Synthesis of SBA-15 with different pore sizes and the utilization as supports of high loading of cobalt catalysts

Several types of SBA-15 with pore diameters of 3.6-12 nm have been synthesi zed under different reaction conditions, followed by air calcination, and u tilized as supports for loading 10-20 mass% Co catalysts. Post-synthesis he at treatment after reaction at 308 K is more effective for increasing the p ore diameter and volume of SBA-15 than the addition of trimethylbenzene bef ore reaction. The combination of the two results in the formation of SBA-15 with large pore diameter but broad size distribution and less organized st ructures. When an acetone, ethanol, or water solution of Co(NO3)(2) is used as a precursor for impregnation with SBA-15 with pore diameter of 3.6 nm, the average crystalline size of Co3O4 observed at 10 mass% Co exceeds the p ore diameter irrespective of the kind of the solvent. On the other hand, th e use of an ethanol solution of Co(CH3COO)(2) or an acetone solution of (CH 3COCHCOCH3)(2)CO provides no X-ray diffraction peaks of Co3O4 even at loadi ng as high as 20 mass% Co, and catalyst addition considerably decreases the pore volume of SBA-15 support regardless Of the pore diameter. These obser vations strongly suggest that Co catalysts exist as nanosized clusters insi de the mesopores. The SAXS measurements show that the hexagonal mesoscopic organization of the SBA-15 support with pore diameter of 5.5 nm is almost r etained even after addition of 20 mass% Co. The 20 mass% Co/SBA catalysts a re also tested preliminarily in Fischer-Tropsch synthesis under 503-523 K a nd 2.0 MPa. (C) 2001 Elsevier Science B.V. All rights reserved.