Ru添加对Co/SiO2费托合成催化剂性能的影响

用初湿含浸法制备了不同Ru添加量的Co/SiO₂模型催化剂,然后进行N₂物理吸附、XRD、H₂-TPD、DRIFTS等表征和微分固定床费托(F-T)反应评价。F-T反应结果表明,催化剂中添加Ru后,CO转化率显著提高,TOF值增大,CO₂和CH₄选择性降低,烯/烷比(O/P)降低。FT-IR表征说明,催化剂添加Ru后Co-O键的强度减弱,相对应的H₂-TPR也表明,催化剂的还原度得到显著提高。还原后的催化剂XRD结果进一步证实,加入Ru后,催化剂无钴氧化物被检出,并且当Ru添加量为0.5%(质量分数)时催化剂中金属钴主要以六方密堆(hcp)形式存在。CO-DRIFTS结果显示,Ru的加入使CO的吸收峰发生红移,即Ru促进了CO的解离。H₂-TPD结果则表明,随着Ru添加量的增加,催化剂表面CO_ads/Co_s和CO^*/Co_s增大,这是CH₄选择性降低的主要原因。

Effect of ruthenium addition on the performance of Co/SiO2 catalyst for Fischer-Tropsch synthesis

Three Co/SiO₂ catalysts doped with different amounts of Ru were prepared by incipient wetness impregnation. These catalysts were characterized by N₂ physisorption, XRD, H₂-TPD, DRIFTS, etc.; their catalytic performance in Fischer-Tropsch (F-T) synthesis was investigated in a micro fixed-bed reactor. The F-T reaction results showed that the Co/SiO₂ catalysts doped with Ru exhibit higher CO conversion, higher turnover frequency (TOF), lower selectivity to CO₂ and CH₄, as well as lower ratio of olefin to paraffin, in comparison with undoped Co/SiO₂. FT-IR spectra indicated that the Co-O bond in the as-prepared catalyst is weakened by the addition of Ru, which facilitates the reduction of the Co/SiO₂ catalysts; such results are also supported by the H₂-TPR profiles and XRD patterns of the reduced catalysts. The main cobalt phase in the reduced catalyst with 0.5% (by weight) of Ru is in a hexagonal close packing (hcp) structure. CO-DRIFTS results revealed that the peak of linearly adsorbed CO is red-shifted by the addition of Ru, suggesting an improvement on the dissociation of adsorbed CO. CO-TPD results showed that the ratio of CO_ads/Co_s and CO^*/Co_s on catalysts surface is increased by the addition of Ru, which may contribute to the decrease of the selectivity to CH₄ in F-T synthesis.