用于甲烷氧化缩合的 MnOx-Na2WO4/SiO2 催化剂的结构和稳定性

Sevinj Osmanova, G. Azimova, S. Zulfugarova, E. Ismailov, Dilgam Taghiyev, J. Thybaut
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引用次数: 0

摘要

以醋酸锰、钨酸钠、四乙氧基硅烷(TEOS)为前驱体,十六烷基三甲基溴化铵(CTAB)为成孔剂,合成了基于介孔二氧化硅基质的 MnOx-Na2WO4/SiO2 样品、通过扫描电子显微镜与能量色散元素分析 (SEM/EDS)、X 射线衍射仪 (XRD)、电子磁共振 (EMR)、N2 吸附-解吸测量对其进行了表征,并将其作为甲烷氧化缩合反应 (OCM) 的催化剂进行了测试。结果表明,MnNaW/SiO2 催化剂由 Mn2O3、MnO2、Na2WO4 和 SiO2 相组成。EMR 和 SEM/EDS 数据表明,反应条件对催化剂结构中的表面结构和催化活性成分的分布有明显影响。随着温度的升高和反应时间的延长,样品的比表面积和孔体积值都发生了显著变化(在 800 °C 的 OCM 反应中,催化剂工作 15 小时后,比表面积和孔体积值分别为 116.8 m2/g 和 0.590 cm3/g;在 800 °C 的 OCM 反应中,催化剂工作 15 小时后,比表面积和孔体积值分别为 46.1 m2/g 和 0.232 cm3/g)。研究表明,在 OCM 反应条件下,MnOx-Na2WO4/SiO2 催化剂表面的元素组成会发生变化,变化程度取决于 OCM 反应的持续时间。在反应混合物 CH4/O2 的影响下,Mn 和 W 的含量在最初两小时内下降,随着 OCM 反应时间的延长,催化剂表面上 Mn 和 W 含量下降的趋势基本保持不变。详细的 X 射线相分析还表明,在 CH4/O2 反应混合物的影响下,该催化剂的相组成发生了变化。据推测,在反应条件(700-800 °C)下,MnOx-Na2WO4/SiO2 催化剂是基本具有嵴烷结构的二氧化硅颗粒,其表面涂有熔融钨酸钠,其中含有被钠离子和 WOx 活化的纳米级 MnOx 结构颗粒。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Structure and stability of MnOx-Na2WO4/SiO2 catalyst for oxidative condensation of methane
Samples of MnOx-Na2WO4/SiO2 based on a mesoporous silica matrix were synthesized using manganese acetate, sodium tungstate, tetraethoxysilane (TEOS) as precursors and cetyltrimethylammonium bromide (CTAB), citric acid and triethanolamine as pore generating agent and characterized by scanning electron microscopy with energy dispersive elemental analysis (SEM/EDS), X-ray diffractometry (XRD), electron magnetic resonance (EMR), N2 adsorption-desorption measurements and tested as a catalyst for the reaction of oxidative condensation of methane (OCM). It is shown that the MnNaW/SiO2 catalyst consists of Mn2O3, MnO2, Na2WO4 and SiO2 phases. The EMR and SEM/EDS data indicate a noticeable effect of the reaction conditions on the surface structure and the distribution of catalytically active components in the catalyst structure. Significant changes in the values of the specific surface area and pore volume of the samples with increasing temperature and duration of the reaction were found (the values of the specific surface area and pore volume, respectively, 116.8 m2/g and 0.590 cm3/g - up to and 46.1 m2/g and 0.232 cm3/g after 15 hours of catalyst operation in the OCM reaction at 800 °C). It has been shown that under the conditions of the OCM reaction, the elemental composition of the surface of the MnOx-Na2WO4/SiO2 catalyst changes, and the degree of change depends on the duration of the OCM reaction. Under the influence of the reaction mixture CH4/O2, the content of Mn and W decreases in the first two hours, and the trend towards a decrease in their amount on the catalyst surface with an increase in the duration of the OCM reaction is generally preserved. A detailed X-ray phase analysis also indicates a change in the phase composition of this catalyst under the influence of the CH4/O2 reaction mixture. It is assumed that under the reaction conditions (700–800 °C) the MnOx-Na2WO4/SiO2 catalyst is silicon dioxide particles basely with the cristabolite structure, the surface of which is coated with molten sodium tungstate containing nanosized particles of MnOx structures activated by sodium ions and WOx.
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