Ru surface density effect on ammonia synthesis activity and hydrogen poisoning of ceria-supported Ru catalysts

Evaluating the effect of metal surface density on catalytic performance is critical for designing high-activity metal-based catalysts. In this study, a series of ceria (CeO2)-supported Ru catalysts (Ru/CeO2) were prepared to analyze the effect of Ru surface density on the catalytic performance of Ru/CeO2 for ammonia synthesis. For the Ru/CeO2 catalysts with Ru surface densities lower than 0.68 Ru nm(-2), the Ru layers were in close contact with CeO2, and electrons were transferred directly from the CeO2 defect sites to the Ru species. In such cases, the adsorption of hydrogen species on the Ru sites in the vicinity of O atoms was high, leading to a high ammonia synthesis activity and strong hydrogen poisoning. In contrast, the preferential aggregation of Ru species into large particles on top of the Ru overlayer resulted in the coexistence of Ru clusters and particles, for catalysts with a Ru surface density higher than 1.4 Ru nm(-2), for which Ru particles were isolated from the direct electronic influence of CeO2. Consequently, the Ru-CeO2 interactions were weak, and hydrogen poisoning can be significantly alleviated. Overall, electron transfer and hydrogen adsorption synergistically affected the synthesis of ammonia over Ru/CeO2 catalysts, and catalyst samples with a Ru surface density lower than 0.31 Ru nm(-2) or exactly 2.1 Ru nm(-2) exhibited high catalytic activity for ammonia synthesis. (C) 2021, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

评估金属表面密度对催化性能的影响对于设计高活性金属基催化剂至关重要。在本研究中，制备了一系列氧化铈（CeO₂）负载的Ru催化剂（Ru/CeO₂），以分析Ru表面密度对Ru/CeO₂氨合成催化性能的影响。对于Ru表面密度低于0.68 Ru nm⁻²的Ru/CeO₂催化剂，Ru层与CeO₂紧密接触，电子直接从CeO₂缺陷位点转移到Ru物种。在这种情况下，氢物种在O原子附近的Ru位点上的吸附较高，导致氨合成活性高且氢中毒现象严重。相反，对于Ru表面密度高于1.4 Ru nm⁻²的催化剂，Ru物种优先聚集成大颗粒位于Ru覆盖层之上，导致Ru簇和颗粒共存，此时Ru颗粒不受CeO₂的直接电子影响。因此，Ru - CeO₂相互作用较弱，氢中毒现象可显著减轻。总体而言，电子转移和氢吸附协同影响了Ru/CeO₂催化剂上的氨合成，Ru表面密度低于0.31 Ru nm⁻²或恰好为2.1 Ru nm⁻²的催化剂样品对氨合成表现出高催化活性。（C）2021，中国科学院大连化学物理研究所。由爱思唯尔出版集团出版。保留所有权利。