Evaluation of the catalytic oxidation of soot by CeO_X-LaMnO₃ at different O₂ pressures synthesized by ultrasonic-assisted hydrothermal method

In this work, the synthesis of catalyst with perovskite structure and chemical formula La_1-XCe_XMnO₃ at x = 0 − 0.5 were successfully obtained by an ultrasonic-assisted hydrothermal method. Results show that the addition of Ce in La_1-XCe_XMnO₃ have not substantial effect in textural and morphological properties; however, the formation of a new crystalline phase with final composition CeO_X-La_1-XCe_XMnO₃ was detected at values x > 0.3. All synthesized catalysts were tested in the soot oxidation under both, loose and tight contact in 20% O₂/N₂ or 5% O₂/N₂ atmospheres. CeO_X-La_1-XCe_XMnO₃ at x = 0.3 resulted in the best catalytic activity with activation energy values of 57.9 kJ^.mol⁻¹. The interaction between Ce³⁺ and Mn⁴⁺ species in this catalyst can transfer electrons generating Mn³⁺ and Ce⁴⁺. This reduction from Mn⁴⁺ to Mn³⁺ is accompanied by migration of vacancies to the surface promoting the adsorbed oxygen from the gas phase, need for balancing the chemical states. By increasing the temperature above 300 °C, the bulk oxygen migration to the surface is enhanced being the responsible for the oxygen availability. The formation of CeO_X-La_1-XCe_XMnO₃ promotes a stable redox cycle allowing the reusability of this catalyst even at low oxygen pressures after three different reaction cycles.