Abstract Together with the high-temperature polymer electrolyte fuel cell, the reactor for the autothermal reforming (ATR) of liquid hydrocarbons, such as diesel fuel or kerosene, is the key component of the Julich fuel cell system in the 5 kWe power class. This paper presents some of Julich’s most recent development in the field of ATR reactors, specifically the ATR 12. ATR 12 is characterized by a new concept for the internal generation of superheated steam as one of the ATR reactants using concentric shells instead of coiled tubing and particularly by the integration of an electric heating wire to enable fast and autonomous start-up. Three different experimental procedures for heating up the ATR 12 are presented and discussed, the most suitable of which enables the start-up of the ATR 12 within approximately 15 min. As a consequence, from the system perspective, the bulky start-up burner, which is also difficult to control, along with the corresponding heat exchanger unit, can be dispensed with. Additionally, comprehensive steady-state experiments identify suitable reaction conditions for the operation of the ATR 12.