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首页> 外文期刊>Catalysis science & technology >The surface phase structure evolution of the fcc MoC (001) surface in a steam reforming atmosphere: systematic kinetic and thermodynamic investigations
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The surface phase structure evolution of the fcc MoC (001) surface in a steam reforming atmosphere: systematic kinetic and thermodynamic investigations

机译：FCC MOC（001）表面在蒸汽重整大气中的表面相结构演变：系统动力学和热力学研究

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The kinetic and thermodynamic aspects of the surface phase structure evolution of an fcc MoC (001) surface under a H2O/H2-rich atmosphere typically found during steam reforming processes were systematically studied via periodic density functional theory (DFT) and ab initio thermodynamic methods. The various stable configurations of surface species (H2O*, OH*, O*, , and H*) at different coverages and their formation rates considering different coverage effects of certain species were explored. At a molecular H2O* adsorption coverage (θH2O) ≤1/3 ML, the adsorption of H2O mainly takes place through single Mo–O coordination, while the capture of H2O above 1/3 ML relies on hydrogen bonds. H2O* dissociation resulting in OH* formation is always facile at different H2O* coverages, whereas it becomes unfavourable as the OH* coverage increases beyond 4/9 ML due to unavoidable strong hydrogen bond breaking. Surface O* can be easily formed via hydroxyl disproportionation with negligible energy barriers, and the protonation of O* by H2O* is also facile. The dissociation of will easily generate surface Mo–H* and C–H* species, where Mo–H* can readily transform to C–H* with significant exothermicity. The average surface binding strengths of various species at 0 K follow the order: H2O* > H* ≈ OH* > > O*, where the average binding strength of O* becomes positive when θO* ≥ 1/3 ML. At 473.15 K and over a wide H2O pressure range, mixtures of H2O*, OH*, and O* are the predominant species on the (001) surface, highlighting the role of the (001) surface in steam reforming reactions, while H* species only emerge at low H2O pressure or high H2 pressure. The proportion of O* species decreases and finally tends to zero as the H2 pressure increases from 10−10 to 10−7 MPa, while the proportion of OH* species increases due to O* protonation. As the H2 pressure increases from 10−7 to 10 MPa, the proportion of OH* species decreased, accompanied by an increase in the H2O coverage. As the H2O pressure decreased, the stable existence of surface H* species became increasingly more favorable, and the emergence of surface H* species was accompanied by the disappearance of surface O-containing species, changing the catalytic role of the (001) surface from catalyzing steam reforming processes to promoting hydrogenation reactions.
机译：通过周期性密度功能理论（DFT）和AB启动热力学方法，系统地研究了FCC MOC（001）表面表面结构的动力学和热力学方面。探索了某些物种的各种稳定构型（H2O*，OH*，O*，和H*）在不同的覆盖范围内探索了某些物种的不同覆盖效果。在分子H2O*吸附覆盖范围（θH2O）≤1/3 mL时，H2O的吸附主要通过单个MO – O协调进行，而H2O的捕获高于1/3 mL，则依赖于氢键。 H2O*解离导致OH*形成始终在不同的H2O*覆盖范围内容易，而随着OH*覆盖率的增加，由于不可避免的强氢键破裂，它变得不利。表面O*可以通过羟基与可忽略的能屏障来轻松形成，而H2O*的O*质子化也很容易形成。将很容易产生表面mo – h*和c – h*物种，其中mo – h*可以很容易地转化为C – H*，并具有显着的放热性。在0 K时，各种物种的平均表面结合强度遵循：H2O*> h*≈oh*>> o*，当O*的平均结合强度在θo*≥1/3ml时变为正。 H2O*，OH*和O*的混合物在473.15 K且在较大的H2O压力范围内是（001）表面上的主要物种，突出了（001）表面在蒸汽改革中的作用，而H*则强调了H*物种仅在低H2O压力或高H2压力下出现。随着H2压力从10-10增加到10-7 MPa，O*物种的比例降低，最终趋于零，而OH*物种的比例由于O*质子化而增加。随着H2压力从10-7增加到10 MPa，OH*物种的比例降低，伴随着H2O覆盖率的增加。随着H2O压力的降低，表面H*物种的稳定存在变得越来越有利，表面H*物种的出现伴随着含有O的表面O的消失，改变了（001）表面的催化作用。催化蒸汽重整过程促进氢化反应。

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