纳米金刚石改性钴基催化剂的费托合成性能研究

Study on catalytic performance of cobalt-based catalysts modified with nanodiamonds in Fischer-Tropsch synthesis

Co基催化剂在费托合成反应中具有优异的反应活性以及碳链增长能力,其催化性能与金属Co纳米颗粒的还原度和粒径紧密相关,通过添加助剂调控金属Co的还原度和分散度是提高其催化费托合成反应性能的重要手段。以具有化学惰性以及良好导热性的SiC为载体,加入少量具有丰富表面官能团的纳米金刚石(NDs)作为结构调节剂,有效提高了催化剂中Co物种的分散度和还原度,提升了其催化费托合成反应性能。N_(2)物理吸/脱附结果表明,NDs的加入对催化剂的比表面积、孔径等参数影响较小。CO化学吸附结果表明,适量NDs的加入促进了催化剂中活性金属Co的分散,增加了金属Co的表面积,为费托合成反应提供了更多的活性位点。透射电镜(TEM)结果表明,在Co/SiC(w(Co)=10%)中加入NDs后,催化剂中金属Co的粒径减小,且NDs在催化剂表面均匀分散。H_(2)程序升温还原(H_(2)-TPR)和CO预吸附的H_(2)程序升温表面反应(CO-H_(2)-TPSR)结果表明,NDs的加入降低了Co_(3)O_(4)还原为金属Co的还原温度,促进了Co_(3)O_(4)的还原以及CO的活化。调节剂修饰的Co/1.0NDs-SiC(w(Co)=10%,m(NDs):m(SiC)=1.0%)与Co/SiC催化剂相比,CO转化率从15.6%提升至29.0%,产物中C5+烃类选择性仍可保持在75%以上,且稳定运行70 h未见明显失活。以上结果可为研发纳米碳材料改性的高效费托合成反应的催化剂提供新的研究思路。

Cobalt-based catalysts exhibit excellent reactivity and carbon chain growth capability in the Fischer-Tropsch synthesis reaction,and their catalytic performance is closely related to the reduction degree and size of metal Co particles.Regulating the reduction degree and dispersion degree of metal Co by adding promoters is an important way to enhance their catalytic performance in Fischer-Tropsch synthesis reaction.By using SiC as a support with chemical inertness and good thermal conductivity,and adding a small amount of nanodiamonds(NDs)with rich surface functional groups as structural regulators,the dispersion degree and reduction degree of Co species in the catalyst were effectively improved,and its catalytic performance in Fischer-Tropsch synthesis reaction was enhanced.The results of N_(2) physical adsorption/desorption show that the addition of NDs has little effect on the parameters such as specific surface areas and pore sizes of the catalysts.The results of CO chemisorption show that the addition of an appropriate amount of NDs promotes the dispersion of active metal Co in the catalysts,increases the surface area of metal Co and provides more active sites for the Fischer-Tropsch synthesis reaction.The results of transmission electron microscopy(TEM)show that after the addition of NDs to Co/SiC(m(NDs):m(SiC)=1.0%),the particle sizes of metal Co in the catalysts are reduced,and NDs are uniformly dispersed on the catalyst surface.The results of H_(2)-temperature programmed reduction(H_(2)-TPR)and CO-H_(2)-temperature programmed surface reaction(CO-H_(2)-TPSR)show that the addition of NDs reduces the reduction temperature of Co_(3)O_(4) to metal Co and promotes the reduction of Co_(3)O_(4) and the activation of CO.Compared with the Co/SiC catalyst,the NDs-modified Co/1.0NDs-SiC(w(Co)=10%,m(NDs):m(SiC)=1.0%)catalyst exhibits an increase of CO conversion rate from 15.6%to 29.0%,and the selectivity of C5+hydrocarbon products still maintains at above 75%,and shows stable operation and no significant deactivation for 70 h.The above results can provide a new research idea for the development of efficient catalysts modified with nanocarbon materials in Fischer-Tropsch synthesis reaction.