This paper describes the investigations of the catalytic activity in soot oxidation over well-defined iron oxide based materials. The nanostructuration of iron oxide by potassium into tunnelled (KFeO 2 ) and layered (K 2 Fe 22 O 34 ) ferrites and the surface promotion with CeO 2 results in the marked increase in the catalytic activity (decrease of the ignition temperature down to 210°C and T 10 % to 310°C). The measurements of the catalysts work function showed that both nanostructuration and surface promotion with ceria of the best KFeO 2 phase led to increase of the electron availability (decrease of the work function). Strong correlation of the catalytic activity in soot combustion of the Ce-K-Fe-O systems with the work function value was revealed for the first time in the model studies, and can be used as a guideline for optimisation of the real catalytic filters.
The samples of K 2 Fe 22 O 34 phase were synthesized and characterized by XRD, BET, SEM-EDX and XPS. K + diffusion was investigated by impedance spectroscopy, whereas the surface segregation and desorption were monitored by Kelvin Probe (changes in work function) and Species Resolved Thermal Alkali Desorption, at the temperature range of 600-1000 K. The analysis of changes in work function and desorption signals (K and K + ) at various temperatures allowed to resolve the kinetic parameters (flux, rate constants, activation energies) of potassium diffusion, surface accumulation and desorption. Based on the obtained results, the simple, functional model of bulk and surface changes of K-β-ferrite was proposed.
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