In situ pyrolysis of Ce-MOF to prepare CeO2 catalyst with obviously improved catalytic performance for toluene combustion

Abstract

Mesoporous CeO2 catalysts (CeO2-MOF) were synthesized by pyrolysis of Ce-MOF precursor (Ce-(1,3,5-benzenetricarboxylic acid) (H2O)6). Physicochemical properties of the samples were investigated by means of various techniques including XRD, SEM, TEM, BET, Raman, XPS, H2-TPR, O2-TPD and NH3-TPD, and their catalytic performance were evaluated by toluene combustion compared with commercial CeO2 (CeO2-C) and CeO2 prepared by precipitation method (CeO2-P). The results show that CeO2-MOF/350 catalyst (pyrolyzed at 350 °C) presents enhanced catalytic activity for toluene oxidation with the conversion of T10%, T50% and T90% at 180, 211, and 223 °C, respectively (SV = 20,000 mL/(g h), toluene concentration = 1000 ppm). Especially for high-temperature region, CeO2-MOF/350 catalyst displays much superior ability to rapidly reach to 100% conversion compared to CeO2-C and CeO2-P catalysts which usually result in a much broader temperature region to achieve complete conversion of toluene. The high catalytic performance of CeO2-MOF/350 can be reasonably ascribed to a series of better properties, such as three-dimensional penetrating mesoporous channels, larger specific surface area, smaller average grain size, higher relative percentages of Ce3+/Ce4+ and OSur/OLatt, higher oxygen storage capacity, higher oxygen vacancy concentration, better low temperature reducibility, more active oxygen species and more acid sites. Furthermore, CeO2-MOF/350 catalyst presented excellent resistance to H2O deactivation and temperature change, and in situ DRIFTs study on CeO2-MOF/350 catalyst suggests that toluene degradation is proceeded in consecutive steps via rapid transformation to aldehydic and benzoate species to finally form CO2 and H2O.