Synthesis And Application Of Iron-Based Nanocatalysts For Direct Coal Liquefaction

The catalyst plays an important role in the process of direct coal liquefaction(DCL). In recent years, Fe-based catalysts have received considerable attention as lowcost and high catalytic activity. It is well known that the particle size and dispersionperformance of the catalysts in DCL largely influences their catalytic activity.Consequently, small-sized and highly dispersive Fe-based catalysts have receivedextensive research in DCL in the past few decades.In this paper, oleic acid-coated (oleylamine-coated) Fe₃O₄nanocatalysts weresynthesized by some different methods. The obtained samples were characterized byX-ray diffraction (XRD), transmission electron microscope (TEM), and Fouriertransform infrared spectra (FT-IR). The catalytic activity of the synthesized Fe₃O₄nanocatalysts was studied for the direct liquefaction of three kinds of coals fromXinjiang, China, and compared with the commercial pyrite, Fe₃O₄,Fe₃O₄nanopowders. The results can be summarized as follows:(1). Fe₃O₄nanocrystals have been synthesized by a pyrolyzation of theiron-oleate complex in high boiling solvent. The synthesized nanocrystals cappedwith oleic acid ligands are spherical shapes with around15nm in diameter. Theresults of the direct liquefaction of Jiangjunmiao coal show that the synthesized Fe₃O₄nanocrystals are highly effective catalysts. With1.5wt%Fe of the nanocatalystsbased on dry and ash-free (daf) coal, the conversion, oil yield, and liquefaction degreereached97.2,86.5and92.0%, respectively. Under the same reaction conditions butwith3.0wt%Fe (based on daf coal) of commercial Fe₃O₄powders, the conversion,oil yield and liquefaction degree are90.0,63.5and85.5%, respectively. It can be seenthat the conversion, oil yield and liquefaction degree given by synthesized Fe₃O₄nanocrystals are7.2,23.0and6.5%higher than commercial Fe₃O₄powder's.(2). An ultra-large-scale of875g Fe₃O₄nanoparticles was synthesized in a singlereaction via a facile solution-based dehydration process. The results of characterization showed that5nm-sized nanoparticles are magnetite capped witholeic acid ligands. The direct liquefaction of Heishan coal indicated that thesynthesized samples exhibited higher catalytic activity compared with commercialpyrite and Fe₃O₄powders. The conversion, oil yield and liquefaction degree with1.4wt%Fe (based on daf coal) of the pyrite are72.6,44.5and59.2%, respectively. Atsimilar liquefaction conditions but with nanometer sized commercial Fe₃O₄catalysts,there are an increase in conversion from72.6%to84.3%, an increase in oil yield from44.5%to51.2%and an increase in liquefaction degree from59.2%to66.2%,respectively. What's more, the conversion, oil yield and liquefaction degree withsynthesized Fe₃O₄nanoparticles, which reached89.6,65.1and77.3%respectively, is5.3,13.9and11.1%higher than that of the commercial Fe₃O₄catalysts, respectively.(3). Hollow Fe₃O₄nanoparticles have been synthesized in H-donor solvent ofDCL.10nm-sized hollow nanoparticles are coated by oleylamine ligands. The resultsof the direct liquefaction of Tiechanggou coal show that the synthesized hollownanocatalysts exhibited higher catalytic activity compared with commercial Fe2O3powders. With the addition3.0wt%Fe (based on daf coal) of the synthesized samplesin the DCL, the conversion, oil yield and liquefaction degree were90.6,73.8, and90.6%, respectively, which were higher than that of commercial Fe₃O₄powders',84.0,58.5and78.5%.In this thesis, we report for the first time the use of oleic acid-coated(oleylamine-coated) Fe₃O₄nanocatalysts in DCL. The synthesized oil-soluble Fe₃O₄samples exhibited excellent catalytic activity which might be their small size and highdispersion in the DCL process. A facile solution-based dehydration process and adirect synthesis strategy are very simple, cheap and can be easily scaled up.Consequently, the synthesized oleic acid-coated (oleylamine-coated) iron-basednanocatalysts are promising catalytic materials for DCL.