Search

A fundamental understanding of the active sites in heterogeneous catalysts is extremely important in the development of effective catalysts. In general, it is difficult to identify the catalytically active sites due to their structural complexity, including the size and specific atomic configurations. In this paper, we prepare different Pt species (single atoms, fully exposed clusters, and nanoparticles) on a nanodiamond/graphene (ND@G) hybrid support to understand their evolution in structure for low-temperature CO oxidation. Remarkably, the atomically dispersed and fully exposed Pt clusters with an ensemble of a few Pt atoms showed the maximum atom utilization of low-coordinated metal sites. As determined by a catalytic performance evaluation, detailed characterizations, and theoretical calculations, the 0.5 wt % Ptn/ND@G catalyst showed a catalytic performance for CO oxidation at low temperature superior to those of single-atom and nanoparticle catalysts, which was attributed to the weakened CO adsorption and facilitated O2 dissociative adsorption on these atomically dispersed and fully exposed Pt cluster catalysts. © 2022 American Chemical Society.

The atomically dispersed metal catalyst or single-atom catalyst (SAC) with the utmost metal utilization efficiency shows excellent selectivity toward ethylene compared to the metal nanoparticles catalyst in the acetylene semi-hydrogenation reaction. However, these catalysts normally work at relatively high temperatures. Achieving low-temperature reactivity while preserving high selectivity remains a challenge. To improve the intrinsic reactivity of SACs, rationally tailoring the coordination environments of the first metal atom by coordinating it with a second neighboring metal atom affords an opportunity. Here, we report the fabrication of a dual-atom catalyst (DAC) that features a bonded Pd1-Cu1atomic pair anchoring on nanodiamond graphene (ND@G). Compared to the single-atom Pd or Cu catalyst, it exhibits increased reactivity at a lower temperature, with 100% acetylene conversion and 92% ethylene selectivity at 110 °C. This work provides a strategy for designing DACs for low-temperature hydrogenation by manipulating the coordination environment of catalytic sites at the atomic level. © 2022 American Chemical Society. All rights reserved.

Atomically dispersed metal catalysts (ADMCs), which offer maximized atom-use efficiency and catalytic performance enhancements for many catalytic systems, have received increasing attention in the catalysis field. Additionally, ADMCs with well-defined architectures are promising for providing valuable information to derive structure-performance relationships. Here, we immobilized Cu1 on a defective nanodiamond-graphene (ND@G) and N-doped nanodiamond-graphene (ND@NG). By changing the coordination environments (Cu-C or Cu-N), the electronic state of Cu ADMCs can be tailored. The highly oxidized Cu atoms in Cu-N AMDCs present distinctively different acetylene hydrogenation activity compared to that in Cu-C AMDCs (i.e., with high conversion (100%), high selectivity (93%), and good stability (more than for 100 h)). Density functional theory and H2-D2 exchange experiments reveal that Cu-C bond anchoring favors H2 dissociative adsorption, which is a rate-limiting step. In addition, the facile desorption of the target product C2H4 over Cu-C ADMCs ensures the outstanding activity and selectivity of the catalyst. This work thus helps to bring perspectives for linking activity and structures of ADMCs and designing active ADMCs for hydrogenation applications. © 2021 American Chemical Society.

Direct dehydrogenation of alkanes is of great interest but presents a significant challenge in activating C-H bond at a low temperature. Here, we report fully exposed Pd clusters consisting of an average of three Pd atoms on a hybrid nanodiamond-graphene support (denoted as Pd3/ND@G) for low-temperature dehydrogenation of ethylbenzene to styrene. The obtained fully exposed and atomically dispersed Pd clusters exhibit good catalytic performance (328 mmol gPd-1 h-1 ethylbenzene conversion rate and >99% styrene selectivity) and much enhanced stability under oxygen-free conditions at 350 °C, compared with the previously reported catalysts. The synergetic interaction between adjacent Pd atoms in each cluster evidenced by density functional theory (DFT) calculations guarantees effective activation of C-H bond on ethyl in ethylbenzene and easy desorption of styrene, which is the key for the higher activity than typical Pd single atom and Pd nanoparticle catalysts. The present method for precise control of fully exposed Pd clusters paves a new way for designing direct dehydrogenation catalyst at the atomic scale. © 2021 American Chemical Society.

Atomically dispersed metal catalysts (ADMCs), which offer maximized atom-use efficiency and catalytic performance enhancements for many catalytic systems, have received increasing attention in the catalysis field. Additionally, ADMCs with well-defined architectures are promising for providing valuable information to derive structure-performance relationships. Here, we immobilized Cu1 on a defective nanodiamond-graphene (ND@G) and N-doped nanodiamond-graphene (ND@NG). By changing the coordination environments (Cu-C or Cu-N), the electronic state of Cu ADMCs can be tailored. The highly oxidized Cu atoms in Cu-N AMDCs present distinctively different acetylene hydrogenation activity compared to that in Cu-C AMDCs (i.e., with high conversion (100%), high selectivity (93%), and good stability (more than for 100 h)). Density functional theory and H2-D2 exchange experiments reveal that Cu-C bond anchoring favors H2 dissociative adsorption, which is a rate-limiting step. In addition, the facile desorption of the target product C2H4 over Cu-C ADMCs ensures the outstanding activity and selectivity of the catalyst. This work thus helps to bring perspectives for linking activity and structures of ADMCs and designing active ADMCs for hydrogenation applications. © 2021 American Chemical Society.