Aromatization of alkanes represents an important process in the chemical industry,traditionally relying on noble metal catalysts.Developing a non-noble metal catalyst and a relevant new process offers significant pote...Aromatization of alkanes represents an important process in the chemical industry,traditionally relying on noble metal catalysts.Developing a non-noble metal catalyst and a relevant new process offers significant potential for promoting technologic progress in this field.Herein,we present Cu-ZSM-5 zeolite as a highly effective catalyst for alkane aromatization,achieving outstanding aromatics selectivity.In-situ Fourier transform infrared spectra of adsorbed nitric oxide,high-angle annular dark field scanning transmission electron microscopy,X-ray absorption spectroscopy,and electron paramagnetic resonance analyses reveal that the Cu^(2+)species act as the primary active centers for aromatics formation.During aromatization of alkanes,the reduction of Cu^(2+)to Cu^(+)species correlates with diminished aromatics selectivity.Notably,introducing CO_(2)into the reaction feed not only enhances aromatics selectivity by maintaining Cu^(2+)species in their active oxidation state under reducing conditions,but also improves catalytic stability by eliminating coke.Furthermore,CO_(2)is converted into CO and aromatic products during the reaction,offering a novel way for CO_(2)utilization through the coupling reaction of alkane and CO_(2).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
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
Methanol to olefins(MTO)reaction as an important non-oil route to produce light olefins has been industrialized,and received over 80% ethylene plus propylene selectivity.However,to achieve high single ethylene or prop...Methanol to olefins(MTO)reaction as an important non-oil route to produce light olefins has been industrialized,and received over 80% ethylene plus propylene selectivity.However,to achieve high single ethylene or propylene selectivity towards the fluctuated market demand is still full of challenge.Small-pore SAPO-14 molecular sieve is a rare MTO catalyst exhibiting extra-high propylene selectivity.It provides us a valuable clue for further understanding of the relationship between molecular sieve structure and MTO catalytic performance.In this work,a seconds-level sampling fixed-bed reactor was used to capture real-time product distributions,which help to achieve more selectivity data in response to very short catalytic life of SAPO-14.Changes in product distribution,especially during the low activity stage,reflect valuable information on the reaction pathway.Combined with in situ diffuse reflectance infrared Fourier-transform spectroscopy,in situ ultraviolet Raman measurements and ^(12)C/^(13)C isotopic switch experiments,a reaction pathway evolution from dual cycle to olefins-based cycle dominant was revealed.In addition,the deactivation behaviors of SAPO-14 were also investigated,which revealed that polymethylbenzenes have been the deactivated species in such a situation.This work provides helpful hints on the development of characteristic methanol to propylene(MTP)catalysts.展开更多
Alkane coupling with CO_(2) by metal-containing zeolites catalysis is found to be a promising way to produce aromatics and syngas in recent years,but the real active sites and the role of CO_(2) are still unclear owin...Alkane coupling with CO_(2) by metal-containing zeolites catalysis is found to be a promising way to produce aromatics and syngas in recent years,but the real active sites and the role of CO_(2) are still unclear owing to the quick evolution of the metallic active sites and the complex reaction processes including direct propane aromatization,CO_(2) hydrogenation,reverse water-gas shift reaction,and propane-CO_(2) coupling aromatization.Herein,Ga/ZSM-5 catalysts were constructed to study the dynamic evolution of the metallic active sites and the role of CO_(2) during the propane and CO_(2) coupling reaction.After optimizing the reaction conditions,a notable propane conversion rate of 97.9%and an impressive aromatics selectivity of 80.6%in hydrocarbons can be achieved at the conditions of 550℃and CO_(2)/C_(3)H_(8) of 4.^(13)CO_(2)isotope experiments illustrate that C-atoms of CO_(2) can enter into CO(86.5%)and aromatics(10.8%)during the propane-CO_(2) coupling reaction process.In situ XANES and FTIR spectroscopies at 550℃and H_(2)/C_(3)H_(8) atmosphere reveal that GaO_(x) species can be gradually dispersed into[GaH_(2)]^(+)/[GaH]^(2+)on the Bronsted acid sites of ZSM-5 zeolite during H_(2) and/or C_(3)H_(8) treatment,which are the real active sites for propane-CO_(2) coupling conversion.In situ CO_(2)-FTIR experiments demonstrate that the[GaH_(2)]^(+)/[GaH]^(2+)species can react with CO_(2) and accelerate the propane and CO_(2) coupling process.This work not only presents a cost-effective avenue for CO_(2) utilization,but also contributes to the active site design for improved alkane and CO_(2) activation in coupling reaction system.展开更多
