Ce改性贵金属催化剂降低卷烟烟气中CO性能的研究

Studies on Cerium modified noble metal catalysts for decreasing CO in cigarette smoke

以浸渍法制备了一系列添加CeO2的Pd-Ce/NaZSM-5负载型催化剂。以CO氧化为模型反应,考察了反应温度、Ce含量、预还原、空速及水蒸气等对CO氧化性能的影响,并利用XRD和XPS等手段对催化剂体相及表面结构进行了表征。结果表明:加入CeO2作助剂可明显提高催化剂的活性,且催化转化率随着反应温度及Ce含量的增加而增加,随着空速的增加而降低,催化剂对水蒸气不敏感,在水蒸气存在的条件下反应可连续进行720h以上保持CO完全转化,H2还原作用使催化剂活性有所提高。XRD测试结果表明,催化剂中Pd组分处于高分散状态,CeO2的引入促进了Pd物种在NaZSM-5载体上的分散。表面XPS分析证实催化剂表面Pd物种处于较高的氧化状态,且CeO2与Pd物种间存在协同作用。Pd的高分散及其与CeO2的相互作用是催化剂具有高活性的关键。通过使用二元复合滤棒,考察了Pd-Ce/NaZSM-5负载型催化剂降低卷烟烟气中CO的作用。结果表明,与对照样相比,主流烟气CO释放量可降低22%。

A series of CeO2-modified Pd/NaZSM-5 supported catalysts were prepared by impregnation method. Effects of reaction temperature, adding promoter of CeO/, H2 pre-reduction, space velocity, and moisture on the catalytic activity for CO oxidation were investigated by taking CO oxidation as a probe reaction. Species of catalysts were characterized by means of XRD and XPS techniques. Results showed that CeO/addition obviously improved the catalytic activity and the catalytic percent conversion increased with the increase of reaction temperature or Ce-loadings, while decreased with the increase of space velocity. The catalyst was insensitive to moisture and can maintain its activity for the complete oxidation of CO for more than 720 hours at 48 ℃ in the presence of moisture. H2 pre-reduction enhanced the catalytic activity, while it was less stable than the catalyst without reduction. Results of XRD testing showed that Pd species were highly dispersed over the NaZSM-5 zeolite which was enhanced by the CeO/addition. XPS profiles analysis revealed that Pd species over the catalyst kept at a high oxidation state and there existed synergism between CeO/and Pd species. Synergism between CeO/and Pd, as well as the high dispersion of Pd species over NaZSM-5 support, were critical to the high catalytic activity. Effect of Pd-Ce/NaZSM-5 catalyst on decreasing CO in cigarette smoke was also investigated with a cigarette dual-filter. Results showed that the amount of CO release could be reduced by 22 %.