Ni/K_2CO_3/MoS_2低碳醇催化剂的表面结构和电子效应

Surficial Structure and Charge Effects of Ni Promoted K_2CO_3/MoS_2 Catalysts for Higher Alcohols Synthesis

制备了不同含量Ni改性的K2CO3/MoS2(ADM)低碳醇催化剂,通过XRD、BET、XPS等表征技术考察了模型催化剂的表面结构和电子特征,结果表明在ADM催化剂中Ni助剂主要以Ni-Mo-S配位结构和独立的NiSx两种形式存在.在nNi/nMo<1/3时,Ni-Mo-S配位结构为主要存在形式,催化剂表面Ni含量低于体相.随着Ni含量的提高,Ni与MoS2配位逐渐饱和,NiSx独立相逐步形成并导致Ni的表面富集,同时Ni的富集导致ADM催化剂形成富含S和K的表面化学环境.作为供电子助剂,Ni-Mo-S结构对应于强的电子作用,而独立NiSx与MoS2之间的电子作用较弱.随Ni含量的增加Ni与MoS2之间的电子作用呈现由强变弱的规律,反映了Ni与MoS2配位饱和与独立NiSx相的形成过程.

The surficial characters and charge effects of the modified K2CO3/MoS2 catalysts with different Ni content were investigated by XRD, BET, XPS. The results suggested that two types of Ni-contained species were formed in Ni/ K2CO3/MoS2 catalysts, namely, pure phases of NiS, and Ni-Mo-S mixed phase. With lower Ni loading （nNi/nMo〈 1/3）, the main Ni species was Ni-Mo-S and Ni content on the surface was lower than that of the bulk. With the increasing of Ni content, the coordination between Ni and MoS2 became saturation and NiSx phases were formed gradually. The formation of NiSx phases resulted in the enrichment of Ni on the surface as well as S and K and a favorable chemical environment for the formation of alcohols but not hydrocarbons. As a donor promoter, the Ni-Mo-S structures corresponded to a strong electron transition between Ni and Mo, however, the electron effect between NiSx and MoS2 was weaker. The regularly decline of electron interaction between Ni and Mo with the increasing of Ni content indicated that the saturation of coordination betweenNi and MoS2 and the formation of NiSx phase.