The low‐temperature hydrothermal stabilities of Cu‐SAPO‐34samples with various Si contents and Cu loadings were systematically investigated.The NH3oxidation activities and NH3‐selective catalytic reduction(SCR)act...The low‐temperature hydrothermal stabilities of Cu‐SAPO‐34samples with various Si contents and Cu loadings were systematically investigated.The NH3oxidation activities and NH3‐selective catalytic reduction(SCR)activities(mainly the low‐temperature activities)of all the Cu‐SAPO‐34catalysts declined after low‐temperature steam treatment(LTST).These results show that the texture and acid density of Cu‐SAPO‐34can be better preserved by increasing the Cu loading,although the hydrolysis of Si-O-Al bonds is inevitable.The stability of Cu ions and the stability of the SAPO framework were positively correlated at relatively low Cu loadings.However,a high Cu loading(e.g.,3.67wt%)resulted in a significant decrease in the number of isolated Cu ions.Aggregation of CuO particles also occurred during the LTST,which accounts for the decreasing NH3oxidation activities of the catalysts.Among the catalysts,Cu‐SAPO‐34with a high Si content and medium Cu content(1.37wt%)showed the lowest decrease in NH3‐SCR because its Cu2+content was well retained and its acid density was well preserved.展开更多
The SAPO‐34 catalysts were modified with metal cations by different processes(conventional ion exchange(CIE),template‐assisted ion incorporation(TII)and alcoholic ion exchange(AIE)),systematically characterized by X...The SAPO‐34 catalysts were modified with metal cations by different processes(conventional ion exchange(CIE),template‐assisted ion incorporation(TII)and alcoholic ion exchange(AIE)),systematically characterized by XRD,XRF,N2 adsorption‐desorption,UV‐VIS,H2‐TPR,EPR,SEM,EDX,XPS,NH3‐TPD,1H NMR and IGA,and applied in MTO reaction.The metal cations incorporation introduces extra diffusion hindrance by metallic species located in the cavity of SAPO‐34.In particular,the Zn cations‐modified SAPO‐34 catalysts exhibit core‐shell like structure,with Si‐rich and Zn‐rich sublayer near the external surface,which favors the coke deposition at the beginning of MTO reaction,exerts marked impact on the diffusion of the generated products with relatively large molecular size(e.g.propylene),and significantly increases the selectivity to ethylene and the ratio of ethylene to propene in the MTO reaction.展开更多
Ball milling modification was performed on Cs/X catalysts before or after cesium ion exchange.Multiple characterization results(such as pyridine-FTIR,XPS,and solid-state NMR)demonstrated that ball milling played a dis...Ball milling modification was performed on Cs/X catalysts before or after cesium ion exchange.Multiple characterization results(such as pyridine-FTIR,XPS,and solid-state NMR)demonstrated that ball milling played a distinct role in these two different preparation procedures of the catalyst.Ball milling performed after the cesium modification has a strong influence on the Cs/X structure and acid-base properties,which results in the enhancement of the catalytic performance for side-chain methylation of toluene with methanol.Detailed studies revealed that ball milling intensified the interactions between oxides and molecular sieves,which not only increased the dispersion of the Cs species but also generated some weaker basic centers.It is proposed that the new basic centers could be Si-O-Cs and Al-O-Cs,which are produced by breaking of the Si-O-Al bonds of the zeolite framework under the synergetic effect of ball milling and alkali treatment.These new active sites may help to promote the side-chain methylation reaction.However,excessive ball milling will lead to the vanishing of zeolite micropores,thus deactivating side-chain methylation activity,which indicates that microporosity plays a key role in side-chain methylation and individual basic centers cannot catalyze this reaction.展开更多
A reconstruction strategy has been developed to synthesize Cu-SAPO-34 with a wide crystallization phase region,high solid yield,and tunable Si and Cu contents.Cu-rich SAPO-34 was prepared from a Cu-amine complex,which...A reconstruction strategy has been developed to synthesize Cu-SAPO-34 with a wide crystallization phase region,high solid yield,and tunable Si and Cu contents.Cu-rich SAPO-34 was prepared from a Cu-amine complex,which acted as a precursor and Cu source for the reconstruction synthesis.The role of the Cu-amine complex as a template was restricted,which allowed easier control over the Cu and Si contents than in the previously reported"one-pot"synthesis method.Characterization of the material revealed that the Si(4Al)coordination environment dominates the synthesized Cu-SAPO-34 catalysts.High-temperature hydrothermal treatment increased the isolated Cu2+content slightly,and the acid sites in the low-silica catalyst are more resistant to hydrothermal treatment than those of the existing catalysts.The obtained materials,especially the low-silica Cu-SAPO-34 sample,exhibit excellent catalytic activity and hydrothermal stability for the selective catalytic reduction of NOx by NH3(NH3-SCR).In addition,the influence of the catalyst acidity on the NH3-SCR reaction was also investigated and is discussed.The high synthetic efficiency and outstanding catalytic performance make Cu-SAPO-34 synthesized by the reconstruction method a promising catalyst for the NH3-SCR process.展开更多
