Superior performance of freeze-dried Ni/ZnO-Al2O3 adsorbent in the ultra-deep desulfurization of high sulfur model gasoline

- ZnO-Al2O3 mixed oxides were synthesized using a freeze drying modified cation-anion double hydrolysis method
- Freeze dried adsorbents exhibited a superior performance in reactive adsorption desulfurization
- A large amount of small sized ZnO gives rise to a large sulfur capacity
- The absence of the inactive NiAl2O4 phase in the adsorbents allows the fast cleavage of C-S bond in thiophene
- High surface area and large pore volume facilitate the mass transfer of reactants and accommodate more sulfur

Reactive adsorption desulfurization (RADS) is an effective approach to the ultra-deep desulfurization under mild conditions. The sulfur adsorption capacity of the adsorbents strongly depends on the pore structure, the chemical states and the dispersion of active species. In this work, ZnO-Al2O3 mixed oxides with an improved structure were synthesized via a freeze-drying modified cation-anion double hydrolysis (CADH) technique and used as the support. The fresh and spent catalysts were characterized through N2 adsorption-desorption, H2-temperature programmed reduction, X-ray diffraction, UV-vis diffuse reflection spectroscopy, Fourier transformed infrared spectroscopy and transmission electron microscopy (TEM). Freeze drying technique provided the adsorbent with a smaller sized ZnO and an improved pore structure compared with the normal oven drying method. Evaluation results in the RADS of a high sulfur model gasoline reveals that the freeze-dried Ni/ZnO-Al2O3 (40 °C) with a crystallization temperature of 40 °C exhibits a superior RADS performance with an accumulative sulfur adsorption capacity of 90 mg S/g, which is 5.3% and 118% higher than those of adsorbents prepared by the normal oven drying and the conventional kneading methods. A high amount of small ZnO particles, improved textural properties and the absence of inactive NiAl2O4 phase are among the factors accounting for the superior RADS performance of Ni/ZnO-Al2O3 adsorbent prepared by the freeze-drying method. Upon four RADS-regeneration cycles, sample Ni/ZnO-Al2O3 (40°C) exhibited a high stability without evident activity loss.

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