Unveiling the deactivation by coke of NiAl2O4 spinel derived catalysts in the bio-oil steam reforming: Role of individual oxygenates

• The stability of NiAl 2 O 4 derived catalyst in the SR of model oxygenates is studied. • The oxygenate nature is related to the catalyst deactivation by coke deposition. • Coke nature, and not its content, is the key factor affecting catalyst deactivation. • Filamentous coke deposited in the SR of aliphatics or catechol has low impact on deactivation. • Pyrolitic and amorphous coke formed in the SR of guaiacol causes rapid deactivation. The catalyst stability, mainly affected by coke deposition, remains being a challenge for the development of a sustainable process for hydrogen production by steam reforming (SR) of bio-oil. In this work, the influence of oxygenates composition in bio-oil on the deactivation by coke of a NiAl 2 O 4 spinel derived catalyst has been approached by studying the SR of a wide range of model oxygenates with different functionalities, including acetic acid, acetone, ethanol, acetaldehyde, acetol, catechol, guaiacol and levoglucosan. A fluidized bed reactor was used in the following conditions: 600 and 700 °C; steam/carbon ratio, 3 (6 for levoglucosan); space–time, 0.034 g catalyst h/g bio-oil (low enough to favor the rapid catalyst deactivation), and; time on stream, 5 h. The spent catalysts were analyzed with several techniques, including Temperature Programed Oxidation (TPO), X-ray Diffraction (XRD), N 2 adsorption–desorption, Scanning and Transmission Electron Microscopy (SEM, TEM) and Raman Spectroscopy. The main factors affecting the catalyst stability are the morphology, structure and location of coke, rather than its content, that depend on the nature of the oxygenate feed. The deposition of pyrolytic and amorphous coke that blocks the Ni sites inhibiting the formation of filamentous carbon causes a rapid deactivation in the guaiacol SR. Conversely, the large amount of carbon nanotubes (CNTs) giving rise to a filamentous coke deposited in the SR of aliphatic oxygenates only causes a slight deactivation. The increase in the temperature significantly reduces coke deposition, but has low impact on deactivation.