Otimização de síntese de Si-MCM-41 a partir da sílica de casca de arroz para a produção de catalisadores aplicados à reforma a seco do biogás

Abstract

The present work aimed to optimize the reactional variables involved in the synthesis of the Si-MCM-41 catalytic supports using tetraethyl orthosilicate (TEOS) and silica extracted from rice husk ash (CCA) as sources of silica. The Si-MCM-41 supports were synthesized following the hydrothermal and ambient temperature methodologies and the variable silica/surfactant and cosolvent/solvent molar ratios, aging temperature and aging time were studied. The synthesized substrates were characterized by N2- physisorption, DRX, EDS, MEV and FTIR techniques. For the support denominated as CCA 3, the conditions of synthesis favored the formation of particles with same results for the analysis of the characterization of the ones obtained for the support called TEOS 3. MET analysis of the TEOS 3 and CCA 3 supports clearly revealed the morphological differences of these materials. The supports identified as TEOS 3, TEOS 4, CCA 2 and CCA 3 were selected and impregnated with 20% Ni to be applied in the dry reforming reaction of methane. The catalysts were characterized by N2- physisorption, DRX, EDS, MEV and FTIR techniques. The catalysts 20Ni/Si-MCM- 41_TEOS 4 and 20Ni/Si-MCM-41_CCA 2 were shown to be more stable within 24 h of reaction. The 20Ni/TEOS 3 catalyst presented better results in terms of conversions and yield. The results for 20Ni/Si-MCM-41_CCA 2 and 20Ni/Si-MCM-41_CCA 3 were very close. The TEOS catalysts had higher coke values whereas the CCA catalysts the coke formation was significantly lower. In this sense, it was possible to conclude that the silica from ash from rice hulls is capable of efficiently replacing TEOS in obtaining the Si-MCM-41 substrates and can be applied as a source of silica in obtaining Si-MCM-41 molecular sieves reducing the costs related to the commercial silica source.