Effect of Pr/Zr atomic ratio on the activity of catalytic oxidation denitration of PrxZr1−xO2–δ
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摘要: 采用溶胶-凝胶法制备了不同Pr/Zr原子比的PrxZr1−xO2−δ催化剂用于催化氧化脱硝。结果表明，催化氧化脱硝效率随Pr原子比的增加而先提高后降低；当Pr/Zr原子比为5∶5时，在250 °C下，最佳脱硝活性可达94.62%。采用SEM、N2 吸附-脱附、XRD、XPS、H2-TPR和FT-IR对催化剂进行了表征。结果表明，活性最好的催化剂（Pr0.5Zr0.5O2−δ）具有“层状”形貌，表面孔隙多，比表面积大，孔体积分别为77.74 m2/g和0.66 cm3/g。此外，随着Pr原子的增加，晶相从c-ZrO2 转变为Pr2Zr2O7。XPS和H2-TPR结果表明，表面化学吸附氧和表面Pr4 + 氧化物增加，Pr原子比的上升有利于产生氧空位（Vӧ），有利于提高催化氧化脱硝效率。FT-IR表征结果表明，Pr0.5Zr0.5O2−δ固溶体具有较高的NO选择性，有利于NO的催化氧化。抗SO2和H2O毒性实验表明，5∶5的Pr/Zr原子比的催化剂具有更好的抗毒性。此外，利用IC分析吸收产物，结果表明，吸收液中的主要产物是
${\rm{NO}}^-_2 $ 和${\rm{NO}}^-_3 $ 。-
关键词:
- 催化氧化 /
- 氮氧化物 /
- PrxZr1−xO2−δ /
- Pr/Zr原子比
Abstract: The PrxZr1−xO2–δ catalyst with different atom ratio of Pr/Zr was prepared by the sol-gel to catalytic oxidation denitration. Results showed that the efficiency of catalytic oxidation denitration increased initially and decreased afterward with the ratio of Pr atom increased. And the optimum denitration activity could achieve 94.62% at 250 °C when the atom ratio of Pr/Zr was 5∶5. The catalysts were characterized by SEM, N2 adsorption-desorption, XRD, XPS, H2-TPR, and FT-IR. The results illustrated that the catalyst (Pr0.5Zr0.5O2−δ) with the best activity has a “layered” morphology, many pores on the surface, and it has a large specific surface area and pore volume of 77.74 m2/g and 0.66 cm3/g, respectively. Furthermore, the crystalline phase transforms from c-ZrO2 to Pr2Zr2O7 with the increasing of Pr atom. XPS and H2-TPR results showed that the surface chemosorption oxygen and surface Pr4 + oxides increased, and the rising of Pr atom ratio was beneficial to produce oxygen vacancy (Vӧ) site which advantageous to improve the efficiency of catalytic oxidation denitration. FT-IR characterization results indicated that Pr0.5Zr0.5O2−δ solid solution had better NO selectivity, which was conducive to the catalytic oxidation of NO. The anti-SO2 and H2O toxicity experiments showed that Pr/Zr atomic ratio at 5∶5 had better anti-toxicity than other ratios. In addition, using IC to analysis absorption products, the result showed that${\rm{NO}}^-_2 $ and${\rm{NO}}^-_3 $ were the main products in the absorption solution.-
Key words:
- catalytic oxidation /
- nitric oxides /
- PrxZr1−xO2−δ /
- atom ratio of Pr/Zr
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Figure 2 Catalytic oxidation deNOx efficiency of PrxZr1−xO2−δ catalysts with different atom ratios of Pr/Zr (the rotator speed was 800 r/min, the solution concentration of Na2CO3 was 0.02 mol/L)
Figure 3 SEM picture of PrxZr1−xO2−δ catalysts with different atom ratios of Pr/Zr
(a): Pr0.1Zr0.9O2−δ; (b): Pr0.2Zr0.8O2−δ; (c): Pr0.3Zr0.7O2−δ; (d): Pr0.4Zr0.6O2−δ; (e): Pr0.5Zr0.5O2−δ; (f): Pr0.6Zr0.4O2−δ
