How Does the Oxidation State of Palladium Surfaces Affect the Reactivity and Selectivity of Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen Gases? A Density Functional Study
How Does the Oxidation State of Palladium Surfaces Affect the Reactivity and Selectivity of Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen Gases? A Density Functional Study
复制标题
钯表面的氧化态如何影响氢气和氧气直接合成过氧化氢的反应性和选择性？
DOI：
10.1021/jacs.8b10281
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发表时间：
2019-01-16
影响因子：
15
通讯作者：
Wang, Yong
中科院分区：
文献类型：
--
作者：
Wang, Fang;Xia, Chungu;Wang, Yong
从 H-2 和 O-2 直接合成 H2O2 是一种环境友好且原子经济的过程，因此是理想的催化途径。然而，目前不存在这种催化的低成本途径，尽管它对于生产 H2O2 的常见工业蒽醌方法来说是一种有吸引力的替代策略。金属基催化剂广泛应用于这种直接合成过程，但通常需要氧化、合金化或添加添加剂以使其具有选择性。为了了解多相催化中的金属氧化态，我们研究了 Pd(111) 和 PdO(101) 表面上分子氧对氢气的选择性氧化，产生 H2O2 或 H2O 产物。我们的结果首次证明，与还原的 Pd(111) 表面相比，氧化的 PdO(101) 表面明显表现出更好的性能和选择性。氧化 Pd 表面上的活化势垒约为 。比还原后的 Pd 表面低 0.2 eV。在氧化表面上，H2O2 合成途径是优选的，而在还原表面上，H2O 途径是主要的。 H2O2的分解在氧化表面也受到极大的抑制。我们通过热化学循环详细分析了不同的途径，发现与 Pd(111) 表面相比，氧化表面对试剂 O-2 和 H-2、关键中间体 OOH 以及产物 H2O2 的吸附能力较弱，我们认为这会影响选择性。这里介绍的工作清楚地表明，金属表面的氧化态是调节化学反应催化的最重要因素之一，可以显着影响选择性和反应模式。
Direct synthesis of H2O2 from H-2 and O-2 is an environmentally benign and atom economic process and as such is the ideal pathway in catalysis. However, currently no low-cost pathway of this kind of catalysis exists, although it would be an attractive alternative strategy to the common industrial anthraquinone method for H2O2 production. Metal-based catalysts are widely employed in such a direct synthesis process but often need to be oxidized, alloyed, or supplied with additives to make them selective. To understand the metal-oxidation state in heterogeneous catalysis, we studied the selective oxidation of hydrogen by molecular oxygen on Pd(111) and PdO(101) surfaces, leading to either H2O2 or H2O products. Our results demonstrate, for the first time, that the oxidized PdO(101) surface clearly shows better performance and selectivity, as compared to the reduced Pd(111) one. The activation barrier on the oxidized Pd surface is ca. 0.2 eV lower than the one on the reduced Pd surface. On the oxidized surface, the H2O2 synthesis route is preferred, while, on the reduced surface, the H2O route is predominant. The decomposition of H2O2 is also greatly inhibited on the oxidized surface. We analyzed the different pathways in detail through thermochemical cycles, which establishes that the oxidized surface shows weaker adsorption ability toward the reagents O-2 and H-2, the key intermediate OOH, and also the product H2O2 in comparison with the Pd(111) surface, which we believe affect the selectivity. The work presented here clearly shows that the oxidation state of metal surfaces is one of the most important factors that tunes the catalysis of a chemical reaction and can affect the selectivity and reaction patterns dramatically.