Insight into the photoexcitation effect on the catalytic activation of H2 and C-H bonds on TiO2(110) surface

• Published in: Chinese chemical letters Vol. 33; no. 10; pp. 4705 - 4709
• Main Authors: Zhou, Min, Wang, Hai-Feng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2022; Key Laboratory for Advanced Materials,Centre for Computational Chemistry and Research Institute of Industrial Catalysis,East China University of Science and Technology,Shanghai 200237,China
• Subjects: C-H bond activation; Density functional theory calculation; H2 activation; Photocatalysis; TiO2; H2 activation; C-H bond activation; Density functional theory calculation; Photocatalysis; TiO2
• ISSN: 1001-8417; 1878-5964
• DOI: 10.1016/j.cclet.2021.12.074

Semiconductor photocatalysis holds great promise for breaking the inert chemical bonds under mild condition; however, the photoexcitation-induced modulation mechanism has not been well understood at the atomic level. Herein, by performing the DFT+U calculations, we quantitatively compare H2 activation on rutile TiO2(110) under thermo- versus photo-catalytic condition. It is found that H2 dissociation prefers to occur via the heterolytic cleavage mode in thermocatalysis, but changes to the homolytic cleavage mode and gets evidently promoted in the presence of photoexcited hole (h+). The origin can be ascribed to the generation of highly oxidative lattice O-radical (Obr•−) with a localized unoccupied O-2p state. More importantly, we identify that this photo-induced promotion effect can be practicable to another kind of important chemical bond, i.e., C–H bond in light hydrocarbons including alkane, alkene and aromatics; an exception is the C(sp1)-H in alkyne (HCCH), which encounters inhibition effect from photoexcitation. By quantitative analysis, the origins behind these results are attributed to the interplay between two factors: C-H bond energy (Ebond) and the acidity. Owing to the relatively high Ebond and acidity, it favors the C(sp1)-H bond to proceed with the heterolytic cleavage mode in both thermo- and photo-catalysis, and the photoexcited Obr•− is adverse to receiving the transferred proton. By contrast, for the other hydrocarbons with moderate/low Ebond, the Obr•− would enable to change their activation mode to a more favored homolytic one and evidently decrease the C–H activation barrier. This work may provide a general picture for understanding the photocatalytic R–H (R = H, C) bond activation over the semiconductor catalyst. [Display omitted] The first-principles DFT calculations have provided a fundamental insight into the R-H (R = H, C) bond activation in thermo- and photo-catalytic conditions and deepen the understanding of photoexcitation-driven reaction; especially, a general framework was revealed to predict the possibility of photo-hole on promoting R-H bond activation.