【作者】 邱业君；

【导师】 张继炎；

【作者基本信息】 天津大学 ， 工业催化， 2003， 硕士

【摘要】 甲烷二氧化碳重整和甲烷部分氧化制合成气是甲烷利用的两条有效途径。本论文针对这两条途径，分别设计和制备了Ni/MgO和NiO/γ-Al2O3两种体系的催化剂，采用BET、XRD、TPR、TEM、TG、XPS、脉冲色谱技术及活性评价等研究方法，分别对催化剂的物化性质和催化性能进行了较为系统深入的研究。 研究结果表明，沉淀剂种类对用共沉淀法制备的Ni/MgO体系催化剂的物化性质和甲烷二氧化碳重整反应催化性能有显著影响。以氢氧化钾为沉淀剂制得的Ni/MgO催化剂与以碳酸钾为沉淀剂制得的催化剂相比，具有较大的比表面和较小的Ni-Mg固溶体晶粒度，还原后催化剂的镍晶粒度也较小；在CH4-CO2重整反应中呈现了较高的活性和选择性，经反应7h后催化剂无明显积碳现象。稀土助剂La2O3、CeO2对Ni/MgO催化剂有一定的改性效果。所得催化剂NLM、NCM具有较大比表面和较小镍晶粒度，以NCM中镍物种的还原性能改善尤为明显。两种助剂的加入均明显改善了Ni/MgO催化剂对 CH4-CO2重整反应的催化性能，La2O3主要作为结构助剂增强了催化剂的抗烧结能力，而CeO2主要作为电子助剂改善了催化剂的抗积碳性能。La2O3和CeO2均可以提高CO2的活化能力和消除积碳的能力，以CeO2的作用更为突出。对于甲烷部分氧化反应而言，MgO助剂对NiO/γ-Al2O3体系催化剂有明显的改性效果。MgO的加入减少了NiAl2O4尖晶石的生成，有利于形成Ni-Mg固溶体，促进NiO在载体上的分散，从而提高了催化反应性能。MgO含量为7wt.%的NiO/MgO-γ-Al2O3催化剂的效果较好。CeO2、MO复合助剂对NiO /MgO-γ-Al2O3催化剂有明显的改良效果。在CeO2、MO助剂共改性的催化剂NiO/CeO2-MO-MgO-γ-Al2O3中，处于最佳配比（CeO2/MO=4∶1）的CeO2和MO之间存在明显的协同作用，它促进了NiO的分散，减小了镍晶粒度，提高了系统储存和释放氧的能力，提高了CH4转化率，并保持了CO的高选择性。助剂含量对NiO /CeO2-MO-MgO-γ-Al2O3催化剂也有明显影响，助剂含量过高，NiO的分散性变差，CeO2在表面的聚集明显，促进了副反应水煤气变换的进行，降低了CO的选择性。在最佳CeO2、MO配比（CeO2/MO=4∶1）和助剂含量下的NiO /CeO2-MO- MgO-γ-Al2O3催化剂是较好的甲烷部分氧化催化剂。此外，浸渍次序对催化剂性能也有影响。先浸镍组分，后浸助剂组分更有利于NiO的分散，减小镍晶粒度，因此可进一步提高其催化性能。更多还原

【Abstract】 In this work, two catalyst series of Ni/MgO and NiO/γ-Al2O3 for two different routines of synthesis gas manufacture, the CH4-CO2 reforming and the partial oxidation of methane, were designed and prepared, and their physico-chemical properties and the catalytic performance were systematically investigated by means of BET, XRD, TPR, TEM, TG, XPS, exchanged pulse reaction and activity evaluation. As to the CH4-CO2 reforming catalyst system, the physico-chemical properties and catalytic performance of co-precipitated Ni/MgO were changed greatly by use of different precipitators. Compared with the catalyst NM2, which was prepared by use of K2CO3 as precipitator, the catalyst NM1 prepared by KOH as precipitator was of higher specific surface area and smaller size of nickel-magnesia solid solution crystallites, as well as smaller size of nickel crystallites after reduction. Therefore, NM1 showed higher catalytic activity and selectivity in methane reforming with carbon dioxide.The addition of rare earth oxide promoters La2O3 and CeO2 into the Ni/MgO catalysts （labeled as NLM and NCM）may affect their physico-chemical properties and catalytic performance. The presence of rare earth oxides could promote reduction of nickel species in nickel-magnesia solid solution, especially CeO2. Therefore, NLM and NCM both showed higher activity and selectivity than the Ni/MgO catalyst NM. However, La2O3, is mainly served as a structural promoter, which could enhanced resistance to sintering of nickel crystallites, but CeO2 is a kind of electronic promoter, which could benefit to eliminate carbon deposition on the catalyst. In addition, La2O3 and CeO2 both can promote the activation of CO2, and the effect of CeO2 was superior to that of La2O3. For the partial oxidation of methane to synthesis gas, the effects of MgO promoter on physico-chemical properties and catalytic performance of NiO/γ-Al2O3 catalyst were obvious. The presence of MgO could reduce the formation of NiAl2O4 spinel, and benefit the formation of NiO-MgO solid solution, which may improve the dispersion of NiO on γ-Al2O3, and also the catalytic performance for methane partial oxidation to synthesis gas. The catalyst Ni/γ-Al2O3 promoted with 7wt.% MgO showed better catalytic effect. The synergic effects of CeO2 and MO composed promoters on the improvement of physico-chemical properties and catalytic performances of NiO/MgO-γ-Al2O3 catalyst CMM1 were rather great. The composed <WP=4>catalyst with CeO2 and MO was showed better dispersion of NiO species, finer nickel crystallites and stronger ability for storage and release of oxygen, thus it exhibited much higher conversion of CH4, and the CO selectivity can be also maintained. The content of CeO2 and MO, and the CeO2 /MO ratio had great influence on the synergetic effect, With the increasing of promoter content, the dispersion of NiO species became worse, and CeO2 would aggregate on the surface of catalysts, which may accelerate the water-gas shift reaction, and result in the decrease of CO selectivity. The optimized catalyst NiO/CeO2-MO-MgO-γ-Al2O3 showed better catalytic reactivity for partial oxidation of methane to synthesis gas. At last, the impregnation sequence of catalyst components had also apparent influences. When Ni is impregnated firstly, and then promoters Ce and M, the prepared catalyst showed better dispersion of NiO, finer size nickel crystallites and ideal activity for conversion of CH4.更多还原