The size of supported metal species is known to have a profound influence on their catalytic activity. However, this structure sensitivity remains ambiguous for metals at the atomic scale due to the lack of single-atom sensitive and statistically significant quantification methods. Here we overcome this difficulty to quantify the catalytic contribution of various surface palladium species, ranging from single atoms to sub-nanometre clusters and nanoparticles, in the dehydrogenation of dodecahydro-N-ethylcarbazole, a reaction of importance for H₂ transportation and utilization. We show that the optimal site is a fully exposed palladium cluster with an average Pd–Pd coordination number of ∼4.4, favouring both the activation of reactants and desorption of products, whereas palladium single atoms are almost inactive. Our study highlights that for certain catalytic reactions, the construction of fully exposed metal clusters without the presence of spectators (that is, palladium single atoms in this work) could help to maximize the reactivity and the atomic efficiency of noble metals.

已知负载金属物质的大小对其催化活性有深远的影响。然而，由于缺乏单原子敏感性和统计上显着的量化方法，这种结构敏感性对于原子尺度上的金属仍然不明确。在这里，我们克服了这一困难，以量化从单原子到亚纳米簇和纳米粒子的各种表面钯物质在十二氢-N-乙基咔唑脱氢中的催化作用，这是一种对 H ₂运输和利用很重要的反应。我们表明，最佳位点是完全暴露的钯簇，平均 Pd-Pd 配位数为~4.4，有利于反应物的活化和产物的解吸，而钯单原子几乎没有活性。我们的研究强调，对于某些催化反应，在没有旁观者存在的情况下构建完全暴露的金属簇（即本工作中的钯单原子）有助于最大限度地提高贵金属的反应性和原子效率。