Kinetics of n-butanol partial oxidation to butyraldehyde over lanthanum-transition metal perovskites

Partial oxidation of butanol to butyraldehyde over a series of LaBO ₃ (B = Mn, Fe, and Co) perovskites was investigated in a continuous fixed-bed system under ambient pressure. Physicochemical properties of catalysts were characterized by X-ray diffraction, H ₂ temperature-programmed reduction, and temperature-programmed oxidation. LaMnO ₃ was more favorable to be reduced and reoxidized than LaFeO ₃ and LaCoO ₃. Catalytic results have indicated that all catalysts show similar butanol and oxygen conversions and over 90% butyraldehyde selectivities below 300 °C. Side reactions such as butanol or butyraldehyde combustion could be enhanced at high temperatures. To gain an in-depth understanding of perovskite's chemistry involved, kinetic analysis has been carried out. Eight reaction pathways based on the Mars-van Krevelen redox cycle were proposed. These pathways have been lumped and associated with the Langmuir-Hinshelwood-Hougen- Watson formalism to derive a set of rate equations. Parameter estimation via nonlinear regression of derived rate equations has shown that surface reaction, evolving chemisorbed butanol and oxygen, is probably rate-determining. The estimated activation energy of LaMnO ₃ (15.0 kcal/mol) by assuming surface reaction as the rate-limiting step was the lowest among all perovskites. This can be ascribed to the better redox property of LaMnO ₃, thereby decreasing the energy barrier in butanol partial oxidation.