The AEI cavity of SAPO-18 catalyst was modified with zinc cations with the conventional ion exchange procedure.The cavity modification effectively tunes the product selectivity,and shifts the products from mainly prop...The AEI cavity of SAPO-18 catalyst was modified with zinc cations with the conventional ion exchange procedure.The cavity modification effectively tunes the product selectivity,and shifts the products from mainly propylene to comparable production of ethylene and propylene in methanol to olefin(MTO)reaction.The incorporation of zinc ions and the generation of bicyclic aromatic species in the AEI cavity of SAPO-18 catalysts introduce additional diffusion hindrance that exert greater influence on the relatively bulky products(e.g.propylene and higher olefins),which increase the selectivity to small-sized products(e.g.ethylene).It appears that the incorporated zinc cations facilitate the generation of lower methylbenzenes which promote the generation of ethylene.The cavity modification via incorporating zinc ions effectively tunes the product selectivity over SAPO molecular sieves with relatively larger cavity,which provides a novel strategy to develop the potential alternative to SAPO-34 catalysts for industrial MTO reaction.展开更多
The SAPO-34 catalyst was fine-tuned with zinc cations through a straightforward template-assisted ion incorporation (TH) process, without the necessary template pre-removal and the preparation of NH4- SAPO-34 intermed...The SAPO-34 catalyst was fine-tuned with zinc cations through a straightforward template-assisted ion incorporation (TH) process, without the necessary template pre-removal and the preparation of NH4- SAPO-34 intermediate, which is more facile, efficient and cost-effective than the conventional ion exchange process. The template-assisted zinc cations incorporated SAPO-34 catalysts were characterized by XRD, XRF, N2 adsorption-desorption, XPS, SEM, EDX,NMR, respectively. Enhanced selectivity to ethylene and ratio of ethylene to propylene in MTO reaction are observed over the zinc cations modified SAPO-34 catalysts, due to the facilitated formation of lower methylbenzenes that favour the ethylene gen eration, as well as the increased diffusion hindrance originated from the zinc cations incorporation and the facil让ated generation of aromatics compound.展开更多
Methylcyclopentenyl cations(MCP+)have been regarded as active intermediates during methanol conversion,however,their function mode in the reaction are still uncertain.In our recent report,trimethylcyclopentenyl cation...Methylcyclopentenyl cations(MCP+)have been regarded as active intermediates during methanol conversion,however,their function mode in the reaction are still uncertain.In our recent report,trimethylcyclopentenyl cation(triMCP+)and its deprotonated counterpart(trimethylcyclopentadiene,tri MCP)were directly captured on H-RUB-50 catalyst with small cavity by the aid of in situ 13C MAS NMR spectroscopy,and their higher catalytic reactivity were clarified by 12C/13C-CH3OH isotopic switch experiment.In this contribution,an alternative route-cyclopentadienes-based cycle was applied on methanol conversion catalyzed on the H-RUB-50,in which ethene was produced with the participation of tri MCP+as critical intermediate.Then the cyclopentadienes-based cycle was predicted to be energetically favorable for ethene formation by density functional theory(DFT)calculations.The energetic comparison of paring mechanism in the aromatics-based cycle and cyclopentadienes-based cycle with the involvements of trimethylcyclopentadienyl(tri MCPdi+)and tri MCP+as the corresponding active intermediates suggests that cyclopentadienes-based cycle is a feasible route for ethene formation.Furthermore,this work highlights the importance of the steric constraint and the host-vip interaction induced by the zeolite with cavity structure in the formation of intermediates and reaction pathway.展开更多
The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO（methanol to olefin） reactions were investigated. The catalytic analysis demonstrates that the py...The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO（methanol to olefin） reactions were investigated. The catalytic analysis demonstrates that the pyridine modified MOR zeolite yielded high selectivity（> 65.3%） of C;-C;, although the conversion dropped from 100% to 54%. Furthermore, both the catalytic lifetime of MOR and the stability of yielding the lower olefins were increased from less than 30 min to more than 120 min after the modification with pyridine.1H MAS NMR on MOR and modified MOR shows that the acid sites in main channel do not benefit the productivity of lower olefins and catalysts’ lifetime. It can be concluded from ex-situ;C CP MAS NMR that the deposit species during the MTO reaction depend on the pore sizes, and the formation of large alkyl aromatic species more likely occurs in the 12-ring main channels rather than the 8-ring side pocket.展开更多
