ZrO2-Al2O3复合载体负载Ni基催化剂COx甲烷化性能

COxmethanation over nickel-based catalysts supported on ZrO2-Al2O3 composite

采用浸渍和粉末压片的方法制备了两种ZrO2-Al2O3复合载体并用于负载Ni基催化剂,并利用氮气等温物理吸附、X射线粉末衍射(XRD)、H2程序升温还原(H2-TPR)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等分析手段对催化剂物化性质进行表征,考察了ZrO2-Al2O3复合载体制备方法及ZrO2的引入对Ni基催化剂在CO、CO2和CO-CO2共存的3种体系下甲烷化反应活性的影响。材料表征和活性测试结果表明,在CO甲烷化体系中,与单一Al2O3载体相比,引入ZrO2的复合载体能有效提高催化剂中Ni物种的分散度从而增强CO甲烷化过程中催化剂活性,且粉末压片法较浸渍法制备的复合载体能有效提高催化剂的还原度,降低还原温度,但前者会大大降低催化剂的比表面积;在CO2甲烷化体系中,当载体形貌和制备方法相同时,载体的变化对催化剂活性的影响较小,CO2转化率主要受到制备方法不同引起的物理性质如比表面积变化的影响;在CO-CO2共存体系中,由于CO在竞争吸附中比CO2更容易占据活性位点,所以呈现出优先进行CO甲烷化再进行CO2甲烷化、CO2的含量先增多后减少的规律。

Two kinds of nickel-based catalysts supported on ZrO2-Al2O3 composite were prepared by impregnation and powder pressing.The obtained catalysts were further characterized by N2 isothermal physisorption,X-ray powder diffraction (XRD),H2 temperature-programmed reduction (H2-TPR),scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques.The influences of zirconia addition and different preparation methods on the performance of the catalysts in CO methanation,CO2 methanation and CO/CO2 co-methanation were investigated.The results indicated that the addition of zirconia in the Al2O3 support could improve the dispersion of Ni species,leading to enhanced catalytic performance in CO methanation.Besides,the composite support made from powder pressing method could effectively improve the reducibility and decrease the reduction temperature of catalysts in contrast to that made from the impregnation method.However,the former method would decrease the specific surface area,pore volume and pore diameter of the catalysts.In the CO2 methanation,catalysts prepared by the same method had little effect on CO2 conversion,which was mainly limited by the physical properties of the catalysts such as specific surface area that originated from the difference in preparation method.In the CO/CO2 co-methanation experiments,the methanation of CO is prior to that of CO2 since in adsorption CO is more easily to occupy the on active sites than CO2 ,which causes the CO2 content increased first and then decreased.