E. Tronconi et al., UNSTEADY ANALYSIS OF NO REDUCTION OVER SELECTIVE CATALYTIC REDUCTION-DE-NOX MONOLITH CATALYSTS, Industrial & engineering chemistry research, 37(6), 1998, pp. 2341-2349
A heterogeneous 1D dynamic model of SCR-de-NOx (SCR = selective cataly
tic reduction) monolith reactors is developed, based on the concept of
the ''active'' catalyst region. Its predictions are practically equiv
alent to those of a previous 2D model, but its numerical solution is f
aster by 1 order of magnitude, making it suitable for predictive contr
ol applications. The model is successfully fitted to transient NO redu
ction data at different temperatures, space velocities, and NH3/NO fee
d ratios over two commercial SCR monolith catalysts. The data indicate
characteristic times up to several minutes. The model analysis shows
that: (i) SCR dynamics are determined by buildup/depletion of the cata
lyst NH3 coverage, which result primarily from a competition between a
dsorption of ammonia and its reaction with NO, the rate of NH3 desorpt
ion being markedly slower; (ii) the dynamic response of NO conversion
is slow compared to changes in the NH3 feed content, which is unfavora
ble for a feedback control system; and (iii) positive/negative peaks o
f NO emissions vs progressive changes of the NH3 slip are predicted up
on sudden load variations.