Figure 4 N2 adsorption-desorption isotherm (a) the pore size distribution (b) of PrxZr1−xO2−δ catalysts with different atom ratios of Pr/Zr
Figure 5 XRD patterns of the PrxZr1−xO2−δ catalysts with different atomic ratios of Pr/Zr
Figure 6 XPS spectrum of PrxZr1−xO2−δ with different atom ratios of Pr/Zr (a): XPS survey; (b): Pr 3d; (c): Zr 3d; (d): O 1s
Figure 9 Effect of SO2 on the catalytic oxidation removal of NOx activity by PrxZr1−xO2−δ catalyst
(Absorbent solution: 0.02 mol/L Na2CO3, absorbent solution flow rate: 60 mL/min, gas flow rate: 300 mL/min, gas-liquid ratio: 5∶1, RPB rotor speed: 800 r/min)
Figure 10 Effect of H2O on the catalytic oxidation removal of NOx activity by PrxZr1−xO2−δ catalyst
(Absorbent solution: 0.02 mol/L Na2CO3, absorbent solution flow rate: 60 mL/min, gas flow rate: 300 mL/min, gas-liquid ratio: 5∶1, RPB rotor speed: 800 r/min)
Figure 11 Product analysis of NOx absorption liquid by catalytic oxidation of PrxZr1−xO2−δ catalyst
(Absorbent solution: 0.02 mol/L Na2CO3, absorbent solution flow rate: 60 mL/min, gas flow rate: 300 mL/min, gas-liquid ratio: 5∶1, RPB rotor speed: 800 r/min)
Table 1 Specific surface area and total pore volume of PrxZr1−xO2−δ with different atom ratios of Pr/Zr
Catalyst Specific area /(m2·g−1) Pore volume /(cm3·g−1) Pr0.1Zr0.9O2−δ 26.52 0.28 Pr0.2Zr0.8O2−δ 30.70 0.30 Pr0.3Zr0.7O2−δ 89.03 0.19 Pr0.4Zr0.6O2−δ 51.77 0.52 Pr0.5Zr0.5O2−δ 77.74 0.66 Pr0.6Zr0.4O2−δ 91.92 0.62 
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Table 2 Results of the Pr 3d spectrum of PrxZr1−xO2−δ with different atom ratios of Pr/Zr
Catalyst Pr /% Pr 3d5/2 /eV Pr 3d3/2 /eV ∆E1 /eV Satellite 1 Satellite 2 ∆E2 /eV Pr4 + /(Pr3 + + Pr4 + ) Pr0.1Zr0.9O2−δ 9.09 953.39 933.22 20.17 948.56 928.98 19.58 0.35 Pr0.2Zr0.8O2−δ 13.77 953.26 933.11 20.15 948.42 928.84 19.58 0.36 Pr0.3Zr0.7O2−δ 20.50 953.54 933.41 20.13 948.81 929.23 19.58 0.37 Pr0.4Zr0.6O2−δ 25.97 954.02 933.81 20.21 949.14 929.56 19.58 0.39 Pr0.5Zr0.5O2−δ 26.36 953.23 933.05 20.18 948.30 928.72 19.58 0.42 Pr0.6Zr0.4O2−δ 29.17 953.24 933.06 20.18 948.22 928.64 19.58 0.59
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Table 3 Result of O 1s spectrum of PrxZr1−xO2−δ with different atom ratios of Pr/Zr
Catalyst Oα /% Oβ /% Oγ /% (Oβ + Oγ)/Oα Pr0.1Zr0.9O2−δ 40.10 10.04 5.81 0.39 Pr0.2Zr0.8O2−δ 38.90 8.91 7.51 0.42 Pr0.3Zr0.7O2−δ 28.42 28.68 5.99 1.22 Pr0.4Zr0.6O2−δ 30.45 24.25 4.51 0.94 Pr0.5Zr0.5O2−δ 23.87 29.16 3.52 1.37 Pr0.6Zr0.4O2−δ 28.61 28.95 1.07 1.04
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Table 4 Integral result H2-TPR reduction peaks of PrxZr1−xO2−δ catalysts
Catalyst α /% β /% α/β Pr0.1Zr0.9O2−δ 9.31 90.69 0.10 Pr0.2Zr0.8O2−δ 13.77 86.23 0.16 Pr0.3Zr0.7O2-δ 14.43 85.57 0.17 Pr0.4Zr0.6O2−δ 31.23 68.77 0.45 Pr0.5Zr0.5O2−δ 72.04 27.96 2.58 Pr0.6Zr0.4O2−δ 62.81 36.48 1.72
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