Trimetallic spinel CuMnCoO₄ as an efficient catalyst for solvent-free nitration of toluene to dinitrotoluene without sulfuric acid

The development of the direct nitration for toluene toward dinitrotoluene (DNT) under solvent-free and without sulfuric acid conditions over a heterogeneous catalyst is critical challenging undertakings for developing the green and efficient synthesis of DNT. Herein, trimetallic spinel CuMnCoO₄ was prepared and investigated its catalytic performance for solvent-free toluene nitration with nitric acid as nitration agent in the absence of sulfuric acid. The selectivity of 2,4-dinitrotoluene (2,4-DNT) of the spinel-catalyzed-toluene-nitration-system was 1.6 times higher than that of the system without spinel. Kinetic studies revealed that the reaction step of MNT to DNT is the rate-limiting step and moderately increasing the nitric acid/toluene ratio and reaction temperature could enhance the toluene dinitration process. Characterization measurements showed that trimetallic spinel CuMnCoO₄ led to an appropriate vacancy-lattice oxygen pair. The reaction mechanism to elucidate the synergetic effect of vacancy-lattice oxygen pair on promoting the activity of toluene and nitrating agent was proposed.