The oxygen distribution and evolution within the oxygen carrier exert significant influence on chemical looping processes.This paper describes the influence of oxygen bulk diffusion within FeVO4 oxygen carrier pellets...The oxygen distribution and evolution within the oxygen carrier exert significant influence on chemical looping processes.This paper describes the influence of oxygen bulk diffusion within FeVO4 oxygen carrier pellets on the chemical looping oxidative propane dehydrogenation(CL-ODH).During CL-ODH,the oxygen concentration at the pellet surface initially decreased and then maintained stable before the final decrease.At the stage with the stable surface oxygen concentration,the reaction showed a stable C3H6 formation rate and high C3H6 selectivity.Therefore,based on Fick’s second law,the oxygen distribution and evolution in the oxygen carrier at this stage were further analyzed.It was found that main reactions of selective oxidation and over-oxidation were controlled by the oxygen bulk diffusion.C3H8 conversion rate kept decreasing during this stage due to the decrease of the oxygen flux caused by the decline of oxygen gradient within the oxygen carrier,while C3H6 selectivity increased due to the decrease of overoxidation.In addition,reaction rates could increase with the propane partial pressure due to the increase of the oxygen gradient within the oxygen carrier until the bulk transfer reached its limit at higher propane partial pressure.This study provides fundamental insights for the diffusion-controlled chemical looping reactions.展开更多
The chemical looping steam reforming(CLSR)of bioethanol is an energy-efficient and carbon-neutral approach of hydrogen production.This paper describes the use of a Ni_(x)Mg_(1-x)O solid solution as the oxy-gen carrier...The chemical looping steam reforming(CLSR)of bioethanol is an energy-efficient and carbon-neutral approach of hydrogen production.This paper describes the use of a Ni_(x)Mg_(1-x)O solid solution as the oxy-gen carrier(OC)in the CLSR of bioethanol.Due to the regulation effect of Mg^(2+)in Ni_(x)Mg_(1-x)O,a three-stage reaction mechanism of the CLSR process is proposed.The surface oxygen of Ni_(x)Mg_(1-x)O initially causes complete oxidation of the ethanol.Subsequently,H_(2)O and bulk oxygen confined by Mg^(2+)react with etha-nol to form CH_(3)COO^(*)followed by H_(2) over partially reduced Ni_(x)Mg_(1-x)O.Once the bulk oxygen is con-sumed,the ethanol steam reforming process is promoted by the metallic nickel in the stage Ⅲ.As a result,Ni_(0.4)Mg_(0.6)O exhibits a high H_(2) selectivity(4.72 mol H_(2) per mole ethanol)with a low steam-to-carbon molar ratio of 1,and remains stable over 30 CLSR cycles.The design of this solid-solution OC pro-vides a versatile strategy for manipulating the chemical looping process.展开更多
CoCu-based catalysts are widely used in CO_(x) hydrogenation reactions to produce higher alcohols due to the C–C coupling ability of Co and the ability of Cu to produce alcohols.This work describes the role of easily...CoCu-based catalysts are widely used in CO_(x) hydrogenation reactions to produce higher alcohols due to the C–C coupling ability of Co and the ability of Cu to produce alcohols.This work describes the role of easily happened CO_(2)dissociation on the CoCu surface during the reaction,using different silica support to tune the metal–support interaction,reaches different selectivity to ethanol.CoCu supported on mesoporous silica MCM-41 shows ethanol selectivity as high as 85.3%,the ethanol space-time yield(STY)is 0.229 mmol/(gmetal∙h),however,poor selectivity to ethanol as low as 28.8%is observed on CoCu supported on amorphous silica.The different selectivity is due to the different intensities of CO_(2)dissociation on the catalysts.The adsorbed O*produced via CO_(2)dissociation can occupy the cobalt hollow sites on CoCu surfaces,which are also the adsorption sites of C1 intermediates for further C–C coupling.展开更多
Defects are ubiquitous in oxide supports and can often tune the catalytic property of supported metal catalysts.This work describes the distinct role of titanium and oxygen vacancies of TiO2 supports in the catalytic ...Defects are ubiquitous in oxide supports and can often tune the catalytic property of supported metal catalysts.This work describes the distinct role of titanium and oxygen vacancies of TiO2 supports in the catalytic performance of supported Pt catalysts for CO oxidation.Pt was loaded on the TiO2 supports with oxygen vacancies(VO-TiO2)and titanium vacancies(VTiTiO2).It was found that different defects of TiO2 could distinctively modify the electron property of Pt and thereby CO adsorption strength.The strength of CO adsorption on Pt/VTi-TiO2 is enhanced,while that of Pt/VO-TiO2 becomes weaker.Additionally,the presence of defects would also promote the reducibility of catalysts.On the account of the superior redox ability,both Pt/VTi-TiO2 and Pt/VO-TiO2 exhibit a higher activity than Pt supported on normal TiO2 for CO oxidation.展开更多
