The acid-catalyzed condensation of acetone and ammonia to directly produce 2,2,6,6-tetramethy-4-piperidone (triacetonamine) was studied under both homogeneous and heterogeneous catalysis. The selectivity to the desired product was affected by the presence of a complex reaction network involving several kinetically parallel and consecutive reactions, leading to by-products such as diacetonealcohol, diacetoneamine, mesityl oxide, acetonine, and 2,2,4,6-tetramethyl-2,5-dihydropyridine. The latter was the most undesired by-product, since its formation was irreversible. Key elements in achieving high selectivity in the direct synthesis of triacetonamine were the molar feed ratio between acetone and ammonia, and the amount of water in the reaction medium; in fact, water was found to play an important role in the transformation of the intermediate acetonine into triacetonamine. Compared with homogeneous catalysis, the selectivity achieved by the use of the heterogeneous H-Y zeolites was controlled by means of a proper selection of the zeolite features. In fact, the use of a highly hydrophilic H-Y zeolite made it possible to achieve the same selectivity as that obtained under homogeneous catalysis conditions, with the additional advantage of using an easily separable and reusable catalyst, which showed no deactivation. (C) 2014 Elsevier B.V. All rights reserved.