减少碳排放并推动碳中和是应对气候变化、促进经济社会绿色转型的重要途径之一,碳中和技术已成为工业界和学术界的关注焦点。目前碳捕集与封存主要对工业固定源排放的CO_(2)进行处置捕集,而对占CO_(2)总排放近50%的分布源CO_(2)关注度...减少碳排放并推动碳中和是应对气候变化、促进经济社会绿色转型的重要途径之一,碳中和技术已成为工业界和学术界的关注焦点。目前碳捕集与封存主要对工业固定源排放的CO_(2)进行处置捕集,而对占CO_(2)总排放近50%的分布源CO_(2)关注度不高。直接空气捕集(direct air capture,DAC)技术不仅可对数以百万计的小型化石燃料燃烧装置以及数以亿计的交通工具等分布源排放的CO_(2)进行捕集处理,还可有效降低大气中CO_(2)浓度。介绍了DAC的发展历史、研究现状以及发展趋势,综述了已有DAC技术的工艺流程以及反应装置,对DAC现行工艺中涉及的空气捕捉模块、吸收剂或吸附剂再生模块、CO_(2)储存模块进行了叙述,对比了几种工艺的优缺点以及吸附剂类型和再生方式,指出DAC技术发展的关键在于研发高效低成本的吸收/吸附材料和设备。分析了DAC吸收/吸附材料的作用原理以及吸附效果,碱性溶液原料成本相对低廉,但再生过程中能耗较高。分子筛及金属有机框架吸附剂虽然再生能耗较低,但对空气中CO_(2)的吸附容量和吸附选择性表现一般。胺类吸附剂具有较好的吸附能力,由于其再生温度较低,可使用工业废热或少量热能为系统供能;使用胺类吸附剂时吸附和解吸在一个单元中逐步发生,具有更高的效率和操作时间,有望降低DAC系统成本。对比了DAC与其他碳捕集技术的成本并进行了技术经济性分析,DAC成本主要包含运营和维护成本(N_(Q&M))、吸附剂材料成本(N_(S))和工厂设备的净成本(N_(bop));指出目前限制DAC工业化应用的主要因素之一在于吸收/吸附材料和相关工艺成本过高,随着阴离子交换树脂等新型吸附剂的出现和工艺的发展,DAC成本逐年下降。全面探究吸收/吸附材料稳定性、动力学、吸附容量、选择性、再生能量损失等综合性能,研发利于快速装载和卸载吸附剂的相关装置,开发成本低廉的工艺系统是目前DAC领域的发展方向和迫切需求。DAC技术将为减少全球碳排放、实现碳中和提供重要技术支撑。展开更多
The one-step conversion of ethanol to 1,3-butadiene has achieved a breakthrough with the development of beta zeolite supported dual metal catalysts.However,the reaction mechanism from ethanol to butadiene is complex a...The one-step conversion of ethanol to 1,3-butadiene has achieved a breakthrough with the development of beta zeolite supported dual metal catalysts.However,the reaction mechanism from ethanol to butadiene is complex and has not yet been fully elucidated,and no catalyst screening effort has been done based on central metal atoms.In this work,density functional theory(DFT)calculations were employed to study the mechanism of one-step conversion of ethanol to butadiene over ZnY/BEA catalyst.The results show that ethanol dehydrogenation prefers to proceed on Zn site with a reaction energy of 0.77 eV in the rate-determining step,and the aldol condensation to produce butadiene prefers to proceed on Y site with a reaction energy of 0.69 eV in the rate-determining step.Based on the mechanism revealed,six elements were selected to replace Y for screening superior combination of Zn-M/BEA(M=Sn,Nb,Ta,Hf,Zr,Ti;BEA:beta polymorph A)for this reaction.As a result,Zn-Y/BEA(0.69 eV)is proven to be the most preferring catalyst compared with the other six ones,and Zn-Zr/BEA(0.85 eV),Zn-Ti/BEA(0.87 eV),and Zn-Sn/BEA(0.93 eV)can be potential candidates for the conversion of ethanol to butadiene.This work not only provides mechanistic insights into one-step catalytic conversion of ethanol to butadiene over Zn-Y/BEA catalyst but also offers more promising catalyst candidates for this reaction.展开更多
