Light-driven toluene ammoxidation via mixture photocatalyst of halide perovskite Cs₃Bi₂Br₉ and TiO₂.

Abstract

Benzonitrile is vital for the production of rubbers, pharmaceuticals, and dyes. Traditional benzonitrile synthesis via toluene ammoxidation requires high temperatures (≥350°C), leading to high energy consumption. Here, we demonstrate a photocatalytic route for benzonitrile synthesis under milder conditions (100° to 120°C, 1 to 4 bar, blue light irradiation). Using ammonia, dioxygen, and toluene as precursors, gram-scale benzonitrile (1.751 grams) was produced over a mixture photocatalyst [lead-free halide perovskite cesium bismuth bromide (Cs₃Bi₂Br₉) + titanium dioxide], demonstrating satisfactory selectivity (85 to 90%) and a linear yield rate of 600 μmol hour^-1. The photocatalyst exhibited excellent quantum efficiencies (up to 40%) and maintained stability over a 30-hour test period. Mechanism studies revealed that, in the presence of an interfacial effect, the perovskite phase primarily activated benzyl carbon (sp³)-hydrogen bonds, while titanium dioxide facilitated the oxidation of alcohol intermediate to aldehydes. These benzaldehydes were subsequently converted to benzonitriles via ammoxidation, predominantly catalyzed by Cs₃Bi₂Br₉ through aldimines (RCH═NH).