二氧化碳與烷類轉換反應在銥原子氧化石墨烯表面之理論計算研究

Abstract

本篇文章藉由密度泛函理論研究二氧化碳和烷類在銥原子氧化石墨烯表面進行轉換反應。銥原子氧化石墨烯表面對甲烷、乙烷和二氧化碳具有高吸附能，其吸附能分別為 -0.86、-0.92和-0.56eV。在甲烷與二氧化碳的轉換反應下，甲烷分子先吸附在表面(Eads = -0.86 eV)後，進行C-H斷鍵形成CH3和H片斷，此步驟經過0.61 eV的反應能障，其中氫原子片斷與表面上的環氧基形成OH，而CH3與OH再進行結合形成甲醇，此步驟經過0.91 eV的反應能障，最後形成的CH3OH分子脫附表面，脫附能量為0.64 eV，此過程不趨向與二氧化碳發生反應，而趨向進行甲烷氧化反應。在二氧化碳分子和乙烷分子的轉換方面，首先乙烷吸附於表面，吸附能為-0.92 eV，接著進行C-H斷鍵而形成乙基和氫原子分別吸附於銥原子以及環氧基，此步驟跨越0.63 eV，接著在二氧化碳吸附(Eads = 0.58 eV)後，有四種可能的反應路徑：乙基與二氧化碳結合分別形成 (1) C2H5COO (Ea = 0.95 eV)； (2) COOC2H5 (Ea = 1.70 eV)；氫原子與二氧化碳結合分別形成 (3) COOH (Ea = 1.49 eV)；(4) HCOO (Ea = 3.54 eV)，而路徑(1)形成的丙酸根為活化能最低，且最可能的反應路徑，因此反應趨向產生丙酸。關鍵字：轉換反應、二氧化碳、乙烷、氧化石墨烯、銥原子。We perform a study to investigate the conversion of CO2 and C2H6 molecules to propanoic acid on Iridium-modified graphene oxide (Ir1-GO) surface by using the density functional theory. The high catalytic activity for conversion of CH4, C2H6 and CO2 into methanol and propanoic acid via the high adsorption energies of CH4, C2H6 and CO2 on Ir1-GO, -0.86, -0.92 and -0.56eV, respectively, are described as follows. At first, CH4 and C2H6 would be dehydrogenated to oxide site of surface to form CH3 + OH and C2H5 + OH with the barriers of 0.61 and 0.63eV, respectively. Secondly, methyl could go through the pathway of CH3 + OH → CH3OH. However, the additional adsorbed CO2 could either react with ethyl to form C2H5COO or COOC2H5 with the barriers of 0.95eV and 1.70eV, respectively, or it could be hydrogenated by the hydroxyl to form HCOO (3.54eV) or COOH (1.49ev). Consequently, the most probable path for the conversion of a CO2 molecule with ethane on the Ir1-graphene oxide surface is the formation of a propanoic acid. To understand the interaction between adsorbates and surfaces, a series of structural calculation and analyzation were carried out.key word : Conversion, CO2, C2H6, graphene oxide and iridium.