Abstract Hydrodeoxygenation (HDO) reactions are one of the most studied oxygen removal processes and are typically carried out at high temperatures and hydrogen pressures with the aid of a solid catalyst. One of the greatest challenges is the development of effective catalysts. In this sense, this work aims to evaluate the metallic dispersion of Ni supported on carbon nanotubes and its performance as a catalyst in the hydrodeoxygenation reaction of bio-oil (using guaiacol as a model molecule). Thermally pretreated CNTs were impregnated to the wet point with a nickel acetate solution and subsequently calcined at 500 °C for 12 h. Catalysts with 2% Ni/NTC, 11% Ni/NTC, and 20% Ni/NTC (by mass) were prepared. The determination of physicochemical properties was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), helium-flow thermoprogrammed desorption (TP-He), N2 physisorption, and chemical quantification by ICP-OES. Selectivity and intrinsic activity (TOF) data were evaluated in a continuous gas-phase system and a fixed-bed reactor. XRD, TEM, and SEM analyses showed that increasing the Ni content decreased metal dispersion. Catalytic tests showed that metallic dispersion influences the performance of catalysts in the HDO reaction, since the TOF for the 2%Ni/NTC catalyst was almost twice as high as the TOF observed for 11% Ni/NTC, and three times higher than for 20%Ni/NTC. However, to obtain fully deoxygenated products, the conversion needs to be high, as only mono-oxygenated intermediates were produced up to 35% conversion. The results obtained in this work can guide future work regarding the metallic particle size to be used and also the use of functionalized supports to improve the selectivity of the HDO reaction.
Caetano et al. (2026) studied this question.