Mesoporous high‐silica zeolite Y with advantages of improved accessibility of acid sites and mass transport properties is highly desired catalytic materials for oil refinery,fine chemistry and emerg‐ing biorefinery....Mesoporous high‐silica zeolite Y with advantages of improved accessibility of acid sites and mass transport properties is highly desired catalytic materials for oil refinery,fine chemistry and emerg‐ing biorefinery.Here,we report the direct synthesis of mesoporous high‐silica zeolite Y(named MSY,SiO_(2)/Al2O_(3)≥9.8)and their excellent catalytic cracking performance.The obtained MSY mate‐rials are mesoporous single crystals with octahedral morphology,abundant mesoporosity and ex‐cellent(hydro)thermal stability.Both the acid concentration and acid strength of H‐form MSY are obviously higher than those of commercial ultra‐stable Y(USY),which should be attributed to the uniform Al distribution of MSY zeolite.The H‐MSY displays an obviously reduced deactivation rate and improved catalytic activity in the cracking reaction of bulky 1,3,5‐triisopropylbenzene(TIPB),as compared with its mesoporogen‐free counterpart and USY.In addition,H‐MSY was investigated as catalyst for the cracking of industrial heavy oil.The MSY‐based catalyst(after aging at 800 oC in 100%steam for 17 h)exhibits superior conversion(7.64%increase)and gasoline yield(16.37%increase)than industrial fluid catalytic cracking(FCC)catalyst under the investigated conditions.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
Coke formation is the primary cause of zeolite deactivation in industrial catalysis,yet the structural identity,spatial location and molecular routes of polycyclic aromatic hydrocarbons(PAHs)within confined zeolite po...Coke formation is the primary cause of zeolite deactivation in industrial catalysis,yet the structural identity,spatial location and molecular routes of polycyclic aromatic hydrocarbons(PAHs)within confined zeolite pores remain elusive.Here,by coupling matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry with multi-dimensional chemical imaging,we unveil a channel-passing growth mechanism for PAHs in ZSM-5 zeolites during methanol conversion through identifying the molecular fingerprints of larger PAHs,pinpointing and visualizing their 3D location and spatiotemporal evolution trajectory with atomic resolution and at both channel and single-crystal scales.Confined aromatic entities cross-link with each other,culminating in multicore PAH chains as the both thermodynamically favorable and kinetically trapped host-vip entanglement wrought and templated by the defined molecular-scale constrained microenvironments of zeolite.The mechanistic concept proves general across both channel-and cage-structured zeolite materials.Our multiscale deactivating model based on the full-picture coke structure-location correlations—spanning atom,molecule,channel/cage and single crystal scales—would shed new light on the intertwined chemical and physical processes in catalyst deactivation.This work not only resolves long-standing puzzles in coke formation but also provides design principles for coke-resistant zeolites.The methods and insights would rekindle interest in confinement effects and host-vip chemistry across broader chemistry fields beyond catalysis and carbon materials.展开更多
Improving the aromatic selectivity in the alkane aromatization process is of great importance for its practical utilization but challenge to make because the high H/C ratio of alkanes would lead to a serious hydrogen ...Improving the aromatic selectivity in the alkane aromatization process is of great importance for its practical utilization but challenge to make because the high H/C ratio of alkanes would lead to a serious hydrogen transfer process and a large amount of light alkanes.Herein,CO_(2)is introduced into the cyclohexane conversion process on the HZSM-5 zeolite,which can improve the aromatic selectivity.By optimizing the reaction conditions,an improved aromatic(benzene,toluene,xylene,and C9+)selectivity of 48.2%can be obtained at the conditions of 2.7 MPa(CO_(2)),450℃,and 1.7 h^(−1),which is better than that without CO_(2)(aromatic selectivity=43.2%).In situ transmission Fourier transform infrared spectroscopy spectra illustrate that many oxygenated chemical intermediates(e.g.,carboxylic acid,anhydride,unsaturated aldehydes/ketones or ketene)would be formed during the cyclohexane conversion process in the presence of CO_(2).13C isotope labeling experimental results demonstrate that CO_(2)can enter into the aromatics through the formation of oxygenated chemical intermediates and thereby improve the aromatic selectivity.This study may open a green,economic,and promising way to improve the aromatic selectivity for alkane aromatization process.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.22288101,22472016)the National Key Research and Development Program of the Ministry of Science and Technology(No.2022YFE0116000)+1 种基金the Chinese Academy of Sciences Strategy Leading Technology Project(No.XDA29000000)the Youth Innovation Promotion Association CAS(No.2021182)。
文摘Aromatization of alkanes represents an important process in the chemical industry,traditionally relying on noble metal catalysts.Developing a non-noble metal catalyst and a relevant new process offers significant potential for promoting technologic progress in this field.Herein,we present Cu-ZSM-5 zeolite as a highly effective catalyst for alkane aromatization,achieving outstanding aromatics selectivity.In-situ Fourier transform infrared spectra of adsorbed nitric oxide,high-angle annular dark field scanning transmission electron microscopy,X-ray absorption spectroscopy,and electron paramagnetic resonance analyses reveal that the Cu^(2+)species act as the primary active centers for aromatics formation.During aromatization of alkanes,the reduction of Cu^(2+)to Cu^(+)species correlates with diminished aromatics selectivity.Notably,introducing CO_(2)into the reaction feed not only enhances aromatics selectivity by maintaining Cu^(2+)species in their active oxidation state under reducing conditions,but also improves catalytic stability by eliminating coke.Furthermore,CO_(2)is converted into CO and aromatic products during the reaction,offering a novel way for CO_(2)utilization through the coupling reaction of alkane and CO_(2).
