Insight into the catalytic oxidation of toluene over M/ZSM-5 (M=Cu, Mn, Fe, Ce, Ti) catalysts
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摘要: 以ZSM-5分子筛为载体,采用浸渍法负载Cu、Mn、Fe、Ce、Ti制备一系列金属氧化物催化剂,利用SEM、XRD、N2吸附-脱附、XPS、H2-TPR对催化剂的理化性质进行了表征,并考察了催化剂的催化氧化甲苯性能。结果表明,Cu/ZSM-5表面粗糙,金属元素分布均匀,具有较好的孔径结构、良好的低温还原性和丰富的吸附氧物种,且负载量为5%的Cu/ZSM-5表现出优异的甲苯催化活性和最佳的抗硫性,在SO2环境下t90为224 ℃ (GHSV=24000 h−1)。原位红外测试结果表明,甲苯的降解遵循以下途径,甲苯首先被吸附在催化剂表面形成吸附态甲苯,随后在催化剂作用下依次被转化为苯甲醛和苯甲酸,再经过开环反应形成马来酸、羧酸等小分子有机物,最终被氧化为CO2和H2O。Abstract: A series of metal oxide catalysts were prepared by impregnating Cu, Mn, Fe, Ce and Ti on ZSM-5 molecular sieve. The physicochemical properties of the catalysts were characterized by SEM, XRD, N2 adsorption/desorption, XPS, H2-TPR, and the catalytic oxidation of toluene was investigated. The results showed that Cu/ZSM-5 had rough surface, uniform distribution of metal, good pore structure, superior low-temperature reducibility and abundant adsorbed oxygen species. Cu/ZSM-5 with 5% loading exhibited excellent catalytic activity for toluene oxidation and the best sulfur resistance performance, with t90 (GHSV=24000 h−1) being 224 ℃ in SO2 environment. In-situ DRIFTS experiments revealed that the degradation path of toluene was as follows: toluene was first adsorbed on the surface of the catalyst to form adsorbed toluene, then it was converted into benzaldehyde and benzoic acid successively on the catalyst. And small molecule organics such as maleic acid and carboxylic acid were formed through ring opening reaction, and finally was oxidized to CO2 and H2O.
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Key words:
- toluene /
- catalytic oxidation /
- Cu/ZSM-5
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表 1 不同催化剂的孔结构参数
Table 1 Structure properties of different catalysts.
Catalyst BET surface area /
(m2·g−1)Micropore volume /
(cm3·g−1)Mesopore volume /
(cm3·g−1)Pore volume /
(cm3·g−1)Average pore diameter /
nmZSM-5 400.7 0.085 0.175 0.261 2.60 Cu/ZSM-5 276.8 0.083 0.097 0.180 2.61 Mn/ZSM-5 291.1 0.082 0.106 0.188 2.58 Fe/ZSM-5 264.9 0.089 0.077 0.166 2.50 Ce/ZSM-5 294.6 0.098 0.078 0.175 2.38 Ti/ZSM-5 310.4 0.075 0.134 0.209 2.69 表 2 不同催化剂中氧物种物质的量比和耗氢量
Table 2 Molar ratio of oxygen species of different catalysts and H2 consumption
Catalyst Cu/ZSM-5 Mn/ZSM-5 Fe/ZSM-5 Ti/ZSM-5 Ce/ZSM-5 Olatt /% 3.98 16.75 12.81 27.98 15.81 Oads /% 94.27 81.31 87.19 67.17 80.87 Oads/Olatt 23.69 4.85 6.81 2.40 5.12 H2 consumption
/(mmol·g−1)2.10 1.44 2.19 0.54 0.15 -
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