In Situ Diffuse Reflectance FTIR Study of CO Adsorbed on a Cobalt Catalyst Supported by Silica with Different Pore Sizes
详细信息 查看全文
- 作者：Dechen Song ; Jinlin Li ; Qin Cai
- 刊名：Journal of Physical Chemistry C
- 出版年：2007
- 出版时间：December 27, 2007
- 年：2007
- 卷：111
- 期：51
- 页码：18970 - 18979
- 全文大小：252K
- 年卷期：v.111,no.51(December 27, 2007)
- ISSN：1932-7455
文摘
A series of Co/SiO2 catalysts with different pore sizes were prepared by the incipient wetness impregnationmethod. Catalytic and characterization results showed that the porosity of the support strongly influenced theadsorption properties and the Fischer-Tropsch (FT) catalytic performance. The large pore size could causethe Co/SiO2 to form a larger cobalt metal crystallite size. The FT activity and the C5+ selectivity increasedas the pore size of the Co/SiO2 catalyst decreased. The dependence of adsorption properties and catalyticperformance on pore size has been investigated by studying the adsorption of CO and syngas (H2/CO = 2)on Co/SiO2 using in situ diffuse reflectance FTIR (DRIFTS). The linear- and bridge-type CO adsorption wasobserved at room temperature on Co/SiO2. In the presence of preadsorbed hydrogen, CO adsorption wasenhanced remarkably, and more Co adsorption sites were observed. The intensities of both linear- and bridge-type CO adsorption changed significantly with increasing pore size. The peaks at around 1937 and 2035cm-1 have the same trend toward FT activity, leading to the speculation that CO has adsorbed on the hexagonalcobalt phase, while the peaks at around 1974 and 2054 cm-1 have the opposing trend toward FT activity,which could be due to CO adsorbed on cubic cobalt. The activity of CS-15 in FT synthesis was much lowerperhaps due to not only the larger crystallite size but also the higher fractions of cobalt cubic metal phase.When CO and H2 were coadsorbed on the cobalt catalyst, a new band appeared around 2030-2060 cm-1with increasing temperatures, which was assigned as a new species "hydrocarbonyl" (HCo(CO)), which wasalso observed during FT reaction. With increasing temperature, the hydrocarbonyl band shifted to lowerwavenumber, indicating that the C-O bond became weaker gradually. The activity of CO adsorbed on thecatalysts with different supports is in the order of CS-6 > CS-10 > CS-15, which is consistent with the orderof CO conversion for FT synthesis.