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挥发性有机物(volatile organic compounds, VOCs)是一类备受关注的气态污染物,严重危害着环境和人体健康[1]. 催化燃烧法是目前最常用的VOCs治理技术之一,具有去除效率高、运行费用低、二次污染少等优点. 贵金属具有优异的催化氧化VOCs的活性[2],但价格昂贵、稳定性较差,因此研究者们将目光转向非贵金属. 其中,过渡金属锰价态丰富,氧传递性好,在VOCs催化燃烧领域具有良好的应用前景[3-5]. Jung等[6]发现,煅烧温度会影响MnOx/γ-Al2O3表面吸附氧的比例,相比于500 ℃和700 ℃,900 ℃下煅烧制备的Mn/Al(900)的表面吸附氧比例最高,催化氧化甲苯的活性也最强(T90≈325 ℃, WHSV= 30000 mL·g−1·h−1);Huang等[7]探究了负载量对MnOx/HZSM-5催化氧化甲苯活性的影响,发现锰负载量为10%的MnOx/HZSM-5活性最佳(T90=267 ℃, WHSV = 15000 mL·g−1·h−1);本课题组[8]发现,增大载体孔径可提升MnOx/MCM-41催化氧化甲苯的活性,以孔径4.64 nm的MCM-41制备的MnOx/M3活性最高(T90=335 ℃, WHSV= 50000 mL·g−1·h−1).
相比于传统的水溶液浸渍法,合适地改变浸渍液溶剂可以改善催化剂性能. Tian等[9-10]和Xie等[11]分别用乙醇浸渍法和乙二醇辅助浸渍法将镍负载于介孔分子筛孔道内,大大提高了镍的分散度,从而改善了催化剂活性和稳定性. 但是,关于浸渍液溶剂对负载型锰基催化剂的结构及催化氧化VOCs性能的影响研究较少.
本文以MCM-41为载体,采用等体积浸渍法制备负载型催化剂MnOx/MCM-41,探究浸渍液溶剂(水、乙醇和乙二醇)对MnOx/MCM-41的结构及其催化氧化甲苯的性能的影响,并借助XRD、TEM、H2-TPR、O2-TPD和XPS等表征手段,探讨催化剂的构效关系.
浸渍液溶剂对负载型MnOx/MCM-41结构及其催化氧化甲苯性能的影响
Influence of impregnation solvent on structure and catalytic oxidation of toluene over MnOx/MCM-41
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摘要: 以MCM-41为载体,用水、乙醇和乙二醇作为浸渍液溶剂制备了3种负载型催化剂MnOx/MCM-41,采用XRD、TEM、H2-TPR、O2-TPD和XPS等对催化剂进行了表征,探究了浸渍液溶剂(水、乙醇、乙二醇)对MnOx/MCM-41的结构及催化氧化甲苯性能的影响. 结果表明,乙二醇作浸渍液溶剂可提高锰氧化物的分散度、氧化还原性和表面吸附氧的含量. 因而,在相同的质量空速下(WHSV = 50000 mL·g−1·h−1),相比于水溶液浸渍法制备的MnOx/M-W(T90=289 ℃)和乙醇溶液浸渍法制备的MnOx/M-ET(T90=277 ℃),乙二醇共浸渍法制备的MnOx/M-EG具有最强的催化活性(T90=268 ℃);20 h的稳定性评价实验结果表明,MnOx/M-EG具有较好的稳定性.Abstract: Three MnOx/MCM-41 catalysts were prepared by incipient wetness impregnation method using water, ethanol and ethylene glycol as solvents, and were marked as MnOx/M-W, MnOx/M-ET, and MnOx/M-EG, respectively. The influence of the impregnation solvents on the properties of MnOx/MCM-41 was studied by XRD, TEM, H2-TPR, O2-TPD and XPS. Moreover, the catalytic oxidation of toluene on three MnOx/MCM-41catalysts was investigated. The results showed that the ethylene glycol as impregnation solvent could improve the dispersion and redox properties of manganese oxides as well as the amount of surface adsorbed oxygen species on MCM-41. Under the same WHSV (50000 mL·g−1·h−1), the MnOx/M-EG exhibited the best catalytic activity (T90=268 ℃) compared to MnOx/M-W (T90=289 ℃) and MnOx/M-ET (T90=277 ℃). In addition, a 20 h stability test showed that MnOx/M-EG had good catalytic stability.
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Key words:
- VOCs /
- MCM-41 /
- solvents of impregnation solution /
- catalytic oxidation.
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表 1 3种MnOx/MCM-41催化剂的孔结构参数
Table 1. Pore structure properties of three kinds of MnOx/MCM-41
样品
Sample负载量
Mn contentBET比表面积/(m2·g−1)
BET surface area孔容/(cm3·g−1)
Pore volume平均孔径/nm
Average pore diameterMCM-41 — 745.9 0.92 4.64 MnOx/M-W 9.63% 609.6 0.73 4.57 MnOx/M-ET 9.16% 606.4 0.72 4.61 MnOx/M-EG 9.29% 624.5 0.71 4.35 表 2 3种MnOx/MCM-41催化剂的H2-TPR表征结果
Table 2. H2-TPR results of three kinds of MnOx/MCM-41
样品
Sample还原温度/℃
Reduction temperature耗H2量/(mmol·g−1)
H2 consumptionOads/Olat 峰Ⅰ
Peak Ⅰ峰Ⅱ
Peak II峰Ⅰ
Peak I峰Ⅱ
Peak II总量
TotalMnOx/M-W 297 421 0.80 0.34 1.14 0.18 MnOx/M-ET 297 421 0.69 0.36 1.05 0.21 MnOx/M-EG 286 339 0.26 0.50 0.76 0.25 表 3 3种MnOx/MCM-41催化剂的XPS结果
Table 3. XPS results of three kinds of MnOx/MCM-41
样品
SampleMn3+/% Mn4+/% Mn3+/Mn4+ Oads/% Olat/% Oads/Olat MnOx/M-W 39.7 60.3 0.66 25.9 74.1 0.35 MnOx/M-ET 46.2 53.8 0.86 34.1 65.9 0.52 MnOx/M-EG 50.8 49.2 1.03 35.8 64.2 0.56 表 4 3种MnOx/M CM-41催化剂催化氧化甲苯的活性
Table 4. The catalytic activity for toluene combustion over three kinds of MnOx/MCM-41
样品
SampleT10/℃ T50/℃ T90/℃ MnOx/M-W 253 275 289 MnOx/M-ET 240 264 277 MnOx/M-EG 233 255 268 -
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