[1
]Biocarbon & Sustainability Group, Instituto Nacional del Carbón (INCAR), CSIC,
Francisco Pintado 26, 33011 Oviedo, Spain
[2
]Scientific-Technical Services, University of Oviedo, Dr. Fernando Bonguera s/n, 33006
Oviedo, Spain
[3
]Instituto de Química-Física “Rocasolano”, CSIC, Serrano 119, 28006 Madrid, Spain
[4
]Department of Physics, University of Oviedo, Federico García Lorca, 18, 33007 Oviedo
Spain