Synthesis of mesoporous alumina with CO2 expanded carbonation and its catalytic oxidation of cyclohexanone

A CO2 expanded carbonation technique is proposed for direct synthesis of alumina powders that does not require structure directing substances or templates. Mesoporous amorphous flower-like alumina was synthesized at relatively low volume expansions (lower ethanol to water volume ratio), whereas mesoporous crystalline honey-comb-like alumina was synthesized at high volume expansions. The alumina powders exhibited high surface area and pore size with small crystallite sizes. The alumina structures were stable from 400 to 800 degrees C. Experimental tests showed that the alumina powders could catalytically convert cyclohexanone to epsilon-caprolactone efficiently. The use of the calcined catalysts (at 400 and 800 degrees C; flower-like alumina) at equal ethanol to water volume ratio avoids the usual and inevitable hydrolysis of epsilon-caprolactone to epsilon-hydroxyhexanoic acid. The catalyst was recyclable and stable for up to five reaction cycles. (C) 2014 Elsevier B.V. All rights reserved.