Alexandre B. Gaspar

Characterization of chromium species in catalysts for dehydrogenation and polymerization

Abstract Chromium catalysts, prepared with different chromium contents, supports and precursor compounds, were characterized by O2 and CO chemisorption, in order to quantify the Cr3+ and Cr2+ sites, active species to dehydrogenation and ethylene polymerization reactions. Both probe molecules, O2 and CO, showed to be selective to the chromium active species, Cr3+ and Cr2+, respectively, and a valid method to quantify these sites. Distinct chromium species, Cr6+, amorphous Cr3+, crystalline Cr3+ and Cr2+, were characterized by XRD, DRS, TPR, FT-IR and DRIFTS in the calcined and reduced catalysts. The distribution of chromium species, which depends on the content, precursor compound and support, was related to the catalytic activity in the dehydrogenation and polymerization reactions. The catalytic activity to cyclohexane dehydrogenation depends on the dispersion of amorphous Cr3+ species. The activity in the ethylene polymerization is related to the amount of CrA2+ and CrB2+ species. Both sites showed similar activities.

The effect of pressure on promoted Ru and Re-Co/Niobia catalysts in the Fischer-Tropsch synthesis

Abstract Co/Nb2O2, Co-Ru/Nb2O5 and Co-Re/Nb2O5 catalysts were prepared and characterized by TPR. The catalysts were investigated on CO hydrogenation under 0.4, 2 and 4Mpa. The total pressure has an important effect on the product distribution. The selectivity toward diesel and C5+ hydrocarbons achieves a maximum at reaction pressure of 2.0Mpa. The catalysts had good stability over 50h on stream at reaction conditions.