Active Sites on Ti–Ce Mixed Metal Oxides for Reactive Adsorption of Thiophene and Its Derivatives: A DFT Study

Abstract

Density functional theory was used to investigate the mechanistic aspects of the adsorption of sulfurcontaining compounds over Ti−Ce mixed metal oxides. We elucidate the promotional effect of the Ce dopant on TiO 2 and report the importance of oxygen vacancy-bound molecular oxygen as an active site on Ti−Ce mixed metal oxides for adsorption of thiophenic sulfur. The presence of surfaceactivated molecular oxygen leads to the oxidation of the sulfur, thus providing strongly bound sulfoxide and sulfone species. Ce doping of TiO 2 makes the oxidation process feasible both thermodynamically and kinetically. Surface oxygen vacancy sites act as catalytic sites in an adsorption cycle. DRIFTS results corroborate the presence of vacancy bound molecular oxygen. Our DFT calculations also examine thiophene and methyl-, dimethyl-, benzo-, and dibenzothiophenes adsorbed on TiO 2 and Ce-doped TiO 2 (001), (101), and (100) surfaces.

Management of γ-Alumina with High-Efficient {111} External Surfaces for HDS Reactions

“…Elongated MoS 2 slabs are located parallelly or perpendicularly to the [001] and [110] direction due to the formation of Mo-S(O)-Ti linkage on the TiO 2 surface [12,13], while MoS 2 slabs lie flatly on the planar rutile TiO 2 (110) surface [14]. Besides, the ZnO (001) facet and (100) facet is also related to the polarity of supports and corresponding catalysts presented desulfurization activity [15], which corroborated previous studies on the TiO 2 that increasing (001) facet ratio led to an increase in the adsorption and catalytic properties [16]. Sulfided Co 3 O 4 nanorods with a preferred growth direction along (110) exhibit much higher HDS activity than nanopolyhedra enclosed by the (111) and (100) facets [17].…”

Oxidation of refractory sulfur compounds with molecular oxygen over a Ce–Mo–O catalyst

“…Based on these results, it is assumed that oxygen was activated by Ce species in the catalyst first, forming some reactive oxygen species. [57][58][59][60][61] These reactive oxygen species further oxidized DBT into DBTO 2 with the assistance of Mo species, which is widely employed as the catalyst when active oxidants such as H 2 O 2 or hydroperoxide were used. [62][63][64] Single MoO 3 showed no activity due to the absence of reactive oxygen species.…”

Taming Interfacial Oxygen Vacancies of Amphiphilic Tungsten Oxide for Enhanced Catalysis in Oxidative Desulfurization

“…It has been well-clarified that the properties of catalysts are more affected by the defects in the structure. − A large number of transition metal oxides (e.g., TiO 2 , ZnO, and WO 3 ) with oxygen vacancies have been reported to obtain high catalytic performance. To date, different preparation methods for oxides with oxygen vacancies, such as element doping, − thermal treatment, , and peroxide decomposition, etc., have been developed. Nonetheless, a great majority of currently known preparation technologies suffer from several drawbacks such as high treatment temperatures or complex synthesis processes.…”