College of Environmental Science and Engineering, North China Electric Power University, Beijing 102206, China.
Department of Chemical and Environmental Engineering, Yale University, New Haven, CT 06520.
Proc Natl Acad Sci U S A. 2023 Feb 28;120(9):e2216879120. doi: 10.1073/pnas.2216879120. Epub 2023 Feb 21.
Atomic dispersion of metal catalysts on a substrate accounts for the increased atomic efficiency of single-atom catalysts (SACs) in various catalytic schemes compared to the nanoparticle counterparts. However, lacking neighboring metal sites has been shown to deteriorate the catalytic performance of SACs in a few industrially important reactions, such as dehalogenation, CO oxidation, and hydrogenation. Metal ensemble catalysts (M), an extended concept to SACs, have emerged as a promising alternative to overcome such limitation. Inspired by the fact that the performance of fully isolated SACs can be enhanced by tailoring their coordination environment (CE), we here evaluate whether the CE of M can also be manipulated in order to enhance their catalytic activity. We synthesized a set of Pd ensembles (Pd) on doped graphene supports (Pd/X-graphene where X = O, S, B, and N). We found that introducing S and N onto oxidized graphene modifies the first shell of Pd converting Pd-O to Pd-S and Pd-N, respectively. We further found that the B dopant significantly affected the electronic structure of Pd by serving as an electron donor in the second shell. We examined the performance of Pd/X-graphene toward selective reductive catalysis, such as bromate reduction, brominated organic hydrogenation, and aqueous-phase CO reduction. We observed that Pd/N-graphene exhibited superior performance by lowering the activation energy of the rate-limiting step, i.e., H dissociation into atomic hydrogen. The results collectively suggest controlling the CE of SACs in an ensemble configuration is a viable strategy to optimize and enhance their catalytic performance.
在各种催化方案中，金属催化剂在基底上的原子分散导致单原子催化剂（SACs）的原子效率相对于纳米颗粒对应物增加。然而，缺乏相邻的金属位点已经表明会在一些工业上重要的反应中（如脱卤、CO 氧化和加氢）降低 SACs 的催化性能。金属整体催化剂（M）是 SACs 的扩展概念，已成为克服这种限制的一种有前途的替代方案。受完全隔离的 SACs 的性能可以通过调整其配位环境（CE）来增强这一事实的启发，我们在这里评估是否也可以操纵 M 的 CE 以提高其催化活性。我们合成了一系列负载在掺杂石墨烯载体上的钯整体（Pd/X-石墨烯，其中 X = O、S、B 和 N）。我们发现，在氧化石墨烯上引入 S 和 N 分别将 Pd-O 转化为 Pd-S 和 Pd-N，从而改变了钯的第一壳层。我们进一步发现，B 掺杂剂通过在第二壳层中充当电子供体，显著影响了钯的电子结构。我们研究了 Pd/X-石墨烯在选择性还原催化方面的性能，如溴酸盐还原、溴代有机氢化和水相 CO 还原。我们观察到 Pd/N-石墨烯通过降低限速步骤（即 H 分解为原子氢）的活化能表现出优异的性能。结果表明，在整体配置中控制 SACs 的 CE 是优化和增强其催化性能的一种可行策略。
