Single-atom catalysts (SACs) have emerged as a frontier in heterogeneous catalysis due to the well-defined active site structure and the maximized metal atom utilization. Nevertheless, the robustness of SACs remains a critical concern for practical applications. Herein, we report a highly active, selective and robust Ru SAC which was synthesized by pyrolysis of ruthenium acetylacetonate and N/C precursors at 900 °C in N₂ followed by treatment at 800 °C in NH₃. The resultant Ru₁-N₃ structure exhibits moderate capability for hydrogen activation even in excess NH₃, which enables the effective modulation between transimination and hydrogenation activity in the reductive amination of aldehydes/ketones towards primary amines. As a consequence, it shows superior amine productivity, unrivalled resistance against CO and sulfur, and unexpectedly high stability under harsh hydrotreating conditions compared to most SACs and nanocatalysts. This SAC strategy will open an avenue towards the rational design of highly selective and robust catalysts for other demanding transformations.

Fine-tuning of the coordination environment of single-atom catalysts (SACs) is effective to optimize their catalytic performances, yet it remains challenging due to the vulnerability of SACs. Herein, we report a new approach to engineering the coordination environment of M-N-C (M = Fe, Co, and Ni) SACs by using glutamic acid as the N/C source and pyrolysis atmosphere as a regulator. Compared with that in N₂, NH₃ was able to promote the doping of N at T < 700 °C yet etch the N-species at higher temperatures, by which the M-N coordination number (CN) and the electronic structure were delicately tuned. It was found that the electron density of Ni single atoms increased with the decrease of Ni-N CN. As a consequence, the capability of Ni-N-C to dissociate H₂ was greatly enhanced and a higher catalytic activity in chemoselective hydrogenation of functionalized nitroarenes was achieved. Moreover, this modulation method could be applied to other transition metals including Fe and Co. In particular, the as-synthesized Co-N-C SAC afforded a turnover frequency of 152.3 h⁻¹ with 99% selectivity to 3-vinylaniline in the hydrogenation of 3-nitrostyrene, which was the highest ever reported thus far and was at least one order of magnitude more active than state-of-the-art noble-metal-free M-N-C catalysts, demonstrating the great potential of engineering the coordination environment of SACs.

The sustainable production of value-added N-heterocycles from available biomass allows to reduce the reliance on fossil resources and creates possibilities for economically and ecologically improved synthesis of fine and bulk chemicals. Herein, we present a unique Ru₁Co_NP/HAP surface single-atom alloy (SSAA) catalyst, which enables a new type of transformation from the bio-based platform chemical furfural to give N-heterocyclic piperidine. In the presence of NH₃ and H₂, the desired product is formed under mild conditions with a yield up to 93%. Kinetic studies show that the formation of piperidine proceeds via a series of reaction steps. Initially, in this cascade process, furfural amination to furfurylamine takes place, followed by hydrogenation to tetrahydrofurfurylamine (THFAM) and then ring rearrangement to piperidine. DFT calculations suggest that the Ru₁Co_NP SSAA structure facilitates the direct ring opening of THFAM resulting in 5-amino-1-pentanol which is quickly converted to piperidine. The value of the presented catalytic strategy is highlighted by the synthesis of an actual drug, alkylated piperidines, and pyridine.

Reppe carbonylation of acetylene is an atom-economic and non-petroleum approach to synthesize acrylic acid and acrylate esters, which are key intermediates in the textile, leather finishing, and polymer industries. In the present work, a noble metal-free Co@SiO₂ catalyst was prepared and evaluated in the methoxycarbonylation reaction of acetylene. It was discovered that pretreatment of the catalyst by different reductants (i.e., C₂H₂, CO, H₂, and syngas) greatly improved the catalytic activity, of which Co/SiO₂-H₂ demonstrated the best performance under conditions of 160 °C, 0.05 MPa C₂H₂, 4 MPa CO, and 1 h, affording a production rate of 4.38 g_MA+MP g_cat⁻¹ h⁻¹ for methyl acrylate (MA) and methyl propionate (MP) and 0.91 g_DMS g_cat⁻¹ h⁻¹ for dimethyl succinate (DMS), respectively. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectra of CO adsorption (CO-DRIFTS) measurements revealed that an H₂ reduction decreased the size of the Co nanoparticles and promoted the formation of hollow architectures, leading to an increase in the metal surface area and CO adsorption on the catalyst. The hot filtration experiment confirmed that Co₂(CO)₈ was generated in situ during the reaction or at the pre-activation stage, which served as the genuine active species. Our work provides a facile and convenient approach to the in situ synthetization of Co₂(CO)₈ for a Reppe carbonylation reaction.