Comparison of Coverage-Dependent Binding Energy Models for Mean-Field Microkinetic Rate Predictions.,Langmuir

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Comparison of Coverage-Dependent Binding Energy Models for Mean-Field Microkinetic Rate Predictions.
Langmuir ( IF 3.7 ) Pub Date : 2019-12-31 , DOI: 10.1021/acs.langmuir.9b03563
Anshumaan Bajpai ₁ , Kurt Frey ₁ , William F Schneider _{1,

2}

Affiliation

The binding energies of adsorbates at catalytic surfaces are in general functions of adsorbate coverage, with corresponding consequences for equilibrium surface coverages and reaction rates under relevant conditions. This coverage dependence is commonly incorporated into mean-field microkinetic models by writing adsorption energies as an algebraic function of coverage and parametrizing against density functional theory models. In this work, we compare the performance of three different analytical coverage-dependent forms, including linear and piecewise models and a logarithmic form inspired by Wilson's activity model, against accurate results obtained from a lattice-based cluster expansion (CE) representation of adsorbate interactions combined with a Monte Carlo evaluation of reaction rates. We take as a model system O2 dissociation-limited NO oxidation to NO2 over Pt(111), parametrize all models against the same set of previously reported coverage-dependent NO and O binding energies, and solve kinetic models under the same set of assumptions. Steady-state coverages from the analytical models are similar to each other and the ensemble-averaged CE result, other than the discontinuities in O and NO coverages that appear in the piecewise model. Predicted steady-state rates differ more substantially, reflecting the sensitivity of the O2 dissociation activation energy to coverage-dependent binding energies. The activity model predicts reaction rates reliably at low temperatures and systematically deviates from CE rates at high temperatures, where minority surface sites, having low local coverage around vacant pairs, dominate overall reaction rates. The results highlight the challenges of developing coverage-dependent microkinetic models that are reliable across a range of conditions.

中文翻译：

均值微动力学速率预测的依赖于覆盖的结合能模型的比较。

催化表面上被吸附物的结合能通常是被吸附物覆盖率的函数，在相关条件下对平衡表面覆盖率和反应速率具有相应的影响。通过将吸附能写为覆盖率的代数函数，并针对密度泛函理论模型进行参数化，通常将这种覆盖率依赖性合并到平均场微动力学模型中。在这项工作中，我们将三种不同的分析覆盖率相关形式（包括线性模型和分段模型以及受威尔逊活动模型启发的对数形式）的性能与吸附剂相互作用的基于晶格的簇扩展（CE）表示所获得的准确结果进行了比较结合反应速率的蒙特卡洛评估。我们将Pt（111）上的O2分解受限的NO氧化为NO2作为模型系统，对所有模型进行参数化，使其针对同一组先前报告的与覆盖相关的NO和O结合能，并在同一组假设下求解动力学模型。除了分段模型中出现的O和NO覆盖范围的不连续性之外，分析模型的稳态覆盖范围彼此相似，并且得到的结果是总体平均的CE结果。预测的稳态速率差异更大，反映了O2解离活化能对依赖于覆盖的结合能的敏感性。活动模型可以可靠地预测低温下的反应速率，并有系统地偏离高温下的CE速率，在高温下，少数表面位点在空位对周围的覆盖率较低，总体反应速率占主导地位。结果突显了开发在各种条件下可靠的依赖于覆盖的微动力学模型所面临的挑战。

更新日期：2019-12-31

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