The unsteady-state kinetics of NH3 adsorption-desorption and of select
ive catalytic reduction (SCR) of NO with NH3 were studied overmodel V2
O5/TiO2 and V2O5-WO3/TiO2 catalysts by transient response techniques.
Over both catalysts the dynamic experiments could be successfully desc
ribed by a kinetic model assuming (1) negligible NO adsorption on the
catalyst surface; (2) nonactivated NH3 adsorption; (3) a Temkin-type N
H3 coverage dependence of the desorption energy; (4) a nonlinear depen
dence of the SCR reaction rate on the NH3 surface coverage. Thus, the
results are supportive of an Eley-Rideal mechanism for the SCR reactio
n 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 t
he SCR reaction, possibly related to the superior redox properties of
the WO3-containing sample. Over both samples the estimates of the acti
vity 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/mo
l ranges, respectively.