CONSPECTUS:Propylene serves as one of the most significant compounds in the chemical industry.Propane dehydrogenation(PDH),an“on purpose”propylene production technology is developing.Pt-and CrOx-based catalysts are ...CONSPECTUS:Propylene serves as one of the most significant compounds in the chemical industry.Propane dehydrogenation(PDH),an“on purpose”propylene production technology is developing.Pt-and CrOx-based catalysts are widely applied in commercialized PDH processes,and both exhibit high activity and propylene yields.However,as an intensively endothermic process,PDH requires operation at high temperatures(generally above 500°C),which restricts the C3H6 selectivity and catalyst structure stability on account of coking side reactions,particle sintering,and so forth.Nanostructured catalysts(NCs)based on metals and/or metal oxides with tunable geometric and electronic properties play significant roles because such features intrinsically influence the adsorption of propyl intermediates on the catalyst surface.However,thermodynamical metastability of these NCs results in grand challenges in their structure-controlled preparation.The regulation of material structure and reaction performance at the molecular and atomic levels has attracted extended attention over the past few years.This Account describes our recent advances in controllable regulation of metal and oxide NCs toward efficient propane dehydrogenation.As a structure-insensitive reaction,the dehydrogenation of propane can occur on an individual active site,while larger ensembles of active sites also induce structure-sensitive side reactions,leading to C−C cracking and coke deposition.This paper is aimed at delivering general fundamentals for rational design of NCs in PDH reactions.We start with the catalytic kinetics on the active sites regarding the adsorption of key propyl intermediates on the surface.In subsequent sections,we present the effective regulation strategies for metal and oxide NCs by promoter and support effects.Upon metal NCs,coke deposition and nanoparticles(NPs)sintering tend to occur,which can be suppressed with the increase of geometric separation and charge density of surface active sites by changing alloy compositions,ordered intermetallic alloys,single-atom catalysts,core−shell,and metal−oxide interface structures.Notably,the confinement approach of embedding active sites in zeolite frameworks significantly inhibits the sintering of metal NPs.As alternatives to metals,metal oxides exhibit lower cost but higher barriers of C−H activation and coking inclination.The C−H bond cleavage has been promoted by inducing intrinsic defect sites,such as oxygen vacancies,hydroxyls,and hydrides on the surface and heterogeneous doping in the bulk.Importantly,the structures of the submonolayer/monolayer triggered by spontaneous dispersion and confinement in mesoporous materials significantly improve the oxide activity and stability.All of these strategies have been essential for the efficient PDH reactions.Moreover,the challenges and perspectives are also discussed.It is hoped that the deliberate manipulation of nanostructured catalysts to regulate the reaction mechanism will hold the key to efficient alkane conversion.展开更多
Rational design and performance promotion are eternal topics and ultimate goals in catalyst preparation.In contrast,trial–and–error is still the common method people take.Therefore,it is important to develop methods...Rational design and performance promotion are eternal topics and ultimate goals in catalyst preparation.In contrast,trial–and–error is still the common method people take.Therefore,it is important to develop methods to intrinsically enhance the performance of catalysts.The most effective solutions are the one from a kinetic perspective based on clear knowledge of the reaction mechanism.This paper describes rate-determining step cognition and modulation to promote CO oxidation on highly dispersed Pt on CeO_(2).The different degrees of metal–support interactions due to variation of hydroxyl density of support could alter the structure of active species and the ability of oxygen activation apparently,further shift the rate-determining step from oxygen activation to oxygen reverse spillover kinetically.The transformation of rate-determining step could enhance the intrinsic activity significantly,and decrease the T_(50) approximately 140℃.The findings of this research exemplify the universal and effective method of performance elevation by rate-determining step modulation,which is promising for application in different systems.展开更多
