Towards practical application of lanthanum ferrite catalysts for NO reduction with H 2

Abstract

A series of perovskite-type catalysts (LaFeO 3, La 0.8Sr 0.2FeO 3, Pd/La 0.8Sr 0.2FeO 3, La 0.8Sr 0.2Fe 0.9Pd 0.1O 3, La 0.7Sr 0.2Ce 0.1FeO 3, Pd/La 0.7Sr 0.2Ce 0.1FeO 3 and La 0.7Sr 0.2Ce 0.1Fe 0.9Pd 0.1O 3) has been prepared by the solution combustion synthesis method and fully characterized by XRD, BET, FESEM and TPD/R analyses. The performance of these catalysts towards the NO reduction mechanism by H 2 has been evaluated in a temperature-programmed reaction apparatus (TPRe) in the absence and in the presence of oxygen. The catalysts have been studied in the 25–350 °C temperature range, and significant catalytic activities were measured at 150–250 °C. Among the catalysts screened, La 0.8Sr 0.2Fe 0.9Pd 0.1O 3, showed the best performance. Hence, it was deposited directly over a ceramic honeycomb monolith by in situ SCS, tested in a lab-scale test rig, then submitted to the specific ageing protocol (thermal treatment at 500 °C for 96 h) in the presence of water vapour and sulfur dioxide, two potentially deactivating species present in diesel exhaust gases, and it showed a good compromise between satisfactory catalytic activity and stability. A mechanistic analysis is presented concerning the relationship between the observed activity and the reducibility of the B site, determined through TPR experiments. Some final conclusions are drawn on the perspective of the practical application of the investigated aftertreatment route for diesel exhaust gases.