The copper weight percentage was measured by ICP analysis. The analysis results
showed a higher amount of copper in Cu/Na-SUZ-4 (1.92%) compared to Cu/H-SUZ-4 (1.49%).
1 shows NO conversion over Cu/SUZ-4 catalysts in the temperature range 150-650°C. Cu/Na-SUZ-4 showed a higher NO
conversion compared with Cu/H-SUZ-4, especially below 400°C. For instance, at 300°C Cu/Na-SUZ-4 showed 89.4% NO conversion, while Cu/H-SUZ-4
under the same conditions showed 76.4% NO
conversion. This indicates that effect of Na+ cation is more pronounced
at low temperature. H2-TPR was conducted to examine the reducibility
of copper species. The TPR profiles clearly
showed that the reduction peaks of the Cu/Na-SUZ-4 (330°C) shift to the
lower temperature compared to Cu/H-SUZ-4 (380°C). This suggests that presence of alkali cation (Na+)
decreasing the reduction temperature of copper species. The H2
consumption of the reduction peak (300-400°C) can be
assigned to the reduction of Cu2+ to Cu+. FTIR of NO and
CO adsorbed showed the presence of a higher amount of Cu+ species in
Cu/Na-SUZ-4 compared to Cu/H-SUZ-4. According
to these results, promoting of alkali cation appears to ease the reduction of
copper species and to provide the formation of Cu+.
3?Results and discussion
with Si/Al = 6.57 was hydrothermally synthesized. Composition of the gel was
the following: 7.35 K2O: Al2O3: 3.10 TeA2O:
33.3 SiO2: 781 H2O. The NH4-SUZ-4 was obtained by an
ion-exchanged the parent zeolite in NH4NO3 aqueous
solution. This procedure was repeated 3 times followed by filtration, washing
and drying at 120°C. The H-SUZ-4 support was obtained by
calcining NH4-SUZ-4 at 650°C. This sample was further ion-exchanged
with NaNO3 solution to form Na-SUZ-4. Finally, H-SUZ-4 and Na-SUZ-4 were
ion-exchanged with Cu(CH3COO)2 at 80°C for 1 h under stirring.
The samples were calcined at 650°C for 3 h. Standard SCR
activities of the catalysts were carried out in a fixed-bed reactor with reaction mixtures containing 240 ppm NH3, 200
ppm NO, 7 vol% O2, 5 vol% H2O and balance N2. The flow rate of feed gas was 135 mL/min and the gas
hourly space velocity (GHSV) was approximately 80,000 h?1 for 50 mg of catalyst. ICP-AES, UV-Vis, NH3-TPD, H2-TPR
and FTIR were conducted for the characterizations of catalyst.
Selective catalytic reduction (SCR) has been studied and successfully
commercialized to reduce the NOx emission. During SCR, NOx selectively reduced
to nitrogen and water over catalyst. SCR catalyst based on copper exchanged
zeolite has received extensive research interest due to high activity and durability1.
Our previous result showed that copper exchanged SUZ-4 gives high activity than
commercial catalyst based on ZSM-52. Thus, the development of SUZ-4 support to improve activity is
required. The activity of the zeolite for NH3-SCR
was reported to be influenced by the counter ions (H+ or Na+).
In this communication, we present detail analysis of effect from alkali
cation on catalytic behavior of copper-exchanged SUZ-4 catalyst.
Promoting effect from Na+
showed on the activity for NO reduction with NH3. The level of NO
conversion on Cu/Na-SUZ-4 was higher than Cu/H-SUZ-4. Catalyst characterization
indicated differences on physicochemical properties