The Cu/SAPO-34 catalysts with different Cu contents were prepared by in situ hydrothermal synthesis. The selected Cu/SAPO-34 was modified by impregnating 1 wt% Pd(NO3)3. The morphology and structure of the samples were characterized via XRD and SEM techniques. The effects of Cu contents and the Pd modification on the de-
NO
As a kind of low-cost active constituent for the SCR of NO, Cu has drawn the attentions of many researchers [
The Cu/SAPO-34 catalysts with different Cu contents were prepared by insitu hydrothermal synthesis, and the details were as follows: CuO, H3PO4, Al(OH)3, and silica gel were used as the sources of Cu, P, Al, and Si, respectively. Morpholine (C4H9NO) was selected as the template. The crystallization gel was prepared according to the mole ratio of
The Pd modified Cu/SAPO-34 catalysts were prepared with pore volume impregnation. The details were as follows: the Cu/SAPO-34 catalysts were impregnated by Pd(NO3)2 solution(1 mol/L) overnight to give a 0.5% Pd loading, and then dried at 120°C and calcined at 600°C for 3 h.
The XRD patterns of powder samples were obtained on a Japanese Rigaku D/MAX2500 diffractometer at 45 kV and 100 mA with CuK
The SEM images were obtained by a Japanese Jeol Jsm-6700 F at 10 kV. The samples were covered with a thin gold layer before scanning.
The Cu content was measured using an atomic absorption spectroscopy (AAS; Varian AA240FS, USA) with a 324.7 nm Cu testing wavelength, operating at 3.0 mA lamp current and a fuel gas of C2H2 (1700 mL/min).
The activities of the Cu/SAPO-34 catalysts for the selective catalytic reduction (SCR) of NO
Firstly, He gas flow of 100 mL/min was used to sweep off for 2 h in order to eliminate the N2 residue in the reactor and then switched to the simulated exhaust. The reactor was heated up to 50°C, holden for 0.5 h, and then risen to 600°C at a rate of 7°C/min. NO, NO2, O2, and C3H6 in the gases before and after the catalytic reaction were analyzed simultaneously online by gas chromatograph (GC-9890A, Shanghai Linghua Instrument Company Limited) equipped with column Porapak Q for separating N2O and CO2 and column molecular sieve 5A for separating N2, O2 and CO.
The aging treatment is also carried out using the above-mentioned fixed-bed flow microreactor. Catalyst samples were exposed to a stream of gases containing 0.03% SO2 and 10% vapor balanced with Ar with the total rate of 400 mL/min at the temperature of 720°C for 10 h. Then, the same way as described above was used to test the aged catalyst activity.
NO conversion was calculated using the following equation:
The NO conversions over the Cu/SAPO-34 catalysts with different Cu contents were investigated using C3H6 and NH3 as the reductant. The Cu content can be represented by the Cu/Si atom ratio of the crystallization gel. In this paper, the Cu/Si atom ratios included 0 (without Cu), 0.025, 0.05, 0.1, 0.2, and 0.4.
The NO conversions of the Cu/SAPO-34 catalysts with different Cu/Si atom ratios are shown in Figure
Effect of the Cu contents of crystallization gel of Cu/SAPO-34 on NO conversion (GHSV: 10,000 h−1).
C3H6-SCR
NH3-SCR
When the reductant was NH3, the NO conversions of all catalysts were much higher than using C3H6 as the reductant in the temperature range of 100–600°C. Particulary, at 600°C, the NO conversions of the Cu/SAPO-34 catalysts can reach to about 96% using NH3 as the reductant, while it only reached 65% using C3H6 as the reductant. In addition, like C3H6, the NO conversions of the catalysts with Cu/Si atom ratios from 0.05 to 0.2 were higher than these with Cu/Si atom ratios of 0.025 and 0.4.
On the basis of the above results, it can be concluded that as the Cu/Si atom ratios of the crystallization gel were in the range of 0.05–0.2, the de-NO
The XRD patterns of the Cu/SAPO-34 catalysts with different Cu contents are shown in Figure
XRD patterns of SAPO-34 catalysts with different Cu contents in the crystallization gel.
The SEM images of the Cu/SAPO-34 catalysts with different Cu contents are displayed in Figure
Physical properties of the Cu/SAPO-34 catalysts with different Cu contents.
Physical properties | Samples | |||||
---|---|---|---|---|---|---|
a | b | c | d | e | f | |
Cu/Si atom ratio of initial gel | 0 | 0.025 | 0.05 | 0.1 | 0.2 | 0.4 |
Cu/Si atom ratio of Cu/SAPO-34 | 0 | 0.023 | 0.038 | 0.065 | 0.120 | 0.171 |
Relative crystallinity % | 98.36 | 94.21 | 93.81 | 94.83 | 99.65 | 92.18 |
Grain size/µm | 0.6–2.0 | 1.5–2.0 | 1.2–2.0 | 0.8–2.0 | 1.0–1.5 | 0.6–18 |
SEM images of Cu/SAPO-34 catalysts with different Cu contents ((a): Cu/Si = 0, (b): Cu/Si: = 0.025, (c): Cu/Si = 0.05, (d): Cu/Si = 0.1, (e): Cu/Si = 0.2, and (f): Cu/Si = 0.4).
For clarifying the effect of different Cu contents in Cu/SAPO-34 explicitly, the physical properties of samples are summarized in Table
For further improving the de-NO
NO conversion of PdCu/SAPO-34 and Cu/SAPO-34 catalysts (GHSV: 40,000 h−1).
When C3H6 was used as reducing agent and the temperature was below 300°C, the NO conversions of the PdCu/SAPO-34 catalysts were similar to the samples without Pd. However, when the temperature rises from 300°C to 600°C, the advantage of Pd became significant. The NO conversions of PdCu/SAPO-34 catalysts were much higher than these of Cu/SAPO-34 catalysts and it can reach to around 70%. It is also found that the de-NO
When NH3 was used as reducing agent, the NO conversions of the PdCu/SAPO-34 catalysts were similar to those of the Cu/SAPO-34 catalysts, especially, at the low temperature. The de-NO
The effects of aging on the de-NO
Figure
XRD patterns of Cu/SAPO-34 samples before and after aging.
In order to investigate the effect of aging on the morphology and structure of the Cu/SAPO-34 catalysts, the samples before and after aging were characterized by SEM and the results are shown in Figure
SEM images of Cu/SAPO-34 before ((a) and (b)) and after aging ((c) and (d)).
The activity test of the PdCu/SAPO-34 catalysts before and after aging in C3H6 and NH3 is also shown in Figures
The XRD patterns of the PdCu/SAPO-34 catalysts are shown in Figure
XRD patterns of PdCu/SAPO-34 before and after aging treatment.
The SEM images of the PdCu/SAPO-34 catalyst with Cu/Si = 0.05 and 0.2 are given in Figure
SEM images of PdCu/SAPO-34 before ((a) and (b)) and after aging ((c) and (d)).
It can be concluded that the de-NO
The Cu/SAPO-34 catalysts were successfully prepared by in-situ hydrothermal synthesis. The results of XRD and SEM analysis indicated that the addition of Cu does not change the CHA structure of SAPO-34 crystal and the prepared Cu/SAPO-34 catalysts were cubic crystals with similar averaged sizes (0.6–2
The antiaging performance of the Cu/SAPO-34 and PdCu/SAPO-34 catalysts was studied and the experiment results suggested that the de-NO
The authors gratefully thank NSFC (20906067), CPSF (2011M500543), and the Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi for their financial support.