Síntese de nanopartículas de cobalto encapsuladas em sílica mesoporosa aplicadas à reação de Fischer-Tropsch

Abstract

Core-shell nanoparticles consisting of cobalt oxide encapsulated in mesoporous silica (Co3O4@SiO2) with different porosities were synthesized, aiming to evaluate the influence of the textural properties of the shell on activity, selectivity and resistance to deactivation when applied to FT synthesis. The solvothermal method was used, with polyvinylpyrrolidone (PVP) as stabilizing agent, followed by the modified Stöber method, with tetraethylorthosilicate (TEOS) as silica precursor and cetyltrimethylammonium bromide (CTAB) as porogenic agent, in different CTAB/TEOS molar ratios: 0.03; 0.06; 0.075 and 0.09. The results demonstrate success in obtaining core-shell nanoparticles. All samples showed dispersed particles of uniform size, core with mean diameter in the range of 30 nm and mean total diameter in the range of 100 nm. N2 adsorption and desorption isotherms are characteristic of mesoporous materials. An increase in the specific area is observed, in the order of 300, 640, 739 and 771 m²/g, as well as a reduction in the pore diameter (9.2; 5.9; 5.9 and 3.5 nm) and a change in the pore volume (0.56; 1.02; 1.22 and 0.83 cm³/g) for CTAB/TEOS ratios: 0.03; 0.06; 0.075 and 0.09, respectively. Catalytic tests indicate a significant change in the distribution of products in the Fischer-Tropsch synthesis, with an increase of up to 17% in the C19-C24 fraction and a reduction of up to 24% in the C25-C29 fraction. The core-shell morphology offers high catalytic stability, avoiding active phase sintering, although the activity is lower in catalysts with smaller pore diameters, ndicating a possible diffusional limitation of high molecular weight products, such as paraffins, in narrower pores.