The flow behaviours of cohesive particles in the ring shear test were simulated and examined using discrete element method guided by a design of experiments methodology.A full factorial design was used as a screening ...The flow behaviours of cohesive particles in the ring shear test were simulated and examined using discrete element method guided by a design of experiments methodology.A full factorial design was used as a screening design to reveal the effects of material properties of partcles.An augmented design extending the screening design to a response surface design was constructed to establish the relations between macroscopic shear stresses and particle properties.It is found that the powder flow in the shear cell can be classified into four regimes.Shear stress is found to be sensitive to particle friction coefficient,surface energy and Young’s modulus.A considerable fluctuation of shear stress is observed in high friction and low cohesion regime.In high cohesion regime,Young’s modulus appears to have a more significant effect on the shear stress at the point of incipient flow than the shear stress during the pre-shear process.The predictions from response surface designs were validated and compared with shear stresses measured from the Schulze ring shear test.It is found that simulations and experiments showed excellent agreement under a variety of consolidation conditions,which verifies the advantages and feasibility of using the proposed“Sequential Design of Simulations”approach.展开更多
基金the National Key Research and Development Program of China (2021YFA1501302)the National Natural Science Foundation of China (22122808, U20B6002)+1 种基金the Haihe Laboratory of Sustainable Chemical Transformations and the Program of Introducing Talents of Discipline to Universities (BP0618007) for financial supportsupported by the XPLORER PRIZE by Tencent Foundation
文摘The oxygen distribution and evolution within the oxygen carrier exert significant influence on chemical looping processes.This paper describes the influence of oxygen bulk diffusion within FeVO4 oxygen carrier pellets on the chemical looping oxidative propane dehydrogenation(CL-ODH).During CL-ODH,the oxygen concentration at the pellet surface initially decreased and then maintained stable before the final decrease.At the stage with the stable surface oxygen concentration,the reaction showed a stable C3H6 formation rate and high C3H6 selectivity.Therefore,based on Fick’s second law,the oxygen distribution and evolution in the oxygen carrier at this stage were further analyzed.It was found that main reactions of selective oxidation and over-oxidation were controlled by the oxygen bulk diffusion.C3H8 conversion rate kept decreasing during this stage due to the decrease of the oxygen flux caused by the decline of oxygen gradient within the oxygen carrier,while C3H6 selectivity increased due to the decrease of overoxidation.In addition,reaction rates could increase with the propane partial pressure due to the increase of the oxygen gradient within the oxygen carrier until the bulk transfer reached its limit at higher propane partial pressure.This study provides fundamental insights for the diffusion-controlled chemical looping reactions.
基金supported by National Natural Science Foundation of China (U20B6002, 51761145012, and 21525626)the Program of Introducing Talents of Discipline to Universities (BP0618007) for financial support
文摘The chemical looping steam reforming(CLSR)of bioethanol is an energy-efficient and carbon-neutral approach of hydrogen production.This paper describes the use of a Ni_(x)Mg_(1-x)O solid solution as the oxy-gen carrier(OC)in the CLSR of bioethanol.Due to the regulation effect of Mg^(2+)in Ni_(x)Mg_(1-x)O,a three-stage reaction mechanism of the CLSR process is proposed.The surface oxygen of Ni_(x)Mg_(1-x)O initially causes complete oxidation of the ethanol.Subsequently,H_(2)O and bulk oxygen confined by Mg^(2+)react with etha-nol to form CH_(3)COO^(*)followed by H_(2) over partially reduced Ni_(x)Mg_(1-x)O.Once the bulk oxygen is con-sumed,the ethanol steam reforming process is promoted by the metallic nickel in the stage Ⅲ.As a result,Ni_(0.4)Mg_(0.6)O exhibits a high H_(2) selectivity(4.72 mol H_(2) per mole ethanol)with a low steam-to-carbon molar ratio of 1,and remains stable over 30 CLSR cycles.The design of this solid-solution OC pro-vides a versatile strategy for manipulating the chemical looping process.
