Multifunctional Materials to Combine NH3-SCR and NSR Cycles

Before discussing the proposed multicomponent material it is useful to recap what this individual issues with SCR-NH and NOx trapping as applied to the removal of NOx from small diesel-powered vehicles. 

SCR-NHj relies on a defined dosage of NH (or an NH precursor) where the levels of reductant dosed are comparable to the levels of NOx that require reduction (recall that the latter changes as a function of driving conditions). Problems with over- or under-dosing the NH will result in the emission of NOx (either indirectly through atmospheric NHj oxidation following NHj slip, or directly if insufficient reductant is added to reduce the engine-derived NOx). 

NOx storage and reduction cannot easily operate on diesel-powered vehicles since the generation of a reductant to regenerate the NOx trap and reduce the released NOx requires periodic fuel-rich operation and this is not possible in a 4-stroke diesel cycle. There is a fuel penalty associated with the direct injection of fuel onto the catalyst to carry out this function and in any case diesel fuel is not a very active reluctant for these processes. 

We have proposed [64,65] a NOx reduction strategy that combines both NOx trapping and SCR-urea approaches and, through judicious choice of the catalytic and non-catalytic materials we propose solutions to the problems mentioned with the individual approaches detailed earlier. 

The material we propose has basic sites (to trap NOx), acidic sites (to activate NH and trap excess NH ) and redox active sites (to promote the NO reduction reaction). 

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