Tm. Salama et al., STUDIES OF THE SELECTIVE REDUCTION OF NITRIC-OXIDE BY CARBON-MONOXIDEIN THE PRESENCE AND ABSENCE OF HYDROGEN OVER AU NAY CATALYSTS/, Journal of the Chemical Society. Faraday transactions, 92(2), 1996, pp. 301-306
Citations number
24
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The selective reduction of NO with CO in the presence and absence of h
ydrogen over Au/NaY catalysts has been studied by in situ FTIR spectro
scopy and under steady-state conditions in a flow mode iii the tempera
ture range 473-723 K. The NCO intermediates found by FTIR absorption a
t 2280-2240 cm(-1) after contacting, at 423-573 K, an Au/NaY catalyst
with an NO-CO-H-2 mixture shows a dependence on the presence of H-2 wh
ich functions in N-O dissociation in this temperature region. Removal
of NCO groups from the catalyst with time at 473 K, proposed to be lim
ited by the prerequisite reaction between adsorbed NCO and NO in the g
as phase, to form N-2 and CO2 is accelerated with increasing temperatu
res. The effect of adding H-2 to an NO-CO-Hestream on the conversions
of both NO and CO to, respectively, N-2 and CO2 were found to be consi
stent with a temperature-dependent mechanism. The yields of N-2 and CO
2 were increased in the presence of hydrogen, when NCO complexes were
present on the gold catalyst, up to 573 K. Above this temperature, whe
re direct NO + CO is the only competing reaction, the presence of hydr
ogen reduced conversion. The activities of the gold catalysts were mai
ntained even at temperatures as high as 723 K, suggesting that a large
fraction of partially charged Au-I cations were stabilized by the fra
mework of NaY zeolite. This species, after pumping off the reacting mi
xture gases at 473 K and collecting the spectra on cooling the gold ca
talyst, gave a characteristic carbonyl IR absorption band at 2188 cm(-
1), reasonably assigned to a CO vibration of carbonyl coordinated to A
u-I.