The sequential cracking of acetic acid (AA) to produce hydrogen was investigated over noble metals and Ni-based catalysts. In this non-stationary process, AA is decomposed into a hydrogen-rich gas, with concomitant carbon deposition on the catalyst, which is periodically removed under oxygen. In this first part, Ni-based catalysts proved to be the most efficient in terms of activity and selectivity to hydrogen, compared to noble metal catalysts. The reaction conditions leading to optimal hydrogen selectivity and complete catalyst regeneration were studied. Continuous hydrogen production by the use of two reactors working alternately was demonstrated. (C) 2007 Elsevier B.V. All rights reserved.