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采用催化加氢的方式将CO2转化为甲醇,既可以减少CO2排放,又制备了化学品,该反应具有重要的研究意义.氧化铟(In2O3)作为CO2加氢制甲醇催化剂,由于其较高的CO2活化能力和甲醇选择性,被科研工作者广泛研究.其中,将具有良好解离H2能力的过渡金属元素引入In2O3(M/In2O3)是有效提高催化剂性能的策略之一,然而,M/In2O3体系催化CO2加氢反应机理及活性位点仍不清楚.本文引入Co制备了In-Co二元金属氧化物催化剂应用于CO2加氢制甲醇,结果表明,相较于In2O3,In-Co催化剂性能有很大提升,其中In1-Co4催化剂上甲醇时空产率(9.7 mmol·gcat-1 h-1)是In2O3(2.2mmol·gcat-1 h-1)的近5倍(反应条件:P=4.0 MPa,T=300℃,GHSV=24000 Cm3STP gcat-1 h-1,H2/CO2=3).值得注意的是,尽管Co是金属元素的主体,In-Co催化剂中Co催化CO2甲烷化的活性受到明显抑制.本文还通过多种技术系统研究了催化剂结构与反应选择性转变间的关系.采用电感耦合等离子体发射光谱、粉末X射线衍射、拉曼光谱、X射线光电子能谱和透射电子显微镜等对催化剂结构以及表面性质进行了表征.结果 表明,在H2还原气氛诱导下,In-Co催化剂表面发生重构,形成以CoO为核,以In2O3为壳的核壳结构,其在高压反应后仍能保持稳定;更重要的是,该核壳结构可以显著增强In-Co催化剂吸附及活化CO2的能力.CO2加氢反应动力学研究表明,Co催化剂上H2分压对CO2加氢为零级反应,而H2分压在In-Co上的反应级数为正数;In-Co催化剂上,CO2分压的反应级数接近于零,表明CO2及其衍生物在In-Co的表面吸附饱和,但在纯Co上,则不会发生这种饱和吸附.通过原位DRIFTS研究了催化反应路径和关键中间物种的吸附及反应行为,发现CO2加氢在纯Co和In-Co上的催化机理均遵循甲酸盐路径.在该催化路径中,CO2首先加氢为甲酸盐(*HCOO)物种,随后加氢为甲氧基(*CH3O).*CH3O在Co催化剂上进一步加氢生成CH4,而*CH3O在In-Co催化剂上则会脱附生成CH3OH.根据表征结果,本文认为,在还原性气氛下,In-Co发生了重构并生成表面富In2O3的核壳状结构,显著提高了催化剂对CO2和含碳物种的吸附能力.Co和In-Co催化剂对CO2加氢反应选择性的差异归因于催化剂对CO2和对*HCOO等含碳中间物种的吸附稳定性不同.CO2及其衍生的含碳中间物种在In-Co催化剂上的吸附能力比在Co催化剂上强,形成了较合适的催化剂表面C/H比,从而使*CH3O能够脱附为CH3OH,而不是进一步加氢为CH4.综上,本文研究为高活性In-Co催化剂体系在CO2加氢反应中的催化机理及行为提供了解释,为金属-氧化铟(M-In2O3)催化剂体系的设计提供了参考.“,”The hydrogenation of CO2 into methanol has attracted much attention and In2O3 is a promising catalyst.Introducing metal elements into In2O3 (M/In2O3) is one of the main strategies to improve its performance.However,its mechanism and active sites remain unclear and need to be further elucidated.Here,the noble-metal-free Inx-Coy oxides catalysts were prepared.Much-improved per-formance and obvious product selectivity shift were observed.The optimized catalyst (In1-Co4) (9.7 mmol gcat-1 h-1) showed five times methanol yields than pure In2O3 (2.2 mmol gcat-1 h-1) (P =4.0 MPa,T =300 ℃,GHSV =24000 cm3STP gcat-1 h-1,H2∶CO2 =3).And the cobalt-catalyzed CO2 methanation activity was suppressed,although cobalt was most of the metal element.To unravel this selectivity shift,detailed catalysts performance evaluation,together with several in-situ and ex-situ characteri-zations,were employed on cobalt and In-Co for comparative study.The results indicated CO2 hy-drogenation on cobalt and In-Co catalyst both followed the formate pathway,and In-Co recon-structed and generated a surface In2O3-enriched core-shell-like structure under a reductive atmos-phere.The enriched In2O3 at the surface significantly enhanced CO2 adsorption capacity and well stabilized the intermediates of CO2 hydrogenation.CO2 and carbon-containing intermediates ad-sorbed much stronger on In-Co than cobalt led to a feasible surface C/H ratio,thus allowing the*CH3O to desorb to produce CH3OH instead of being over-hydrogenated to CH4.