Structure dependence of Nb2O5-X supported manganese oxide for catalytic oxidation of propane: Enhanced oxidation activity for MnOx on a low surface area Nb2O5-X

Abstract

A series of Nb2O5-x with different structures were prepared as a carrier to manganese oxide catalysts for total oxidation of propane. The results demonstrated that a monoclinic structure of Nb2O5-x pre-calcined at 1025 °C, leads to significantly and surprisingly higher catalytic oxidation activity when MnOx is deposited at 400 °C even with extremely low specific area (around 3.94 m2/g) relative to the performance of MnOx/Nb2O5-x (∼>50 m2/g pre-calcined at 500 °C). Conversion vs temperature profiles for fresh and aged catalysts were generated and performance compared for different materials. Brunauer Emmett Teller (BET) and X-ray diffraction (XRD) were conducted to reveal the textural and structural features of niobium-based catalysts. Raman, X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) were performed to further understand the interaction between manganese and niobium oxides. Raman spectra indicated a new Nb-O-Mn species formed due to the strong interaction between the activated niobium oxide carrier at 1025 °C and manganese oxide. This study describes a synergistic catalytic oxidation effect between Mn oxides deposited on a specific phase structure of Nb2O5-x with very low specific surface area. The enhanced catalytic performance is directly related to the proper ratio of Mn3+/Mn4+ coupled with high ratio of Nb4+/Nb5+ on the surface and the oxygen vacancies generated between monoclinic Nb2O5-x and MnOx.