Synthesis of sol-gel aluminas : correlation of the textural, structural, morphological and chemical properties of aluminas with reactivity in the catalytic epoxidation of olefins / Sintese de aluminas sol-gel : correlação das propriedades texturais, estruturais, morfologicas e quimicas da alumina com a reatividade na epoxidação catalitica de olefinas

AUTOR(ES)

Roberto Rinaldi Sobrinho

DATA DE PUBLICAÇÃO

2006

RESUMO

Epoxidation is a pivotal transformation for organic synthesis of fine and bulk chemicals. The aim of this research is the replacement of stoichiometric oxidative processes or non-environmental friendly catalytic processes by economically sustainable catalytic reactions of oxygen transfer using non-toxic catalysts and oxidants. The alumina/aqueous 70 wt. % H2O2 catalytic system shows the intrinsic advantages of heterogeneous catalysts as well as low cost, low toxicity, high activity and high selectivity for epoxide synthesis. The scope of this work was to understand the chemical processes involved in this catalytic system and in its deactivation. The research strategy was to synthesize ultra-pure aluminas by the sol-gel method with well-defined structural, textural and chemical properties and characterize them by XRD, SEM, TGA, AI MAS NMR, TDP-NH3, elemental analysis, nitrogen adsorption-desorption at 77 K and also use H and C MAS NMR in the deactivation studies. The correlation between these physico-chemical properties with the catalytic epoxidation of cis-cyclooctene allowed the assignment of the active sites for epoxidation (type Ia AI-OH sites) and for H2O2 decomposition (type IIa, IIb and III AI-OH sites). The role of surface hydrophilicity was also explained, showing that the approach of the hydrophobic olefin to the hydrophilic alumina surface is the kinetically limiting step. The chemical and physical changes related to the deactivation of alumina in recycling experiments showed that water has a dual role: it prolongs the catalyst lifetime, however, it also causes deleterious changes to the structure of the catalyst.

ASSUNTO(S)

epoxidação sol-gel epoxidation alumina alumina ahydrogen peroxide sol-gel agua oxigenada

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