Hidrogenação seletiva do adipato de dimetila a 1,6-hexanodiol em presença de catalisadores suportados de Ru e Sn

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The hydrogenation of dimethyl adipate was studied focusing on the selectivity towards 1,6-hexanediol over supported RuSn catalysts. The main variables investigated were: - support; - calcination temperature; - Sn/Ru atomic ratio; - preparation method and reduction temperature. The selectivity to diol revealed to be associated with the surface Sn oxidic species. The Sn/Ru atomic ratio of 2 on RuSn/Al2O3 impregnated catalyst calcined at 400 °C was found to provide the highest diol selectivity (49%). However, it was seen that the rise in calcination temperature to 600 °C and the use of sol gel methodology led to thoroughly different systems as regarding diol production. Such difference is attributed to a Sn oxidic species location effect as the Mossbauer spectroscopy results showed that high amounts of Snn+ (Sn4+ and Sn2+) are formed in all samples whereas XPS analyses revealed that their surface Sn concentration were quite distinct. The increase in the calcination temperature promotes the migration of Snn+ phases to the alumina structure and, as for sol gel catalyst, a lower surface Snn+ concentration is a natural consequence of the preparation route. TiO2-supported catalysts, reduced at 250 °C, presented a different optimal Sn/Ru atomic ratio (Sn/Ru = 1), which could provide a higher concentration of Snn+ as showed by Mossbauer spectroscopy. Increasing the reduction temperature to 400 °C, the products distribution is strongly affected. A new Sn/Ru atomic ratio of 2 is thus found to be the most suitable to the reaction, suggesting a synergistic effect between Sn and TiOx moieties. The main role in the C=O activation is attributed to Snn+, however the existence of TiOx species seems to be crucial to deactivate the unselective sites responsible for undesired side reactions. The selectivity to diol of 70% achieved over RuSn/TiO2 (Sn/Ru = 2) is the highest reported in the literature up to now as concerning the hydrogenation of dicarboxylic acid derived esters, especially taking into account the low hydrogen pressure applied (P = 50 atm) and the low reactivity of such chemicals.

ASSUNTO(S)

mossbauer alumina espectroscopia de compostos carbonilicos quimica fina hidrogenação

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