^(129)Xe NMR has been proven to be a powerful tool to investigate the structure of porousmaterials. Xenon is a monatomic noble gas which could be used as a probe due to theextremely sensitive to its local environment....^(129)Xe NMR has been proven to be a powerful tool to investigate the structure of porousmaterials. Xenon is a monatomic noble gas which could be used as a probe due to theextremely sensitive to its local environment. Optical pumping techniques for production ofhyperpolarized (HP) xenon have led to an increase of sensitivity up to orders of magnitudecompared with traditional ^(129)Xe NMR. This review summarizes the application of thistechnique in porous materials and heterogeneous catalysis in recent ten years, involving ofzeolites, metal-organic frameworks (MOFs), catalytic process and kinetics.展开更多
Low-carbon process for resource utilization of polycyclic aromatic hydrocarbons(PAHs)in zeolitecatalyzed processes,geared to carbon neutrality-a prominent trend throughout human activities,has been bottlenecked by the...Low-carbon process for resource utilization of polycyclic aromatic hydrocarbons(PAHs)in zeolitecatalyzed processes,geared to carbon neutrality-a prominent trend throughout human activities,has been bottlenecked by the lack of a complete mechanistic understanding of coking and decoking chemistry,involving the speciation and molecular evolution of PAHs,the plethora of which causes catalyst deactivation and forces regeneration,rendering significant CO_(2) emission.Herein,by exploiting the high-resolution matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry(MALDI FT-ICR MS),we unveil the missing fingerprints of the mechanistic pathways for both formation and decomposition of cross-linked cage-passing PAHs for SAPO-34-catalyzed,industrially relevant methanol-to-olefins(MTO)as a model reaction.Notable is the molecule-resolved symmetrical signature:their speciation originates exclusively from the direct coupling of in-cage hydrocarbon pool(HCP)species,whereas water-promoted decomposition of cage-passing PAHs initiates with selective cracking of inter-cage local structures at 8-rings followed by deep aromatic steam reforming.Molecular deciphering the reversibly dynamic evolution trajectory(fate)of full-spectrum aromatic hydrocarbons and fulfilling the real-time quantitative carbon resource footprints advance the fundamental knowledge of deactivation and regeneration phenomena(decay and recovery motifs of autocatalysis)and disclose the underlying mechanisms of especially the chemistry of coking and decoking in zeolite catalysis.The positive yet divergent roles of water in these two processes are disentangled.These unprecedented insights ultimately lead us to a steam regeneration strategy with valuable CO and H_(2) as main products,negligible CO_(2) emission in steam reforming and full catalyst activity recovery,which further proves feasible in other important chemical processes,promising to be a sustainable and potent approach that contributes to carbon-neutral chemical industry.展开更多
This paper reports a new strategy for the structural reconstruction of biomass carbon sulfonic acid(BCSA)to its solid superacid counterpart.In this approach,a cheap layered biomass carbon(BC)source is chemically exfol...This paper reports a new strategy for the structural reconstruction of biomass carbon sulfonic acid(BCSA)to its solid superacid counterpart.In this approach,a cheap layered biomass carbon(BC)source is chemically exfoliated by cetyltrimethyl ammonium bromide and then converted to silica-isolated carbon nanosheets(CNSs)by a series of conversion steps.The state of the silica-isolated CNSs and the stacking density of their nanoparticles are regulated by the dehydration temperature.Only the highly isolated and non-crosslinked CNSs with loose particle stacking structures obtained upon dehydration at 250℃ can be turned into superacid sites(with stronger acidity than that of 100%H2 SO4)after sulfonation.This is accompanied by the creation of abundant hierarchical slit pores with high external surface area,mainly driven by the strong hydrogen bonding interactions between the introduced sulfonic acid groups.In typical acid-catalyzed esterification,etherification,and hydrolysis reactions,the newly formed superacid exhibits superior catalytic activity and stability compared to those of common BCSA and commercial Amberlyst-15 catalysts,owing to its good structural stability,highly exposed stable superacidic sites,and abundance of mesoporous/macroporous channels with excellent mass transfer rate.This groundbreaking work not only provides a novel strategy for fabricating bio-based solid superacids,but also overcomes the drawbacks of BCSA,i.e.,unsatisfactory structural stability,acidity,and porosity.展开更多
Professor Xiuwen Han is the founder and pioneer of Nuclear Magnetic Resonance(NMR)spectroscopy in Dalian Institute of Chemical Physics,the Chinese Academy of Sciences(DICP,CAS).She has long consistently been engaged i...Professor Xiuwen Han is the founder and pioneer of Nuclear Magnetic Resonance(NMR)spectroscopy in Dalian Institute of Chemical Physics,the Chinese Academy of Sciences(DICP,CAS).She has long consistently been engaged in the field of NMR spectroscopy,structural chemistry,and catalytic chemistry,and has made fruitful achievements in the structural analysis of organic compounds,natural products,biomolecules,homogeneous and heterogeneous catalysts.展开更多
