Ruthenium Nanoparticles Anchored on Nitrogen-Doped Carbon Nanocages for Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis (FTS) is an important heterogeneous catalytic process in post-petroleum era, which can convert syngas from natural gas, coals and biomass into high value-added chemicals such as low-carbon olefins and fuel oil. In general, the target products have low selectivity owing to the limitation of Anderson-Schulz-Flory distribution law. The selectivity of target products can be adjusted by controlling the composition and structure of catalysts, supports and promotors. Carbon materials have been used as the remarkable supports due to the merits of rich morphological structure, high specific surface area, easily-regulated surface properties by doping and modification, good stability and so forth. Herein, taking advantage of the high specific surface area and high N content of N-doped carbon nanocages (NCNC), Ru/NCNC catalysts is prepared by equal volume impregnation method. As compared, Ru/CNC catalyst is prepared using undoped carbon nanocages (CNC) as support. Ru nanoparticles with ca. 3.9 nm in size were homogeneously dispersed on NCNC. The Ru nanoparticles on NCNC have the smaller sizes and more narrow distribution than those on CNC owing to the anchoring effect of nitrogen dopants for the former. The Ru/NCNC catalyst showed excellent catalytic performance, including good catalytic activity, high selectivity of C5+ products (55.7%), low selectivity of CH4 (13.5%) and high stability (60 h, CO conversion maintained at the level of approximate to 33%), evidently surpassing Ru/CNC. Such excellent FTS performance of Ru/NCNC can be attributed to the following reasons. (i) N doping increases the number of catalytic centers and density of electronic states of metallic Ru, and subsequently improving the catalytic activity, inhibiting the hydrogenation of intermediate products, increasing the chain growth possibility, and finally producing more long-chain products (C5+). (ii) N doping enhances the surface alkalinity of nanocages and then is conducive to inhibiting the formation of CH4. (iii) The metal-support interaction is enhanced due to the participation of N, leading to significantly improved anti-sintering ability and catalytic stability. This finding provides a promising strategy for developing high-performance FTS catalysts via designing N-doped carbon supports.