Novel mesoporous silicoaluminophosphate molecular sieves with an MCM-41 type structure were synthesized and characterized using various techniques, including XRD, N-2 adsorption, DRIFT, TEM, and Al-27, Si-29, and P-31 MAS NMR. The surface acidity of the materials was determined by using pyridine and 2,6-dimethylpyridine as probe molecules. The catalytic activity of the mesoporous silicoaluminophosphates in the Beckmann rearrangement of cyclohexanone and cyclododecanone oximes was investigated and compared under gas- and liquid-phase (conventional vs microwave-assisted heating) conditions. The mesoporous silicoaluminophosphate materials are extremely active and selective in both reactions, giving yields comparable to those obtained on aluminosilicates and zeolites in the case of the vapor-phase Beckmann rearrangement of cyclohexanone oxime and the microwave-assisted Beckmann rearrangement of cyclododecanone oxime, respectively. The materials were also highly reusable after reactivation in vapor-phase reactions, with an increase in selectivity to the oxime, although a decrease in the durability (expressed as lifetime at quantitative conversion of the oxime) was also found. (c) 2007 Elsevier Inc. All rights reserved.