Co–Cr–O mixed oxides for low–temperature total oxidation of propane: Structural effects, kinetics, and spectroscopic investigation

Abstract

A series of Co–Cr–O mixed oxides with different Co/Cr molar ratios are synthesized and tested for the total oxidation of propane. The reaction behaviors are closely related to the structural features of the mixed oxides. The catalyst with a Co/Cr molar ratio of 1:2 (1Co2Cr) and a spinel structure has the best activity (with a reaction rate of 1.38 μmol g−1 s−1 at 250 °C), which is attributed to the synergistic roles of its high surface acidity and good low-temperature reducibility, as evidenced by the temperature-programmed desorption of ammonia, reduction of hydrogen, and surface reaction of propane. Kinetic study shows that the reaction orders of propane and oxygen on the 1Co2Cr catalyst (0.58 ± 0.03 and 0.34 ± 0.05, respectively) are lower than those on the 2Co1Cr catalyst (0.77 ± 0.02 and 0.98 ± 0.16, respectively) and 1Co5Cr (0.66 ± 0.05 and 1.30 ± 0.11, respectively), indicating that the coverages of propane and oxygen on 1Co2Cr are higher than those on the other catalysts due to its higher surface acidity and higher reducibility. In addition, in-situ diffuse reflectance infrared spectroscopic investigation reveals that the main surface species on 1Co2Cr during the reaction are polydentate carbonate species, which accumulate on the surface at low temperatures (< 250 °C) but decompose at relatively high temperatures.