| 摘要: | 二氧化碳/甲烷重組反應可將同為溫室氣體之二氧化碳與甲烷轉化成合成氣(CO + H2)，此氣體可用於生產甲醇或更高經濟價值的有機化合物，為一項值得研發的技術。為提高應用於此反應之LaNiO3觸媒的反應活性、穩定性及抗積碳能力，藉Ce及Cu的添加來製備改質之觸媒。並比較LaNiO3、La1-xCexNiO3與La0.9Ce0.1Ni1-yCuyO3三種觸媒於之諸特性。
研究結果發現，在CO2/CH4進氣比例為1、空間流速10000 h-1、反應溫度400~800°C、一大氣壓之操作參數下，LaNiO3觸媒於800°C之CH4和CO2之轉化率分別為95%和93%，H2和CO選擇率分別為57%和49%。以Ce部分取代La合成La1-xCexNiO3(x = 0.1)之觸媒於800°C之CH4和CO2之轉化率亦均高於90%，和LaNiO3觸媒無顯著差別，但提升H2選擇率至62%。再以Cu部分取代Ni合成出La0.9Ce0.1Ni1-yCuyO3(y ? 0.5)之觸媒，其CH4和CO2之轉化率和H2選擇率與LaNiO3和La0.9Ce0.1NiO3觸媒無顯著差別，但CO選擇率隨著Cu的添加比例為0.1、0.3、0.5而略為上升，於800°C之CO選擇率分別為49%、50%、51%。
經H2-TPR分析，La1-xCexNiO3觸媒具有儲氧釋氧能力，可利於激活C-H鍵以提升H2選擇率。而La0.9Ce0.1Ni1-yCuyO3觸媒不僅有儲氧釋氧能力亦可降低觸媒還原溫度，表示活性佳，其所提供的氧原子不僅利於激活C-H鍵，還利於和觸媒表面的碳反應形成CO。故結果顯示La0.9Ce0.1Ni0.7Cu0.3O3觸媒有最佳的穩定性，反應時間可長達84小時。ESCA分析結果也證實添加Ce和Cu至LaNiO3作改質之觸媒，可抑制積碳的生成。
CH4 reforming of CO2 reaction could transform the greenhouse gas (CH4 and CO2) to synthesis gas (CO and H2). The synthesis gas could be used to produce methanol, liquid fuel and so on. To enhance the activity and stability of the LaNiO3 catalyst used in this reforming reaction, the catalyst was substituted by Ce and Cu elements. The activities of LaNiO3, La1-xCexNiO3 and La0.9Ce0.1Ni1-yCuyO3 for CO2/CH4 reforming are then experimentally compared.
The results show that conversions of CH4 and CO2 over LaNiO3 catalyst are 95% and 93%, and the selectivites of H2 and CO achieved are 57% and 49%, respectively, at 800 oC. La of LaNiO3 catalyst was partially substituted by Ce to form La1-xCexNiO3 (x = 0.1) catalyst, the conversions of CH4 and CO2 are both also more than 90%, which are not much different from LaNiO3 catalysts, however, the selectivity of H2 is increased to 62%. Ni of LaNiO3 catalyst was partially substituted by Cu to form La0.9Ce0.1Ni1-yCuyO3 (y ? 0.5) catalyst. The conversions of CH4 and CO2 and the selectivities of H2 are not much different from LaNiO3 and La1-xCexNiO3 catalysts, however, the selectivity of CO increases slightly with increasing Cu (y = 0.1, 0.3, 0.5). The selectivities of CO with three catalysts (y = 0.1, 0.3, 0.5) are 49%, 50%, 51%, respectively, at 800 oC.
The H2-TPR result shows that La1-xCexNiO3 (x = 0.1) catalyst provides the lattice oxygen vacancies, which activate C-H bond, and increase the selectivity of H2. The H2-TPR result also confirms that Cu metals are of the capability for storage and provision of the oxygen and can be reduced easily, experimental results also prove the good activity of La0.9Ce0.1Ni1-yCuyO3 (y ? 0. 5) catalyst. The oxygen atoms of La0.9Ce0.1Ni1-yCuyO not only activate C-H bond but also react with carbon which form on catalyst surface to form CO. Therefore, La0.9Ce0.1Ni0.7Cu0.3O3 catalyst has the best stability and the reaction time can be extended up to 84 hours. Additionally, the ESCA results show that adding Ce or Cu into LaNiO3 catalyst is beneficial to suppress carbon deposition. |
