Effect of Mn content on the catalytic performance of CeO2-ZrO2-MnOx in the oxidation of toluene
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摘要: 采用氧化还原沉淀法制备了一系列CeO2-ZrO2-MnOx催化剂（CZMX，X为Mn在催化剂总金属中的摩尔含量），探讨了Mn含量对CZMX催化甲苯燃烧性能的影响。结果表明，CZM0.6催化剂具有最好的活性，在230℃下即可实现甲苯的完全转化。XRD表征结果发现，随着锰掺杂量的增加，CZMX催化剂结晶度先降低后增加。H2-TPR表征结果表明，随着Mn含量的增加，Ce-Zr-Mn之间的相互作用力先增强后减弱。CZM0.6结晶度最差，金属之间相互作用力最强，表面氧物种更易溢出；同时，Raman和O2-TPD表征结果也证明CZM0.6催化剂上具有较高的表面氧空位浓度，有利于催化剂表面活性氧物种的迁移，促进了甲苯的氧化。此外，通过in-situ DRIFTS对中间产物进行观测，发现苯甲酸盐是CZM0.6催化剂上甲苯氧化反应的重要中间体；在O2参与下，苯甲酸盐可迅速转化为CO2和H2O。
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关键词:
- 氧化还原沉淀法 /
- CeO2-ZrO2-MnOx /
- 甲苯催化氧化 /
- 表面氧物种 /
- 苯甲酸盐
Abstract: A series of CeO2-ZrO2-MnOx catalysts with different Mn contents (denoted as CZMX, where X is the molar fraction of MnOx) were prepared by the redox precipitation method; the effect of Mn content on the catalytic performance of CZMX in the oxidative degradation of toluene was then investigated. The results indicate that that the CZM0.6 catalyst exhibits the best performance in toluene oxidation; a complete conversion of toluene can be achieved at 230℃. The XRD results suggest that the crystallinity of CZMX decreases first, steps over the valley and then increases again with the increase of Mn content. From the H2-TPR characterization, in contrast, a volcanic tendency is observed for the interaction among Ce-Zr-Mn. In particular, the CZM0.6 catalyst displays poorest crystallinity and strongest Ce-Zr-Mn interaction, which can enhance the surface oxygen species. Meanwhile, the Raman and O2-TPD results prove that the abundant oxygen vacancies on the catalyst surface can promote the migration of surface active oxygen species and then enhance the catalytic performance of CZMX in toluene oxidation. In addition, the in-situ DRIFTS results illustrate that the reaction of toluene oxidation over the CeO2-ZrO2-MnOx catalysts proceeds via benzoic acid as the essential intermediate, which is rapidly converted to CO2 and H2O in the presence of O2. -
图 1 Mn含量对CZM催化剂甲苯催化性能的影响
Figure 1 Effect of Mn content on the catalytic performance of CZMX in toluene oxidation
图 2 不同催化剂的N2吸附-脱附等温线(a)及平均宽度曲线(b)
Figure 2 N2 adsorption-desorption isotherms (a) and average width curves (b) of various CZMX catalysts
图 7 不同催化剂上甲苯吸附(a)和纯N2吹扫(b)及CZM0.6共吸附(c)的DRIFTS光谱谱图
Figure 7 DRIFTS spectra of toluene adsorption on different catalysts (a) and pure N2 purge on different catalysts (b) and O2 and toluene co-adsorption on CZM0.6 (c)
图 8 CZM0.6不同空速测试(a)和稳定性测试(b)
Figure 8 Toluene oxidation over CZM0.6 under different space velocity (a) and stability test of CZM0.6 at 280 ℃ (b)
表 1 不同催化剂的孔结构参数
Table 1 Pore structure parameters of various CZMX catalysts
Sample ABET/(m2·g-1) Average pore size d/nm CZM0.8 139.2 5.4 CZM0.6 122.9 5.4 CZM0.4 126.1 4.9 CZM0.2 156.8 4.1 
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