The methanol-to-olefins(MTO)reaction offers an alternative pathway for the production of low-carbon olefins from non-oil feedstocks.Fundamental research has been impeded by a lack of comprehensive understanding of its...The methanol-to-olefins(MTO)reaction offers an alternative pathway for the production of low-carbon olefins from non-oil feedstocks.Fundamental research has been impeded by a lack of comprehensive understanding of its underlying mechanism,despite the significant progress made in industry.In-situ solid-state nuclear magnetic resonance(ss NMR)spectroscopy has emerged as a pivotal tool,offering crucial insights into key species under real-time operando conditions.Furthermore,the host–vip interaction between zeolites or surface species residing on zeolites and the reactant/active intermediates is revealed by the combination of in-situ^(13)C MAS NMR and 2D correlation spectroscopy.Moreover,recent technological advancements in hyperpolarization(HP)methods,including HP^(129)Xe NMR and dynamic nuclear polarization(DNP),have significantly improved the sensitivity of ssNMR,enabling detailed structural and kinetic analysis as well as the detection of trace species.In this feature article,we summarized recent advancements in(in-situ)ssNMR spectroscopy applied to MTO reaction processes,encompassing mechanistic investigations at various stages and the intricate host–vip interactions.These theoretical insights into the dynamic evolution of MTO reactions lay a solid foundation for the optimization of catalytic processes and the development of efficient catalysts,thereby advancing the techniques towards more sustainable and economical production route for olefins.展开更多
MOR zeolite has been effectively utilized for dimethyl ether(DME)carbonylation reaction due to its unique pore structure and acidity.During industrial production,the transformation of ammonium type MOR zeolite(NH_(4)-...MOR zeolite has been effectively utilized for dimethyl ether(DME)carbonylation reaction due to its unique pore structure and acidity.During industrial production,the transformation of ammonium type MOR zeolite(NH_(4)-MOR)into proton type MOR zeolite(H-MOR)causes inevitable dealumination.Therefore,understanding the influencing factors and dynamic evolution mechanism of zeolite dealumination is crucial.In this work,the stability of framework aluminum was studied by X-ray diffraction(XRD),Fourier transform infrared(FT-IR)spectroscopy,^(29)Si,^(27)Al,^(1)H magic angle spinning nuclear magnetic resonance(MAS NMR),and DME carbonylation performance evaluation.These results indicate that extra-framework cation Na^(+)and NH_(4)^(+)could better preserve the aluminum structure of the MOR zeolite framework compared to H^(+),primarily due to the different'attraction'of the framework to water.Furthermore,the impact of water on the zeolite framework aluminum at high temperature was studied by manipulating the humidity of the calcination atmosphere,revealing the formation of extra-framework six-coordinated aluminum(Al(Ⅵ)-EF)and the mechanism of water influence on the zeolite framework aluminum.展开更多
Understanding the properties and behavior of water molecules in restricted geometries, such as the nanopores of rocks, is of interest for shale gas exploitation. We present herein ex situ and in situ nuclear magnetic ...Understanding the properties and behavior of water molecules in restricted geometries, such as the nanopores of rocks, is of interest for shale gas exploitation. We present herein ex situ and in situ nuclear magnetic resonance （NMR） studies on the effects of water on the adsorption and diffusion of methane in nanopores. Silica materials with one-dimensional pores of ZSM-22, MCM-41, and SBA-15, with pore sizes ranging from 0.5 to 6 nm, were chosen as models. Hyperpolarized （HP） 129Xe NMR results show that water adsorption does not affect the pore sizes of ZSM-22 and MCM-41 but reduces that of SBA-15. The presence of water suppresses methane adsorption; this suppression effect is stronger in smaller pores. The self-diffusion coefficients of methane within ZSM-22 and MCM-41 are not significantly influenced by the presence of water, as measured by ~H pulsed field gradient （PFG） NMR. However, within SBA-15, which has a pore size of 6 nm, the diffusion coefficient of methane increases as the amount of water adsorption increases, peaks, and then decreases to a constant value with further water adsorption. These experiments reveal the effects of the pore size and the presence of water on methane adsorption and diffusion in constrained spaces, which could have important implications for flow simulations of methane in shales.展开更多
Catalysis research has witnessed remarkable progress with the advent of in situ and operando techniques.These methods enable the study of catalysts under actual operating conditions,providing unprecedented insights in...Catalysis research has witnessed remarkable progress with the advent of in situ and operando techniques.These methods enable the study of catalysts under actual operating conditions,providing unprecedented insights into catalytic mechanisms and dynamic catalyst behavior.This review discusses key in situ techniques and their applications in catalysis research.Advances in in situ electron microscopy allow direct visualization of catalysts at the atomic scale under reaction conditions.In situ spectroscopy techniques like X-ray absorption spectroscopy and nuclear magnetic resonance spectroscopy can track chemical states and reveal transient intermediates.Synchrotron-based techniques offer enhanced capabilities for in situ studies.The integration of in situ methods with machine learning and computational modeling provides a powerful approach to accelerate catalyst optimization.However,challenges remain regarding radiation damage,instrumentation limitations,and data interpretation.Overall,continued development of multi-modal in situ techniques is pivotal for addressing emerging challenges and opportunities in catalysis research and technology.展开更多
