The promotional effects of ZrO2 modification on the activity and selectivity of Co/SiC catalysts for Fischer-Tropsch synthesis
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摘要: 本研究采用 ZrO2 对 SiC 表面进行改性，制得系列 Co-ZrO2/SiC 催化剂，借助N2物理吸附、XRD、H2-TPR、XPS等表征手段对催化剂物化性质进行结构分析，并利用微型固定床反应器对催化剂的活性进行评价，研究 ZrO2 改性 SiC 载体对钴基费托合成催化剂的影响。研究结果表明，由于 ZrO2 体相存在氧空穴等不同的活性位，H2 在 Co 表面被活化后形成的部分 H* 溢流到 ZrO2 表面并储存到 ZrO2 表面，而 ZrO2 与 Co 之间存在相对较强的相互作用，使得 Co 周围的 H* 浓度增加，进而 Co/SiC 催化剂的还原度显著增加。同时， ZrO2 与 SiC 表面的无定形相发生相互作用形成 Zr-O-Si 键。由于 Si (1.90)的电负性高于 Zr (1.33)，部分电子可以通过 Zr-O-Si 结构从 Zr 转向 Si，形成富电子的 SiOxCy 相和 SiO2 相。从而降低了 SiC 表面无定形相的对 Co 物相吸电子能力，减弱了 Co 与 SiC 表面的无定形相的相互作用，进而提高了Co 相的电子密度。采用 ZrO2 对 SiC 进行修饰后，同时提高了 Co/SiC 催化剂中 Co 物相的电子密度和还原度，使得催化剂对长链烃的选择性显著提升。Abstract: Co/SiC catalysts have exhibited excellent performance in Fischer-Tropsch synthesis reaction.,However, few research focuses on investigating the effect of SiC supports surface properties of on catalyst performance. In this study, ZrO2 was utilized to modify the SiC surface,leading to the preparation of a series of Co-ZrO2/SiC catalysts. The physicochemical properties of the catalyst were comprehensively analyzed by using N2 adsorption, XRD, H2-TPR, XPS analyses. Catalytic performance was evaluated using a fixed bed reactor, shedding light on the effect of ZrO2 modified SiC support on cobalt-based Fischer-Tropsch synthesis catalysts. The results indicated that ZrO2 surface modification on SiC resulted in an enhanced reduction degree of Co/SiC catalysts. Additionally, ZrO2 exhibited strong interaction with the amorphous phase on the SiC surface, thereby weakening the interaction between Co and the amorphous phase., This led to an increase in the electron density of cobalt species, consequently improving the selectivity of Co/SiC catalysts towards long-chain hydrocarbons.
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Key words:
- cobalt-based catalyst /
- SiC /
- ZrO2 /
- Fischer-Tropsch synthesis
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Table 1 Physicochemical properties of the catalysts
Catalyst BET area/
(m2·g−1)Pore diameter/nm Total pore volume/(cm3·g−1) Crystallite size of Co3O4a/nm Reduction degreeb/% Ratio of measured Co to
actual Co contentbCo-SiC 31.1 21.4 0.166 24.6 50.2 0.96 Co -SiC-Zr -2 31.2 24.1 0.189 25.9 78.8 1.33 Co -SiC-Zr -5 29.2 21.6. 0.148 23.8 81.5 1.45 Co-SiC-Zr -10 33.6 23.2 0.195 25.9 86.9 1.51 a: Average diameter of particle size calculated from the XRD; b: Determined from the TPR. 
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Table 2 Catalytic performance of the catalysts
Catalyst Con./% $s_{{\mathrm{CH}}_4} $ $s_{{\mathrm{C}}_2-{\mathrm{C}}_4} $ $s_{{\mathrm{C}}_{5+}} $ Co-SiC 55.3 14.0 11.0 75.0 Co -SiC-Zr-2 47.8 12.0 11.0 77.0 Co -SiC-Zr -5 55.7 10.3 9.2 80.5 Co -SiC-Zr-10 55.4 10.0 9.1 80.9 Reaction conditions: 2.0MPa, 220 oC, H2/CO=2.
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