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Effects of SO 2 on selective catalytic reduction of NO with NH 3 over a TiO 2 photocatalyst

View Article: PubMed Central - PubMed

ABSTRACT

The effect of SO2 gas was investigated on the activity of the photo-assisted selective catalytic reduction of nitrogen monoxide (NO) with ammonia (NH3) over a TiO2 photocatalyst in the presence of excess oxygen (photo-SCR). The introduction of SO2 (300 ppm) greatly decreased the activity of the photo-SCR at 373 K. The increment of the reaction temperature enhanced the resistance to SO2 gas, and at 553 K the conversion of NO was stable for at least 300 min of the reaction. X-ray diffraction, FTIR spectroscopy, thermogravimetry and differential thermal analysis, x-ray photoelectron spectroscopy (XPS), elemental analysis and N2 adsorption measurement revealed that the ammonium sulfate species were generated after the reaction. There was a strong negative correlation between the deposition amount of the ammonium sulfate species and the specific surface area. Based on the above relationship, we concluded that the deposition of the ammonium sulfate species decreased the specific surface area by plugging the pore structure of the catalyst, and the decrease of the specific surface area resulted in the deactivation of the catalyst.

No MeSH data available.


FTIR spectra of the catalysts and the reference samples in the region of (A) 900–1800 cm−1 and (B) 2400–4000 cm−1. (a) BR, (b) AR-373K, (c) AR-433K, (d) AR-533K, (e) (NH4)2SO4 and (f) Na2SO4. Spectra are offset for clarity.
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Figure 3: FTIR spectra of the catalysts and the reference samples in the region of (A) 900–1800 cm−1 and (B) 2400–4000 cm−1. (a) BR, (b) AR-373K, (c) AR-433K, (d) AR-533K, (e) (NH4)2SO4 and (f) Na2SO4. Spectra are offset for clarity.

Mentions: Figure 3(A) shows the FTIR spectra of the catalysts in the region of 900–1800 cm−1. In all the catalysts, a band at 1633 cm−1 was observed and was attributed to the deformation vibration of water molecules adsorbed on the TiO2 surface. New bands at 1401, 1242, 1116, 1054 and 978 cm−1 appeared after the reaction in the presence of SO2 at 373 K. The sharp band at 1401 cm−1 was assigned to the bending vibration of ammonium (NH4+) ions [20] and was also observed in the case of the reference (NH4)2SO4 powder. Free sulfate ions (Td symmetry) show two infrared peaks at 1104 (ν3) and 613 (ν4) cm−1 [20]. The band at 1116 cm−1 was due to ν3 vibration of free sulfate ions and was also observed in both the cases of (NH4)2SO4 and Na2SO4. When a ion is bound to the TiO2 surface, the symmetry can be lowered to either C3v or C2v. The lowering symmetry causes the split of the ν3 vibration band into two peaks for a C3v symmetry and splits into three peaks for a C2v symmetry [20]. Thus, the bands at 1242, 1054 and 978 cm−1 are assigned to the surface-coordinated ions. The surface-coordinated ions could have the C2v symmetry based on the number of bands. The ion with a C2v configuration is either chelating bidentate or bridge bidentate [20]. In AR-433K, the shape of the spectrum was similar to that of AR-373K, although the absorbance of the bands at 1401 and 1116 cm−1 were slightly weaker than those of AR-373K. In AR-553K, the band at 1116 cm−1 disappeared, which means that the deposition of free sulfates was inhibited in the reaction at 553 K, although the other bands at 1401, 1054 and 978 cm−1 remained. In the region of 2400–4000 cm−1 (figure 3(B)), three adsorption bands at 3425, 3136 and 3023 cm−1 were observed after the reaction at 373 K. The broad band between 3600–2800 cm−1 is the stretching vibration of OH groups derived from surface hydroxyl groups and adsorbed water molecules, which also appeared in the sample before the reaction. The other two bands were observed in the catalysts after the reaction. The bands at 3136 and 3023 cm−1 are attributed to the asymmetric stretching vibration (ν3) and symmetric stretching vibration (ν1) of the NH4+ ions, respectively. The two bands also appeared in the case of (NH4)2SO4, which strongly advocated the generation of NH4+ ions after the reaction. The peak intensity at 3136 and 3023 cm−1 decreased as the reaction temperature increased, which was consistent with the decrease of the band at 1401 cm−1 in figure 3(A). The FTIR results clearly revealed the generation of the free and surface-coordinated ions and NH4+ ions on the TiO2 surface after the reaction. The conversion of NO after 300 min of the reaction decreased in the following order: AR-553K (80.1%) > AR-433K (37.2%) > AR-373K (12.9%). The order was consistent with that of the peak intensities of the free ions and NH4+ ions, which suggests that the generation of ammonium sulfate species (e.g. (NH4)2SO4 and (NH4)HSO4) induced the deactivation of the catalyst.


