Temperature and Concentration Gradients During NOX Storage and Reduction Cycling

William  Epling, University of Waterloo

William Epling, Alan Shaw, Khurram Aftab, Aleksey Yezerets and Neal Currier

In emissions catalyst applications, axial distributions of reaction rates, surface chemistry, and temperature all exist along the catalyst surface. To develop physically relevant models of such systems, understanding these distributions is required. IR thermography can be used to measure the temperature distributions on a monolith-supported catalyst, but can also be used to indirectly measure surface concentrations of sorbed species. This indirect method consists of measuring the temperature rise associated with an exothermic or endothermic reaction, with the target surface species as a reactant in such a reaction. IR thermography was used to measure the distribution of nitrate species on model and commercial diesel NOX adsorber catalysts. Axial distributions of the nitrate species as a function of lean-phase time, temperature and using NO2 and NO as NOX source were evaluated by measuring temperatures along the catalyst surface during the regeneration phase. With increasing lean-phase time, more NOX was trapped, and larger temperature rises were observed. This was also true of increasing rich-phase times since more NOX could be trapped with the more fully regenerated surface. The data indicate that with shorter trapping times, NOX is trapped near the front of the catalyst and the surface concentration of trapped NOX moves from back-to-front, as expected. The data also demonstrate quantitatively, the relative amounts as a function of axial position. With longer trapping times, more surface NOX species were still found at the front half of the catalyst, however within the front half, more NOX was trapped slightly downstream relative to the amounts at the very inlet. This indicates that there was not a smooth saturation wave that propagates simply from front-to-back as more NOX is trapped on the catalyst.

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