Effect Of Glow Discharge Plasma Treatment On The Support And Catalyst Precusors,their Catalytic Performance In Fischer-Tropsch Synthesis And The Mechanism Studied By DFT

In this work,Si O2 was used as the carrier and Pt as promoter,to prepare cobalt-based catalyst by incipient wetness impregnation(IWI).Glow discharge plasma technology was introduced to deal with the support and as an alternative to traditional calcination in the process of catalyst preparation,to decompose the catalyst precursor(cobalt nitrate).This research mainly focused on the influence of glow discharge plasma treatment on the catalyst structure and catalytic performance from the aspects of support properties,cobalt dispersion and reducibility;meanwhile,the properties of catalyst surface were also studied by the way of theoretical calculation.The detailed works are as follows:(1)The impact of glow discharge plasma treatment on morphology and catalytic performance of cobalt-based catalyst by different precursor treatment temperature was investigated.Glow discharge plasma was applied to treat Co Pt/Si O2 catalysts drying /calcining at temperatures of 100 ℃,210 and ℃ 400 ℃,and the structure properties and catalytic performance of the catalysts were characterized and evaluated.Characterization results showed that the cobalt dispersion of plasma treated catalysts were higher than the corresponding calcined samples.FTS reaction results showed that the catalytic activity of plasma treated catalysts were significantly higher than that of calcined samples,among all the investigated samples,the plasma treated catalyst with precursor dried at 100 ℃ presented the highest FTS activity.With the increase of thermal treating temperature,the promotion effect by plasma treatment was decreased.Therefore,we can draw the conclusion that the plasma treatment was mianly affect the decomposition process of cobalt precursor,the optimal thermal treating temperature of catalyst precursor was 100 ℃.(2)The silica support was decorated by glow discharge plasma,and the effect of glow discharge plasma treatment on morphology and catalytic performance of cobalt-based catalyst was studied.The Si O2 before and after plasma decoration were used as supports,and the cobalt-based catalyst precursors were prepared by IWI method.The dried catalyst precursors were calcined or plasma treated in air atmosphere,to obtain supported Co Pt/Si O2 catalysts.The results indicated that high-energy electrons in plasma field bombarded the support and surface atoms of cobalt species,which influenced not only the decomposition process of cobalt precursor,improved the cobalt dispersion;but also modified the surface properties of support,and then affected the structure and performance of the catalyst.The catalyst with both support plasma decoration and precursor plasma decomposition showed the highest FTS activity.(3)Density functional theory calculations were performed to study the mechanisms of the CO activation and dissociation on the single-atom vacancy of cobalt surfaces,which models the surface defect by the plasma treatement.Both the direct and H-assisted dissociations were investigated on two representative cobalt surfaces(fcc-Co(111)and hcp-Co(101)).Results showed that the single-Co vacancies greatly favor the CO dissociation with lower barriers than the prefect surfaces.Direct and H-assisted dissociations were favored for the vacant hcp-Co(101)and fcc-Co(111)surfaces,respectively.Different from those on the prefect surfaces,H-assisted dissociation was more likely to occur via the COH-mediated pathway,rather than the commonly known HCO-mediated one.