One-Step Synthesis of Transition Metal Modified Uio-66-Ce Metal-Organic Framework: Catalytic Oxidation of Toluene and Investigation of the Mechanism

UiO-66-Ce and a series of transition metals-doped UiO-66-CeM (M=Cu, Co, Mn, Fe, Zr) are prepared through a rapid and facile one-step synthesis method to investigate the catalytic oxidation of toluene. UiO-66-CeCu exhibits extremely high catalytic capacity. XRD, BET, SEM and EDS-mapping indicate the successful synthesis of metal-organic frames topology of UiO-66-CeCu with high specific surface area and large pore volume. Raman, EPR, XPS results confirm that the oxygen vacancies formed between Ce and the doped metal. Better redox performance play a key role in the oxidation of toluene (Ce 4+ +M n+ →Ce 3+ +M (n+1)+ ). Among them, UiO-66-CeCu has the highest specific surface, the largest pore volume and the most oxygen vacancies, as well as the strong redox interaction between Ce 3+ and Cu 2+ , resulting in the highest catalytic efficiency. Toluene-TPD and GC confirm that the introduction of transition metals can facilitate toluene adsorption, conversion and selectivity. 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 ......CO 2 and H 2 O.