Effects of SO 2 on selective catalytic reduction of NO with NH 3 over a TiO 2 photocatalyst
FTIR spectra of the catalysts and the reference samples in the region of (A) 900–1800 cm−1 and (B) 2400–4000 cm−1. (a) BR, (b) AR-373K, (c) AR-433K, (d) AR-533K, (e) (NH4)2SO4 and (f) Na2SO4. Spectra are offset for clarity.
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Figure 3: FTIR spectra of the catalysts and the reference samples in the region of (A) 900–1800 cm−1 and (B) 2400–4000 cm−1. (a) BR, (b) AR-373K, (c) AR-433K, (d) AR-533K, (e) (NH4)2SO4 and (f) Na2SO4. Spectra are offset for clarity.
Mentions: Figure 3(A) shows the FTIR spectra of the catalysts in the region of 900–1800 cm−1. In all the catalysts, a band at 1633 cm−1 was observed and was attributed to the deformation vibration of water molecules adsorbed on the TiO2 surface. New bands at 1401, 1242, 1116, 1054 and 978 cm−1 appeared after the reaction in the presence of SO2 at 373 K. The sharp band at 1401 cm−1 was assigned to the bending vibration of ammonium (NH4+) ions [20] and was also observed in the case of the reference (NH4)2SO4 powder. Free sulfate ions (Td symmetry) show two infrared peaks at 1104 (ν3) and 613 (ν4) cm−1 [20]. The band at 1116 cm−1 was due to ν3 vibration of free sulfate ions and was also observed in both the cases of (NH4)2SO4 and Na2SO4. When a ion is bound to the TiO2 surface, the symmetry can be lowered to either C3v or C2v. The lowering symmetry causes the split of the ν3 vibration band into two peaks for a C3v symmetry and splits into three peaks for a C2v symmetry [20]. Thus, the bands at 1242, 1054 and 978 cm−1 are assigned to the surface-coordinated ions. The surface-coordinated ions could have the C2v symmetry based on the number of bands. The ion with a C2v configuration is either chelating bidentate or bridge bidentate [20]. In AR-433K, the shape of the spectrum was similar to that of AR-373K, although the absorbance of the bands at 1401 and 1116 cm−1 were slightly weaker than those of AR-373K. In AR-553K, the band at 1116 cm−1 disappeared, which means that the deposition of free sulfates was inhibited in the reaction at 553 K, although the other bands at 1401, 1054 and 978 cm−1 remained. In the region of 2400–4000 cm−1 (figure 3(B)), three adsorption bands at 3425, 3136 and 3023 cm−1 were observed after the reaction at 373 K. The broad band between 3600–2800 cm−1 is the stretching vibration of OH groups derived from surface hydroxyl groups and adsorbed water molecules, which also appeared in the sample before the reaction. The other two bands were observed in the catalysts after the reaction. The bands at 3136 and 3023 cm−1 are attributed to the asymmetric stretching vibration (ν3) and symmetric stretching vibration (ν1) of the NH4+ ions, respectively. The two bands also appeared in the case of (NH4)2SO4, which strongly advocated the generation of NH4+ ions after the reaction. The peak intensity at 3136 and 3023 cm−1 decreased as the reaction temperature increased, which was consistent with the decrease of the band at 1401 cm−1 in figure 3(A). The FTIR results clearly revealed the generation of the free and surface-coordinated ions and NH4+ ions on the TiO2 surface after the reaction. The conversion of NO after 300 min of the reaction decreased in the following order: AR-553K (80.1%) > AR-433K (37.2%) > AR-373K (12.9%). The order was consistent with that of the peak intensities of the free ions and NH4+ ions, which suggests that the generation of ammonium sulfate species (e.g. (NH4)2SO4 and (NH4)HSO4) induced the deactivation of the catalyst.

View Article: PubMed Central - PubMed

ABSTRACT

The effect of SO2 gas was investigated on the activity of the photo-assisted selective catalytic reduction of nitrogen monoxide (NO) with ammonia (NH3) over a TiO2 photocatalyst in the presence of excess oxygen (photo-SCR). The introduction of SO2 (300 ppm) greatly decreased the activity of the photo-SCR at 373 K. The increment of the reaction temperature enhanced the resistance to SO2 gas, and at 553 K the conversion of NO was stable for at least 300 min of the reaction. X-ray diffraction, FTIR spectroscopy, thermogravimetry and differential thermal analysis, x-ray photoelectron spectroscopy (XPS), elemental analysis and N2 adsorption measurement revealed that the ammonium sulfate species were generated after the reaction. There was a strong negative correlation between the deposition amount of the ammonium sulfate species and the specific surface area. Based on the above relationship, we concluded that the deposition of the ammonium sulfate species decreased the specific surface area by plugging the pore structure of the catalyst, and the decrease of the specific surface area resulted in the deactivation of the catalyst.

No MeSH data available.