Marcinkowski Matthew D, Adamsen Kræn C, Doudin Nassar, Sharp Marcus A, Smith R Scott, Wang Yang, Wendt Stefan, Lauritsen Jeppe V, Parkinson Gareth S, Kay Bruce D, Dohnálek Zdenek
Physical and Computational Sciences Directorate and Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99354, USA.
Interdisciplinary Nanoscience Center (iNano) and Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark.
J Chem Phys. 2020 Feb 14;152(6):064703. doi: 10.1063/1.5139418.
The interaction of methanol with iron oxide surfaces is of interest due to its potential in hydrogen storage and from a fundamental perspective as a chemical probe of reactivity. We present here a study examining the adsorption and reaction of methanol on magnetite FeO(001) at cryogenic temperatures using a combination of temperature programmed desorption, x-ray photoelectron spectroscopy, and scanning tunneling microscopy. The methanol desorption profile from FeO(001) is complex, exhibiting peaks at 140 K, 173 K, 230 K, and 268 K, corresponding to the desorption of intact methanol, as well as peaks at 341 K and 495 K due to the reaction of methoxy intermediates. The saturation of a monolayer of methanol corresponds to ∼5 molecules/unit cell (u.c.), which is slightly higher than the number of surface octahedral iron atoms of 4/u.c. We probe the kinetics and thermodynamics of the desorption of molecular methanol using inversion analysis. The deconvolution of the complex desorption profile into individual peaks allows for calculations of both the desorption energy and the prefactor of each feature. The initial 0.7 methanol/u.c. reacts to form methoxy and hydroxy intermediates at 180 K, which remain on the surface above room temperature after intact methanol has desorbed. The methoxy species react via one of two channels, a recombination reaction with surface hydroxyls to form additional methanol at ∼350 K and a disproportionation reaction to form methanol and formaldehyde at ∼500 K. Only 20% of the methoxy species undergo the disproportionation reaction, with most of them reacting via the 350 K pathway.
甲醇与氧化铁表面的相互作用因其在储氢方面的潜力以及从作为反应活性化学探针的基本角度来看而备受关注。我们在此展示一项研究，该研究使用程序升温脱附、X射线光电子能谱和扫描隧道显微镜相结合的方法，在低温下研究甲醇在磁铁矿FeO(001)上的吸附和反应。来自FeO(001)的甲醇脱附曲线很复杂，在140 K、173 K、230 K和268 K处出现峰，对应于完整甲醇的脱附，以及由于甲氧基中间体反应在341 K和495 K处出现的峰。单层甲醇的饱和对应于约5个分子/晶胞（u.c.），这略高于表面八面体铁原子的数量4/u.c.。我们使用反演分析来探究分子甲醇脱附的动力学和热力学。将复杂的脱附曲线解卷积为各个峰，能够计算每个特征的脱附能和指前因子。最初的0.7甲醇/u.c.在180 K反应形成甲氧基和羟基中间体，在完整甲醇脱附后，这些中间体在室温以上仍留在表面。甲氧基物种通过两个通道之一反应，与表面羟基发生重组反应，在约350 K形成额外的甲醇，以及在约500 K发生歧化反应形成甲醇和甲醛。只有20%的甲氧基物种发生歧化反应，其中大部分通过350 K途径反应。
