Sintese e caracterização de [Nb]-MCM-41 e NbxOy(OH)z-montmorilonita e aplicações em catalise redox e acida / Synthesis and characterization of [Nb]-MCM-41 and NbxOy(OH)z-montmorillonite and its applications in redox and acid catalysis

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

Nb-MCM-41 synthesis was optimized at room temperature varying the hydroxide, the silica and niobium sources and the order of addition of the niobium source. The materials, before and after the calcinations, were characterized by XRD and UV-Vis diffuse reflectance. The Nb-MCM-41 with best results was silylated and characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES) to quantify the niobium, thermogravimetric analysis (TGA) , adsorption-desorption of nitrogen, magic angle spinning nuclear magnetic resonance (RMN-MAS) of Si, elementary analysis of carbon, hydrogen and nitrogen (CHN) and infrared spectroscopy (FTIR). The calcined and the silylated Nb-MCM-41 were used in the epoxidation of ciclooctene with feributylhydroperoxide (TBHP) 69,4 % in ciclohexane obtaining after 48 h, 46,6 and 62,2 % of conversion and 77 and 94 % of selectivity, respectively. Using hydrogen peroxide 70 % in water it was obtained after 5 h, 8% of conversion and 80 % of selectivity for the calcinated sample and 13 % of conversion and 70 % of selectivity for the silylated. When using hydrogen peroxide all the peroxide was decomposed after 10 h, showing that niobium decompose easily hydrogen peroxide Montmorillonite K10 was ion-exchanged with polyhydroxyniobium characterized by XRD, TGA, adsorption-desorption of nitrogen and ICP. Then the material was calcined at 300, 500 e 900°C to obtain the Nb-pillared montmorillonite. These materials were characterized by XRD, and even when calcined at 900°C the microporosity is maintained, which is surprising since most of metal oxide pillared clays lose the microporosity at temperatures around 600°C. The montmorillonite K10 pure, niobium exchanged and Nb-pillared were used as acid catalysts in the oxirane ring-oppening reactions of the epoxidazed methyl oleate with methanol as nucleophile, to obtain the correspondent b-hydroxyether. The ion-exchanged clay was more active that the pure clay, proving than niobium incorporation improves Bronsted acidity. The calcined samples were less active the higher was the calcination temperature

ASSUNTO(S)

montmorillonite catalise mcm-41 catalysis niobio montmorilonita niobium mcm-41

ACESSO AO ARTIGO

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