基金supported by the National Key R&D Program of China(2021YFA1501302)the National Natural Science Foundation of China(22121004,U1862207,and 22122808)+1 种基金Haihe Laboratory of Sustainable Chemical Transformations,the Program of Introducing Talents of Discipline to Universities(BP0618007)the XPLORER PRIZE.
基金the National Key R&D Program of China(No.2021YFA1500704)the National Natural Science Foundation of China(No.22121004)+2 种基金the Haihe Laboratory of Sustainable Chemical Transformations(No.CYZC202107)the Program of Introducing Talents of Discipline to Universities(No.BP0618007)the XPLORER PRIZE for financial support.
文摘CoCu-based catalysts are widely used in CO_(x) hydrogenation reactions to produce higher alcohols due to the C–C coupling ability of Co and the ability of Cu to produce alcohols.This work describes the role of easily happened CO_(2)dissociation on the CoCu surface during the reaction,using different silica support to tune the metal–support interaction,reaches different selectivity to ethanol.CoCu supported on mesoporous silica MCM-41 shows ethanol selectivity as high as 85.3%,the ethanol space-time yield(STY)is 0.229 mmol/(gmetal∙h),however,poor selectivity to ethanol as low as 28.8%is observed on CoCu supported on amorphous silica.The different selectivity is due to the different intensities of CO_(2)dissociation on the catalysts.The adsorbed O*produced via CO_(2)dissociation can occupy the cobalt hollow sites on CoCu surfaces,which are also the adsorption sites of C1 intermediates for further C–C coupling.
基金the National Key Research and Development Program of China(2016YFB0600901)the National Science Foundation of China(21525626,U1862207)the Program of Introducing Talents of Discipline to Universities(B06006)。
文摘Defects are ubiquitous in oxide supports and can often tune the catalytic property of supported metal catalysts.This work describes the distinct role of titanium and oxygen vacancies of TiO2 supports in the catalytic performance of supported Pt catalysts for CO oxidation.Pt was loaded on the TiO2 supports with oxygen vacancies(VO-TiO2)and titanium vacancies(VTiTiO2).It was found that different defects of TiO2 could distinctively modify the electron property of Pt and thereby CO adsorption strength.The strength of CO adsorption on Pt/VTi-TiO2 is enhanced,while that of Pt/VO-TiO2 becomes weaker.Additionally,the presence of defects would also promote the reducibility of catalysts.On the account of the superior redox ability,both Pt/VTi-TiO2 and Pt/VO-TiO2 exhibit a higher activity than Pt supported on normal TiO2 for CO oxidation.
基金supported by the National Natural Science Foundation of China (21525626 and 21761132023)the Program of Introducing Talents of Discipline to Universities (BP0618007)。
基金We acknowledge the National Natural Science Foundation of China(21525626,U1862207)the Program of Introducing Talents of Discipline to Universities(No.B06006)for financial support.
