Alvarado Perea, Leo; Colín Luna, José Antonio; López Gaona, Alejandro; Wolff, Tanya; Pacheco Sosa, José Guadalupe; García Martínez, Julio César
Resumen:
In this study, two mesoporous materials such as MCM-41 and Ni/MCM-41 were modified with Al
at different Si/Al ratios. The mesoporous materials were proved as sorbents of heterocyclic nitrogen
and sulfur compounds employing quinoline (Q) and dibenzothiophene (DBT), respectively, as
model molecules of that precursor pollutants at the same concentrations of ppmw of nitrogen and
sulfur (N:S = 1 ratio). The sample with the highest Si/Al ratio showed the highest specific surface,
and at low Si/Al decreased the specific surface. With X-ray diffraction (XRD) the Ni containing in
MCM-41, there is a clear trend and the highly hexagonal ordered sample is the one without Al and
once the Al is added, the hexagonal ordering is highly modified. Employing NH3-TPD and NMR
revealed that the samples with Si/Al = 5 and 16 have higher Lewis acid sites than another ratio of
Si/Al. The modification successfully added small amounts of Ni that did not collapse the pore
structure but increased the density of surface (acidic) groups that in turn favored the uptake of the
sulfur compound through π-complexation adsorption mechanism. It is also possible to recognize
that the samples with a Si/Al ratio of 5 and 16 revealed the presence of the highest surface density
of weak acid sites for both sorbents. Adsorption experiments were carried out in a batch adsorption
system at 313 K and atmospheric pressure using a model mixture from diesel containing: DBT, Q,
and 40 ml of dodecane. The sulfur adsorption was substantially improved when Ni was
incorporated to MCM-41; for example, at 250 ppmw of N uptake of DBT was almost twice than
MCM-41 alone. This result would indicate that Ni/MCM-41 could remove both molecules but
mainly the nitrogen molecule at high concentrations. The Langmuir and Freundlich adsorption
isotherms were used for all materials considering Q in the presence of DBT depending on the Si/Al
ratio. This behavior did not happen for the DBT whose behavior was modelled by an isotherm of
the Freundlich type for Ni/MCM-41 and adsorbed in acid sites and multilayer. Lastly, experimental results indicated that MCM-41 with Si/Al = ∞ has the highest (Q/DBT) selectivity of 13,390 at 50
ppmw N compared to another Si/Al ratio, for example, at 250 ppmw N.