Rational strategy for boosting productivity of salicylamide from urea and phenol over metal oxides via modulation their acidic-basic characters

The industrial viability of green synthesis of salicylamide from urea and phenol is obstructed by the low salicylamide productivity using metal oxides as the catalysts. Here, a series of single- and mixed-oxides having different metal compositions (Zn, Mg, Fe, Al) with varied acidic-basic characters were prepared to catalyze all the identified comprising paths of reaction between urea and phenol. Based on in situ FTIR characterization, a bifunctional mechanism that urea and phenol were separately activated on the acidic and basic centers to collaboratively promote the synthesis of salicylamide, was disclosed. Nevertheless, the surface active sites would be blocked due to the strong absorption of urea when catalysts exhibited extra acidity. Additionally, the secondary reactions would aggravate sharply over too basic samples. Thanks to its well-balanced acidity/basicity, Zn-Al mixed oxide provided the best catalytic performance. Herein, we offer a rational approach to develop metal oxides for the effective manufacture of salicylamide.