Selectively catalytic upgrading of bio-oil to aromatic hydrocarbons over Zn, Ce or Ni-doped mesoporous rod-like alumina catalysts

•Metal doped mesoporous rod-like Al2O3 catalysts with high surface area was successfully prepared.•2.5 wt.% metal loading amount resulted in the highest catalytic activity and selectivity for upgrading of bio-oil.•Zn or Ni doped Al2O3 catalyst showed high selectivity towards MAHs.•Metal-doped mesoporous rod-like Al2O3 catalysts exhibited excellent reusability and regeneration property.

Zn, Ce or Ni metal was doped on mesoporous rod-like Al2O3 prepared by using cationic surfactant cetyl-trimethyl ammonium bromide (CTAB) assisted hydrothermal method for in-situ catalytic upgrading of bio-oil derived from the fast pyrolysis of sunflower stalk. The morphology, crystal structure, surface area, reduction behaviour and acidity of the as-prepared catalyst were characterized. Uniform rod-like γ-Al2O3 particles with a surface area as high as 412 m2/g and an average mesopore diameter of 3.51 nm were obtained at a CTAB/Al molar ratio of 0.5 and Zn, Ce or Ni metal was found to be able to homogeneously disperse on it. The catalysts with 2.5 wt.% metal (Zn, Ce or Ni) loading amount exhibited the high catalytic activity and selectivity for upgrading of bio-oil with high content of oxygenated components to aromatic hydrocarbons, especially benzene, toluene and xylene (BTX). The total relative maximum hydrocarbon amount of 92% in the upgraded bio-oil was obtained by using 2.5 wt.% Ni/Al2O3. Four-cycle reusability test indicated that the metal-doped microporous rod-like γ-Al2O3 alumina catalysts had long-term stability in their performance. Moreover, the regeneration of spent catalysts (4th reuse) by calcination at 650 °C in air for 30 min recovered their activity perfectly. It is expected that such metal-doped rod-like alumina catalysts can be applied as bio-oil upgrading catalysts in a practical process.

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