Oxidação seletiva de cicloexano catalisada por zeolita Y contendo terras raras

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

Catalysts of the type LnY (Ln = Ce, Me, Nd, Sm and Yb) were synthesized starting from the respective rare earth chlorides and of zeolites Y (Si: AI = 2,6 , 12,5, 28, 60 and 100) by means of solid state exchange (T = 800 K, p = 13 kPa and t = 6 h). Such catalysts were characterized by X-ray difraction, infrared espectroscopy, AI and Si nuclear magnetic resonance and X-ray fluorescence; this methods revealed that the exchange extensions were of 30 and 50% for zeolites with Si: AI = 2,6 and 12,5, respectively and of 40% for the other zeolites. The structures were maintained intact during the synthesis procedure. The catalysts were used in cyclohexane oxidation in order to obtain cyclohexanol and cycloexanone, using tert-butylhydroperoxide, tBHP; as oxidant (T = 343 K, t = 24:00) and acetone, acetonitrile, pyridine, dichlorometane and 1,2-dichloroetane as solvents. The catalysts showed activity for the oxidation. The efficiency depends of the metal introduced into the zeólita (Ce >Yb >Nd >Me >Sm) and of Si: AI ratio of the zeolite (12,5 >2,6 >28 >60 >100), with conversions of about 8% and a good turnover number of 403 for the CeY-12,5 catalyst. Although the relative high conversions (approximately the double of the values reached in the industrial process) the selectivity is limited, as carboxilic acids and n-hexanal are formed, besides the products of interest. Better selectivity is obtained with the use of solvents with basic character (pyridine), suggesting the participation of acid sites in the process.

ASSUNTO(S)

catalise peneiras moleculares hidrocarbonetos

ACESSO AO ARTIGO

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