The temperature-programmed desorption (TPD) of CO2 has been performed to elucidate the strength and the number of base sites on mesoporous alumina (mesoAl(2)O(3)). It was demonstrated that the surface of mesoAl(2)O(3) adsorbs a much smaller amount Of CO2 than those of MgO and conventional gamma-Al2O3 with irregular pores, but that there exist a small number of strong base sites on mesoAl(2)O(3) that adsorb CO2 very strongly. The CO2-TPD results clearly account for the high activity of mesoAl(2)O(3), the low activity of gamma-Al2O3, and no activity of MgO for a typical base-catalyzed reaction of the Knoevenagel reaction in supercritical CO2. (c) 2006 Elsevier B.V. All rights reserved.