Direct syngas conversion to light olefins on bifunctional oxide-zeolite(OX-ZEO)catalysts is of great interest to both academia and industry,but the role of oxygen vacancy(Vo)in metal oxides and whether the key interme...Direct syngas conversion to light olefins on bifunctional oxide-zeolite(OX-ZEO)catalysts is of great interest to both academia and industry,but the role of oxygen vacancy(Vo)in metal oxides and whether the key intermediate in the reaction mechanism is ketene or methanol are still not well-understood.To address these two issues,we carry out a theoretical study of the syngas conversion on the typical reducible metal oxide,CeO2,using density functional theory calculations.Our results demonstrate that by forming frustrated Lewis pairs(FLPs),the VOs in CeO2 play a key role in the activation of H2 and CO.The activation of H2 on FLPs undergoes a heterolytic dissociative pathway with a tiny barrier of 0.01 eV,while CO is activated on FLPs by combining with the basic site(O atom)of FLPs to form CO2^2-.Four pathways for the conversion of syngas were explored on FLPs,two of which are prone to form ketene and the other two are inclined to produce methanol suggesting a compromise to resolve the debate about the key intermediates(ketene or methanol)in the experiments.Rate constant calculations showed that the route initiating with the coupling of two CO*into OCCO*and ending with the formation of ketene is the dominant pathway,with the neighboring FLPs playing an important role in this pathway.Overall,our study reveals the function of the surface FLPs in the activation of H2 and CO and the reaction mechanism for the production of ketene and methanol for the first time,providing novel insights into syngas conversion over OX-ZEO catalysts.展开更多
基金supported by the National Natural Science Foundation of China(No.22038011,No.22078257,No.22108213,No.52176142)the China Postdoctoral Science Foundation(2021M692548)+1 种基金the Joint Fund of the Yulin University and the Dalian National Laboratory for Clean Energy(Grant YLU-DNL Fund 2022001)the Young Talent Support Plan of Shaanxi Province。
文摘减少碳排放并推动碳中和是应对气候变化、促进经济社会绿色转型的重要途径之一,碳中和技术已成为工业界和学术界的关注焦点。目前碳捕集与封存主要对工业固定源排放的CO_(2)进行处置捕集,而对占CO_(2)总排放近50%的分布源CO_(2)关注度不高。直接空气捕集(direct air capture,DAC)技术不仅可对数以百万计的小型化石燃料燃烧装置以及数以亿计的交通工具等分布源排放的CO_(2)进行捕集处理,还可有效降低大气中CO_(2)浓度。介绍了DAC的发展历史、研究现状以及发展趋势,综述了已有DAC技术的工艺流程以及反应装置,对DAC现行工艺中涉及的空气捕捉模块、吸收剂或吸附剂再生模块、CO_(2)储存模块进行了叙述,对比了几种工艺的优缺点以及吸附剂类型和再生方式,指出DAC技术发展的关键在于研发高效低成本的吸收/吸附材料和设备。分析了DAC吸收/吸附材料的作用原理以及吸附效果,碱性溶液原料成本相对低廉,但再生过程中能耗较高。分子筛及金属有机框架吸附剂虽然再生能耗较低,但对空气中CO_(2)的吸附容量和吸附选择性表现一般。胺类吸附剂具有较好的吸附能力,由于其再生温度较低,可使用工业废热或少量热能为系统供能;使用胺类吸附剂时吸附和解吸在一个单元中逐步发生,具有更高的效率和操作时间,有望降低DAC系统成本。对比了DAC与其他碳捕集技术的成本并进行了技术经济性分析,DAC成本主要包含运营和维护成本(N_(Q&M))、吸附剂材料成本(N_(S))和工厂设备的净成本(N_(bop));指出目前限制DAC工业化应用的主要因素之一在于吸收/吸附材料和相关工艺成本过高,随着阴离子交换树脂等新型吸附剂的出现和工艺的发展,DAC成本逐年下降。全面探究吸收/吸附材料稳定性、动力学、吸附容量、选择性、再生能量损失等综合性能,研发利于快速装载和卸载吸附剂的相关装置,开发成本低廉的工艺系统是目前DAC领域的发展方向和迫切需求。DAC技术将为减少全球碳排放、实现碳中和提供重要技术支撑。
基金This work was supported by the National Natural Science Foundation of China(No.22078257,No.22038011,and No.22108213)the National Key R&D Program of China(No.2020YFA0710000)+1 种基金the China Postdoctoral Science Foundation(No.2018T111034 and No.2021M692548)the Rising Star Program in Science and Technology of Shaanxi Province(No.2020KJXX-079).Chun-Ran Chang also acknowledges the support from the K.C.Wong Education Foundation.The calculations were performed by using the HPC Platform at Xi’an Jiaotong University。