文摘CONSPECTUS:Propylene serves as one of the most significant compounds in the chemical industry.Propane dehydrogenation(PDH),an“on purpose”propylene production technology is developing.Pt-and CrOx-based catalysts are widely applied in commercialized PDH processes,and both exhibit high activity and propylene yields.However,as an intensively endothermic process,PDH requires operation at high temperatures(generally above 500°C),which restricts the C3H6 selectivity and catalyst structure stability on account of coking side reactions,particle sintering,and so forth.Nanostructured catalysts(NCs)based on metals and/or metal oxides with tunable geometric and electronic properties play significant roles because such features intrinsically influence the adsorption of propyl intermediates on the catalyst surface.However,thermodynamical metastability of these NCs results in grand challenges in their structure-controlled preparation.The regulation of material structure and reaction performance at the molecular and atomic levels has attracted extended attention over the past few years.This Account describes our recent advances in controllable regulation of metal and oxide NCs toward efficient propane dehydrogenation.As a structure-insensitive reaction,the dehydrogenation of propane can occur on an individual active site,while larger ensembles of active sites also induce structure-sensitive side reactions,leading to C−C cracking and coke deposition.This paper is aimed at delivering general fundamentals for rational design of NCs in PDH reactions.We start with the catalytic kinetics on the active sites regarding the adsorption of key propyl intermediates on the surface.In subsequent sections,we present the effective regulation strategies for metal and oxide NCs by promoter and support effects.Upon metal NCs,coke deposition and nanoparticles(NPs)sintering tend to occur,which can be suppressed with the increase of geometric separation and charge density of surface active sites by changing alloy compositions,ordered intermetallic alloys,single-atom catalysts,core−shell,and metal−oxide interface structures.Notably,the confinement approach of embedding active sites in zeolite frameworks significantly inhibits the sintering of metal NPs.As alternatives to metals,metal oxides exhibit lower cost but higher barriers of C−H activation and coking inclination.The C−H bond cleavage has been promoted by inducing intrinsic defect sites,such as oxygen vacancies,hydroxyls,and hydrides on the surface and heterogeneous doping in the bulk.Importantly,the structures of the submonolayer/monolayer triggered by spontaneous dispersion and confinement in mesoporous materials significantly improve the oxide activity and stability.All of these strategies have been essential for the efficient PDH reactions.Moreover,the challenges and perspectives are also discussed.It is hoped that the deliberate manipulation of nanostructured catalysts to regulate the reaction mechanism will hold the key to efficient alkane conversion.
基金the National Key R&D Program of China (2021YFA1501302)the National Natural Science Foundation of China (22121004,U1862207)+1 种基金the Haihe Laboratory of Sustainable Chemical Transformations and the Program of Introducing Talents of Discipline to Universities (BP0618007) for financial supportsupported by the XPLORER PRIZE
文摘Rational design and performance promotion are eternal topics and ultimate goals in catalyst preparation.In contrast,trial–and–error is still the common method people take.Therefore,it is important to develop methods to intrinsically enhance the performance of catalysts.The most effective solutions are the one from a kinetic perspective based on clear knowledge of the reaction mechanism.This paper describes rate-determining step cognition and modulation to promote CO oxidation on highly dispersed Pt on CeO_(2).The different degrees of metal–support interactions due to variation of hydroxyl density of support could alter the structure of active species and the ability of oxygen activation apparently,further shift the rate-determining step from oxygen activation to oxygen reverse spillover kinetically.The transformation of rate-determining step could enhance the intrinsic activity significantly,and decrease the T_(50) approximately 140℃.The findings of this research exemplify the universal and effective method of performance elevation by rate-determining step modulation,which is promising for application in different systems.
基金Advanced Manufacturing Supply Chain Initiative‘Advanced Digital Design of Pharmaceutical Therapeutics’(ADDoPT)project(Grant No.14060)the EPSRC grant INFORM 2020(EP/N025075/1).
文摘The flow behaviours of cohesive particles in the ring shear test were simulated and examined using discrete element method guided by a design of experiments methodology.A full factorial design was used as a screening design to reveal the effects of material properties of partcles.An augmented design extending the screening design to a response surface design was constructed to establish the relations between macroscopic shear stresses and particle properties.It is found that the powder flow in the shear cell can be classified into four regimes.Shear stress is found to be sensitive to particle friction coefficient,surface energy and Young’s modulus.A considerable fluctuation of shear stress is observed in high friction and low cohesion regime.In high cohesion regime,Young’s modulus appears to have a more significant effect on the shear stress at the point of incipient flow than the shear stress during the pre-shear process.The predictions from response surface designs were validated and compared with shear stresses measured from the Schulze ring shear test.It is found that simulations and experiments showed excellent agreement under a variety of consolidation conditions,which verifies the advantages and feasibility of using the proposed“Sequential Design of Simulations”approach.
