过渡金属对分子筛担载Pd催化剂上CO氧化性能影响

分别采用共浸和连续浸渍法制备了一系列添加过渡金属的Pd-M-Ox-NaZSM-5(M=Cr，Mn，Fe，Co，Ni，Cu，Zn，Mo，Zr等)负载型催化剂．以CO氧化为探针反应，考察了不同制备方法对CO氧化性能影响，结果表明共浸法制备的各催化剂其活性明显优于连续浸渍法．详细考察了反应温度、Fe含量、氢气预还原、空速以及水蒸气等对共浸Pd-Fe-Ox-NaZSM-5催化剂上CO氧化行为影响，并应用XRD和XPS等手段对催化剂体相结构和表面状态进行了表征．结果表明：加入Fe2O3可明显提高Pd/NaZSM-5催化剂活性，且催化CO氧化的转化率随反应温度及Fe含量增加而增加；空速增加以及H2预还原作用导致Pd-Fe-Ox-NaZSM-5活性有所降低；催化剂对水蒸气较为敏感．XRD测试结果表明催化剂中Pd组分处于较高分散状态，以红铁矿形式存在的Fe2O3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Fe2O3与Pd物种间存在较强的相互协同作用，且催化剂表面Pd物种处于较高氧化状态．Pd的高分散及其与Fe2O3的相互协同作用是共浸催化剂具有高活性的关键因素．

Influences of Transition Metal Additives on CO Oxidation over NaZSM-5 Supported Pd

A series of transition metal-modified Pd-M-O_x-NaZSM-5 (M=Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Zr) catalysts were prepared by co-impregnation and sequential impregnation methods separately. Influences of different preparation methods on CO oxidation have been studied. It was found that catalysts prepared by co-impregnation method were superior to those of the sequential one. Effects of temperature, content of the promoter, H_2 pre-reduction, space velocity and moisture in the feed gas on Pd-Fe-O_x/NaZSM-5 catalyst prepared by co-impregnation method for CO oxidation have been investigated in detail. XRD and XPS techniques were used to verify the species in the catalyst. The addition of Fe_2O_3 obviously improved the activity and CO conversion increased with the increase of reaction temperature or Fe-loading amount. However, high space velocity as well as H_2 pre-reduction decreased the activity. The catalyst was sensitive to moisture and its activity was easily depressed by moisture in the feed gas. XRD showed that Pd species were highly dispersed on the surface of NaZSM-5, which was dependent upon the Fe-loading amount of hematite. XPS profiles revealed the presence of synergism between Fe_2O_3 and Pd species, and the Pd species kept a high oxidation state in the special structure of NaZSM-5. High dispersion of the Pd species as well as the synergism between Fe and the Pd species was responsible for the enhancement of catalytic activity.