Synthesis and Application of Metallosilicate Supports for Cobalt- Based Fischer-Tropsch Synthesis Catalysts

摘要

Metallosilicates (metal = Al, Ti, Zr, V and Ce) and silica supports were synthesized by a one-pot surfactant-free process for use in cobalt-based Fischer-Tropsch catalysts. The in-depth physical, chemical, and textural properties of all supports were determined by several characterization techniques. The introduction of metal precursors to the synthesis gel reduced the pore size of the support by 24-60%, but the use of Al, Ti, and Zr increased the surface area by 5-35%. Cobalt (15 wt %) was loaded on the supports; hydrogen chemisorption and X-ray diffraction revealed that the dispersion and cobalt crystallite sizes in all catalysts were comparable. X-ray photoelectron spectroscopy and temperature-programmed reduction techniques revealed a greater interaction between Co and metallosilicates, necessitating a higher reduction temperature for these catalysts. The Fischer-Tropsch activities of all the catalysts were determined under industrially relevant conditions (220 degrees C, 1.83 MPa and 2000 mL(syngas)/mL(catalyst)/h) after in situ reduction. The addition of metal oxides (Ti and Zr) to the supports enhanced the CO conversion by 6-10% but reduced the formation of waxes in the liquid product. The addition of zirconia to the support suppressed the formation of CO2 and CH4 while improving the olefin to paraffin ratio from 0.46 to 1.19 compared to silica-supported catalyst. The addition of titania improved the cobalt-time yield (11 x 10(-5) mol(CO)/g(Co)/s compared to 9.6 X 10-5 mol(CO)/g(Co)/s for silica). The Fischer-Tropsch activity was retained by titania and zirconia-based metallosilicate supports for over 100 h time-on-stream which could be due to the abatement of catalyst deactivation by mechanisms involving active metal agglomeration.