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.
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.
文摘Methanol to olefins(MTO)reaction as an important non-oil route to produce light olefins has been industrialized,and received over 80% ethylene plus propylene selectivity.However,to achieve high single ethylene or propylene selectivity towards the fluctuated market demand is still full of challenge.Small-pore SAPO-14 molecular sieve is a rare MTO catalyst exhibiting extra-high propylene selectivity.It provides us a valuable clue for further understanding of the relationship between molecular sieve structure and MTO catalytic performance.In this work,a seconds-level sampling fixed-bed reactor was used to capture real-time product distributions,which help to achieve more selectivity data in response to very short catalytic life of SAPO-14.Changes in product distribution,especially during the low activity stage,reflect valuable information on the reaction pathway.Combined with in situ diffuse reflectance infrared Fourier-transform spectroscopy,in situ ultraviolet Raman measurements and ^(12)C/^(13)C isotopic switch experiments,a reaction pathway evolution from dual cycle to olefins-based cycle dominant was revealed.In addition,the deactivation behaviors of SAPO-14 were also investigated,which revealed that polymethylbenzenes have been the deactivated species in such a situation.This work provides helpful hints on the development of characteristic methanol to propylene(MTP)catalysts.
基金supported by the National Key Research and Development Program of China (No.2022YFE0116000)the National Natural Science Foundation of China (No.22288101,21991092,21991090,22202193,and 22172166)+1 种基金the Youth Innovation Promotion Association CAS (2021182)the Innovation Research Foundation of Dalian Institute of Chemical Physics,Chinese Academy of Sciences (DICP I202429 and I202217)。
文摘Alkane coupling with CO_(2) by metal-containing zeolites catalysis is found to be a promising way to produce aromatics and syngas in recent years,but the real active sites and the role of CO_(2) are still unclear owing to the quick evolution of the metallic active sites and the complex reaction processes including direct propane aromatization,CO_(2) hydrogenation,reverse water-gas shift reaction,and propane-CO_(2) coupling aromatization.Herein,Ga/ZSM-5 catalysts were constructed to study the dynamic evolution of the metallic active sites and the role of CO_(2) during the propane and CO_(2) coupling reaction.After optimizing the reaction conditions,a notable propane conversion rate of 97.9%and an impressive aromatics selectivity of 80.6%in hydrocarbons can be achieved at the conditions of 550℃and CO_(2)/C_(3)H_(8) of 4.^(13)CO_(2)isotope experiments illustrate that C-atoms of CO_(2) can enter into CO(86.5%)and aromatics(10.8%)during the propane-CO_(2) coupling reaction process.In situ XANES and FTIR spectroscopies at 550℃and H_(2)/C_(3)H_(8) atmosphere reveal that GaO_(x) species can be gradually dispersed into[GaH_(2)]^(+)/[GaH]^(2+)on the Bronsted acid sites of ZSM-5 zeolite during H_(2) and/or C_(3)H_(8) treatment,which are the real active sites for propane-CO_(2) coupling conversion.In situ CO_(2)-FTIR experiments demonstrate that the[GaH_(2)]^(+)/[GaH]^(2+)species can react with CO_(2) and accelerate the propane and CO_(2) coupling process.This work not only presents a cost-effective avenue for CO_(2) utilization,but also contributes to the active site design for improved alkane and CO_(2) activation in coupling reaction system.