基金supported by the National Natural Science Foundation of China(21676262,21506207,21606221)the Key Research Program of Frontier Sciences,CAS(QYZDB-SSW-JSC040)~~
文摘The low‐temperature hydrothermal stabilities of Cu‐SAPO‐34samples with various Si contents and Cu loadings were systematically investigated.The NH3oxidation activities and NH3‐selective catalytic reduction(SCR)activities(mainly the low‐temperature activities)of all the Cu‐SAPO‐34catalysts declined after low‐temperature steam treatment(LTST).These results show that the texture and acid density of Cu‐SAPO‐34can be better preserved by increasing the Cu loading,although the hydrolysis of Si-O-Al bonds is inevitable.The stability of Cu ions and the stability of the SAPO framework were positively correlated at relatively low Cu loadings.However,a high Cu loading(e.g.,3.67wt%)resulted in a significant decrease in the number of isolated Cu ions.Aggregation of CuO particles also occurred during the LTST,which accounts for the decreasing NH3oxidation activities of the catalysts.Among the catalysts,Cu‐SAPO‐34with a high Si content and medium Cu content(1.37wt%)showed the lowest decrease in NH3‐SCR because its Cu2+content was well retained and its acid density was well preserved.
文摘The SAPO‐34 catalysts were modified with metal cations by different processes(conventional ion exchange(CIE),template‐assisted ion incorporation(TII)and alcoholic ion exchange(AIE)),systematically characterized by XRD,XRF,N2 adsorption‐desorption,UV‐VIS,H2‐TPR,EPR,SEM,EDX,XPS,NH3‐TPD,1H NMR and IGA,and applied in MTO reaction.The metal cations incorporation introduces extra diffusion hindrance by metallic species located in the cavity of SAPO‐34.In particular,the Zn cations‐modified SAPO‐34 catalysts exhibit core‐shell like structure,with Si‐rich and Zn‐rich sublayer near the external surface,which favors the coke deposition at the beginning of MTO reaction,exerts marked impact on the diffusion of the generated products with relatively large molecular size(e.g.propylene),and significantly increases the selectivity to ethylene and the ratio of ethylene to propene in the MTO reaction.
文摘Ball milling modification was performed on Cs/X catalysts before or after cesium ion exchange.Multiple characterization results(such as pyridine-FTIR,XPS,and solid-state NMR)demonstrated that ball milling played a distinct role in these two different preparation procedures of the catalyst.Ball milling performed after the cesium modification has a strong influence on the Cs/X structure and acid-base properties,which results in the enhancement of the catalytic performance for side-chain methylation of toluene with methanol.Detailed studies revealed that ball milling intensified the interactions between oxides and molecular sieves,which not only increased the dispersion of the Cs species but also generated some weaker basic centers.It is proposed that the new basic centers could be Si-O-Cs and Al-O-Cs,which are produced by breaking of the Si-O-Al bonds of the zeolite framework under the synergetic effect of ball milling and alkali treatment.These new active sites may help to promote the side-chain methylation reaction.However,excessive ball milling will lead to the vanishing of zeolite micropores,thus deactivating side-chain methylation activity,which indicates that microporosity plays a key role in side-chain methylation and individual basic centers cannot catalyze this reaction.
文摘A reconstruction strategy has been developed to synthesize Cu-SAPO-34 with a wide crystallization phase region,high solid yield,and tunable Si and Cu contents.Cu-rich SAPO-34 was prepared from a Cu-amine complex,which acted as a precursor and Cu source for the reconstruction synthesis.The role of the Cu-amine complex as a template was restricted,which allowed easier control over the Cu and Si contents than in the previously reported"one-pot"synthesis method.Characterization of the material revealed that the Si(4Al)coordination environment dominates the synthesized Cu-SAPO-34 catalysts.High-temperature hydrothermal treatment increased the isolated Cu2+content slightly,and the acid sites in the low-silica catalyst are more resistant to hydrothermal treatment than those of the existing catalysts.The obtained materials,especially the low-silica Cu-SAPO-34 sample,exhibit excellent catalytic activity and hydrothermal stability for the selective catalytic reduction of NOx by NH3(NH3-SCR).In addition,the influence of the catalyst acidity on the NH3-SCR reaction was also investigated and is discussed.The high synthetic efficiency and outstanding catalytic performance make Cu-SAPO-34 synthesized by the reconstruction method a promising catalyst for the NH3-SCR process.
