Highly catalytic activity of Mn/SBA-15 catalysts for toluene combustion improved by adjusting the morphology of supports

Rod-like, hexagonal and fiber-like SBA-15 mesoporous silicas were synthesized to support MnO_x for toluene oxidation. This study showed that the morphology of the supports greatly influenced the catalytic activity in toluene oxidation. MnO_x supported on rod-like SBA-15 (R-SBA-15) displayed the best catalytic activity and the conversion at 230°C reached more than 90%, which was higher than the other two catalysts. MnO_x species consisted of coexisting MnO₂ and Mn₂O₃ on the three kinds of SBA-15 samples. Large amounts of Mn₂O₃ species were formed on the surface and high oxygen mobility was obtained on MnO_x supported on R-SBA-15, according to the H₂ temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) results. The Mn/R-SBA-15 catalyst with greater amounts of Mn₂O₃ species possessed a large amount of surface lattice oxygen, which accelerated the catalytic reaction rate. Therefore, the surface lattice oxygen and high oxygen mobility were critical factors on the catalytic activity of the Mn/R-SBA-15 catalyst.