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

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 NiAl2O4 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 degrees C; steam/carbon ratio, 3 (6 for levoglucosan); space-time, 0.034 gcatalyst h/gbio-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), N2 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.This work has been carried out with the financial support of the Ministry of Science and Innovation of the Spanish Government (grant RTI2018-100771-B-I00 funded by MCIN/AEI/10.13039/501100011033 and by "ERDF A way of making Europe") , the European Commission (HORIZON H2020-MSCA RISE 2018. Contract No. 823745) and the Department of Education, Universities and Investigation of the Basque Government (Project IT1645-22, IT1218-19 and PhD grant PRE_2021_2_0147 for L. Landa) . The authors thank for technical and human support provided by SGIker (UPV/EHU/ERDF, EU)