Ni纳米晶表面微结构调控及其对催化性能的影响机制

Ni-based catalysts have attracted extensive attention for a wide range of applications in chemical industry and environmental catalysis. However，they often suffer from poor activity at low temperature, high-temperature sintering, carbon formation and sulphur poisoning, which are the focuses of industry and scientific research. The present researches mainly focus on improving the catalytic performance via gropingly tuning the component of catalyst or the synthesis method; however, atomic level insight into the interplay between active sites and catalytic activity are still poorly understood. Particularly, the elusive nature of the active site on Ni nanocatalyst is still an open question. Thus, this stimulates us to pursue a suitable material model for studying the active sites–catalytic performance relationship. Ni nanocrystal with controlled surface microstructure (with defect sites such as, step, kink and corner atoms) could serve as an ideal model, which was prepared by kinetic control via liquid-phase synthesis method. This project aims at revealing the types of active sites and theirs difference in activity, and elaborating the correlation among the surface microscopic structure and the catalytic performance. Furthermore, we also try to disclose the structural evolution of active sites during sintering, carbon formation and sulphur poisoning processes, and expect to understand the mechanism of catalyst deactivation at atomic level. The achievements in this project will provide technical support and theoretical basis for understanding the catalytic mechanism deeply and effectively designing novel Ni-based catalysts with enhanced activity and stability.

Ni基催化剂广泛应用于化工、环境等领域的催化反应中，其低温活性差、高温烧结、积碳和硫中毒等问题，一直是工业界普遍关注的焦点，也是科学研究的热点。现有研究大多从宏观上来开展，通过改变催化剂配方或制备方法提高其催化性能，然而从微观上对Ni纳米颗粒表面微细结构的调控及其催化性能的关联研究报道却很少，缺乏从表面原子层面上对活性位演变过程的认识。本项目拟通过液相合成过程中的动力学调控，制备表面微细结构（台阶位、扭结位、角等缺陷位）可控的Ni纳米晶，并负载到Al2O3上作为模型催化剂，结合先进表征技术、实验手段与理论计算模拟，以工业上常用的CO甲烷化为探针反应，探明Ni纳米晶表面活性位类型及活性差异，建立表面微观结构和催化性能之间的关联；并从原子层面上解析硫中毒、积碳及烧结过程中活性位结构的演变机制。项目成功实施将为揭示催化活性位、理解反应机理以及合理设计高效Ni基催化剂提供科学判据和理论指导。

Ni基催化剂广泛应用于化工、环境等领域的催化反应中，然而其存在低温活性差、易烧结、积碳等问题，一直是工业界普遍关注的焦点，也是科学研究的热点。为了解决上述问题，现有研究大多从宏观上来开展，通过改变催化剂配方或制备方法提高其催化性能，然而从微观上对Ni纳米颗粒表面微细结构的调控及其催化性能的关联研究报道却很少，缺乏从表面原子层面上对活性位演变过程的认识。本项目通过液相合成过程中的动力学调控，制备了尺寸均一的、具有面心立方的Ni正二十面体纳米晶（fcc-IC）和具有亚稳态六方密排的Ni六棱柱纳米晶（hcp-HP），fcc-IC Ni为暴露（111）晶面的十重孪晶结构，hcp-HP Ni为暴露（001）、（100）晶面的单晶结构。通过动态监测和一系列结构精细表征，发现hcp-HP Ni的成核与生长过程中，经历了形貌和晶相的双重演变，建立了过渡金属Ni基纳米晶表面微细结构的可控合成方法，明确了Ni基纳米晶表面微细结构调控过程的影响因素，理解了表面缺陷位形成的化学原理和动力学因素，揭示了Ni基纳米晶表面微细结构的调控机制。在CO甲烷化反应中，hcp-HP Ni表现出更好的低温活性和高温稳定性，通过原位监测及DFT计算，发现主要与hcp-HP Ni在反应气氛中的再分散特性以及CO在其表面的较强吸附与活化有关；另外，再分散后的Ni与基底有较强的相互作用，抑制了Ni颗粒的迁移团聚；同时较小的颗粒表面缺陷台阶位增加，提高了其表面碳物种的加氢活性，进而增强了抗积碳性能，解析了Ni纳米晶表面微细结构与其催化性能的内在联系。基于前期的研究理论指导，我们通过调变Ni纳米晶的表面微细结构，制备了一系列低温下具有高活性及高温稳定的CO/CO2甲烷化催化剂，为高效Ni基催化剂的设计合成提供实验基础和理论指导。