent candidates to capture the six exhaust gases.In this work, we performed grand canonical ensemble Monte Carlo(GCMC) simulations to examine the capability of 95 kinds of all-silica zeolites in the removal of the six toxic gases, and to predict the adsorption isotherms of the six gases on all the zeolites.The simulation results showed that, H_2S, NO, NO_2, CO and NH_3 are well-captured by zeolite structures with accessible surface area of 1600–1800 m^2·g^(-1) and pore diameter of 0.6–0.7 nm, such as AFY and PAU, while SO_2 is well-adsorbed by zeolites containing larger accessible surface area(1700–2700 m^2·g^(-1)) and pore diameter(0.7–1.4 nm) at room temperature and an atmospheric pressure.However, at saturated adsorption, zeolites RWY, IRR, JSR, TSC, and ITT are found to exhibit better abilities to capture these gases.Our study provides useful computational insights in choosing and designing zeolite structures with high performance to remove toxic gases for air purification, thereby facilitating the development and application of exhaust gas-processing technology in green industry.
基金supported by the National Basic Research Program of China (2009CB623504)the National Science Foundation of China (21103231)Shanghai Science Foundation (11ZR1449700)
文摘Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins(MTO)conversion.It has been experimentally established that the topology of zeolite catalysts influenced the distribution of products.Besides the topology effect on reaction kinetics,the topology influences the diffusion of reactants and products in catalysts as well.In this work,by using COMPASS force-field molecular dynamics method,we investigated the intracrystalline diffusion of ethene and propene in four different zeolites,CHA,MFI,BEA and FAU,at different temperatures.The self-diffusion coefficients and diffusion activation barriers were calculated.A strong restriction on the diffusion of propene in CHA was observed because the self-diffusion coefficient ratio of ethene to propene is larger than 18 and the diffusion activation barrier of propene is more than 20 kJ/mol in CHA.This ratio decreases with the increase of temperature in the four investigated zeolites.The shape selectivity on products from diffusion perspective can provide some implications on the understanding of the selectivity difference between HSAPO-34 and HZSM-5 catalysts for the MTO conversion.
基金Supported by the National Natural Science Foundation of China(No.20576012)the Doctoral Fund of Qingdao University of Science and Technology China(No. 0022430)
文摘The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics（MD） and grand canonical Monte Carlo（GCMC） simulations. The diffusion coefficients of benzene and propylene in MFI, MWW and BEA zeolites were calculated by simulating the mean-square displacements（MSD） at 298 and 600 K. Benzene and propylene showed the different adsorption rules in the channels of the three zeolites. For propylene, the molecular loadings decreased in the order： BEA（linear channel）〉BEA （tortuous channel）〉MFI（linear channel）〉MWW（12-membered rings, 12MR channel）〉MFI（tortuous channel）〉MWW （10-membered rings, 10MR channel）; for benzene, the molecular loadings decreased in the order： BEA（linear chan-nel）〉BEA（tortuous channel）〉MWW（12MR channel）〉MFI（linear channel）〉MFI（tortuous channel）〉MWW（10MR channel）. Besides, the adsorption isotherms of benzene and propylene in the three zeolites at 298 and 443 K were simulated. The results show that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the different rules for the adsorption of benzene and propylene molecules in the zeolites. At a low pressure, the unfavorable energy would make the loadings of propylene lower than those of benzene. When pressure was higher than 0.25 kPa, the adsorption of benzene in MFI would nearly reach saturation.
