Sn-doped nanoconfinements of SBA-15 for oxidative desulfurization: Kinetics and thermodynamics

SnO2-containing catalysts are highly active in oxidative desulfurization (ODS) of fuels, and their activity depends on the size and dispersion extent of SnO2 NPs. Herein, we report a facile but efficient strategy for dispersing SnO2 NPs by utilizing the nanoconfined spaces formed between silica walls and template of as-synthesized SBA-15 (AS-15). The Sn precursor is introduced directly into the nanoconfined spaces of AS-15 by solid phase dispersive (SPD) strategy and converted to SnO2 via calcination, during which template P123 was also eliminated. Char-acterization results demonstrated that up to 10 wt% SnO2 (Sn10AS) can be highly dispersed with smaller size; however, severe aggregation of SnO2 NPs occur in the catalyst obtained from calcined SBA-15 (Sn10CS) with similar loading. Nanoconfined spaces in AS-15 and stronger SnO2 interactions with AS-15 caused by abundant hydroxyl groups are responsible for high dispersion of SnO2 NPs. Moreover, Sn10AS exhibited superior catalytic activity in ODS of fuel and convert 94.5% of DBT within 20 min under ambient conditions with O/S molar ratio of 5 and a catalyst dose of 0.09 g, which is much better than its analogue Sn10CS in terms of DBT conversion rate and time. The ODS process followed pseudo first-order kinetics and activation energy (Ea = 32.38 kJ/mol), enthalpy (Delta H = 35.02 kJ/mol), entropy (Delta S = -376.8 J/mol.K) and Gibbs free energy (Delta G = 149.21 kJ/mol) indicates that the ODS over Sn10AS catalyst is endothermic, non-spontaneous and favorable under ambient conditions. In addition, the regeneration ability and stability of the Sn10AS catalyst made it cost-effective for the ODS of fuel.