Abstract
Chemical interactions between metal particles (Ag or Ni) dispersed in a low-cost MCM-41M produced from beach sand amorphous silica and sulfur compounds were evaluated in the deep adsorptive desulfurization process of real diesel fuel. N2 adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy (STEM-EDX) were used for characterizing the adsorbents. HRTEM and XPS confirmed the high dispersion of Ag nanoparticles on the MCM-41 surface, and its chemical interaction with support and sulfur compounds by diverse mechanisms such as π-complexation and oxidation. Thermodynamic tests indicated that the adsorption of sulfur compounds over Ag(I)/MCM-41M is an endothermic process under the studied conditions. The magnitude of ΔH° (42.1 kJ/mol) indicates that chemisorptive mechanisms govern the sulfur removal. The best fit of kinetic and equilibrium data to pseudo-second order (R2 > 0.99) and Langmuir models (R2 > 0.98), respectively, along with the results for intraparticle diffusion and Boyd’s film-diffusion kinetic models, suggest that the chemisorptive interaction between organosulfur compounds and Ag nanosites controls sulfur adsorption, as seen in the XPS results. Its adsorption capacity (qm = 31.25 mgS/g) was 10 times higher than that obtained for pure MCM-41M and double the qm for the Ag(I)/MCM-41C adsorbent from commercial silica. Saturated adsorbents presented a satisfactory regeneration rate after a total of five sulfur adsorption cycles.
Highlights
The demand for clean energy has attracted great attention in recent years and has generated an increasing focus on sulfur compounds removal from fuels [1]
This paper proposes a low-cost method for mitigating sulfur content in diesel fuel based on the adsorption of organosulfur compounds over Ag and Ni impregnated MCM-41 supports from beach sand silica, in a complementary process to the hydrodesulfurzation (HDS) applied in refineries with a greener and effective approach
The higher value of parameter α obtained by Elovich equation (Table 3) suggests that there is a strong affinity between the recalcitrant compounds containing S and the active sites of AgNO3 /MCM-41M adsorbent, strengthening the hypothesis that this adsorption is highly influenced by Ag sites and its different active forms (Ag(0) and Ag-O), and mainly occurs via π-complexation and oxidation [47,48]
Summary
The demand for clean energy has attracted great attention in recent years and has generated an increasing focus on sulfur compounds removal from fuels [1]. The combustion of these compounds results in liberating sulfur oxides (SOx ), which poison catalytic converters and are corrosive to fuel cell electrodes [2], in addition to polluting the environment; governments worldwide have adopted standards to decrease sulfur concentration to 10 ppm for diesel fuel [3]. Catalysts 2019, 9, 651 at hard conditions (>573 K, >4 MPa) using sophisticated Co-Mo/Al2 O3 or Ni-Mo/Al2 O3 catalysts. Some recalcitrant organosulfur such as thiophene derivatives are not removed by this method [4]
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