A. Trunschke et al., Influence of lanthana on the nature of surface chromium species in La2O3-modified CrOx/ZrO2 catalysts, J CATALYSIS, 191(2), 2000, pp. 456-466
Infrared spectroscopy of the adsorbed probe molecules CO, NO, and NH3, phot
oelectron spectroscopy, temperature-programmed desorption of NH3, X-ray dif
fraction, and BET surface analysis have been used to study surface and bulk
characteristics of lanthana-modified CrOx/ZrO2 catalysts. La2O3 addition t
o CrOx/ ZrO2 strongly modifies the structure of supported chromia species a
nd stabilizes coexisting isolated Cr3+ and highly dispersed Cr2O3 particles
. Unlike that, chromia in La2O3-free CrOx/ZrO2 undergoes considerable sinte
ring at 823 K, which is the necessary reduction and reaction temperature fo
r n-octane aromatization, applied as a test reaction. The strong interactio
n between chromia and La2O3ZrO2 could be due to an increased number of nona
cid hydroxyl groups, which are possibly responsible for a more efficient an
choring of chromia species on the La2O3-containing support rather than on p
ure zirconia. The performances of La2O3-promoted and La(2)O(3)free CrOx/ZrO
2 catalysts in n-octane aromatization do not differ so dramatically as woul
d be expected from the large differences in the structure of surface chromi
a species. (C) 2000 Academic Press.