基金supported by the Key Research Program of Frontier Sciences,CAS(QYZDY-SSW-JSC024)the Youth Innovation Promotion Association of the CAS(2014165)the National Natural Science Foundation of China(21603223,21473182,91334205,91545104)~~
文摘The AEI cavity of SAPO-18 catalyst was modified with zinc cations with the conventional ion exchange procedure.The cavity modification effectively tunes the product selectivity,and shifts the products from mainly propylene to comparable production of ethylene and propylene in methanol to olefin(MTO)reaction.The incorporation of zinc ions and the generation of bicyclic aromatic species in the AEI cavity of SAPO-18 catalysts introduce additional diffusion hindrance that exert greater influence on the relatively bulky products(e.g.propylene and higher olefins),which increase the selectivity to small-sized products(e.g.ethylene).It appears that the incorporated zinc cations facilitate the generation of lower methylbenzenes which promote the generation of ethylene.The cavity modification via incorporating zinc ions effectively tunes the product selectivity over SAPO molecular sieves with relatively larger cavity,which provides a novel strategy to develop the potential alternative to SAPO-34 catalysts for industrial MTO reaction.
基金the National Natural Science Foundation of China(21603223,91745109,91545104,21473182,91334205)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2014165)for financial support
文摘The SAPO-34 catalyst was fine-tuned with zinc cations through a straightforward template-assisted ion incorporation (TH) process, without the necessary template pre-removal and the preparation of NH4- SAPO-34 intermediate, which is more facile, efficient and cost-effective than the conventional ion exchange process. The template-assisted zinc cations incorporated SAPO-34 catalysts were characterized by XRD, XRF, N2 adsorption-desorption, XPS, SEM, EDX,NMR, respectively. Enhanced selectivity to ethylene and ratio of ethylene to propylene in MTO reaction are observed over the zinc cations modified SAPO-34 catalysts, due to the facilitated formation of lower methylbenzenes that favour the ethylene gen eration, as well as the increased diffusion hindrance originated from the zinc cations incorporation and the facil让ated generation of aromatics compound.
基金the financial support from the National Natural Science Foundation of China(Nos.91745109,21703239 and 21972142)the Key Research Program of Frontier Sciences,CAS,Grant No.QYZDY-SSW-JSC024+2 种基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2014165)the International Partnership Program of Chinese Academy of Sciences,Grant No.121421KYSB20180007Liaoning Revitalization Talents Program(XLYC1807227)。
文摘Methylcyclopentenyl cations(MCP+)have been regarded as active intermediates during methanol conversion,however,their function mode in the reaction are still uncertain.In our recent report,trimethylcyclopentenyl cation(triMCP+)and its deprotonated counterpart(trimethylcyclopentadiene,tri MCP)were directly captured on H-RUB-50 catalyst with small cavity by the aid of in situ 13C MAS NMR spectroscopy,and their higher catalytic reactivity were clarified by 12C/13C-CH3OH isotopic switch experiment.In this contribution,an alternative route-cyclopentadienes-based cycle was applied on methanol conversion catalyzed on the H-RUB-50,in which ethene was produced with the participation of tri MCP+as critical intermediate.Then the cyclopentadienes-based cycle was predicted to be energetically favorable for ethene formation by density functional theory(DFT)calculations.The energetic comparison of paring mechanism in the aromatics-based cycle and cyclopentadienes-based cycle with the involvements of trimethylcyclopentadienyl(tri MCPdi+)and tri MCP+as the corresponding active intermediates suggests that cyclopentadienes-based cycle is a feasible route for ethene formation.Furthermore,this work highlights the importance of the steric constraint and the host-vip interaction induced by the zeolite with cavity structure in the formation of intermediates and reaction pathway.
基金supported by the Ministry of Science and Technology of China(2012CB224806)
文摘The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO（methanol to olefin） reactions were investigated. The catalytic analysis demonstrates that the pyridine modified MOR zeolite yielded high selectivity（> 65.3%） of C;-C;, although the conversion dropped from 100% to 54%. Furthermore, both the catalytic lifetime of MOR and the stability of yielding the lower olefins were increased from less than 30 min to more than 120 min after the modification with pyridine.1H MAS NMR on MOR and modified MOR shows that the acid sites in main channel do not benefit the productivity of lower olefins and catalysts’ lifetime. It can be concluded from ex-situ;C CP MAS NMR that the deposit species during the MTO reaction depend on the pore sizes, and the formation of large alkyl aromatic species more likely occurs in the 12-ring main channels rather than the 8-ring side pocket.
基金This work was supported by Natural Science Foundation of china(grant no.22022202,21972142,91745109,91545104)the LiaoNing Revitalization Talents Program(grant no.XLYC1807227)This work is dedicated to Professor Xiuwen Han on the occasion of her 80th birthday。
文摘^(129)Xe NMR has been proven to be a powerful tool to investigate the structure of porousmaterials. Xenon is a monatomic noble gas which could be used as a probe due to theextremely sensitive to its local environment. Optical pumping techniques for production ofhyperpolarized (HP) xenon have led to an increase of sensitivity up to orders of magnitudecompared with traditional ^(129)Xe NMR. This review summarizes the application of thistechnique in porous materials and heterogeneous catalysis in recent ten years, involving ofzeolites, metal-organic frameworks (MOFs), catalytic process and kinetics.
