Adsorptive desulfurization of model diesel fuel over mono-functionalized nickel/γ-alumina and bi-functionalized nickel/cerium/γ-alumina adsorbents

Abstract

In this study, the S–M direct interaction and π-complexation mechanisms for selective adsorption of 4,6-dimethyldibenzothiophene (4,6-DMDBT) onto the prepared mono-functionalized nickel/γ-alumina (Ni/γ–Al2O3) and bi-functionalized nickel/cerium/commercial γ-alumina (Ce–Ni/γ–Al2O3) were investigated. To characterize the prepared adsorbents, X-ray fluorescence spectroscopy, energy-dispersive X-ray, X-ray diffraction, N2 adsorption–desorption, and temperature-programmed desorption of ammonia (NH3-TPD) were used. The influence of nickel–cerium contents, 4,6-DMDBT and competitive aromatic concentrations on the adsorptive desulfurization performance were also studied. The equilibrium and kinetic data were well described by Langmuir and pseudo-second-order models, respectively. The maximum adsorption capacity of γ-Al2O3, Ni/γ–Al2O3 and Ce–Ni/γ–Al2O3 was found to be 1.253, 15.970 and 17.970 mg/g, respectively. Diffusion studies showed that both π–Ni and S–Ce were the major adsorption mechanisms in the first fast adsorption stage, and the external mass transfer limited the adsorption rate. In the second stage, the adsorption rate was controlled by intra-particle diffusion (R2 = 0.976 for Ni/γ–Al2O3 and R2 = 0.981 for Ce–Ni/γ–Al2O3) confirming that acid–base interaction (S–H) was formed. The results showed that selective binding formation of sulfur compounds on adsorbent active sites was proceeded via π-interaction (π–Ni), direct sulfur–cerium interaction (S–Ce), and acid–base interaction (S–H). The multifunctional Ce–Ni/γ–Al2O3 exhibited a higher adsorptive selectivity for 4,6-DMDBT compared to Ni/γ–Al2O3 in diesel fuel in the presence of aromatic content. The regeneration results showed that the prepared adsorbents can be reused easily for three cycles.