Catalytic steam reforming of biomass fast pyrolysis volatiles over Ni–Co bimetallic catalysts

[Display omitted] •Ni/Al2O3 catalyst show the best performance in terms of stability and carbon deposition.•Ni–Co alloy formation on bimetallic catalysts hinders the oxidation of Co0 species.•Coke deposition greatly influenced Ni/Al2O3 and bimetallic catalysts deactivation.•Co0 active phase is more prone to coke deposition than Ni0.•The presence of steam leads to the oxidation of Co0 to inactive catalytic phases. The influence of the metal selected as catalytic active phase in the two-step biomass pyrolysis-catalytic reforming strategy has been analyzed. The pyrolysis step was carried out in a conical spouted bed reactor at 500°C, whereas steam reforming was performed in a fluidized bed reactor at 600°C. Ni/Al2O3, Co/Al2O3 and two bimetallic Ni-Co/Al2O3 catalysts with different metal loadings were synthesized by wet impregnation method, and fresh and deactivated catalysts were characterized by N2 adsorption/desorption, X-ray Fluorescence (XRF), Temperature Programmed Reduction (TPR), X-Ray powder Diffraction (XRD), Temperature Programmed Oxidation (TPO), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Although Ni/Al2O3 and both bimetallic catalysts had similar initial activity in terms of oxygenate conversion, (higher than 98%), the poorer metal dispersion observed in both bimetallic catalysts led to a fast decrease in conversion due to the promotion of coke formation on large particles. This occurred even though Ni–Co alloy formation has a positive influence by hindering the oxidation of Co0 species. The main cause for the deactivation of these catalysts is the formation of a coke with amorphous structure. The poor initial performance of Co/Al2O3 catalyst is related to changes in the Co0 oxidation state induced by the presence of steam, which led to a fast deactivation of this catalyst.