Visible-light-driven aldehyde ammoxidation to nitrile via •O2– and •NHx radicals generation over Ni(OH)2/TiO2 p-n heterojunctions

Abstract

Aldehydes ammoxidation is a green and promising route for selective synthesis of nitrile, but developing low-cost and efficient catalytic system under mild condition remains a challenge. Herein, we explore a novel catalytic system where the designed Ni(OH)₂/TiO₂ p-n heterojunction catalyst could efficiently drive aldehydes ammoxidation with NH₃·H₂O and O₂ at ambient temperature and pressure by using visible-light as the only energy input. The superoxide (^•O₂^–) generated by reducing O₂ with photogenerated electrons and amino radicals (^•NH_x) produced by oxidizing NH₃·H₂O with photogenerated holes, are successfully identified as key species for the formation of nitriles. Meanwhile, ^•NH_x and ^•O₂^– radicals individually work on the formation of the intermediate aldimine intermediate and its oxidation to nitrile. The performance of the engineered Ni(OH)₂/TiO₂ p-n heterojunctions in the reaction process is much more superior to other catalyst systems. This study develops nitrile synthesis route under mild conditions and present new opportunities for constructing low-cost photocatalyst for chemical synthesis. It also provides a better understanding of the radical species and how they work in aldehydes ammoxidation reactions.