Ethanol dehydrogenation is a vital elementary step in ethanol upgrading, for which Cu-based alloy catalysts are the most promising candidates. Nevertheless, elucidating the underlying reasons for the synergistic effect between alloying components and host metals remains challenging due to the intrinsic structural complexity and dynamic evolution of alloy catalysts under operational conditions. Herein, single-atom Pd modified Cu-MFI catalysts with well-defined structures were designed for ethanol dehydrogenation to acetaldehyde and hydrogen. Comprehensive characterizations using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed that Pd atoms are isolated by surrounding Cu atoms with a coordination number of 9–10, forming −0.36 e charged single-atom sites and being uniformly dispersed on the surface of Cu catalysts. The newly generated Pd δ − and Cu δ + sites synergistically reduced the activation energy barrier for C–H bond cleavage in ethanol. These sites simultaneously enhanced hydrogen adsorption and H–H bond coupling, leading to improved ethanol conversion and acetaldehyde productivity over Pt/Cu-MFI catalysts.
Jing Yang,Heng-Quan Chen,Fen Qiao,Xifeng Zhu,Tao Wang,Wei-Ping Pan
Engineering metal-based nanoarchitectures and their atomic-scale arrangement is a promising avenue for enhanced mercury adsorbent activities. Interactions between metal single atoms and substrates result in regulated transitions between distinct reaction processes that boost mercury adsorption activity. Herein, a novel sorbent of porous Co 3 O 4 with Palladium atomic dispersed was successfully prepared by one-step pyrolysis of zeolitic imidazolate framework 67 (ZIF-67) precursors. Via engineering single Pd atoms into ZIF-derived Co 3 O 4 (Pd 1 /Co 3 O 4 -ZIF), the strong metal-support interaction (SMSI) activated the reducibility of Co 3+ in porous Co 3 O 4 to efficiently adsorb and oxidize Hg 0 , enhancing its mercury removal efficiency. Specifically, Pd 1 /Co 3 O 4 -ZIF exhibited superior sorption performance for Hg 0 over a broad range of temperatures (30–350 °C) and high gaseous hourly space velocity (about 555,500 hr −1 ) with the average Hg 0 removal efficiency higher than 98%. The strategy of constructing atomic active sites on the surface of porous metal-oxide to convert adsorbed Hg 0 into HgO is a promising approach to solve the problem that Hg 0 in flue gas is challenging to remove. Density functional theory (DFT) calculation further proved that the existence of a single Pd site on the surface of Co 3 O 4 significantly reduced the energy barrier of Hg 0 to HgO at the atomic level. This work contributed to a thorough comprehension of the structural and adsorption properties of the ZIF-derived Co 3 O 4 sorbent engineering with a single atom and enabled the efficient capture of elemental mercury in flue gas by such ZIF-derived sorbent.
The construction of nanozymes at the atomic level that hold structural stability and high enzyme-like activity is now a key factor in the optimization of an artificial enzyme. Single-atom metal/cerium oxide (CeO2)-based nanozymes have been demonstrated to possess a variety of enzymatic activities and radical scavenging abilities, which are mainly attributed to the single-atom active site, redox valence states, and abundant defect chemistry. Here, we developed a single-atom Pd/CeO2 nanostructure by aqueous phase synthesis that exhibits the advantages of high yield and good stability. The Pd/CeO2 nanostructure possesses peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities as well as reactive nitrogen species free-radical scavenging activity, exhibiting multienzyme-like activities and stability compared with CeO2 and other metal-based nanozymes. It is worth mentioning that the Pd/CeO2 nanostructure exhibits high POD-mimicking activity with a reaction rate of 0.88 μM/min, about 5 times higher than that of the CeO2 nanozyme. In addition, the CAT-like activity of the Pd/CeO2 nanostructure is excellent, and its scavenging rate of hydrogen peroxide reached nearly 100% at a concentration of 50 ng/μL. The present work shows that single-atom Pd substitution is a promising strategy for the design of CeO2 nanozymes to exert better effects on biomedical applications, especially with diseases related to oxidative stress.
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