Photosynthesis of Benzonitriles on BiOBr Nanosheets Promoted by Vacancy Associates

Photocatalytic organic functionalization reactions represent a green, cost‐effective, and sustainable synthesis route for value‐added chemicals. However, heterogeneous photocatalysis is inefficient in directly activating ammonia molecules for the production of high‐value‐added nitrogenous organic products when compared with oxygen activation in the formation of related oxygenated compounds. In this study, we report the heterogeneous photosynthesis of benzonitriles by the ammoxidation of benzyl alcohols (99 % conversion, 93 % selectivity) promoted using BiOBr nanosheets with surface vacancy associates. In contrast, the main reaction of catalysts with other types of vacancy sites is the oxidation of benzyl alcohol to benzaldehyde or benzoic acid. Experimental measurements and theoretical calculations have demonstrated a specificity of vacancy type with respect to product selectivity, which arises from the adsorption and activation of NH3 and O2 that is required to promote subsequent C−N coupling and oxidation to nitrile. This study provides a better understanding of the role of vacancies as catalytic sites in heterogeneous photocatalysis. BiOBr photocatalysts with different surface vacancy associates were successfully synthesized. Vacancy associates of Br−Bi−Br triple atom vacancy (VBrBiBr) and oxygen vacancies can generate benzonitrile with high selectivity in the photocatalytic ammoxidation of benzyl alcohol by providing adsorption activation sites for NH3 and O2 and reaction sites for the multi‐step formation of imine intermediates and oxidation to benzonitrile.