基金financial support from the National Natural Science Foundation of China(21991092,21991090,22022202,21972142,21902153,21974138)the Chinese Academy of Sciences(QYZDY-SSW-SC024)the Dalian Institute of Chemical Physics(DICP I201926,DICP I201947)。
文摘Low-carbon process for resource utilization of polycyclic aromatic hydrocarbons(PAHs)in zeolitecatalyzed processes,geared to carbon neutrality-a prominent trend throughout human activities,has been bottlenecked by the lack of a complete mechanistic understanding of coking and decoking chemistry,involving the speciation and molecular evolution of PAHs,the plethora of which causes catalyst deactivation and forces regeneration,rendering significant CO_(2) emission.Herein,by exploiting the high-resolution matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry(MALDI FT-ICR MS),we unveil the missing fingerprints of the mechanistic pathways for both formation and decomposition of cross-linked cage-passing PAHs for SAPO-34-catalyzed,industrially relevant methanol-to-olefins(MTO)as a model reaction.Notable is the molecule-resolved symmetrical signature:their speciation originates exclusively from the direct coupling of in-cage hydrocarbon pool(HCP)species,whereas water-promoted decomposition of cage-passing PAHs initiates with selective cracking of inter-cage local structures at 8-rings followed by deep aromatic steam reforming.Molecular deciphering the reversibly dynamic evolution trajectory(fate)of full-spectrum aromatic hydrocarbons and fulfilling the real-time quantitative carbon resource footprints advance the fundamental knowledge of deactivation and regeneration phenomena(decay and recovery motifs of autocatalysis)and disclose the underlying mechanisms of especially the chemistry of coking and decoking in zeolite catalysis.The positive yet divergent roles of water in these two processes are disentangled.These unprecedented insights ultimately lead us to a steam regeneration strategy with valuable CO and H_(2) as main products,negligible CO_(2) emission in steam reforming and full catalyst activity recovery,which further proves feasible in other important chemical processes,promising to be a sustainable and potent approach that contributes to carbon-neutral chemical industry.
基金financial support for this work by the National Natural Science Foundation of China(21690080,21676079,21546010,21690083,21878288)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB17020100)+2 种基金DNL Cooperation Fund CAS(DNL180302)the Natural Science Foundation of Hunan Province(2018JJ3335)the Innovation Platform Open Fund of Hunan College(18K016)~~
文摘This paper reports a new strategy for the structural reconstruction of biomass carbon sulfonic acid(BCSA)to its solid superacid counterpart.In this approach,a cheap layered biomass carbon(BC)source is chemically exfoliated by cetyltrimethyl ammonium bromide and then converted to silica-isolated carbon nanosheets(CNSs)by a series of conversion steps.The state of the silica-isolated CNSs and the stacking density of their nanoparticles are regulated by the dehydration temperature.Only the highly isolated and non-crosslinked CNSs with loose particle stacking structures obtained upon dehydration at 250℃ can be turned into superacid sites(with stronger acidity than that of 100%H2 SO4)after sulfonation.This is accompanied by the creation of abundant hierarchical slit pores with high external surface area,mainly driven by the strong hydrogen bonding interactions between the introduced sulfonic acid groups.In typical acid-catalyzed esterification,etherification,and hydrolysis reactions,the newly formed superacid exhibits superior catalytic activity and stability compared to those of common BCSA and commercial Amberlyst-15 catalysts,owing to its good structural stability,highly exposed stable superacidic sites,and abundance of mesoporous/macroporous channels with excellent mass transfer rate.This groundbreaking work not only provides a novel strategy for fabricating bio-based solid superacids,but also overcomes the drawbacks of BCSA,i.e.,unsatisfactory structural stability,acidity,and porosity.
文摘Professor Xiuwen Han is the founder and pioneer of Nuclear Magnetic Resonance(NMR)spectroscopy in Dalian Institute of Chemical Physics,the Chinese Academy of Sciences(DICP,CAS).She has long consistently been engaged in the field of NMR spectroscopy,structural chemistry,and catalytic chemistry,and has made fruitful achievements in the structural analysis of organic compounds,natural products,biomolecules,homogeneous and heterogeneous catalysts.
