We herein report on the hydrothermal catalytic conversion of pyridine to hydrocarbons. The catalytic activity of several supported noble metal (5 wt%) catalysts (Pt/C, Pd/C, Ru/C and Rh/C, sulfided Pt/C, and Pt/gamma-Al2O3), a traditional hydrodenitrogenation (HDN) catalyst (sulfided CoMo/gamma-Al2O3), a transition metal carbide (Mo2C) and sulfide (MoS2), and a noble metal oxide (PtO2) toward the HDN of pyridine in a hydrothermal reaction medium between 250 and 400 degrees C was determined. The Pt/gamma-Al2O3 catalyst proved to be the most active for hydrothermal HDN of pyridine, and we report the effects of batch holding time, reaction temperature, catalyst loading, initial hydrogen pressure, and water density on the Pt/gamma-Al2O3-catalyzed HDN of pyridine in supercritical water. The latter two process variables had the greatest influence on the product yields and distribution. Conditions were identified that lead to essentially 100% conversion of pyridine to N-free hydrocarbons. The catalyst shows some modest loss in activity upon being reused. An HDN reaction network for pyridine under hydrothermal conditions was proposed. The main HDN products are n-butane and n-pentane. Nitrogen was removed as ammonia. (C) 2011 Elsevier B.V. All rights reserved.