Comparison of titania nanotubes and titanium dioxide as supports of low-temperature selective catalytic reduction catalysts under sulfur dioxide poisoning

Figures & data

Figure 1. Schematic diagram of the experimental setup.

Table 1. Characterization of the MnFe-TiO₂ and MnFe-TNT catalysts.

Support	Catalyst	Calcination temperature (°C)	Specific surface area (m^2/g)	Metal content		NH3-TPD desorption amount (mmol/g)
				Mn (wt%)	Fe (wt%)	200– 500 °C	500– 850 °C
TiO2 support	MnFe-P25	350	70	11.4	12.0	0.23	0.42
		450	73	—	—	0.36	0.49
		550	52	—	—	0.10	0.38
	MnFe-ST01	350	140	12.0	12.7	0.40	0.31
		450	123	—	—	0.38	0.50
		550	78	—	—	0.26	0.55
	MnFe-TiO(OH)2	350	100	11.1	13.4	0.44	0.89
		450	87	—	—	0.38	0.90
		550	66	—	—	0.24	0.93
TNT support	MnFe-TNT(P25)	350	305	11.7	12.0	0.92	0.30
		450	220	—	—	0.75	0.35
		550	112	—	—	0.39	0.49
	MnFe-TNT(ST01)	350	281	10.8	12.1	0.84	0.26
		450	247	—	—	0.74	0.36
		550	182	—	—	0.32	0.42
	MnFe-TNT(TiO(OH)2)	350	243	11.9	12.5	0.88	0.35
		450	136	11.3	11.8	0.60	0.43
		550	122	11.7	12.1	0.57	0.51

Figure 2. SEM images of catalysts prepared at calcination temperature 350 °C: (a) MnFe-TiO(OH)₂; (b) MnFe-TNT(TiO(OH)₂).

Figure 3. XRD patterns of catalysts prepared under different calcination temperatures: (a) MnFe-TiO₂; (b) MnFe-TNTs.

Figure 4. NH₃-TPD patterns of MnFe-TiO₂ and MnFe-TNT catalysts at calcination temperature of 350 °C. The solid lines represent for the results of MnFe supported on TiO₂, whereas the dash lines are for those on TNTs.

Figure 5. NH₃-TPD patterns of (a) MnFe-TiO₂ and (b) MnFe-TNTs (both made from TiO(OH)₂) calcined at different temperatures.

Figure 6. Correlation between NH₃-TPD desorption amounts (200~500 °C, Brønsted acid sites) and the specific surface areas of all TiO₂- and TNT-based MnFe catalysts.

Figure 7. Comparison of NO conversion between TiO₂- and TNT- (both made from TiO(OH)₂) based MnFe catalysts calcined at 350 °C in the NH₃-SCR reaction. Reaction conditions: reaction temperature = 150 °C, [NO] = 220 ppm, [NH₃] = 200 ppm, [SO₂] = 100 ppm, [O₂] = 15%, balanced with air, and GHSV = 20,000 hr⁻¹.

Figure 8. NO conversion with and without the presence of SO₂ in the NH₃-SCR reaction over MnFe-TiO₂ and MnFe-TNT (both made from TiO(OH)₂) catalysts at different calcination temperatures. Reaction conditions: reaction temperature = 150 °C, [NO] = 220 ppm, [NH₃] = 200 ppm, [SO₂] = 100 ppm, [O₂] = 15%, balanced with air, and GHSV = 20,000 hr⁻¹.

Figure 9. The effect of specific surface area of catalysts on the NO conversion at SCR temperature of 150 °C with and without the presence of SO₂. The data of without SO₂ were averaged over 3 hr of operation time, whereas the data with SO₂ was after 5 hr of SO₂ poisoning.

Figure 10. XPS spectra of Mn 2p spectra for (a) MnFe-TiO₂ and (b) MnFe-TNTs before and after poisoning by SO₂. The two MnFe-TiO₂ and MnFe-TNT catalysts were both made from TiO(OH)₂.

Figure 11. Effect of gas hourly space velocity (GHSV) on the NO conversion over the MnFe-TNT(TiO(OH)₂)(350) catalyst. Reaction conditions: reaction temperature = 150 °C, [NO] = 220 ppm, [NH₃] = 200 ppm, [SO₂] = 100 ppm, [O₂] = 15%, balanced with air.

Figure 12. Effect of reaction temperature on the NO conversion over the MnFe-TNT(TiO(OH)₂)(350) catalyst. Reaction conditions: [NO] = 220 ppm, [NH₃] = 200 ppm, [SO₂] = 100 ppm, [O₂] = 15%, balanced with air, and GHSV = 20,000 hr⁻¹.

Figure 13. Effect of [NH₃]/[NO] ratio on the NO conversion over the MnFe-TNT(TiO(OH)₂)(350) catalyst. Reaction conditions: reaction temperature = 150 °C, [NO] = 220 ppm, [NH₃] = 200~400 ppm, [SO₂] = 100 ppm, [O₂] = 15%, balanced with air, and GHSV = 20,000 hr⁻¹.

Figure 14. (a) TGA spectra and (b) DTG spectra of fresh and poisoned catalysts. Reaction conditions: reaction temperature = 150 °C, [NO] = 220 ppm, [NH₃] = 200 ppm, [SO₂] = 100 ppm, [O₂] = 15%, balanced with air, and GHSV = 20,000 hr⁻¹.

Table 2. The specific surface areas after SO₂ poisoning and the amounts of SO₂ poisoning products on the MnFe-TiO(OH)₂ and MnFe-TNT(TiO(OH)₂) catalysts.

Parameter	MnFe-TiO(OH)2			MnFe-TNT(TiO(OH)2)
	8 hr^a		24 hr	8 hr	24 hr
Specific surface area (m^2/g)	53	—		155		—
Ammonium sulfate^b (wt.%)	0.74	1.49		0.53		1.10
Metal sulfates (wt%)	3.36	4.69		3.71		5.81

^aFor the 8-hr SO₂ poisoning test, it was conducted by 3-hr test in the absence of SO₂ first, then followed by 5 hr in the presence of SO₂. For the 24-hr test, it was conducted by 3-hr test in the absence of SO₂ first, then followed by 21 hr in the presence of SO₂.

^bThe amount of ammonium sulfate may include both (NH₄)₂SO₄ and NH₄HSO₄, since these two sulfate and bisulfate compounds could not be differentiated from the TGA results.