摘要
催化转化CO_(2)为乙醇、乙醛等高值C_(2)含氧化合物是一个具有科学意义和经济价值的化学过程.然而,由于碳氧键活化难、多电子(≥10)转移过程复杂以及C–C偶联动力学缓慢等问题,导致该过程的反应效率低.CO_(2)因热力学稳定、动力学惰性,其加氢活化通常是强吸热过程(如CO_(2)活化成CO的ΔH_(2)98K=42.1 kJ mol^(–1)),因此需要在一定温度下才能获得满意的CO_(2)转化率.与此同时,CH_(4)作为碳化学价态最低的化合物,其氧化过程与CO_(2)的还原过程可以耦合,共同转化为高值化学品,同样受到了广泛关注.但CH_(4)的活化同样需要高温等苛刻条件,因此,在温和条件下共转化CO_(2)和CH_(4),选择性构建高值C_(2)含氧化合物,是一个重要且具有挑战性的研究方向.本文提出利用光外场和水活化策略,即利用光解水产生的活性氢和活性氧物种,在温和条件下实现CO_(2)和CH_(4)的高效、高选择性活化及共转化.光照下,在钛酸锶(SrTiO_(x))负载的具有丰富Cu-Co界面的催化剂上,光解水产生的活性氢和活性氧物种,分别活化CO_(2)的碳氧键和CH_(4)的碳氢键,在Cu和Co位点上分别形成*CH_(x)O和*CH_(3)物种,进而通过C–C偶联高效生成C_(2)含氧化合物.在200°C和光照条件下,C_(2)含氧化合物(CH_(3)CHO和CH_(3)CH_(2)OH)的生成速率高达2.05 mmol g^(–1)h^(–1),同时产物选择性>86%.同位素标记、红外光谱示踪的原位反应和催化实验结果表明,紫外光激发下,SrTiO_(x)上的金属位点促进了光催化水裂解,生成活性氢和活性氧物种(该过程为整个反应的决速步骤).活性氢物种使吸附在SrTiO_(x)上的CO_(2)活化并转化为CO;随后,在CuI/Cu^(0)对上,CO加氢生成*CH_(x)O中间体.另一方面,在Co位点上,CH_(4)与活性氧物种发生反应,被活化为*CH_(3)中间体.最后,*CH_(x)O与*CH_(3)两种中间体在CuCo界面处发生C–C偶联反应,进而形成C_(2)含氧化合物.与传统的热催化下的CO_(2)和CH_(4)共转化过程相比,光热协同策略使该反应温度降低了超过600°C,并且反应活化能降低了约12 kJ mol^(–1),表明光热协同策略不仅可以大幅降低反应温度,还能极大提升反应动力学,为强吸热反应过程提供了一条提效降耗的反应途径.综上所述,本工作通过构建结构精准可控的SrTiO_(x)负载的CuCo邻近界面结构,同时利用光解水产生的活性氢/氧物种促进CO_(2)和CH_(4)活化,实现了高效定向共转化.本文提出的“光热协同”策略为高效活化CO_(2)制高值化学品提供了新的研究思路,同时显著降低了能耗,对解决强吸热催化反应高能耗问题提供了参考.
Photosynthesis is a potential strategy to enable endergonic process that usually needs high-temperature in thermochemistry to supply the energy for inert-bond activation and/or strong endothermic reaction.The conversion of CO_(2)into value-added C_(2)-oxygenates is a promising process to realize artificial photosynthesis,but suffers from relatively lower efficiency due to complex multi-electron(≥10)transfer processes and sluggish kinetics of C–C coupling.This work proposes an all-new H_(2)O-promoted strategy for efficient production of C_(2)oxygenates from the concurrent activation and subsequent co-conversion of CO_(2)with CH_(4)under photo-thermal cooperation,in which photocatalytic H_(2)O-splitting derived active hydrogen species for CO_(2)activation,and concomitant active oxygen species for CH_(4)activation.A formation rate of as high as 2.05 mmol g^(–1)h^(–1)for C_(2)-oxygenates(CH_(3)CHO and CH_(3)CH_(2)OH)in a selectivity of>86%has been afforded over SrTiO_(x)supported CuCo under 200°C and ultraviolet-visible illumination.It has been revealed that SrTiO_(x)drives photocatalytic H_(2)O-splitting under the excitation primary from ultraviolet light,paired CuI/Cu^(0)sites promote the formation of*CH_(x)O intermediate from CO_(2),Co sites conduct CH_(4)-to-*CH_(3),and C–C coupling of*CH_(x)O and*CH_(3)on adjacent Cu-Co facilitates the generation of C_(2)-oxygenates.
作者
朱彦儒
张志军
张健
蒋双江
安哲
宋红艳
舒心
习卫
郑黎荣
何静
Yanru Zhu;Zhijun Zhang;Jian Zhang;Shuangjiang Jiang;Zhe An;Hongyan Song;Xin Shu;Wei Xi;Lirong Zheng;Jing He(State Key Laboratory of Chemical Resource Engineering,&Beijing Advanced Innovation Center for Soft Matter Science and Engineering,Beijing University of Chemical Technology,Beijing 100029,China;Quzhou Institute for Innovation in Resource Chemical Engineering,Quzhou 324000,Zhejiang,China;Center for Electron Microscopy and Tianjin Key Laboratory of Advanced Functional Porous Materials,Tianjin University of Technology,Tianjin 300384,China;Institute of High Energy Physics,the Chinese Academy of Sciences,Beijing 100049,China)
基金
国家重点研发项目(2021YFB3801602)
国家自然科学基金(22288102).
