Desenvolvimento dos catalisadores Co/SBA-15 e Ru/Co/SBA-15 a partir das fontes de sílica tetraetilortosilicato (TEOS) e cinzas da casca de arroz (CCA) destinados à reação de Fischer-Tropsch.

Abstract

The aim of this work was to prepare the mesoporous molecular sieve SBA-15 using conventional silica sources (TEOS) and alternative (Ash rice husk) and uses them as support for cobalt catalysts for the Fischer-Tropsch process. And investigate the introduction of ruthenium as a promoter. It was prepared SBA- 15 from a gel of molar composition : 1.0 silica source : 0.017 P123 : 5.7 HCl : 193 H2O. The catalysts were prepared by wet impregnation process using 0.1 M solution (Co(NO3)2.6H2O) (Vetec). Following ruthenium promoter was incorporated using 0.1 M aqueous solution of ruthenium chloride (RuCl3xH2O). The samples were characterized by XRD, EDX , TG/DTA, SEM, TEM, TPR and adsorption of N2. The Fischer-Tropsch reaction is conducted at 240 °C , pressure of 20 bar using a molar ratio H2/CO = 1, on a slurry reactor for a reaction time of 8 h. Obtaining the SBA -15 silica using conventional sources and alternative could be confirmed by X ray diffraction , with emphasis on the SBA -15 obtained with the alternative source of rice husk ash , a residue of agriculture abundant and cheap that is usually discarded. The XRD patterns of the catalysts in the angular range 0-8º showed that after impregnation and calcination of the metal changes did not occur in the hexagonal structure of mesoporous materials , observing the main peaks of the phase of SBA -15. The physical adsorption of N2 analysis of SBA -15 molecular sieves (CCA) and SBA -15 (TEOS) show with type IV isotherm profile and H1 hysteresis characteristics of mesoporous material. The thermal analysis of SBA -15 molecular sieves (TEOS) and SBA -15 (CCA) indicated the elimination of the template (Pluronic) in the calcination process. The specific surface areas of the catalysts decreases , and the pore volume changes due to partial blockage of the pores by cobalt and ruthenium promoter, but the structure of SBA -15 molecular sieve is not changed. TPR profiles of the catalysts of the series Co /SBA- 15 and Ru /Co /SBA -15 evidenced the presence of distinctive peaks that can be caused by the reduction of cobalt oxides. TEM showed cobalt species on spherical 20 nm in size, and after co- impregnation with ruthenium was a better dispersion of these cobalt species resulting in particles with average size smaller than 10 nm. The results obtained from the Fischer- Tropsch the catalysts showed high selectivity to hydrocarbons C5+ of high value, and it was found that co- impregnation of the ruthenium promoter in the Co catalyst /SBA -15 promoted the increase of selectivity to C5+ hydrocarbons and decreased the selectivity to methane, highlighting the performance of the catalyst 20 % Co/0.5 % Ru/SBA-15 prepared with the ashes of the rice husk .