Comparison of the Reactive Adsorption Desulfurization Performance of Ni/ZnO–Al2O3 Adsorbents Prepared by Different Methods

In this study, a series of Ni/ZnO–Al 2 O 3 mixed oxide (MO) adsorbents were prepared by the one-step homogeneous precipitation method and the cation–anion double hydrolysis (CADH) method for reactive adsorption desulfurization (RADS) using thiophene as a model fuel in a fixed bed reactor. The synthesized adsorbents were characterized by N 2 sorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H 2 temperature-programmed reduction (H 2 -TPR), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS), and Raman spectroscopy. Results show that both Ni loading and the preparation method have a significant effect on the RADS activities of the adsorbent. Among the studied adsorbents, 10% Ni/ZnO–Al 2 O 3 prepared by the one-step urea precipitation method showed the best RADS performance, with a thiophene conversion up to 96% and a sulfur adsorption capacity of 86 mg of S/g, which is 34% larger than that of CADH adsorbents. In addition, upon five RADS–regeneration cycles, sample 10% Ni/ZnO–Al 2 O 3 exhibited a drop of only 3% in thiophene conversion, indicating the high stability of the Ni/ZnO–Al 2 O 3 adsorbent prepared by homogeneous precipitation. Characterization results show that the one-step homogeneous precipitation method could facilitate the formation of small ZnO particles while suppressing the formation of inactive ZnAl 2 O 4 . On the other hand, by decreasing the formation of NiAl 2 O 4, the homogeneous precipitation method could also generate high concentration of Ni 0 sites, which are the active centers for the hydrogenolysis of C–S bonds. These findings indicate that a high-performance adsorbent for RADS can be obtained by employing a proper preparation method with good control on the adsorbent structure.