A novel approach to the decomposition of biogas consisting in the simultaneous production of syngas (H-2 and CO mixture) and bio-nanostructured filamentous carbon (BNFC) is proposed. Catalysts with different active phases such as Ni, Co or Fe on Al2O3 are studied in the temperature range between 600 and 900 degrees C. Their behavior was analyzed considering CH4 and CO2 conversions, reaction rates, catalyst stability and carbon production. Additionally, the BNFC produced were characterized by transmission electron microscopy. Depending on the active phase and the reaction temperature, different carbon types were identified: fishbone, parallel and chain-like BNFC and encapsulating carbon. Large amounts of BNFC and good catalyst stability were achieved with the Ni/Al2O3 catalyst at 600 degrees C, pointing out that carbon accumulation is not directly responsible of catalyst deactivation and that the key factor is the nature of carbon formed during the reaction. (C) 2014 Elsevier Ltd. All rights reserved.