The selective reduction of NOx over H-mordenite (H-m) was studied using CH3
OH as reducing agent. Results are compared with those obtained with other c
onventional reducing agents (ethylene and methane), with gas-phase reaction
s, and with other metal-exchanged mordenites (Cu-mordenite (Cu-m) and Co-mo
rdenite (Co-m)). H-m was found to be an effective catalyst for the SCR of N
Ox with CH3OH. When different reducing agents were compared over H-m, CH3OH
> C2H4 > CH4 was the order according to the maximum NO conversion obtained
using 1% of oxygen in the feed. Instead, if selectivity is considered, the
order results CH4 > CH3OH > C2H4. In reaction experiments, two distinct zo
nes defined by two maxima with NO to N-2 conversion are obtained at two dif
ferent temperatures. A correlation exists between the said zones and the CO
:CO2 ratio. At low temperatures, CO prevails whereas at high temperatures C
O2 prevails. These results indicate that there exist different reaction int
ermediates. Evidence from reaction experiments, FTIR results, and transient
experiments suggest that the reaction mechanism involves formaldehyde and
dimethyl ether (DME) as intermediates in the 200-500 degrees C temperature
range. The surface interaction between CH3OH (or its decomposition products
) and NO is negligible if compared with NO2, indicating that the oxidation
of NO to NO2 on acid sites is a fundamental path in this system. Different
from other non-oxygenated reductants (methane and ethylene), a gas-phase NO
x initiation effect on hydrocarbon combustion was not observed. (C) 1999 El
sevier Science B.V. All rights reserved.