Formation of hierarchical pore structure OMS-2 by etching with H2C2O4 and its excellent catalytic performance for toluene oxidation: Enhanced lattice oxygen activity

OMS-2 with the hierarchical pore structure (OMS-2-OA) was successfully synthesized by etching with H2C2O4 and applied for catalytic toluene oxidation. A series of characterizations (including XRD, SEM, TEM, N2 adsorption-desorption, O2-TPD and so on) were performed to explore the relation between the activity and properties of OMS-2-OA. The results confirm the formation of mesopore on the OMS-2-OA after etching with H2C2O4, but it still maintains the cryptomelane structure and nano-rod morphology of OMS-2. Compared with OMS-2, OMS-2-OA shows the better catalytic toluene oxidation performance that the temperatures of 50% and 100% toluene conversion get to 212 and 225 °C, respectively, which can be attributed to the more amount of K+ and Mn4+ on OMS-2-OA than those on OMS-2, enhancing its lattice oxygen activity and oxidation ability. Moreover, a small amount of H2O addition in the feed can improve the catalytic performance and stability of OMS-2 and OMS-2-OA. In addition, a series of OMS-2-OA samples after long-term use were treated at different reaction conditions and characterized to investigate the factors in affecting catalytic activity for OMS-2-OA. This work provides a method to change surface chemical environment and form mesopore structure of MnOx to tune its catalytic activity by etching with H2C2O4.