Síntese e caracterização de sistemas catalíticos compostos por sílicas porosas contendo Mn

Abstract

Solids, such as ordered M41S family, are often considered for supporting the transition metals. The M41S family has tubules and ducts, with mesoporous, which could play the role of sieves to select molecules according to the diameter of their pores. The reactants are confined in the pores and it also reduces the potential energy of the molecules, acting as active sites for reactions. Manganese is a metal related with catalysts employed in various chemical processes, such as oxidation reactions of alcohols and aldehydes, the oxidative coupling of methane and the oxidation of CO in automotive exhausts. In order to study the properties of Mn as catalyst in inert supports, samples with different manganese content were immobilized in mesoporous silica and synthesized by the sol-gel method. All samples were evaluated by XRD, SAXS, SEM, ATR-FTIRS and AAS. These samples were also analyzed by thermal methods, such as DTG, DSC, and H2-TPR (whose profiles allowed to calculation of AOS). The N2-adsorption results of the synthesized samples have shown that mesoporous solids with higher contents of Mn have smaller specific surface areas and larger pore diameters. Moreover, the material was indexed in the hexagonal system, indicating the formation of MCM-41 in all samples, regardless of the amount of inoculated Mn. However, the proportion of amorphous silica in the samples increase with the increment of Mn content, although no relationship was observed between the relative amount of Mn/SiO2 and water loss or samples dehydroxylation.