One-step synthesis of transition metal modified UiO-66-Ce metal-organic framework: Catalytic oxidation of toluene and investigation of the mechanism

As a kind of VOCs, the direct catalytic oxidation of toluene to CO2 and H2O is a great challenge. A high-performance catalyst plays a crucial role in catalytic oxidation. Herein, UiO-66-Ce and a series of transition metals-doped UiO-66-CeM (M = Cu, Co, Mn, Fe, Zr) through a rapid and facile one-step synthesis method are prepared to investigate the catalytic oxidation of toluene. Experiments disclose that the UiO-66-CeCu exhibits extremely high catalytic capacity. A range of characterizations reveals that the oxygen vacancies formed between Ce and the doped metal. Better redox performance play a key role in the oxidation of toluene (Ce4++Mn+→Ce3++M(n+1)+). Most importantly, the analysis of the catalytic oxidation mechanism in situ DRIFTS in different conditions. Concluded that toluene oxidation is the coexistence of MvK mechanism and L-H mechanism. Furthermore, the oxygen vacancies increase the mobility of gaseous oxygen on the surface, which is essential in improving catalytic activity. Finally, the degradation pathway of toluene in UiO-66-CeM was concluded as follows: toluene → benzyl alcohol → benzoic acid → acid anhydride …...CO2 and H2O.