文摘The one-step conversion of ethanol to 1,3-butadiene has achieved a breakthrough with the development of beta zeolite supported dual metal catalysts.However,the reaction mechanism from ethanol to butadiene is complex and has not yet been fully elucidated,and no catalyst screening effort has been done based on central metal atoms.In this work,density functional theory(DFT)calculations were employed to study the mechanism of one-step conversion of ethanol to butadiene over ZnY/BEA catalyst.The results show that ethanol dehydrogenation prefers to proceed on Zn site with a reaction energy of 0.77 eV in the rate-determining step,and the aldol condensation to produce butadiene prefers to proceed on Y site with a reaction energy of 0.69 eV in the rate-determining step.Based on the mechanism revealed,six elements were selected to replace Y for screening superior combination of Zn-M/BEA(M=Sn,Nb,Ta,Hf,Zr,Ti;BEA:beta polymorph A)for this reaction.As a result,Zn-Y/BEA(0.69 eV)is proven to be the most preferring catalyst compared with the other six ones,and Zn-Zr/BEA(0.85 eV),Zn-Ti/BEA(0.87 eV),and Zn-Sn/BEA(0.93 eV)can be potential candidates for the conversion of ethanol to butadiene.This work not only provides mechanistic insights into one-step catalytic conversion of ethanol to butadiene over Zn-Y/BEA catalyst but also offers more promising catalyst candidates for this reaction.
文摘Direct syngas conversion to light olefins on bifunctional oxide-zeolite(OX-ZEO)catalysts is of great interest to both academia and industry,but the role of oxygen vacancy(Vo)in metal oxides and whether the key intermediate in the reaction mechanism is ketene or methanol are still not well-understood.To address these two issues,we carry out a theoretical study of the syngas conversion on the typical reducible metal oxide,CeO2,using density functional theory calculations.Our results demonstrate that by forming frustrated Lewis pairs(FLPs),the VOs in CeO2 play a key role in the activation of H2 and CO.The activation of H2 on FLPs undergoes a heterolytic dissociative pathway with a tiny barrier of 0.01 eV,while CO is activated on FLPs by combining with the basic site(O atom)of FLPs to form CO2^2-.Four pathways for the conversion of syngas were explored on FLPs,two of which are prone to form ketene and the other two are inclined to produce methanol suggesting a compromise to resolve the debate about the key intermediates(ketene or methanol)in the experiments.Rate constant calculations showed that the route initiating with the coupling of two CO*into OCCO*and ending with the formation of ketene is the dominant pathway,with the neighboring FLPs playing an important role in this pathway.Overall,our study reveals the function of the surface FLPs in the activation of H2 and CO and the reaction mechanism for the production of ketene and methanol for the first time,providing novel insights into syngas conversion over OX-ZEO catalysts.
