The optimal calcination temperature was 600 degrees C and the highest activities were obtained at Al:K molar ratios of 3:1, 1:1 and 1:1 for Al2O3/KNO3, Al(NO3)(3)/KNO3 and Al2O3/KOH precursor combinations, respectively. The active compound in the catalyst prepared by Al(NO3)(3)/KNO3 was KNO3 exclusively. However, the catalytic activity of the catalysts prepared by Al2O3/KOH was affected by the formation of K2Al2O4 and K2CO3 compounds. The catalysts prepared by all precursor combinations behaved a comparable thermal stability. High temperature aging of the catalysts would result in the loss of surface area and/or active compounds, and hence the deterioration of their catalytic activities. (c) 2007 Elsevier B.V. All rights reserved.