Deactivation Modes of a Field-Aged Urea SCR Fe Zeolite Catalyst

A field-aged Fe zeolite urea selective catalytic reduction (SCR) catalyst with 4,000 hrs of operation was obtained and analyzed in the laboratory using various experimental techniques to determine the main modes of deactivation.  Flow bench reactor tests on small core samples revealed that catalyst bricks from each layer of the aftertreatment system had experienced a significant amount of hydrothermal aging, and the layer closest to the engine had also experienced a measurable performance loss due to chemical aging.  BET surface area results showed essentially no change due to the engine aging whereas ammonia temperature programmed desorption (TPD) results showed a significant loss in total storage capacity as well as a change in the distribution of ammonia adsorption sites.  Dealumination of the Fe zeolite was confirmed via diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and changes to Fe utilizing various probe molecules was monitored.  Implications for developing accelerated laboratory aging methods will be discussed.