【作者】 李云华；

【导师】 王亚权；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 博士

【摘要】 甲烷部分氧化制合成气是目前甲烷利用的有效途径之一。该反应因投资小、能耗低、反应速率快等优点广受研究者关注。本论文工作采用泡沫镍制备成Ni金属整体型,通过酸处理获得Ni金属整体型催化剂;进一步用酸处理过的Ni金属整体型负载铈、锆、镁等金属氧化物制得负载金属氧化物的Ni金属整体型催化剂;用XRD、XPS、SEM等技术对制得的催化剂进行了表征;研究了上述两类催化剂催化甲烷部分氧化及部分氧化与H2O和CO2重整耦合的反应性能;考虑到Ni金属整体型催化剂稳定性好,但活性低于负载催化剂的特点,还研究了Ni monolith-Ni/MgAl2O4双床体系催化甲烷部分氧化反应的性能;此外,根据甲烷部分氧化的间接机理,对三种催化体系催化甲烷部分氧化反应进行了模拟。SEM结果表明,经酸处理后Ni金属整体型催化剂上形成很多缝隙,比表面积从0.3m2/g增加到0.5m2/g。在CH4/O2为2,温度为1123K,空速为1.0×105h-1的反应条件下,与未经酸处理的催化剂相比,经20wt. %HCl处理后的Ni金属整体型催化剂的CH4转化率,H2和CO选择性从84%,92%和94%分别增到90%,98%和95%。对于负载氧化物的Ni金属整体型催化剂,CeO2的单独负载量为2.87wt. %时最佳;ZrO2的单独负载量为1.52wt. %时最佳;MgO的单独负载量为4.03wt. %时最佳;负载CaO没有显示任何促进作用。0.87%Ce-1.77%Zr/Ni催化剂不仅具有较高的甲烷部分氧化的活性和选择性,而且具有良好的稳定性。XRD分析表明,此催化剂上负载的CeO2和ZrO2形成了固溶体。甲烷部分氧化与CO2和H2O重整耦合的反应结果表明,无论是在Ce-Zr/Ni金属整体型,还是在Mg/Ni金属整体型上,甲烷部分氧化和水蒸汽重整耦合反应性能都优于甲烷部分氧化和二氧化碳重整耦合的反应性能。Ni monolith-Ni/MgAl2O4双床在重整催化剂的镍负载量为10wt. %时,催化活性和选择性最高。当进料流速分别为500ml/min,1000ml/min,氧化床层的最小值分别为2.3mm和4.7mm,重整床层最小值分别为2.4mm和3.7mm时,双床既有高的部分氧化活性和选择性,又有高的稳定性。根据间接反应机理,对Ni金属整体型催化剂上的甲烷部分氧化反应进行了模拟。实验和模拟结果比较显示二者吻合很好。这说明Ni金属整体型催化剂的甲烷部分氧化反应很可能是遵循间接反应机理。Ce-Zr/Ni上甲烷部分氧化反应的模拟结果表明,Ce-Zr/Ni活性的提高是因为CeO2-ZrO2固溶体高的氧化还原性。Ni monolith-Ni/MgAl2O4的模拟表明,在一定流量下,双床中的氧化床层和重整床层的长度都分别有一个能使双床既具有高催化活性又具有高稳定性的最小值。更多还原

【Abstract】 Methane partial oxidation to syngas is one of the promising ways to efficiently utilize methane. Because of its low investment and energy consumption with instant reaction rate, it has attracted much attention. In the present work, Ni metallic monolith catalyst was prepared with Ni foam and further treated by acid. It was loaded by promoter oxides, such as ceria, zirconia, magnesia, ceria-zirconia, etc., to obtain the Ni monolith with oxides. The sample characterization was made by XRD、XPS、SEM、ICP and BET. Considering that the deactivation of the Ni metallic monolith could not occur and it had lower activity than the supported catalysts, the dual bed, Ni monolith-Ni/MgAl2O4, was also studied for methane partial oxidation. Moreover, on the basis of an indirect reaction mechanism, simulations of methane partial oxidation were conducted for these three kinds of catalyst systems.SEM micrographs showed that the crystal defects on the surface of the Ni monolith were formed. The surface area increased from 0.3m2/g of untreated Ni monolith to 0.5m2/g of the Ni monolith treated by acid. At inlet temperature 1123 K, CH4/O2 ratio of 2 and GHSV 1.0×105 h-1, methane conversion and selectivities to H2 and CO on the Ni monolith treated by acid were 90%, 98% and 95%, respectively, much higher than those of the untreated Ni monolith, which were 84%, 92% and 94%, respectively.The optimal loadings of ceria and zirconia, separately, were 2.87% and 1.57%, respectively. The optimal loading of magnesia was 4.03% while calcium oxide had no role for promotion of the activity and the selectivities. 0.87%Ce-1.77%Zr/Ni showed not only high activity and selectivities, but also high stability. XRD patterns showed that CeO2-ZrO2 solid solution was formed on 0.87%Ce-1.77%Zr/Ni.The results showed that the reaction performance for the combined partial oxidation and steam reforming of methane was better than the combined partial oxidation and carbon dioxide reforming of methane on both Ce-Zr/Ni monolith and Mg/Ni.The dual bed, Ni monolith-Ni/MgAl2O4, had the highest activity and selectivities when the nickel loading on the reforming catalyst was 10wt. %. The results showed that when the feed flowrates were 500 ml/min or 1000 ml/min, 2.3 or 4.7 mm of the minimum length of the Ni monolith were needed, respectively, to achieve nearly constant methane conversion and the selectivities to hydrogen and carbon monoxide and the maximum temperatures were within the Ni monolith bed. In order to obtain high methane conversion and high selectivities to syngas, the minimum length of the Ni/MgAl2O4 bed length was 2.4 mm at 500 mol/min or 3.7 mm at 1000 ml/min, respectively.On the basis of an indirect reaction mechanism, the simulations for the partial oxidation of methane on the Ni metallic monolith catalysts were conducted. The results showed that the simulations agreed well with the experimental data on the Ni monolith bed, and it was likely that the methane partial oxidation followed an indirect reaction mechanism. The simulation results for Ce-Zr/Ni monolith showed that the reaction performance of Ce-Zr/Ni was promoted due to high redox of CeO2-ZrO2 solid solution. The simulation results for Ni monolith-Ni/MgAl2O4 showed that the oxidation bed and the reforming one in the dual bed had an optimal bed length, respectively, which made the dual bed have not only high activity and selectivities but also high stability under the certain flowrates.更多还原