H-FER-Catalyzed Conversion of Methanol to Ethanol and Dimethyl Ether: a First-Principles DFT Study
H-FER-Catalyzed Conversion of Methanol to Ethanol and Dimethyl Ether: a First-Principles DFT Study
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DOI：
10.17159/0379-4350/2021/v74a6
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Cecil H. Botchway;R. Tia;E. Adei;N. Dzade;N. D. de Leeuw
中科院分区：
文献类型：
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作者：
Cecil H. Botchway;R. Tia;E. Adei;N. Dzade;N. D. de Leeuw
甲醇在沸石中的吸附和脱水反应是催化转化生成长链烃过程中的重要步骤。本文用第一性原理密度泛函理论(DFT)研究了甲醇在铁氧体(FER)中的吸附和转化，预测了甲醇吸附的基本几何构型和能量。分子筛的吸附能力受硅铝比的影响，在硅铝比为5的材料中有较强的吸附能力。吸附强度也随四面体结合位的不同而不同，在硅铝比=5(EADS=-22.5kcal·mol-1)时，T1O2位产生最稳定的甲醇吸附结构。而在Si/Al=8时，T1O1位的吸附几何构型最稳定(EADS=-19.2kcal mol-1)。在平动和旋转运动中，甲醇被质子化，导致其C-O键断裂，形成与骨架氧结合的甲氧基物种(O-CH3距离为1.37A)，而水分子通过氢键稳定在酸性中心(Owat-H=2.0A)。甲氧基物种与第二个甲醇分子进一步反应生成乙醇和质子化二甲醚，其吸附能分别为-42和-25千卡·摩尔-1。本研究的结果为研究FER分子筛的酸性对甲醇的吸附和转化的影响提供了原子学上的见解。关键词：沸石、铁氧体、甲醇吸附、酸中心、密度泛函理论。
ABSTRACT Methanol adsorption and dehydration reactions within zeolites represent important steps in the catalytic conversion process to form long-chain hydrocarbons. Herein, first-principles density functional theory (DFT) is employed in the determination of methanol adsorption and conversion in ferrierite (FER), where we predict the fundamental adsorption geometries and energetics of methanol adsorption. The methanol molecule is shown to physisorb at all explored binding sites, stabilized through hydrogen-bonded interactions with the acid site atOmeth-Hframbond distances ranging from 1.33-1.51 A. We demonstrate that the zeolites' adsorption capability is affected by the silicon/aluminium ratio, with stronger adsorptions predicted in the material with silicon to aluminium fractions of 5 than 8. The adsorption strength is also found to vary depending on the tetrahedral binding site, with the T1O2 site yielding the most stable methanol adsorption structure in the Si/Al ratio = 5(Eads = -22.5 kcal mol-1), whereas the T1O1 site yields the most stable adsorption geometry (Eads = -19.2 kcal mol-1) in the Si/Al ratio = 8. Upon translational and rotational motion, methanol is protonated resulting in the breaking of its C-O bond to form a methoxy species bound to the framework oxygen (O-CH3 distance of 1.37 A), whereas the water molecule is stabilized at the acid site through H-bonding (Owat-H = 2.0 A). Further reaction between the methoxy species and a second methanol molecule results in the formation of ethanol and protonated dimethyl ether, with adsorption energies of -42 and -25 kcal mol-1, respectively. The results in this study provide atomistic insight into the effect of acidity of the FER zeolite on the adsorption and conversion of methanol. Keywords: Zeolites, ferrierite, methanol adsorption, acid sites, density functional theory (DFT).