Probing the Catalytic Activityof Sulfate-DerivedPristine and Post-Treated Porous TiO2(101) Anatase Mesocrystalsby the Oxidative Desulfurization of Dibenzothiophenes

摘要

Mesocrystals (basically nanostructures showing alignment of nanocrystals well beyond crystal size) are attracting considerable attention for modeling and optimization of functionalities. However, for surface-driven applications (heterogeneous catalysis), only those mesocrystals with excellent textural properties are expected to fulfill their potential. This is especially true for oxidative desulfuration of dibenzothiophenes (hard to desulfurize organosulfur compounds found in fossil fuels). Here, we probe the catalytic activity of anatases for the oxidative desulfuration of dibenzothiophenes under atmospheric pressure and mild temperatures. Specifically, for this study, we have taken advantage of the high stability of the (101) anatase surface to obtain a variety of uniform colloidal mesocrystals (approximately 50 nm) with adequate orientational order and good textural properties (pores around 3–4 nm and surface areas around 200 m²/g). Ultimately, this stability has allowed us to compare the catalytic activity of anatases that expose a high number of aligned single crystal-like surfaceswhile differing in controllable surface characteristics. Thus, wehave established that the type of tetrahedral coordination observedin these anatase mesocrystals is not essential for oxidative desulfurationand that both elimination of sulfates and good textural propertiessignificantly improve the catalytic activity. Furthermore, the mostactive mesocrystals have been used to model the catalytic reactionin three-(oil–solvent–catalyst) and two-phase (solvent–catalyst)systems. Thus, we have been able to observe that the transfer of DBTfrom the oil to the solvent phase partially limits the oxidative processand to estimate an apparent activation energy for the oxidative desulfurationreaction of approximately 40 kJ/mol in the two-phase system to avoidmass transfer limitations. Our results clearly establish that (101)anatase mesocrystals with excellent textural properties show adequatestability to withstand several post-treatments without losing theirinitial mesocrystalline character and therefore could serve as modelsfor catalytic processes different from the one studied here.