贵金属Pt促进Co基费托合成催化剂的原子尺度结构分析

选取化学惰性的β-SiC为载体, 通过共浸渍法制备了Co-Pt/SiC催化剂； 利用球差校正的电子显微镜(AC-STEM), 结合氢气程序升温还原(H₂-TPR)、 CO化学吸附以及准原位X射线吸收光谱(XAS)等手段, 研究了Co-Pt/SiC催化剂中贵金属Pt对于钴基费托反应的促进作用. 结果表明, Pt助剂从提高分散度和还原度两个方面增加了Co⁰活性相的数量, 从而提升了催化剂的费托反应活性. 通过AC-STEM表征了Pt在催化剂上的微观结构状态, 发现Pt助剂主要以单原子或团簇的形式分散在金属Co上. 这种分散形式的Pt对钴基催化剂的促进作用可能遵循氢气解离和氢溢流机理: 分布在Co上的Pt显著提高了催化剂解离氢气的能力, 这有利于促进钴物种的还原， 提高还原度, 同时也有利于促进费托反应过程中H₂的活化以及CO的氢助解离, 提高了催化剂的反应活性, 以及饱和烷烃的选择性.

Atomic Scale Investigation of Pt Atoms/clusters Promoted Co-catalyzed Fischer-Tropsch Synthesis

By utilizing scanning transmission electron microscopy with spherical aberration（AC-STEM）， combining with H₂-TPR， CO-chemisorption and quasi in situ XAS， we investigated the promotion effect of the noble metal， platinum in cobalt-based Fischer-Tropsch catalysts， and the effect of metal-support interaction was excluded by the use of the chemical inert support， β-SiC. It was concluded that the Pt promoter improved both the dispersion and reduction of cobalt nanoparticles， which increase the amount of Co⁰ active sites， and therefore facilitate the catalytic performance of Fischer-Tropsch synthesis. With the aid of AC-STEM， it was observed that Pt was in atomic dispersion in the form of single atoms and clusters. According to this structure， we speculated that the promotion effect of Pt followed the H₂ dissociation and spillover mechanism. The Pt dispersed on cobalt nanoparticles stimulated the H₂ dissociation on the catalyst to a great extent. On one hand， this favored the reduction of cobalt species， on the other hand， it facilitated the H₂ activation and hydrogen-associated CO dissociation during Fischer-Tropsch synthesis， and thus enhanced the activity of the catalyst and improved the selectivity of saturated hydrocarbons.