Catalysis and kinetics of diesel soot oxidation over nano-size perovskite catalyst

Abstract

The present work reports a comparative study of perovskite catalysts prepared by sol–gel (SG) and reactive grinding (RG) methods for the diesel soot/PM oxidation. The optimal formulated perovskite, La0.9Sr0.1Co0.5Fe0.5O3 (Cat-D) prepared by RG with a ZnO additive and reactively calcined (RC) in a 4.6% CO–air mixture, exhibited the highest surface area (94.8 m2/g), smallest crystallites (8.4 nm) and the best activity for the PM oxidation. Oxidation was initiated at ∼ 235 °C, reached a peak at ∼ 276 °C and was completed at 318 °C. Catalysts were characterized by N2 sorption, XRD, FTIR and SEM. The high activity of Cat-D may be related to its unusual characteristics arising from RG and RC. Indeed, the severe mechano-chemical deformation during ball-milling leads to fractures and cold welding, in addition to oxygen-deficient structure produced by RC resulting high density of active sites in nano-size catalyst. The kinetics of air oxidation of the PM over Cat-D under isothermal condition is reported in the present paper. Kinetics data were composed under the environment of free heat and mass transfer limitations in a specifically designed mini-semi-batch reactor. With the intention of defining the kinetic model, activation energy and Arrhenius constant of the soot oxidation with high air flow rate, pseudo-first-order reaction was presumed. The kinetics for PM oxidation in the temperature range 325–355 °C can be represented by the following rate expression: $${\text{Rate}}\left( r \right) = 6.46 \times 10^{10}\exp \, \left( { - 101.08/RT} \right) \, \left( {\text{m}} \right){\text{ g}}\,PM/{\text{g}}\,{\text{cat}}.{\text{s}}$$ The activation energy was found to be 101.08 kJ/mol.