The article “Low-temperature standard-SCR over Cu-SSZ-13: selective inhibition of the oxidation half-cycle by mild hydrothermal aging”, authored by researchers from the Department of Energy at Politecnico di Milano in collaboration with Cummins Inc., has been selected as the Front Cover of the July issue of Reaction Chemistry & Engineering, the Royal Society of Chemistry journal dedicated to chemical reaction engineering.

The study was carried out by Andrea Gjetja, Nicola Usberti, Nicole Daniela Nasello, Umberto Iacobone, Isabella Nova, and Enrico Tronconi, together with researchers from Cummins Inc.

The research focuses on Selective Catalytic Reduction (SCR) systems, one of the most widely used technologies for the aftertreatment of diesel engine exhaust gases and the reduction of nitrogen oxide (NOx) emissions. Over time, however, SCR catalysts undergo progressive degradation due to prolonged exposure to high temperatures and water vapor. This phenomenon reduces their efficiency, particularly during cold start conditions, when emission control is most critical.

The study addresses a long-standing research question: why do SCR catalysts lose efficiency as they age? By combining experimental investigations with reaction modeling, the researchers demonstrate that hydrothermal aging does not impair the entire pollutant conversion process, but selectively affects a key step of the chemical reaction. This discovery enables a more accurate description of catalyst performance degradation over time and provides valuable insights for the design of more efficient, reliable, and durable emission aftertreatment systems.

The research also shows that the effects of catalyst aging can be experimentally mitigated by increasing oxygen availability. This finding opens new perspectives for the development of advanced control strategies and aftertreatment systems capable of maintaining high performance even after years of operation.