Microkinetic Modeling with Size-Dependent and Adsorbate–Adsorbate Interactions for the Direct Synthesis of H<sub>2</sub>O<sub>2</sub> over Pd Nanoparticles
Jinyan Zhao, Zihao Yao, Rhys J. Bunting, P. Hu, Jianguo Wang
Abstract
As a bottleneck in the direct synthesis of hydrogen peroxide, the development of an efficient palladium-based catalyst has garnered great attention. However, elusive active centers and reaction mechanism issues inhibit further optimization of its performance. In this work, advanced microkinetic modeling with the adsorbate–adsorbate interaction and nanoparticle size effect based on first-principles calculations is developed. A full mechanism uncovering the significance of adsorbate–adsorbate interaction is determined on Pd nanoparticles. We demonstrate unambiguously that Pd(100) with main coverage species of O<sub>2</sub> and H is beneficial to H<sub>2</sub>O<sub>2</sub> production, being consistent with experimental operando observation, while H<sub>2</sub>O forms on Pd(111) covered by O species and Pd(211) covered by O and OH species. Kinetic analyses further enable quantitative estimation of the influence of temperature, pressure, and particle size. Large-size Pd nanoparticles are found to achieve a high H<sub>2</sub>O<sub>2</sub> reaction rate when the operating conditions are moderate temperature and higher oxygen partial pressure. We reveal that specific facets of the Pd nanoparticles are crucial factors for their selectivity and activity. Consistent with the experiment, the production of H<sub>2</sub>O<sub>2</sub> is discovered to be more favorable on Pd nanoparticles containing Pd(100) facets. The ratio of H<sub>2</sub>/O<sub>2</sub> induces substantial variations in the coverage of intermediates of O<sub>2</sub> and H on Pd(100), resulting in a change in product selectivity.