苯在赤鐵礦表面的吸附與開環反應機制：密度泛函理論研究

Adsorption and C-C Bond Cleavage Mechanisms of Benzene on Hematite (α-Fe2O3) Surfaces: A DFT Study

黃昱銘(Yu-Ming Huang)

指導教授 ： 鄭原忠

國立臺灣大學/理學院/化學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102766

摘要

開發可再生能源是維持永續社會的關鍵議題，生物質的催化裂解反應是發展可再生能源的一種有潛力的方式。在生物質裂解過程中，焦油形成造成催化劑失去活性是一個主要的問題，因此將焦油分子重組成較小的氣體分子成為利用生質能源的關鍵挑戰。在目前實驗的研究中，已經證明赤鐵礦(α-Fe2O3)是焦油分子催化重組的有效催化劑，儘管如此，焦油的詳細重組機制仍不清楚。在這項工作中，我們應用密度泛函理論研究了赤鐵礦的表面結構，並使用苯作為焦油模型化合物，進而研究赤鐵礦表面與芳香族焦油類似物的吸附和重組反應。我們的結果顯示，苯與鐵原子曝露的(0001)表面之間的主要作用力是凡得瓦力，而苯可以透過強碳氧鍵的相互作用力化學吸附在鐵氧原子共曝露的(01"-1"2)表面上。此外，我們使用微動彈性帶(nudged elastic band)方法研究了反應機制，結果表示赤鐵礦(01"-1"2)表面上的苯分子經碳碳鍵裂解後，會形成兩種可能產物，分別為(a)鍊狀烯烴和(b)羰基物質，其活化能分別為1.78 eV和2.62 eV。最後，經過我們的計算結果證明了氧化加成對赤鐵礦表面上芳香族化合物的碳碳鍵裂解的重要性，這為焦油在氧化物催化劑上的裂解機制提供了新的理解。

關鍵字

生質能源 ； 焦油 ； 赤鐵礦(α-Fe2O3) ； 密度泛函理論 ； 碳碳鍵斷裂

並列摘要

Developing renewable energy sources is a critical issue in maintaining a sustainable society, and catalytic pyrolysis of biomass is a promising way to exploit renewable biomass energy. During the pyrolysis process, deactivation of catalysts caused by tar formation is a major problem, therefore the reforming of tar molecules into smaller gaseous molecules becomes a critical challenge for the utilization of biomass energy. To this end, hematite (α-Fe2O3) has been demonstrated as an effective catalyst for catalytic reforming of tar molecules. Nevertheless, the detailed reforming mechanism of tar is still unclear. In this work, we applied density functional theory to investigate surface structures of hematite and the adsorption and C-C bond cleavage of aromatic tar analogue on hematite surfaces. We use benzene as a tar model compound. Our results showed that the dominant interactions between benzene and single Fe-terminated (0001) surface are van der Waals forces, yet benzene could be chemisorbed on the Fe and O co-exposed (01"-1"2) surface via strong C-O interactions. Furthermore, we studied reaction mechanisms using nudged elastic band method, and the results indicate that two types of potential products might form after C-C bond cleavage of benzene on the hematite (01"-1"2) surface, namely chain-like alkene species and carbonyl species, with the activation energy of 1.78 eV and 2.62 eV, respectively. In summary, our calculations demonstrate the importance of co-adsorption on both Fe and O centers and oxidative addition on C-C bond cleavage of aromatic compounds on the α-Fe2O3 surface, which provides novel insight on the mechanisms of tar cracking on oxide catalyst.

並列關鍵字

biomass energy ； tar ； hematite(α-Fe2O3) ； density functional theory ； C-C bond cleavage

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