Influence of nitrogen vacancies on selective oxidation of aromatic alcohols on g-C3N4: A comparative DFT study

The development of new metal-free catalysts that effectively oxidise alcohols to aldehydes or ketones is one of the fundamental goals of research on environmental photocatalysis. In this study, the influence of nitrogen vacancies on the catalytic process was investigated. We performed calculations using the density functional theory (DFT) to elucidate the mechanism of selective oxidation of benzyl alcohol to benzaldehyde with molecular O2 on g-C3N4. Through modelling of the pathways of the reaction, we found that vacancy defects strongly promote the formation of aldehyde. Our results clearly depicted that there are different interaction patterns that determine the reaction energy profiles for defective and defect-free systems. Furthermore, we estimated the energy barrier for the postulated rate-limiting step for a few alcohols by using the climbing image nudge elastic band (CI-NEB) method. The obtained values agreed very well with the benzaldehyde yield reported by Ding et al. (2018) [23]. In addition to the energetic effects, the electronic properties of the nitrogen-vacancy-containing g-C3N4 were also discussed. Our results demonstrated the underlying mechanism of selective oxidation of alcohols to aldehydes on both the catalysts in a comprehensive and systematic manner. Thus, by knowing the individual reaction steps, further increase in the substrate conversion may be attained by modification of the catalyst structure.