文摘Mesoporous high‐silica zeolite Y with advantages of improved accessibility of acid sites and mass transport properties is highly desired catalytic materials for oil refinery,fine chemistry and emerg‐ing biorefinery.Here,we report the direct synthesis of mesoporous high‐silica zeolite Y(named MSY,SiO_(2)/Al2O_(3)≥9.8)and their excellent catalytic cracking performance.The obtained MSY mate‐rials are mesoporous single crystals with octahedral morphology,abundant mesoporosity and ex‐cellent(hydro)thermal stability.Both the acid concentration and acid strength of H‐form MSY are obviously higher than those of commercial ultra‐stable Y(USY),which should be attributed to the uniform Al distribution of MSY zeolite.The H‐MSY displays an obviously reduced deactivation rate and improved catalytic activity in the cracking reaction of bulky 1,3,5‐triisopropylbenzene(TIPB),as compared with its mesoporogen‐free counterpart and USY.In addition,H‐MSY was investigated as catalyst for the cracking of industrial heavy oil.The MSY‐based catalyst(after aging at 800 oC in 100%steam for 17 h)exhibits superior conversion(7.64%increase)and gasoline yield(16.37%increase)than industrial fluid catalytic cracking(FCC)catalyst under the investigated conditions.
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.
文摘Coke formation is the primary cause of zeolite deactivation in industrial catalysis,yet the structural identity,spatial location and molecular routes of polycyclic aromatic hydrocarbons(PAHs)within confined zeolite pores remain elusive.Here,by coupling matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry with multi-dimensional chemical imaging,we unveil a channel-passing growth mechanism for PAHs in ZSM-5 zeolites during methanol conversion through identifying the molecular fingerprints of larger PAHs,pinpointing and visualizing their 3D location and spatiotemporal evolution trajectory with atomic resolution and at both channel and single-crystal scales.Confined aromatic entities cross-link with each other,culminating in multicore PAH chains as the both thermodynamically favorable and kinetically trapped host-vip entanglement wrought and templated by the defined molecular-scale constrained microenvironments of zeolite.The mechanistic concept proves general across both channel-and cage-structured zeolite materials.Our multiscale deactivating model based on the full-picture coke structure-location correlations—spanning atom,molecule,channel/cage and single crystal scales—would shed new light on the intertwined chemical and physical processes in catalyst deactivation.This work not only resolves long-standing puzzles in coke formation but also provides design principles for coke-resistant zeolites.The methods and insights would rekindle interest in confinement effects and host-vip chemistry across broader chemistry fields beyond catalysis and carbon materials.
基金the National Key Research and Development Program of China(Grant No.2022YFE0116000)the National Natural Science Foundation of China(Grant Nos.22202193,21991092,21991090,22172166 and 22288101)+2 种基金the China Postdoctoral Science Foundation(Grant No.2019M661147)the Excellent Postdoctoral Support Program of Dalian Institute of Chemical Physics,CAS,the Excellent Research Assistant Funding Project of CAS,the Youth Innovation Promotion Association CAS(Grant No.2021182)the Innovation Research Foundation of Dalian Institute of Chemical Physics,Chinese Academy of Sciences(Grant No.DICP I202217)。
文摘Improving the aromatic selectivity in the alkane aromatization process is of great importance for its practical utilization but challenge to make because the high H/C ratio of alkanes would lead to a serious hydrogen transfer process and a large amount of light alkanes.Herein,CO_(2)is introduced into the cyclohexane conversion process on the HZSM-5 zeolite,which can improve the aromatic selectivity.By optimizing the reaction conditions,an improved aromatic(benzene,toluene,xylene,and C9+)selectivity of 48.2%can be obtained at the conditions of 2.7 MPa(CO_(2)),450℃,and 1.7 h^(−1),which is better than that without CO_(2)(aromatic selectivity=43.2%).In situ transmission Fourier transform infrared spectroscopy spectra illustrate that many oxygenated chemical intermediates(e.g.,carboxylic acid,anhydride,unsaturated aldehydes/ketones or ketene)would be formed during the cyclohexane conversion process in the presence of CO_(2).13C isotope labeling experimental results demonstrate that CO_(2)can enter into the aromatics through the formation of oxygenated chemical intermediates and thereby improve the aromatic selectivity.This study may open a green,economic,and promising way to improve the aromatic selectivity for alkane aromatization process.
