Desenvolvimento de catalisadores (Co/MCM-41) destinados à reação de Fischer-Tropsch.

Abstract

In this work, molecular sieve MCM-41 was prepared as well as the Co/MCM-41 catalyst, via humid impregnation with concentrations of 5%, 10%, 15% and 20% Co/MCM-41. The catalysts with 5% and 15% Co/MCM-41 were evaluated in the reaction of Fischer-Tropsch during a reaction as long as 92 h, in the temperatures leveis of 270 and 350 °C, pressure of 1 atm, and using a molar ratio H2/CO = 2. The attainment of the mesoporous molecular sieve, Si-MCM41, was confirmed by the x-ray diffractogram. It was verified that after the calcination ali the bromine (Br) was removed indicating that the calcination process removed ali surfactant in the mesoporous structure. DRX and EDX analyses indicated that cobalt was found in the form of Co302 in the Co/MCM41 catalysts. The diffraction standards showed that the impregnation and calcination processes caused changes in the structure only for catalyst with 10% Co/MCM-41. The ATD/TG curves showed that cobalt nitrate was totally decomposed on the MCM-41. The RTP profiles of the Co/MCM-41 catalysts showed the presence of distinct peaks that could be caused by the dispersion of cobalt, the size of particles, and the interaction between the MCM-41 and the species of cobalt oxide. From the images of MEV, it was possible to observe that the Co/MCM-41 catalysts were composed by clusters of small crystals. The images obtained from MET showed clearly the presence of metal cobalt particles in a well dispersed form for catalysts with 5%, 15% and 20% Co/MCM41, except for the catalyst with 10% Co/MCM41. The results obtained from the synthesis of Fischer-Tropsch for catalysts with 5% and 15% Co/MCM41 presented high selectivity for commercially important hydrocarbons (C2-C4). These catalysts presented diffusion limitations, which gave high selectivity for methane gas, whereas for hydrocarbons in the C5+ range the selectivity was low