Temperature Programmed Oxidation Coupled with In Situ Techniques Reveal the Nature and Location of Coke Deposited on a Ni/La₂O₃-αAl₂O₃ Catalyst in the Steam Reforming of Bio-oil

The characterization of coke deposited on a Ni/La₂O₃-αAl₂O₃ catalyst used in the steam reforming of bio-oil has been studied by temperature programmed oxidation (TPO) coupled with different in situ techniques: thermogravimetry (TG), modulated thermogravimetry (MTG), FTIR spectroscopy with mass spectrometry (MS), Raman spectroscopy, and differential scanning calorimetry (DSC). The steam reforming of bio-oil was carried out in a reactor equipment with two steps in series, comprising bio-oil thermal treatment (500 °C) and subsequent reforming in a fluidized bed reactor (550–700 °C; and steam-to-carbon ratio, 1.5–6). TG/MS-TPO experiments identify encapsulating and filamentous coke, and a more detailed analysis using other in situ techniques enable to characterize the nature and location of 4 types of coke: (i) an encapsulating coke with aliphatic nature placed in the most superficial layers; (ii) an encapsulating coke with higher aromatic nature in inner layers; (iii) the most superficial layers of a filamentous coke, further from active sites and with a more carbonized structure compared to encapsulating coke; and (iv) an innermost and mainly polyaromatic filamentous coke with a low oxygenates content.