Promoting effect of surface acidities on efficiency of copper modifier for ordered mesoporous carbon-SiO2-Al2O3 nanocomposites in adsorptive desulfurization

Abstract

The ordered mesoporous carbon-silica-alumina nanocomposites (MCSAs) with different ratios of Si/Al (10, 20 and 100) were synthesized by a multi-component co-assembly method followed by pyrolysis at high temperatures. The Si/Al ratio has an important effect on the acidic characteristics of the nanocomposite. The pyridine FT-IR results show that the nanocomposite with a Si/Al ratio of 100 has maximum amount of Brønsted acid sites. This may be because more non-framework Al-O-Si species are generated in the MCSA samples with lower Si/Al ratio due to the dealumination of the precursor in an acidic media during the surfactant-based assembly procedure and/or partial dealumination occurring during high temperature calcination. The copper-modified MCSAs were prepared by incipient wetness impregnation followed by calcination. The desulfurization performance of the as-prepared adsorbents was evaluated by the selective adsorption of dibenzothiophene (DBT) as a model sulfur compound from model fuels at ambient conditions. The dispersion extent of copper species increases with the increase of Brønsted acid sites, which results in a higher selectivity for DBT in competition with benzene. Compared with our previously prepared ordered mesoporous carbon-silica nanocomposite (MCS), the promotion effect of aluminum incorporation on the desulfurization selectivity is demonstrated. Moreover, the ordered mesoporous carbon-alumina nanocomposite (MCA) was also prepared. Its ordered mesostructure partially collapsed and the micropore volume is increased after copper incorporation, resulting in a good enhancement in sulfur capacity and selectivity.