Identifying Photocatalytic Active Sites of C₂H₆ C–H Bond Activation on TiO₂ via Combining First-Principles Ground-State and Excited-State Electronic Structure Calculations

Abstract

The activation of C–H bonds at low temperatures has attracted widespread interest in heterogeneous catalysis, which involves complex thermocatalytic and photocatalytic reaction processes. Herein, we systematically investigate the photothermal catalytic process of C–H bond activation in C2H6 dehydrogenation on rutile TiO2(110). We demonstrate that the photochemical activity of the C2H6 molecule adsorbed on TiO2(110) is site-sensitive and that C2H6 is more easily adsorbed at the Ti5c site with a lower dehydrogenation energy barrier. The first C–H bond activation of the C2H6 adsorbed at the Ti5c site tends to occur in the ground state, whereas Obr-adsorbed C2H6 is more photoactive during the initial adsorption. During the dehydrogenation of C2H6, the photogenerated electrons are always located at the Ti4+ sites of the TiO2 substrate while the photogenerated holes can be captured by C2H6 to activate the C–H bond.

Photocatalytic ethane conversion on rutile TiO2(110): identifying the role of the ethyl radical

“…However, when the O b 2− and O Ti 2− centers trap photogenerated holes, the nucleophilic O b 2− and O Ti 2− convert into electrophilic O b − and O Ti − centers, 47,48 which have a stronger ability than O b 2− and O Ti 2− to abstract the H atoms of the small alkanes. 20,21,25 Correspondingly, the study of the photocatalytic EB dehydrogenation on R-TiO 2 (110) 39 demonstrated that both the O b − and O Ti − centers produced by trapping the holes can activate the α-C–H bond of the side chain alkyl groups of EB. In addition, theoretical works also suggest that the O b − centers formed upon the UV irradiation play a vital role in the C–H bond activation of CH 4 and C 2 H 6 on R-TiO 2 (110).…”

“…Namely, the initial C–H bond activation of C 2 H 6 on R-TiO 2 (110) seems to occur ineffectively at the ground state via thermocatalysis. 21,22,24…”

“…In addition, theoretical works also suggest that the O b − centers formed upon the UV irradiation play a vital role in the C–H bond activation of CH 4 and C 2 H 6 on R-TiO 2 (110). 20,21 Unfortunately, no product signal of photocatalytic ODHE was detected on reduced R-TiO 2 (110) (Fig. S1, ESI†) under 355 nm irradiation, indicating that the O b − center produced with the 355 nm irradiation finds it difficult to activate the inert C–H bond of C 2 H 6 under the current conditions.…”

Low-Temperature Ethylbenzene Conversion on Rutile TiO2(100) via Photocatalysis: The Strong Photon Energy Dependence

“…On the basis of the desorption temperature of HT C 6 H 5 CHCH 2 , the energy barrier of the second C–H bond cleavage on the ground state is about 1–1.3 eV. The energies of photogenerated electrons/holes by 257 nm (∼4.8 eV) and 343 nm (∼3.6 eV) light are much higher than the energy barrier, while a series of theoretical works on photocatalytic C–H bond activation on R–TiO 2 (110) ,, suggest that the formation of an excited radical intermediate by trapping a hole will largely decrease the energy barrier of the C–H bond cleavage and then facilitate the C–H bond cleavage. In addition, when one methyl group on the end of the C 3 H 8 molecule is substituted by a phenyl group, C 6 H 5 C 2 H 5 forms.…”

Modulating the Energetics of C–H Bond Activation in Methane by Utilizing Metalated Porphyrinic Metal–Organic Frameworks

“…Many terminal metal-oxo complexes serve as active sites for activating the strong C–H bonds of light alkanes at moderate reaction conditions. − However, the fleeting nature of these metal-oxo intermediates makes it difficult to probe them experimentally. Density functional theory (DFT) has been extensively used to computationally model metal-oxo intermediates to understand their role in C–H bond activation. − Furthermore, computational modeling using DFT can help in finding out structure–activity relationships that will speed the discovery of efficient catalysts and hence guide experimental efforts toward their synthesis. − …”