Dynamics of the SCR-DeNO(x) reaction by the transient-response method

The unsteady-state kinetics of NH3 adsorption-desorption and of selective catalytic reduction (SCR) of NO with NH3 were studied overmodel V2O5/TiO2 and V2O5-WO3/TiO2 catalysts by transient response techniques. Over both catalysts the dynamic experiments could be successfully described by a kinetic model assuming (1) negligible NO adsorption on the catalyst surface; (2) nonactivated NH3 adsorption; (3) a Temkin-type NH3 coverage dependence of the desorption energy; (4) a nonlinear dependence of the SCR reaction rate on the NH3 surface coverage. Thus, the results are supportive of an Eley-Rideal mechanism for the SCR reaction and of a significant heterogeneity for adsorption-desorption process and surface reaction of the catalyst surface. The binary and ternary catalysts exhibit similar acid properties, but different activity in the SCR reaction, possibly related to the superior redox properties of the WO3-containing sample. Over both samples the estimates of the activity energies for NH3 desorption at zero coverage and for the surface reaction of NO with NH3 are similar and in the 23-26 and 14-16 kcal/mol ranges, respectively.