高级检索

    CO2低温甲烷化反应的高活性CoAlOx催化剂研究

    Study on CoAlOx as an active catalyst for the low-temperature CO2 methanation

    • 摘要: 温室气体CO2经加氢制甲烷,即CO2甲烷化反应(CMR),不仅能够将CO2转化为直接输入现有商业化天然气管道的CH4,而且如果以绿氢为氢源,有望实现CO2的可持续资源化利用。根据低温下CMR反应速率慢但CO2热力学平衡转化率高的特点,低温高活性催化剂成为影响CMR工业化应用的关键。针对低温条件下CMR催化剂活性偏低的共性难题,结合费托合成Co基催化剂结构和性能关系的认知,提出了高金属钴含量和低焙烧温度的催化剂设计策略。为此,采用共沉淀法制备了一系列Co/Al摩尔比介于1∶4~4∶1的CoAlOx催化剂,采用XRD、Raman、H2-TPR和CO2-TPD等方法较为系统地表征了催化剂的结构、还原特点等,并在250  ℃考察了其催化CMR反应的活性。表征结果表明:CoAlOx催化剂经400  ℃焙烧后,钴物种为立方相Co3O4,而铝物种则为低结晶度γ-Al2O3和无定形氧化物。同时,Co/Al摩尔比显著影响金属Co(Co0)与金属氧化物之间的相互作用程度,进而影响CoAlOx催化剂的还原度、Co0分散度及弱和中等强度碱性位点的总量。反应结果表明:Co/Al摩尔比=4∶1的4Co1AlOx表现出最佳的CH4选择性(>99%)和催化活性,即CO2转化率达87%,CH4的转化频率和时空收率分别为1.00 s−1和5.39 g/(g·h),明显高于Co基催化剂的文献报道结果。结构和性能关联分析结果表明:Co0原子数和碱性位点量的平衡及二者之间的协同效应,是影响CoAlOx催化CMR反应低温活性的关键,该认知有望为低温高活性Co基CMR催化剂的进一步优化设计提供指导。

       

      Abstract: The hydrogenation of carbon dioxide to methane, which is also known as the CO2 methanation reaction (CMR), not only converts CO2 into CH4 ready for the current infrastructure of natural gas, but also is a promising route for the effective utilization of greenhouse gas CO2 as the one-carbon resource provided that green hydrogen is used. For higher conversions, the CO2 methanation reaction is thermodynamically favored at lower temperatures. However, kinetic rates of the CO2 methanation reaction are slow at lower reaction temperatures. As a result of this contradiction, the key for the industrial implement of the CRM technology is highly active catalyst at lower temperatures. To address this issue, in this work, we propose a strategy, i.e., higher Co loadings but lower calcining temperatures, for the design of Co-based CMR catalysts provided understandings of cobalt catalyzed Fischer-Tropsch synthesis. In this case, a series of CoAlOx catalysts with Co/Al molar ratios varied from 1∶4 to 4∶1 are prepared by the co-precipitation method. The catalysts are characterized by XRD, Raman, H2-TPR and CO2-TPD techniques, and are evaluated for CRM at 250  ℃. The characterization results indicate that after calcination at 400  ℃, the cobalt species in the CoAlOx catalyst exist as cubic-phase Co3O4, while the aluminum species are present as low-crystallinity γ-Al2O3 and amorphous oxides. Meanwhile, the Co/Al molar ratio significantly influences the extent of interaction between metallic Co (Co0) and metal oxides, thereby affecting the reducibility of the CoAlOx catalyst, the dispersion of Co0, and the total amount of weak and medium-strength basic sites. The reaction results demonstrate that the 4Co1AlOx catalyst with a Co/Al molar ratio of 4∶1 exhibits optimal CH4 selectivity (>99%) and catalytic activity, namely: a CO2 conversion of 87%, a turnover frequency (TOF) for CH4 formation of 1.00 s−1, and a space-time yield (STY) of 5.39 g/(g·h), which are notably higher than those reported in the literature for Co-based catalysts. The structure–performance correlation analysis reveals that the balance between the number of Co0 atoms and the quantity of basic sites, along with the synergistic effect between them, is key to influencing the low-temperature activity of CoAlOx in the CO2 methanation reaction (CMR). This understanding is expected to provide guidance for the further optimization and design of low-temperature highly active Co-based CMR catalysts.

       

    /

    返回文章
    返回