基金the financial support provided by the National Key Research and Development Program of China(2022YFE0116000)the National Natural Science Foundation of China(22241801,22022202,22032005,22288101,21972142,21991090,21991092,and 21991093)Dalian Outstanding Young Scientist Foundation(2021RJ01)。
文摘The methanol-to-olefins(MTO)reaction offers an alternative pathway for the production of low-carbon olefins from non-oil feedstocks.Fundamental research has been impeded by a lack of comprehensive understanding of its underlying mechanism,despite the significant progress made in industry.In-situ solid-state nuclear magnetic resonance(ss NMR)spectroscopy has emerged as a pivotal tool,offering crucial insights into key species under real-time operando conditions.Furthermore,the host–vip interaction between zeolites or surface species residing on zeolites and the reactant/active intermediates is revealed by the combination of in-situ^(13)C MAS NMR and 2D correlation spectroscopy.Moreover,recent technological advancements in hyperpolarization(HP)methods,including HP^(129)Xe NMR and dynamic nuclear polarization(DNP),have significantly improved the sensitivity of ssNMR,enabling detailed structural and kinetic analysis as well as the detection of trace species.In this feature article,we summarized recent advancements in(in-situ)ssNMR spectroscopy applied to MTO reaction processes,encompassing mechanistic investigations at various stages and the intricate host–vip interactions.These theoretical insights into the dynamic evolution of MTO reactions lay a solid foundation for the optimization of catalytic processes and the development of efficient catalysts,thereby advancing the techniques towards more sustainable and economical production route for olefins.
基金support provided by the National Key Research and Development Program of China(No.2022YFE0116000)the National Natural Science Foundation of China(22241801,22022202,22032005,22288101,21972142,21991090,21991092,21991093)Dalian Outstanding Young Scientist Foundation(2021RJ01).
文摘MOR zeolite has been effectively utilized for dimethyl ether(DME)carbonylation reaction due to its unique pore structure and acidity.During industrial production,the transformation of ammonium type MOR zeolite(NH_(4)-MOR)into proton type MOR zeolite(H-MOR)causes inevitable dealumination.Therefore,understanding the influencing factors and dynamic evolution mechanism of zeolite dealumination is crucial.In this work,the stability of framework aluminum was studied by X-ray diffraction(XRD),Fourier transform infrared(FT-IR)spectroscopy,^(29)Si,^(27)Al,^(1)H magic angle spinning nuclear magnetic resonance(MAS NMR),and DME carbonylation performance evaluation.These results indicate that extra-framework cation Na^(+)and NH_(4)^(+)could better preserve the aluminum structure of the MOR zeolite framework compared to H^(+),primarily due to the different'attraction'of the framework to water.Furthermore,the impact of water on the zeolite framework aluminum at high temperature was studied by manipulating the humidity of the calcination atmosphere,revealing the formation of extra-framework six-coordinated aluminum(Al(Ⅵ)-EF)and the mechanism of water influence on the zeolite framework aluminum.
文摘Understanding the properties and behavior of water molecules in restricted geometries, such as the nanopores of rocks, is of interest for shale gas exploitation. We present herein ex situ and in situ nuclear magnetic resonance （NMR） studies on the effects of water on the adsorption and diffusion of methane in nanopores. Silica materials with one-dimensional pores of ZSM-22, MCM-41, and SBA-15, with pore sizes ranging from 0.5 to 6 nm, were chosen as models. Hyperpolarized （HP） 129Xe NMR results show that water adsorption does not affect the pore sizes of ZSM-22 and MCM-41 but reduces that of SBA-15. The presence of water suppresses methane adsorption; this suppression effect is stronger in smaller pores. The self-diffusion coefficients of methane within ZSM-22 and MCM-41 are not significantly influenced by the presence of water, as measured by ~H pulsed field gradient （PFG） NMR. However, within SBA-15, which has a pore size of 6 nm, the diffusion coefficient of methane increases as the amount of water adsorption increases, peaks, and then decreases to a constant value with further water adsorption. These experiments reveal the effects of the pore size and the presence of water on methane adsorption and diffusion in constrained spaces, which could have important implications for flow simulations of methane in shales.
基金financially supported by the Office of Science,Office of Basic Energy Sciences,of the U.S.Department of Energy under Contract No.DE-AC02-05CH11231.
文摘Catalysis research has witnessed remarkable progress with the advent of in situ and operando techniques.These methods enable the study of catalysts under actual operating conditions,providing unprecedented insights into catalytic mechanisms and dynamic catalyst behavior.This review discusses key in situ techniques and their applications in catalysis research.Advances in in situ electron microscopy allow direct visualization of catalysts at the atomic scale under reaction conditions.In situ spectroscopy techniques like X-ray absorption spectroscopy and nuclear magnetic resonance spectroscopy can track chemical states and reveal transient intermediates.Synchrotron-based techniques offer enhanced capabilities for in situ studies.The integration of in situ methods with machine learning and computational modeling provides a powerful approach to accelerate catalyst optimization.However,challenges remain regarding radiation damage,instrumentation limitations,and data interpretation.Overall,continued development of multi-modal in situ techniques is pivotal for addressing emerging challenges and opportunities in catalysis research and technology.
