The selective catalytic reduction of nitric oxide with methane over La2O3-CaO systems: Synergistic effects and surface reactivity studies of NO, CH4,O-2, and CO2 by transient techniques
Cn. Costa et al., The selective catalytic reduction of nitric oxide with methane over La2O3-CaO systems: Synergistic effects and surface reactivity studies of NO, CH4,O-2, and CO2 by transient techniques, J CATALYSIS, 194(2), 2000, pp. 250-265
Dispersing La2O3 crystallites in a 5 wt% La2O3-CaO mixed oxide system signi
ficantly enhances the intrinsic rate of NO reduction by CH4 in the presence
of 5% O-2 at 550 degrees C compared to pure La2O3 and CaO phases. A synerg
istic effect between La2O3 and CaO crystallites due to doping of lanthana w
ith Ca2+ ions at 800 degrees C is largely responsible for the observed cata
lytic behavior. Support of this view was provided by photoluminescence stud
ies and a large number of transient experiments for determining the surface
reactivity of x wt% La2O3/CaO (x wt% = 0, 5, 80, 100) solids toward NO, CH
4, O-2 and CO2. The intrinsic site reactivity of the 5 wt% La2O3-CaO system
at 550 degrees C (TOF = 6 x 10(-3) s(-1)) competes favorably with that of
other similar oxides for the same reaction reported in the literature. X-ra
y diffraction (XRD) and scanning electron microscopy (SEM) techniques have
been used for crystal phases and particle morphology characterization of th
e x wt% La2O3/CaO mixed oxide system. The information obtained from the XRD
measurements was related to that obtained from the surface transient react
ivity studies. By the addition of La2O3 crystallites to CaO crystallites in
a wet mixing procedure followed by calcination in air at 800 degrees C, re
sults in dramatic changes in the chemisorptive properties (amount and bond
strength) of NO, O-2, and CO2 compared to the case of pure oxide phases. Pr
etreatment of the catalyst surface with H-2 or CH4 was found to strongly af
fect the amount of NO chemisorption and the kinetics of its desorption. The
se alterations were found to strongly depend on catalyst composition. (C) 2
000 Academic Press.