Efeito da adição de cromo em hidrotalcita MgAl sobre a distribuição de produtos na conversão catalitica de etanol

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

Hydrotalcite-like compounds Mgo,666(Al, Cr )0,334( OH)Z(CO3 )0,167. yHzO,were synthesized, calcined, characterized, and tested in the catalytic vapour phase conversion of ethanol. The synthesis was performed by co-precipitation and by replacing aluminium by chromium in the proportion of O, 10, 20, 50 and 100%.. AlI ofthe synthesized materiaIs showed diffiatograms characteristic of hydrotalcites. The superficial areas increased with the amount of chromium ITom 79 to 250 mZjg. The calcination of hydrotalcites with O to 50 % of chromium at 500 and 650°C yielded solid solutions with the magnesium oxide X-ray diITaction pattem. The material with 100% of chromium yielded magnesium chromate when calcined at 500°C, and magnesium chromite when calcined at 650°C. BET surface areas of the calcined materiaIs ranged ITom 90 to 382 mZjg. The materials contained no micropores. Catalytic tests were performance in a fixed bed reactor at atmospheric pressure and 350°C using a mixture of ethanolJNz in the molar proportion of 1:2. The identified compounds were n-butanol, ethyl ether, acetaldehyde, ethylene, butyraldehyde, ethyl acetate and crotonaldehyde. The replacement of aluminium by chromium, inhibed the formation of ethyl ether and ethylene, both ethanol dehydration products, and favoured the formation of acetaldehyde by dehydrogenation. The substitution of 100.10 to 20% of aluminium by chromium into the MgAl-hydrotalcite favoured the global yield of n-butanol, wich was maximum for the material with 10% of chromium calcined at 650°C. The total conversion of ethanol increased with the substitution of 10% of aluminium by chromium into the MgAl-hydrotalcite and then decreased continuosly with increasing percentages of chromium. The ethanol conversions for materiaIs calcined at 650°C were larger than those for materiaIs calcined at 500°C

ASSUNTO(S)

catalisadores alcool desidrogenação compostos de cromo

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