鎳與鈣鈦礦結構氧化物BaMO3 (M=Ti、Zr、Hf) 催化劑對二氧化碳甲烷化反應的影響

Abstract

本實驗經由三種不同合成方法製備NiO/BaMO3 (M=Ti, Zr, Hf)催化劑。並藉由改變NiO與BaMO3 的莫爾比例、反應溫度去探討Ni/BaMO3對於二氧化碳甲烷化反應觸媒活性的影響。我們使用X光粉末繞射儀、X光光電子能譜儀、熱程控還原反應、感應耦合電漿原子放射光譜以及比表面積分析去鑑定合成材料之性質。本實驗以溶膠凝膠法、含浸法及水熱法製備催化劑去探討不同合成方法對於二氧化碳甲烷化反應之影響。此三種合成方法中，以含浸法所製備的催化劑有最好的催化表現，比另外兩個合成方法能在較低溫(350□C)下有較佳的二氧化碳轉換率及較高的甲烷選擇率。當反應溫度高過350□C時，催化劑反應性便開始下降，這是由於二氧化碳甲烷化反應是個放熱反應，不偏好在高溫底下進行之緣故。在所有催化材料中，莫爾百分比20%的Ni/ BaZrO3催化劑有最好的催化表現，其在反應溫度350□C的條件下能達到86(1)%的二氧化碳轉換率，以及99(1)%的甲烷選擇率。在催化劑的穩定性方面，經過64小時的反應並未出現衰退的現象。

NiO/BaMO3 (M=Ti, Zr, Hf) catalysts were successfully prepared via sol-gel, impregnation, and hydrothermal methods. All catalysts were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), inductively coupled plasma-atomic emission spectrometer (ICP-AES), and specific surface areas (SSA). CO2 methanation performance of each catalyst was examined by changing many factors, such as different compositions, varied Ni loading and several reaction temperatures. The catalysts prepared via impregnation method showed better performance than the others. It revealed the highest value of CO2 conversion and CH4 selectivity at 350□C. When the reaction temperature rose above 350□C, the reactivity started to decline. This phenomenon was due to the thermodynamic limitation since CO2 methanation is a slightly exothermic reaction. Among all catalysts, the best performance was achieved by 20 mol% Ni/BaZrO3 with 86.8% CO2 conversion and 99.9% CH4 selectivity at 350□C. The stability of this optimum catalyst was tested for 64 hours and showed no deactivation. It revealed that CO2 conversion maintained at 86% and the CH4 selectivity was around 99%.