Studies On The Performance Of Ordered Mesoporous Aluminosilicate Supported Cobalt And Ruthenium Fischer-tropsch Synthesis Catalysts

Ordered mesoporous aluminosilicate molecular sieves, which have acidic sites ofmicroporous zeolite and high specific surface area as well as uniform pore diameter ofordered mesoporous material, have been widely used. In this paper, ordered mesoporousaluminosilicate molecular sieves were used as supports to prepare bifunctional catalysts forFischer-Tropsch synthesis （FTS）. The cobalt and ruthenium catalysts were prepared byeither a “double-solvent method” or “incipient wetness impregnation”. X-ray diffraction（XRD）, N₂adsorption-desorption, Transmission electron microscopy （TEM）,Temperature programmed reduction （TPR）, X-ray photoelectron spectroscopy（XPS）,H2-temperature programmed desorption （H₂-TPD）and oxygen titration were used tocharacterize the supports and catalysts. The performance of the bifunctional catalysts forFTS was investigated in a fixed bed reactor.1. The natural mesoporous aluminosilicate halloysite nanotubes（HNT） were used as asupport to prepare10%cobalt catalyst. The catalytic performance of two cobalt catalysts,prepared by the double-solvent method （10Co/HNT-ds） and incipient wetnessimpregnation method （10Co/HNT-im）, have been studied for FTS. The10Co/HNT-dscatalyst exhibited a higher activity（12.2%） and C5+selectivity （78.6%） and lower CH4selectivity （7.7%）than10Co/HNT-im.2. Al-SBA-15molecular sieves with low aluminum content （Al/Si<0.1） was used as asupports to prepared4%ruthenium catalysts. The effects of the aluminum content and siteson FTS were investigated in the fixed bed reactor at230℃,4S L h^-1g^-1（H₂/CO=2）. Theresults showed that the ordered mesoporous Al-SBA-15materials prepared by the directsynthesis method（Al（x）-D） have higher content of tetrahedral-coordinate frameworkaluminum （Altetra） of Al-SBA-15than that of Al-SBA-15prepared by the post-syntheticgrafting method（Al（x）-P）. With increasing Altetracontent, the catalysts’ activity decreased and the selectivity of olefin and lower hydrocarbon increased in FTS.3. Al-SBA-15materials with higher aluminum content Al/Si （0.2≤Al/Si≤1.0） havebeen synthesized in strongly acidic media using “pH-adjusting” method. Al-SBA-15withAl/Si=1.0(molecular sieves （Al（1.0）） showed highly ordered2D-hexagonal （p6mm）mesostructures with large surface areas and uniform mesopore size distribution. FT-IR ofpyridine adsorption confirmed the very low Br nsted acidity of Al-SBA-15. The4%Rucatalysts prepared by the incipient wetness impregnation methods were tested for FTS atthe higher temperature （250℃）. The results showed the activity decreased and olefinincreased with increasing Al content; the catalysts4Ru（1.0）（Al/Si=1.0）exhibited thelower hydrocarbon selectivity （Cn≤35） in FTS.4. Mesoporous aluminosilicates （SZM） with ordered hexagonal struture （p6mm） havebeen prepared by assembly of ZSM-5precursors with a triblock copolymer in a stronglyacidic condition. The material has a highly ordered2D-hexagonal （p6mm） mesostructureswith high surface areas (724.4m2g^-1) and pore volume (1.37cm3g^-1). The20%Co catalystsupported on SZM molecular sieves （20Co/SZM-1） prepared using the incipient wetnessimpregnation method and tested for FTS in fixed bed reactor at220.℃, showed that thecatalyst with a small amount of ZSM-5precursors has the highest activity （64.7%）andC₅+selectivity（83.6%）and the lowest CH4selectivity （8.4%） among the three catalysts.With increased ZSM-5precursor content, the catalysts （20Co/SZM-2） exhibited loweractivity and higher iso-paraffin selectivity.5. Three ordered mesopores aluminosilicate molecular sieves with the same ZSM-5precursor content but with different morphologies were synthesized in the strong acidcondition to obtain: SZM-1molecular sieves with ordered hexagonal structure （p6mm）,MZM-2molecular sieves with three-dimensional cage foam structure and MZM-1with thetwo mixed structures. The20%Co catalysts supported on these mesopore aluminosilicatemolecular sieves were prepared by the incipient wetness impregnation methods and thecharacteristics and their performances for FTS were investigated in a fixed bed reactor at220℃. It was found that MZM-2molecular sieves with3D cage structure have largeraverage pore diameter （11.34nm） and higher volume (1.99cm³g^-1) than SZM-1with2Dstructure. The corresponding catalyst （20Co/MZM-2） with3D cage structure exhibited lower activity and higher gasoline product and iso-parraffin selectivity than20Co/SZM-1catalyst with the2D structure. These results provide guidance for the design of betterbifunctional catalysts for FTS in the future.