Effects of metal modification on the performance of Pt/β-zeolite catalysts in the oxidation of HC, CO and SO2 in diesel exhaust
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摘要: 采用共浸渍法制备了Ce、Cr、Mo和Cu改性的Pt/β-分子筛催化剂, 运用氮吸附、XRD、H2-TPR、NH3-TPD和XPS等手段对该催化剂进行了表征, 研究了不同金属改性对催化剂的织构性质、骨架结构、表面酸性以及在模拟柴油车尾气中抑制SO2氧化性能和催化HC、CO氧化活性的影响。结果表明, 金属改性对催化剂织构性能和骨架结构影响较小。Cr、Mo和Cu的添加可以调变催化剂酸强度, 进而抑制SO2的氧化; Cu改性的催化剂具有最好的抑制SO2氧化的能力, 在350和450 ℃条件下, 与未改性Pt/β-分子筛催化剂相比, Cu改性催化剂上SO2转化率分别下降了70.4%和70.2%。然而, 改性金属与Pt物种之间产生的相互作用, 会使Pt物种更难还原, 导致Pt对HC和CO氧化的催化活性降低。Abstract: Pt/β-zeolite catalysts were modified with Ce, Cr, Mo and Cu by impregnation method and characterized by nitrogen sorption, XRD, H2-TPR, NH3-TPD and XPS; the effects of metal modification on the textural properties, skeletal structure, surface acidity as well as the catalytic performance in the oxidation of SO2, HC and CO in the simulated diesel exhaust gas were investigated. The results indicate that metal modification has little influence on the textural properties and skeletal structure of the Pt/β-zeolite catalyst, whereas the addition of Cu, Cr and Mo can change the acid strength and has a stronger inhibition effect on the oxidation of SO2. Especially, the Cu-modified Pt/β-zeolite catalyst exhibits the best ability to inhibit the oxidation of SO2; the SO2 conversions over Cu modified catalyst under 350 and 450 ℃ are decreased by 70.4% and 70.2%, respectively, in comparison with those over the unmodified Pt/β-zeolite catalyst. However, because of the interaction between metal and Pt species, Pt species becomes more difficult to reduce over the metal modified Pt/β-zeolite catalysts, which may lead to a decrease of their catalytic activity in the oxidation of HC and CO.
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Key words:
- metal modification /
- beta zeolite /
- diesel vehicles /
- exhaust purification /
- catalytic oxidation /
- HC /
- CO /
- SO2
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图 1 催化剂对C2H4和CO的氧化活性的影响
Figure 1 Activity of various catalysts in the oxidation C2H4 and CO
图 2 各催化剂的XRD谱图
Figure 2 XRD patterns of various catalysts
a: Pt-Cu/β; b: Pt-Mo/β; c: Pt-Cr/β; d: Pt-Ce/β; e: Pt/β; f: β
图 3 催化剂上Pt 4f XPS谱图
Figure 3 Pt 4f XPS spectra of various catalysts
a: Pt-Cu/β; b: Pt-Mo/β; c: Pt-Cr/β; d: Pt-Ce/β; e: Pt/β
图 4 催化剂的H2-TPR谱图
Figure 4 H2-TPR profiles of various catalysts
a: Pt-Cu/β; b: Pt-Mo/β; c: Pt-Cr/β; d: Pt-Ce/β; e: Pt/β
图 5 催化剂的NH3-TPD谱图
Figure 5 NH3-TPD patterns of catalysts
a: Pt-Cu/β; b: Pt-Mo/β; c: Pt-Cr/β; d: Pt-Ce/β; e: Pt/β
表 1 催化剂上C2H4和CO的起燃温度和完全转化温度以及SO2转化率
Table 1 Light off (t50) and complete conversion temperature (t90) for C2H4 and CO oxidation and the conversion of SO2 over various catalysts
Catalyst C2H4 oxidation CO oxidation SO2 conversion x/% t50/℃ t90/℃ Δ t /℃ t50/℃ t90/℃ Δ t /℃ 350 ℃ 400 ℃ Pt/ β 193 208 15 197 210 13 69.9 82.8 Pt-Ce/ β 198 219 21 197 208 11 80.2 100.0 Pt-Cr/ β 214 231 17 226 251 25 24.1 31.4 Pt-Mo/ β 222 236 14 204 230 26 34.4 45.4 Pt-Cu/ β 234 254 20 242 255 13 20.7 24.7 reaction conditions: 0.07% NO, 0.056% C2H4, 0.112% CO, 0.02% SO2, 6% CO2, 12% O2, 10% H2O, balanced with N2; GHSV=30 000 h-1, t50 and t90 are defined as the temperatures for 50% and 90% conversion, respectively, Δt is difference between t90 and t50 
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表 2 Pt-M/β-分子筛催化剂的比表面积和孔体积
Table 2 Specific surface area and pore volume of the Pt-M/β-zeolite catalysts modified with different metals
Catalyst ABET /(m2·g-1) vs/(mL·g-1) Pt/ β 429 0.46 Pt-Ce/ β 431 0.46 Pt-Cr/ β 424 0.46 Pt-Mo/ β 421 0.45 Pt-Cu/ β 435 0.47
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