A set of experiments was carried out in a continuous fixed-bed reactor to investigate the relative catalytic activities of LaMnO3 and LaMn 0.95Pd0.05O3 for the partial oxidation of ethanol to acetaldehyde. Both catalysts were prepared by the sol-gel method. The resultant data have indicated that LaMn0.95Pd0.05O 3 is more active than LaMnO3 and that acetaldehyde selectivities of both are close at around 90%. To gain an in-depth understanding of perovskite's chemistry involved, kinetic analysis of the data has been conducted with the differential method. Accordingly, eight elementary reactions have been proposed by resorting to the Mars-van Krevelen redox cycle. Subsequently, these elementary reactions have been lumped into five steps comprising ethanol adsorption, oxygen adsorption, surface reaction, acetaldehyde desorption, and water desorption. This has rendered it possible to derive a set of rate equations based on the Langmuir-Hinshelwood-Hougen-Watson formalism. The exploration of these rate equations has revealed that surface reaction, evolving chemisorbed ethanol and oxygen, is rate-limiting. The estimated activation energies of 11.72 kcal/mol for LaMnO3 and 12.44 kcal/mol for LaMn0.95Pd0.05O3 are nearly identical; however, the pre-exponential factor of the latter is about twice the value of the former. This can be attributed to the better reducibility of Pd-promoted LaMnO3, thereby leading to greater reactivity in ethanol partial oxidation.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Industrial and Manufacturing Engineering