Acetonylacetone conversion at 250 and 350 degrees C was carried out over various transition aluminas (eta- to theta-Al2O3) in order to estimate simultaneously their acid-base properties. The formation of 2,5-dimethylfuran (DMF) was associated to the presence of acid site, and the formation of 2-methyl-3-cyclopenten-1-one (MCP) associated to basic site. First, from carbon dioxide adsorption measurement, hydroxyl basic group was found to be the active site for MCP formation and 2,6-dimethylpyridine (DMP) adsorption measurement shows that Bronsted acid site is active site for DMF formation. Secondly, from catalytic results, we show that theta-Al2O3 possesses a basic/acid ratio (MCP/DMF = 16) higher than the other aluminas (MCP/DMF < 10), and from comparison with cyclopentanol/cyclohexanone mixture transformation (acid alcohol dehydration and acid-base hydrogen transfer between alcohol and ketone), we also show that acetonylacetone cyclization are a more difficult reaction. Finally, the combination of model reactions and CO2 and DMP adsorption allows us to propose a description of the nature and the strength of the various aluminas surface. (C) 2009 Elsevier B.V. All rights reserved.