Abstract
Ceria-based catalysts, with Cu in substitution of noble metals, were studied in a vertical microreactor system under isothermal conditions, where NOx was previously stored, followed by the reduction step conducted under H2. The possible remaining ad-NOx species after the reduction stage, were investigated by Temperature Programmed Desorption in He. In situ DRIFTS was used as a complementary technique for the analysis of the surface species formation/transformation on the catalysts’ surface. Catalysts containing both Ba and Cu were found to be selective in the NOx reduction, producing N2 and minor amounts of NH3 during the reduction step, as well as NO. The different ceria-based formulations (containing copper and/or barium) were prepared and tested at two different temperatures in the NOx reduction (NSR) processes. Their catalytic activities were analyzed in terms of their compositions and have been useful in the elucidation of the possible origin and relevant pathways for NOx reduction product formation, which seems to involve the oxygen vacancies of the ceria-based materials (whose generation seems to be promoted by copper) during the rich step. The scope of this work involves an interdisciplinary study of the impact that catalysts’ formulations (noble metal-free) have on their LNT performance under simulated conditions, thus covering aspects of Materials Science and Chemical Engineering in a highly applied context, related to the development of control strategies for hybrid powertrains and/or the reduction of the impact of cold-start emissions.
Highlights
Europe has proposed ambitious reductions in CO2 limits for both light- and heavyduty sectors, and discussions have already started on the continent regarding the level of regulations, beyond Euro 6 [1]
The different ceria-based formulations were prepared and tested at two different temperatures in the NOx reduction (NSR) processes. Their catalytic activities were analyzed in terms of their compositions and have been useful in the elucidation of the possible origin and relevant pathways for NOx reduction product formation, which seems to involve the oxygen vacancies of the ceria-based materials during the rich step
Ba-Cu/ceria—zirconia catalysts were synthetized, characterized, and tested by means of lean/rich cycles under isothermal conditions, at low temperatures, with particular attention to the reduction step in order to investigate their catalytic behavior in terms of the influence of copper presence on the catalytic formulations and the incorporation of different barium loadings to the ceria–zirconia support
Summary
Europe has proposed ambitious reductions in CO2 limits for both light- and heavyduty sectors, and discussions have already started on the continent regarding the level of regulations, beyond Euro 6 [1]. NOx emissions from in-use diesel vehicles have come under intense scrutiny, and while meeting current and upcoming regulations is a significant challenge, several studies have been carried out to demonstrate that diesels can be very clean under a wide range of operating conditions [3]. Various recent studies support that engine improvements coupled with advanced after-treatment systems enable vehicles to meet post-Euro 6 NOx limits under challenging real-world driving conditions. Very recent studies demonstrate that LNT and SCR coated filters offer further cold start emission reduction, and that the innovative diesel mild hybrids can offer synergistic gains for lower NOx as well as CO2 improvements [2]
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